Waves of Silence: Digisonix, Active Noise Control, and the Digital Revolution [1 ed.] 0972187529, 9780972187527

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Waves of Silence Digisonix, active noise control, and the digital revolution

Larry J. Eriksson co-founder of Digisonix

Waves of Silence Digisonix, active noise control, and the digital revolution This book presents the unique story of Digisonix, its research partner, the University of Wisconsin-Madison, and their pioneering work on active sound and vibration control. An intrepreneurial start-up at a muffler company in the heart of the so-called rust belt, Digisonix was one of the first commercial users of the innovative Texas Instruments TMS32010 Digital Signal Processor that marked the beginning of the digital revolution. Today, active noise control technology reduces noise in headphones, fan ductwork, automobiles, and aircraft. Waves of Silence describes the excitement and challenges at Digisonix as it commercialized this interesting technology.

Reactions of readers to Waves of Silence ...a fun read...the story of an interesting, exciting time... ...down to earth...real world feel...enough technical explanation for the scientist while conveying the up and downs of startup businesses...

About the author... Larry J. Eriksson was vice-president of research at Nelson Industries for 25 years where he was also a co-founder, vice-president, and director of Digisonix. Author of many papers and patents on active sound and vibration control, he received his B.S.E.E. from Northwestern University, his M.S.E.E. from the University of Minnesota, and his Ph.D. in electrical engineering from the University of Wisconsin-Madison. He is a Fellow of the Acoustical Society of America and the Society of Automotive Engineers.

Waves of Silence Digisonix, active noise control, and the digital revolution

Initial Digisonix field installation at Sheboygan site

Waves of Silence Digisonix, active noise control, and the digital revolution

Larry J. Eriksson

Quarter Section Press Madison

Also by Larry J. Eriksson “Silencers,” Chapter 5, Noise Control in Internal Combustion Engines (Wiley, 1982) “Active Noise Control,” Chapter 15, Noise and Vibration Control Engineering (Wiley, 1992) Business Decisions (Quarter Section Press, 2002) Broken Strings, Missing Notes (Quarter Section Press, 2005) Poetry chapbooks (available at www.quartersectionpress.com) First Edition ISBN-10: 0-9721875-2-9 (ebook version) ISBN-13: 978-0-9721875-2-7 (ebook version) www.quartersectionpress.com Quarter Section Press 6105 Fairfax Lane Madison, WI 53718-8262 U.S.A. Copyright © 2015 by Larry J. Eriksson All rights reserved. Produced in the United States of America. The Waves of Silence PDF file may be copied and distributed without charge provided that no changes are made to the contents of the file unless permission is obtained from Quarter Section Press. Disclaimer The statements in this book are the personal opinions of the author based on his work as vice-president of research for Nelson Industries, Inc. and as a co-founder, manager, officer, and director of Digisonix, Inc.

Contents Preface!!

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ix

Prologue! ! ! ! Nelson Industries, Inc. “Artificial Quiet”...1913 notice

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1 1 10

Part I - Innovations! ! ! 1 - Sound Fighting Sound 2 - Back to School 3 - Adventures with Algorithms 4 - Riding the Digital Wave Reflection: Shoestring Budgets “Active Sound Control”...ASC haiku

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11 13 21 31 41 51 52

Part II - Digisonix! ! ! 5 - Getting Down to Business 6 - Quieting Fans 7 - Driving Ahead 8 - Digisonix, Inc. 9 - DigiWare 10 - Taking Flight 11 - Digital Voice Enhancement Reflection: Cutting Back “Turn on the Quiet”...ANC in headlines

53 55 65 79 91 105 115 121 129 130

Part III - Challenges! ! ! 12 - Technical Issues 13 - Business Issues 14 - Strategic Issues 15 - End of an Era Reflection: The Life of a Company

131 133 139 149 157 163

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Epilogue! ! ! ASVC Today “Ode to Digisonix”

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165 165 173

Acknowledgments

175

Table 1 - Perspectives on ASVC Table 2 - Automotive applications Table 3 - Nelson/Digisonix timeline Table 4 - Selected Digisonix controllers Table 5 - Selected Nelson/Digisonix patents Table 6 - Abbreviations and acronyms

178 180 182 184 185 188

Figures Photographs For More Information Bibliography and Review Articles References and Notes Index

189 191 193 194 196 221

In memory of Richard “Doc” Greiner (1931-2015) and To his graduate students at the University of Wisconsin in Madison and the employees at Nelson Industries and Digisonix who worked together to create a world leader in active sound and vibration control in America’s Dairyland.

>

Preface It was an early fall day when our small group stood high atop a multistory manufacturing plant in Sheboygan, Wisconsin, overlooking the beautiful waters of Lake Michigan. Rather than enjoying the view, we were making plans to install our innovative active noise control (ANC) system on a large industrial fan. Although our system had worked well in the relatively benign conditions of our laboratory, we still needed to demonstrate its effectiveness in a rugged industrial setting. The industrial fan and its ductwork were much larger than the small scale systems used for our earlier testing. The sound and vibration were intimidating and anxiety was high, since the modest loudspeakers of our ANC system had to quiet this powerful machine. Fighting noise with noise. The sounds of silence. Just some of the headlines of articles on active noise control, also known as electronic noise cancellation. Active noise control combines microphones, electronics, and loudspeakers to reduce undesired noise. Today, after years of development, it is finally reaching widespread application. Electronic noise-canceling headsets have become a popular accessory for many airline passengers. Active noise control reduces the interior sound levels of many cars. In 1981, I decided to return to school to complete my Ph.D. at the University of Wisconsin in Madison. I was vice-president of research at Nelson Industries, Inc., a medium-sized manufacturing company based in Stoughton, Wisconsin, that produced exhaust mufflers, industrial silencers, and filters. It had been twelve years since I received my master’s degree, but the wave of change that was building around active noise control and digital signal processing interested me as well as Nelson Industries.

At that time, to perform the massive number of calculations required for most applications of digital signal processing, you needed an array processor and a mid-range computer (i.e. what was then called a minicomputer or superminicomputer). These systems were large, heavy, and cost well into five or six figures, hardly suitable for most commercial products. In the early 1980s, Texas Instruments released its groundbreaking microprocessor, the TMS32010 Digital Signal Processor. This microchip enabled the development of signal processing systems that were much smaller and less expensive. In the following years, many of the producers of array processors and minicomputers either disappeared or were purchased by other companies. The availability of the powerful, low cost TMS32010 Digital Signal Processor triggered a revolution in digital signal processing and a tidal wave of change for many applications. This included the development of innovative approaches to active noise control that far surpassed what had been possible using more traditional analog electronics. The evolution of science and technology passes through an endless series of waves. To play an active role in these changes, it is important to get on a new wave as it is forming. In a happy stroke of serendipity, my doctoral research caught the new wave of technological change in digital signal processing at almost the perfect moment. The primary focus of this book is on the pioneering work of research engineers at Nelson Industries and the Electroacoustics Laboratory at the UW-Madison. The joint work of these engineers from industry and academia using digital electronics and adaptive digital signal processing led to new approaches to active noise control and the formation of Digisonix. This book presents the story of Digisonix as well as the fascinating history of active noise control. x

Digisonix was a high-tech start-up within Nelson Industries, a muffler company in the heart of the so-called rust belt. It was one of the first companies to incorporate the TMS32010 Digital Signal Processor into its products and rode the rising wave of digital technology to become a global leader in active noise control. This book describes the rapid growth and successes of its early years as well as the challenges that it faced as it matured. One of those challenges was the difficulty Digisonix encountered in convincing those in industry to replace what they perceived as rugged and dependable passive silencers with what they perceived as fragile, complex computer-based systems. The proper and effective use of the new active technology required a paradigm shift in their approach to acoustical noise control. This book discusses the cultural barriers that stood in the way of making this shift. While I was writing this book, I was sometimes asked why I wanted to tell a story that is now more than fifteen years old. Part of the answer is that applications of active noise control are now becoming more widespread. It is also true that the passage of years allows an improved perspective for viewing the achievements and shortcomings of Digisonix. But most of all, I wrote it simply because I think it’s a good story. I hope you agree.

April, 2015

Larry J. Eriksson Madison, Wisconsin

xi

Taking a well-trod path, Nelson Corporate Research was started in the garage at right in 1973

The original Nelson office building and new home of Corporate Research in 1975

Prologue >

Nelson Industries, Inc. ca. 1973-81 On a warm summer day in 1973, I was driving through the rolling farmland of southern Wisconsin on my way to an important job interview when my car started smoking. Fortunately, a near-by service station was only a few miles away from my destination, the Nelson Muffler Corporation’s Bryant Building. While mechanics worked on my car, I arranged a ride to the interview. It wasn’t a great way to begin. The Nelson Muffler Corporation was founded in 1939 by Charles “Pete” E. Nelson, Edwin “Ed” E. Bryant, and Oscar “Ockie” F. Gusloff, in Stoughton, Wisconsin. The company was one of a number of spin-offs from Burgess Laboratories, a research company in nearby Madison formed in 1910 by C. F. Burgess, a noted electrical and chemical engineering professor at the University of Wisconsin. Nelson’s primary business was manufacturing mufflers, and later filters, for engine-powered vehicles and machinery. In the 1930s, many heavy duty and off-road vehicles had little, if any, muffling of the engine exhaust noise and so there were many opportunities in this area. Nelson developed a reputation as being able to supply custom designed quality mufflers in relatively low volumes at competitive prices. By 1972, it was still a rather small, privately traded company with sales just over 11 million dollars when it was hit by a double tragedy. First, its president, co-founder Ed Bryant, died of a

Waves of Silence

sudden heart attack. Following his death, Bjarne Lysne, the vicepresident of the company, took over only to also die of a sudden heart attack just three months later. Facing a management crisis, the Nelson board selected Rockne “Rock” Flowers, its longtime accountant, to be its next president. Fortunately, he didn’t suffer the fate of his predecessors and served as Nelson’s president for more than 25 years. Nelson was at a critical point in its history when Rock Flowers became president. New noise control regulations were creating increased demands and opportunities for its muffler and silencer businesses. One of the first things that Rock Flowers wanted to do as Nelson’s new president was to create a larger, more formal corporate research program. One small step in this process was to pick me up from the service station for my job interview. For many years, Nelson’s research activities were rather modest and had been directed by Dean Thomas. The focus was mainly on monitoring new developments in noise control equipment and measurement standards. After his retirement, Ralph Nelson and Eddy Seils continued Nelson’s research activities. When I learned that Nelson was looking for a new research director, I saw myself as a perfect fit. I was working at HarleyDavidson, an important Nelson customer, which gave me an inside perspective on Nelson’s products and technological needs. My background also included three years working at the Honeywell Research Center where I learned a great deal about acoustics and managing a corporate research department. Finally, I was interested in Nelson’s acoustical products, and, coming from a family of small business entrepreneurs, found Nelson’s small company culture appealing. Despite my anxiety over the state of my car, the job interview went well. In late August, I became Nelson’s director of research and began organizing a new Corporate Research department. Although our facilities and equipment were quite limited, they did 2

Nelson Industries, Inc.

include a small hemi-anechoic chamber that provided an echo-free space for muffler testing. We also had a larger quiet room and several engines for test purposes. My top priority was to assemble a staff of engineers and technicians for our research program. Like many other new ventures, our research offices were at the back of a small garage behind Nelson’s Stoughton headquarters. We shared space with a small metal working shop and a dusty storage area. It was cold in the winter and hot in the summer. We walked across a small parking lot to get to the main building for coffee breaks with other Nelson employees. Despite our humble offices, I was excited about the future. I knew from past experiences that the quality of our work would not depend on having fancy offices. Soon, our small, but welleducated research staff began to carry out a variety of research projects related to mufflers, catalytic convertors, and filters. Nelson’s headquarters was located in a small building on the edge of Stoughton, but its product manufacturing was done at a number of plants located in small towns throughout Wisconsin. These included muffler plants in Neillsville, Black River Falls, Viroqua, and Mineral Point, filter plants in Neillsville and Bloomer, and a silencer plant in Muscoda. Its muffler and filter products were sold to original equipment manufacturers (OEMs) of products like trucks, farm tractors, and small engines by a group of sales engineers based in Stoughton and also through an aftermarket distribution system. Its industrial silencers were sold through a national network of independent sales representatives as well as to a few direct customers. In January of 1974, the Nelson Muffler Corporation changed its corporate name to Nelson Industries, Inc. The new name distinguished the corporation from its main business unit, the Nelson Muffler Division, and served as an umbrella for its Universal Silencer Division, Nelson Filter Division, and Nelson’s Corporate Research department. 3

Waves of Silence

Nelson Industries, Inc. (formerly Nelson Muffler Corporation)

Nelson Muffler Division

Nelson Filter Division

Universal Silencer Division

Corporate Research

Fig. 1 - Nelson Industries, Inc. (1974)

At Nelson, the corporate management and board encouraged employees to develop new technology, improve existing products, and create new products. The culture both encouraged and required individual initiative; no large staff groups existed to provide support or bureaucracy. It was attractive to action oriented individuals who liked to see things get done. I enjoyed it after working for large businesses where change was often difficult. Employee education was a priority for the company in the early 1970s. Soon after I became director of research at Nelson, I presented a series of technical lectures on acoustics, noise control, and exhaust systems to a large group of Nelson employees. About this same time, Nelson approved a generous tuition refund program for those employees who wished to obtain jobrelated education on their own time and placed greater emphasis on formal education when hiring new employees. Nelson also supported employees who became participants and leaders in technical societies and trade associations.

4

Nelson Industries, Inc.

The atmosphere was friendly and informal. The company held coffee breaks in the hallway and everyone participated from the president to the newest employee. Meetings often included eating together or at least sharing a cup of coffee and perhaps a donut. > In 1975, Corporate Research entered a period of rapid change. Nelson completed its Gusloff office building, named for the third founder of Nelson, which became its new headquarters. Corporate Research moved from the old garage into Nelson’s former headquarters which was renamed the Nelson Technical Center. This move provided larger, much improved office space as well as welcome space for other specialized equipment. At the same time, the first of three major additions to the Technical Center was begun that would expand the original building into a first class research, development, and engineering facility. The 1975 addition included a very large hemi-anechoic test chamber big enough for large trucks or muffler measurements at a distance of fifty feet. It included an under-floor engine dynamometer test cell for testing vertical exhaust systems, a reverberant test chamber, several other engine Interior of large test cells, and a metal shop. hemi-anechoic chamber

5

Waves of Silence

Entrance to large hemi-anechoic chamber added to Nelson Technical Center in 1975 expansion

Also in 1975, Corporate Research received the first of its four grants from the National Science Foundation Faculty/Industry Research (NSF/FIR) Participation program. These grants supported visiting university professors to do summer research at the Nelson Corporate Research department. The participants joining us for a summer of research under our first NSF grant were Dr. John “Ed” Sneckenberger and Dr. Ivan Morse, both professors of mechanical engineering at West Virginia University and the University of Cincinnati, respectively. Ed and Ivan had extensive experience in research as well as teaching and brought a new energy to our research group. This included leading a series of “lunch hour discourses” in which they or someone else from research would make a presentation on a topic of interest that the group would then discuss.

6

Nelson Industries, Inc.

During their time with us, Ed and Ivan also pursued their own research projects. At this time, we needed a computer model to evaluate various muffler designs. Ed adapted a muffler modeling program published by NASA in 1973 to run on the time share computer network that we used at Nelson. Although it would later be succeeded by new and improved programs, it was an important step for our young research program. In addition to modeling muffler acoustical performance, we were interested in the effect of the acoustical pulses in an exhaust system on engine performance. On some engines, the proper tuning of the exhaust system response to these pulses can provide a significant increase in power output from the engine. Ivan developed a new pulse tube technique that enabled us to study these effects in a laboratory setting without an engine. A later NSF grant led to a relationship with Dr. Krishnamurthy “Jay” Jayaraman, a professor of chemical engineering at Michigan State University with a strong background in mathematical analysis and modeling. Jay developed a new decoupling approach for modeling the behavior of perforated tube muffler components. This resulted in several papers, one of which he co-authored with Dr. Prakash Thawani, a member of our Corporate Research staff with extensive experience in the computer modeling of mufflers. Ed, Ivan, and Jay were followed by a number of other visiting researchers, some under NSF/FIR grants, who worked on acoustics or filtration, another important technology for Nelson. Later, Nelson sponsored research projects at several of their universities. As a small company, it was important for us to connect with the outside world. Our NSF participants provided some of these connections and served as valuable role models. They increased the professionalism and expectations of the members of our research group.

7

Waves of Silence

Perhaps even more important, these NSF grants provided independent evidence that we were building a credible industrial research program. Receiving an NSF grant and having engineering professors from major research universities join us for a summer were heady activities for a small Wisconsin company. > Nelson’s connections with academia predated our NSF grants. Not long after I joined the company, Nelson’s president Rock Flowers suggested that I organize a Research Advisory Council (RAC). This group served as an informal board of directors for the Corporate Research department and was primarily composed of professors interested in Nelson’s products and technologies. The initial members were Dr. Phillip Myers, a mechanical engineering professor specializing in diesel engines at the University of Wisconsin-Madison, Dr. George Keulks, a chemistry professor specializing in catalysis at the University of WisconsinMilwaukee, Dr. Bradford Sturtevant, a professor of aeronautics specializing in nonlinear acoustics at the California Institute of Technology, Dr. Ernest Fitch, a professor specializing in fluid power at Oklahoma State University, and Dr. Herrell DeGraff, a specialist in agricultural economics who brought a business sensibility to our meetings. Later, Ed Sneckenberger and Ivan Morse, the first participants in the NSF/FIR program at Nelson, as well as Dr. Darsh Wasan, a professor of chemical engineering at the Illinois Institute of Technology, and Dr. Richard Greiner, a professor of electrical engineering at the UW-Madison, would also serve as members of the RAC and play important roles in Nelson’s research activities. The council met twice a year, typically near Stoughton at Nelson’s Bryant Building overlooking the waters of Lake Kegonsa. This building was named for co-founder Ed Bryant who 8

Nelson Industries, Inc.

had been an avid outdoorsman. The building’s striking contemporary design, scenic location, and distance from the main offices created a thoughtful atmosphere conducive to resolving problems, generating new ideas, and thinking about the future. The members of the Research Advisory Council increased our awareness of engineering research throughout the country. They also encouraged a creative mindset within our relatively small research group and more active involvement with the greater technical community. During our all day meetings, we would discuss our research activities as well as the latest developments in technology. It was not long before these discussions would have a major impact on the direction of our research program and the future of Nelson.

Nelson’s Bryant Building named after co-founder, Ed Bryant

9

Waves of Silence

“Oh, for a machine that will make artificial quiet!” (originally published in 1913 under the heading “Disquieting Noise” and republished 75 years later on June 15, 1988, in the International Herald Tribune)

10

Part I Innovations >

Waves of Silence

Nelson Technical Center in Stoughton, Wisconsin (1975)

12

-1Sound Fighting Sound ca. 1978-81 Beginning in about 1978, active noise control became a topic of recurring interest at meetings of the Research Advisory Council. This fascinating technology uses a microphone, some electrical circuitry, and a loudspeaker to generate a sound wave that is an exact mirror image of the undesired noise. Combining the sound from the loudspeaker with an undesired noise can, in principle, eliminate the undesired noise. The process is like smoothing the waves on a lake by creating “anti-waves” so that the peaks and valleys of the two sets of waves cancel each other. The loudspeaker pushes air into the less dense portions of the sound wave and pulls air from the more dense portions to eliminate the sound wave. It is completely different from sound masking systems in which sound is added to cover-up the undesired noise with music, rushing water, or random noise. The thought of somehow canceling or absorbing noise has captured the imagination of writers for a surprisingly long time. As long ago as 1913, a note in the International Herald Tribune called for a machine that would create quiet. In 1952, Radio-Electronics ran an April Fool’s Day article on a purported “electronic noise neutralizer.” The magical appeal of such a device even inspired Arthur C. Clarke to write his 1954 short story “Silence Please.” Anthologized in “Tales From the White Heart,” the story revolves around capacitors that absorb energy from sound waves, but later explode and kill the inventor. I first learned about active noise control from papers in the Journal of the Acoustical Society of America (JASA) when I worked at the Honeywell Research Center in the late 1960s. Since that time, I have continued to monitor the technology.

Waves of Silence

Fig. 2 - U.S. Patent 2,043,416 by Paul Lueg; microphone M senses the undesired noise and loudspeaker L generates the cancellation wave

The basic idea was described in U.S. patent 2,043,416, dated June 19, 1936, and issued to Paul Lueg, a German professor of physics at the University of Bonn. Although the Lueg patent was thought for many years to be the earliest published description of the electronic control of acoustic noise, a somewhat older French patent 722,274 on the topic, dated March 15, 1932, and issued to H. Coanda, was later uncovered. Dieter Guicking of the University of Göttingen has done considerable research on the life and work of Paul Lueg. He reports that Lueg probably got his idea late in 1932 and filed for a German patent on January 27, 1933. The German military initially classified Lueg’s work as secret. For some reason, perhaps due to a controversy over his invention, Lueg lost his position at the 14

Sound Fighting Sound

university by October of 1933. After an experimental demonstration, on Feb. 7, 1934, failed to convince the army of the feasibility of Lueg’s idea, they declassified his invention. Nonetheless, Guicking writes that when Lueg filed for a patent in the U.S. on March 8, 1934, as well as in several other European countries, he was regarded as a traitor. As a result, he was persecuted by the Nazi authorities and could not get a position in physics at any university. After working for some time on an unfinished textbook on physics, he survived this sad story to study medicine and later became a respected physician.

Fig. 3 - U.S. Patent 2,983,790 by H.F. Olson

15

Waves of Silence

Fig. 4 - U.S. Patent 2,776,020 by Conover, et al.

16

Sound Fighting Sound

In the years that followed, other researchers also began studying active noise control. In 1941, R. L. Wallace, Jr. at the Harvard University Electro-Acoustics Laboratory proposed active noise cancellation at the ear for use in communications systems. In the early 1950s, H. F. Olson filed a patent application on a feedback system in which a loudspeaker was driven by an amplified signal from a microphone. A few years later, William B. Conover, et al. applied for a patent on the electronic quieting of power transformers. From its beginning, active noise control often led to patentable inventions. Although the serious technical work of the 1950s led to papers and patents on the technology, there was not any widespread use of active noise control. As successive generations of researchers revisited the technology, laboratory demonstrations were often effective, but commercial applications remained elusive. A number of practical problems prevented the widespread application of active noise control to real world problems. The sound canceling wave must be an almost perfect mirror image of the undesired noise to obtain good results. It is difficult to obtain and maintain this precision over long periods of time in field installations. In addition, the undesired noise often contains a wide range of frequencies. In some applications, the sound is distributed in complex patterns that cannot be duplicated by only a few loudspeakers. These issues complicate the generation of the necessary noise canceling waveform in both time and space. In many applications, feedback from the loudspeaker to the input microphone can produce instabilities in the system. The effect is similar to the howling sound so familiar with public address systems when the microphone gets too close to the loudspeaker or the volume is turned up too high. Other problems included the high cost of the hardware, the need for powerful loudspeakers, and the harsh environments often present.

17

Waves of Silence

Fig. 5 - Tripole loudspeaker configuration from U.S. Patent 4,177,874 by Theophile A. Angelini, Bernard J. P. Nayrole, Maurice J. Jessel, Georges Canevet, Gerard A. Mangiante, Bernard Carbone

In the 1960s and 1970s, a new generation of researchers including Jessel, Mangiante, Swinbanks, Leventhall, and Kido continued to work on active noise control. Analog systems were developed using various combinations of two or even three loudspeakers to reduce acoustic feedback from the noise canceling loudspeakers to the microphone sensing the undesired noise. Geoff Leventhall, whose group at Chelsea College developed the Chelsea Monopole and Chelsea Dipole, presented an excellent overview of this era in his 1982 review paper at a meeting of the Acoustical Society of America (ASA) in Orlando. By the early 1980s, new approaches using digital techniques were beginning to appear, including systems developed by Chaplin, Ross, and Swinbanks. Although there were several demonstration projects, commercial activity remained limited. 18

Sound Fighting Sound

Nelson saw active noise control as both a threat and an opportunity. On the one hand, it had the potential of replacing some of the company’s traditional sheet metal mufflers and silencers with electronic systems. Such a change could affect the company’s existing investment in metal manufacturing as well as require major new investments in electronic systems. On the other hand, active silencing could provide new opportunities in silencing. Electronic or active silencers have a number of potential advantages compared to traditional passive silencers. They are most effective on low frequencies where passive silencers tend to be large, heavy, and expensive, their low flow restriction can save energy, and they can avoid or reduce the need for fibrous linings that may release fibers, clog, or catch fire. However, active silencers do require some degree of maintenance including occasional replacement of components. In some ways, active and passive silencing are complementary technologies that can be combined to produce compact broadband silencers. In addition to reducing noise, active systems can also reduce undesired vibrations in solids or liquids, For this reason, the technology is sometimes described as “active sound and vibration control (ASVC)” since it can control waves in gases, liquids, or solids. Although early active silencing systems were much more expensive than passive silencers, by the late 1970s and early 1980s, it appeared that the decreasing cost of electronics might soon make these systems more cost competitive. The question was how a metal bending company could explore a technology so heavily based upon electronics and computers.

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Waves of Silence

Electrical and Computer Engineering building at the UW-Madison (ca. 1980s)

20

-2Back to School ca. 1981-82 In late 1981, Craig Anderson, a research scientist in the Corporate Research department, approached me about arranging a meeting with the Electrical and Computer Engineering (ECE) department at the University of Wisconsin. He and Professor William Birkemeier, the chair of the department and a personal friend, had discussed how such a meeting could help Nelson develop a closer relationship with the ECE department. This meeting would have a far greater impact than I expected. I was quite familiar with the UW-Madison. I had taken several business classes at the university and was a regular lecturer at the annual UW-Extension program on internal combustion engine noise. Through this program as well as Nelson’s Research Advisory Council and other activities, I had become acquainted with a number of well-known professors of mechanical engineering at the UW-Madison. Ironically, despite my personal background in electrical engineering, I was not very familiar with the ECE department. For this reason, I found the meeting that we soon had with Professor Birkemeier and several other ECE professors very interesting. Most significantly, one of the professors at this meeting was Dr. Richard A. Greiner, a long time ECE faculty member who was developing a research program in audio and electroacoustics following a number of years in engineering administration. During the meeting, we discussed various ways in which Nelson might become better connected with the department. As we prepared to leave, Professor Birkemeier mentioned in passing that one good way to develop a better relationship would be if some Nelson engineers pursued graduate study in the department.

Waves of Silence

When I got home and discussed his suggestion with my wife, Karen, she thought this was a good idea and that I should be one of those students. I had always wanted to complete my graduate studies that had been interrupted by the draft during the Vietnam War. Obtaining my Ph.D. would give me a mid-career updating of my technical skills and provide the credential that I would need if I wanted to teach at the college level. In addition, returning to school would enable me to investigate active noise control for Nelson and give me a new direction for my work. Soon after our initial discussions at the ECE department meeting, I had a personal meeting with Dr. Greiner. I hoped he would be receptive to accepting me as a graduate student and beginning a research program on active noise control. It turned out that we shared a mutual excitement about the potential of digital signal processing (DSP) and active noise control. He was busy setting up a laboratory and beginning to recruit graduate students. My proposal came at the perfect time. Even though I looked forward to returning to school, I never imagined that I was about to begin the most productive and rewarding period of my career. It was also the beginning of a long professional and personal relationship with Dr. Greiner. In addition to our mutual interests in acoustics and digital signal processing, we also shared an early career interest in solid state physics, the area in which I had received my master’s degree. In fact, during the first phase of his academic career, Dr. Greiner had written the book Semiconductor Devices and Applications, one of the early textbooks on solid state devices. After my meeting with Dr. Greiner, I arranged a meeting at Nelson to discuss active noise control and my educational goals with Rock Flowers, my immediate superior and president of Nelson Industries. To pursue a doctorate in electrical engineering, I needed a flexible work schedule to attend some day classes at the university. I also asked for his approval to work part-time for two 22

Back to School

semesters while I was a full-time graduate student. In addition, Dr. Greiner would need financial support to begin a research program in active noise control. Fortunately, Rock was a progressive, forward thinking manager who gave me his approval and support in all three areas. Under his leadership, Nelson had a history of supporting the development of new technology as well as employee education through its tuition reimbursement program. > In January of 1982, I resumed my graduate study in electrical engineering and began taking courses in digital signal processing, control theory, and other topics. In addition, Dr. Greiner and I developed plans for a modest joint research program on active noise control at the UW-Madison and Nelson. In September, Nelson began supporting research by Dr. Greiner and one graduate student in his Electroacoustic Laboratory. In addition to Nelson’s funding, Dr. Greiner had several other research contracts which also supported his research activities. At this time, our collective knowledge of active noise control was very limited. Mark Allie, one of Dr. Greiner’s graduate students, studied active sound absorption in tubes using analog electronics. Mike Poimboeuf, another of Dr. Greiner’s graduate students, studied cancellation noise source design. My initial vision was that Nelson would continue the work on analog approaches that it began in 1981, while the UW would look at digital techniques. In reality, both groups studied analog systems for a brief period before shifting their focus to digital techniques in 1983. In 1982, Glenn Warnaka of the Lord Corporation published an excellent review of the history of active noise control in the journal Noise Control Engineering. In his paper, he noted that the 23

Waves of Silence

older approaches using analog signal processing were beginning to yield to techniques using digital signal processing. Warnaka suggested that “modern...computer technologies...require a level of expertise that may not be available to many acousticians.” In addition, a 1994 article in Design News by Lane Miller, also of the Lord Corporation, accurately noted that ASVC is “really a collection of technologies.” When our research began, Dr. Greiner, Mark Allie, and I had a good mix of skills and experience in a diverse range of electrical and mechanical technologies. These included acoustics, noise control, silencers, audio systems, analog electronics, and microprocessors. As a team, we were well-positioned to develop new systems using the emerging technology in digital signal processing and adaptive systems for active noise control. The combined resources of Nelson and the UW-Madison provided an excellent setting to advance the technology. Nelson had engineers, test equipment, acoustical facilities, and funding. The UW Electroacoustic Lab had graduate students, laboratory equipment, computers, and access to a broad range of university resources including other engineering faculty members and various engineering classes. The Wendt Engineering Library at the UW-Madison, with its extensive collection of journals and books, was particularly useful for tracking down papers and patents on digital signal processing, adaptive filter algorithms, and modern control theory. In addition, the various classes that I was taking added to my understanding of these topics. However, at this time, the number of courses or textbooks available on digital signal processing and adaptive filters was still rather limited. As a supplement, Dr. Greiner met with me and and several other graduate students on a regular basis to work our way through one of the few books that were relevant to our research interests. I also had discussions with researchers from other labs at conferences and meetings. 24

Back to School

As our research progressed, we wasted little time on lengthy meetings or waiting for management approvals. Dr. Greiner and I had the authority to make and carry out decisions quickly in our respective organizations. We generated many new ideas, evaluated them quickly, kept what worked, and moved on. As both vice-president of research at Nelson and one of Dr. Greiner’s graduate students, I bridged the gap between the two research groups and met regularly with Dr. Greiner often before or after one of my classes. > In the 1950s, television shows featured the new Univac “electronic brain.” However, despite the publicity gained by the Univac and later IBM mainframes, the computer was not an instant success. Campbell-Kelly and Aspray in their 1996 book Computer point out that in the 1950s, even smaller computers were still more expensive than old punched card systems, less reliable, and required specialists to write their programs. Early computers were giant machines by today’s standards. In the early 1960s, I saw a soon to be obsolete IBM 709 computer at Northwestern University that filled a large room with row upon row of cabinets packed with thousands of glowing vacuum tubes. A short time later, Northwestern built a new computer center for its first transistor-based computer. Using an early version of FORTRAN, students submitted programs on a stack of punched cards to the computer center. The next day, they would return to see if their programs had run correctly. If not, they had to resubmit the program and wait another day often due to simple mistakes such as having a single card missing or out of order. It wasn’t until I began work at Honeywell in 1968 that shared access to a digital computer through a time share terminal became available. Although a big improvement over stacks of punched 25

Waves of Silence

cards, early terminals were slow and noisy teletype machines that printed using simple block letters. Since many users were sharing a single computer, the response times were often very slow. Despite the spread of time share computing for engineering programs, the use of computers for other applications was still quite limited in most companies. Even in the 1970s, it was mainly larger companies that had mainframe computers for batch processing business data. Many smaller companies like Nelson continued to process their business data with adding machines and tabulating equipment using punched cards. Even in engineering laboratories, computers were not common. Laboratories in larger companies might have a minicomputer, but those at smaller firms often did not. Similarly, virtually all instruments still used analog electronics. A technological breakthrough occurred in 1971 when Intel produced the first microprocessor, the Intel 4004. Designed for an electronic calculator, it packed 2300 transistors onto a chip that was just 1/6” long and 1/8” wide. Engineers soon began abandoning their slide rules for fast, accurate, and later programmable, handheld calculators. Intel released a stream of improved versions of the 4004 and other companies also began producing microprocessors. By the late-1970s, engineers recognized that microprocessors could be used to create what became known as personal computers. This enabled Apple, Radio Shack, Commodore, Atari, and others to bring some of the capabilities of mainframe Atari 800 Personal Computer computers to individual 26

Back to School

users. These early personal computers, although very modest by current standards, were by no means toys. Accountants soon purchased Apple II computers to perform financial analyses using VISICALC, an early spreadsheet program. Engineers created models using programs in BASIC. After many years with computers that were large, expensive, and inaccessible, I found the new machines amazing. In 1981, I bought an Atari 800 personal computer with 48 KB of memory. By the late 1990s, typical laptops would have perhaps 32 MB of memory, and by 2013, perhaps 32 GB, an increase of almost 1000 times and 1,000,000 times, respectively, or about 20 doublings of size in 32 years – Moore’s law in action. Karen used the Atari to analyze survey data for her master’s degree research. Our kids used it to learn computer programming when they were in middle school. I would soon use it to evaluate adaptive control algorithms in my research on active noise control. > Even in the early stages of our research, we were convinced of the great potential of digital signal processing for active noise control. Digital systems convert the smoothly varying electrical voltage generated by a microphone into a series of numbers that can be readily processed with a computer program before being converted back into a smoothly varying voltage to power a loudspeaker. The calculations performed with the computer program implement a sequence of specific mathematical steps known as an algorithm designed to accomplish a desired goal. For example, a computer program might store the last five values of the input signal in its memory, multiply each value by its specified weight or coefficient, and add the resulting products to form an output signal. This simple process or algorithm is called a finite impulse response (or FIR) filter due to fact that its response 27

Waves of Silence

to an impulse ends when the last value of the signal is no longer stored in memory. An FIR filter algorithm implemented on a computer can modify a measured signal much like the capacitors and inductors of an analog filter. The response characteristics of an FIR filter are controlled by the values of the five coefficients that are used. On an active noise control system, the coefficients are automatically adjusted using an error signal to minimize the undesired noise. This is done using an adaptive algorithm that will be discussed in the next chapter. In my research on active noise control, I ran simulations of various adaptive filter algorithms on my Atari microcomputer. This was possible because the calculations did not have to occur in real-time. My relatively slow computer could take as much time as necessary to make the extensive calculations that were required on each digital sample of the sound wave.

coefficients

input

output

+

delay delay delay delay

Fig. 6 - A five tap Finite Impulse Response (FIR) filter; the digital inputs pass through four sample period delays, at each sample period, the values at each tap are multiplied by their respective coefficients, and summed to produce the filter output 28

Back to School

Of course, real world applications of active noise control systems have to operate at the actual frequency of the undesired noise. An analog to digital convertor must sample the signal from a microphone at a frequency at least twice the highest frequency of interest. The system might generate hundreds or even thousands of digital samples each second and perform over a million arithmetic operations per second. Half of these operations are multiplications. Multiplications were notoriously slow on general purpose microprocessors in the 1970s. Depending on the approach taken, there was typically at least an order of magnitude increase in the number of operations required for a multiplication compared to an addition which only required a single operation. General purpose microprocessors of that era were too slow for use in practical ANC systems. For this reason, L. Robert Morris notes in a 1986 technology review that in the 1970s digital signal processing algorithms were usually implemented on an array processor. These systems were large (about the size of a file cabinet), heavy (weighing close to 100 pounds), power hungry (consuming about a kilowatt of power), and expensive (costing tens of thousands of dollars). In order to create commercially successful active noise control systems, the price and size of the signal processing equipment had to be dramatically reduced. In 1981, despite the rapid advances in computers, there were not any microprocessors that met our needs. However, the prices of microprocessors were falling and their capabilities improving. We hoped that suitable hardware would be available when we were ready for product development.

29

Waves of Silence

Work bench with test system, controller, and spectrum analyzer

30

-3Adventures with Algorithms ca. 1983-84 By 1981, Nelson began to feel the effects of a severe economic recession. In its 1982-3 fiscal year, Nelson had a net annual loss for only the second time in its history. Nonetheless, the company focused on retaining its work force and continuing programs critical for its future. During this difficult period, there were no widespread layoffs or salary reductions. Despite shared belt-tightening and increased budget controls, Nelson maintained funding for the development of new technology and products. Many publicly traded firms look to these expenses as the first to be reduced. As a privately traded company, Nelson’s shareholders took a long term view of their investment in the company and its research on ASVC. This support was bolstered in mid-1984 when Nelson and the UW-Madison received a Technology Development Fund grant of $91,720 from the state of Wisconsin for research and development on ASVC. The funds from this three year grant went to the UWMadison, but the grant also had other benefits for our program. It helped validate our research activities for Nelson management and shareholders, provided more overall resources to the program, and enabled the UW to make longer term commitments to its graduate students. Nelson would later become one of the few companies that would exceed their stated job goal under this grant. > By 1983, our research activities were focused on developing adaptive approaches to active noise control using digital signal processing technology. Most previous research on ASVC had used

Waves of Silence

analog electronics. A microphone would sense the undesired noise, analog electronics would amplify it to the desired level, and one or more loudspeakers would generate an inverted noise canceling wave. However, with these relatively simple analog approaches, it was difficult to maintain optimum noise cancellation as the system or environment changed over time. In addition, as mentioned earlier, instability due to acoustic feedback from the loudspeaker to the input microphone was a persistent concern. On some systems, acoustic feedback from the loudspeaker to the sensing microphone was reduced with dipole or tripole arrangements of loudspeakers. Others avoided acoustic feedback by using a sync signal from a sensor on the noise generating machinery as the input signal to the cancellation system. Although this approach was an effective means of eliminating feedback, it could only be used for the control of periodic sounds (i.e. one or more tones). Adaptive approaches use software-based, self-learning algorithms that respond to environmental changes. They automatically optimize their performance by adjusting various parameters within the system. Since they are software-based, they can also provide sophisticated diagnostics and allow regular product upgrades. Adaptive control systems typically use an error signal that represents the difference between the current value of a system output and a desired value to guide their behavior. This error signal is used to modify the characteristics of the control system until the system output matches the desired value reducing the error signal to zero. If future changes in the system cause the error signal to increase, the control system automatically adapts itself until the system output once again matches the desired value. In an active noise control system, an error signal is formed by a microphone that measures the combination of the undesired noise with the canceling noise from the loudspeaker. 32

Adventures with Algorithms

One simple approach to reducing the error between an actual and desired signal is the Least Mean Squares (LMS) adaptive filter developed by Bernard Widrow and M. E. Hoff, Jr. in 1960. Widrow’s chapter in the 1971 book Aspects of Network and Systems Theory gives an excellent overview of the behavior of this adaptive filter algorithm. The LMS adaptive input algorithm uses an FIR digital desired signal filter to generate an output delay signal. The difference C between the system output – and the desired signal forms the error signal. The value of delay the error signal is multiplied by a gain factor as well as the + value of the input signal at each step or tap of the FIR -2k filter. This product is then X added to the previous value of the coefficient for that tap to create an updated value of Fig. 7 - LMS algorithm for a simple the coefficient. In this way, single coefficient adaptive FIR filter; C=weighting coefficient; the product every coefficient is modified of the input and error signals is on each iteration of the added to the old coefficient to form a algorithm by a term that is new value of the coefficient; “–2k” = proportional to the previous small gain factor value of the error signal. If the gain factor that is used to scale the error signal is small enough, the coefficients of the adaptive filter will converge to a stable solution that minimizes the mean squared error for the system. Relatively few computations are required per iteration of the algorithm and the results are often startlingly effective. error

+

33

Waves of Silence

Over the years, the LMS algorithm has found a diverse range of applications. These include modeling the behavior of unknown systems, creating a filter that will remove undesired noise from a system, or matching the output of a system to a desired result. > While learning about the LMS algorithm, I came across two papers that helped to further define the direction of our research program. John Burgess of the University of Hawaii published the first paper in JASA in 1981. It demonstrated the use of the LMS algorithm for active noise control using computer simulations. This paper describes several modification to the classic LMS algorithm that can be difficult to explain. The primary difference between the classic LMS algorithm and that used for active noise control is the presence of error path transfer functions including the loudspeaker, error path acoustics, and error microphone. As a consequence, the input signals to the coefficient updating process or error correlators in the LMS algorithm must be filtered by these error path transfer functions. The paper by Burgess was published independently, but at about the same time as related work by Dennis Morgan and Bernard Widrow. Morgan referred to the problem as a “...cancellation loop with a filter in the auxiliary path.” Widrow referred to the LMS adaptive filter algorithm with filtered input signals as the filtered-X algorithm. A research team from Penn State University and the Lord Corporation presented the second paper at the International Conference on Acoustics, Speech, and Signal Processing (ICASSP 84) conference that I attended in San Diego (see Poole, Warnaka, and Cutter, 1984; also patent by Warnaka, Poole, Tichy, 1984). Their paper described a partially adaptive three-model active noise control system using the LMS algorithm. As in the paper by 34

Adventures with Algorithms

Burgess, it used an adaptive LMS filter to cancel the undesired noise. It also included a second predetermined fixed filter to compensate for the error path acoustics. Finally, it included a third fixed filter to reduce the effects of feedback using a predetermined fixed model of the feedback path. The systems described by Burgess and Poole, et al. both used a microphone to sense the undesired noise and provide an input signal for an LMS adaptive filter. A second microphone measured the residual noise downstream from the loudspeaker and provided an error signal that the LMS algorithm minimized by modifying the response of the adaptive filter. Two basic problems remained with both systems. The first problem was the need to adaptively compensate for the acoustic feedback from the loudspeaker to the upstream sensing microphone that could cause the system to go unstable. The system described by Poole, et al. used a predetermined, fixed electrical feedback model to compensate for the feedback from the loudspeaker to the input microphone. This model was derived from a training signal used to model the feedback path through the system. However, in general, the characteristics of the feedback path in actual applications will vary with temperature, flow, and other parameters. For optimum performance, an adaptive rather than fixed approach to feedback compensation was desirable. The second problem was the need to adaptively compensate for the transfer functions in the error path due to the loudspeaker, error microphone, and error path acoustics. Both of the previous systems used a predetermined, fixed error path model that could be derived using a training signal. However, as with acoustic feedback, the characteristics of the loudspeaker and the error path will vary over time in actual applications due to temperature, flow, aging, and other factors. And as with acoustic feedback compensation, an adaptive rather than fixed approach to error path compensation was more desirable. 35

Waves of Silence

After reviewing these papers as well as many others, I visualized a fully adaptive approach that would not require any pre-training or initial knowledge of the acoustical system or noise source. It would automatically compensate for changes in the noise source as well as the system acoustics including the feedback path and the error path. System identification is a useful framework for the development of active noise control systems. In system identification, a computer-based adaptive “model” is connected in parallel with a physical “plant.” The plant for an active noise control system includes the duct, pipe, or other structures between the input microphone and the output loudspeaker. The model includes the input microphone, related electronics, computer, power amplifier, and loudspeaker. The system identification configuration has a number of advantages. When the model adapts to match the response of the plant, the undesired noise is eliminated. Changes in the plant will be tracked by changes in the model to maintain cancellation. In general, the model does not have to track changes in the noise source. When the characteristics of the noise source change, the modified noise passes through the parallel configuration of the plant and model, and the noise remains cancelled.

noise source

plant

+

model Fig. 8 - System identification approach

36

–

Adventures with Algorithms

Rather than treating feedback compensation as a problem separate from noise cancellation, I thought it might be possible to combine the problems. Perhaps the feedback path could be considered as an inherent part of the model. This rather vague thought led me to think about adaptive algorithms that included a feedback path in their filter structure. The LMS adaptive algorithm uses a feedforward FIR filter structure in which the output goes directly to the loudspeaker. However, there are also recursive filter structures in which the output of the adaptive filter depends on both the input signal as well as its own output due to a feedback loop within the filter. These structures are known as infinite impulse response (or IIR) filters since their response to an impulse continues indefinitely due to the feedback loop. At the time, I didn’t know of any adaptive filters with a recursive structure. A report later published in 1984 by Steve Elliott and Phil Nelson from the University of Southampton in the United Kingdom, briefly discussed a recursive filter structure for active noise control, but stated that they didn’t know of an adaptive approach for this recursive structure either. While thinking about this problem and considering various approaches, serendipity played a valuable role. While browsing through the journal archives of the Wendt Engineering Library in Madison, I found a paper on a recursive adaptive filter published in 1976 by Paul Feintuch. In this brief paper, Feintuch described a recursive adaptive IIR filter that he called the Recursive Least Mean Squares (RLMS) algorithm. In the RLMS algorithm, the input signal again passes through an LMS adaptive filter. However, the output of this filter is added to the output of a second LMS adaptive filter to form the overall filter output. The input to this LMS second filter is the filter output. This gives the overall system a feedback loop from its output through the second filter to the output of the first filter. 37

Waves of Silence

Fig. 9 - RLMS adaptive filter on a duct (from U. S. Patent 4,677,677 by Larry J. Eriksson) After discovering the Feintuch paper, I ran a simple active noise control simulation of his RLMS algorithm with error path compensation on my Atari 800 microcomputer. My simulation studies enabled me to evaluate various algorithms, use pure tones or broadband noise, adjust acoustic feedback, modify the error path, and change the physical system. Although it was convenient to have my own computer, by today’s standards, the Atari and its printer were extremely slow. I spent many long evenings in my basement trying various combinations of parameters. The modified RLMS algorithm seemed to work very well. Without any specific physical information on the system or the characteristics of the noise source, the adaptive system adjusted itself to cancel both pure tones as well as random noise with or without acoustic feedback using only information from the input and error signals.

38

Adventures with Algorithms

Error path compensation required a process similar to that used in the filtered-X algorithm. However, with a recursive filter, the composite input vector (the combined input vector to both the first and second LMS adaptive filters) to the coefficient updating process or error correlators had to be filtered by the error path transfer functions. The composite input vector for a recursive filter is designated “U” in Widrow and Stearn’s 1985 book Adaptive Signal Processing, Inspired by the “filtered-X” designation used by Widrow for a non-recursive adaptive filter with error path compensation, I decided to call my adaptive recursive algorithm the “filtered-U” algorithm. This algorithm could cancel the undesired noise by simultaneously modeling the acoustic plant and compensating for acoustic feedback. The new approach and its development is described in detail in U. S. Patent 4,677,677 as well as my 1991 JASA paper. The filtered-U algorithm could be used to reduce undesired waves propagating through air, liquids, or solids. Depending on the application, the input and error sensors might be microphones, hydrophones, or accelerometers. Similarly, the output transducers might be loudspeakers, pneumatic actuators, or electrodynamic shakers. In the early stages of our work, simulation programs on low cost personal computers like my Atari 800 were adequate, but realtime signal processing could produce results much faster than simulations on personal computers. In addition, any hope of developing a commercial product was dependent on finding a reasonably priced microprocessor with sufficient power to run our algorithms on a real time basis. Fortunately, a solution to this problem was just around the corner.

39

Waves of Silence

Initial Nelson dX-30 Digital Sound Controller (the only control is the power switch)

Close-up of Digisonix double sine wave logo (designed by Jim Galbraith)

40

-4Riding the Digital Wave ca. 1983-86 The serendipitous release in 1983 of the Texas Instruments TMS32010 Digital Signal Processor, the first member of its TMS320 family, gave us the powerful microprocessor that we needed for our ASVC systems. The features and architecture of this breakthrough product were ideal for the high speed number crunching used in digital signal processing, and it rapidly became a big commercial success. The TMS32010 Digital Signal Processor used fixed point arithmetic and featured a built-in multiplier that could perform a multiply-accumulate in one cycle, on-chip random access memory (RAM), fast cycle times, and long word lengths. It could also access external memory and used external analog to digital (A/D) and digital to analog (D/A) convertors which avoided potential noise problems on the chip. About twenty-five years after the DSP project was initiated at Texas Instruments, Tony Leigh, who was the design manager for the TMS32010, wrote a very interesting personal memoir of the history of its development. According to Leigh, Texas Instruments began working on the Signal Processing Computer (SPC) that would become the TMS32010 Digital Signal Processor in 1979. He reports that its name stemmed from its 32 bit arithmetic logic unit combined with an “01” for the first unit and a final zero to make the five digit name that Texas Instruments used for its high speed chips in that era. Interestingly, the chip was first envisioned with a microcomputer architecture, but this was later changed to a microprocessor architecture. This fortuitous development led to its ability to use external memory and other features.

Waves of Silence

Leigh writes that the development project was encouraged by a paper by Intel, already a dominant supplier of microprocessors, on its new i2920 DSP chip. This generated additional interest at Texas Instruments in digital signal processing and the new SPC project. Although it came out earlier, the Intel chip did not have a hardware multiplier which was a major limitation. It was the hardware multiplier and flexible architecture that led to the broad acceptance of the TMS32010 for digital signal processing. Leigh notes that this led to T.I. becoming a dominant supplier of digital signal processor chips for decades to come. Coincidentally, Texas Instruments development of its TMS32010 Digital Signal Processor took place virtually in parallel with Nelson’s development of its active noise control signal processing algorithms. The projects had a surprising number of similarities. Both traced their roots to the late 1970s, were inspired by new developments in digital signal processing, were encouraged by competitive pressures, and were led by a small team of dedicated engineers driven by an exciting, new project. These two completely independent efforts came together in the 1983 when we decided to use the TMS32010, that T.I. had just released, in the new controller we were developing for ANC. The perfect timing of the two projects couldn’t have been better if it had been planned. In years to come, Texas Instruments announced a steady stream of improved digital signal processors in its TMS320 family. The initial 32010 and 32020 chips used NMOS technology, but this was soon replaced by improved CMOS technology on all T.I. DSP chips. This included the 320C1x, 320C2x, and 320C5x devices that used fixed point arithmetic, and the 320C3x and 320C4x devices that used floating point arithmetic. Other manufacturers soon produced similar families of chips including the Analog Devices ADSP2100, Motorola DSP56000/96000, and AT&T DSP16/32. 42

Riding the Digital Wave

These revolutionary new digital signal processing chips brought the signal processing capabilities of the array processors used in the 1970s to small integrated circuit chips. Morris noted in his 1986 review that they were three orders of magnitude better than array processors with respect to size, weight, power consumption, and cost. Two year later, in 1988, Morris and Dyer wrote a brief note that favorably compared the raw number crunching performance of a low cost TMS320C30 Digital Signal Processor to that of various supercomputers. These dramatic changes enabled active noise control systems to move from racks of expensive equipment to compact, reasonably priced controller boxes. > Nelson was among the first companies to use the new TMS32010 computer chip. Dr. Greiner from the UW-Madison and Mark Allie, his graduate student who soon began working at Nelson, attended one of the first training classes offered by T.I. on their new processor. At this class, thanks to their extensive background in electronics and ability to master new technology, Dr. Greiner and Mark Allie soon moved from students to helping instruct other attendees in the class. After the course, Mark Allie began using a T.I. evaluation board equipped with a TMS32010 processor at Nelson. He quickly confirmed the effectiveness of the filtered-U algorithm on a realtime system. In the months that followed, Mark and I worked closely together to create many improvements to our filtered-U algorithm. As we discussed various refinements, Mark was able to quickly modify the software and evaluate the changes using the TMS32010 evaluation board. It wasn’t long before he also began designing a signal processing board that would become the heart of our first ASVC controller. 43

Waves of Silence

Development controller using TMS32010 evaluation board (left)

As mentioned earlier, Mark Allie and I had technical backgrounds that were virtually ideal for our ASVC product development program. I had experience in acoustics, silencers, digital signal processing, and adaptive systems. In addition, as vice-president of research for Nelson, I had ready access to the resources that we needed to move the project along. Mark brought experience in electroacoustics, analog electronics, digital electronics, and DSP software. As a recent graduate student at the UW-Madison, he also had a close working relationship with Dr. Greiner and other students at the UW-Madison. Mark and I also shared an enthusiastic, “can-do” attitude that enabled us to make things happen fast. Our complementary talents and good working relationship led to a long and productive partnership that resulted in many papers, patents, and products.

44

Riding the Digital Wave

In the summer of 1985, after nearly four years of study and research, I completed my doctoral thesis entitled Active Sound Attenuation Using Adaptive Digital Signal Processing Techniques. In the fall, I presented the results of my research at a faculty seminar of the ECE department. I later attended a graduation ceremony in the old UW-Madison field house on a wintry December day. This completed a long journey that I had begun as a graduate student at the University of Minnesota in 1967. Afterwards, I received a three year appointment as an adjunct assistant professor at the UW-Madison and taught or co-taught two courses on digital signal processing and adaptive filters. At this time, the UW had very few faculty members with a background in DSP. However, within a year or two of my graduation, several additional professors were added in this fast-growing area. As business demands on my time were increasing, I was happy to be replaced by highly qualified instructors. Various groups also began expressing interest in hearing more about our work. Active noise control was becoming a popular topic because of the growing interest in digital signal processing, the commercial potential of our technology, and the magical appeal of canceling noise with noise. I made presentations at technical conferences and university seminars as well as meetings of local civic groups interested in a local company that was doing some intriguing work. In some cases, Dr. Greiner would join me for a joint presentation on our research activities. I always enjoyed an opportunity to describe the interesting field of ANC. > Although I had completed my thesis, one troubling technical problem remained. I remained dissatisfied with our ad hoc approaches to error path modeling. I felt sure that there had to be a more elegant solution for the products we were developing. 45

Waves of Silence

In October of 1985, Jim Galbraith, a colleague at Nelson, showed me a brief magazine article in Forbes magazine that he thought I would find interesting. The article described Manfred Schroeder’s research on designing sound absorbing diffusers using principles from number theory. I knew very little about these techniques, but did enjoy reading the article and wanted to learn more about them. Although they had no apparent connection with active noise control, I had developed the life-long habit of following up on whatever curiosity came my way. And so, I obtained a copy of Schroeder’s book Number Theory in Science and Communication that was cited in the article. The book included a discussion of the challenges facing acoustical engineers in determining the acoustical properties of performance halls. Since the presence of the audience has a significant effect on the acoustics of a large hall, measurements must be made when the hall is full of people. This requires a patient and cooperative audience which is inconvenient and not always possible. In his book, Schroeder describes a technique that avoids these problems. It injects a very low level of random noise into the hall while it is occupied and being used for a concert. The added noise is quiet enough that the audience cannot hear it, but through signal processing, the acoustics of the hall can still be identified. As I read about this technique, I immediately recognized that we could use a similar approach to model the response of the loudspeaker and error path. By introducing a low level of random noise into the system that is inaudible to the listeners, we could model the loudspeaker and error path while we were canceling the undesired noise. The random noise is sent to both the loudspeaker as well as an additional adaptive filter. An error signal for this adaptive filter is formed from its output and the signal from the error microphone. Any changes in the response of the loudspeakers and error path would be determined by this modeling process and incorporated in the filtered-U algorithm. 46

Riding the Digital Wave

Fig. 10 - RLMS adaptive filter with on-line error path modeling (from U. S. Patent 4,677,676 by Larry J. Eriksson)

The additional adaptive filter creates a model of the speaker and error path that can be used to filter the input signals to the coefficient updating process or error correlators (associated with the multipliers) for the RLMS adaptive filter. This approach worked extremely well. It led to ASVC systems that were fully self-adapting and that responded to all changes in the physical system and noise source. The complete system is described in detail in U. S. Patent 4,677,676. This new approach to error path modeling was an example of finding a new way of looking at a vexing problem by exploring the nooks and crannies of the literature. I’m not sure whether this is easier or harder now that we are in the Internet era. It is easier to find what you are looking for, but not everything is available, especially the older and more obscure sources. In addition, you don’t always know exactly what you want, and on-line scanning is often quite difficult. 47

Waves of Silence

undesired noise feedback

canceling noise acoustical

mic

electrical

speaker

mic

dX-30 controller

- filtered-U algorithm (IIR/RLMS) - on-line error path modeling - power amplifier

error signal Fig. 11 - Overview of Digisonix active control system using dX-30 controller with TMS32010 processor

By late 1986, a small Corporate Research team that included Mark Allie, Rich Hoops, Mike Diederich, Henri Dutilly, and Ron Kindschi, a local consultant experienced in the design of electronic products, had a prototype of our first active noise controller ready for testing. The initial Nelson Digital Sound Controller placed the electronics in a single metal enclosure for ease of installation. The TMS32010-based control board was mounted vertically beneath a shelf that held an audio power amplifier to drive the loudspeakers. This arrangement, conceived by Ron Kindschi, enhanced the convective flow of cooling air across the computer board and placed the warm power amplifier at the top of the unit. 48

Riding the Digital Wave

top: dX-30 board with TMS32010 (long black chip at left center) bottom: dX-40 board with TMS32020 (square chip at left center)

The unit, designed to be wall-mounted, had only a single control, the power switch. It required no setup procedure or special programming – it was completely self-adjusting. Initially, we built five prototypes units for field testing. We had gone from virtual novices in ASVC in 1982 to having a prototype product using a custom-designed TMS32010 computer board and patented signal processing algorithms ready for field testing by late 1986 – from nothing to a sophisticated commercial product in a little over four years. At first, we considered calling our new controller the “DSC-320,” combining the initials of Digital Sound Controller with numerals from its processor, the TMS32010. We also considered various permutations such as dX-320, DC-320, DC-30, and NX-30, before finally settling on dX-30, a simple variation on the “30 dB” reduction in sound levels that the unit could produce for pure tones (almost a ten-fold reduction in loudness). As it 49

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turned out, the dX-30 name for our controller also worked very well with the Digisonix name that we would select a few months later for the name of our new business unit. > Our early use of adaptive digital filters and digital signal processors was a classic example of joining a new wave of technological change at almost the perfect moment. This led to a steady stream of innovations and patents. In the early years, we had regular meetings with Michael Taken, our patent attorney at the Andrus law firm in Milwaukee, to discuss our patent strategy and the preparation of patent applications. In later years, Ed Williams from the Andrus firm joined Mike due to the increase in patent activity at Digisonix. These meetings often broadened our view of our inventions and led to stronger patents, a process mentioned by Walter Isaacson in his recent book The Innovators. Since the patents illustrated in Figs. 9 and 10 covered major advances in ASVC technology, they contained relatively broad claims. They also led to additional patents many of which were later cited by others. Nelson and Digisonix would ultimately receive at least 45 patents with 28 different inventors from Nelson, Digisonix, and the UW-Madison as listed in Table 5. Many of these patents also had foreign counterparts in other countries. By the end of 1986, our progress in active noise control had received relatively little attention. We had only demonstrated our prototype systems in a laboratory setting and were just beginning to present papers on our work. We continued to work in relative anonymity both at Nelson and within the general technical community. However, our innovations and new products would soon have a significant impact on Nelson and the world of active sound and vibration control.

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Reflection: Shoestring Budgets The innovative portfolio of ASVC technologies and products that we developed at Nelson through our partnership with Dr. Greiner and his Electroacoustics Laboratory at the UW-Madison was created on a very modest budget. In the early years of our ASVC program, some employees quipped that they worked at a little firm they called “Three Guy’s Cancellation.” The research staff working on ASVC was indeed rather small, about 3-4 Nelson employees most of whom also had other responsibilities, several graduate students at the UW, and a few summer students. The students at the UW were funded by Nelson as well as our grant from the Wisconsin Technology Development Fund. In addition to a small staff, we minimized expenses whenever possible. The research that we performed with our frugal budget led to major innovations in active sound control protected by multiple patents and a broad range of commercial opportunities for Nelson Industries. Small, quick, and cheap are often the watchwords to achieving rapid progress in a research and development program.

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– haiku –

Active Sound Control Searching for silence, smart computers controlling sound canceling sound

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Part II Digisonix >

Waves of Silence

Introduction of the Nelson dX-30 controller at the Anaheim ASA meeting in December of 1986

Side view of Sheboygan field test site; the loudspeakers are installed on the first vertical stack from the right (with the dark extension); note flag blowing in wind and Lake Michigan in the distance on the left.

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-5Getting Down to Business ca. 1986-87 In November of 1986, after extensive testing in the laboratory, we were ready to test our new ANC system on a full scale industrial fan on the roof of a large manufacturing plant in Sheboygan, Wisconsin. A typical passive silencer for this fan would have arrived on a large truck and required a crane for its installation. We only needed to pack a loudspeaker, two microphones, and our dX-30 controller into the back of my station wagon. We also loaded a spectrum analyzer to evaluate system performance and headed north. After several hours, we arrived at the manufacturing plant and hauled our apparatus to the roof of the building high above Lake Michigan. The installation of new technology in the field can often be challenging, and this job was no exception. The unusually cold and windy weather that fall compounded the difficulty. On our first visit, we used just one loudspeaker on the fan discharge duct. Despite our best efforts in the blustery weather, we were disappointed, though not too surprised, when we could not get the system to function properly. After several more visits, we realized we needed more power and added a second loudspeaker with a short length of additional ductwork to obtain the sound levels required to cancel the undesired noise. The selection and placement of loudspeakers was often a challenge on early installations involving large fans. After these modifications were made with the help of Mike Diederich, a technician from Corporate Research, the system performed beautifully. We could turn on the controller, watch it automatically adjust itself, and hear the dramatic reduction of the sound levels of the two strong tones generated by the fan. I never

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grew tired of pushing the switch on the controller and hearing the noise from this large fan suddenly drop by over 20 decibels. This experience inspired the slogan “Turn on the Quiet” that I crafted for use with our ASVC products. Reality sometimes literally matched the marketing. In 1992, Popular Science published an article on a Digisonix system installed on a waste incinerator fan. The article quoted an environmental engineer who reported that switching on the Digisonix silencing system was “like switching the fan off.” At about the same time, I worked with Mike Diederich on the installation of an active silencing system on the large air handling system used in Nelson’s Gusloff office building in Stoughton. During this installation, I mentioned that Steve Jobs of Apple Computer placed the signatures of the team that developed the Macintosh computer on the inside of its case. With this encouragement, Mike proceeded to sign his name with a marker boldly across the speaker module that he was installing. It was a physical affirmation of the personal commitment that we all felt to our new technology at this time. The noise produced by the air handler on the heating, ventilation, and air conditioning (HVAC) system in our office building was dominated by broadband low frequency “rumble” rather than the two strong tones of the industrial fan in Sheboygan. In addition, installation space was limited, and the duct size was much larger than that used by most industrial fans. The flow from large fans typically contains turbulent pressure fluctuations that do not propagate down the duct at the same rate as the undesired noise, but do cause problems for the microphones. The impact of these slow moving pressure fluctuations on the microphone signals can be reduced through the use of antiturbulence probe tubes attached to the microphone and aimed at the fan. Covered with an acoustically resistive material, they effectively perform a spatial average of the turbulent pressure 56

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fluctuations over their length that leaves the undesired noise as the primary microphone signal. Initially, we used metal tubes with a long slit along their length that we wrapped with layers of felt or cloth. We obtained a patent on our design, and they worked fairly well. However, they were difficult and costly to produce. We soon changed to probes using a hard, porous plastic tube that worked well and was much easier to make. You simply cut a tube of suitable length, usually about three or four feet, plug one end and attach a microphone to the other end. We also received a patent on probe tubes using this approach. The other critical element of our active sound control systems was the output transducer. In large air handlers, the environment was rather benign and standard loudspeakers were suitable. However, in industrial applications, the loudspeakers sometimes had to be protected from harsh environments. It was usually sufficient to simply cover the loudspeaker cone with a flexible membrane. In some applications, condensation inside the loudspeaker enclosure was also a problem. This led to the development of a patented approach in which air flow through the enclosure prevented condensation. > In the summer of 1986, I presented a paper that I wrote with Mark Allie and Dr. Greiner at the 12th International Congress on Acoustics (ICA) meeting in Toronto, Canada. This was our first paper on ANC and the RLMS algorithm that we subsequently called the filtered-U algorithm. Our joint program with the UWMadison was also featured in a number of UW-Madison publications. After years of hard work, it was good to see the results of our joint research program finally being presented.

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In December, at the Anaheim meeting of the Acoustical Society of America, Mark Allie and I displayed our new controller in a public setting for the first time. At this meeting, we had an opportunity to discuss our work with John Burgess from the University of Hawaii whose paper had played a major role in our research. I also presented a technical paper that I authored with Mark Allie on our new technique for on-line modeling of the error path using random noise. In Anaheim, we distributed an Advance Product Information sheet entitled “Nelson dX-30 Digital Sound Controller with Single Switch Silencing” and a sheet with a list of “Frequently Asked Questions (FAQ).” The information sheet emphasized the advantages of our active silencers compared to passive silencers including improved low frequency effectiveness, spectral shaping, low flow restriction, compact size, and easy retrofits. The FAQ also discussed four specific applications where these advantages might be particularly valuable: • Quieting HVAC systems in recording studios and broadcast facilities which are especially noise sensitive, in medical and biological facilities where duct linings often used in passive silencers may be unacceptable, and in semiconductor manufacturing facilities where noise and vibration can affect product quality. In future years, we would install successful systems in virtually all of these areas. • Quieting large industrial fans with high levels of noise to protect workers and the surrounding neighborhood. This application also became one of our more successful product opportunities for active noise control.

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• Quieting ventilation noise from specialized modules and enclosures which might otherwise escape through the cooling ducts used to bring air into and out of the enclosure. This application, though seemingly an excellent opportunity for active noise control, was never pursued to any significant degree. • Reducing pump pulsations and noise in water and other liquids that can affect product quality or damage equipment in processes such as paper manufacturing. This application used the same controller as the other areas, but required transducers designed for use in liquids to replace the normal loudspeaker and microphones. This application was one of the first that we investigated with some success, but it never developed into a meaningful business. Some of the questions and answers were fairly straightforward. For example, FAQ responses noted that our technology was effective on broadband as well as as tonal noise and automatically adjusted itself when the power was turned on. It successfully followed changes in the amplitude or frequency of the noise. It adapted to environmental changes such as temperature. It required minimal maintenance and was easy to install and repair. Others questions and answers were more complicated. For example, how do you select the number of loudspeakers – depends on the sound power level. Where do you place the microphones and loudspeakers – place the input microphone close, but not too close, to the fan with four to six feet between the input microphone and loudspeakers. How do you handle noise radiation from the speaker module or duct walls upstream from the speaker – try to place these elements in the mechanical room. In hindsight, some of the answers on the sheet were a bit facile. For example, questions about where to place the input 59

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microphone and how much distance is required between the input microphone and the loudspeaker would remain troubling application issues. In addition, system performance could be compromised by higher order modes in large ducts that might require multiple transducers and multi-channel signal processing. The FAQ sheet became a mainstay of our ANC literature. People often asked many of the same questions when they first encountered the fascinating concept of electronic noise cancellation. > In February of 1987, Nelson formed a new business unit in Corporate Research to commercialize our ASVC technology. Up to this point, we had used the Nelson name on our early controllers, but now a new name was needed. After considering a number of alternatives, the new unit became Digisonix – a name that combined the digital and sonic aspects of the business with a contemporary look and sound. The initial mission of the new unit was to design, manufacture, and sell active noise control systems for industrial fans and HVAC systems. In the 1980s, a number of other companies were also pursuing ASVC technology. The Lord Corporation had announced an active noise attenuation system in the early 1980s. Noise Cancellation Technologies (NCT) was formed in the mid-1980s and used the technology developed by Barrie Chaplin at the University of Essex in the United Kingdom. Also in the United Kingdom, Topexpress, a research and consulting firm formed in 1978, and the Lotus Technology division of Group Lotus were exploring the use of ASVC for interior quieting in automobiles. In the United States, Active Noise and Vibration Technologies (ANVT) was founded in 1987. Nissan and Hitachi were among the Japanese companies also pursuing active noise control. 60

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Soon after Digisonix was formed, Art Hallstrom joined Corporate Research and became marketing manager for Digisonix. Art had gained considerable experience at Trane, a major HVAC system manufacturer based in La Crosse, Wisconsin. He was soon joined by Steve Wise who became sales manager. Steve was familiar with industrial fans and had previously Nelson Industries, Inc. worked at Dresser Industries. Digisonix also added Ron Weber as a marketing engineer, and Cary Bremigan, who had Universal Nelson Corporate just received his MSEE Silencer Division Research with Dr. Greiner as his Division advisor. Dennis Johnson and Mike Diederich transferred from Nelson Digisonix to work on administration unit and manufacturing respectively. Fig. 12 - Digisonix (Feb., 1987) Mark Allie, Rich Hoops, and Henri Dutilly remained with me in Corporate Research where we continued to further develop the technology. Jim Galbraith worked on market research and projects related to our ASVC program. He also designed the Digisonix double sine wave logo that we used on the front of our first controller and subsequent Digisonix literature. With space at a premium in the Tech Center, Digisonix, like Corporate Research, found its first home in an old garage that had once been a John Deere tractor dealership. Although the building was well-worn, it was fairly large and had a convenient location just a short walk away. Digisonix added a modern mobile office unit next to this building for its growing staff. 61

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With the increased staff, product development activities accelerated. Digisonix built another batch of twenty dX-30 controllers. Based on the unexpectedly high power requirements we were encountering, the latest design included a built-in fan with space for a more powerful power amplifier. Our first full color brochure featured the heading “Turn on the Quiet” and focused on the effectiveness of Digisonix systems on low frequency noise. In June, Mark Allie and I presented a paper at the Noise-Con 87 meeting at Penn State University on the effectiveness of our new products in reducing low frequency rumble in HVAC systems.

Nelson Industries, Inc.

Nelson Division

Universal Silencer Division

Digisonix Division

Corporate Research

Fig. 13 - Digisonix Division (Sept., 1987)

At the end of August, Nelson decided to separate the embryonic Digisonix unit from Corporate Research and made it the Digisonix Division of Nelson Industries. Art Hallstrom became general manager and was later elected president. Digisonix continued to add staff, construct new test facilities, and expand its marketing program, although its sales were still very modest. That fall, Art Hallstrom hosted a gathering of the ASVC team at his home on Lake Waubesa. The small group gathered around a large bonfire to celebrate the beginning of our new business. 62

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Outside the company in 1987, Nelson began funding ASVC research at Purdue University led by Robert Bernhard, a professor of mechanical engineering at Purdue’s Herrick Laboratories which had a long history of noise control research. In the coming years, a number of Purdue graduate students would complete thesis projects on ASVC often involving computer modeling. I also served on Herrick’s Industrial Advisory Council. Through its meetings as well as additional meetings at both Purdue and Nelson, we developed a close relationship that made this new collaborative research program very useful. About the same time, Manohar Munjal, a noted scientist from the Indian Institute of Science in Bangalore, worked with us in Stoughton as a visiting researcher. He was a long time friend of Prakash Thawani, a senior research engineer at Nelson who had his Ph.D. in mechanical engineering. Dr. Munjal specialized in acoustical modeling and applied his skills to various research topics in ASVC. Papers generated from his work at Nelson soon appeared in the Journal of the Acoustical Society of America and the Journal of Sound and Vibration. Media interest in ASVC technology and Digisonix was also increasing. Publications began producing news articles on ANC such as the Industry Week article “Industrial Noise Control.” Press releases on Digisonix products appeared in publications including NoiseNews; Air, Conditioning, Heating and Refrigeration News; IMN; Heating/Piping/Air Conditioning, and Power. Perhaps most noteworthy, The New York Times published a major article “New Technology Defeats Unwanted Noise” on June 6, 1987. It included a review of ASVC technology, a discussion of the companies that were involved including Digisonix, and a few of my comments from a brief interview. Active noise control had clearly begun to emerge from the laboratories.

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Original Digisonix sign in front of the former garage that was its initial home (ca. 1987)

Mobile office next to Digisonix building (ca. 1988)

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-6Quieting Fans ca. 1988-89 In January of 1988, Digisonix demonstrated its new dX-45 controller in a hotel suite during the Dallas meeting of the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). This demonstration, competing with the Super Bowl on television, exposed many people to Digisonix and its products for the first time. The dX-45 controller, designed for commercial HVAC applications, used a smaller shoe-box sized “black box” enclosure with an external power amplifier. This system was easier to install and less expensive to build than the large enclosure developed for the dX-30. The larger enclosure continued to be used on industrial applications due to its rugged construction and single package design. The Digisonix dX-4X family of controllers evolved from research by Cary Bremigan and other students at the UW-Madison led by Dr. Greiner on the more powerful, second generation TMS32020 Digital Signal Processor chip. The dX-35 and dX-45 controllers used the TMS32010 and TMS32020 chips respectively in the new smaller, less expensive black box enclosure. In addition to the dX-45 controller aimed at commercial HVAC applications, Digisonix also developed a new dX-47 controller based on the latest TMS320C25 chip. It had greater flexibility and was aimed at research and development activities at original equipment manufacturers (OEMs) and universities. The goal was to gain acceptance of Digisonix technology and to encourage OEMs to incorporate it into their products. It foreshadowed the DigiWare development system that Digisonix would announce a few years later.

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Cut-away dX-45 controller for development work

Back in Stoughton, Digisonix established the Digisonix Testing Laboratory (DTL) in the old garage building that was now its headquarters. Managed by Ron Weber, this laboratory enabled Digisonix to demonstrate the performance of its ANC systems on actual fans. A short time later, a small metal building across the highway from Nelson provided additional testing space. It was known by some as the annex and by others with tongue in cheek as the “Greater Nelson Acoustics Research Laboratory.” Digisonix products were relatively small, but the ductwork and fans on which they were used were often very large. The active system was sometimes integrated with a passive silencer to form a hybrid active-passive silencer. Our first patent described ways to incorporate an active silencing system into both rectangular and circular passive duct silencers. Other patents described more practical packages for installation under a car or for protecting the loudspeakers from the high temperatures in an exhaust system. On the marketing side, the cover of the February, 1988, issue of Sound and Vibration magazine featured a photo of our 66

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Sheboygan installation. This issue also included an article on that installation that I wrote with Mark Allie entitled “A Practical System for Active Attenuation in Ducts.” Along with this article, Digisonix ran a full page ad with the heading “We’re Changing the Way Industry Controls Noise.” Eleven additional active silencing systems were later installed on other large fans at the Sheboygan plant. The number of sites with Digisonix active noise control systems on commercial HVAC systems also steadily increased. Some installations were retrofit applications, while other systems were installed in new buildings. Newsletters described these installations to a growing audience. Initially, Digisonix active silencing business was divided between industrial fan installations like Sheboygan dominated by high level, tonal noise, and commercial HVAC fan installations like the Gusloff building dominated by broadband, low frequency rumble. Despite the great differences in the nature of the noise encountered in these applications, the flexibility of our hardware and adaptive control algorithm enabled the same controller and software to be used for both types of problems. In one early HVAC retrofit installation, a university wanted to convert some basement space to offices. However, this space was very noisy due to low frequency “rumble” from a nearby HVAC fan. There was little space available for the installation of a passive silencer that was only expected to provide a modest 2-3 dB improvement and would require expensive modifications. In addition, the increased restriction on the air flow might have required a new fan and increased energy consumption. Instead, a Digisonix system was installed on a supply-side duct, and broadband cancellation of 15-20 dB was achieved from 40-300 Hz. Noise Criterion (NC) ratings are used to rate noise in enclosed spaces, and the office area went from a noisy NC 56 to an acceptable NC 42, a reduction of 14 NC points. The customer called the system a “life-saver.” 67

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Active silencing on centrifugal fans (photos courtesy of Steve Wise)

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Active silencing on material handling fan

Active silencing on vacuum pump discharge (photos courtesy of Steve Wise)

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Another case history involved quieting the HVAC systems in a broadcast studio. Digisonix systems were installed on the supply and return ducts for two studios. In the larger studio, broadband attenuation of 12-20 dB was achieved from 40-160 Hz. Again, the low frequency noise would have been difficult to reduce with passive silencers, particularly in a retrofit installation. > We continued to take advantage of every opportunity to make presentations or publish papers on Digisonix technology and products. In April of 1988, I co-authored two papers with Mark Allie, Cary Bremigan, and Dr. Greiner. They were presented in New York at ICASSP 88 sponsored by the Institute of Electrical and Electronics Engineers (IEEE). The first paper focused on our adaptive algorithms. The second focused on the hardware and software used to implement these algorithms on the TMS32010 and TMS32020 microprocessors. This conference also provided an opportunity to meet other ANC researchers including Steve Elliott from the Institute of Sound and Vibration Research (ISVR) at the University of Southampton, Stuart Flockton from the University of London, Colin Ross from Cambridge University, Alain Roure from NCRS in France, and Dave Swanson from Textron. In June, I went to Helsinki, Finland, where I presented a paper co-authored with Mark Allie at the International Symposium on Circuits and Systems (ISCAS). This trip concluded with a stop in Sweden for a conference in Stockholm and a visit to Chalmers University in Göttenburg. At Chalmers, I met with several ANC researchers and made another presentation on our work. Digisonix enjoyed a growing reputation as a leader in the application of active noise control to fan noise. This led to an invitation for a Digisonix team to attend a meeting in Hawaii of 70

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the National Council of Acoustical Consultants (NCAC) in November of 1988. The meeting was held at the Coco Palms resort on the island of Kauai, a beautiful resort that was heavily damaged not long after our meeting by a major hurricane that hit the island. At this meeting, the Digisonix team made presentations on Digisonix technology and its active noise control products. After enjoying the beauty of Kauai, I returned to Oahu to attend a national meeting of the ASA. Just a few weeks after returning home, the national meeting of the American Society of Mechanical Engineers (ASME) was held much closer to home in Chicago. I presented a paper co-authored with Mark Allie, Cary Bremigan, and Jim Gilbert that gave a broad overview of both our technology as well as some of our installations. At this meeting, I also spoke with Bob Bernhard from Purdue University and again saw Stuart Flockton from the University of London whose recent work focused on the RLMS IIR algorithm. After the meeting, I drove back to Madison with Dieter Guicking, an active noise control researcher from the University of Göttingen in Germany. The interdisciplinary nature of active noise control overlaps physics as well as electrical, mechanical, and automotive engineering. For this reason, Digisonix and Nelson personnel regularly attended conferences of the ASA, IEEE, ASME, ASHRAE, Society of Automotive Engineers (SAE), and Institute for Noise Control Engineering (INCE). For many years, INCE had sponsored the annual Inter-Noise conferences that were held throughout the world. It also sponsored Noise-Con meetings that were held in alternate years when InterNoise was held outside of the United States. Sessions on active sound and vibration control quickly became a significant part of both meetings.

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A week before Christmas in 1988, I accompanied a small group from Nelson on another trip to Europe that completed a very busy year. In addition to several business meetings, we met with Colin Ross at Cambridge University as well as Geoff Leventhall at Southbank Polytechnic in London. It was an interesting trip and fun to see England dressed up for Christmas, but also good to return home. Trips to Europe would become somewhat routine for many of us at Digisonix in the coming years to attend technical conferences and make presentations to potential partners or customers. There was a high level of international interest in ASVC with significant research activities in many countries. These included the United States, the United Kingdom, Germany, France, Sweden, Australia, and Japan. The relatively small group of researchers in ASVC soon began meeting on a fairly regular basis at various conferences around the world to present and discuss the latest developments in this emerging field. > Digisonix staff now included Chris Depies and Stu Austin in sales, and Rich Hoffman, Tim Funk, and David Kapsos in engineering. Although Digisonix was still a tiny division of Nelson, it had installed its ANC products in a growing number of commercial installations, primarily on industrial fans and building HVAC systems. In addition, a number of companies began visiting Nelson and Digisonix to explore incorporating its technology into their own products. This led Nelson to explore a wider range of applications of ASVC. Foreshadowing future developments, the first installation at Nelson of active noise control on a diesel engine exhaust occurred in 1988. This was followed by the installation of active exhaust and active intake silencing on a car in 1989. 72

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Digisonix display (ca. early 1990s) “We’re Changing the Way Industry Controls Noise”

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In addition to our work on active silencers, Autoweek ran an article “Noise+Noise=Silence” on April 25, 1988. This article discussed the work of other researchers on using active noise control to control the interior low frequency “boom” in cars equipped with 4-cylinder engines. It foreshadowed what would become, many years later, another successful application of ANC. Articles in the trade press continued to build interest in ASVC. In May of 1989, Popular Mechanics became the latest mainstream publication to carry an article on the technology. There were also articles at this time on the business side of the emerging industry in The Milwaukee Sentinel and High Technology Business. The headlines of the articles became ever more creative. The Chicago Sun-Times ran the article “Anti-Noise Waves Douse Din” in December. A new textbook, Fundamentals of Noise Control Engineering by Thumann and Miller, was published that also included a section on active noise control. An article by Rebecca Kolberg in the Los Angeles Times gave a particularly good overview of active sound and vibration control technology and products at this time. It included my comment that active noise control products are most effective on tones with frequencies below the A above middle C (i.e. 440 Hz) – a rough estimate that may be more descriptive for some people. One of the more novel applications that Corporate Research had briefly explored in 1986 was reducing the pressure pulsations from pumps that transport the pulp slurry in paper making machines. These pulsations can produce density variations in the paper that is produced. Our system was quite effective, but did not generate any significant commercial activity. Regardless, it was an interesting application that I discussed in a presentation at the 1989 Wood and Paper Seminar at the UW-Madison. Also in 1989, Wisconsin Professional Engineer published an article by Jim Galbraith that gave a good overview of active noise control, our technology, and the relationship we had with the UW74

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Madison. I made presentations at a Technology Outlook Seminar at the UW-Madison and at Northwestern University where I had done my undergraduate studies. This was followed by a presentation in 1990 at a colloquium at the University of Minnesota where I had received my master’s degree. The number of meetings and conferences that featured presentations from Digisonix on ASVC continued to grow. I presented papers at ICASSP 89 in Glasgow, Scotland, Inter-Noise 89 in Newport Beach, California, and two meetings in 1989 and 1991 of the IEEE Workshop on Signal Processing at the Mohonk Mountain House. Mohonk, a particularly intriguing conference venue, was placed near the top of a craggy mountain overlooking a beautiful mountain lake near New Paltz, New York. The Mountain House was an old rustic, but multistory hotel with a long history and filled with character. Countless hiking paths wound their way through the rocky outcroppings around the lake and provided exceptional views of the countryside beyond. The unique location was perfect for a small meeting of specialists working on acoustical signal processing and active noise control. In 1989, Digisonix added new staff members including Susan Dineen, who had worked in Corporate Research, in marketing and Seth Goodman and Kirk Burlage in product development. It also promoted its new controllers through various articles, press releases, and advertisements. One of these press releases resulted in Designfax designating the Digisonix controller as its Five-Star Product of the Month for April of 1989 due to the large response that it generated. In addition, Time magazine published the article “Fighting Noise with Antinoise” in its December 4, 1989, issue. In one interesting development and perhaps in response to Digisonix marketing of active fan silencers, a major manufacturer of acoustical products announced a new line of passive silencers. They claimed that these silencers offered reduced flow restriction 75

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and improved attenuation of low frequency noise. These were also among the most important advantages that Digisonix used to promote its active fan silencers. Whatever their motivation, it certainly seemed to be a response to Digisonix claims and products. It was in some ways encouraging to learn that our well-established competitor seemed to be responding to our activities. Of course, their response also might make selling our new products that much more difficult. > Despite all of the progress being made at Digisonix, we were entering a difficult period. Expectations were high for this new division of Nelson. However, sales were slow to develop. ASVC was a new and unfamiliar technology for most people. They were often reluctant to use what they saw as an unproven technology. There were also other issues. Our experience was still quite limited. It was barely two years since our first industrial fan installation in Sheboygan. It was less than that for our first HVAC installations. We regularly encountered unexpected problems in new installations. These were due to the complexities of retro-fit installations as well as our still limited understanding of some technical questions. We had to simultaneously resolve various technical issues, convince potential customers to use this promising new technology, and maintain the financial support of our parent company. To compound our problems, in April of 1989, the Wisconsin State Journal reported that Nicolet, a noted Madison-based electronics firm, was discontinuing sale of its innovative digital hearing aid. This announcement was in some ways a cautionary tale for Digisonix. Although digital hearing aids are very different than digital active silencers, the Nicolet report still generated some concern about the commercial future of new digital products. 76

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There were undoubtedly many differences between the Nicolet hearing aid program and the Nelson ASVC program. Nicolet cited marketing issues including a lack of distributors and a suitable partner, as well as product issues. These included the large size of their product and its two-piece design that required a connecting wire between the units. In addition, the Nicolet unit cost about 2-3 times the cost of competitive units. Although some of these concerns also applied to Digisonix, our active silencing products appeared better aligned with Nelson’s core businesses of mufflers and silencers. In addition, the article reported that Nicolet had spent a substantial amount to acquire the rights to their technology. Over a somewhat longer period from 1982-1987, Nelson had spent the comparatively modest amount, by my rough estimate, of about one million dollars in developing its ASVC technology, products, and business which it owned outright. Nonetheless, I still found the Nicolet story disconcerting. Despite these diverse issues, throughout 1989, more encouraging news items continued to appear concerning automotive applications. The automotive market is difficult to penetrate, but its extremely high volumes have long attracted the interest of many companies. On November 11, 1989, a brief news announcement appeared in the Automotive Electronics Journal under the headline “Quiet Please” that discussed the possibility of a joint development program between the Ford Motor Company and Nelson Industries. This program would soon have a major impact on both Nelson Industries and Digisonix.

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Experimental active muffler system on Ford Explorer at a Digisonix Open House (mirror at right shows underside of vehicle with prototype electronic muffler installed; controller housed behind exposed side panel at upper right)

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-7Driving Ahead ca. 1990-91 As suggested by the note in the Automotive Electronics Journal, Nelson Industries was indeed having discussions with the Ford Motor Company. These discussions stemmed from a series of earlier meetings between engineers of both companies. In August of 1988, Dr. Earl Geddes of the Ford Electronics Division visited Nelson with several others to discuss our work on exhaust systems and active noise control. In February of 1989, I went to Dearborn to meet with Earl, make a presentation on exhaust systems, and discuss the possible purchase by Ford of Digisonix equipment. The following September, we had another meeting in Stoughton with Earl that included Mark Allie, Cary Bremigan, and myself to discuss active noise control. These initial technical meetings evolved into a series of business meetings between managers from both companies beginning in the fall of 1989. In November, Steve Dickmann, Nelson’s general counsel, and I met with managers from the Ford Electronics Division in Dearborn, Michigan. Later meetings included Rock Flowers, president of Nelson Industries, as well as several senior managers from Ford. In the spring of 1990, these activities culminated in a major joint development agreement between Nelson and Ford involving the application of ASVC technology to cars and light trucks. On May 10, a wintry day in Madison with several inches of very late snow, Nelson sent its representative to Detroit to personally receive the substantial check that sealed the deal. According to the Nelson financial report for the quarter ending May 31, 1990, the agreement added about one million dollars to Nelson’s net income for the quarter.

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Nelson Industries, Inc.

Nelson Division

Universal Silencer Division

Digisonix Division

Corporate Research

Advanced Development Group

Fig. 14 - Nelson/Digisonix ASVC program (ca. 1990)

Nelson’s annual report later stated that the Ford program added $2,706,550 of revenue for the 1990 fiscal year, much of which dropped down to the bottom line. This was a significant amount for Nelson, a company whose overall net income for 1990 was slightly more than five million dollars. Equally important to those of us involved with Digisonix and ASVC, the agreement and its financial impact helped to further validate Nelson’s continuing investments in its ASVC program. It changed the perception of Digisonix and ASVC at Nelson in a big way. In the early 1980s, when Nelson’s investment was very modest, I think ASVC was seen as simply an interesting technology related to mufflers and silencers. With the Ford program in 1990, the former “science project” had brought in big dollars and a relationship that appeared to have great potential. 80

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Although most people saw the Ford and Nelson joint development program as a great opportunity, some felt it was an unwelcome distraction to Digisonix existing activities. I appreciated both points of view, but in addition to opportunities with Ford, I felt that the program also brought time and resources that helped our efforts to commercialize other applications. After the signing of the joint development agreement with Ford, activities quickly accelerated. Nelson personnel working on the Ford program became part of the new Nelson Advanced Development Group (ADG) within Corporate Research directed by Cary Bremigan. This group occupied a leased facility on Stewart Street in Madison along with Ford engineers assigned to the joint development program. Nelson’s ASVC activities now included the ADG working on automotive applications with Ford and the Digisonix Division working on fans. At first, only the front portion of the large Stewart Street building was used, but the program rapidly expanded and soon filled the entire building. The initial focus was primarily on electronic mufflers for vehicles, an area that Nelson had only given limited attention to prior to the Ford program. However, there were many other potential applications of active sound and vibration control on automobiles. In the years to come, our development activities would also investigate active intake silencing, active interior quieting, and active engine mounts. > In June of 1990, Digisonix announced a combination active/ passive HVAC silencing system under the name “Digiduct.” It featured an acoustically lined duct section with built-in speakers, microphones and controller. This approach combined the low frequency effectiveness of active noise control with the high frequency effectiveness of passive silencing. Many trade 81

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magazines published the press release on this product including Engineered Systems, Consulting/Specifying Engineer, Sound and Vibration, and Contracting Business. Also in 1990, the UW-Madison and Digisonix began presenting a series of short courses entitled “Applying ‘Active’ Silencers to Ducts and Fans Seminar” directed by Donald Baxa of the UW-Madison Extension Division. Digisonix and Nelson staff members made presentations which included a tour of the Digisonix laboratories. They were another good way to familiarize potential customers with Nelson and Digisonix ASVC technology and products. The UW College of Engineering also published an article on “Controlling Industrial Noise: The Computer Age is Here.” The article discussed our joint research with the UW Electroacoustics Laboratory and was one of a number of articles published by the UW-Madison during this period. The response that it generated was described by a UW staff member as “quite amazing.” Another UW article in Wisconsin Spotlight was entitled “The UW helped us develop a new technology at Nelson Industries.” It focused on the advantages derived by companies working with the university. Interest in active sound and vibration control continued to grow throughout the world. Articles discussing this rapidly evolving field had already appeared in publications such as The New York Times, Time magazine, and the Financial Times. In addition, a number of televised reports at the local and national level featured active noise control. I also attended and made presentations at Acoustics 90 in Southampton, England, Noise-Con 90 at the University of Texas, and numerous seminars. Meanwhile, Steve Wise had become president of the Digisonix Division. In 1991, Digisonix moved into a larger facility on Murphy Drive in Middleton just west of Madison. It needed more space to mock-up full-size HVAC and industrial fan installations for demonstrations and testing. At this time, Digisonix was still 82

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focused on business opportunities for active silencing systems on commercial and industrial fans. > Early in 1991, I joined a group from Nelson and Ford that went to Osaka, Japan, to meet with the staff of a large electronics firm and visit several of their facilities. The joint development program with Ford was proceeding smoothly, and we wanted to meet with potential partners that might assist us with components for the systems that we were developing. After these meetings, most of the group returned to the United States, but I flew to Tokyo to give a presentation at the International Symposium on Active Control of Sound and Vibration. After one night in a small, but ultramodern room in a high rise hotel, I moved to a room provided by the organizers in a smaller, but still comfortable hotel specifically used for conference guests. This major conference featured presentations by researchers in ASVC from around the world and included simultaneous translation into a number of languages. In Tokyo, I also joined a team from Digisonix and visited several companies interested in our technology. One of these was Ebara, a Japanese company that had become a partner of Digisonix. Their brochures for their EQAS active silencing systems for HVAC applications in the Japanese market featured Digisonix products and technology. For the week that I was in Tokyo, we were lucky enough to find the cherry blossoms in full bloom. With other friends from the conference and Digisonix, I walked along the various lagoons and parks near the Imperial Palace that were lined with beautiful flowering trees. People filled the walks and spread blankets to sit and enjoy the extravagant scene. For some of us, this beautiful and

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evocative setting also led to lengthy discussions on the future of Digisonix and active noise control. The next morning before my flight home, I wanted to take advantage of the remaining hours of my visit and took the subway – alone during rush hour, quite an experience – to visit Shinjuku Gyoen, a large park in Tokyo with extensive Japanese gardens. It was an overcast gray morning, and the park was almost empty at that early hour. The cherry blossoms were falling like snow and gathering in small drifts along the walks.

Shinjuku Gyoen park in Tokyo after ASVC Symposium

At one especially lovely spot, I saw a traditional Japanese building across a small lake surrounded by fallen cherry blossoms. A photo that I took of its wistful beauty now hangs in my home as a constant reminder of this remarkable trip. It was memorable not only because of the interesting culture, wonderful people, and beautiful sights that I saw, but also because of the enthusiasm generated by the international interest in active noise control.

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After the conference, I received an invitation to have an abbreviated version of my paper from the conference proceedings published in the Transactions of the I.E.E. Japan. It was the first time that I had seen one of my papers in Japanese – fortunately, the journal took responsibility for the translation. It put a nice sense of closure to an experience that was personally enjoyable and from a business perspective very exciting. > Immediately upon my return to Wisconsin and reflecting the hectic pace of this period, Karen and I drove to yet another major technical meeting. This was the initial 1991 conference on Recent Advances in Active Control of Vibration and Sound held at the Virginia Polytechnic Institute (VPI) in Blacksburg, Virginia. I made a rather philosophical presentation entitled “The Continuing Evolution of Active Noise Control with Special Emphasis on Ductborne Noise.” It reflected on the future of ANC and introduced the concept of a “virtual acoustic reality.” Two years later, in 1993, a second conference was also held at VPI. By 1995, it was called Active 95 and was held in Newport Beach, California. These biennial meetings evolved into a series of the largest conferences focused exclusively on ASVC. The year continued to be full of new developments. In addition to the new facility for Digisonix on Murphy Drive, Nelson also began construction of the largest addition in the history of its Technical Center in Stoughton. Many years earlier, the Technical Center started out as a small building that had been Nelson’s original office building. Previous additions over the years had added new laboratories for its work on acoustical and filtration products. However, growth in all areas of the company had created a demand for a much larger facility.

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The new addition provided new offices for my Corporate Research department as well as more space for ASVC research and Nelson’s work on mufflers, industrial silencers, filtration products, and emissions control devices. This project doubled the size of what was already a large facility to about 78,000 square feet. The result of this addition along with extensive remodeling was virtually a new building. The extension of the joint development program with Ford led to the other big news of 1991. Nelson combined all of its ASVC activities into a newly formed Nelson ASVC Group with Steve Dickmann as the general manager. Steve had been with Nelson for a number of years and continued to serve as Nelson’s corporate secretary and general counsel. The new ASVC group included both the Digisonix Division of which Steve Wise remained president and the Advanced Development Group working on the joint development program with Ford engineers on Stewart Street. The ADG had previously been part of the Nelson Corporate Research department. Automotive applications of ASVC had become a hot topic and were featured in a flurry of news articles. The Wall Street Journal published “Anti-Noise System May Exhaust Need for Car Mufflers” in a February issue that mentioned Ford’s interest in the technology. The Atlantic Monthly published “Cut Out That Racket” in November. Also in November, articles in Automotive Industries and The Nikkei Weekly discussed Nissan’s use of an active system developed with Lotus for quieting the interior of its Bluebird ARX-Z model in Japan. The Automotive Industries article also mentioned patent claims raised by Noise Cancellation Technologies. It was an early indication of how patent issues might affect the commercial future of ASVC. Other articles also appeared at both the state and national level. The Milwaukee Journal published “Sh-h-h-h...New devices cut noise” in February. The highly regarded journal Science 86

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Nelson Industries, Inc.

Nelson Division

Universal Silencer Division

ASVC Group

Digisonix Division

Corporate Research

Advanced Development Group

Fig. 15 - Nelson ASVC Group (1991)

published “Antinoise Creates the Sounds of Silence” in April that included comments from an interview with Dr. Greiner. In September, U.S. News and World Report published “Good News About Noise” and The Milwaukee Sentinel published two articles “Shhharp ideas at UW” as well as “Sounds of Silence.” In addition to these articles in the popular media, Geoff Leventhall, as co-editor, announced a new publication called the International Journal of Active Control and invited me to join its editorial board along with several other ASVC researchers. Locally, the Ford program led to a one hour interview that I had with Matt Joseph on his public radio program “About Cars” broadcast on WHA in Madison. I enjoyed the opportunity to discuss the technology and the work that we were doing. We received calls from listeners throughout the state that covered a wide range of interests and questions. ASVC was a topic that always seemed to generate considerable curiosity.

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At the end of 1991, Karen joined me on another long trip, this time to Sydney, Australia. I made a presentation at the Inter-Noise 91 conference and reconnected with the global ASVC community. The following weekend, we drove to Canberra, the beautiful capital of Australia, and Melbourne. From there, we took the Great Ocean Road with its fabulous views to Adelaide. Colin Hansen at the University of Adelaide had invited me to lecture at a week-long course on “Active Control of Noise and Vibration.” Other lecturers included Steve Elliott and Phil Nelson from ISVR in Southampton, Colin Ross from 2020 Science in the U.K., Chris Fuller from Virginia Polytechnic Institute, Andy von Flotow from MIT in the U.S., and Colin Hansen, Scott Snyder, and Jie Pan from the University of Adelaide. After the course, Karen and I flew to Alice Springs and drove to Yulara to see Uluru, also known as Ayers Rock. We then went to Cairns in northeastern Australia to see the Great Barrier Reef. It was a great ending to a very interesting trip. When we returned home, the Ford program was proceeding as planned and field tests were underway of electronic mufflers on a small fleet of Ford Explorers. Major original equipment manufacturers (OEMs) were contacting Digisonix on a regular basis. Some of these were interested in HVAC systems and industrial fans, but manufacturers of other products were also beginning to explore the technology. We were adding new customers and employees on almost a weekly basis. A number of the new employees were joining Nelson or Digisonix after their graduate study at the UW-Madison with Dr. Greiner. Mark Allie and Cary Bremigan had led the way in the mid-1980s after completion of their master’s degrees, and others soon followed. In addition to Dr. Greiner’s former students, Nelson and Digisonix also hired other engineers from the UWMadison as well as other well-known engineering schools.

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Some Digisonix employees also began returning to school, as I had, for part-time graduate study, often with Dr, Greiner. The two-way flow of engineers strengthened the relationship between the UW and Nelson. We gained a better appreciation of the issues and constraints for both university students and engineers in industry. Graduate students had demands from their coursework that sometimes got in the way of their research. Nelson engineers had demands on their time from other projects and activities. Nelson personnel had to temper their sometimes too impatient, product-oriented perspective, while university personnel had to temper their sometimes too theoretical, academic perspective. Our close working relationship helped to minimize conflict from these issues. The combined research effort became a smoothly integrated team of engineers from Nelson and the university. > From a tiny start-up in 1987, Digisonix had progressed in just four years to a substantial, growing, and complex business. It was pursuing the commercialization of its ASVC technology with a variety of customers in a number of different industries. In order to meet these growing demands and anticipated future opportunities, Nelson decided to significantly increase its investment in Digisonix. The rate of change was accelerating and often disorienting. In the earlier days, there was time to reflect without the need to make almost continuous decisions. Now, event followed event with barely a break. By 1991, we were entering a world of almost continuous action – and the real growth was yet to come.

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Eriksson-Geddes Development Center (Nelson–Ford) on Stewart Street in Madison (1992)

Close-up of Nelson-Ford sign on Stewart Street facility

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-8Digisonix, Inc. ca. 1992-1993 On a mild winter day early in 1992, Dr. Earl Geddes of the Ford Motor Company and I jointly removed the covering from a large new sign on the Nelson facility on Stewart Street. It revealed that the building had become the Eriksson-Geddes Development Center. Earl and I were the technical leaders from each company most closely associated with the joint development program. The name recognized our individual contributions, but also emphasized the growing relationship between Ford and Nelson. The new name did lead to a few problems. Some years later, I learned that some people incorrectly believed that Ford was the owner or co-owner of Digisonix. On a lighter note, I laughed when people told me they thought only dead people got buildings named after them. Despite the accolades, I was more interested in making Digisonix a sustainable business and active noise control an accepted technology. A short time later, Digisonix announced that it had granted Ford a non-exclusive, worldwide license to its ASVC technology for use on cars and light trucks. This license agreement and the Eriksson-Geddes Development Center encouraged the growing expectations that many people had for the Ford program. I shared their enthusiasm and had already devoted more than a decade of my life to ASVC technology and Digisonix. However, some of these expectations were probably becoming somewhat unrealistic. After all, the Ford program was only a development program to explore a promising new technology. The automotive industry considers and rejects many new technologies and product ideas every year. We were a long way from having a product ready for production.

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Interest in ASVC continued unabated. In 1992, articles on ASVC appeared in Popular Science magazine as well as Newsweek. Virtually all major news and science magazines had now published one or more articles on this interesting and powerful technology. The Hansen Report on Automotive Electronics published a report in June, 1992, on automotive applications of electronic noise and vibration control. The article discussed activities at ANVT, Digisonix, Lotus Engineering, Nissan, Hitachi, and NCT as well as many of the companies with which they had affiliations. Although The Hansen Report discussed many applications including active engine mounts, active air induction, and cabin quieting, its primary focus was on electronic mufflers. The potential advantages of electronic mufflers were said to be improved fuel economy, more power, better silencing, and decreased weight. It also reported on the results of a Delphi study conducted at the University of Michigan using OEM panelists. The study concluded that by the year 2000, 20% of North American cars would have electronic mufflers and 10% would have active cabin quieting. An air of optimism was clearly evident. Product development activity was expanding in many different directions. During this time of rapid growth, Dieter Guicking at the University of Göttingen in Germany published several papers and a series of extensive bibliographies on ASVC publications and patents. He concluded that the number of publications and patents on ASVC was doubling about every five years (see Fig. 28). > During this period, major changes were occurring on an almost daily basis. Early in 1992, Digisonix expanded into the entire building at its Murphy Drive location in Middleton to 92

Digisonix, Inc.

Nelson Industries, Inc.

Nelson Division

“new” Digisonix Division

Universal Silencer Division

Advanced Development and Engineering

Vehicle Systems

Corporate Research

Commercial and Industrial Systems (“old” Digisonix)

Fig. 16 - The Nelson ASVC Group, renamed the “new” Digisonix in February, became Digisonix. Inc. in November, 1992

provide more space for offices, fan testing, electronics laboratories, and manufacturing. In anticipation of a continuing growth in revenue, Digisonix began adding staff at this facility as did the Advanced Development Group at Stewart Street. About the same time, we were surprised to learn that Digisonix former building in Stoughton, then vacant, had been destroyed by fire. On a happier note, one summer, a duck laid its eggs next to the Stewart Street building. After a contest to pick when the so-called “Digi-Duck” would hatch its eggs, several employees escorted the new family across Stewart Street to reach the nearest water. One of the most significant changes for Digisonix occurred in February of 1992. Rock Flowers, president of Nelson Industries, announced that the Nelson ASVC Group would be renamed the “new” Digisonix Division with Steve Dickmann as president. Nelson had formed the ASVC Group in September of 1991 to coordinate all of Nelson’s ASVC activities. The “new” Digisonix Division included the original Digisonix Division focused on 93

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active fan silencing, the Nelson Advanced Development Group focused on the Ford program, and a new business group established for Vehicle Systems. The “new” Digisonix made the newly expanded Murphy Drive facility its headquarters.

New Nelson Technical Center in Stoughton with abstract sculpture suggestive of Nelson’s products (ca. 1993)

Both Madison newspapers, the Wisconsin State Journal and The Capital Times, soon ran lengthy articles on Nelson Industries and Digisonix that featured Steve Dickmann and myself. Later in the year, the Wisconsin State Journal published another article entitled the “Sweet sounds of silence” that focused on the contributions of Rock Flowers to both Nelson and Digisonix. As a result of the reorganization, Steve Wise became vicepresident of Digisonix Commercial and Industrial Systems (the “old” Digisonix). Ed Braun became vice-president of Digisonix Vehicle Systems and continued as president of Professional Data Processing (PDP), Nelson’s data processing subsidiary. Rick Barry became the Digisonix controller. 94

Digisonix, Inc.

Nelson Technical Center - Stoughton Corporate Research Acoustics Research Group Digisonix Advanced Development Group - active noise control research - active vibration control research

Eriksson-Geddes Development Center Digisonix Advanced Development Group Stewart Street - Madison - automotive applications of ASVC

Digisonix Division headquarters Murphy Drive - Middleton - commercial and industrial fan testing - product design, manufacture, marketing

Fig. 17 - Nelson/Digisonix ASVC facilities (1992)

I became vice-president of Digisonix Advanced Development and Engineering (ADE), while continuing to be vice-president of the Nelson Corporate Research in Stoughton. The Digisonix ADE group included the ADG engineering staff at Stewart Street that worked on the Ford program as well as the “old” Digisonix engineering staff at Murphy Drive that worked on fans. Murphy Drive engineering included teams led by Seth Goodman, and later Mark Rae, for electronic hardware, Jeff Havens for software, Bill Mathias for mechanical hardware, Kirk Burlage for commercial systems (HVAC), and Mike Zuroski for industrial systems. I now had three offices. One in the Nelson Stoughton Technical Center, one at the Digisonix headquarters on Murphy Drive facility, and one in the Eriksson-Geddes Development 95

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Center on Stewart Street. Digisonix did ASVC research and product development work at all three locations. In addition, the Nelson Corporate Research department continued to work on ASVC as well as other acoustical and filtration research. My dual positions enabled me to coordinate the technical activities of Digisonix with those at Nelson Corporate Research. It wasn’t unusual for me to visit all three locations on a given day. However, with the rapid growth of Digisonix, I focused most of my attention on Digisonix despite remaining vice-president of research at Nelson. My days were filled with hosting customers, recruiting staff, reviewing projects, writing papers, attending conferences, planning facilities, and many other tasks. At the same time, Steve Dickmann and I travelled throughout the United States making so many presentations to prospective customers that we could almost finish each others sentences. In addition, customers often visited Digisonix where we could include tours of our test facilities. In hindsight, I was probably over-extended. As a relatively small company, Nelson had always maintained a very flat, horizontal management style that I enjoyed. We probably should have added more experienced managers, particularly in the product development area, to take over some of my responsibilities. However, things were moving so fast that it would have been hard to do. In addition, I felt a sense of ownership and responsibility for Digisonix and would probably have been reluctant to relinquish some of my authority to other managers – not unusual for a founder. In many ways, this period represented a turning point in the ASVC program at Nelson and Digisonix. From the beginning of our work on ASVC in 1981 until 1991, our annual budgets had been relatively small. We had become a leader in ASVC with a talented staff, a growing portfolio of patents, several innovative

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products, and a partnership with a major auto company with a comparatively modest investment by Nelson. However, in the early 1990s, an increasing number of companies were approaching Digisonix with proposals for development projects. The number of possible applications of ASVC continued to grow. At that time, the spectacular successes of other high tech companies, exemplified by Apple Computer, were still fresh in everyone’s mind. Although not in that league, Digisonix still appeared to be a company with great potential. The business literature has many stories of companies who were not equipped to handle the success of an innovative technology. Nelson and Digisonix were preparing for success and continued the expansion that had begun in 1991. Considering the opportunities that were available, it was not surprising that Nelson decided to significantly increase its investment in its ASVC program and Digisonix. As a result, expenditures rapidly increased as Digisonix added staff, expanded marketing, developed new products, and enlarged facilities. > On the product front in 1992, Digisonix introduced the new dX-5X controller family. This controller integrated the computer board and power amplifier into a compact package dominated by an elegant, curved heat sink. The dX-52 and the dX-57, a researchoriented version, used the TMS320C26 processor and provided independent two channel operation. Each controller had four input and four output channels that could be used for various applications including fans, pumps, and blowers. Seth Goodman, the lead design engineer for the dX-5X controller family, wrote a 1993 VPI conference paper on controller hardware design with a detailed discussion and block diagram of the dX-52. 97

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Digisonix dX-57 controller Digisonix dX-52 controller

Product development activities were further aided by the development of the monitor program, GOMON, by Jim Allard, a software specialist at Digisonix. This program enabled the parameter settings on Digisonix controllers to be easily modified for optimum performance. Meanwhile, Steve Wise and his staff, in what was now the Digisonix Commercial and Industrial Systems Group, continued to produce a wide variety of brochures, case histories, and press releases. They also wrote papers and made numerous presentations on their growing experience in the design and application of active silencing systems to fans, pumps, compressors, and blowers. Although things were going well during this period, the movement was not always upward. Digisonix briefly pursued applications of its active control technology to vibration control with Applied Power, Inc. and its Barry Controls unit, located in the Boston area. Since my son was about to begin graduate school at 98

Digisonix, Inc.

Harvard, I was happy to see a relationship develop that might bring me to the area on a regular basis However, this program lasted less than a year. After the program began in March of 1992, Steve Dickmann announced the termination of the program the following November. The incompatible visions and personalities of the two companies ended the program before it really had a chance to get started.

Platform with active mounts for studying active vibration control

Nonetheless, I still made regular trips to Boston during the mid-1990s including a presentation at an SAE TOPTEC in 1993, a paper at a meeting of the Acoustical Society of America in 1994, and several business meetings that Nelson had with a Cambridge company in 1994 and 1995. The serendipitous Boston location of these meetings allowed me to still make brief visits to follow my son’s doctoral research at Harvard. In addition to these domestic activities, we were well aware of the continuing interest in ASVC in Europe and sought to raise the European profile of Digisonix. In April of 1992, Steve Dickmann, Steve Wise, and I presented a seminar in London entitled “Update on ASVC Technology” to various customers and partners.

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Commercial Systems Development

Digisonix Advanced Development and Engineering Group

Advanced Product Development

Vehicle Systems Development

Industrial Systems Development

Software Products Development

Mechanical Systems

Software

Electronic Systems

Acoustical Systems

Software

Vibration Control

Signal Processing

Mechanical Laboratory

Fig. 18 - Digisonix Advanced Development and Engineering Group. (ca. 1993)

This was followed by the announcement in the summer of 1992 that Geoff Leventhall, a prominent British researcher and consultant, would head up the new Digisonix European office in London. I first met Geoff at a conference in 1982 where he presented a talk on recent progress in ASVC. After his presentation, we had a brief discussion of the exciting opportunities that digital signal processing appeared to offer for active noise control. It was good to see him join the Digisonix team. 100

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Back in Wisconsin, a growing group of engineers from Ford and Digisonix was now busy at the Eriksson-Geddes Development Center on Stewart Street. Cary Bremigan directed Digisonix teams led by Kent Delfosse for software development, Mike Hoppe for acoustical systems, and Henri Dutilly for the mechanical lab. At this time, Digisonix teams were also in Stoughton and led by Jay Warner for active vibration control, Mike Zuroski for industrial systems, and Doug Melton for software products. Later in 1992, there were also several organizational changes in Digisonix engineering and the Corporate Research department to make more effective use of our engineering staff. The most significant move transferred the Corporate Research acoustics research group from Nelson to Digisonix. Meanwhile, Dr. Greiner and I continued to give presentations on our work including occasional talks at the UW-Madison short courses directed by Don Baxa. The UW also continued to publish a variety of news articles on our joint work. Wisconsin Engineer magazine published an article that gave an excellent overview of the relationship between the UW and Digisonix. I also received an invitation on rather short notice to write a chapter on “Active Noise Control” for the book Noise and Vibration Control Engineering: Principles and Applications. This book, published in 1992 by Wiley-Interscience, was edited by two very well-known acousticians, Leo L. Beranek and István L. Vér. Active noise control was such a hot topic that the cover of the book featured diagrams from my chapter on active noise control. > Culminating a year of major events, in November of 1992, the Digisonix Division became Digisonix, Inc., a wholly owned subsidiary of Nelson Industries, Inc. Nelson’s 1993 annual report announcement of this change noted that ASVC was a “promising, 101

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but still fledgling technology.” In 1994, the Digisonix board consisted of myself, Steve Dickmann, president of Digisonix, Rock Flowers, president of Nelson Industries who also served as chairman of the Digisonix board, Glenn LaZotte, president of the Nelson Division, and four outside members of the Nelson board. Now that Digisonix was a separate corporation, it issued its first employee stock options early in 1993. Although no one knew it at the time, Digisonix stock would soon reach its highest appraised value. As a result, those employees who exercised Digisonix stock options received very modest returns. It was an exciting time for all of us at Digisonix and Nelson. We were receiving technical recognition, several major companies were working with us, and the national print and broadcast media were giving Digisonix considerable attention. Several of us even made a trip to San Francisco for preliminary meetings with some venture capital firms. Although we learned that it was still too early to work with one of these firms, these meetings and other activities reflected the high level of enthusiasm for Digisonix and ASVC present at this time. It was difficult to balance the almost unbounded enthusiasm of some with the cautious realism of others. Although I was usually optimistic and took a positive approach, I tried to avoid crossing the line from supporter to promoter. This wasn’t always easy, especially considering my own enthusiasm for the technology. Nonetheless, a 1992 article in Canadian Business, entitled “The Quiet Revolution,” quoted my warning that with regard to active noise control, we should not “promote this prematurely.” We were far from the only ones with an abundance of enthusiasm. The 1987 article in the New York Times, had included comments from a number of researchers and managers involved in ASVC. Among the ambitious applications mentioned were reducing noise from aircraft, military tanks, large power transformers, ships to avoid detection by the enemy, and vibrations 102

Digisonix, Inc.

in large space structures. Also mentioned were quieting noisy compressors, engines, fans, and pumps, and quieting the noise inside airliners and automobiles. Other than noise canceling headphones, significant commercial success for the other applications was to prove much more difficult. Later articles took a more guarded view. An article in Electronic News in July of 1992, reporting on the panelists that projected that 20 percent of the cars produced in North America would have electronic mufflers by the year 2000, suggested that there were “big bucks available to winners in this market.” More pointedly, the article took note of the fact that the “patent situation is muddied” again foreshadowing the problems that patents would create for widespread use of ASVC technology. Additional pertinent comments by Jim Paulson, executive director of Corporate Quality for Ford, were reported in the September, 1992, issue of The Hansen Report on Automotive Electronics. He noted that their studies showed that consumer interest in fuel economy had sharply declined from being the second most important reason for buying a car in 1980 to ninth place in 1991. A general lack of interest in energy conservation in the 1980s and 1990s, encouraged by our national political leadership, undermined one of the prime advantages of less restrictive active silencers, particularly for fans. Finally, in October of 1992, the New York Times published a reflective article entitled “Marketplace: True Believers in Value of Noise” that discussed the optimism regarding ASVC including the $180 million valuation of Noise Cancellation Technologies, a competitor of Digisonix. The bullish comments of some in the article were balanced by the skepticism of others. The latter views reflected the growing difficulties that we and others were experiencing in commercializing ASVC technology. We had a great solution, but found it hard to convince others of its value.

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Digisonix prototype multiple-input, multiple-output controller

On May 10, 1994, the Digisonix team took a break to view a partial solar eclipse at the Murphy Drive facility (tree leaves created pinhole cameras to view the eclipse)

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-9DigiWare ca. 1993-94 In April of 1993, I presented an invited talk on ASVC to a session at ICASSP 93 in Minneapolis. The attendance was very large due to the rapidly growing interest in digital signal processing. After I presented an overview of Digisonix applications, the many requests for more information were a bit overwhelming and were not unusual for that time. One of the challenges facing Digisonix was that a wide range of manufacturers from many different industries were showing interest in ASVC. In most cases, ASVC had to be integrated into their OEM products to reduce costs and maximize performance. As a small company, Digisonix didn’t have the engineering resources to meet these growing demands. It needed a better way to help these divergent companies evaluate Digisonix technology as we tried to make it an industry standard. In response to this problem, Ed Braun and a new Software Products Development group led by Doug Melton developed the DigiWare system that Digisonix introduced in August of 1994. DigiWare was a sophisticated hardware and software package that enabled OEM customers to evaluate Digisonix technology in their own laboratories on their own products. The hope was that these systems would increase the likelihood of OEMs using our technology, while producing a welcome new revenue stream. Physically, a DigiWare system was configured around a Compaq computer with a Pentium processor, 16 MB of random access memory (RAM), and a 420 MB hard drive – a powerful system for its time, as well as a monitor, high-speed modem, and Digisonix multi-channel controller. The initial version of DigiWare featured a dX-100 multi-channel controller using a

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floating point T.I. TMS320C30 Digital Signal Processor with 4 to 18 analog inputs and outputs. Later versions featured a dX-200 controller using the T.I. TMS320C40 Digital Signal Processor with 8 to 128 analog inputs and outputs. These were both modular units that could be readily expanded to the desired configuration of inputs and outputs.

Fig. 19 - Selected components of a DigiWare development system: computer (266), controller (212), amplifier (272), mic. preamp (256) (from U. S. Patent 5,627,747 by Douglas E. Melton, James E. Allard, Brian M. Finn, Jerry J. Trantow, Steven R. Popovich, Trevor A. Laak, Mark C. Allie, Larry J. Eriksson)

In addition to the computer and controller, customers could purchase a Sound Development System or a Vibration Development System. The sound system included an acoustic waveguide, loudspeakers, microphones, and power amplifier. The vibration system included a vibration table, mounts, actuators, accelerometers, and two power amplifiers. With either package, customers had everything they needed to assemble a complete active control system. 106

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DigiWare systems also came with all the necessary software including the Digisonix filtered-U algorithm with on-line error path modeling as well as the Digisonix adaptive recursive multiple-input, multiple-output (MIMO) control algorithms developed by Doug Melton and Steve Popovich as described later in this chapter. The package gained flexibility by taking the generalized view of the various Digisonix algorithms shown in Fig. 20, an approach

Fig. 20 - Signal processing elements of a DigiWare development system (from U. S. Patent #5,627,747 by Douglas E. Melton, James E. Allard, Brian M. Finn, Jerry J. Trantow, Steven R. Popovich, Trevor A. Laak, Mark C. Allie, Larry J. Eriksson)

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that evolved from my 1991 paper in Japan and that was presented in a Digisonix paper at ICASSP-94. By selecting or deselecting various elements of a combined block diagram, engineers could create single or multi-channel versions of the filtered-X or filteredU algorithms, adaptive systems with error signal inputs for use on tonal noise, and many other configurations. Complete DigiWare systems including a development license, hardware, software, development tools, technical support, and training were available from $17,500 to $33,000. They were designed to enable OEMs to work with Digisonix technology in their own laboratories and also appealed to university researchers. Ultimately, DigiWare systems formed the core of the Digisonix Technology Products group. > Many of Digisonix industrial applications did not require multi-channel signal processing. These systems were typically installed on relatively small diameter ducts. They cancelled low frequency sound waves that have long wavelengths and produce a uniform pressure distribution across the duct. A single channel controller could produce excellent results. As the frequency of an undesired noise increases, the distance between the peaks and valleys of the sound pressure waves, or wavelength, decreases. More complex sound patterns known as higher order modes may occur above a cut-off frequency where the height or width of the duct is greater half the wavelength. The larger the duct, the lower the cut-off frequency and longer the wavelength above which higher order modes may occur. When the frequency of the undesired noise is above the cut-off frequency, multiple microphones and output transducers are required to characterize the undesired noise and cancel the more complex sound field. 108

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Ducts with large cross-sectional dimensions are more often found on air handlers in building HVAC systems. These applications may require multiple-input, multiple-output (MIMO) systems to control noise at frequencies above the cut-off frequency. Many other applications of ASVC may also require MIMO systems including building interiors or large structures. Digisonix received an early patent in 1989 covering the use of multiple independent adaptive filters for the control of higher order modes. At that time, a more comprehensive solution to the problem of higher order modes and multi-channel MIMO systems that included cross-coupling between the channels was not available.

Fig. 21 - Multi-channel active acoustic attenuation system (from U. S. Patent 5,216,721 by Doug E. Melton; note that Fig. 22 explicitly shows the various speaker/error path models (SE) used in updating the coefficients of the adaptive filters resulting in greater apparent complexity of the process)

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Fig. 22 - Multi-channel active acoustic attenuation system with error signal inputs (from U. S. Patent 5,216,722 by Steve R. Popovich) 110

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In the early 1990s, Doug Melton and Steve Popovich studied the MIMO control problem for their doctoral research at the UWMadison with Dr. Greiner as their advisor. Their work resulted in patented approaches to multi-channel, cross-coupled ASVC algorithms. Doug developed a fully adaptive, cross-coupled multiple-input, multiple-output version of the filtered-U RLMS algorithm. Steve developed a similar fully adaptive, cross-coupled multiple-input, multiple-output approach that used the error signals for its inputs. These fully adaptive MIMO systems have the ability to create a sound field that matches a complex undesired sound field in both time and space. Similar MIMO digital signal processing systems are also used with adaptive antenna arrays for electromagnetic waves. A recent article by Rappaport, et al. described the potential application of MIMO signal processing techniques to antenna arrays in 5G wireless systems. > Although Melton and Popovich developed generalized approaches for cross-coupled multi-channel systems, Seth Goodman and Kirk Burlage of Digisonix took a different approach to the problem. They expanded the potential frequency range for plane wave cancellation by placing the sensors and sources to suppress the detection and generation of higher order modes. For a duct with a 4:1 aspect ratio, the summed output from two sensors properly placed along the wide side of the duct will not respond to the first two higher order modes. The first higher order mode has a nodal line dividing the duct as shown on the left side of Fig. 23. The acoustic pressure will sum to zero for sensors placed on opposite sides of the nodal line. The second higher order mode has two nodal lines and will not be detected by sensors placed on these lines as shown on the right side of Fig. 23. 111

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Fig. 23 - Cross-section of duct with nodal lines for the first two modes (from U. S. Patent 5,283,834 by Seth D. Goodman and Kirk G. Burlage)

Fig. 24 - Controlling two modes with two independent controllers (from U. S. Patent 5,420,932 by Seth D. Goodman)

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Similarly, the first two higher modes will not be excited by two sources properly placed along the wide side of the duct and driven by the same signal. With this patented approach, single channel controllers can control plane waves in the presence of higher order modes. Seth and Kirk received a patent on this technique and discussed it at the 1993 VPI conference. Seth Goodman later took this basic idea a step further. His new approach, for which he also received a patent, could control two modes in a duct with two single channel controllers. It requires fewer filters than a full MIMO system – only two filters for a two mode system compared to four filters for a full 2x2 MIMO system. The modes are decoupled by forming the sum (for the plane wave mode) and difference (for the first higher order mode) of both the input and error signals as well as forming the sum and difference of the two output signals. Seth, Kirk, and Doug Pedersen discussed this approach, which was often called “poorman’s MIMO” at Digisonix, in a paper at Inter-Noise 93. > In 1993 and 1994, Digisonix was operating in high gear. It had a major development program underway with the Ford Motor Company. Sales of its fan silencing systems were increasing along with interest from OEMs in the air handler and fan industry both in this country as well as abroad. DigiWare had been developed with powerful controllers using the very latest in Digital Processor chips. Our strong technical team had a growing list of publications and patents. We had several first class development facilities on Stewart Street and Murphy Drive as well as the Nelson Technical Center in Stoughton. Although there was more good news to come, unexpected challenges would also soon arrive.

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Digisonix headquarters on Murphy Drive in Middleton

Mock-up of HVAC duct at Murphy Drive to evaluate active silencing

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- 10 Taking Flight ca. 1993-95 By the mid-1990s, the use of ASVC to reduce noise had become a popular topic on television news shows featuring great videos of machinery and vehicles. Reports on CNN’s Headline News and ABC’s World News Tonight with Peter Jennings presented NVX active systems for quieting turboprop and jet aircraft. These NVX systems were developed by the Lord Corporation of Erie, Pennsylvania, with technology and engineering assistance from Digisonix. Offsetting our disappointment over the early end to the Applied Power/Barry Controls agreement, Digisonix had announced a technical services and license agreement early in 1994 with the Lord Corporation. This agreement covered the use of Digisonix ASVC technology on aerospace applications including aircraft. It was the most significant single event for Digisonix since the beginning of the Ford program in 1990. Lord had long been a recognized leader in sound and vibration control. In the early 1980s, they had introduced their own active noise control system. In fact, Lord was the company that had supported the research behind the ICASSP 84 paper that I found useful when we began our work in ASVC. With this latest agreement, Digisonix again received substantial new revenue and access to a new industry for its ASVC technology. Later in the 1990s, the Lord Corporation moved its headquarters to Raleigh, North Carolina. After this change, we alternated our management meetings between Madison and Raleigh. Winter meetings in Raleigh were particularly welcome due to its milder weather. At both locations, we sometimes enjoyed a round of golf after our meetings. A good working relationship

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quickly developed between the managers of the two medium-sized companies that had many similarities. Lord and Digisonix engineers soon worked together to develop the Lord NVX Active Control System using the Texas Instruments TMS320C3X digital signal processor with Digisonix algorithms and software. Digisonix engineers Kent Delfosse and Shawn Steenhagen played key roles in the software development. Lord NVX systems could be used for active noise control, active structural control, or active isolation control on aircraft. Active noise control uses loudspeakers to reduce the noise in the cabin. Active structural control uses actuators on the fuselage to reduce vibrations which radiate noise into the cabin. Active isolation control uses actuators integrated into the engine mounts to reduce the transmission of vibrations from the engines into the fuselage which also radiate noise into the cabin. In all three cases, accelerometers can be used as input transducers and microphones in the cabin can be used as error transducers. In October of 1995, Digisonix held a short course in which Lane Miller of Lord presented an overview of their work on active sound and vibration control including installations on helicopters, turboprops, and business jets. He also gave a detailed description of a highly effective active noise control system installed on a Beech King Air turbo prop aircraft. On this application, two reference accelerometers on the structure measured the vibrations from the prop wash on the aircraft. These signals were passed through the controller and used to drive twelve loudspeakers. The system used sixteen error microphones to reduce the sound levels of the two primary tones by about 15--20 dB throughout most of the cabin. It was a time of peaks and valleys, ebbs and flows. The good news of the Lord agreement in 1994 was balanced by the announcement on the same day of the suspension of the development program with Ford’s Electronics Division. 116

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Automotive applications of ASVC did not develop nearly as rapidly as initially anticipated. The expectations of participants in the 1992 Delphi Study carried out at the University of Michigan would not come close to being met. Even today, more than 20 years later, electronic mufflers have seen little, if any, use on production motor vehicles. Only recently, more than 10 years later than the Delphi study participants expected, has active interior silencing finally begun to find more widespread application in production vehicles. The suspension of the joint development program with the Ford Electronics Division marked yet another turning point for Digisonix. Despite its major new relationship with Lord, Digisonix prospects had significantly diminished. By late 1994, the size of the Digisonix engineering staff peaked at about 55 employees. Ironically, despite the loss of the Ford program, overall interest in ASVC technology was still quite strong and other automotive opportunities continued to appear. As a result, Randy Eppli became a vice-president of Digisonix and focused on the sales and marketing of Digisonix vehicle systems. This high level of interest was further confirmed when, in 1994, Digisonix hosted a meeting of the Milwaukee Section of the SAE. It included tours of both the Nelson Technical Center as well as the Digisonix Murphy Drive facility. After dinner, Cary Bremigan, manager of Digisonix Vehicle Systems Development, gave a presentation on our ASVC technology and products. We also continued to be visited by prospective customers representing companies, both domestic and foreign, from a broad range of industries. During these visits, I often made a presentation on our ASVC technology. These presentations were usually wellreceived, and I enjoyed explaining our work. However, sometimes there were problems. For example, one visitor interrupted my presentation to ask that I only “tell them what they do not know.” I paused for a moment to read their minds. 117

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A major product event in 1993 was the use of Digisonix active silencing systems in a new 500,000 square foot office building in Florida. Digisonix installed 85 active silencing systems on 33 air handling units, most with an active silencer on the supply duct and one on each of two return ducts. The operation of these systems could be monitored via telephone for maintenance purposes. Noise levels in the occupied spaces met the design goal of NC 40, and the active systems were anticipated to save over $38,000 per year using then current electrical rates of $0.07/kWH. In July, 1994, Sound and Vibration magazine published a detailed review of this installation by Howard Pelton, Steve Wise, and William Sims. At this time, Digisonix and the Universal Silencer division of Nelson Industries also announced their development of an active/ passive silencer called the Dyna-Quiet “Dynamic Silencer.” In addition, agreements were reached with several partners in the HVAC industry who produced their own literature featuring Digisonix products and technology. In the fall of 1993, Digisonix also began sponsoring research at the UW-Madison directed by Barry Van Veen, a professor of electrical engineering who specialized in signal processing. About the same time, the UW-Madison published a booklet with profiles of various Wisconsin companies with ties to the UW. The profile on Digisonix noted that it had three Madison locations, a sales office in the United Kingdom, and over 80 employees. Steve Dickmann continued as president of Digisonix. Steve Wise was responsible for industrial and commercial systems, Ed Braun for vehicle systems, Randy Eppli for vibration control systems, Randy Huebner for manufacturing, and Pat Lyke for administration. Susan Dineen and Barbara Stephenson worked on marketing and business projects. I continued to be responsible for engineering at Digisonix as well as Nelson Corporate Research. By 1994, Digisonix was well-established as one of the global leaders in active sound and vibration technology and products. 118

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Noise & Vibration Worldwide published the article “Digisonix leads in active silencing systems.” The new publication Active Sound & Vibration Control News placed a story on Digisonix on the front page of their first issue. The Financial Times published the “Sound of Silence” with comments by Steve Dickmann. However, other observers began to express more critical views. A quote in an October article in Automotive News described the electronic muffler as “gimmicky.” Noise & Vibration Worldwide in its December article entitled “Active noise control on the brink” gave a generally positive review of the field. However, it also noted that “sufficient gray area” existed in the various ASVC patents to allow “costly litigation.” Another December article in Noise Regulation Reporter, entitled “Active noise cancellation systems face technology, market challenges,” kindly mentioned “Digisonix, a pioneer of ASVC.” However, it also noted that ASVC was “more difficult than expected.”

Stewart Street facility with modified sign after suspension of Ford program

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Digisonix dX-510 controller

Close-up of dX-510 control board with TMS32031 Floating Point Processor (square black chip left of center)

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- 11 Digital Voice Enhancement ca. 1995-96 While some were pondering the future of active sound and vibration control, Digisonix was busy working with automotive OEMs on a related technology that Digisonix called “Digital Voice Enhancement (DVE).” This technology grew out of our early work on the application of ASVC to Magnetic Resonance Imaging (MRI) scanners. These machines can expose patients to high noise levels that make communications difficult between the patient and the medical staff. In 1989, Nelson applied for a patent on an enhanced communications system that Mark Allie and I invented for use in noisy environments such as MRI machines. Our system used several adaptive filters to reduce the acoustic noise exposure for the patient as well as the noise and echoes transmitted over the communications intercom. In an intercom that connects two people, there is a loudspeaker and microphone at each location. Much of the hardware needed for DVE at each location is therefore already available. The Digisonix DVE system adds a digital controller providing up to three adaptive filters at each end of the intercom. At one end, there is a filter driven by a microphone that measures the undesired acoustic noise around the first person. This first filter sends a signal to the first person’s loudspeaker to reduce the undesired acoustical noise. A second filter driven by the same microphone generates a signal that reduces electrical noise produced by the acoustical noise on the line to the second person. A third filter is driven by the signal received from the second person and added to the signal sent by the first person to reduce the echo back to the second person.

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A similar set of adaptive filters is provided at the other end of the communications system for the second person. The complete system has six adaptive filters. Multi-channel systems between more than two people require a larger number of adaptive filters. Cary Bremigan and I received a second patent in 1997 that extended these ideas to multi-channel communications systems.

Fig. 25 - Digital Voice Enhancement system (Fig. 1 of U. S. Patent 5,033,082 by Larry J. Eriksson and Mark C. Allie)

The original 1989 patent discusses the use of the system in MRI scanners as well as in automobiles. At that time, cell phones were still under development, and the patent mentions the use of the system with a “radio telephone.” By the mid-1990s, cell phones and even hands-free operation were becoming more common. Most of the hardware needed to use enhanced Digisonix DVE technology was often already installed. In addition to improving communications when using cell phones, enhanced DVE can also improve communications between occupants of a vehicle while they are speaking. 122

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Interestingly, the desire for improved communications within a motor vehicle is very old. In 1995, Automotive Industries reprinted an ad that its predecessor The Horseless Age published in 1914 for the “Stentor Autophone.” This early electrical device, named for a Greek herald with a loud voice, used a microphone and loudspeaker to enable a passenger in the back seat to talk to the driver, presumably a chauffeur, often separated from the owner by a glass partition.

Fig. 26 - Multi-channel Digital Voice Enhancement system (Fig. 1 of U. S. Patent 5,602,928 by Larry J. Eriksson and Cary D. Bremigan)

The Digisonix DVE system improved communications between the passengers in the front, middle, or back rows of a vehicle. This system made it easier and safer for passengers and especially the driver to converse without the need to turn around. This is especially helpful in minivans and SUVs where passengers are separated by greater distances. The system could adapt to varying loudness levels from different passengers and included a 123

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privacy setting to disable front to back communications if desired. Digital voice messaging and voice recognition capabilities were also available. Brian Finn, a talented Digisonix engineer who died in a tragic small plane crash in California in 2010, directed the development of this new system with a software team from the Vehicle Systems Group and Software Products Group. The system was designed for use in a variety of applications including automobiles and aircraft. It utilized many of Digisonix strengths and had the potential of enabling Digisonix to move into the much larger and rapidly expanding field of digital communications systems. In 2000, Volkswagen Research displayed a vehicle equipped with a Digital Voice Enhancement System developed with Digisonix at the CeBIT trade show for information technology in Hanover, Germany. Three years later in 2003, VW introduced “the world’s first” Digital Voice Enhancement system in their new Multivan. > While new applications of ASVC were being developed for vehicles, the Digisonix Commercial and Industrial Systems Group continued to install active duct silencers. In one case, Digiduct silencers were installed on fans for a two million square foot semiconductor manufacturing clean room. In anther, ABB Fläkt Marine AB in a joint program with the FINCANTIERI Marghera shipyard installed a Digisonix active noise control system on a new Holland America cruise ship. This was believed to be the first such installation on a cruise ship. In addition, Digisonix introduced a new line of mini-Digiduct active/passive silencers. These small systems were designed to be incorporated within the HVAC distribution system ductwork rather than at the primary air handling unit. They could be used to quiet 124

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the noise from fan powered mixing boxes, after other small secondary fans, or before especially noise sensitive areas. The mini-Digiduct silencers provided about a 10 NC-point noise reduction at the amazing price of about $500. This included a complete active noise control system with a dX-510 controller, loudspeaker, and microphones mounted on a small section of ductwork. The dX-510 was a small, but powerful controller that used an advanced TMS320C31 floating point processor. On the industrial front, Digisonix active silencers continued to solve difficult noise problems. The Eau Claire Leader-Telegraph published an article in 1995 entitled “Sound off” about an incinerator and scrubber with a noisy fan. A neighbor who lived “a few miles away” was losing sleep due to the high pitched hum from the fan that travelled across a valley to his home. The neighbor, who had heard about active noise control, provided the operator of the incinerator with a list of possible suppliers which included Digisonix. The company purchased a Digisonix system costing $20,000 that reduced the objectionable noise by about 20 dB. The result was a happy neighbor and a satisfied company. Digisonix also continued to work with a variety of OEMs on applying ASVC to their products. It demonstrated its DigiWare system at the 13th IMAC conference on modal analysis in January of 1995. In addition, Digisonix engineers presented papers at the SAE Noise and Vibration Conference in Traverse City, Michigan, and Active 95 in Newport Beach, California. One of these papers discussed the use of active interior quieting in a car powered by a four-cylinder engine. This work anticipated its production use in cars with four cylinder engines about 15 years later. In one of the more interesting demonstration projects, a team led by Mike Zuroski developed a multi-channel active control system that reduced the blade noise from a riding lawnmower. Although the system was quite effective, it was also expensive and impractical for use on a moving machine at that time. 125

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Digisonix and Lord joint activities continued at a very high level of effort. In 1996, Lord demonstrated its NVX system with Digisonix technology and software on King Air and other turboprops, the Cessna Citation X business jet, as well as DC-9/ MD-80 commercial jetliners. The following year, ABC’s World News Tonight profiled the use of Lord’s NVX Systems on DC-9 and MD-8X airliners which the FAA had recently certified. Late in 1996, I traveled to Munich, Germany, to make a presentation with Jay Warner of Digisonix and Guy Billoud of the Lord Corporation at a workshop “Implementing Active Control.” Digisonix hosted this workshop in cooperation with Texas Instruments as part of their Third Party Support program. In Munich, we also had the opportunity to visit the famous Deutsches Museum, the world’s largest museum of science and technology. Later, I also went to Friedrichshafen, a German city on the Bodensee long associated with the construction of dirigibles, to visit another prospective customer. > In February of 1997, the magazine Sensors published an edited version of my 1994 booklet “A Primer on Active Sound and Vibration Control” that was also reprinted by Digisonix. The reprint included an added note that Digisonix was offering “its ASVC technology through products, joint development relationships, and licensing agreements in several areas” such as: • the aerospace industry through an exclusive license with Lord Corp. for aerospace applications of ASVC • the automotive industry through Digital Voice Enhancement systems for improving communications in motor vehicles • the heating, ventilation, and air conditioning (HVAC) industry through active silencing systems for air handlers 126

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• the duct silencer industry through active silencers for industrial fans, blowers, compressors, and pumps • product development through the software and hardware of the DigiWare development system for ASVC Despite many successful applications of active noise control and a number of new, innovative products, the financial side of the business was proving ever more challenging. Digisonix continuing business did not justify the large staff and extensive facilities that had been added to support the Ford program. It needed to contract and reduce its expenses to be more in line with its diminished, but still significant business opportunities. At the beginning of 1995, Digisonix transferred several employees to Nelson Corporate Research. Mike Zuroski became the new manager of a reconstituted acoustics research group in Nelson’s Corporate Research department. This group also included Raymond Cheng, Mike Diederich, and Jason McIntosh. In addition, Barbara Stephenson transferred to Corporate Research to work on technology assessment. In 1997, Digisonix further reduced its costs by moving its headquarters from Murphy Drive to Stewart Street. This was followed by additional staff reductions and the closure of its Murphy Drive facility. In addition, the Digisonix engineering group was divided into two groups roughly along product lines. Since 1992, after the formation of the “new” Digisonix, I had been responsible for the combined Digisonix engineering group. At that time, having a combined engineering group gave us greater flexibility in utilizing our engineering resources. However, it also made it more difficult to coordinate engineering activities with the sales activities of the individual business groups.

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Nelson Industries, Inc.

Nelson Division

Universal Silencer Division

Technology Products

Digisonix, Inc.

Vehicle Systems

Corporate Research

Commercial Systems

Fig. 27 - Digisonix, Inc. (ca. 1997)

With the 1997 change, about one-third of Digisonix engineering joined the Commercial Systems business unit and the other two-thirds supported the closely related Vehicle Systems and Technology Products units. These changes reflected the fact that the primary focus of engineering had gradually evolved from research and development to product engineering and installations. I continued to work with Steve Popovich on Digisonix research activities. Advanced research also continued at the UWMadison where Barry Van Veen’s group developed a novel distributed approach for high dimensional MIMO systems. In a final change, the Digisonix Dyna-Quiet active industrial silencer business was transferred to the Universal Silencer Division of Nelson Industries, while Digisonix continued marketing Digiduct systems for HVAC applications. The goal of these various changes was to better align Digisonix resources with its ASVC market opportunities. 128

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Stewart Street headquarters of Digisonix in 1997

Reflection: Cutting Back It is more fun to build a growing business than to cut back or sell a struggling business. Building a business brings new people, new facilities, new customers, and new opportunities for your goods and services. Contracting or selling a business means saying good-bye to employees who are no longer needed, leaving facilities that had felt like home, and abandoning products and services that were developed with great effort. The retrenchment process resembles the death and grieving process described by Kübler-Ross in her 1969 book On Death and Dying. First, there is denial of the need to cut back, then attempts to bargain your way out of your financial difficulties, accompanied by anger and depression over the reality of the problems that you face. Finally, you accept your situation and find a way to move forward. In 1997, Digisonix was searching for this path.

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>

Turn on the Quiet ...active noise control in headlines The future of silence Good news about noise Cut out that racket Pleeeeease hold down the noise Noise cancellation poised for takeoff Taking control of noise Sh-h-h-h...new devices cut noise Fighting noise with noise ‘Anti-noise’ waves douse din Creates the Sounds of Silence Noise, begone! Now you hear it – now you don’t All quiet on the industrial front The sweet sounds of silence Inspiring wonderment Firm quietly building its name Fights noise by making some Their product could be music to your ears Companies profit from sounds of silence The quiet sound of success I guess this is what we wanted, but the patent situation is muddied and expectations are excessive – The Quiet Revolution will be long and slow

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ASVC publications per year

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1000 100 10 1 year (1952-1994)

Fig. 28 - The number of ASVC publications published each year from 1952-1994 doubled about every five years; the dips in the last few years may be due to the timing of major conferences and a time lag in gathering data (data from Dieter Guicking, Active Sound and Vibration Control Reference Bibliography, 3rd ed., 2nd suppl., Nov., 1995, Univ. of Göttingen, Germany)

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- 12 Technical Issues ca. 1997 Why didn’t Digisonix continue to thrive? Was it too far ahead of the curve? What about technical and cost issues? Would a different strategy have helped? Even today, more than 15 years later, it remains difficult to answer these questions. The barriers to commercialization have proved to be very high in virtually all applications that were pursued in the 1980s and 1990s. Despite the enthusiasm for the technology reflected by the many papers being published, the special sessions on ASVC at many technical conferences, and the numerous companies developing products, commercial progress proceeded very slowly. This chapter will examine the technical issues that emerged as Digisonix tried to commercialize ASVC technology. > Some of these technical issues were illustrated by a problem that I investigated during a visit to a major research university. A large HVAC fan in the student union was generating very high noise levels and some thought that an active silencing system might alleviate the problem. The main HVAC supply duct had a large cross-section that filled the space above a hallway. There was virtually no space available to install the expensive array of loudspeakers and microphones as well as the multi-channel controller required to control the higher order modes that were likely present. There was also inadequate distance available between the fan and the input microphone as well as the input microphone and the loudspeaker. The input microphone must be far enough away from

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the fan to avoid the extreme flow turbulence that the fan generates. In addition, there must be enough space between the input microphone and the loudspeaker to allow enough time for the system to produce the canceling waveform before the undesired noise has passed the loudspeaker. The need for length in an active noise control systems was originally perceived as due to excessive delays in the electronics and loudspeakers. However, a paper presented at Inter-Noise 96 by Trevor Laak and Steve Popovich, Digisonix signal processing researchers, suggested that the problem is more fundamental. Their paper noted that power-limited loudspeakers and uncorrelated noise on the input signals result in an ideal controller response that is in general non-causal. The system must begin to respond before the noise arrives – a physical impossibility. In systems with a large distance between the input microphone and the loudspeaker, only a small portion of the ideal response is non-causal. The controller is able to find a solution that is a good approximation to the ideal response. In short systems, a much larger portion of the ideal response is non-causal. The controller can only create a very poor approximation to the ideal response. There are several possible solutions. These could include more and larger loudspeakers, system layouts that provided more length, and improved anti-turbulence microphone probe tubes. However, all of these changes affect HVAC system design and add cost. Retrofit applications often face physical constraints that make installations complex and performance requirements more difficult to meet. Changes may be required for the building and ductwork that can add significant cost and complexity. In new applications, the air handling system can be designed from the beginning to accommodate the desired layout. However, it was not easy to convince customers to do this for an unfamiliar technology. The development of improved application know-how,

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improved product technology, and increased familiarity among the users could overcome this resistance, but that takes time. In some buildings, passive silencers serve as acoustical patches on noisy HVAC systems. Their exact location is usually not too critical and some degree of improvement is usually heard. Conversely, even though active silencing systems can provide superior low frequency performance, they are more sensitive to system layout. Many existing HVAC systems are not well designed from a noise or flow standpoint. High levels of low frequency noise sometimes breaks out through the walls of the duct before it reaches the noise canceling loudspeakers. Some layouts generate severe flow turbulence which can be a problem even for antiturbulence microphone probe tubes. Many of these issues could have been handled quite easily in the design stage, but again create major problems in existing installations. Installations on industrial fans introduced other potential problems. In some cases, the environment for the loudspeakers could be hot, moist, and corrosive. The vulnerable loudspeakers might need to be covered with flexible membranes. A rugged enclosure was also often needed to protect the controller and amplifier electronics further adding to the system cost. In the early years, it was also difficult to accurately predict the size, number, and optimum location of the loudspeakers required to cancel the undesired noise. Other issues revolved around failure modes. The performance of passive silencers tends to decline gradually over time as linings deteriorate or structures corrode and fail. Active silencing products depend on complex digital control systems. Like digital television, their failure mode is more extreme – they either work or they don’t. Provisions need to be placed in the software to ensure stable operation over long periods of time with the ability to reset the system after power failures or other disturbances. 135

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In addition, trouble shooting procedures are required to identify the cause of system failures as quickly as possible so that repairs can be made. Small companies, often having university connections like Digisonix, were prominent in early efforts to commercialize ASVC technology. Their small size limited their ability to develop the national or global infrastructure needed to assist customers in the design, installation, maintenance, and service of active systems. It was yet another factor that limited the successful commercialization of ASVC. > Active silencing products faced other unique issues that few, if any, of us had anticipated. For example, customers can easily determine the effectiveness of active silencers by turning off the power. On the one hand, this provides a good demonstration of the effectiveness of the active silencing system. On the other hand, the silenced levels are often not as low as some customers might expect. Substantial noise may remain due to both the high initial sound levels (which may have been underestimated) as well as the contributions of other noise sources and paths. Perhaps the use of the word “cancellation” contributed to the problem. It may have led some people to believe that the undesired noise would be completely eliminated with an active control system. For them, the presence of any residual noise would be disappointing even if it was at a substantially reduced level. In contrast, it is more difficult to confirm or deny the effectiveness of a passive silencer in the field. I suspect that many customers might be surprised if they knew how little noise reduction their passive silencer is providing, particularly at low frequencies where passive silencers are not very effective. It was also sometimes difficult to convince prospective customers of the value of the low frequency effectiveness of active 136

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noise control. In some cases, this was because A-weighted sound level measurements, which are relatively insensitive to low frequencies, were used to evaluate the noise problem and guide decisions regarding improvements. Without using narrowband spectral analysis and improved sound quality metrics, the value of active noise control for the reduction of annoying tones or low frequency rumble was often discounted. For example, Steve Wise described a noisy wood processing plant that had produced relatively high A-weighted sound levels in the surrounding community for many years, but generated few complaints from nearby residents many of whom worked at the plant. However, a new fan generated many new complaints due to its strong low frequency tone at 80 Hz even though the Aweighted sound level was virtually unchanged. An active silencing system reduced the tone by 25 dB, but not surprisingly had only a modest effect on the A-weighted sound level. As a result, new demands emerged to reduce the A-weighted sound levels even after the annoying tone was virtually eliminated because this was the metric used in the local noise ordinance. Considerable progress was made by Digisonix in all of these technical areas, but as will be discussed in the following chapters, the business and strategic issues that it faced were in some ways perhaps even more difficult.

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Test set-up for active silencing displayed at a Digisonix Open House

Close-up of Sheboygan installation showing two loudspeakers

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- 13 Business Issues ca. 1997 In his 1996 review article on ASVC, Jiri Tichy noted that it was “...regrettable that the building industry and HVAC manufacturers generally ignore this technology, which could provide substantial improvement(s)...” The next year, a thoughtful editorial on ASVC in Noise & Vibration Worldwide also suggested that progress was happening “not quite as rapidly as anticipated” and that perhaps “...some...tried too hard, too soon.” It also pointed out that although cost “has dropped enormously...if potential users all hold back...it will take much longer to happen.” Widespread use of active silencing systems requires a paradigm shift. Robert Massie in his 1991 book Dreadnought, reports that 19th century naval officers resisted the use of steam engines on their beautiful sailing ships. Opponents cited the cost of the coal, difficulty in storing it on a ship, and the dirt that it generated. Although many ships had steam engines, they were considered as subordinate to the masts and sails that remained on warships until the late 1880s. Few wanted to lose the routines and traditions on a warship that revolved around the sails – after all, naval personnel are still called “sailors.” This chapter will examine some of the business issues that contributed to the slow rate of acceptance of active noise control products. > New technology is often rather expensive. Those developing the new technology typically have two alternatives. They can focus on low volume, high value, high cost products and develop a niche market like the supercomputer industry. Alternatively, they

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can focus on high volume, lower cost, mass market products like the personal computer industry. Active sound and vibration control has found itself trapped between these extremes for many years. There are some relatively successful small markets for high value applications such as aircraft interiors and military applications. Alternatively, there are a few high volume markets for relatively low cost products such as noise canceling headphones. Intermediate sized markets of moderate volume, such as that for active silencers, have been among the most difficult to successfully commercialize. Product sales of active silencing systems were generally limited to exceptional situations that justified the use of relatively expensive technology. These included quieting noisy areas in existing buildings or quieting noisy fans that were bothering nearby neighbors. Despite considerable technical success, the industry found it difficult to make the transition from a niche technology to widespread usage. Active noise control systems require an array of components including microphones, cables, controllers, amplifiers, and loudspeakers. Today, many of the required components are already present in automobiles and other vehicles for the audio system or cell phone. This is not the case for most industrial or building applications which increases the incremental cost of active silencing in those applications. It is difficult for an active noise control system to be as inexpensive as a simple passive silencer. The end user must be willing to pay a premium price for a premium product. This is usually only found in situations where the noise problem is severe as in some retrofit installations. Even then, decisions on noise control are usually not made by those exposed to the noise, but by the owner of a building or manufacturing plant.

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In addition, although expensive and unfamiliar technologies are often hard to sell, the lack of interest in active sound control is compounded because: • noise may be ignored • noise exposure may be short term • the impact of noise may not be immediately evident • noise is difficult to eliminate • those exposed may not control the noise • noise may be appealing and desirable In an attempt to respond to some of these issues and create a quieter nation, Congress had passed a series of noise control laws including the Walsh-Healey Act in 1969 to protect workers on federal contracts, the Occupational Safety and Health Act (OSHA) in 1971 for all workers, and the Noise Control Act of 1972 for the regulation of product noise. Under this act, the Environmental Protection Agency established the Office of Noise Abatement and Control (ONAC) to implement product noise control regulations. However, during the 1980 election campaign, Ronald Reagan described ONAC efforts to control the noise of garbage trucks as a good example of unnecessary regulations. In fact, existing garbage trucks were rather noisy, were often used in densely populated urban settings, and could certainly be made quieter. Nonetheless, one of Reagan’s first actions as president in 1981 was to abolish ONAC along with its proposed regulations on garbage trucks and other products. As a small program without strong congressional support, it was a fairly painless way to fulfill a campaign pledge even though the total savings to the government was modest.

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Noise control was officially relegated to the back seat of environmentalism. This change significantly reduced the commitment of many potential customers to product noise control and diminished interest in emerging technologies like ASVC. Under the Reagan administration, there was also an emphasis on energy production rather than energy conservation. This philosophy reduced the incentive for businesses to invest in energy saving technologies like active fan silencers with their low flow restriction. Much like noise control, it became even more difficult to sell energy saving technologies. Businesses heavily discounted future savings and often focused on the initial cost. They had little interest in energy efficient technologies that produced long term savings. More recently, after a long rise in gas prices, the situation finally appears to be changing. Active systems are now being used for interior silencing on many vehicles with 4-cylinder engines. They enable the shift points on the transmissions of these engines to be tuned for improved fuel economy while maintaining acceptable sounds levels. It is a cost effective solution, especially today when vehicles are routinely equipped with audio systems, microphones for hands-free cell phone usage, and powerful microprocessors. In the 1990s, there was much less interest in 4-cylinder engines or fuel economy and without cell phone technology already installed, the cost for an ANC system would have been higher. > Digisonix also had to deal with problems in its own embryonic industry. This included the tendency of some to over-hype the new technology. This is not uncommon with a new technology. Campbell-Kelly and Aspray closed their 1996 book Computer with a brief discussion of the Internet. It was still early in the 142

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history of the Internet and they noted that there was “...far more hype than reality.” Of course, that attitude has pretty much faded away with the rapid improvements and amazing success that the Internet has displayed. But negative notions do make commercialization of a new technology more difficult, whether it is the Internet or active noise control. To some extent, even today, the Internet and active noise control are still working to overcome them. Another major problem for the commercialization of ANC in the 1990s was the aggressive position that some ASVC patent owners took on the interpretation of the claims in their patents. This undoubtedly discouraged some potential customers who didn’t want to get involved in a patent dispute. The patent issues that arose over active noise control technology in the 1990s foreshadowed the patent conflicts that have occurred more recently in many other fields. A recent paper by Harbert reports that from 2010 to 2012 the number of patent lawsuits in the U.S. “skyrocketed” from 3200 filings to 5000 filings. Ironically, and perhaps in response to aggressive patent positions, others questioned the validity of seemingly all ASVC patents. They seemed to look suspect at almost any attempt to obtain patent coverage on ASVC technology and products. There has long been a conflict between those who develop new technology and those who want to make this technology widely available. Inventors want to keep their inventions secret; competitors and the public want to see them publicized. Inventors want broad patents with long lives; competitors and the public want narrow patents with short lives. The patent system has evolved as a compromise between these conflicting interests. I think most lawyers and business managers including myself take a middle road on these issues. They accept the need for patent rights that protect and encourage innovation, but insist that patent 143

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claims be limited by the prior art that exists. Overly broad interpretations of patent claims do not serve society or inventors since they restrict the commercialization of the technology. Patent clashes over new technology are not unusual. Early conflicts over telephone and airplane patents and more recent disputes over Internet, cell phone, and genetic engineering patents have often led to protracted lawsuits. These battles do not appear to have seriously impeded the widespread commercialization of most new technologies. Almost always, other factors have played a more important role. However, they can limit the financial returns to individual inventors and their companies. > Active noise control is an amazing technology. It often generates quite remarkable reactions when it is described or demonstrated. After giving a presentation on ANC to a group of engineering students, I received a thank you letter that suggested that the technology resembled “a perpetual motion machine” and that my talk gave some “wonderment” to their students. I enjoyed these comments and often had similar reactions to the technology. However, the “wonderment” and “magic” often associated with active noise control has a commercial downside. Active silencing introduces a computer-based electronic product into a setting dominated by mechanical equipment. This brings a wide range of new issues in their design and use including: • active silencing systems replace large, heavy passive silencers with light weight computer-based systems of digital controllers, microphones, and loudspeakers • active silencing systems are more sensitive to the layout of the air handling system than passive silencers

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• active silencers are highly effective at reducing low frequency noise, but this performance may not be reflected in the A-weighted sound pressure level that is often used to quantify an undesired noise • active silencers bring to the mechanical world new functionalities not previously available such as remote monitoring and operation • active silencers can be connected to other equipment and systems – common in the inherently interconnected electrical world, but somewhat less common in the mechanical world of independent machines • active silencing systems either work or they don’t, there is generally no gradual deterioration of performance as with passive silencers • active silencers can be somewhat more fragile, but easy to repair – again common in the electrical world; passive silencers can be more rugged, but hard to repair – again not unusual in the mechanical world • active silencers can result in energy savings on some applications, but this savings is often undervalued • active silencers have higher purchase prices, but lower operating costs; passive silencers have lower purchase prices, but higher operating costs The net effect of these issues was that many potential customers viewed passive silencers as familiar, rugged, and dependable, while they perceived computer-based active silencers as unfamiliar, complex, and unreliable. In late 1998, I presented a paper entitled “A Brief Social History of ANC in Ducts” at a national meeting of the Acoustical 145

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Society of America in Norfolk, Virginia. This paper, later published in 1999 in Sound and Vibration magazine, discusses the limited commercial success of active sound and vibration control in the context of the issues listed above. It focused on the cultural and business changes required for the radically new technology to gain greater acceptance. Soon after my paper appeared, representatives of a passive silencer manufacturer wrote a lengthy response that took strong exception to what I felt was a thoughtful summary of the challenges facing ASVC products. Apparently, the cultural nerve that I had struck was more sensitive than even I had realized. The need for a paradigm shift to overcome the resistance to new technologies is a long standing phenomenon. Similar to the reluctance of 19th century naval officers to replace sails with steam engines, it took years for military leaders to understand the new weapons that emerged during World War I. Machine guns, armored tanks, and aircraft challenged their education, assumptions, and strategies. Much more recently, there was resistance to replacing the mechanical control cables in aircraft with fly-by-wire electrical systems. It took time for the advantages of these electrical systems to overcome the perceived reliability of mechanical cables. One last example from music and acoustics further illustrates the power of culture and tradition in the acceptance of new technology. Amazingly, electric violins were first conceived almost one hundred years ago. Today, as Ben Heaney notes in his recent article in Strings magazine, electric violins are still much less widely accepted in the classical world than electric guitars and keyboards. The world of classical music is driven by tradition and resists technological innovations. As a musical art form, this may be appropriate. For engineering innovations like active noise control, it can be frustrating and harder to accept. 146

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Nonetheless, these examples help explain why Digisonix experienced resistance to its computer-based ASVC systems more than 20 years ago. The business and engineering community may pride itself on its scientific approach and objectivity, but a paradigm shift always presents challenges – and active noise control is a significant paradigm shift for the traditionally mechanically-minded world of noise control engineering.

Digisonix headquarters on Murphy Drive in Middleton

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New Nelson Technical Center in Stoughton (ca. 1994)

dX-50I industrial controller being tested at Murphy Drive

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- 14 Strategic Issues ca. 1997 What is active noise control? A technology, a product, a system? Hardware, software, or an algorithm? Digisonix primarily looked at ANC as a product similar to the silencers produced by its parent company, Nelson Industries. The problem with this point of view is that silencers are discrete elements that are easily added to an exhaust system. ANC is a system of components that must be integrated into a larger system. Today, some products often already contain many of the components required for the application of active noise control. What is left for an independent ANC company to sell? Perhaps licenses for more advanced technology, perhaps engineering services to help manufacturers integrate ANC into their noisy products, or perhaps complete systems for quieting noisy equipment in specific applications. Digisonix started with a single controller, the dX-30 family, built around the TMS32010 Digital Signal Processor followed by the more powerful dX-40 family. A few years later, Digisonix introduced the dX-52 and its research version, the dX-57, the dX-50I industrial controller and the much smaller, less expensive dX-510. With the introduction of DigiWare, two multi-channel controllers were developed, the dX-100 and dX-200. Over about eight years, Digisonix developed at least four generations of controllers, listed in Table 4, to take advantage of the latest technology and meet the demands of various markets. In addition to developing controllers for its own products, Digisonix engineers worked with Ford engineers on a controller for automotive applications. A few years later, Digisonix engineers

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also worked with Lord engineers on a Lord controller for aerospace applications. Digisonix may have thought it was in the ASVC business, but these various controller developments might lead one to wonder what Digisonix really was? A manufacturing firm producing active sound and vibration control products? A consulting firm specializing in active noise control? A product development firm specializing in DSP hardware and software? A software company specializing in signal processing? In many ways, it was all of these and more. They were the natural result of the systems needed for ASVC, but where do you focus your efforts when so many opportunities are available? We often thought that the broad applicability of Digisonix ASVC technology was an advantage, but it made the development of a strategic focus for the business more difficult. > Digisonix also faced strategic challenges caused by its relationship with Nelson Industries. Digisonix had many of the characteristics of a typical high-tech start-up. It had a small, highly educated staff, had innovative products and technology, and had experienced rapid early growth. However, as an intrepreneurial effort, Digisonix differed from most start-ups in that it was funded by its parent company, Nelson Industries, Inc. New technology companies typically receive revenue from a succession of sources perhaps beginning with the founders and a few relatives or other private investors. This is often followed by some combination of development contracts, license agreements, or product sales. As the business matures, it sometimes turns to venture capital firms for additional funding. In the case of Digisonix, this sequence was reversed. Its initial funding came from Nelson – effectively, its venture capital firm. 150

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As a result, Digisonix employees didn’t have to worry about whether the bills would be paid as do many start-ups. And unlike many start-ups, they didn’t have to risk their own savings. On the other hand, without any ownership position, their rewards from any potential success were much more constrained. High-tech start-ups are inherently risky investments that may not succeed. It can be difficult to recover your investment even in a successful business. This is one reason why venture capital firms diversify their activities among a number of investments. They know that some will not succeed. Nelson was more like a venture capital firm investing in a single company. Nelson’s investment in Digisonix generated significant benefits for Nelson, although it did consume resources that other Nelson units would have appreciated. Digisonix insured Nelson against the potential threat that active silencing posed to its existing muffler and silencer businesses. It provided new business opportunities in Nelson’s core business of acoustic noise control. In a broader sense, it gave Nelson an increased focus on innovation, greater expectations for success, and an enhanced image as a forward looking and progressive company. With Nelson as its owner, Digisonix gained access to Nelson’s extensive facilities and equipment as well as assistance in establishing relationships with suppliers and potential customers. Nelson also provided Digisonix technical, manufacturing, and administrative support, especially in its early years, that often included transferring personnel to Digisonix. However, Nelson’s support also created challenges for Digisonix. Although Nelson was a supportive and relatively patient venture capital source for Digisonix, this funding brought early financial pressures while Digisonix products and business plan were still rapidly evolving. I suspect that many venture capital firms have some of the same tendencies, but they usually don’t step in until the start-up is more mature. 151

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From one perspective, it was understandable that financial expectations would begin to increase when Digisonix became a division of Nelson in the fall of 1987. It was time to deliver on the promise of our ANC research after five years of support. However, from another perspective, five years earlier, we had virtually nothing – simply a desire to do ANC research. It was less than two years since the development of our control algorithm and only about nine months since we had field tested our first system. This work had been done by a very small team with limited resources. We still needed to develop a much better understanding of our new technology and its commercial potential. In its early years, I think Digisonix was like an army that had outrun its supply lines. Our progress had been achieved with a bare bones staff. We needed time to fill in the gaps that we had left behind. However, when building a new business, there is little time for a break. We had to fill in the gaps while continuing to move rapidly ahead – probably a common problem among many high-tech start-ups. > Throughout the history of Digisonix, management decisions were understandably made within the context of the culture and needs of Nelson, its much larger parent. In the early years, when I decided to return to school and complete my Ph.D., my personal interests as well as Nelson’s business interests in mufflers and silencers strongly influenced the direction of my research on active noise control. Our subsequent research and development activities focused on duct silencers and exhaust mufflers due in some part to Nelson’s funding of the ASVC research program at Nelson and the UW-Madison. And so, from the beginning, business considerations in addition to technical and market factors influenced the direction of 152

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Digisonix. If Digisonix funding had come from other sources, our research program in active noise control might have taken a somewhat different path. In later years, our dependence on Nelson sometimes got in the way of the single-minded focus on survival that is essential for a struggling startup. Following the end of the Ford program in early 1994, Digisonix went through a period of retrenchment in 1995 and 1996 as it attempted to find the proper balance between its resources and expenses on the one hand and its opportunities and revenues on the other. This led to a gradual reduction in the size of its staff and contraction of its facilities. At this time, DigiWare and Digital Voice Enhancement were new products that could have opened the door for Digisonix to refocus its efforts on communications systems or control systems unrelated to ASVC. They might have enhanced the possibilities for the long term survival of Digisonix. However, it was not easy for Digisonix to move away from active silencers or perhaps even ASVC – the opportunities that had driven Nelson’s support in the first place, in favor of more attractive possibilities. Any such change would probably have made it difficult to retain Nelson’s attention and investment. In addition, as we would all soon discover, Nelson’s management was too preoccupied at this time with its own future to spend much time considering the future of a minor subsidiary. > When I returned to school, I had a number of ambitious goals. Initially, I wanted to create a new outlet for my talents and complete my Ph.D. in electrical engineering. With the successes of our early research, these goals expanded into a desire to create a viable new business at Nelson that could help change the way in which the world controlled noise. 153

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However, I also envisioned Digisonix as a means to transform Nelson’s core businesses. With its highly skilled, creative, and energetic staff, I saw Digisonix as a way to help Nelson utilize the rapid advances in computer technology in the design, manufacturing, and marketing of its products. Unfortunately, I underestimated the difficulty in changing a larger organization. In fact, over time I think Nelson changed Digisonix to be more like Nelson rather than the other way around. The innovative and dynamic culture of a small startup at Digisonix gradually faded as the organization matured and grew more like its more traditional parent. From its founding, the Digisonix Division had a culture distinct from the other divisions of Nelson. This was due to the significant differences between their products, technologies, and personnel. Rather than welded sheet metal products, Digisonix products were electronic systems. Its staff included specialists in computer technology rather than the mechanically-oriented specialists of the other Nelson units. Nelson tended to be manufacturing driven, while Digisonix tended to be technology driven. For example, an early decision at Digisonix to use Apple Macintosh computers due to their innovative design, ease of use, and excellent drawing software was less than popular with some Nelson managers. They preferred to standardize all computer purchases around IBM PCs. Another example of the differences between the Nelson and Digisonix cultures involved the Internet. The Internet evolved virtually in parallel with Digisonix from the ARPANET in 1983 and the release of the World Wide Web in 1991. Digisonix engineers were early users of this new technology. However, some managers at Nelson and Digisonix seemed more concerned with the potential for misuse of the Internet than with its advantages. These advantages became particularly important as Digisonix began sharing information with its partners on a daily basis. 154

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In any event, Digisonix did, in fact, get its Apple computers and was, in fact, able to take early advantage of the Internet in working with its partners. Despite occasional conflicts due to differing cultures between Digisonix and its much larger parent, it was usually able to obtain the resources that it needed. > Following the changes in the engineering organization at Digisonix in 1997, I increasingly found myself at the margins of the business that I had helped create. It was not an unusual position for someone involved in forming a high-tech start-up. As Digisonix had grown and matured, my technical and management roles had gradually diminished. I found it increasingly difficult to make a personal contribution. As a consequence, I began refocusing my work on Nelson’s Corporate Research department where I continued to be vicepresident of research. After fifteen years of intensive involvement with active noise control and Digisonix, this was not as easy as it might seem. The changes at Digisonix and my time away from Corporate Research made me feel like a stranger in my native land. Although I didn’t know it at the time, events would soon occur that would bring major changes for me, Nelson, and Digisonix.

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Nelson Industries, Inc. sign in front of the Gusloff Building in Stoughton

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- 15 End of an Era ca. 1997-98 Throughout the 1990s, there had been continual speculation about the possible purchase of Nelson by another company. Nelson had excellent operating results and a strong balance sheet. This made the company attractive to potential purchasers as merger-mania was growing throughout world. I suspect there were also companies interested in buying Digisonix with its established product line, strong portfolio of patents, and skilled technical staff. A sale might have generated a substantial return for Nelson and positioned Digisonix for future success. And so, for me and perhaps others, the question became, what would be sold first – Nelson or Digisonix? Despite its good times, there were a number of non-financial issues facing Nelson. It had an aging board and several senior managers who were approaching retirement age. In addition, as a privately traded corporation with a relatively small number of shareholders, the liquidity of the company’s stock as well as its long term capital needs were topics of continuing discussion. Perhaps more importantly, many mergers were occurring throughout the automotive parts industry. Among the forces driving these mergers were the movement of large companies towards fewer suppliers, a concern over being too small to compete, and a fear of being left behind. As rumors of a possible sale swirled among the employees, Nelson often reiterated that although it was gathering information, it preferred to remain private and independent. Nonetheless, in the first week of December in 1997, Nelson told employees that it had received a cash offer to purchase Nelson from Cummins, a major producer of diesel engines located in

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Columbus, Indiana. On the following Saturday, Nelson Industries held its regular annual meeting at the new Monona Terrace Convention Center in downtown Madison. The highly regarded architect, Frank Lloyd Wright, created the unique design that was the inspiration for this building, and it would ordinarily have drawn a great deal of attention. However, not surprisingly, the proposed sale of Nelson dominated discussions. Despite the premium price, the shareholder response was rather muted due to the long relationship that many had with Nelson and their reluctance to see it come to an end. On January 8, 1998, the management and shareholders of Nelson Industries, Inc. convened in a small building that Nelson had recently purchased just down the road from its Stoughton headquarters to take the final vote on the proposed sale. Months or even years of speculation were finally put to rest when the shareholders quickly approved the sale of Nelson Industries, Inc. to the Cummins Engine Company for about $450 million. > After the sale, Nelson Industries, as well as its subsidiaries including Digisonix, Inc., became part of the Cummins Filtration and Acoustics Systems group. This group also included the Cummins Fleetguard unit, a leading manufacturer of filtration products for engines. In some ways, I think Cummins soon became to Nelson, what Nelson was to Digisonix. Cummins managers assumed key positions and brought the culture of the larger organization with them. Some Nelson managers struggled under what they saw as too much bureaucracy and corporate control. Although this might be natural in a larger company, some of it was probably also due to cultural differences. It was again difficult for the smaller business to escape the dominance of its larger parent. 158

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In the new organization, Digisonix became a very small part of a very large company. In addition, its ASVC products and technology were quite unrelated to Cummins primary businesses in diesel engines and filtration systems. In contrast to the near perfect timing of our research on ASVC, the purchase of Nelson came at an awkward time for Digisonix. Digisonix was a corporate teenager trying to work out the problems of young adulthood. The harsh reality was that its primary business of active noise control was not developing as fast as many people throughout the world had expected. And so, Digisonix faced the proverbial “perfect storm” of three difficult coincident events – the need for strategic changes due to the weaknesses of its core businesses, the “death” of its parent company, and problems in its own organization due to employee departures and organizational changes. What alternatives were open to Digisonix? In the mid-1990s, I think Digisonix could have been sold to another company for an attractive price. However, in 1998, I think its options were rather limited. Even before its sale to Cummins, Digisonix had been consolidating its operations and a number of its key employees had departed. The license agreements with the Ford Motor Company and the Lord Corporation had diluted the value of its technology rights. Some of its key patents had only about half of their life remaining. Long term commercial success was proving much more difficult than its early successes with its products and partnerships had suggested. By the late 1990s, the enthusiasm for active silencing was beginning to recede. Some ASVC suppliers went out of business. Guy Billoud of the Lord Corporation wrote in his thoughtful 2001 paper on active control that the “...predicted appearance [of active control] in all areas of one’s everyday life have failed to materialize.” He goes on to note that other than a still limited market for noise canceling headsets, consumer applications of 159

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active control remained nonexistent. However, he does discuss several industrial applications commercialized by Lord in the aerospace, machining, and precision instrument industries. The following year, in 2002, Noise & Vibration Worldwide published another editorial on the status of active noise control on the occasion of the Active 2002 Symposium in Southampton, England. The title of the editorial was “Active noise control – tortoise or dead parrot.” It noted that most of the papers presented at Active 2002 were by academic researchers and that the range of commercial products “remains disappointingly narrow.” Much like my own concerns at least 10 years earlier, it again pointed out that early expectations were unrealistically high. As recently as 2013, Kenneth Cunefare presented an invited paper at the San Francisco meeting of the ASA on the history of active noise control over eight decades. His abstract notes that the rate of academic publications has remained roughly constant over the past decade. The only applications that he explicitly mentions as commercial successes in his abstract are ANC headsets and systems (noise and vibration control) installed in automobiles. A short list for a field that once held so much promise. With the exception of noise-canceling headphones, a specialty product that had little relationship to the various commercial and industrial applications that Digisonix and others had pursued, the industry failed to find a “killer” application for ASVC – a product opportunity where the price and performance could generate the production volumes that were needed for a successful business in active noise control. What the future may bring for this always alluring technology will be examined in the Epilogue. Despite these uncertainties, in the summer of 1998, a small group briefly explored the possibility of putting together a proposal to purchase Digisonix from Cummins. This effort apparently collapsed when it failed to garner much support from the remaining Digisonix employees. 160

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Investors risk money, but employees risk time. In some ways, time is an investment more valuable than money. Money can be replaced, but time is lost forever. Many Digisonix employees had already invested years of their lives at Digisonix and had made major contributions to its successes. Perhaps, the remaining employees were reluctant to invest further in a business with an uncertain future and ready to move on to the next phase of their lives as had many others. I don’t know. In any event, it’s also probably true that most, if not all, had limited financial resources. > For Digisonix it was a time of continuing travel cuts, salary freezes, hiring freezes, and other cost cutting measures. In addition, plans were considered to move Digisonix from its most recent headquarters on Stewart Street to the Nelson Product Development Center in Stoughton. This idea was soon dropped when it became apparent that there was inadequate laboratory space available. Concerned for the future, Digisonix staff members continued to resign. With key employees and managers having left or leaving, the energy and creativity that had built Digisonix steadily declined. To my knowledge, there was no formal announcement regarding the closure of Digisonix, but by the end of 1998, Digisonix had virtually faded away – not with a bang, but with a whimper. Throughout this process, Digisonix employees took a variety of different paths. Some accepted new positions within Cummins, although an economic slowdown in the fall of 2001 led to some leaving the company. Others accepted positions with other companies, universities, or organizations. Some started their own businesses including several who became consultants. A few decided to retire. For some, the sale of their Nelson stock helped them in their pursuit of a new direction for their lives. 161

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Steve Dickmann joined the software firm Epic Systems in Madison. Steve Wise formed his own consulting firm, Wise Associates, and continued to work on active noise control. Mark Allie stayed with Cummins for a few years and later joined the ECE Department at the UW-Madison. Cary Bremigan briefly left Cummins, but returned and remained with Universal Silencer after Cummins later sold it to a private investor group. In January of 2001, several Digisonix engineers formed the consulting firm Applied Signal Processing (ASP), Inc., in Madison. After the merger, I was named the chief technical officer of the new Fleetguard/Nelson Filtration and Acoustic Systems unit of Cummins. This position included responsibility for the technical staff of Fleetguard as well as the Nelson Corporate Research department. However, I found it difficult to adapt to the new corporate culture and soon resigned to form my own consulting practice, Eriksson Research, LLC. In 1999, I co-authored a technical paper with Trevor Laak and Mark Allie that I presented at the Active 99 symposium in Fort Lauderdale, Florida. It was the last technical paper that I would present on active sound and vibration control. I enjoyed the meeting, but was ready to move on to the next stage of my life. When I left the company in 1998, Digisonix gave me a dX-52 and dX-510 controller which were no longer needed. I later donated these controllers to the Wisconsin State Historical Society where they serve as a small physical reminder of the pioneering work of Digisonix on active noise control.

162

End of an Era

Reflection: The Life of a Company Census Bureau data shows that in recent decades only about 50% of new companies have survived for 5 years. The Family Business Institute reports that only 30 percent of family-owned businesses survive into the second generation, only 12 percent survive into the third generation, and only 3 percent survive into the fourth generation. Nelson Industries was a long-lived company that had two generations of management lasting nearly 60 years before being acquired by Cummins. As a privately traded company, Nelson was able to support research activities at the boundaries of its traditional businesses. Managed for long term success, it had less pressure than many publicly traded corporations to produce immediate results. With this support, Corporate Research and Digisonix produced major innovations in active sound and vibration control. Most remarkably, this happened in a well established, midwestern company that produced a mature line of relatively generic products, not the usual environment in which revolutionary innovation occurs. Nelson’s Corporate Research department was organized in 1973. By 1998, it had functioned for 25 years and had helped Nelson develop a strong technical staff, excellent facilities, new technology, and improved products. Its research engineers had published many technical papers, received many patents, and served as leaders in a variety of technical organizations. Inspired by a vision that most companies have now abandoned, it demonstrated the value of a central research program. In 1981, Corporate Research began its research program in ASVC. Digisonix was formed in 1987 and operated through 1998. During those years, not quite a generation, Digisonix became a

163

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pioneer in the use of Digital Signal Processor chips and a world leader in active sound and vibration control. Digisonix products solved many difficult noise control problems for its customers and paved the way for future work on ASVC. Throughout its history, Digisonix engineers and technicians worked with some of the largest and most sophisticated engineering organizations in the world. In every case, they more than held their own. They helped Nelson and Digisonix get ahead of the curve and stay there for many years. Digisonix also enhanced the value of Nelson Industries during the negotiations that led to its sale. In the years that followed, former Digisonix employees continued to play significant roles in companies and universities throughout the world. As with many high-tech companies, Digisonix lived fast and died too soon. It was sad to see it end, but many still have fond memories of its relatively brief time in the limelight.

Corporate Research offices in the Nelson Technical Center (ca. 1995)

164

Epilogue >

ASVC Today ca. 2014 The progress of new technologies is often difficult to predict. Liquid crystals were first studied in the 1880s and remained a scientific curiosity for almost 80 years before their highly successful use in flat screen displays. Fluidics, a hot new technology in the 1960s that fell short of its initial promise, evolved in the 1980s into micro-fluidic systems such as inkjet printer heads and “lab-on-a-chip” devices. Active sound and vibration control has followed a somewhat similar path. From its invention in the 1930s, the limited success of digital systems in the 1980s, and its subsequent decline in the 1990s, it has become an accepted, widely used technology in a growing number of applications.

Noise canceling headphones Noise canceling headphones are now a common product especially enjoyed by passengers on airplanes. They are available at moderate prices ranging from about $150-350. Many noise canceling headphones use analog signal processing rather than the digital signal processing often used in other applications of active noise control. This is driven by the relative simplicity of the application and the desire for low cost and small size. As noted in Table 1, their moderate cost and the high perceived value of their

Waves of Silence

effectiveness has created an attractive cost/benefit ratio and significant market for these products. In addition to their effective use on airplanes, a recent study found that patients in intensive care units of hospitals tolerated the attendant noises and stresses “better with less need for sedation” when using noise canceling headphones. Their near ubiquitous nature is reflected by their mention in the recent best-selling novel, A Tale for the Time Being, by Ruth Ozeki and their use by artist Marina Abramovic in an exhibition where the audience performed while wearing blindfolds and noise canceling headphones.

Active silencers for HVAC and industrial fans The advantages of active silencers on fans include good low frequency performance, low flow restriction which reduces the load on the fan lowering energy consumption, and reduced need for porous or fibrous acoustical linings. Acoustical linings can be a problem for installations in food handling or medical facilities where they can accumulate dirt and bacteria or shed fibers. Despite numerous successful installations of active silencers on fans, their moderate to high cost and the moderate to low perceived value of their benefits has restricted their widespread application. For retrofit installations in noise sensitive areas, the high perceived benefit often results in a more attractive cost/ benefit ratio. Unfortunately, there are a relatively small number of these opportunities available. The number of suppliers of active silencers for HVAC and industrial fans has remained quite limited. In addition to cost, the reluctance to use active silencers has sometimes been justified by concerns over product reliability. In 2013, Steve Wise of Wise Associates, and former president of Digisonix, reported that the Digisonix units installed at Sheboygan about 25 years ago were still operating satisfactorily with only the occasional replacement of a loudspeaker. Steve also noted that as 166

ASVC Today

of a few years ago the units installed in the large Florida office building by Digisonix were also still operating. Reliability appears to be less of a concern than had once been thought. It is possible that in the future, rising energy costs may generate more interest in low flow restriction active duct silencers, particularly for new installations. The passage of time has resolved most of the remaining technical issues, and progress in electronics has enabled continuing cost reductions. Widespread use of active silencing on fans may yet become a reality.

Automotive applications In the 1990s, a wide variety of automotive applications of active control were under consideration at Digisonix and elsewhere. These included electronic mufflers, active intake silencers, active fan silencers for the HVAC system, active engine mounts, active suspension systems, active interior silencing, and digital voice enhancement for improved communication. The Hansen Report on Automotive Electronics of June, 1992, reported that such active systems might be in production before 1997. Each has its own story. Electronic mufflers Despite the optimistic expectations reported in The Hansen Report of June, 1992, I do not know at this writing of any electronic mufflers in production in the automotive industry. Current exhaust systems are reasonably quiet, long-lived, and trouble-free. For these reasons, after the mid-1990s, there was limited interest in electronic mufflers which some viewed as a complex and expensive “gimmick.” This view may now be changing again due to the desire for improved fuel economy and reduced vehicle weight. The web site for Eberspächer, a major exhaust system manufacturer, discusses 167

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the potential of active noise control technology for reducing the size and weight of exhaust silencers. As Eberspächer demonstrated in 2009, ANC can also be used to tailor the sound for aesthetic purposes or for safety purposes on inherently quiet vehicles. In the 1990s, Digisonix also had investigated the use of active noise control to modify the spectral shape of an undesired noise rather than simply reduce it. This led to several papers and patents (see U. S. Patent 5,172,416, and others in Table 5). Active suspension systems and engine mounts With appropriate output transducers and sensors, the same technology used to control noise can be used to control vibration. Active suspension systems and active engine mounts are two automotive applications of active vibration control that have been intensively explored. However, as with many applications of active control, their use has been limited by a variety of factors including cost, weight, and reliability. Active engine mounts can reduce the transmission of engine vibrations into the frame of a car. These vibrations and the noise they may produce can both be annoying. Although Digisonix gave active engine mounts considerable attention in the 1990s, I am not aware of any production use on automobiles. Active suspension systems are able to improve the ride and handling characteristics of the vehicle on various road conditions. They can be fully active systems that control the response of the suspension on a real-time basis using transducers such as electrodynamic actuators. Alternatively, they can be semi-active systems that adjust the response more slowly using transducers such as pneumatic actuators. Lotus was a pioneer in the development of fully active systems in the 1980s. Although apparently quite effective on Formula One race cars, their use was banned in 1994 as noted in an EDN article by Brian Kerridge. 168

ASVC Today

Another type of active suspension system uses shock absorbers filled with a magneto-rheological fluid, an oil containing many small magnetic particles. An electrical field can change the alignment of the magnetic particles which varies the viscosity of the fluid. This enables rapid independent adjustment of the damping of each shock absorber based on the roughness of the road. This can result in a more comfortable ride and improved handling characteristics for the vehicle. These types of systems have reportedly been used on a number of high end vehicles. A 2010 technical note at WhyHighEnd.com provides a brief overview of these systems. Active interior silencing In the spring of 1991, I had suggested that widespread use of active control on automotive applications might not occur until the primary patents began expiring after about 2000. This was perhaps a bit more conservative compared to the expectations of the Delphi panelists in 1992, but it too proved to be somewhat optimistic. Nonetheless, active interior noise control finally began to appear on some production vehicles in about 2005. By this time, there was much less concern with patent complications since many of the core patents on ASVC were beginning to expire. In addition, with the onset of hands-free cell phones, active noise control could now be added to a vehicle for minimal additional cost since many automobiles were already equipped with virtually of all of the required hardware. Additional features, such as the Digital Voice Enhancement system that Digisonix had developed in the 1990s, could also now be readily added. Some people presumed that active interior silencing would be initially limited to upper end vehicles that could justify the increased cost. Others worried that customers might think there was a flaw in a vehicle that had an active noise control system.

169

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For many years, automobiles equipped with 4-cylinder engines that can generate low frequency “boom” in their interiors were viewed as an especially attractive application for active interior silencing. Unfortunately, in the 1990s, 4-cylinder engines were primarily used on economy vehicles where cost was a bigger factor than interior noise levels. However, as mentioned earlier, today’s concerns with fuel economy have led to many vehicles across the market spectrum being equipped with 4-cylinder engines. In some of these vehicles, active interior silencing enables engineers to move transmission shift points to lower engine speeds to further optimize fuel economy. Ordinarily this would increase the undesirable low frequency “boom” noise in the interior, but active interior silencing can maintain the interior noise at acceptable levels. Table 2 lists some recent applications of ANC in automobiles.

Aerospace/aircraft applications ASVC has been successfully applied to quiet the interior of aircraft ranging from small turboprops and business jets to large commercial airliners. Some of these systems have used vibration actuators on the engine mounts with an array of error microphones in the fuselage of the aircraft. Additional information on the Lord NVX systems is available in references from 1995 and 1996 as well as the 2001 paper by Guy Billoud. Other companies involved with aircraft ASVC applications include Ultra Electronics, Quiet Flight, and Cooper Tire and Rubber.

Enclosures The improvement of the performance of sound enclosures has always seemed like a good application for active noise control. According to its website, Silentium has developed an active noise 170

ASVC Today

control module with a chip, loudspeaker, and microphone that can be placed close to noisy products. Acousti Products’ website reports that it has worked with Silentium to develop a soundproof cabinet using active and passive technologies for silencing computer and telecommunications equipment. The TK Server website also has information on an enclosure with active silencing for Intel servers. Although the current usage of such devices is not known, they would appear to have good potential.

Manufacturing machines and processes ASVC can be applied to various manufacturing machines and processes to improve product quality. One example mentioned earlier was the Digisonix work in reducing the pressure pulsations from the pump that moves the pulp slurry on a paper-making machine. These pulsations can create irregularities in the paper. Another example is the reduction of mechanical vibrations on a cutting machine to improve the smoothness of the cut. Additional information is available in my 1993 IEEE paper and the 2001 paper by Guy Billoud of the Lord Corporation.

Some final thoughts In the 1960s, time sharing was quite the rage for enabling efficient widespread usage of scarce and expensive computer resources. Many people began talking about the emerging idea of a “computer utility” that would provide computer service like the power company. Campbell-Kelly and Aspray in their 1996 book Computer quote with skepticism from a 1967 article by Paul Baran in which he describes the future of the computer at home. Today, I find Baran’s descriptions of future uses of computers amazingly prescient. Much of what he describes, written before the personal computer and the World Wide Web, was a reality by 2010. However, the computer has entered our homes via personal 171

Waves of Silence

computers, smart phones, and the Internet rather than via time sharing connections to remote computers – mainly a change in form, not content. This example shows how hard it is to predict the future of technology. Active noise control was a hot idea in the 1980s and early 1990s. By the late 1990s, it had become a bit passé – just another idea that didn’t quite pan out as expected. But today, it is being used in an increasingly wide range of applications. In hindsight, it appears that Digisonix was perhaps 10-20 years too early in its efforts to commercialize ASVC. The use of a computer to control noise may have been too big a leap in the early 1990s. At that time, most people knew little about the Internet, cell phones and the World Wide Web were just emerging, and smart phones were still years away. Although digital computers were common, the vast majority of electronic devices, including radios, televisions, and communications systems still used analog electronics. The inter-connected world of digital products and controls was still far in the future. Today, we are immersed in a digital world of smart phones, digital television, and pervasive Wi-Fi. Powerful, low cost microprocessors are used in a broad range of applications. And now, active silencing is used in headphones and in the interiors of automobiles and aircraft. People are often not even aware of its presence – perhaps the ultimate achievement in the acceptance of a new technology. I was quoted in the 1987 article in the New York Times as saying “We’re on the verge of a new era, in the next century these techniques will be ubiquitous.” At the time, this was a speculative, perhaps a bit optimistic, statement about the future of active noise control. Twenty-eight years later – now that we’re “in the next century” – it seems more accurate as active sound and vibration control continues to make a growing impact on our lives.

172

ASVC Today

Ode to Digisonix Waves of silence controlled by smart computers, innovative technology from a small muffler company in America’s Dairyland. Products designed for energy savings and noise control in an era when they were not commercial or political priorities. Riding the crest of a technological wave that faded away when too few decided to “Turn on the Quiet.”

173

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>

174

Acknowledgments The genesis of this book began when my wife, Karen, and I were discussing some of my experiences at Digisonix. As we talked, she asked me how Digisonix came to be so far ahead of the curve in its technology. I soon realized that it would take a book to properly answer her question. Since I had been involved in active noise control research at Nelson from its beginning, I was in a unique position to write the story. The history of Digisonix is a rather complex tale involving several different organizations, a large number of individuals, and a rapidly evolving technology. Trying to connect the threads tying together these various themes was a difficult task. I must say that I enjoyed the process. The research and writing refreshed my fading memories of the interesting years when Nelson, Digisonix, and the UW-Madison worked together on the development of innovative approaches to active noise control. The preparation of the book also led to enjoyable discussions with some of my former colleagues at Nelson, Digisonix, and the UW-Madison who read early drafts of this book. Their comments filled gaps in my own knowledge and improved the book in many ways. I am indebted to all of these early readers of this book and their comments are much appreciated. Dr. Richard A. Greiner, professor of electrical and computer engineering at the UW-Madison and my advisor during my doctoral studies, was my always helpful advisor, colleague, and friend beginning with my graduate study at the UW and continuing for the rest of his life. Although he did not live to see the final version of the book, he was the first reader of an early draft and shared many insights that helped clarify the focus of the book in its early stages.

Waves of Silence

Dr. Greiner’s willingness to work with an older doctoral student and enthusiasm for the joint research program with Nelson laid the foundation for Digisonix. The students that he advised and worked with in his Electroacoustic Laboratory at the UW-Madison provided a steady stream of excellent engineers for Digisonix. Without his interest in and many contributions to Nelson and Digisonix, there would have been no story to tell. Steve Wise, who served in a number of sales, marketing, and senior management positions at Digisonix, including being president of the “old” Digisonix, shared many helpful comments on Digisonix and provided several photographs. Mark Allie and Cary Bremigan, both senior engineers and engineering managers at Digisonix in its earliest days who made major contributions to its success, provided detailed comments on both business and technical aspects of the text. Ed Braun, who was a Digisonix vice-president and served earlier as president of Nelson’s subsidiary Professional Data Processing, provided a number of thoughtful comments on the business aspects of the Digisonix story. Steve Dickmann, who served as general manager of the Nelson ASVC Group and president of the “new” Digisonix, made useful observations on various business issues at high tech companies as well as the relationship of Digisonix with Nelson. In addition to my former colleagues at Digisonix and the UWMadison, several other readers with extensive experience in science, engineering, and business were also helpful. They include my son, Mark Eriksson, my brother, Neal Eriksson, my brother-inlaw, David Chappell, and my friend, Terry Larson. The other person that deserves special mention is Rock Flowers, long time president of Nelson Industries. He gave me much appreciated guidance and support during my twenty-five years as Nelson’s vice-president of research, as a graduate student at the UW-Madison, and as a manager at Digisonix. Rock had a 176

Acknowledgments

rare combination of vision and attention to detail. As with Dr. Greiner, without Rock’s support, there would again have been no story to tell. A great many other individuals at the UW, Nelson, and Digisonix contributed to the success of our ASVC research program and helped make Digisonix a world leader in ASVC. I have tried to note as many of their contributions as possible and apologize for any errors or omissions. I wish that I could have included everyone. Many of the questions examined in this book do not have simple answers. I have tried to be as accurate, objective, and inclusive as possible, but I’m sure that others may have a different perspective. Finally, I want to acknowledge the contributions of my wife, Karen. Her love and support have been constants throughout my life. In addition to her role in initiating this book, she provided valuable comments, both large and small, on the content and structure of the book. They greatly improved the final result. Any remaining shortcomings are mine alone.

April, 2015

Larry J. Eriksson Madison, Wisconsin

177

Table 1a A technical perspective on ASVC application

potential advantages

technical issues

active headsets

effective noise reduction

mostly solved

HVAC fans retrofits

low frequency effectiveness length required low flow restriction flow turbulence no porous lining

retrofits/sensitive area

same as above

same as above

new installations

same as above

mostly solved

industrial fans new or retrofits

low frequency effectiveness mostly solved low flow restriction compact, light

retrofits/sensitive area

same as above

mostly solved

automotive applications electronic mufflers

low frequency effectiveness hostile environment low flow restriction packaging spectral shaping weight

active suspensions and engine mounts

improved handling reduced noise/vibration

automotive interiors

low frequency effectiveness mostly solved improved communications

automotive interiors w/adjusted shift points for 4 cylinder engines

reduces low freq. “boom” enables fuel savings (1)

mostly solved

aerospace/aircraft

noise reduction

mostly solved

machines & processes (e.g.cutting, paper pulp)

reduce noise/vibration to improve product quality

identify problem develop system

reliability weight

(1) reduces low frequency “boom” produced in cars with 4-cylinder engines when shift points are lowered for optimum fuel economy

178

Table 1b A business perspective on ASVC application

total costs(2)

active headsets

benefits(3) cost/benefit potential

moderate

high

low

+++

retrofits

high

high

retrofits/sensitive areas

high

very high

low

++

moderate

very high

low

+++

new or retrofits

moderate

moderate

retrofits/sensitive areas

moderate

high

electronic mufflers

moderate

moderate

moderate

+

active suspensions and engine mounts

moderate

moderate

moderate

+

HVAC fans

new installations

moderate

+

industrial fans moderate low

+ ++

automotive applications

automotive interiors (4)

low

moderate

low

++

automotive interiors (4) w/adjusted shift points for 4 cylinder engines

low

high

low

+++

aerospace/aircraft

moderate

moderate

moderate

+

machines & processes (e.g.cutting, paper pulp)

moderate

high

low

++

(2) including purchase price, maintenance, impact on design process (3) perceived value of silencing, energy savings, and other benefits (4) system integrated into vehicle; much of hardware is already in car

179

Table 2 A Sampling of Automotive Applications of Active Sound and Vibration Control • 2015 Infiniti Q70 (with V6/V8 engines): interior quieted with active noise cancellation using door-mounted speakers and microphones in ceiling (also uses “Vehicle Sound for Pedestrians (VSP)” alert system when operating as an electric vehicle), Wisconsin State Journal – Autos, “2015 Infiniti Q70,” Feb.. 15, 2015. • 2015 GMC Yukon Denali and Cadillac Escalade: premium-equipped models use active noise cancellation for interior noise control, Auto. Eng., “GM revamps its full-size SUVs for 2015,” Sept. 2, 2014. • 2015 Buick Enclave: uses active noise control to quiet interior on fourcylinder engine vehicle, Wisconsin State Journal – Autos, “2015 Buick Enclave,” Sept. 21, 2014. • 2014 Chevrolet Impala: uses active noise control on models with fourcylinder engines, Auto. Eng., “2014 Impala: Slick outside, big inside,” Nov. 5, 2013. • 2014 Cadillac ELR coupe: Bose 10-channel audio system with active noise cancellation, Auto. Eng., “Cadillac ELR,” Feb. 5, 2013. • 2013 Honda Accord: uses active noise cancellation system, aeionline.org (Auto. Eng.), “Honda Accord: the 9th gen.,” Oct. 2 , 2012. • 2012 Acura ZDX: uses active noise cancellation, Wisconsin State Journal – Autos, “2012 Acura ZDX,” Mar. 4, 2012. • 2013 Ford Fusion: uses active noise cancellation on the hybrid and Energi PHEV versions, aei-online.org (Auto. Eng.), “Ford’s 2013 Fusion is a tech blockbuster,” Feb. 7, 2012.

180

• 2011 GMC Terrain: uses active noise control on four-cylinder engines to reduce boom when shift points are lowered to improve fuel economy, torquenews.com, Oct. 30, 2011 (see also Wisconsin State Journal – Autos, “2011 GMC Terrain,” Aug. 7, 2011). • 2011 Infiniti M-series: uses active noise control to quiet interior, Wisconsin State Journal – Autos, “2011 Infiniti M-series,” Oct. 23, 2011. • 2010 “Magnetic Suspension–Magnetic Ride Control,” discusses the use of magneto-rheological fluids in automotive suspension systems, WhyHighEnd.com, 2010 (mentions Cadillac, Corvette, Ferrari, Audi). • 2010 Chevy Equinox: uses active noise control on models with fourcylinder engines, USA Today, “New Equinox Plenty Pleasing,” Sept. 4, 2009. • 2009 Honda Accord EX-L: uses active noise control on models with four-cylinder engines, The New York Times Magazine, Honda ad, 2009. • Toyota Crown Hybrid: uses three microphones and three loudspeakers to reduce noise at low engine speeds, Gizmag on web, “Toyota employs noise-canceling tech on hybrid,” Darren Quick, July 15, 2008. • Audi TT: uses magneto-rheological fluid in suspension system, Gizmag on web, “Audi’s new magnetic semi-active suspension system,” Mike Hanlon, June 17, 2006. • 2005 Honda Accord Hybrid: reduces interior booming with active noise control when half of cylinders on V6 engine are shut down, IEEE Spectrum, “2005 Honda Accord Hybrid,” March 2005. • 2003 VW Minivan: equipped with “the world’s first” Digital Voice Enhancement (DVE) technology, AEI, “Sound engineering for new VW Minivan,” April, 2003.

181

Table 3 Nelson/Digisonix timeline 1939 1972 1973 1975 1978 1981

1982

1983 1984 1985 1986 1987

1988

1989 1990

1991

Nelson Muffler Corporation begins operation Rockne Flowers becomes president of Nelson Muffler Corp. Corporate Research organized under direction of Larry Eriksson Nelson receives first of four NSF Industry/Faculty Research Participation grants; forms Research Advisory Council (RAC) active noise control discussed at meetings of Nelson RAC Nelson begins initial work on active noise control; Larry Eriksson, Craig Anderson, and Rajan Jaisinghani meet with ECE Dept. at UW-Madison Nelson and UW-Madison begin joint ANC program; Larry Eriksson begins ASVC doctoral research with Dr. Richard A. Greiner as advisor Dr. Greiner and Mark Allie lead way for Nelson’s use of new Texas Instruments TMS32010 chip new algorithms developed for ANC (filtered-U algorithm) on-line error path modeling developed Nelson initial field tests of dX-30 controller at Sheboygan plant; later 11 additional units installed and remain in operation Corporate Research forms Digisonix unit; later in year becomes Digisonix Division of Nelson with Art Hallstrom as president; Nelson/Digisonix receives first patents Digisonix presentation to NCAC in Hawaii; dX-40 controller developed; initial meetings with Ford engineers; installation of active exhaust silencing on diesel engine at Nelson; Digisonix staff expands; discussions with Ford continue; demonstration of active exhaust and intake silencing on car Steve Wise becomes president of Digisonix; Nelson and Ford begin joint ASVC program; Corporate Research forms Advanced Development Group (ADG) at Stewart Street with Cary Bremigan as manager Nelson forms ASVC Group that includes Digisonix and ADG under direction of Steve Dickmann; 182

Digisonix Division moves to new Murphy Drive facility; Nelson expands Stoughton Technical Center; teams from Nelson/Ford and Nelson/Digisonix visit Japan; first VPI conference, second in 1993, third becomes Active 95; Inter-Noise 91 and short course in Australia 1992 Nelson expands Stewart Street facility; becomes Eriksson-Geddes Development Center; Nelson ASVC Group is renamed in February, becomes the “new” Digisonix Division (includes the “old” Digisonix Division and ADG), continues under direction of Steve Dickmann; The “old” Digisonix engineering group, the Nelson acoustics research group, and Eriksson-Geddes Advanced Development Group form the new Digisonix Advanced Development and Engineering Group under the direction of Larry Eriksson; expanded Murphy Drive facility becomes Digisonix headquarters; Digisonix Division becomes Digisonix, Inc. in November with Steve Dickmann as president 1993 cross-coupled MIMO developed by Melton and Popovich; Digisonix issues first employee stock options; 85 active silencers installed on HVAC systems in 500,000 square foot building, met NC 40, over $38,000/year energy savings 1994 Digisonix and Lord Corporation begin joint ASVC program on products for aerospace applications; Ford Electronics Division suspends joint ASVC program; Digisonix introduces DigiWare development system 1995 Digisonix begins reducing costs, transfers some staff to Nelson 1996 Digisonix introduces Digital Voice Enhancement (DVE) system 1997 Digisonix moves headquarters to Stewart Street; leaves Murphy Drive; divides engineering by business sector; makes additional staff reductions; Universal Silencer begins marketing Dyna-Quiet silencers; announcement of proposed purchase of Nelson by Cummins 1998 Cummins purchase of Nelson and Digisonix approved by Nelson shareholders; Digisonix dissolved later in year ca. 2004 Nelson/Digisonix ASVC patents begin to expire ca. 2005-15 ANC begins to be widely used on cars 183

Table 4 Selected Digisonix Controllers unit

processor

I/O arith.* notes channels

dX-30

32010

4/2

fixed

large sloped box

dX-40

32020

4/2

fixed

large sloped box

dX-45

320C25

4/2

fixed

smaller black box

dX-47

320C25

4/2

fixed

R&D focus

dX-51

320C26

2/1

fixed

curved heat sink

dX-52

320C26

4/4

fixed

curved heat sink

dX-57

320C26

4/4

fixed

R&D focus

dX-52A

320C31

8/4

floating curved heat sink

dX-510

320C31

2/1

floating mini-box

dX-50I

320C26

4/4

fixed

large rectangular enclosure

dX-100

320C30

4/4 to 18/18

floating

R&D focus

dX-200

320C40

8/8 to 128/128

floating R&D focus

* fixed point or floating point arithmetic

184

Table 5 Selected Nelson/Digisonix U.S. ASVC patents number

title and inventor(s)

4,665,549

Hybrid active silencer Larry J. Eriksson, Mark C. Allie, Richard H. Hoops

4,677,676

Active...system...with on-line modeling of..error path... Larry J. Eriksson

4,677,677

Active...system...with on-line...feedback cancellation Larry J. Eriksson

4,736,431

Active...system with increased dynamic range Mark C. Allie, Geoffrey S. Bailey

4,811,309

Microphone probe for...measurement in turbulent flow Larry J. Eriksson, Mark C. Allie, Richard H. Hoops

4,815,139

Active...system for higher order mode...in a duct Larry J. Eriksson, Mark C. Allie, Richard H. Hoops

4,837,834

Active...system with differential filtering Mark C. Allie

4,903,249

Rigid foraminous...probe for...turbulent flow Richard H. Hoops, Larry J. Eriksson, Mark C. Allie

4,987,598

Active...system with overall modeling Larry J. Eriksson

5,022,082

Active...system with reduced convergence time Larry J. Eriksson, Mark C. Allie

5,033,082

Communication system with active noise cancellation Larry J. Eriksson, Mark C. Allie

5,044,464

Active...attenuation mixing chamber Cary D. Bremigan

5,088,575

Acoustic system with transducer and venturi Larry J. Eriksson

5,172,416

Active...system with specified output acoustic wave Mark C. Allie, Larry J. Eriksson, Cary D. Bremigan 185

5,206,911

Correlated...system with error and correction...input Larry J. Eriksson, Mark C. Allie

5,216,721

Multi-channel active acoustic attenuation system Douglas E. Melton

5,216,722

Multi-channel active...system with error signal inputs Steven R. Popovich

5,278,913

Active...system with power limiting Kent F. Delfosse, Shawn K. Steenhagen

5,283,834

Acoustic system suppressing detection of...modes Seth D. Goodman, Kirk G. Burlage

5,386,477

Active...system matching model reference Steven R. Popovich, Trevor A. Laak, Mark C. Allie

5,390,255

Active...system with error and model copy input Steven R. Popovich

5,396,561

Active...attenuation and spectral shaping... Steven R. Popovich, Mark C. Allie

5,418,873

Active...system with indirect error sensing Larry J. Eriksson

5,420,932

Active...system that decouples wave modes... Seth D. Goodman

5,446,249

Dry acoustic system preventing condensation Seth D. Goodman, Richard A. Hoffmann

5,513,266

Integral active and passive silencer Michael T. Zuroski

5,541,373

Active exhaust silencer C. Raymond Cheng

5,557,682

Multi-filter set...active control system Jay V. Warner, Kent F. Delfosse, Scott D. Kuhn

5,561,598

Adaptive...system...constrained output and adaptation Michael P. Nowak, Barry D. Van Veen

5,570,425

Transducer daisy chain Seth D. Goodman, Larry J. Eriksson, Douglas E. Melton, Edward R. Braun 186

5,586,189

Active...system with spectral leak Mark C. Allie, Steven R. Popovich

5,586,190

Active...system with...selective leakage Jerry J. Trantow, Brian M. Finn

5,590,205

Adaptive...system with a corrected-phase...error update Steven R. Popovich

5,602,928

Multi-channel communications system Larry J. Eriksson, Cary D. Bremigan

5,602,929

Fast adapting control system and method Steven R. Popovich

5,621,803

Active...system with on-line modeling of feedback Trevor A. Laak

5,627,747

System for developing...an active...control system Douglas E. Melton, James E. Allard, Brian M. Finn, Jerry J. Trantow, Steven R. Popovich, Trevor A. Laak, Mark C. Allie, Larry J. Eriksson

5,633,795

Adaptive tonal...system with constrained output and... Steven R. Popovich

5,680,337

Coherence optimized active...system Douglas G Pedersen, Trevor A. Laak

5,693,918

Active exhaust silencer Cary D. Bremigan, C. Raymond Cheng

5,701,350

Active...control in remote regions Steven R. Popovich

5,706,344

Acoustic echo cancellation in...audio...system Brian M. Finn

5,715,320

Active adaptive selective control system Mark C. Allie, Larry J. Eriksson, Charles W. Brokish

5,930,371

Tunable acoustic system C. Raymond Cheng, Jason D. McIntosh, Michael T. Zuroski, Larry J. Eriksson

5,963,651

Adaptive...system having distributed processing... Barry D.VanVeen, Olivier E.Leblond,Daniel J.Sebald 187

Table 6 Abbreviations and acronyms ADE

ADG ANC (J)ASA ASHRAE ASME ASVC CMOS DSP DTL DVE ECE FIR HVAC IEEE IIR INCE ICASSP LMS MIMO NC curve NCAC NMOS PDP OEM RLMS RAC SAE VPI UW

Advanced Development and Engineering Group (“new” Digisonix engineering staff, included ADG, ”old” Digisonix engineering and Nelson Acoustics Research) Advanced Development Group (Nelson/Digisonix staff at Eriksson-Geddes) active noise control (Journal of the) Acoustical Society of America American Society of Heating, Refrigeration, and Air Conditioning Engineers American Society of Mechanical Engineers active sound and vibration control complementary metal-oxide-semiconductor digital signal processing Digisonix Testing Laboratory Digital Voice Enhancement Electrical and Computer Engineering finite impulse response heating, ventilation, and air conditioning Inst. of Electrical and Electronics Engineers infinite impulse response Institute for Noise Control Engineering International Conference on Acoustics, Speech, and Signal Processing Least Mean Squares multiple-input, multiple-output Noise Criterion curve (used to rate noise in an enclosed space) National Council of Acoustical Consultants N-type metal-oxide-semiconductor logic Professional Data Processing (Nelson sub.) original equipment manufacturer Recursive Least Mean Squares Research Advisory Council Society of Automotive Engineers Virginia Polytechnic Institute University of Wisconsin

188

Figures Fig. 1 - Nelson Industries, Inc. (ca.1974) - p. 4 Fig. 2 - U.S. Pat.Pat. 2,043,416 by Paul Lueg - p. 14 Fig. 3 - U.S. Pat. 2,983,790 by H.F. Olson - p. 15 Fig. 4 - U.S. Pat. 2,776,020 by Conover, et al. - p. 16 Fig. 5 - Tripole loudspeaker configuration (from U.S. Pat. 4,177,874 by Theophile A. Angelini, Bernard J. P. Nayrole, Maurice J. Jessel, Georges Canevet, Gerard A. Mangiante, Bernard Carbone) - p. 18 Fig. 6 - A five tap Finite Impulse Response (FIR) filter; the digital inputs pass through four sample period delays, at each sample period, the values at each tap are multiplied by their respective coefficients, and summed to produce the filter output - p. 28 Fig. 7 - LMS algorithm - p. 33 Fig. 8 - System identification approach - p. 36 Fig. 9 - RLMS adaptive filter on a duct (from U. S. Pat. 4,677,677 by Larry Eriksson) - p. 38 Fig. 10 - RLMS adaptive filter with on-line error path modeling (from U. S. Pat. 4,677,676 by Larry Eriksson) - p. 47 Fig. 11 - Overview of Digisonix active control system using dX-30 controller with TMS32010 processor - p. 48 Fig. 12 - Digisonix (Feb., 1987) - p. 61 Fig. 13 - Digisonix Division (Sept., 1987) - p. 62 Fig. 14 - Nelson/Digisonix ASVC program (ca. 1990) - p. 80 Fig. 15 - Nelson ASVC Group (1991) - p. 87 Fig. 16 - In 1992, the Nelson ASVC Group, renamed the “new” Digisonix in February, became Digisonix. Inc. in November - p. 93 189

Fig. 17 - Nelson ASVC Facilities (1992) - p. 95 Fig. 18 - Digisonix ADE Group (ca. 1993) - 100 Fig. 19 - Selected physical components of a DigiWare development system (from U. S. Pat. 5,627,747 by Melton, Allard, Finn, Trantow, Popovich, Laak, Allie, and Eriksson) - p. 106 Fig. 20 - Signal processing elements of a DigiWare development system (from U. S. Pat. 5,627,747 by Melton, Allard, Finn, Trantow, Popovich, Laak, Allie, and Eriksson) - p. 107 Fig. 21 - Multi-channel active acoustic attenuation system (from U. S. Pat. 5,216,721 by Doug Melton) - p. 109 Fig. 22 - Multi-channel active acoustic attenuation system with error signal inputs (from U. S. Pat. 5,216,722 by Steve Popovich) - p. 110 Fig. 23 - Cross-section of duct with nodal lines for the first two modes (from U. S. Pat. 5,283,834 by Seth Goodman and Kirk Burlage) - p. 112 Fig. 24 - Controlling two modes with two independent controllers (from U. S. Pat. 5,420,932 by Seth Goodman) - p. 112 Fig. 25 - Digital Voice Enhancement system (from U. S. Pat. 5.033,082 by Larry Eriksson and Mark Allie) - p. 122 Fig. 26 - Multi-channel Digital Voice Enhancement system (from U. S. Pat. 5,602,928 by Larry Eriksson and Cary Bremigan) - p. 123 Fig. 27 - Digisonix, Inc. (ca. 1997) - p. 128 Fig. 28 - The number of ASVC publications published each year from 1952-1994 doubled about every five years; the dips in the last few years may be due to the timing of major conferences and a time lag in gathering data (data from Dieter Guicking, Active Sound and Vibration Control Reference Bibliography, 3rd ed., 2nd suppl., Nov., 1995, Univ. of Göttingen, Germany) - p. 132

190

Photographs (all photos by the author except as noted) • Initial Digisonix field installation at Sheboygan site - p. ii • Corporate Research was started in the garage at right in 1973 - p.xii • The original Nelson office building and new home of Corporate Research (1975) - p. xii • Interior of large hemi-anechoic chamber - p. 5 • Entrance to large hemi-anechoic chamber added to Nelson Technical Center in 1975 expansion - p. 6 • Nelson’s Bryant Building named after co-founder, Ed Bryant - p. 9 • Nelson’s Technical Center in Stoughton, Wisconsin - p. 12 • ECE building at the UW-Madison (ca. 1980s) - p. 20 • Atari 800 microcomputer - p. 26 • Work bench with test system, controller, and spectrum analyzer - p. 30 • Initial Nelson dX-30 Digital Sound Controller - p. 40 • Close-up of Digisonix double sine wave logo - p. 40 • TMS32010 evaluation board (left) used for development - p. 44 • top: dX-30 board with TMS32010 (long chip at left) - p. 49 bottom: dX-40 board with TMS32020 (square chip at left) - p. 49 • Introduction of the Nelson dX-30 controller at the Anaheim ASA meeting in December of 1986 - p. 54 • Side view of Sheboygan field test site; note flag blowing in wind and Lake Michigan in the distance on the left - p. 54 Original Digisonix sign in front of former garage (ca. 1987) - p. 64 • • Mobile office next to Digisonix building (ca. 1988) - p. 64 • Cut-away dX-45 controller for development work - p. 66 • Active silencing on centrifugal fans* - pp. 68 • Active silencing on material handling fan and vacuum pump discharge* - p. 69 • Digisonix display “We’re Changing the Way Industry Controls Noise” - p. 73 • Experimental active muffler system on Ford Explorer at Digisonix Open House - p. 78 • Shinjuku Gyoen park in Tokyo after ASVC Symposium - p. 84 191

• Eriksson-Geddes Development Center (Nelson–Ford) on Stewart Street in Madison in 1992 - p. 90 • Close-up of Nelson-Ford sign on Stewart Street facility - p. 90 • New Nelson Technical Center in Stoughton with abstract sculpture suggestive of Nelson’s products (ca. 1993) - p. 94 • Digisonix dX-52 and dX-57 controllers - p. 98 • Platform with active mounts for studying active vibration control - p. 99 • Digisonix prototype multiple-input, multiple-output controller - p. 104 • In May of 1994, the Digisonix team took a break to view a partial solar eclipse at the Murphy Drive facility - p. 104 • Digisonix headquarters on Murphy Drive in Middleton - p. 114 • Mock-up of HVAC duct at Murphy Drive to evaluate active silencing - p. 114 • Stewart Street facility with modified sign after suspension of Ford program - p. 119 • Digisonix dX-510 controller - p. 120 • Close-up of dX-510 control board with TMS32031 Floating Point Processor (square black chip left of center) - p. 120 • Stewart Street headquarters of Digisonix in 1997 - p. 129 • Test set-up for active silencing displayed at Digi. Open House - p. 138 • Close-up of Sheboygan installation showing two loudspeakers - p. 138 • Digisonix headquarters on Murphy Drive in Middleton - p. 147 • New Nelson Technical Center in Stoughton - p. 148 • dX-50I industrial controller being tested at Murphy Drive - p. 148 • Nelson Industries, Inc. sign in front of the Gusloff Building - p. 156 • Corporate Research offices in the Nelson Technical Center - p. 164 • Recognizing history, Digisonix employees played softball for “Lueg’s Laurel” - p. 224 * courtesy of Steve Wise

192

For More Information Noise and Vibration Control Engineering: Principles and Applications (1992), edited by Leo L. Beranek and István L. Vér, has an overview in chapter 15, “Active Noise Control” by the author. Also see “A Primer on the Digisonix Approach to ASVC,” by the author and published by Digisonix in Mar., 1994; an edited version was published in Sensors, Vol. 14 (2), Feb. 1997, pp. 18-31 and reprinted by Digisonix. Active Control of Sound (1992) by P. A. Nelson and S. J. Elliott covers the entire field in detail (also see their review article, “Active Noise Control,” IEEE Signal Processing Magazine, pp. 12-35, Oct., 1993). Active Noise Control Systems (1996) by Sen M Kuo and Dennis R. Morgan reviews various signal processing algorithms including much of the work done at Nelson, Digisonix, and the UW-Madison (also see their review article “Active Noise Control: A Tutorial Review,” Proc. IEEE, vol. 87, no. 6, June, 1999, and Design of Active Noise Control Systems With the TMS320 Family by Sen M. Kuo, et al., published by Texas Instruments, SPRA042, June, 1996). Adaptive Signal Processing (1985) by Widrow and Stearns contains a clear and detailed discussion of the LMS algorithm. The First Fifty Years: 1939-1989, published by Nelson Industries, has a summary of Nelson’s history. “A Case Study in University-Industry Cooperation on ASVC Research” by L. J. Eriksson, M. C. Allie, and R. A. Greiner, presented at the 1994 ASA meeting in Cambridge, Massachusetts, describes the joint research activities of Nelson and the UW-Madison. Business Decisions (2002) by the author and published by Quarter Section Press discusses the sale of Nelson to Cummins (the latter two are available from the author). Filtered-U algorithm/RLMS algorithm: My 1991 JASA paper describes the development of the filtered-U algorithm. Detailed studies related to the RLMS algorithm can be found in papers by Flockton and Abbott in 1988, Flockton in 1989, Scheper in 1991, Scheper and Bernhard in 1992, Brokish and Greiner in 1993, and Nowak and Van Veen in 1995. 193

Bibliography and Review Articles S. J. Elliott and P. A. Nelson, “Active Noise Control,” IEEE Signal Processing Magazine, pp. 12-35, Oct., 1993. Larry John Eriksson, “Active Sound Attenuation Using Adaptive Digital Signal Processing Techniques,” Ph.D. thesis, UW-Madison, 1985. L. J. Eriksson, “Computer-Aided Silencing - An Emerging Technology,” Sound and Vibration 24(7), June 1990, pp. 42-45 (on tech. change). L. J. Eriksson, “Development of the filtered-U algorithm for active noise control,” J. Acoust. Soc. Am. 89(1), 257-265 (1991). L. J. Eriksson, “Active Noise Control,” Ch. 15 in Noise and Vibration Control Engineering: Principles and Applications, Leo L. Beranek and István L. Vér (eds.), pp. 565-583, John Wiley & Sons, Inc., 1992. Larry J. Eriksson, A Primer on the Digisonix Approach to Active Sound and Vibration Control, Digisonix, Inc., March, 1994. (edited version in Sensors, Vol. 14 (2), Feb. 1997, pp. 18-31, and reprinted by Digisonix). L. J. Eriksson, “ASVC: A Technology in Transition,” Noise Control Eng. J. 44 (1), Jan.-Feb., 1996, pp. 1-9 (on tech. change). L. J. Eriksson, “A Brief Social History of Active Noise Control,” Sound and Vib., 33 (7), July, 1999, pp. 14-17 (on tech. change). L. J. Eriksson, T. A. Laak, and M. C. Allie, “On-Line Secondary Path Modelling for FIR and IIR Adaptive Control in the Presence of Acoustic Feedback,” Active 99, 949-960, Fort Lauderdale, Florida. D. Guicking, Active Sound and Vibration Control Reference Bibliography, 3rd ed., Feb. 1988, University of Göttingen, Germany (see also 1st supplement, Aug., 1991, and 2nd supplement, Nov., 1995). D. Guicking, “From Paul Lueg to DSP – 55 years of active noise control,” IEEE ASSP Workshop on Applications of Signal Processing to Audio and Acoustics, Lake Mohonk, NY, 1989. D. Guicking, “Active Noise Control, A Review Based on Patent Specifications,” International Congress on Noise and Vibration Control, St. Petersburg, Russia, May 31-June 3, 1993. D. Guicking, “Active control of sound and vibration–an overview of the patent literature,” Proceedings of ISMA21, 1996 International Conference on Noise and Vibration Engineering, Sept. 18-20, 1996.

194

Sen M. Kuo and Dennis R. Morgan, Active Noise Control Systems, Wiley, New York, 1996. Sen M. Kuo, Issa Panahi, Kai M. Chung, Tom Horner, Mark Nadeski, and Jason Chyan, Design of Active Noise Control Systems With the TMS320 Family, DSP Products—Semi. Group, SPRA042, June, 1996. Sen M. Kuo and Dennis R. Morgan, “Active Noise Control: A Tutorial Review,” Proc. IEEE, vol. 87, no. 6, June, 1999. S. M. Kuo and D. R. Morgan, “Review of DSP Algorithms for ANC,” Proc. IEEE Int. Conf. on Control Applications, Anchorage, Sept. 25-27, 2000, pp. 243-248 (available through IEEE Xplore Digital Library). H. G. Leventhall, “Active Attenuators: Historical Review and Some Recent Developments,” Inter-Noise 80, 697-682. H. G. Leventhall, “Historical Review and Recent Development of Active Attenuators,” 104th Meeting, ASA, Orlando, FL, Nov., 1982. Gérard Mangiante, “An Introduction to Active Noise Control,” Int. Journal of Active Control, Vol. 1, No. 4, pp. 303-330, 1995. P. A. Nelson and S. J. Elliott, Active Control of Sound, Academic, London, 1992. C. M. Schepper, “An investigation of the behavior of adaptive recursive algorithms...,” M.S.M.E. thesis, Purdue Univ., 1991 (Herrick rep. 91-10). Manfred R. Schroeder, Number Theory in Science and Communication, Springer-Verlag, 1984. David C. Swanson, “Active Attenuation of Acoustic Noise: Past, Present, and Future,” ASHRAE Transactions, Vol. 95, pt. 2, 1989. Jiri Tichy, “Applications for Active Control of Sound and Vibration,” Noise/News International, June, 1996, pp. 73-86. Glenn E. Warnaka, “Active Attenuation of Noise – The State of he Art,” Noise Control Eng. J., Vol. 18 (3), 100-110, May-June, 1982. B. Widrow, “Adaptive Filters,” Aspects of Network and System Theory, R.E.Kalman and N.Declaris, eds., Holt, Rinehart, & Winston, NY, 1971. Bernard Widrow and Samuel D. Stearns, Adaptive Signal Processing, Prentice-Hall, Englewood Cliffs, NJ, 1985.

195

References and Notes pre-1980 1.

H. Coanda, French patent 722,274, Mar. 15, 1932, and French patent 762,121, Apr. 4, 1934.

2.

P. Lueg, “Process of Silencing Sound Oscillations,” U.S. patent 2,043,416, June 19, 1936.

3.

“Noise Neutralizer,” April Fool’s Day spoof on an electronic system that will allegedly annihilate noise, Radio-Electronics, April, 1952.

4.

Arthur C. Clarke, “Silence Please” (short story on capacitors storing absorbed sound), published in Tales From the White Heart, 1954.

5.

H. F. Olson, “Electronic Control of Noise, Vibration, and Reverberation,” J. Acoust. Soc. Am. 28, 966-972 (1956).

6.

Conover, William B., “Fighting Noise With Noise,” Noise Control, March, 1956.

7.

B. Widrow and M. E. Hoff, Jr., “Adaptive Switching Circuits,” IRE WESCON Convention Record, pt.4, 96-104, 1960 (LMS algorithm).

8.

R. A. Greiner, Semiconductor Dev. and Appl., McGraw-Hill, 1961.

9.

Paul Baran, “The future computer utility,” National Affairs, no. 8, summer, pp. 75-87, 1967 (also in The Computer Impact by Irene Taviss, Prentice-Hall, pp. 81-92, 1970).

10. Elisabeth Kübler-Ross, On Death and Dying, 1969. 11. B. Widrow, “Adaptive Filters,” Aspects of Network and System Theory, R. E. Kalman and N. Declaris, eds., Holt, Rinehart, and Winston, New York, 1971. 12. Tony L. Parrott, “An Improved Method for Design of ExpansionChamber Mufflers...,” NASA Tech. Note TN D-7309, Oct., 1973. 13. K. Kido, “Reduction of Noise by Use of Additional Sound Sources,” Proc. Inter-Noise 75, pp. 647-650, Sendai, Japan. 14. P. L. Feintuch, “An Adaptive Recursive LMS Filter,” Proc. IEEE, 1622-1624, Nov., 1976. 15. David F. Noble, America by Design, Oxford, 1977 (Burgess, p.124). 16. ”Active silencer for low-frequency noise,” J. Acoust. Soc. Am. 66, p. 1215 (1979) (tech note and news on ASVC in ducts and pipes). 196

1980-1984 1.

H. G. Leventhall, “Active Attenuators: Historical Review and Some Recent Developments,” Proc. Inter-Noise 80, 697-682.

2.

D. R. Morgan, “Analysis of multiple correlation cancellation loop with a filter in the auxiliary path,” IEEE Trans. Speech Signal Processing, ASSP-28, (4) 454-467 (1980).

3.

J. C. Burgess, “Active adaptive sound control in a duct: A computer simulation,” J. Acoust. Soc. Am. 70, pp. 715-726 (1981).

4.

B. Widrow, D. Shur, and S. Shaffer, “On adaptive inverse control,” Proc. 15th Asilomar Conf. on Circuits, Systems and Computers, pp. 185-189, Pacific Grove, CA, Nov. 9-11, 1981.

5.

C. F. Ross, “A demonstration of active control of broadband sound,” J. Sound Vib., 74 (3), pp. 411-417, 1981.

6.

L. J. Eriksson, “A Review of Recent Progress in Exhaust System Design,” Paper 820622 presented at the SAE Earthmoving Industry Conf., Peoria, Illinois, April 19-21, 1982 (brief mention of ANC).

7.

M. A. Swinbanks, “The active control of low frequency sound in a gas turbine compressor installation,” Inter-Noise 82, San Francisco.

8.

Glenn E. Warnaka, “Active Attenuation of Noise – The State of he Art,” Noise Control Eng. J., Vol. 18 (3), 100-110, May-June, 1982.

9.

H. G. Leventhall, “Historical Review and Recent Development of Active Attenuators,” 104th Meeting, ASA, Orlando, FL, Nov., 1982.

10. Barrie Chaplin, “Anti-Noise – the Essex breakthrough,” Chartered Mechanical Engineer, pp. 41-47, Jan., 1983 (also Proc. Inter-Noise 80, pp. 699-702). 11. S. J. Elliott and P. A. Nelson, I.S.V.R. Technical Report No. 127, University of Southampton, UK (published as U.S. Dept. of Commerce NTIS Bulletin No. PB85-189777, Apr., 1984). 12. Lynn A. Poole, Glenn E. Warnaka, and Richard C. Cutter, “The Implementation of Digital Filters Using a Modified Widrow-Hoff Algorithm for the Adaptive Cancellation of Acoustic Noise,” Proc. ICASSP 84, pp.21.7.1-4, 1984 (see also Glenn E. Warnaka, Lynn A. Poole, and Jiri Tichy, “Active Acoustic Attenuator,” U.S. Patent 4,473,906, Sept. 25, 1984). 13. Manfred R. Schroeder, Number Theory in Science and Communication, Springer-Verlag, 1984. 197

1985 1.

Bernard Widrow and Samuel D. Stearns, Adaptive Signal Processing, Prentice-Hall, Englewood Cliffs, NJ, 1985.

2.

L. J. Eriksson, “Active Attenuation - Past, Present, and Future,” presented at the SAE Surface Vehicle Noise and Vibration Conf., May 15-17, 1985, Traverse City (repeated at SAE Off-Highway Meeting, Milwaukee, Sept. 10, 1985).

3.

Larry John Eriksson, “Active Sound Attenuation Using Adaptive Digital Signal Processing Techniques,” Ph.D. thesis, Dept. of Electrical and Computer Engineering, UW-Madison, 1985.

4.

L. J. Eriksson, “Active Sound Attenuation,” presented at faculty seminar, ECE Dept., UW-Madison, Oct. 2, 1985.

5.

William Baldwin, “Applied Gozinta,” Forbes, Oct. 21, 1985.

1986 1.

L. J. Eriksson, “Noise Control,” presented to class at Carroll College, Waukesha, Wisconsin, January 29, 1986.

2.

L. J. Eriksson, “Active Attenuation: Past, Present, and Future,” M.E. Graduate Seminar, Univ. of Cincinnati, Feb. 6, 1986.

3.

L. J. Eriksson, “Digital Signal Processing in Acoustics,” presented to Wisconsin Chapter of the ASA, Madison, Wisconsin, June 3, 1986.

4.

L. J. Eriksson, M. C. Allie, and R. A. Greiner, “A New Approach to Active Attenuation in Ducts,” Proceedings of the 12th Int. Congress on Acoustics, Toronto, Canada, July 24-31, 1986, paper C5-2.

5.

L. J. Eriksson and M. C. Allie, “The Use of Random Noise for OnLine Transducer Modelling in an Adaptive Active Attenuation System,” J. Acoust. Soc. Am. 80 (Supp. 1), S11(A) (1986).

6.

“Baffling a Noisy Problem,” UW News release, Nov. 28, 1986.

7.

“Firm fights noise by making some,” The Milw. Jrnl., Nov. 30, 1986.

8.

“UW battles noise with more noise,” Wis. St. J., Dec. 3, 1986.

9.

“Digital signal processing microprocessors: forward to the past,” L. Robert Morris, IEEE MICRO, Dec., 1986 (overview of DSP chips).

10. “Nelson dX-30 Digital Sound Controller with single switch silencing,” Adv. Product Info., Nelson Industries, Inc., Dec., 1986. 198

1987 1.

“Industrial Noise Control,” Industry Week, Feb. 23, 1987.

2.

“All Quiet on the Industrial Front,” Corp. Report Wis., March, 1987.

3.

“Nelson...Digital Sound Control System,” NoiseNews, 1987.

4.

“Turn on the Quiet” dX-30 product brochure, DX-S1-487.

5.

L. J. Eriksson, M. C. Allie, and R. A. Greiner, “The Selection and Application of an IIR Adaptive Filter for Use in Active Sound Attenuation,” IEEE Trans.ASSP, Vol.ASSP-35, 433-437, Apr., 1987.

6.

L. J. Eriksson, “Active Noise Control,” presented at a meeting of Wisconsin Section of AiChE, Brookfield, Wisconsin, April 15, 1987.

7.

L. J. Eriksson, “Active Noise Control - Technology for Today,” Chicago Chapter of ASA, Schiller Park, IL, April 22, 1987.

8.

Nelson Digisonix Newsletter, 586:1(1) (ca. May, 1987, announces formation of Digisonix business unit at Nelson).

9.

L. J. Eriksson and M. C. Allie, “A Digital Sound Control System for Use in Turbulent Flows,” Noise-Con 87, 365-370, Penn. State Univ.

10. William J. Broad, “New Technology Defeats Unwanted Noise, New York Times, June 30, 1987. 11. “Sound can produce the sound of silence,” The Orange County Register, Aug. 12, 1987 (edited version of New York Times article; includes diagram of active silencing attributed to Nelson Industries). 12. “Fan Silencing Syst.,” Air Cond., Heat. & Ref. News, Aug. 17, 1987. 13. “Digisonix...division of Nelson,” Nelson release, Aug. 29, 1987. 14. L. J. Eriksson, “ANC Using Adaptive DSP,” Signal Proc. Seminar, ECE Dept., UW-Madison, Madison, WI, Sept. 28, 1987. 15. “Announcing...dX-40,” DX-S-2/987; “Digital Sound Cancellation Systems,” DX-DS-1/987; “...dX-35 and dX-45,” DX-S-6/1087. 16. “Now You Hear It–Now You Don’t,” IMN, Oct., 1987. 17. “Silencing System,” Power, Oct., 1987. 18. “Fan Silencing System,” ASHRAE Journal, Oct., 1987. 19. L. J. Eriksson, “Active Noise Control,” presented at a meeting of Upper Midwest Chapter, ASA, Roseville, Minnesota, Nov. 24, 1987. 20. “Duct silencer” Heating/Piping/Air Conditioning, Dec., 1987. 199

1988 1.

L. J. Eriksson, “Active Sound Cancellation Systems,” presented at 1988 ASHRAE Winter Mtg., Dallas, TX, Jan. 30-Feb. 3, 1988.

2.

L. J. Eriksson and M. C. Allie, “A Practical System for Active Attenuation in Ducts,” Sound and Vib. 22(2), Feb. 1988, pp. 30-34 (Digisonix ad featuring “We’re Changing the Way Industry Controls Noise,” p. 29, Sound and Vib., Feb. 1988).

3.

D. Guicking, Active Sound and Vibration Control Reference Bibliography, 3rd ed., Feb. 1988, Drittes Physikalisches Institut, University of Göttingen, Germany (see also 1st supplement, Aug., 1991, and 2nd supplement, Nov., 1995).

4.

“Low frequency noise problems in air distribution systems,” Air Conditioning, Heat & Refrigeration News, Feb. 29, 1988.

5.

“Sound Cancellation System,” Mechanical Eng., March, 1988.

6.

L. J. Eriksson, M. C. Allie, C. D. Bremigan, and R. A. Greiner, “Active Noise Control Using Adaptive Digital Signal Processing,” Proc. ICASSP 88, New York, vol. I, paper A3.5, pp. 2594-2597.

7.

M. C. Allie, C. D. Bremigan, L. J. Eriksson, and R. A. Greiner, “Hardware and Software Considerations for Active Noise Control,” Proc. ICASSP 88, New York, vol. I, paper A3.6, pp. 2598-2601.

8.

“Active sound/vibration control, explore the possibilities...with the Digisonix dX series digital controllers,” Digisonix, DX-RM-1/488.

9.

“Noise+Noise=Silence” Autoweek, April 25, 1988 (on ASVC for interior ‘boom’ noise control on cars with 4-cylinder engines).

10. “Companies profit from sounds of silence,” High Technology Business, April 1988. 11. L. J. Eriksson, “Active Attenuation,” presented at a meeting of the East Mad. Optimist Club, Monona, Wisconsin, April 20, 1988. 12. M. L. Munjal and L. J. Eriksson, “An Analytical, One-Dimensional, Standing-Wave Model...,” J. Acoust. Soc. Am. 84, 1086-1093 (1988). 13. “Companies profit from sounds of silence,” High Technology. Business, Apr. 1988. 14. S. J. Flockton and N. J. Abbot, “Simulation of the behavior of the Eriksson adaptive noise control system in a reverberant duct,” Proc. Inst. of Acoustics, vol. 10, pp. 641-648, 1988. 15. L. J. Eriksson, “Active Att.,” Kiwanis Club, Monona, May 12, 1988. 200

16. “Active sound cancellation system,” Research & Dev., May, 1988. 17. “Counternoise,” Popular Mechanics, May, 1988. 18. “State rewards bright ideas” Wisconsin State Journal, May 11, 1988. 19. L. J. Eriksson and M. C. Allie, “System Considerations for Adaptive Modelling Applied to Active Noise Control,” Proc. ISCAS 88, June 7-9, 1988, Espoo, Finland, vol. 3, pp. 2387-2390. 20. L. J. Eriksson, “Active Attenuation,” presented at Chalmers Institute of Technology, Göteborg, Sweden, June 13, 1988. 21. “75 years ago - 1913: Disquieting Noise, ‘Oh, for a machine that will make artificial quiet!’ ” International Herald Tribune, June 15, 1988. 22. L. J. Eriksson, M. C. Allie, C. D. Bremigan, and J. A. Gilbert, “Active Noise Control and Specifications for Fan Noise Problems,” Noise-Con 88, 273-278, Purdue University, West Lafayette, Indiana. 23. “Firm quietly building its name by eliminating industrial noise” The Milwaukee Sentinel, July 21, 1988. 24. “The microprocessor’s first two decades: the way it was,” James F. Donohue, EDN Microprocessor Issue, Oct. 27, 1988. 25. Opening of Digisonix Test Laboratory, Noise News, Sept./Oct., 1989. 26. “Digisonix dX-47 controller,” Digisonix, DX-SS-4/1188. 27. L. J. Eriksson, “Active Sound Control,” presented to a meeting of the National Council of Acoustical Consultants, Lihue, Kauai, Hawaii, November 11-12, 1988. 28. Rebecca Kolberg, “Science works to muffle the sounds no one wants to hear,” Los Angeles Times, Nov. 13, 1988 (available online). 29. L. J. Eriksson, M. C. Allie, C. D. Bremigan, and J. A. Gilbert, “Active Noise Control on Systems with Time-varying Sources and Acoustical Elements,” J. Acoust. Soc. Am. 84 (Supp. 1), S183(A) (1988) (presented at Hawaii ASA meeting). 30. L. J. Eriksson, M. C. Allie, C. D. Bremigan, and J. A. Gilbert, “The Use of Active Noise Control for Industrial Fan Noise,” presented at the ASME Winter Annual Meeting, Nov. 27-Dec. 2, 1988, Chicago. 31. “ ‘Anti-noise’ waves douse din” Chicago Sun-Times, Dec. 4, 1988. 32. L. Robert Morris and Stephen A. Dyer, “Floating-point digital signal processing chips: the end of the supercomputer era?” IEEE MICRO, December, 1988. 201

1989 1.

James Galbraith, “Modern Methods Make an Old Idea a Sound One,” Wisconsin Professional Engineer, January/February, 1989.

2.

“Active Noise Controller” Mechanical Engineering, February,1989.

3.

“Active Cancellation using Adaptive Filters,” Syn-Aud-Con Newsletter, Winter, 1989.

4.

M. L. Munjal and L. J. Eriksson, “Analysis of a Linear OneDimensional ANC System by Means of Block Diagrams and Transfer Function,” J. Sound Vib. 129(3), 443-445 (1989).

5.

M. L. Munjal and L. J. Eriksson, “Anal. of a Hybrid Noise Control System for a Duct,” J. Acoust. Soc. Am. 86, 832-834 (1989).

6.

L. J. Eriksson and M. C. Allie, “Use of random noise for on-line transducer modelling in an adaptive active attenuation system,” J. Acoust. Soc. Am. 85(2), 797-802 (1989).

7.

David C. Swanson, “Active Attenuation of Acoustic Noise: Past, Present, and Future,” ASHRAE Transactions, Vol. 95, pt. 2, 1989.

8.

L. J. Eriksson, “Adaptive Signal Processing,” Technology Outlook Seminar, March 2, 1989, UW-Madison.

9.

Digisonix brochure “Digital Sound Cancellation Systems” with dX-45 controller (DX-DS-1/389).

10. “Active controller cancels noise,” Designfax, April, 1989 (Five-Star product of the month). 11. “Nicolet stops hearing aid sale” Wis. St. J., April 22, 1989. 12. D. A. Olson, S. S. Wise, L. J. Eriksson, and M. C. Allie, “Airmoving devices and active noise control,” J. Acoust. Soc. Am. 85 (Suppl. 1), S2 (A) (1989). 13. “IAC Announces New Silencers” Noise News, May/June 1989 (designed for low restriction, low frequency performance). 14. L. J. Eriksson, M. C. Allie, C. D. Bremigan, and J. A. Gilbert, “Weight Vector Analysis of an RLMS Adaptive Filter with On-Line Auxiliary Path Modelling,” Proc. ICASSP 89, May 23-26, 1989, Glasgow, Scotland, U.K., pp. 2029-2032. 15. “U.K. Researcher Seeks Silence at Low End” Automotive Electronic News, June 19, 1989 (on ‘boom’ re Colin Ross,Topexpress, Lotus).

202

16. L.J. Eriksson, M.C. Allie, C.D. Bremigan, and J.A. Gilbert, “Active noise control on systems with time-varying sources and acoustical elements,” Sound and Vibration, 23 (7), 16-21, July, 1989. 17. S. J. Flockton, “The use of FIR and IIR adaptive filtering algorithms in the active control of acoustic noise,” 32nd Midwest Symposium on Circuits and Systems,” August, 1989, Urbana, IL. 18. L. J. Eriksson, “Adaptive Signal Processing: ANC, Liquid-Borne Noise,” Wood and Paper Seminar, UW-Madison, Aug. 28, 1989. 19. The First Fifty Years: 1939-1989, Nelson Industries, 1989. 20. Albert Thumann and Richard K. Miller, Fundamentals of Noise Control Engineering, Fairmont Press, 1989. 21. “Computerized Quiet,” PC/Computing, October, 1989. 22. L. J. Eriksson, “Observability Considerations in Active Noise Control Systems,” IEEE ASSP Workshop, Mohonk Mountain House, New Paltz, NY, Oct. 15-18, 1989. 23. D. Guicking, “From Paul Lueg to DSP – 55 years of active noise control,” IEEE ASSP Workshop, Mohonk Mountain House, New Paltz, NY, Oct. 15-18, 1989. 24. L. J. Eriksson, “Adaptive Signal Processing Applied to the Active Control of Acoust. Noise,” M.E. Coll., Northwestern, Nov. 2, 1989. 25. “Quiet Please,” Automotive Electronics Journal, Nov. 20, 1989 (re possible Ford/”Nelson Res.” joint program). 26. “Fighting Noise with Antinoise” Time, Dec. 4, 1989. 27. L. J. Eriksson, M. C. Allie, R. H. Hoops, and J. V. Warner, “Higher Order Mode Cancellation in Ducts Using Active Noise Control,” Proc. Inter-Noise 89, Dec. 4-6, 1989, Newport Beach, pp. 495-500. 28. “M&B Fights Noise with Noise,” Health & Safety Digest, Winter 1989/90 (Work. Comp. Board, Brit. Col., Canada). 29. M. L. Munjal and L. J. Eriksson, “An exact one-dimensional analysis of the acoustic sensitivity of the anti-turbulence probe tube in a duct,” J. Acoust. Soc. Am. 85(2), 582-587 (1989). 30. M. L. Munjal and L. J. Eriksson, “Anal. of a Hybrid Noise Control System for a Duct,” J. Acoust. Soc. Am. 86, 832-834 (1989). 31. L. J. Eriksson and M. C. Allie, “Use of random noise for on-line transducer modeling in an adaptive active attenuation system,” J. Acoust. Soc. Am. 85(2), 797-802 (1989). 203

1990 1.

L. J. Eriksson, “Noise Reduction with Active Mufflers Using Adaptive DSP,” E.E. Coll., Univ. of Minnesota, Feb. 1, 1990.

2.

“Loudspeakers that kill the noise” Financial Times, Feb. 2, 1990 (Lotus ‘boom’ control).

3.

L. J. Eriksson, “Active Mufflers Using DSP,” Society of Physics Students, UW-Platteville, Feb. 8, 1990.

4.

L. J. Eriksson, “Intro. to ANC,” Applying ”Active” Silencers to Ducts and Fans, Mar. 26-27, 1990, UW-Mad., (also Nov. 7-8, 1990).

5.

L. J. Eriksson, “Technological Change and Active Noise Control,” Proc. I.O.A., Acoust. 90, V. 12, Part 1, 653-660 Southampton, UK.

6.

D. Guicking, “On the invention of active noise control by Paul Lueg,” J. Acoust. Soc. Am. 87(5), 2251-2254 (1990).

7.

“Controlling industrial Noise: The computer age is here,” Perspective, UW College of Engineering, Spring, 1990.

8.

John Papamarcos, “Stack add-on cancels fan noise” Plant Services, April, 1990.

9.

“The UW helped us develop a new technology at Nelson Industries,” Wisconsin Spotlight, June 9, 1990.

10. L. J. Eriksson, “Computer-Aided Silencing - An Emerging Technology,” Sound and Vibration 24(7), June 1990, pp. 42-45. 11. “Active/Passive silencer,” Consult/Specifying Engineer, Aug., 1990. 12. “Active/passive silencer,” Contracting Business, August, 1990. 13. “Noisy basement can be usable space,” Air Conditioning, Heating, & Refrigeration News, Sept. 17, 1990. 14. L. J. Eriksson and M. C. Allie, “Annoyance Reduction Using ANC with Adaptive Sig. Proc.,” Noise-Con 90, 163-166, Univ. of Texas. 15. “Active/passive silencer,” Sound and Vibration, November, 1990. 16. “Duct silencer,” Engineered Systems, November/December, 1990. 17. “Noisy Silence,” ASC news feature on WKOW-TV, December 7, 1990, Madison, Wisconsin (featured Nelson and Digisonix). 18. “As quiet as a refrigerator?” Japan Econ. Journal, Dec. 8, 1990 (re Toshiba work). 204

1991 1.

Pugh, Emerson W., Lyle R. Johnson, and John H. Palmer, IBM’s 360 and Early 370 Systems, MIT Press, Cambridge, MA, 1991.

2.

“HVAC noise reduced 15-17 decibels,” Plant Services, Feb., 1991.

3.

“Anti-Noise System May Exhaust Need for Car Mufflers,” The Wall Street Journal, Feb. 6, 1991 (mentions Ford’s interest).

4.

“Sh-h-h-h...New devices cut noise,” The Milw. Jrnl., Feb. 24, 1991.

5.

“DSP boards find uses,” Electronic Eng. Times, April 8, 1991.

6.

L. J. Eriksson, “Development of the filtered-U algorithm for active noise control,” J. Acoust. Soc. Am. 89(1), 257-265 (1991).

7.

L. J. Eriksson, “Active Sound Cancellation Systems Using Adaptive Digital Signal Processing,” presented at the Dept. of ECE Spring Colloquium, Marquette University, Milwaukee, Mar. 19, 1991.

8.

L. J. Eriksson, “Recursive Algorithms for Active Noise Control,” Proceedings of the Int. Symposium on Active Control of Sound and Vib., Tokyo, Japan, Apr. 8-11, 1991, pp. 137-146. Edited version in Trans. IEE Japan, Vol. 111-D, No. 10, pp. 819-822, Oct., 1991.

9.

D. Guicking, “Active noise control - achievements, problems, and perspectives,” Proceedings of the Int. Symposium on Active Control of Sound and Vibration, Tokyo, Japan, Apr. 8-11, 1991.

10. L. J. Eriksson, “The Continuing Evolution of Active Noise Control with Special Emphasis on Ductborne Noise,” Proceedings of the Conference on Recent Advances in Active Control of Vibration and Sound, Apr. 15-17, 1991, VPI, Blacksburg, Virginia, pp. 237-245. 11. Joe Alper, “Antinoise Creates the Sounds of Silence,” Science, April 26, 1991. 12. “Putting a lid on noise pollution,” Mechanical Engineer, June, 1991. 13. Larry J. Eriksson, interview and comments on active noise control on Matt Joseph’s program “About Cars,” WHA, Wisconsin Public Radio, June 8, 1991, Madison, Wisconsin. 14. Kirk Burlage, David Kapsos, Chris Depies, Susan Dineen, Seth Goodman, Steve Wise, “An update of commercial experience...,” Noise-Con 91, 253-258, Tarrytown, New York. 15. William F. Allman, “Good News About Noise” U.S. News & World Rep., Sept. 9, 1991. 205

16. “Shhharp ideas at UW” The Milwaukee Sentinel, Sept. 10, 1991 (on the UW, Ford, and Digisonix). 17. “Sounds of Silence,” The Milwaukee Sentinel, Sept. 11, 1991. 18. “Active silencing for HVAC retrofit,” Digisonix, DX-CH-5/1091. 19. “Broadcast studio quiet assured,” Digisonix Newsletter, Winter/ Spring, 1991, DX-SHD-4. 20. ASC news feature on ABC’s World News Tonight (WNT) with Peter Jennings, October 4, 1991 (featured a Digisonix competitor). 21. L. J. Eriksson and M. C. Allie, “Active Atten. with Overall System Modeling,” IEEE ASSP Workshop, Oct. 20-23, 1991, New Paltz, NY. 22. “Active Quiet,” Automotive Industries, Nov., 1991 (discusses Nissan Bluebird system dev. by Lotus and NCT patent complaints). 23. “Nissan auto glides quiet as a Bluebird,” The Nikkei Weekly, Nov. 9, 1991 (interior noise control). 24. John Sedgwick, “Cut Out That Racket,” The Atlantic Monthly, November, 1991. 25. “Active Noise Control,” Automotive Engineering (Tech Brief), November, 1991 (Lotus Engineering and interior noise control). 26. C. M. Schepper, “An investigation of the behavior of adaptive recursive algorithms applied to the control of modal systems,” M.S.M.E. thesis, Purdue Univ., 1991 (also Herrick report 91-10). 27. L. J. Eriksson, “Effect of Uncorrelated Noise on System Identification Applied to Active Noise Control,” Proceedings InterNoise 91, December 2-4, 1991, Sydney, Vol. 1, pp. 153-156. 28. L. J. Eriksson, “Acoustic Feedback Control and IIR Filters,” pp. 5-1 to 5-27, Chap. 5; “Application Considerations and Case Histories for Active Noise Control in Ducts,” pp. 17-1 to 17-17, Chap. 17; Notes for a Course on the Active Control of Noise and Vibration, C. H. Hansen (ed.), December. 9-12, 1991, University of Adelaide, Vol. 1. 29. “Anti-Noise,” ASC news feature on ABC’s Good Morning America (GMA), Dec. 16, 1991 (featured a Digisonix competitor). 30. “Digisonix dX-57 digital sound and vibration cancellation controller,” Digisonix, DX-SS-7/1291. 31. Robert K. Massie, Dreadnought, Random House, 1991 (see pp. 389-391 regarding resistance to steam power on ships).

206

1992 1.

ASC news feature on WISC-TV, ca. 1992, Madison, Wisconsin (featured Nelson and Digisonix ASVC activities).

2.

L. J. Eriksson, “Active Noise Control,” Chapter 15 in Noise and Vibration Control Engineering: Principles and Applications, Leo L. Beranek and István L. Vér (eds.), pp. 565-583, Wiley, 1992.

3.

P. A. Nelson and S. J. Elliott, Active Control of Sound, Academic, London, 1992.

4.

“Noise silences noise,” Popular Science, Jan., 1992 (on incinerator “like switching the fan off”; misspells “Eriksson” as ”Ericksson”).

5.

“Nelson Industries and Ford Dedicate Joint Development Center,” Digisonix Press Release, Middleton, Wisconsin, February 3, 1992.

6.

“Turn on the quiet,” Air Conditioning, Heating and Refrigeration News, Feb. 17, 1992 (includes photo of Digisonix display booth).

7.

“Nelson Industries Reorganizes and Expands Digisonix Division,” Digisonix Press Release, Middleton, Wisconsin, February 21, 1992.

8.

Nathan Seppa, “Noise creates silence,” Wisconsin State Journal, Feb. 25, 1992 (cited in Rotary News, Feb. 29, 1992).

9.

D. Guicking, “Recent Advances in Active Noise Control,” Second Int. Congress on Recent Developments in Air- and Structure-Borne Sound and Vibration, Auburn University, AL, Mar. 4-6, 1992.

10. “Building fire,” Wis. St. J., Mar. 7, 1992 (former Digisonix building). 11. “Stoughton building gutted,” The Capital Times, March 8, 1992. 12. Jonathan D. Silver, “Their product could be music to your ears,” The Capital Times, Mar. 11, 1992 (cited in Rotary News, Mar. 21, 1992). 13. “Sound silencing firms meld effort,” The Cap. Times, Mar. 25, 1992. 14. D. E. Melton and R. A. Greiner, “Adaptive feedforward multipleinput, multiple-output active noise control,” Proc. ICASSP 92, Mar. 23-26, 1992, San Francisco, CA. 15. “Hear No Evil,” Popular Science, April, 1992. 16. “Fight Noise with Noise,” Med. Industry Exec., April/May, 1992. 17. “Update on ASVC Technology”, London, by Steve Dickmann, Larry Eriksson, and Steve Wise, Apr. 2, 1992 (“over 100 systems”). 18. L. J. Eriksson, presentation at the Up-date on ASVC Technology seminar sponsored by Digisonix, Apr. 2, 1992, London, England. 207

19. Christine M. Scheper and Robert J. Bernhard, “Modal control using the RLMS adaptive recursive algorithm,” presented at the 112th meeting of the ASA, May 11, 1992, Salt Lake City, UT (see also Herrick Labs. report HL 91-10, Internal 197, M.S.M.E. thesis, by Christine M. Scheper, August, 1991). 20. Digisonix ASVC technology licensed to Ford (Digisonix press release May 13, 1992; Nelson shareholder letter Dec. 7, 1991). 21. “Nelson-Applied Power development programme,” Noise & Vibration Worldwide, May, 1992. 22. “Digisonix Reorganizes,” Sound and Vibration, May, 1992. 23. “...(LJE) Executive VP of Digisonix...,” ASME News, May, 1992. 24. Jennifer Riddle, “Ford, Stoughton company deal on sound technology” Wis. St. J., May 15, 1992 (Rotary News, May 23, 1992). 25. “Digisonix license to Ford” The Capital Times, May 15, 1992. 26. Larry Eriksson, Dr. Greiner, Howard Pelton, David Kapsos, Bob Bernhard, Ivan Morse, short course at UW-Mad., May 28-29, 1992. 27. Susan Dineen, Steve Wise, “Energy-Efficient Silencing of Air Moving Devices w/ANC,” HVAC Expo, June 10-11, 1992, Boston. 28. “Sound control licensed,” Automotive News Insight, June 22, 1992. 29. “Electronic Noise and Vibration Control – By Model Year 1997,” The Hansen Report on Automotive Electronics, June, 1992, (includes summary and results of Delphi study at the University of Michigan). 30. S. Goodman, K. Burlage, S. Dineen, S. Austin, S. Wise, “Using ANC for recording studio...,” AES, San Fran., June 1-4, 1992. 31. Alan Morantz, “The Quiet Revolution,” Canadian Business, June, 1992 (LE quote on ANC, do not “promote this prematurely”). 32. “Nissan: ANC System,” Auto. Interiors International, Summer 92. 33. “Active Control of Low Frequency Noise (dX-57),” and “ANC (Digisonix and EG Dev. Center),” Sound and Vibration, July, 1997. 34. Pete Millard, “Your Blades For Their Razors,” Corporate Report Wisconsin, July, 1992 (includes interview with Steve Dickmann). 35. Michael J. Sheldrick, “Noise Cancellation Poised for Takeoff,” Electronic News, July 13, 1992 (“patent situation is muddied... panelists projected by 2000 that 20 percent of the cars produced in North America would have electronic mufflers...big bucks to winners in this market”). 208

36. Steven S. Wise, Chris R. Depies, Susan H. Dineen, “Case histories of active control...,” Inter-Noise 92, 307-312, Toronto, Canada. 37. “New adaptive multi-channel control systems for sound and vibration,” S. R. Popovich, D. E. Melton, and M. C. Allie, InterNoise 92, 405-408, Toronto, Canada. 38. “Active cancellation of higher order modes in a duct using recursively-couple multi-channel adaptive control systems,” S. P. Rubenstein, S. R. Popovich, D. E. Melton, and M. C. Allie, InterNoise 92, 337-340, Toronto, Canada. 39. “Active vibration isolation and stabilization of rigid body systems using recursively coupled multi-channel adaptive control systems,” J. V. Warner, S. P. Rubenstein, D. E. Melton, and S. R. Popovich, Inter-Noise 92, 387-390, Toronto, Canada. 40. “...Leventhall... head...office” Wis. St. J., July 27, 1992. 41. “The Sounds of Silence,” Newsweek, Aug. 10, 1992. 42. “Electroacoustics Laboratory,” UW ECE News, Summer, 1992. 43. “The quiet sound of success,” UW-Madison, 1992 (good history). 44. “Steady Development in Fuel Economy,” The Hansen Report on Automotive Electronics, Sept., 1992. 45. “Pleeeeease hold down the NOISE,” Milw. Jrnl. Mag., Oct. 4, 1992. 46. “Automotive NVH Control,” Sound and Vibration, Oct., 1992. 47. “Noise, Begone!” UW Touchstone, Oct., 1992 (good summary). 48. “Marketplace: True Believers in Value of Noise,” New York Times, Oct. 16, 1992 (discusses optimistic projections for ANC). 49. “Sweet sounds of silence,” Wisconsin State Journal, Nov. 26, 1992, (article on Nelson and President Rockne Flowers). 50. Jonathan D. Silver, “Nelson Ind. nixes joint venture,” The Capital Times, Nov. 26, 1992. 51. “Nelson Ind...program w/AP terminated” Wisconsin State Journal, Nov. 26, 1992. 52. Thomas Bedell, “Noises Off,” Destination Discovery, Nov., 1992. 53. “Ahh! The sweet sound of Silence,” Wisconsin Engineer, Nov., 1992 (good overview of UW, RAG, LE and Nelson/Digisonix).

209

1993 1.

“The future of silence,” Sound & Communications, Jan., 1993 (a review of the state-of-the-art of ASVC).

2.

“Active Control of Low-Frequency Noise,” Sound and Vibration, Jan., 1993 (re literature on dX-57 controller).

3.

“Ford Motor Co, to lic. Digi. tech.” Noise/News Int., Mar., 1993.

4.

“Lotus uses car stereo to tune out noises,” Auto. News Insight, Mar. 1, 1993.

5.

L. J. Eriksson, “Active Sound and Vibration Control Using Adaptive Digital Signal Processing,” Proc. ICASSP 93, V. 1, 51-54, Minneapolis, (includes pulsation control on pulp delivery pump).

6.

Seth D. Goodman, “Electronic design considerations for active noise and vibration control systems,” Recent Advances in Act. Control of Sound and Vibration, 519-526, VPI, Apr. 28-30, 1993 (includes discussion of Digisonix dX-52 design).

7.

Seth D. Goodman and Kirk G. Burlage, “Active noise cancellation in ducts in the presence of higher order modes,” Proc. Recent Adv. in Act. Control of Sound and Vib., VPI, Apr. 28-30, 1993.

8.

Charles W. Brokish and R. A. Greiner, “Pole-position sensitivity of adaptive recursive filters,” Proc. Recent Advances in Active Control of Sound and Vibration, 790-801, VPI, Apr. 28-30, 1993.

9.

John Gregerson, “Reducing the frequency of HVAC noise,” Building Design & Construction, April, 1993 (re active silencing).

10. “Dyna-Quiet Dynamic Silencer” active-passive silencer for blowers, pumps, compressors (w/Universal Silencer), DX-SS-8/493. 11. Susan Dineen, Chris Depies, Mick Lowe, Steve Wise, “Evaluating the performance of active noise control...,” Noise-Con 93, 213-218, Williamsburg, VA. 12. Digisonix Press Release, May 3, 1993, “Universal Silencer & Digisonix will demonstrate Dyna-Quiet at Powder and Bulk Solids Show,“ May 4-6, 1993, Chicago.

210

13. D. Guicking, “Active Noise Control, A Review Based on Patent Specifications,” International Congress on Noise and Vibration Control, St. Petersburg, Russia, May 31-June 3, 1993. 14. “The Big(quiet) Apple,” Road and Track, June, 1993. 15. “Taking control of noise,” Occ. Hazards, July, 1993 (Sheb. photo). 16. Seth D. Goodman, Kirk G. Burlage, and Douglas G. Pedersen, “Active Control of Low-Frequency Fan Noise in Building Systems,” Inter-Noise 93, Leuven, Belgium (discusses full MIMO and mode decoupling for higher order modes). 17. “Sound technology as a muffler,” Motor Wise, Sept., 1993. 18. L. J. Eriksson, “Fully Adaptive Feedforward and Feedback Active Attenuation Systems,” SAE Active Noise Cancellation TOPTEC Workshop, Sept. 13-15, 1993, Boston, Massachusetts. 19. L. J. Eriksson, “Active Sound and Vibration Control Using Adaptive Digital Signal Processing” and “Active Engine Exhaust and Intake Silencing” presented at the Active Control of Excessive Sound and Vibration Seminar, Oct. 5-6, 1993, Univ. of Wis., Madison, Wis. 20. S. J. Elliott and P. A. Nelson, “Active Noise Control,” IEEE Signal Processing Magazine, pp. 12-35, Oct., 1993. 21. “Digisonix is awarded active noise patents,” Noise/News International, Dec., 1993. 22. “Digisonix, Inc.” in The Campus, Technology, and Wisconsin, UWMadison, Dec., 1993, p.18 (notes that Digisonix employs over 80 people at three Madison locations and has sales office in UK). 23. Brian Kerridge, “Lotus active suspension pushes the racing envelope,” EDN, pp. 50-53, Dec. 23, 1993 (good summary of active and partially active suspension systems including comments on Formula One racing).

211

1994 1.

“Lord NVX systems for ANVC,” product literature, March, 1994.

2.

Larry J. Eriksson, A Primer on the Digisonix Approach to Active Sound and Vibration Control published by Digisonix, Inc., in March, 1994. Edited version published in Sensors, Vol. 14 (2), Feb. 1997, pp. 18-31, and reprinted by Digisonix.

3.

“Active Noise Control,” ASME Mech. Eng., April, 1994 (good review of applications, Digi photo of fan).

4.

Digisonix press release on aero. tech. services & license agreement with Lord Corp., Apr. 12, 1994, (parallel Lord press release).

5.

“Digisonix deals with Lord Corp.,” Wis. St. J., Apr. 14, 1994.

6.

“VW’s in-cabin noise cancellation,” Auto. Industries, Apr., 1994.

7.

L. J. Eriksson and R. A. Greiner, “Active Sound and Vibration Control,” The Physics Club of Milw., Waukesha, April 12, 1994,

8.

L. J. Eriksson, M. C. Allie, D. E. Melton, S. R. Popovich, and T. A. Laak, “Fully Adaptive Generalized Recursive Control System for Active Acoustic Atten.,” Proc. ICASSP 94, V. 2253-2256, Adelaide.

9.

L. J. Eriksson, “Recent trends in the development of active sound and vibration control systems,” Noise-Con 94, 271-278, Ft. Laud.

10. Charles W. Brokish, “Causality constraints of adaptive-active control algorithms,” Noise-Con 94, Ft. Lauderdale. 11. “Digisonix leads in active silencing systems,” Noise & Vibration Worldwide (w/photo), June,1994. 12. Howard K. Pelton, Steve Wise, and William S. Sims, “Active HVAC noise control systems provide acoustical comfort,” Sound and Vibration, July, 1994. 13. “Applying adaptive control systems for active mounts,” J. V. Warner, Inter-Noise 94, 1265-1270, Yokohama. 14. K. F. Delfosse, M. C. Allie, and S. R. Popovich, “A method of improving stability in an ANC system via an adaptive spectral constraint,” Inter-Noise 94,1187-1190, Yokohama. 15. “Air travel enters the quiet zone,” Design News, Sept. 12, 1994 (good review of Lord NVX systems, mentions Digisonix).

212

16. L. J. Eriksson, M. C. Allie, and R. A. Greiner, “A Case Study in University-Industry Cooperation on ASVC Research,” J. Acoust. Soc. Am. 95 (5), part 2, 2988 (A) (1994). 17. “Sound and vibration control,” UW Coll. of Eng. Annual Report, (discusses Barry Van Veen’s work with Digisonix, includes photo w/ dX-50I controller), 1994. 18. Active Sound & Vibration Control News, Vol. 1, no. 1, Sept., 1994 (lead story on Digisonix). 19. ASVC is “really a collection of technologies,” Lane Miller, quoted in “Air Travel Enters the Quiet Zone,” Lawrence D. Maloney, Design News, Sept. 12, 1994. 20. “New Lotus LS400 skips razzle dazzle,” Automotive News, Oct. 17, 1994 (includes comment that active muffler is “gimmicky”). 21. Electrical.Engineering Times, Oct. 31, 1994 (DSP chips; 1982: $150, 50k trans.; 1994: $15, 500k trans.; 2002(proj): $1.50, 5M trans (+faster, +more memory). 22. “Easier sound and vibration control,” Noise and Vibration Worldwide, re Digiware, Nov., 1994. 23. “Japan’s quiet revolution,” Automotive Industries, part 1 (Nov., 1994), part 2 (Dec., 1994) (on ANC in Japan including Nissan Bluebird ANC system developed with Lotus). 24. “Sound of silence,” Financial Times, Dec. 6, 1994. 25. “Active noise control on the brink,” Noise & Vibration Worldwide, Dec., 1994, (good review of field, mentions users “challenged in the courts by...Chaplin Holdings...sufficient grey area to allow Chaplin Holdings to bring costly litigation..,” discusses FIR and IIR filters). 26. “Active noise cancellation systems face technology, market challenges,” Noise Regulation Report, Dec. 12, 1994 (claims that ASVC technology “more difficult than expected,” mentions “Digisonix, a pioneer of ANC”). 27. Geoff Nairn, “Sound of silence,” Financial Times, Dec. 6, 1994 (on turboprops, includes comments by Steve Dickmann).

213

1995 1.

Note on DigiWare exhibit at 13th IMAC, Sound and Vib., Jan., 1995.

2.

“Appl. Dev. System,” DigiWare lit., Sound and Vib., Jan., 1995.

3.

“The profit. sounds of silence,” Midwest Exp. Mag., Jan./Feb., 1995.

4.

“Turn on...” Digisonix ad on Digiduct”, Jan., 1995.

5.

S. Wise and S. Dineen, “Application experience of ANC of air moving devices,” Int. J. Active Control, v.1,(1), 1-14 (1995).

6.

DigiWare Application Development System, brochure, 1995.

7.

“Tech. is the raw material,” DigiWare pamphlet, 1995.

8.

DigiWare “Tools for Educ. & Res.,” ca.’95/96 (lists users: Bernhard (Purdue), Elliott (ISVR), Craig (Renssaleur), Singh (OSU).

9.

DigiWare Work Station Version 2.02 tech specs.

10. DigiWare 1995 application notes: Active vibration control, AN9505-01; Active interior silencing, AN9505-02rev.A; Active cab interiors, AN9505-03revA. 11. L. J. Eriksson, “The Future of Active Sound and Vibration Control,” meeting of Milw. Section of the IEEE, Mar. 23, 1995, Milwaukee. 12. L. J. Eriksson, “Active Sound Control,” at the Visiting Lecture Series at MSOE, March 31, 1995, Milwaukee, WI. 13. L. J. Eriksson, “Silencers: The Impact of Active Control,” J. Acoust. Soc. Am. 97 (5), part 2, 3267 (A) (1995). 14. “Madison’s gifts...,” Mad. Mag., Apr., 1995, (note on Digisonix). 15. Gérard Mangiante, “An Introduction to Active Noise Control,” Int. Journal of Active Control, Vol. 1, No. 4, pp. 303-330, 1995. 16. C. D. Bremigan, M. H. Hoppe, C. R. Cheng, and S. T. Riggs, “New opportunities for vehicle NVH refinement using active control,” SAE paper 951323, Noise and Vibration Conference (P291), vol. 2, pp. 729-736, May 15-18, 1995 Traverse City, Michigan. (includes interior noise reduction for car with four-cylinder engine). 17. The technology of quiet: Dyna-Quiet system, DX-SS-13/795. 18. “Digiduct silencers achieve NC-35,” DX-CH-11/795. 19. C. D. Bremigan, L. J. Eriksson, R. J. Eppli, and E. S. Stroup, “Future of ASVC in Vehicles,” Active 95, 791-802, Newport Beach. 214

20. “Stentor Autophone,” from The Horseless Age, July 8, 1914 (reprinted in Automotive Industries, July, 1995). 21. “Get to know...” Lord/Stevens Aviation ad on NVX, July, 1995. 22. Michael Zuroski, Thomas Roe, Dana Lonn, “Multi-ch. active control of blade noise on a rotary lawn.,” Act. 95, 697-706, Newport Beach. 23. “Sound off,” Eau Claire Leader-Telegram, Aug. 13, 1995 (example of fan noise quieting, 20 dB reduct., $20k, happy neighbor). 24. L. J. Eriksson, “SETC 2000: A Vision for the Future,” Small Engine Tech. Conf. and Exposition, Sept. 14, 1995, Milwaukee, Wisconsin. 25. Lane R. Miller, “Active control of noise in aircraft,” presentation at short course Implementing Active Control, Oct. 3-4, 1995. 26. “Music to fliers’ ringing ears,” Business Week, Oct. 10, 1995. 27. Michael P. Nowak and Barry D. Van Veen, “An active noise controller based on a constrained transform domain adaptive IIR filter,” Conf. Record of 29th Asilomar Conf. on Signals, Systems, and Computers, Oct. 30- Nov. 1, 1995, Pacific Grove, California. 28. “Digi. brings ASC to the HVAC industry,” ASHRAE J., Dec., 1995. 29. Lord NVX system featured on CNN Headline News, Dec., 1995. 30. “Digisonix ASVC Systems” ad. Wis. Engineering Journal, 1995.

1996 1.

“Active noise control silences aircraft cabins,” T.I. DSP Solutions, vol. 1, no. 1, 1996 (Digisonix and Lord NVX).

2.

Sen M. Kuo and Dennis R. Morgan, Active Noise Control Systems, Wiley, New York, 1996.

3.

flyer on ANVC in vehicles with enhanced comm., Digisonix, 1996.

4.

Digital Voice Enhancement literature, Digisonix, 1996.

5.

L. J. Eriksson, “ASVC: A Technology in Transition,” Noise Control Eng. J. 44 (1), Jan.-Feb., 1996, pp. 1-9.

6.

“Digisonix Digiduct active duct silencer attenuates low frequency “rumble”– noisy basement becomes usable space,” DX-CH-9/496.

7.

“FINCANTIERI first with ANC,” release, April 24, 1996 (joint program w/ABB Fläkt Marine AB; Digisonix ANC system installed on HVAC system on cruise liner; first ANC installation on ship). 215

8.

“DigiWare catalog and pricing guide,” Digisonix, May, 1996.

9.

“First-ever noise cancellation system on FINCANTIERI cruiseship,” MER, June, 1996.

10. Jiri Tichy, “Applications for Active Control of Sound and Vibration,” Noise/News International, June, 1996, pp. 73-86. 11. Texas Instruments TMS320 Third Party Support, 1996 (DigiWare Application Development System for ASVC). 12. Sen M. Kuo, Issa Panahi, Kai M. Chung, Tom Horner, Mark Nadeski, and Jason Chyan, Design of Active Noise Control Systems With the TMS320 Family, Digital Signal Processing Products— Semiconductor Group, SPRA042, June, 1996. 13. “NVX active systems expand into Europe,” release June 6, 1996 (discusses King Air, other turboprop, and Cessna Citation X). 14. “Active control of low frequency noise from HVAC equipment,” seminar 31 at ASHRAE mtg., June 22-26, 1996, San Antonio. 15. “Noise control products and services at Inter-Noise 96,” Noise & Vibration Worldwide, July, 1996. 16. T. A. Laak and S. R. Popovich, “Linear Filter Theory and Causality Constraints for Active Silencing in Ducts,” Inter-Noise 96, 1029-1034, Liverpool. 17. H. G. Leventhall, S. Dineen, J. Walker, and S. Wise, “Active Noise Attenuation as a Route to Quiet Duct Systems without using Fibrous Materials,” Inter-Noise 96, 1091-1096, Liverpool, UK. 18. Lord NVX systems for DC-9/MD-80 aircraft, Aug., 1996. 19. D. Guicking, “Active control of sound and vibration–an overview of the patent literature,” Proceedings of ISMA21, 1996 International Conference on Noise and Vibration Engineering, Sept. 18-20, 1996. 20. “DigiWare for ASVC,” Matlab News & Notes, Fall, 1996. 21. Implementing Active Control: A Workshop on Designing and Integrating ASVC Systems, hosted by Digisonix, Inc. with T.I., Munich, Germany, Nov. 12-13, 1996, presenters: Guy Billoud (Lord Corp), Larry Eriksson and Jay Warner(Digisonix). 22. Martin Campbell-Kelly and William Aspray, Computer...a history of the information machine, Basic Books, 1996 (p. 132 - resistance to computers; pp. 216-219 - “computer utility” and quote from Paul Baran (1967); p. 300 - Internet is “more hype than reality”). 216

1997 1.

L. J. Eriksson, “How Technology Evolves: The Role of Complexity and Asymmetry in Technological. Development and Adaptive Systems,” Complexity 2 (3), J/F, 1997, pp. 23-30.

2.

“New product winners team up for sound solution,” Wisconsin Engineer, 1997 (silencing vacuum pump exhaust., operating now for 2 years, 27 dB reduction on tone).

3.

“NVX systems for King Air, Conquest, Turbo-Commander aircraft, info. sheet Lord Corporation, Mar., 1997.

4.

“Active control for DC-9/MD-80 w/Lord NVX systems,” on ABC’s World News Tonight with Peter Jennings, April 22, 1997 (featured Lord NVX system and Digisonix installation on fan).

5.

“NVX active system cert. on DC-9 series,” NVX active systems news release, Lord Corporation, May, 1997, Spring, 1997.

6.

“Whither active noise control?” editorial, Noise & Vibration Worldwide, June, 97, (mentions that “ANC...developed, but not quite as rapidly as anticipated...some..tried too hard, too soon...Cost...has dropped enormously...if potential users all hold back...it will take much longer to happen!”).

7.

L. J. Eriksson and M. T. Zuroski, “From Passive to Active: A Family of Silencing Possibilities,” Noise-Con 97, 325-336, Penn. State U.

8.

“Dyna-Quiet active noise control systems,” Universal Silencer Product Bulletin No. 251, USD-251-6/97.

9.

“Digiduct active silencers for fan powered mixing boxes,” Digisonix, DX-SS-19/897 (features dX-510 controller).

10. “Digiduct active duct silencer,” Digisonix, DX-SS-20/897 (includes detailed history of Digisonix and use in HVAC applications). 11. L. J. Eriksson, “The Fundamentals of Computer-Aided Silencing,” presented at the Tutorial Workshop of the 1997 Fall Technical Conf. of the I.C. Engine Division of the ASME, UW-Madison, Sept. 27Oct. 1, 1997 (review of Digisonix technology with references).

217

1998-2005 1.

“Real-Time embedded signal processing,” IEEE Signal Processing Magazine, Sept., 1998 (defines current challenges, some of which Digisonix met or nearly met years earlier).

2.

L. J. Eriksson, “A Brief Social History of ANC in Ducts,” J. Acoust. Soc. Am. 104 (3), part 2, 1807 (A) (1998) (see also “A Brief Social History of Active Noise Control,” Sound and Vib., 33 (7), July, 1999, pp. 14-17; response paper and my comments in Sound and Vib., 34 (8), August, 2000); on paradigm shifts, see also Tim Travers, The Killing Fields, Pen and Sword Military Classics, 2003, pp. 77-78, 89-90, and Thomas S. Kuhn, The Structure of Scientific Revolutions, 2nd ed., The University of Chicago Press, 1970).

3.

L. J. Eriksson, T. A. Laak, and M. C. Allie, “On-Line Secondary Path Modelling for FIR and IIR Adaptive Control in the Presence of Acoustic Feedback,” Active 99, 949-960, Fort Lauderdale, Florida (inspired by David H. Crawford and Robert W. Stewart, “Adaptive IIR filtered-v algorithms for active noise control,” J. Acoust. Soc. Am. 101 (4), 2097-2103, (1997)).

4.

Sen M. Kuo and Dennis R. Morgan, “Active Noise Control: A Tutorial Review,” Proc. IEEE, vol. 87, no. 6, June, 1999.

5.

S. M. Kuo and D. R. Morgan, “Review of DSP Algorithms for Active Noise Control,” 2000 IEEE International Conference on Control Applications, 243-248, Anchorage, (available through IEEE Xplore Digital Library).

6.

Guy Billoud, “Active control at Lord Corporation – A Reality,” Report LL-6508, Lord Corporation, 2001.

7.

“Active noise control – tortoise or dead parrot,” editorial, Noise & Vibration Worldwide, July, 2002.

8.

Larry J. Eriksson, Business Decisions, Quarter Section Press, 2002.

9.

“Sound engineering for new VW Minivan,” AEI, April, 2003.

10. Anthony W. Leigh, “The TMS32010. The DSP chip that changed the destiny of a semiconductor giant,” T.I. Houston Alumni Association, ca. 2005? (at http://www.tihaa.org/historian/TMS32010-12.pdf). 11. “2005 Honda Accord Hybrid,” IEEE Spectrum, March 2005.

218

2006-2010 1.

“Audi’s new magnetic semi-active suspension system,” Mike Hanlon, Gizmag on web, June 17, 2006.

2.

David Pogue, “Headphones to shut out the world,” The New York Times, June 14, 2007.

3.

“Noise canceling headphones,” Sennheiser, Logitech, Sony, Bose, AARP Magazine, Nov./Dec., 2007 (~$150-350).

4.

“Toyota employs noise-canceling tech on hybrid,” Darren Quick, Gizmag on web, July 15, 2008.

5.

Honda ad, The New York Times Magazine, 2009.

6.

“New Equinox Plenty Pleasing,” USA Today, Sept. 4, 2009.

7.

“Making tailpipe music,” aei-online.org, Oct., 2009 (discusses demonstration of spectrum shaping with ANC by Eberspächer; see also Digisonix U.S. patent 5,172,416).

8.

Chuck Squatriglia, “Tesla Engineers Killed In Crash ‘Worked On Something They Believed In,’ ” wired.com, Feb. 18, 2010 (on small plane crash that killed Brian Finn).

9.

“Magnetic Suspension–Magnetic Ride Control,” WhyHighEnd.com, 2010 (mentions Cadillac, Corvette, Ferrari, Audi).

10. Katherine Tweed, “Cheap Wi-Fi Thermostats Arrive at Home Depot,” greentechmedia.com, Dec. 7, 2010.

2011-present 1.

“2011 GMC Terrain,” Wis. St. J. - Autos, Aug. 7, 2011.

2.

“2011 Infiniti M-series,” Wis. St. J. - Autos, Oct. 23, 2011.

3.

“2011 GMC Terrain,” torquenews.com, Oct. 30, 2011.

4.

“Ford’s 2013 Fusion is a tech blockbuster,” aei-online.org (Auto. Eng.), Feb. 7, 2012.

5.

“2012 Acura ZDX,” Wis. St. J. - Autos, Mar. 4, 2012.

6.

“Honda Accord: the 9th gen.,” aei-online.org (Auto. Eng.), Oct. 2 , 2012.

7.

“Cadillac ELR,” Auto. Eng., Feb. 5, 2013. 219

8.

Dr, Zorba Paster, Wisconsin State Journal, July 14, 2013 (discusses finding that ICU patients who used noise reduction headphones tolerated the ICU better with less need for sedation).

9.

Ruth Ozeki, A Tale for the Time Being, Viking, 2013 (several mentions of “noise-canceling headphones” on pp. 225, 311).

10. Ucilia Wang, “The Battle Over the Smart Connected Thermostat Rages On,” gigaom.com, Aug. 2, 2013. 11. Tam Harbert, “The Law Machine,” IEEE Spectrum, (NA), Nov., 2013, p. 31-34, 53-54 (patent litigation). 12. “ENIAC Computer,” Steven Levy, Smithsonian, Nov., 2013. 13. “2014 Impala: Slick outside, big inside,” Auto. Eng., Nov. 5, 2013. 14. Kenneth Cunefare, “Active noise control: Eight decades of research and applications,” J. Acoust. Soc. Am. 134 (5, pt.2), 4188 (2013), presented at San Francisco ASA mtg., Dec. 2-6, 2013. 15. Ben Heaney, “The Electric Company,” Strings, Feb., 2014 (discusses the evolution of the electric violin). 16. Theodore S. Rappaport, Wonil Roh, and Kyungwhoon Cheun, “Mobile’s Millimeter-wave Makeover,” IEEE Spectrum, (NA), Sept., 2014, p. 35-38, 52-58 (discusses MIMO systems with antenna arrays for 5G cell phone networks). 17. “2015 Buick Enclave,” Wis. St. J. - Autos, Sept. 21, 2014. 18. “Artist Marina Abramovic’s body of work,” CBS News Sunday Morning, Nov. 30, 2014 (http://www.cbsnews.com/news/artistmarina-abramovics-body-of-work/). 19. Walter Isaacson, The Innovators, Simon and Schuster, 2014 (see p. 175 on patent application process). 20. “GM revamps its full-size SUVs for 2015,” Auto. Eng., Sept. 2, 2015.

220

Index Acousti Products 171 “Active” conferences 85, 125 Active Noise and Vibration Control (ANVT) 60, 92 active noise control advantages 19, 58, 166 business issues 139 Conover patent 17 cost issues 139, 166, 179 cultural resistance 144-147 Delphi Study 92, 117, 169 description 13 energy savings 142 error path model 35, 45-48, 107, 109 FAQ 58 feedback issues 17, 35, 37 flow turbulence 56, 134 hype 142 infrastructure 136 length issues 133 Lueg patent 14 modes 59, 108, 133 Olson patent 17 opportunities 19 patents 17, 50, 92, 103, 119 stories about 13 strategic issues 149 technical issues 133 threat to mufflers 19 active noise control applications ! active suspension 168 aerospace 115-116, 170 auto “boom” 74, 118, 169 automotive summary 167 business summary 165

electronic mufflers 72, 78-88 92, 103, 119, 167 enclosures 59, 170 HVAC silencers 56, 133, 166 industrial silencers 118, 128 intercoms 121 lawnmower noise 125 manufacturing machines 171 manufacturing processes 171 noise canceling headphones 103, 140, 165 pump pulsations 59, 74, 171 rumble 56, 62, 67, 137 tones 32, 38, 49, 55, 74, 137 active vibration control 99, 168 Australia 72, 88 University of Adelaide 88 Barry Controls unit of Applied Power 98 Cambridge Univ. 70, 72 Chalmers Univ. 70 computers array processors 29, 43 mainframes 25 Univac computer 25 microprocessors x, 26, 29, 41, 70, 142 mid-range computers x minicomputers x, 26 personal computers Apple 26, 56, 97, 154 Atari 26-28, 38-39 Commodore 26 IBM 25, 154 Macintosh 56, 154 Radio Shack 26 real-time systems 28, 39, 43 221

simulations 28, 34, 38 supercomputers 43, 139 superminicomputers x time sharing 7, 25, 26, 171 Cooper Tire and Rubber 170 Cummins 157-163 Digisonix and Nelson culture 154-155 budgets 51, 96 business opportunities 127 closure 161 cut backs 127-129 keys to success skill mix 24, 44 small team 51 timing 22, 42, 159 limits to success business issues 139 cultural issues 144-147 energy issues 142 noise issues 140-142 over-hyping 142 timing 159 patent issues 119, 143 strategic issues 149 technical issues 133 patents 50, 185 structure as business unit 60 as corporation 100 as division 62 “old” and “new” 93-95 Digisonix facilities Eriksson-Geddes Center 91, 95 European office 100 mobile offices 61, 64 Murphy Drive 82, 95 original building 61 Stewart Street 81, 95 test lab (and annex) 66 Nelson Technical Center 5, 12, 85, 94, 113, 118, 148

Digisonix installations aerospace 115-116 automotive exhaust muffler 72, 78-88 intake system 72, 81 interior noise 81 engine mounts 81, 99, 116 commercial HVAC fans basement office 67 cruise ship 124 Florida office 118, 167 Gusloff building 56, 67 broadcast studio 70 Digital Voice Enhancement 124 DigiWare 108 industrial fans and pumps centrifugal fans 68 incinerator fan 125 material handling fan 69 Sheboygan fans ii, ix, 54-56, 67, 138, 166 slurry pump 59, 74, 171 vacuum pump 69 Digisonix products Digisonix controllers dX-30, dX-35 40, 48-50, 54-55, 58, 62, 65, dX-40, dX-45, dX-47 49, 65, 149 ! ! dX-50I 148-149 ! ! dX-52, dX-57 97, 149, 162 dX-100 105, 149 dX-200 106, 149 dX-510 120, 125, 149, 162 Digiduct 81, 124, 128 Digital Voice Enhancement 121-124, 153, 167, 169 Stentor Autophone 123 DigiWare 65, 105-108, 113, 125, 127, 149, 153 Dyna-Quiet silencers 118, 128 loudspeakers 135 mini-Digiduct 124-125 222

probe tubes 56, 134 Digisonix organization Advanced Development Group (ADG) 81, 86, 93, 95, 182-183 Advanced Development and Engineering (ADE) 93, 95, 103, 182-183 Commercial Systems 118, 128 Technology Products 108, 128 Vehicle Systems 124, 128 digital signal processing 27 adaptive systems 38, 107 array processor 29, 43 broadband 19, 38, 56, 67 filtered-U algorithm 39 ! filtered-X algorithm 34 FIR filters 27 echo cancellation 121 IIR filters 37 LMS algorithm 33 MIMO systems 107, 109, 122, 133 RLMS algorithm 37, 111 system identification 36 digital signal processor chips Analog Devices 42 AT&T 42 Motorola 42 Texas Instruments 41 TMS32010 41-44, 48, 49 evaluation board 43 ! ! TMS32020 42, 49, 65, 70 ! ! TMS320C25,C26 65 ! ! TMS320C30, C31 43, 106 TMS320C40 106 Eberspächer 167 electric violins 146 Environmental Protection Agency (EPA) 141 Eriksson-Geddes Center 91, 95 Essex, University of 60 Finland 70

Fleetguard 158 Florida office building 118, 167 Ford program 79-95, 101, 113, 116-117, 127, 149, 153, 159 France 70, 72 Germany 72, 124, 126 ! Göttingen, Univ. of 14, 71, 92, 132 Harley-Davidson 2 Hawaii, Univ. of 34, 58, 70 Hitachi 60, 92 Holland America 124 Honeywell 2, 13, 25 ICASSP 34, 70, 75, 105, 108, 115 Intel 26, 42 Internet 47, 142, 154, 172 Inter-Noise 71, 75, 88, 113, 134 intrepreneurial 150 Japan 60, 72, 83 Kübler-Ross, Elisabeth 129 Lord Corp. 23, 34, 60, 115, 126, 150, 159, 170 Lotus Engineering 60, 86, 92, 168 Lueg patent 14 Minnesota, Univ. of 45, 75 Motorola 42 NCAC Hawaii meeting 71 NSF faculty/industry grants 6 Nelson Industries, Inc. acoustics research 95, 101, 127 ASVC Group 86 Bryant Building 1, 8, 9 Burgess 1, 196 Corporate Research 2, 3, 21, 86 96, 101, 127, 155, 162-164 Gusloff Building 5, 56, 67, 156

Professional Data Processing (PDP) 94 Research Advisory Council 8, 13 sale to Cummins 157-163 223

support of Digisonix 151 Technical Center 5, 12, 85, 94 113, 117, 148, 164 Universal Silencer 3, 118, 128, 162, 183 Nicolet Instrument 76 Nissan 60, 86, 92 Noise Cancellation Technologies 60, 86, 103 Noise-Con 62, 71, 82 Northwestern Univ. 25, 75 NVX systems 115, 126, 170 paradigm shift xi, 139, 144-147 Penn State University 34, 62 Purdue University 63, 71 Quiet Flight 170 Research Advisory Council 8, 13 Sheboygan test site ii, ix, 54-56, 67, 138, 166 Silentium 170 Southbank Polytechnic 72 Southampton, Univ. of 37, 70, 82, 88, 160 Super Bowl 65 Texas Instruments 41, 116, 126 TK Server 171 Topexpress 60 Ultra Electronics 170 United Kingdom 37, 60, 72, 118 Cambridge University 72 Chelsea College 18 Southbank Polytechnic 72 University of Essex 60 Southampton, Univ. of 37, 70, 82, 88, 160 UW-Madison ECE Dept. 21, 45, 162 Electroacoustics Lab. 51, 82 Wendt Library 24, 37 VPI 85, 97, 113 Volkswagen 124 Wisconsin Technology Development Fund 31, 51

concluding postscript...

Acknowledging history, Digisonix employees played softball for “Lueg’s Laurel”

224