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Interview of Richard Lyon by Robert Fricke on 2001 July 26, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/24720
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Topics include: his childhood and education in Evansville, Indiana, and college at Evansville College where he studied physics and electrical engineering; graduate school at MIT where he worked with Dick Bolt, Ted Heuter, and Uno Ingard while developing research for his PhD. in 1955; serving on the faculty at University of Minnesota for three years; his year in the UK doing research at Southampton and Manchester where the initial concepts of Statistical Energy Analysis were developed. In 1960, Lyon joined the staff at BBN in Cambridge, Mass. where he stayed until 1970. During that time, he continued development of Statistical Energy Analysis in collaboration with Ira Dyer, Preston Smith, Gideon Maidanik, and others. He also worked on areas related to transportation noise and aerodynamic noise. In 1970 he began his 25-year tenure of research and teaching in the Mechanical Engineering Dept. at MIT. During these years, he developed work related to machinery diagnostics, sound quality, and phase analysis. Also during this period he started his consulting company, RH Lyon Corp. In 1995, he retired from MIT and committed his full efforts to the company, which focused on product sound quality.
I’m Robert Fricke. Today is July 26, 2001. We’re at Dick Lyon’s house in Belmont, Massachusetts in the United States. It’s approximately 4:30 in the afternoon and I’m interviewing Richard H. Lyon for the Acoustical Society of America Technical Committee on Noise and Engineering Acoustics. All right. Let’s get started. The oral history recorded portion asks, Dick, that you provide some information on – for instance what is your present address?
60 Prentiss Lane, Belmont, Massachusetts 02478.
And what’s the best phone number to contact you?
My company office number is (617) 864-7260.
And who is that company?
RH Lyon Corp in Cambridge, Mass.
Your current employer you said was RH Lyon Corp. What is their present business?
The company is a services company that provides engineering services and product design related to sound and vibration, so companies will come to us with a product that has a noise or vibration problem and we’ll help them to test that product and then redesign it so that it’s more acceptable.
And what’s your present job title there?
Chairman and CEO.
And how long have you been with RH Lyon Corp.?
The company has existed since 1976 and was basically my personal consulting over most of that time. But since I retired from MIT in ‘95 it’s been more or less a full-time occupation.
The question is what do you do there. Do you care to amplify on any of the other things that you’ve already commented on?
Well, I still do a lot of the technical work and meet with clients and do experimental work and the calculations and so on, but of course I also run the company and work with the office manager, who is my wife, and our receptionist and the other technical staff of whom now there are three.
Excellent. Let’s move on to the specific ASA-related questions. Sort of three in a row here. What year did you join the ASA, what was your age and profession at that time, and what areas of acoustics were you interested in at that time?
I joined fairly shortly after I came to MIT as a graduate student, so that would have been about 1955 or 1956. And of course at that time I was very much interested in my projected thesis work, which was work on vibrations of thick plates and then my actual thesis was on turbulence and excitation of structures. So I had actually gotten involved in acoustics originally through high fidelity work that I did in college building amplifiers and sound systems for people. But when I came to MIT that was behind me.
And why did you join the ASA at that time?
I think simply to get the journal primarily and I knew I was going to prepare for a profession in acoustics. I was probably also influenced by the fact that my professor Uno Ingard was very active in the Society.
All right. And that leads to the next question. Presumably Uno and others perhaps encouraged you to join.
Yes, although I have a hard time remembering exactly now.
What ASA committees were you or are you a member of?
I’ve been a member of the engineering acoustics committee, the noise committee, I think I was briefly involved in the architectural acoustics committee. And then I served with the New Fellows Committee. I was involved in that, but I haven’t been involved in a lot of committees. I was also in the long-range planning committee for a couple years.
So maybe not all the committees but certainly more than a few.
What positions in the ASA have you held presently or in the past?
I was a member of council and then I was vice president and president. I think I was president ‘93-‘94 and vice president about three or four years before that.
All right. Here’s an open-ended question. Is there any particular ASA meeting or meetings that stand out as being something special, humorous or different?
I really have a hard time remembering individual meetings. I remember the meetings in Hawaii of course. And the first one was particularly interesting because the Japanese had a reception and the ASA president had a reception in adjacent rooms. And the ASA president had pretzels and potato chips and the usual and the Japanese had sushi and all kinds of wonderful things. And the president’s room, the ASA room emptied out pretty quickly.
All right. That’s fun. What year was that? Do you remember approximately?
I don’t remember. It must have been in the eighties.
Are there any ASA members that you met that had special influence on your future?
Dan Martin. Actually I met Dan Martin when I was a fourth year student at the University of Evansville. He came and gave a talk and at that time I was trying to decide whether or not to go to graduate school or take a job at that point. And I had a chance to talk to Dan, and he was so strong that I should go to graduate school that it really did have an influence on my choice to apply at MIT. So that would have been either the end of my junior year or the beginning of my senior year – because of course then I had to apply can get accepted.
Right. And how was it that he came to Evansville and you happened to meet him there?
Well, of course he was from Cincinnati, which is not very far from Evansville, and he had come to give a talk to the local IEEE student organization about – and I still remember his slides about how to generate organ tones with optical masks that they were using. So they had spinning disks with these optical masks and they would generate the tones.
So that was the hook that got you in. Very interesting.
Yeah. He was probably the first member of the Acoustical Society I ever met.
Is there anything you care to say particularly about the ASA, past, present or future?
Well, I think that the ASA has been an enormously important organization for me and I just can’t imagine that– Well, there is no other professional organization that I’ve had even remotely the contact and involvement with that I’ve had with the ASA. I’m a member of the ASME and SAE and others, but I just haven’t had near the involvement with any of them that I’ve had with the ASA. And I think it’s partly the size. You go to the meeting, you know people. It’s also this volunteer bent that it has. Getting volunteers to run the meetings is a far more effective way of having meetings than these other organizations with their large staffs, which are very impersonal. And you go to those other meetings and there is very little corridor conversation and very little socializing that I can see, and so I really feel that the ASA has been terrific for me.
I’d like to see the ASA be a little more oriented toward industry activities. I feel that it is a bit too academic and a lot of the subjects that are very important for industry tend to get put aside at the expense of other more academic subjects.
Yes, I think from an industrial perspective that is the perception of the ASA. You’ve mentioned other professional societies, ASME and so forth. The question is what others do you belong to? Are there others that stand out that you haven’t listed yet?
I’m a member of the AAAS, the Association for Advancement of Science. I am a member of the Sigma Xi, the ASME, SAE. I think that’s about it. I’m not a big joiner.
Okay. The National Academy of Engineering?
The National Academy of Engineering, which I guess is a Society.
In some sense.
Yes. In some sense.
You’ve been invited to join them.
The only organization I ever joined without knowing what the dues were.
All right, let’s move on. Early years and pre-college, past history. Give us a little history there. Where were you born?
Okay. I was born on the 24th of August in 1929 in Evansville, Indiana. Evansville, Indiana is a – I guess it would be proper to call it a provincial town. It’s the largest town within about 100 miles in any direction. South you have to get to Memphis, west you have to get to St. Louis, north to Indianapolis and east to Louisville, and in that area it is the largest town. So it is a small commercial center. It’s an industrial center, it’s a banking center for that area. And I lived there until I came to MIT as a graduate student. In fact I lived closer to college than I did to high school.
But you know you asked before entering college what are some of the places you lived, well that was it.
That was it. What made you choose to go to Evansville College?
Basically it was cost. It did happen, luckily, that I started college in 1947 when the veterans were just coming back. And some of the veterans who were coming back were excellent engineers who became also faculty members because they were looking for jobs. So we had some, two or three – even though it was a very small college. I think it had almost about a thousand students when I was there. We were very lucky that the electrical engineering and physics program – and they were very closely related to each other – had some really good people. And so I think in a way I was very lucky, but the main reason I went there was that I could live at home. And even though I had to pay tuition it was far cheaper than going to Purdue or Cincinnati schools that were considered the engineering schools in that area.
So it made sense in just your particular circumstances?
What were your parents’ occupations?
Well, my mother was a housekeeper. Now what do we say? Homemaker.
My father was an analytic chemist, but interestingly did not have a high school diploma. He had gone to work in a chemistry lab and taken some correspondence courses and taught himself analytic chemistry through this job and was I think very well respected. He worked for Serval Company, which made the absorption refrigerators. And of course that’s a chemically pretty intense product.
He was good. He had concepts of pH and oxidation and reduction and so forth that were quite different from textbook definitions.
But they were operational definitions.
Right. And they worked.
And they worked.
Right. And you got an early exposure to appliances through him, it sounds like.
Right. Although it was an extremely silent appliance. The only thing moving in it was a flame, and there were no fans.
That was your benchmark, to quiet appliances.
Right. They haven’t come back to that yet.
So how would you describe yourself in early years? What were some of the activities and so forth that you did?
I wasn’t particularly studious. I enjoyed you know most of the sort of normal sports that people did, you know, baseball and basketball. Of course in Indiana you played basketball even if you didn’t know how.
Roller skating, swimming, you know, just the normal stuff a kid does.
Good kid stuff. And what did you want to be when you grew up?
Oh. It depended on which week you asked me. I wanted to be a journalist, I wanted to be a foreign correspondent, I wanted to be a writer, I wanted – I didn’t really, I don’t think that I ever at least in high school considered myself to be a scientist or an engineer. But I did buy one of these kits that you can build radios with, the electronic things.
Sure. Those with the little spring clips on them. Yeah, yeah, sure.
Yeah, yeah. And it was absolutely fascinating to me that you could take a bunch of inert things and put something together and it would play music. I thought, “Boy, that’s pretty neat.” So I think that got me interested in radio first, and then radio got me interested through audio into acoustics.
Into acoustics. Interesting. Correspondence and journalism, literature, writing and things like that was something that was intriguing to you as well.
Yeah. But I think more of the image of the activity rather than any particular skill and writing or whatever.
All right. We’ve talked a little bit about some hobbies. Any other special interests? It asked about heros. Who did you look up to in those young days?
If I can remember. I think just the normal things that kids looked up to – aviators and ball players and stuff like that.
Right. What subjects, events, activities did you enjoy most in high school getting up into the high school years?
Well, one subject I remember particularly was of course a subject I took in aeronautics. It was taught by, again, a returning veteran, because this would have been around ‘46-‘47.
Even in high school, aeronautics?
Yeah, well, you know, they had a physics course and if you passed physics then you could take this aeronautics course as kind of an extended physics. And of course I’m sure it was in his course because he was interested in that, but that I still remember lift = coefficient of lift × ½ rho [?] V2 times area. And the idea that you could actually calculate something like that. And of course everything was in that coefficient of lift, you know.
Right, right. All the magic happened there.
But that was in a book. You know, you didn’t have to know anything. You’d just look up the number in a book. And the drag was the same way and I thought, “Boy, that was really interesting.” And then the other thing that was very interesting about that course was what he taught about in meteorology. And often I will remember the one phrase that he would say, and even today I’ll think about it. And it was, “Wind doesn’t blow on an airplane.”
Wind doesn’t blow on an airplane?
Yeah. You know, you are in the air mass actually moving with it. I think nothing could make it blow on you. You’re getting everything.
Do you remember his name?
I think Reardon but I’m not sure. I think Reardon.
Reardon. It’s neat that those fellows came back from the war and were able to share a lot of their learning and practical experience and so forth.
Well that actually leads into the next question, asking about special people that were influential to you in that time frame. Anybody else stand out?
Before college, yes. Well, I stayed out a year and a half between high school and college, and during that period I took some evening courses at the college. And one of the courses I took was chemistry, and my chemistry lab partner was a fellow who had come back from the war who had a degree in history and he thought he would become an engineer so he was taking these courses. And of course he was substantially older than I was. But he was very interested in audio, in sound reproduction. He knew nothing technically, but he was very interested in music and had lots of records and so forth. In fact he and I are the ones that started building these sound systems together. And you know he would say, “Well, we ought to have such-and-such” and I would build it. Because by that time I was doing some radio repairing, and so I had the equipment, you know, the volt meters and soldering irons and–
All that stuff.
Audio oscillators and whatnot.
In some sense he got you along the path towards the next step getting towards acoustics.
Yeah, yeah, that’s right. Yeah, my interest in acoustics pretty much developed during that period because first of all, I was doing radio servicing. Then I decided radio frequency circuits were too erratic and too hard to understand, but the audio of part of the radio was pretty straightforward so I was going to do that. That seemed okay. And then I discovered – and I could do things with feedback and change the output impedance of the amplifier and all kinds of things with current feedback and voltage feedback and it was, you know, you could do all kinds of nice stuff. And during that period I read something. I don’t know whether it was Jordan Baruck or Leo Beranek, but it said something about if you reduce the output impedance of the amplifier too much the speaker will lose its low frequency response. And I was really intrigued by that and I couldn’t see why that was. I thought low output impedance out to be good for everything.
Later on I did understand why that was true. It got me interested in the interaction between the amplifier of the speaker and what came out of the speaker. And I realized that once I connected the wires to the speaker it was all a big mystery beyond that point. So you know my world was between the end of the RF section and the beginning of the speaker.
So, but that’s actually what got me interested in acoustics and the dynamics of loudspeakers and that kind of stuff.
Right. The speaker becomes part of the circuit and that’s all a unit. That’s very interesting. That’s neat. Now let’s see. All right, moving on into college itself. Oh now let’s see, this fellow you were just talking about was in this year and a half before college.
Yeah, that’s right.
So you were working days and going to school at night?
Yeah, yeah. Working days and also working with him and doing my radio servicing and all that kind of stuff.
All right. So you went to Evansville College. What was your major there?
Right. I was a physics major. By that time I had decided that I was going to be technical. And I liked the idea of physics being sort of a very general and broad approach to science. I didn’t at that time have any distinct understanding of the difference between engineering and physics. And as I said, at the school there was a very close linkage between double-e and physics and I had taken a lot of double-e classes as well as physics classes when I was in college. But Evansville College, is now called the University of Evansville changed its name twenty years ago or so.
Let’s see. We’ve talked a little bit about why you chose that college and–
Yeah. Well, it was pretty simple. It was close and it was cheap.
Right. Let’s see. As an undergraduate did you ever change your college or major?
Physics from the beginning?
Physics only. Yeah.
Right to the end. Your year and a half off had given you time to think about that and you knew what track you were on when you started.
Right, right. And I had taken – and during that period I took math courses and a chemistry course. And I think that may have been it. I might have taken an English course or so, but I was– I should explain something. When I graduated from high school I was in the bottom third of my class. And one of the reasons that I had trouble in high school was that if I understood something I didn’t see why I should do homework. [laughs] And they tended to think homework was pretty important.
I understand exactly that situation.
So the point was that I probably couldn’t have gotten into many other schools also, and it turns out the college didn’t care really. But when I started these courses in college–the math and the chemistry and so on, I was getting all A’s. And I said, “Huh. This isn’t so bad. I’ll just keep doing it.”
Right. That’s good. So it was interesting and you got connected with it.
Yeah, yeah, yeah.
As an undergraduate did you belong to special clubs, participate in any school activities?
Not very much. I think I did belong to clubs, but I didn’t join any fraternities and a lot of the time I was in college I was working part time and there was no time for it.
Let’s see. Well, you’ve answered this a little bit, “Tell us about your undergraduate college days.” More particularly, were there any special people – professor, somebody – that were an influence on you in college?
I think the one person who stands out was Bob Artman, who was the professor of physics who I admire greatly, and he had a strong influence. The double-e professor, Jim he was very good and I learned a lot from him but we didn’t get along very well. And so in a way he influenced me, but not in the positive way Artman did.
He influenced you to stay in physics.
The next question relates to who was an inspirational model. It sounds like Artman may have been one in some sense.
Yeah. Bob Artman was certainly one, and I think that the person that I got to know about at that stage, Leo Beranek, also he was an influence even at that point. Because, an anecdote, we were building these feedback amplifiers for audio systems and I was in about the 2nd year and this continued on through part of the college years – and this fellow who was the historian found this article by Beranek on loudspeaker design and gave it to me and we were reading that, and this word called poles came up. Now what the hell did poles have to do with amplifiers. But there is a reference, and the reference was to Bode’s book on feedback amplifier design. And we thought, “Well, if we get that book then we’ll understand what these poles are.” [laughs] You know, what they have to do with feedback amplifiers. So he bought the book, [laughs], and of course he was mystified by it and he said, “Here, you can have it,” and I looked at it and I was almost as nonplused as he was by the whole thing. But do you know that in the last fifteen or twenty years I have been very much involved in phase characteristics of transfer functions and so forth, and I’ve gone back to Bode’s book many times during that period. So, you know, things come around and go around.
That’s right. When there’s a goldmine you go back to it again and again.
Yeah. But Beranek name and his writing came up during that period, which was kind of interesting. That would have been in 1949 or ‘50.
And it was roughly in that time frame that Dan Martin came around as well.
So that’s pretty interesting. The questionnaire asks about participation in rallies or protests or causes. What was going on in ‘49-‘50?
[laughs] Well, we had a little local protest. Somebody on the – one of the prominent people in town was involved in firing somebody from the school board, and all of us for some reason or other decided this was a terrible to have done and we marched.
And unjust event.
Yeah, and so for Evansville that was pretty wild. But the big thing of course that happened toward the end of my college career was the whole McCarthy period. And in fact I went to a talk given by McCarthy at the local coliseum during that period. And I must say he was a galvanizing speaker and people were on their feet.
A real charismatic fellow?
Let’s see. Would you have gone back to the same college looking back, take the same major and so on?
Well, I don’t feel that there was– In many ways there is a great advantage in being at a small place, and we’ll get into the MIT period later, but I didn’t feel terribly badly prepared to go into MIT, and maybe in some ways it was beneficial because if I had gone to Purdue or to Cincinnati which were then the logical alternatives, and if I had known more about the possibilities for financial support and things like that. Although the financial support did not exist then the way it does now, if I had known more about that I might have considered going there, and then I might very well have stayed for graduate work. But going to Evansville I really had no choice. If I was going to go beyond it I had to go somewhere else. And so I think the answer is probably not, but in a way it was kind of lucky that it turned out the way it did.
Funny circuitous path of life.
All right. So let’s move on and talk about graduate work. Did you go on to graduate training immediately? Was there a gap? What happened next?
No, I went – I graduated from Evansville in June of 1952 and in July of 1952 I was at MIT.
So Dick Bolt had given me an assistantship before I got there, and so I went there and that summer I was an RA in the physics department. How that happened was kind of interesting. T. K. Sherwood was the dean of engineering at MIT at that time. He is a physical chemist, and he was a consultant to Servel. And the summer between my junior and senior years I had worked with Servel in the research lab as a sort of a gofer and met him and somehow my interest in acoustics – and by that point you know I had had this discussion about graduate school with Dan Martin, and so I was thinking about graduate school and I knew that MIT was one of the schools – somehow I knew that – one of the schools that had graduate work in acoustics. And so Tom Sherwood said well he would talk to Dick Bolt and see if I could – if he had an assistantship available. And the word came back from Dick Bolt that if I were admitted to MIT he would give me an assistantship. So MIT is the only school I applied to from Evansville College [laughs]. And of course I was the only one who had ever applied to MIT from Evansville College, and I suppose if anybody else had ever applied and had not been successful I wouldn’t have had a chance to get in.
But I was willing to take a chance.
Yeah, I had good grades, but what did they know what grades meant to Evansville College?
Right. Interesting. But it was a nice connection there, just happenstance that there was a connection through your father’s company.
Interesting. So we talked about the school, your choice of school. I guess that the fact that you chose physics there at MIT was by virtue of the fact that somebody was willing to support you there.
Yes. And of course I had the physics degree, so it was logical to continue in physics.
And when you got there it asks: What are specific projects that you worked on?
Yeah. Well, first of all of course as a physics major in general you do not get a master’s degree unless you are unsuccessful in passing your qualifying exams.
Was that true in this case?
So you went directly into the Ph.D. program.
Everybody in effect does. So even though the physics and the engineering departments work under the same rules they actually operate differently.
You said you had an assistantship that summer to begin. Was that actually an academic piece of work or was he doing course teaching?
No, no. It was a research assistantship, so – and the person that I first started working with was Ted Hueter. And I worked with Ted for– Well, I was a graduate student for three years, and the first year or maybe a little beyond that I was working with Ted Hueter and I did a project on vibrations of thick plates – which actually ended up as a paper and I met with Phil Morse and so maybe after a year and a half or two years I met with Phil Morse and he said, “Well,” he says, “if that’s your thesis you should just apply for a degree.” But I hadn’t learned anything yet. So about that time also I had started working with Uno Ingard on this problem of turbulence and Uno had this very simple experiment. He had this plate and he had this air hose and he was blowing the air, this turbulent air plate and it was vibrating and making noises. Says, you know, “Why is it doing that?”
So I took that problem and my structure was basically just a string or a strip of metal and the flow was axially flowing along with the strip, and so the response of the ribbon strip depending on turbulence level and decay rate of the turbulence as it moved and so forth was the thesis.
Was the jet impinging on the edge or just on one side of the ribbon?
It was actually flowing along the length of the ribbon.
Along the length of the ribbon.
Yeah. I still have the rig.
Yeah, yeah. They were a simple little thing.
And just running on compressed air?
Did you do vibration measurements?
I did vibration measurements, I had an optical device which we’d look at the, would reflect light off the ribbon and the light was half occluded and reflecting and so that the ribbon vibrated up and down and the amount of light that came out would vary and so I measured the vibration.
And what was your recording medium? Was it photographic or how did you record the information?
I think at that time I simply put the output – well, I had a photoelectric detector of course, and it gave me an electrical signal, and then I don’t remember whether I recorded it or simply just measured the RMS vibration amplitude.
So either a meter or–?
I think it was probably just an AC true RMS voltmeter. I still remember Ballantine at that time made the only true RMS voltmeter.
Let’s see, so that sounded like that was a major focus of your whole effort there while you were getting a Ph.D.
We talked about your doctoral thesis then. So who at the school was the greatest influence on your future at that point?
Well, I think that clearly Uno Ingard, who was my thesis advisor, had a great deal of influence, but so did Ted Hueter, who had been my sort of pre-thesis advisor. And the two people were very different. I mean Ted is really very focused on the application and Uno was far more focused on the science. And I think between the two of them I got a good background. Ted was very disappointed when I decided to work with Uno, not to follow the project he had, but I felt that his project had a great deal of nitty gritty in it and just burdened with detail and I didn’t want to get bogged down.
So the theoretical simplicity in his project.
The cleanness of it, yeah, and it was very clear to me what you were trying to do and how you were going to do it and I thought that was a better way to go.
You know, I’ve been on many research projects. You always somehow see the end of it before you start.
It’s a self-fulfilling prophecy in some sense. Let’s see. While you were a student did you ever conduct any classes for the college or at MIT? Were you a TA in any classes?
I was never a TA, but in fact I did teach the course in waves and vibrations. That was the fourth year course based on Morse’s book at MIT for undergraduates.
For undergraduates, so this is not Morse and Feshbach. This is–
No, this is Morse’s Vibration and Sound.
I know the book. It’s on my bookshelf.
Yeah, right. And Uno had been teaching it, but for some reason he couldn’t teach at that term and asked me if I would teach it, so I did. And it was worthwhile.
Let’s see, these questions go on to military.
You can pass that quickly.
All right. So no military service.
I was in the Naval Reserve for a while.
Was that during MIT or after MIT?
It was at a very crucial time. It was right before the Korean War that I was staying this year and a half between high school and college, and I joined the Naval Reserve and that kept me out of the draft. And then I started college and the unit I was in was called up to go to Korea, but I had been out of the unit long enough, just long enough not to get called, so I sidestepped that. I mean I didn’t do it intentionally, but it just happened.
Life is full of that.
Technical and business schools. Did you ever take any business classes at Evansville?
No. No, I never did. But I did take a correspondence course.
Yeah, you mentioned that.
That’s how I got started in radio servicing, from the DeVry Institute in Chicago.
Oh really? Now let’s see. Past professional career. After college what was your first place of employment? What did you do?
I spent a year at MIT on the research staff kind of finishing up some of my thesis work.
After you finished your Ph.D. you stayed on.
So that would have been from – I graduated in ‘55 and I stayed another year or so from ‘55 to ‘56, and just doing research in the same lab with the same desk I had when I was a graduate student.
Right. And presumably filing of papers and things like that?
I can’t specifically what I did, and I assume I just must have written some papers and continued some stuff on random vibration.
Right. And then after that?
My first real job, let’s put it that way, was teaching at the University of Minnesota. When I finished at MIT I was very anxious to get out of the Boston area and wanted to get back to the Midwest where life is real and so on. So I had met Bob Lambert, who was at that time assistant professor in the double-e department at Minnesota. And with my semi-double-e background he said, “Wouldn’t you like to come and teach at Minnesota?” and so I took that job and I went to Minnesota in the fall of ‘56. And I was at Minnesota for three years teaching double-e, and officially I was at Minnesota a fourth year because that was the year I had the NSF Fellowship to England.
So, but I only stayed at Minnesota three years. I learned a lot while I was there. I taught an undergraduate course in acoustics using Beranek’s book, I taught a graduate course in acoustics using notes that I developed, and I also taught some signal processing and random processes.
This is in the double-e department?
In the double-e department, yeah.
Just out of curiosity, with your signal processing and random processes and all, at that time the digital computer wasn’t what it is today.
How about doing Fourier transforms and in fact I guess that the FFT algorithm, was it Singleton’s algorithm, hadn’t been developed yet and so forth, so what were the kinds of things that were done in signal processing?
That was mostly filter design. If you have a signal in noise how do you design a filter. And a lot of it of course came out of the Rad Lab series of books.
Right. So optimal estimation theory and things like that, detection theory.
Also VanTrees kinds of analysis?
That’s exactly it, yeah.
Good. Because that, ultimately it’s all math in the end, a very simple equation, you can turn that into op amps or in those days transistors and whatnot, vacuum tubes I guess. Anyway, square low devices and integrators, things like that.
So how is it you got to England? You mentioned an NSF grant.
Yeah. I had an NSF postdoc fellowship. Minnesota I liked very much, and Minneapolis is a great town. There is all kinds of stuff going on. But if you want to go to Minneapolis, you go to Chicago and then you take a side trip from Chicago. In other words, no one goes through Minneapolis in the natural course of things, so I tended to feel a little bit like I was in an outpost. And the things that were happening in my field, the interesting things that were happening in my field were happening somewhere else and I couldn’t stand it. And so even though I liked the place and I liked the people very much and they did a lot for me – they were very good to me – I took that year in England just to think about what I wanted to do.
Just to feel like a place you could grow.
So what were you doing in England?
Yeah. I spent the summer at Southampton working with the people at the very new ISVR under Prof. Richards, met a lot of people – Shown Ffowes Williams, who was a graduate student at the time, Brian Clarkson, Dennis Mead, Peter Davies, all these people who are now either gone or gray eminences. And then I went – and that in fact was not part of the original plan, to go Southampton, but I went the summer early and they agreed to have me. And then I spent the rest of the year, the nine months, at Manchester intending to work with Lighthill on turbulence. Because of my thesis and other things, I was very interested in turbulence. And I got to Manchester and it turned out that Lighthill was on his way to become the scientific officer of Farnborough, the Royal Aircraft Establishment Research Center. But I was very interested in random processes and M. S. Bartlett of Stodiastic Processes fame was there, and so I ended up going over and working with his group. And it was during that period that I did the first calculations on couplings of resonators and the energy flow between randomly excited resonators.
I’ve seen that note. What year was it that you went to Southampton?
Wait, let me think, let me think. I’m sorry the summer of ‘59 I was at Southampton and then the fall of ‘59 and the spring of ‘60 I was at Manchester.
So you began your coupled resonators and were thinking about new career options and alternatives and so forth.
And where did that lead?
Well, while I was at Southampton Ira Dyer came by, and we were talking about, you know, what was happening at BBN and it was very, very appealing because all the people I had known in graduate school were at BBN. It would be like going back to graduate school again. And by that time I wasn’t feeling so negative about working in the east. So we came to terms and in the fall of 1960 then I started at BBN.
Had you known Ira before over at MIT?
Oh yeah, because he was finishing his doctoral work in the Acoustics Lab when I came, so we overlapped maybe a year.
So he happened to be visiting there in Southampton and you all struck up a conversation and it seemed like a good match?
At that time he was at BBN.
He was at BBN. Well, he went directly to BBN after he got his degree.
So you came back to the east coast, Boston area, started at BBN in 1960 you said.
And so what transpired thereafter?
Well, it was from ‘60 to ‘65 I suppose is a pretty rich period, because that was when I came to BBN, I had these ideas about energy flow between resonators and equipartition and so on, and Preston Smith had just done a study of the interaction between a resonator and a sound field. And I said, “You know, I’ll bet that”– And he had a calculation of what the response it achieved. And I said, “You know, I’ll bet that’s the average energy of the modes in the room.” And we calculated them and sure enough.
In fact, you know thinking back you know it would have been absolutely astonishing if it weren’t because you know thermodynamics would almost require it.
That’s 20/20 hindsight.
Yeah, right, right. And so then we began applying that to– It turns out that BBN at that time, had about four or five projects for which this idea just fit in beautifully, even in existing projects. And then it went very rapidly from there, and at one time I think I had five or six projects at BBN just on the general area of statistical energy analysis – or what became known as statistical energy analysis. It didn’t even have a – for several years it didn’t even had a name.
Just what we were doing.
You called it coupled resonators or something like that?
So that was in that five years in the early sixties.
And that was your primary focus then at that time.
The primary focus but work supported by NASA, Navy and Air Force a little bit.
You mentioned air acoustics and structural acoustics. Were these projects that you just mentioned looking at both of those, combined versions of those?
Yeah, some were. Some were and some were strictly vibration transmission. There was studies of the vibration transmission into electric equipment in reentry vehicles and–
Shaking of the chassis.
Yeah, right. Right. And others were the response of lift vehicles due to turbulent exhaust and noise from that. It just happened to be the right place at the right time with the right kind of support.
The right kind of people, it sounds like. So you worked with Preston Smith. Who else was in that cadre of people?
Don Ross, Ed Kerwin, Ira Dyre, Preston Smith, and Ewald Eichler was there, Gideon Maidanik.
So you had a critical mass of people that were all thinking about these kinds of things.
That’s right. And the support was present, and the nature of the support was such that you could actually do really basic work and you know it’s always one of the things that bothers about people who want to define basic versus applied because if the problems are there and you think basically about them, you know, you are going to do stuff that relates to solving those problems.
Right, right. So that’s neat. So it gave you an opportunity to develop theories, make application of those theories, see results, and the kind of problems that were coming along seemed like by chance or what have you, just the right kind of problems for what you are working on.
That’s neat. I’ll bet that was pretty exciting and maybe quite gratifying.
It was. Oh, and Manfred Heck was there for part of that time too.
Wow. What an all-star team.
We had a great, great group. And we would come to our desks in the morning and find the mimeographed notes of responses to the discussion that was yesterday at yesterday’s lunchtime.
And that’s great.
That’s really fun. So it sounded as though it’s quite a collegial environment, a lot of support between people and through the ferment of new ideas and so forth. That’s really neat. It’s not very common in lots of quote-unquote industrial and commercial settings.
It’s not. It’s not very common, I’d say, anywhere now.
Yeah. Because the nature of the support changed.
What was it like then versus now?
Well, the big killer was the Mansfield Amendment which occurred in the mid-sixties.
And what was that about?
Well, Mike Mansfield – from Montana, wasn’t he? – was chairman of the appropriations committee, I think. Anyway, he came up with an idea which seemed very logical. Namely, that the Navy should support research that relates to the mission of the Navy and the Army should support research– Well, given something like that, you are so – any bureaucrat who is doling out money is going to be very, very careful because it’s so easy to say, “What’s this energy flow between resonators? What the hell has that got to do with our submarine?” you know.
And the guy would have to defend it if it’s put that way. And it just really changed the nature of the research. In the early sixties we would get Commerce Business Daily and every week we would find two or three topics that were basic and interesting and things we could apply to. And after that it just dried up.
That’s very interesting. After the Amendment it was easier to sell a propeller design for submarines rather than, as you say, some more esoteric kinds of things.
Yeah. But you know topics that seemed esoteric.
Right, right. That nevertheless applied but weren’t but it wasn’t quite so easy to explain. So up to the mid-sixties there was this intense activity period developing SEA. When did the name SEA get attached to that?
Probably around ‘63 or ‘64. I don’t remember exactly. I do remember a conversation that Ira and I had in the hallway one day which he now claims he doesn’t remember but I remember, and he said to me, “You know, these things we’re doing really ought to have a name.” And I began thinking about it. Well, statistical because it’s a random model. Statistical is random models, models of the system, and energy, well that’s a primary variable; analysis, I didn’t want to call it a method because method implies a specific routine. Analysis implies a way to think about a problem, and that’s what I was – that’s the way I looked at. So that’s the way we came up with the name.
So SEA has grown lots of legs since then.
Oh yeah. I wish I’d patented it.
That’s right. I’m curious to hear your comments about where it has gone now over the last – let’s see, since ‘65 so now say thirty-five years.
Well, of course the big thing is that it’s now computerized. We had the idea that the great thing about SEA was that you could do it on the back off, on one sheet of paper. Well, the Japanese got hold of SEA and they started having models of entire ships and so forth with thousands of subsystems. Well, you can’t do that on a sheet of paper. You’ve got to have a computer. And then you know Jerry Manning developed SEAM and AUTOSEA came along and various other codes now which– But interestingly there really has been very little in terms of conceptual development.
New theoretical underpinnings.
It’s been making it easier to use and making it easier to visualize the models and so forth. Which of course is very valuable. But just this last year I did something for Jerry where we looked at a simple question, “How many interacting modes are there?” And it turned out that the old formula in my book is wrong, because if you have N1 modes of one system and N2 modes of the other system and you look at the parameters it’s possible that the number if interacting modes is greater than the product N1 times N2 – which of course is nonsense. [laughs]
Oh. If you look at your results. Based on the equation, right?
Yeah, but now we’ve developed a new equation which behaves properly.
That’s neat. So what happened ‘65? What happened after that?
Well, basically the work changed. BBN began to get more structured. I got involved in other areas such as transportation noise and helicopter blade radiation and less involved in the SEA – which of course was fine. I certainly didn’t mind changing my directions and I did it because I was interested in these other things. But it did mean that – and also I became a division director and vice president. And so a certain amount more of my time became business-oriented and that kind of stuff. And in the late sixties – well, actually by the mid-sixties around ‘64 or ‘65 I had given a talk at MIT. Steve Crandall had asked me to come over and give a talk on some of the random stuff we were doing. And so I did. And in conjunction with that, very shortly after that I was asked if I would be interested in coming on the faculty. But at that time my career at BBN was surging ahead and – also MIT really didn’t offer a full professorship and I felt well, you know. I wasn’t going to move for a non-tenured position.
So around ‘69 or so I had begun feeling like I was churning the same water and feeling less as though I were making a useful contribution to BBN.
So I called Steve Crandall up and I said, “Hey, is that offer still open?” Said, “Let’s talk.” And so it led to my joining MIT then in February of 1970.
All right. So that began I guess perhaps your second academic career. The first at the University of Minnesota for a period of time and then come back around.
And your second tenure at MIT.
So what was life like? What was on your plate at that time?
Well, I went to MIT because I thought it would be nice to be able to go to a place where I could have good academic involvement but at the same time have a certain amount of entrepreneurial freedom. And MIT offered that. So I went and got involved in the Acoustics and Vibration Lab with Steve Crandall and Pat Leehey and started having graduate students. Some of the early work, you know, I had some work at BBN on transportation noise and in fact had written a book on transportation noise and coming to MIT I wanted to follow up on that so I got involved in propagation of sound in city streets and scale modeling and effect of ground impedance and height of barriers on noise reduction. And by the way did you know that you can put a barrier between a source and receiver and have the sound go up?
Sound go up.
I know about the diffraction off the top of the barrier but I don’t know about the sound going up. How so?
When you have sound near grazing on the ground you get this Lloyd mirror effect which you will know about, right?
And so you get the direct and the reflected wave out of phase and you get a notch, but if you get a barrier you kill that.
Right. You don’t get the reflected.
Yeah. So it’s not hard to have that situation.
Right. Interesting. So you were doing scale models at MIT in the–?
Scale modeling at MIT, and so I was doing some teaching, running some workshops on scale modeling and you know a number of papers came out of that. And Richard Cann eventually developed a business around building scale modeling systems by Grozier. And then gradually at MIT I got more involved in machinery and the engines. We had some work for the – I think it was originally spurred by NSF – on diesel engine diagnostics, which kind of partly came out of some of the EPA work that Cambridge Collaborative was doing, and that led to the interest in machine diagnostics. And I suppose the first thing that we ever did in machine diagnostics was around 1970 or at least early seventies from when Afi Ordubadi as my graduate student came and she did some work on diagnostics.
And that was on diesel engines?
That was on diesel engines, yeah. We had a diesel engine down in one of the test cells in the basement of Building 3 and running it, probably unsafely.
So then the engine diagnostics, you’ve mentioned a couple of things that I’d like to maybe get a little more information on. You mentioned Cambridge Collaborative. You were also involved in Cambridge Collaborative in that early time, right?
Yes. When I left BBN Jerry Manning left fairly shortly afterward and he was interested in starting a company and we agreed that we would, if he left then that we would start Cambridge Collaborative together. And we did. And it had some offices near MIT for a fair number of years. It was originally designed as a – you know, it was going to be the next BBN, and so it was concentrating on some government contracting and things like that. There was a lot of work at Cambridge Collaborative early on on scale modeling. We modeled the Los Angeles Airport and some of the runways and surrounding community for penetration of noise.
And they were going to buy up house and tear them down and the question was how much–
How far to go, right.
Yeah, and how much would that increase the noise on the other properties because of the loss of shielding effects and so on. So we worked all that out with our scale model and it was a very, very interesting project. Gregg Tocci and Richard Cann worked on that with us.
All right. Well now you’ve hit on some other people. You mentioned Richard Cann before about scale modeling. How did he come into the picture?
Well, during that period Richard Cann had been working with Ewald Eichler when Eichler was in Cambridge and when Eichler left I knew that Richard had been working with him so I asked him to do some work with Cambridge Collaborative. And so he basically built this LA model that I was talking about and helped run the log of data. And then we had the bright idea that we would develop a scale modeling workshop at MIT and during one of the IAP periods. And so he – built a spark source and some of the instrumentation, which of course at that time was all analog.
Right. A sparker. Interesting. So that’s how you had your source excitation was with a sparker.
Yeah. That’s right. An impulse as a source has a lot of advantages. You can so-called electronically dry the air because the farther the spark travels, the more it’s attenuated by the air absorption, but if you can have a variable gain amplifier that it has triggered by the spark and then its gain increases with time so that it counteracts the effect of the absorption in the air.
And that was one of the things that was done and the instrumentation that we developed, and I assume it’s still in the instrumentation that Richard sells. I don’t think he sells Spark systems these days.
So your early days at MIT then, you had mentioned the entrepreneurial spirit which was permitted at MIT. You were taking advantage of that with your Cambridge Collaborative activities.
Developing classes, having graduate students. It sounds as though you had made a shift from SEA into transportation, then into it sounds like machine diagnostics and this air acoustics.
And then in the early days at MIT it sounded like a mix of air acoustics and machine diagnostics.
Yes. Certainly the air acoustics was early and then it trailed off into the machinery noise and diagnostics – and which is how I eventually ended up being concerned about product sounds and so on. So it was that kind of migration.
That’s the evolution. Right. So then through the seventies you did more and more machine diagnostics.
I know that you had a bit of work with Singer Sewing Machine. When was that?
Yes. That was in the seventies, and I got very much involved with them. It was probably in the late seventies. I don’t remember the exact dates. But in that project we got involved in machine balance and the motion of mechanisms and affecting imbalance and structural analysis, because they were interested in changing materials from aluminum to certain kinds of reinforced plastics–
Composites. And so it was a great interaction, because we just got involved in all kinds of aspects of the machine – including some of the early work in sound quality where we actually ran jury tests of people responding to sewing machine sounds. Because the vice president that we were working with at Singer said that people just like the sound of the Bernina sewing machine better than the Singer sewing machine, and he wanted to know why.
Right. What made that so.
What made it so. And so we were working both the subjective perceptual aspects through jury studies and in the design aspects to figure out how you could modify the sound radiation from the machine and how you could modify the noise generators. And that Singer project probably had as much effect on me as anything in terms of interest in product sound and in terms of sound quality.
It sounds like it laid the groundwork for an awful lot of your professional development and interest thereafter for a good many years.
That’s right, yeah. And gave a tremendous amount of teaching materials. I know when people used to take my course they thought – some of them were complaining that I had all these sewing machine examples. But I still maintain a sewing machine you get more interesting mechanisms per dollar than any other product you can buy.
That’s right. It’s a very complex piece of machinery. I’v e always been fascinated with it. The bobbin and the needle. And so you were at MIT up until ‘95 or so as a full-time professor.
During that period – that’s twenty-five years.
Twenty-five years, yeah. When I went to MIT I thought maybe I’d stay ten.
Two and a half times longer and two and a half times later you developed a lot of collegial relationships with people it sounds like at MIT as well as through the Acoustical Society.
Any people or events stand out during that time period? We’ve talked about the Singer for professional development, but what about other things?
It’s an enormous number, but I do have trouble picking out any one thing. Interestingly a lot of those earlier relationships continued. Dan Martin was someone that I worked with and got involved with over the years. Oh, and Bruce Lindsay. I was associate editor of the journal for a while and I got to know him a bit and I admired him tremendously. You know, he could sound a bit gruff, but he was a kind man and had this great, great personality. And Bob Beyer, who was again an erudite, gentle, really wonderful person. And the Acoustical Society really has been probably more of a source of my closer friendships than almost any other activity.
That’s neat. That’s quite a testament to the Society. Let’s see. Well after MIT, just in terms of professional career, you went full time with RH LYON Corp.
Give us a little bit of history of when that got started and then what happened after you left MIT.
Well, what happened was that I had started Cambridge Collaborative with Jerry Manning in 1970 and about five or six years later even though I was still involved with Cambridge Collaborative a lot of my personal consulting didn’t seem to fit very well because I would want to use a graduate student and if you are going to use a graduate student you had to hire him into the Cambridge Collaborative and so on. It just didn’t make sense. So I began doing a certain amount of separate consulting and it didn’t really impact Cambridge Collaborative at that time very much because their work was almost entirely government work. So there was a logical division. Of course that. over time that began to smear out. But it did mean that I gradually drifted farther away from Cambridge Collaborative even though I remained a board member and I would still have conferences with people there and so forth. But RH LYON Corp, first of all its originally didn’t have that name of course, but it almost immediately it specialized in product sound. And some, a few projects in diagnostics. We did some work for Bosch on diesel engine diagnostics. And we were doing that, first of all I was doing it by myself, then a friend of mine Gene Bachman worked with me and Richard Cann and for a while Bob Powell worked and some of my other graduate students. Eileen Bush Vishniak who of course is now dean at Johns Hopkins, and Rebecca Fleischman. And for a while there at the house here at 60 Prentiss Lane the RH LYON Corp. was doing business in the basement, and every day there would be about four cars parked in front of the house. So by the late eighties we thought well, you know, the neighbors are being very kind but they are not going to be kind forever.
So we moved into offices then on Concord Avenue right under, the floor underneath Cambridge Collaborative. It was about that time that then I completely severed my relationship to Cambridge Collaborative.
Just out of curiosity, you said that RH LYON Corp. started almost immediately as a sound quality focus. When did the Singer Sewing Machine come into play? Was that about the same as when RHLYON Corp started?
That was before.
It was before. So you had already been thinking along those lines.
I was doing– It was part of the work that– Well, the work that I did for Singer was private consulting, so I was acting as a consultant for them probably in the late seventies. And so that got me involved, but I was doing that pretty much on my own with a bit of help from Gene Bachman. And also Rebecca Fleischman actually ran the early jury studies that we did. So that was one of the first major clients of RHLYON Corp.
Even though it wasn’t RHYLON Corp at the time.
So then through the eighties you were at Prentiss Lane. When did you move to Concord Avenue?
I think it was around ‘89.
So through the eighties you were here at Prentiss Lane and then in ‘89 or so you moved there.
And it wasn’t too long after that that you retired from MIT.
Yeah. Well, in ‘95 I retired.
Yeah. We were in the offices for about–
Six years before I retired.
So, what’s happened since ‘95?
Well, I’ve continued to run RH LYON Corp. I have continued to do some book writing, teaching my summer course at MIT on – originally my summer course was called engineering acoustics, then it became – oh, for a while it was even called transportation noise. And that was machinery noise and diagnostics and in the last few years it’s been called designing for product sound quality. So it changes a little bit over time, and then as the emphasis changes the name changes.
Well that’s actually a good sequence. This whole next section is on publications. You mentioned your book. Earlier on you mentioned your transportation book. Give us some sense of your papers and book publications and so forth over the years.
Well, the books are easier to count. My first book was a very small little book, ninety pages, but it was actually a hardbound book put out by the Department of – what was it? It was part of DOD. The topic was random vibration, noise and vibration of space vehicles. That was done while I was at, basically that was done while I was at BBN.
And was that an SEA-oriented text?
SEA was mentioned in it, but it wasn’t. It was oriented towards first of all defining the environment through characteristics of turbulent boundary layers and reverberant sound fields that were important and exciting structure and how the structure responded. And of course the ideas of radiation, resistance, got into that.
And then comparing the SEA calculations to the– At that time there were two or three other ways of kind of estimating response, some of which were purely empirical, some of which were kind of semi-analytic. And so I compared those methods and then talked about the use of the I guess criteria with regard to fatigue and things like that. So it’s a fairly terse discussion of all those topics.
So that got you on the book writing path.
Right. I think the next book was the transportation noise, Lectures in Transportation Noise, which was based on material almost exclusively that I had gathered at BBN but I think actually got written after I left or at least while I – about the same time. And I still use the stuff in that book. I think it was published early seventies. I can’t tell you, say exactly when. And then in 1973 I spent two months in Berlin on an exchange program that MIT had working with the Acoustical Institute right before Manfred Heck went there. The Technical University of Berlin. And I wrote the first half of the Statistical Energy book while I was there. And then came back and then finished it and then it got published. The publication date was ‘75? That seems late. But in any case, that was the third book.
That was your first SEA book?
First SEA book, right.
Was that, at the time, the first book on the scene that really described that in any level of detail?
There were collections of papers presumably before that.
Yes. Yes. Although – and there were collections of papers after that also. It certainly was the first book that really tried to lay it out. And then the Machinery Noise and Diagnostics book came after that. That was based largely on my course, my summer course, and somewhere during that time period there was also another – which I guess would qualify as a book. It was by Richard Cann and myself and it was on acoustical scale modeling. It was written partially to explain acoustical scale modeling so that people who bought the Grozier system could use it and understand what they were doing. And then the Machinery Noise and Diagnostics also became an MIT video course, published as a video course, and in connection with that then there was another book that got printed which was basically a workbook for the course, but it was a substantial piece of work. And then there was the second edition of the statistical energy book that I did with Rich DeJong, and then the last book of course has been the designing for product sound quality.
And how did you get connected with Rich DeJong for that?
Well, Rich had been my student.
At MIT. And did a very nice thesis. One of my best students. And then he went to work for Cambridge Collaborative and he did a lot of the code development for SEAM. And so he remained interested and involved – very much involved in statistical energy analysis. And has remained, and still does.
I was going to say that.
Anyway, I had had some questions about, from various publishers about, “Well, what about a second edition of this book?” The book basically has two parts. The first part is the theory part and the second part is a how do you do SEA. And I felt I would be willing to redo the first part but I needed someone to come in and really – particularly with all the computerization of SEA, that somebody who knew about that had to come in and work on that. So anyway, Rich agreed to do that.
Was that a long-distance collaboration?
Yes, it was, because he was in Michigan and he and I never met face-to-face while the book was being put together.
Phone calls and manuscripts going back and forth and so on?
Yeah, right, right.
Right. That’s interesting. And then your most recent book–
Designing for Product Sound Quality is based again on the course, and is more of a – I won’t call it a handbook, but it’s very different from the other book in that very little is derived. Because when you get into product sound there are so many considerations, and it’s really, the course is built around a design concept rather than an analytic concept. So you know and then the designer has to somehow know enough about a lot of things and then use their own creativity to put them together in the right way to design something. Well, so you can’t have formulas for design, whether it’s acoustics or anything else. So what you have to do is give the people the basic information about the different ingredients that go together to make up a design and then they have to – and give them the sort of thinking pattern you have to go through, but you can’t do the design.
They try to find that piece of the parameter space that happens to satisfy their own particular design goals.
That’s right. That’s right.
And I note recently you were working on another book. Where do you stand with that?
Well, it’s about – depending on how you would count – I’m on the fifth chapter. It’s called Transfer Functions and the basic idea is that most work on transfer functions has been done by electrical engineers because traditionally you know you go back to Bode’s. Traditionally the idea was to design a filter – to design something that had a desired frequency and phase and amplitude response versus frequency. Well, people in acoustics and vibration are interested in transfer functions but in a different way – they don’t design the transfer function; they want to understand it and be able to anticipate what it’s going to be like. And the number of degrees of freedom in these transfer functions is typically you know very, very large compared to a typical electrical engineering filter – particularly one mode with inductors and capacitors.
I guess if you were doing a Z transform you can have a hundred parameters, you don’t care very much, but very few physical filters have a hundred elements in them.
A whole bunch of stages of cascaded filter. Right.
Right. So anyway, the idea then is to pull together a lot of the stuff. In a way you see statistical energy analysis is a way of estimating the magnitude of the transfer function.
But we’ve also done all this work on phase of transfer functions which was started at MIT and that work is important because particularly in diagnostics you want to be able to understand what’s happened to a signal in between the time where that valve impact occurred that you’re concerned about and the vibration that happens on the housing where you can be at the data.
And the effect of the transfer function on distorting that information. So the whole idea is to approach transfer functions from a point of view that it would be more interesting to an acoustician.
A physical process rather than an engineering filter process.
Interesting. Well, without getting into counting your papers, could you sort of bracket the bodies of literature that you feel like you’ve been able to contribute to acoustics over the years?
Yeah. That’s probably better than counting. Well at first, I guess the first major set of papers – I mean there were a couple of papers that occurred early on, but the first major set probably is the statistical energy stuff which as I say was early sixties. And then there is a set of papers that relates to transportation noise primarily – well, propagation in city streets, but perhaps more importantly some of the work on barriers and the use of scale modeling to evaluate barrier performance. That would be the next block. And then I guess we get into the machine diagnostics, which led naturally into the work on this transfer function phase.
Yeah. I was thinking of your clouds of zeros and stuff like that.
Yeah. Because the phase from a – one of the things you like to do in diagnostics if you can is get a simple waveform that relates to an event in the machine. Whether it’s combustion in a cylinder, a valve seat impacting or whatever, typically there is some little waveform you would like to extract and it is primarily distorted by the phase characteristics of the path.
The constructive-destructive interference of all these various paths.
Yeah. And actually, you know, the two classic forms of filtering to pull out such a signal from a source, from a path, are (1) an inverse filter, and secondly a matched filter. Well the thing that’s common between an inverse filter and a match filter is the phase. They both try to invert the phase and they–
Realign the phase somewhere. Right.
The difference between them has to do with the magnitude. And it turns out when you actually get to it, the magnitude of the transfer function is pretty unimportant compared to the phase.
So I got very much involved in phase, and that led to a collaboration with Mikio Toyama in Japan and a whole bunch of papers then came out about various aspects of phase and complex transfer function and transmission systems. And then I guess the next and maybe the current major block of activity has related to sound quality and evaluation of sound quality of product sounds.
So all in all a pretty substantial body of literature has evolved over the years.
Yeah. And it’s varied, which to me, I’ve never been able to understand people who can – I won’t give any names or examples because they’ll identify who I am talking about, but who sort of stick to the same subject all their lives, which I would find pretty tough.
Great. Well, this is probably a good time for us to take a break. We’re out of our time here. Let me say thank you for sharing that fascinating and, as you say, wide history of your life.