Per Brüel

[Editor’s note: This interview was conducted in 1998 but not publicly posted until 2024. The quality of the digitized tape recording did not allow for a fully accurate transcript and researchers may wish to cross-reference statements made here with other sources. Other biographical sources on Brüel include an interview conducted by Frederik Nebeker in 1996 for the IEEE History Center and Per V. Brüel and Harry K. Zaveri, “Of Acoustics and Instruments ― Memoirs of a Danish Pioneer,” published in two parts in the February and August 2008 issues of Sound & Vibration.]

Peppin:

Today’s date is the 26 of June, 1998. We are in Seattle, the Sheraton Hotel, Per Brüel’s room, in the State of Washington. I am Richard Peppin and we are going to interview Per Brüel. Dr. Brüel, what is your present address? [Response redacted] Okay, thank you. Who is your present employer; are you working?

Brüel:

I work for myself, for the time being. I just started five years ago when I sold the shares in Brüel & Kjær. I started a little company called Brüel Acoustics, and we are making developments on both absorbers ― acoustical absorbers ― and on test equipment. And that I have done now for the last five years

Peppin:

And do you design them?

Brüel:

We design them and we make prototypes.

Peppin:

Do you have a lot of people working with you?

Brüel:

Yes, but not on a regular basis. They get a task and get it, and there’s a plenty of them, because many people have left Brüel & Kjær, and I could get a lot of those, and I could give a person a very good job.

Peppin:

That’s wonderful. Okay, now we have the background. These are Acoustical Society of America-related questions. Do you remember what year you joined the Acoustical Society of America?

Brüel:

Oh, that was a long time ago. That was very early, I think it was just in the ‘50s.

Peppin:

In about 1950?

Brüel:

Yes, maybe 1949. I think 1950. I remember I was over here in 1950, and I gave a lecture, somewhere in an ASA meeting.

Peppin:

Was it an invited lecture?

Brüel:

No.

Peppin:

Just a paper you gave?

Brüel:

Yes.

Peppin:

And where were you working at the time? At Brüel & Kjær?

Brüel:

I was working at Brüel & Kjær. I was manager, together with Viggo Kjær, and I was over here for about four months and trying to set up some business in the United States.

Peppin:

It wasn’t in business in the U.S. before that?

Brüel:

No, just some small amount, Viggo Kjær was over here, but he mainly was running around MIT.

Peppin:

And so you graduated school, worked at Brüel & Kjær for a while, and was that your first adventure into the States?

Brüel:

It was my first adventure into the States, but I made a lot of things before that, of course, in Europe.

Peppin:

Oh sure. Okay. Why did you join ASA?

Brüel:

Because it was just in the middle of my interest in my work and, you know, I graduated in an acoustic program, and I made my doctor’s thesis also in acoustics, and I made the first acoustical laboratory in Sweden. So, I have been in that business all my life.

Peppin:

Right, and so you felt that it would be useful for your career, or maybe for your business, or both, to join the ASA?

Brüel:

No, it was interest, pure interest.

Peppin:

Just interest.

Brüel:

Oh, yes. And as I used the journal (JASA) much. But it was broken off because of the war, and I couldn’t get it anymore. But when I was at the university, both as a student and with a master’s degree, and later on beginning on the doctor’s thesis, I used a lot of the articles.

Peppin:

JASA articles?

Brüel:

Yes, articles.

Peppin:

Did anybody encourage you to join or did you just come to the meeting and decide to join?

Brüel:

Natural, it was just so natural. It was the only thing you had to do. It was really the only society and paper in the world, so there was no…

Peppin:

No choice. (laughter)

Brüel:

No choice. And that was the same with all other Europeans. There was some tentative group in Germany, but that was all smashed in the war.

Peppin:

Right. Did you hold any positions in ASA, like officer or...?

Brüel:

No, never.

Peppin:

No committee membership?

Brüel:

No, never. I just was there. Then later, Fellow. Then I got a Silver Medal, too.

Peppin:

Yes, right. Do you remember any ASA meetings that stood out for some reason? Maybe because you got the Silver Medal or because of some technical thing that jogged your mind?

Brüel:

Okay, let’s take the technical things. You know, we made the level recorder which was out of this world, according to other people.

Peppin:

Right.

Brüel:

No, that was not the level recorder, sorry. That has nothing to do with it. We made the first constant percentage analyzer. General Radio had a heterodyne analyzer, a beautiful instrument, but that was with constant bandwidth. We made the constant percentage bandwidth, and that was initiated in such a fun way. We saw just before the war, I think, it must be before 1938, a little article here where a fellow ― I can’t even know his name ― describing a Double T network, which uses a copper back over an amplifier, so that only one frequency band was standing out. The other was negative feedback. Now negative feedback was a very unusual thing at that time, too. But then it happened that we had some components manufacturer in Denmark that could make very accurate resistors, and also very good condensers, and by combining all that together, we had a possibility to make a variable analyzer based on that Double T principle.

Peppin:

Wow.

Brüel:

And that came out to be the first in the world, of an analyzer.

Peppin:

That was based on a JASA paper?

Brüel:

It was based on a small little article that one fellow had just made as a [fixed figure?]. But both condensers and capacitors had to be fairly accurate, and when you are moving them, and then you can see the problem.

Peppin:

I see.

Brüel:

It was doubled. We have a cascade, two figures after, so we can make the bandwidth a little wider, as we like to do. That we made for a long time. But I started that then, when I was drafted at that time. And in the army, I was making radios for armed vehicles. So, that was just the year when the Germans were walking in on Poland but had not gone up to Denmark and occupied that yet. And in that period, I had plenty of time to make that analyzer, so that was in the end of ‘39 and the beginning of ‘40. I have some pictures of it somewhere.

Peppin:

Was there anybody in ASA who influenced you?

Brüel:

Yes, but that was a little later, and in a different way, in a funny way. Leo Beranek went over to see us, together with a Japanese fellow, and he saw the level recorder and said you have to go to the United States and show it. And that was in ‘48, ‘49.

Peppin:

Before the level recorder, what were they using?

Brüel:

For analyzing? For writing? Neumann had made a recorder. It was really Mr. Braunmühl, who later became the manager of the German Post and Telegraph, a very high position. But he didn’t do it too well during the war, so he was forgotten after that. (laughs) But he made the principle and they made a few at German Post and Telegraph. Then Neumann took over and later Siemens took it over. But that was in ‘35, I think. So, it was more or less the same principle we used, but, if you know the Neumann recorder, it was a fork that was going front and back and driven by three discs, where, when it was the two-disc [level?], and that was [innestized?]. Then it was in the lower spot, then it was the other way, and then by increasing the friction you could have the fork go in front and back, and then it was controlled by a low-grade potentiometer. This is just what we do today. But the difficulties with that was that it was either no voltage on it, it would run over to one side and then was grinding in that, and it was too much of it, it was going over to the other side and grinding. So, we changed that into an electrodynamic system. There again America had an influence, because Viggo was over to MIT and saw Professor Campbell, who was the first, that I know, that included negative feedback, including mechanical motors and engines, and so on. It was absolutely new for us. And we put that in our recorders. We put an extra coil on it, so we had this differential control on it, so it would start braking before we come into a [station?].

Peppin:

Yes, that was amazing, I think we’ll get to that later, but I’m real interested in that. Do you have anything to say about ASA, the past, the present, the future, of the Acoustical Society?

Brüel:

No, not really. We are reading JASA and following it. I come at least once a year to one of the ASA meetings.

Peppin:

For sure it’s been influential in promoting Brüel & Kjær by having B&K presence here, either you or the exhibits, it was always a very good thing.

Brüel:

Maybe I should tell you a story about the Journal. We should like to advertise in that and that was not possible. And certainly it was open to that. And I think that was in the beginning of the ‘50s, when we put some advertising in it. And the funny thing was that it didn’t really work, there were too few responses. But it worked tremendously in Russia, and the reason behind it was that the Russians bought two copies, I think, of JASA, then they published 2,000 more. And they published the advertising, too, so we got immense advertising, more or less, in Russia, and that is where it worked! (laughs) But then we had to stop doing that, advertising.

Peppin:

I guess the copyright was a problem. What other professional organizations do you belong to?

Brüel:

Oh, I belong to many of the acoustical societies around the world. Of course, the Danish. The Swedish, I founded. And then I belong to the French, too. And then I, of course, belong to a completely different field. I am very interested in aircraft and flying, so I have a lot to do with that, too, and also combined it a little by trying to reduce the aircraft noise with acoustic techniques.

Peppin:

Okay, now we go to the pre-college years, when you were young. When and where were you born?

Brüel:

I was born in Copenhagen.

Peppin:

What year?

Brüel:

That was 1915.

Peppin:

Before entering college, what were some of the places you lived?

Brüel:

I lived in Southern Jutland. It was a little different from other parts of the country, because that was a part of Denmark we got back from the Germans in 1920. So, there was a lot of Germans there, German influence. But Denmark lost it in 1864. Bismarck, he took that part of the country. But we got it back after the First World War, in 1920.

Peppin:

What did your parents do?

Brüel:

My parents and their parents again, and all of them, six places down, were all foresters, and there was a big trouble in the family that I didn’t want to be a forester. I wanted to go into the electronics field.

Peppin:

Did you want to do electronics when you were, say, in elementary school or high school?

Brüel:

As a kid, all boys want to do that.

Peppin:

How did you get interested in it?

Brüel:

I think it was interest in physics, in some way, even in all the things that happened in physics, in those days. Then, I was interested in loudspeakers and making loudspeakers.

Peppin:

So, these were kind of hobbies you had.

Brüel:

Hobbies, yes. I was also a radio amateur, very young, at 15 years old. But, you know, together with other things, I was hang-gliding.

Peppin:

Hang-gliding, then, pre-California?

Brüel:

Yes.

Peppin:

Were there people, well-known people, who you admired? Were there some that you said you wished you were that person?

Brüel:

Yeah, there were several, but Valdemar Poulsen, does that say anything for you? He was a good friend of Professor P. O. Pederson, Valdemar Poulsen. He invented many things, also the first tape recorder in the world. It was a wire, but it was the first in the world. Of course, it could be called a telegraphone. They made a company and were trying to make it, but there were no amplifiers so it died out. The next thing was, he was the first to make continuous radio waves. It was Marconi who was taking the whole thing from sparks, and Valdemar Poulsen and P. O. Pedersen, who was the Dean of the Technical University ― they were very good friends and he took all of the theoretical parts that the Marconi set lacked, and so they got really the first continuous radio waves that were made with an arc. You know that principle? You can have an arc in the helium content, and you can get that to be unstable and make continuous radio waves in very high frequencies. The problem was to modulate it, because we had no modulation. So, we have to modulate on the power end of the whole thing, so we were burning microphones up like hell, and that lasted only for three years.

Peppin:

Did you know these people as teachers?

Brüel:

P. O. Pederson, I was assistant to him in his old days, and Valdemar Poulsen I only have spoken to.

Peppin:

So, what events or subjects did you enjoy most in high school? The science part?

Brüel:

Yeah, I can say that. The first part of the university is like here: you go the maths and get all three, and I think education is quite good because it was chemistry and a bit of mechanical dynamics. Then, of course, another part was mostly electronics.

Peppin:

Did you get involved in music at all?

Brüel:

No, not really. I am very much interested in radio studios and microphones and loudspeakers.

Peppin:

Not playing an instrument?

Brüel:

No, no. But I was very lucky in some way, because as I was very young, going in to take the full responsibility for all the acoustics in the new big radio house they were building in Copenhagen.

Peppin:

This was when you had graduated?

Brüel:

I had graduated but had not made my doctor’s-degree thesis yet. And that was very interesting because they happened to have… Here is a long story. They made the radio house. It was very bad and we can talk to that later. The new one, they took the man who was responsible for this, Mr. [Nurenberg?], he was a building fellow and interested in statics and was used as engineer for that. He was a professor at university, too, and his only interest or knowledge about acoustics was that he would sing in the choir. His assistant was a young engineer, Johann, I think that was the name. He was responsible for the acoustics, but didn’t. And then Mr. [Nurenberg?] came and took me and said you can help me. So, Johann was three years older than me had been my teacher, and then, wow, I was his boss. But, okay, that went out very nicely, but then I had two wonderful years with making all those studios.

Peppin:

So, these were studios for one station, or all of Denmark?

Brüel:

State radio, Denmark. But only radio, not TV. And that was a big concert hall, still working in a [long theater?].

Peppin:

So, you did a lot of architectural acoustics?

Brüel:

Yes, well, let me tell you some details. You could study around Europe and the United States, and it was a big mess, and you couldn’t really find out what to do in acoustic work. Then when you make a studio, the idea was that you should take all the real big conductors, and those people that know something, and listen to what we had done, and then they should evaluate it and say if you had to do something, and change and give it a go again. And it was one mess. Those people, even though they were brilliant musicians, couldn’t evaluate it. So, we could make ones and they could say, “No, no, that’s not very good ― more vibration, low frequency.” And finally, sometimes I said, “Okay, I will do that,” but I didn’t do a thing. And they would say, “Okay, much better,” and it turns out it was so bad, and they were very good people, but most of them were listening to the music and saying, “Oh that’s a fault there.” They would not distinguish the music from the acoustics. So finally, I ended up by asking the musicians, and that was logical, too, because that was a radio, so to hell with the audience. It didn’t matter. The thing is to have the musicians there. What we did was we increased the reverberation and that’s what Vern O. Knudsen prescribed in his book, what you should have. They liked that and played better. So that went very well, and we got very good studios.

Peppin:

In your undergraduate years where did you go to college? What school?

Brüel:

It was in Copenhagen. I was born over there in Copenhagen. I went to school there, but that was practically the only college.

Peppin:

What was the name of it?

Brüel:

That was the Polytechnic Learning School, now it’s called the Technical University.

Peppin:

Did you major in anything? Was there a major field, or you just took classes in everything?

Brüel:

More or less. It’s like a class you go through, then you can decide what direction you want to have and then you end up with a master’s degree.

Peppin:

What direction did you choose in school, physics?

Brüel:

It was electronics. I made my master’s in electronics, but on acoustic problems.

Peppin:

Like loudspeakers?

Brüel:

No, that was really Professor P. O. Pederson that made you have a transducer to measure the vibration of the wall. He had some bright ideas from time to time and he always took his best students to get them out. Viggo Kjær and I were supposed to be the best in that class. So, we worked on our master’s degree for about 5 months.

Peppin:

Is that where you met Viggo Kjær?

Brüel:

Yes, it was there. Because he had some illness, tuberculous, so he was one year out, and I caught up to him.

Peppin:

So, had he not been sick, you may not have met?

Brüel:

No, no.

Peppin:

Did you choose that university or did your parents choose it?

Brüel:

There was no other choice.

Peppin:

There was no other choice. You just go there. That was the rule. As an undergraduate, did you do anything unusual or special in school that you want to mention?

Brüel:

I made a glider that couldn’t fly. And then I was a radio amateur. I liked that very much.

Peppin:

The gliding, was that going to be a glider for a person? Were you supposed to be on it?

Brüel:

I was hanging in it. You’re running down a hill and hanging there.

Peppin:

I’ve seen movies like that.

Brüel:

And then you guide it by pushing it.

Peppin:

Were you ever politically motivated, in any way?

Brüel:

No, not really.

Peppin:

So, there were no rallies, or protests, or anything like that?

Brüel:

No, no. First of all, it was that part of the country where we had that very strange situation between the Germans and the Danish. And then, at the same time we had the Nazis movement coming in and many people were interested in that. And of course I was interested in that, too, but it was certainly not my main interest.

Peppin:

You were mostly a student? You didn’t care about that topic?

Brüel:

Yeah. And it was so hard and unhuman. I can say it that way.

Peppin:

If you had to do it again would you have gone back to the same school?

Brüel:

Oh, yes.

Peppin:

It was a good experience for you?

Brüel:

Of course. But the funny thing is that when I finished with the master’s degree, I said, gosh, now I should like to start over again. I could really learn something.

Peppin:

You know what you missed?

Brüel:

Right.

Peppin:

And so, your master’s was at the same technical university as your bachelor’s?

Brüel:

Yeah.

Peppin:

What about funding? Did it cost money to go to school?

Brüel:

No, the school was free. You had to pay for your books and everything like that, but the university is free in Denmark. I could stay with my grandparents who lived in Copenhagen, so it was rather cheap.

Peppin:

And your folks were still in Jutland?

Brüel:

They were still in Jutland. I moved to Copenhagen and stayed with my grandfather, and he was a very interesting man. He was my mother’s father. He was a professor of Arabic languages, and later on he was a dean at the university, so he was quite famous. And so that was a very interesting home to stay in, a lot of people came there.

Peppin:

Did you have part-time jobs when you were a kid?

Brüel:

No, very little.

Peppin:

So, the books and things like that, your folks or grandfather paid for? Where did the money come from for you to get along?

Brüel:

Oh, you could really manage with very little money at that time.

Peppin:

Now, your master’s thesis, that was on electronics?

Brüel:

The master’s should have been on electronics, but it ended up to be on the tube.

Peppin:

Vibration walls on tubes?

Brüel:

And of course, the microphones and things like that.

Peppin:

Was there anybody in school, I guess it was Pedersen, who gave you the most influence?

Brüel:

Yes, but also this Professor [Nurenberg?]. He was a brilliant fellow, too. He made many interesting things, a specialist in tall towers.

Peppin:

So, you got your degree, and you knew Viggo Kjær. What did you do after your master’s degree?

Brüel:

After the master’s degree, with Viggo Kjær now, we agreed that we should learn something. We shouldn’t start any company before had been out 5 years, so I was assisted by Professor P. O. Pedersen. And then I was drafted and the war came. And we made this radio house there. Then I found my way to Sweden, in the middle of the war, in 1943.

Peppin:

You were still drafted then, or it was after you were drafted?

Brüel:

No, when the Germans came, then the military was gone.

Peppin:

Oh, I see, so they occupied all of Denmark?

Brüel:

They occupied the whole thing and the army was disarmed.

Peppin:

And so, what made you get to Sweden? You were living in Sweden?

Brüel:

No, there was a lot of trouble with the Germans there [in Denmark], so I went over there.

Peppin:

So, did you know people there?

Brüel:

Yes, I knew people there. I really got a job before I went, and that was in acoustics. That was in the glass factory; they wanted to expand.

Peppin:

What city was that?

Brüel:

In the beginning, that was Stockholm. Then I went to Gothenburg. Later then, I went to make this acoustical laboratory in Chalmers.

Peppin:

They hired you to make the laboratory?

Brüel:

Yes, and also to give some lectures.

Peppin:

So, by now you’ve become relatively influential and famous.

Brüel:

Oh yes, certainly.

Peppin:

When did that start? When did you recognize and say to yourself, “Hey, I’m smart?”

Brüel:

I think it was when the radio house was finished, because that was really something to show.

Peppin:

This is the Danish state radio?

Brüel:

Yeah.

Peppin:

And then all of a sudden, somehow, your reputation got around?

Brüel:

Yes, it got around.

Peppin:

Did you write papers about that station?

Brüel:

Not really at that time. A lot went into my doctor’s thesis.

Peppin:

So, it was all word of mouth, essentially?

Brüel:

Yeah, but I was also a little into some papers that make absorbing materials and vibration dampers, things like that.

Peppin:

This is in Sweden?

Brüel:

Also in Denmark. Even very young, I had ideas of how a vibrator should be, and so on.

Peppin:

So, you end up in, say, Gothenburg, and what happened then?

Brüel:

At the end of my military thing, I had this wonderful analyzer. That was a really remarkable thing. It was battery-driven, and you could go around and analyze sound with it. And then I had a lot to do with standing-wave tubes. We made a lot of that, also, before I went to Sweden.

Peppin:

What made you think of doing that? Because you had to measure the properties of the studio wall?

Brüel:

No, that was really Professor P. O. Pedersen that started this, and first was to measure absorbing material, but also to calibrate microphones. What we did with the radio disc, we didn’t know it was possible at the time, even if Lord Rayleigh had written about it, we didn’t get it, so we made such long radio discs and could calibrate the microphone. We put that up in the end, and then a quarter-wavelength away, we took the particle velocity.

Peppin:

And these were like projects that Pedersen had and you worked on?

Brüel:

Yes, when I was his assistant.

Peppin:

Now, this analyzer came from this work, too?

Brüel:

No, the analyzer came from my military.

Peppin:

What function did you have in the military? You were a scientist?

Brüel:

The lowest grade you could have, but as it was so close to the war, the Germans were in Poland, fighting. So, if they could get some people, they took the normal people. I was running as a motor ordnance on a motor bike. Then, they found out I know something about radio, so they put me in a complete [inaudible].

Peppin:

That was in where?

Brüel:

That was in Copenhagen, so I was working like an engineer there.

Peppin:

So, what next? Then you went for your doctorate?

Brüel:

Then I had made most of the thing for doctorate, but that was interrupted. Then I went to Sweden, and there I just finished writing it and sent it back to Copenhagen.

Peppin:

Yes, because that is where it should be, the Technical University, the same place?

Brüel:

Right, the Technical University. And that took about two years. I had difficulty in coming home, I thought.

Peppin:

What was that on? What was the topic of your thesis?

Brüel:

The topic was called, “The Tube Method for Room Acoustics.” We were trying to work and make something with how the angle of incidence was affecting absorption. So, you measure that with perpendicular to the sample and included the angle of incidence to it. That was really the main thing and got that practical.

Peppin:

There’s not much since then on that.

Brüel:

No, the funny thing is, it was based on the theory of P. M. Morse, which he wrote in ‘38 or ‘37, I think. A very simple theory. It ended up in formulas like that, you see [Brüel shows a formula to Peppin]. At that time, also, Beranek and [Bolt?] were working with the wave equation, where they put the boundary walls in the wave equation. So, it’s coming a little from there. Also, the Chinese man, [Maa Dah] You, was also in the picture. But before that, Morse had made a theory of that, where [inaudible section] you get the absorption coefficient. So, what I did was, I verified that theory.

Peppin:

Dr. Brüel is referring to Page 9 of his technical review course, standing-wave tubes. So, you got your degree from the Technical University of Denmark, your doctorate degree. And then what did you do?

Brüel:

Then I was an associate professor in Gothenburg, up to about ‘47.

Peppin:

So, you were in Sweden when you got your degree from Denmark, and you stayed there and went to Gothenburg.

Brüel:

No, I had a contract, so I had to stay there.

Peppin:

Did you teach other places too?

Brüel:

No.

Peppin:

So, you were a professor until 1947, and then what?

Brüel:

It was called docent, and that was given normally for a three-year period for a special purpose, or project. But over here, I think you call that associate professor. It was only for three years, but I could have had it for another three years, but you promised to stay for three years and finish the project. And this project was to make an acoustical absorber in Sweden.

Peppin:

In Sweden?

Brüel:

Yes, and that’s the same as Kihlman has now. That’s it.

Peppin:

So, after that, what?

Brüel:

Then after that, I went to Denmark and was running Brüel & Kjær.

Peppin:

So, while you were an associate professor, you were talking with Viggo about potentially starting Brüel & Kjær?

Brüel:

Yes.

Peppin:

So, was that a tough decision for you to say, “I am going out on my own and start making these instruments?”

Brüel:

No, not at all, because that’s what we decided when we left high school.

Peppin:

So, that was the plan?

Brüel:

Yes, to stay our 5 years, and now it turned out to be 6, but...

Peppin:

So, you formed Brüel & Kjær in what? In 1947?

Brüel:

Officially, it was formed in 1942, I think, because we don’t really know, because we make so many. But we made the first invoice in 1942. That was still in Denmark. Then shortly after, I was in Sweden and Viggo was in Denmark.

Peppin:

Was Brüel & Kjær in the same location in Lyngby that it was when you started?

Brüel:

Yes.

Peppin:

And it was just two people, or did you have assistants?

Brüel:

No, we are two people, and later on we had a third fellow coming in and helping.

Peppin:

And so, you had this analyzer design for the military…

Brüel:

Yes.

Peppin:

And you had experience with the standing-wave tubes and…

Brüel:

And we made analyzers, different models. We had a power-driven one, which was far more powerful, more selective, and we made tubal meters for tolerances, and the idea for the level recorder started up in Sweden.

Peppin:

While you were a teacher in Sweden? So, you had all these ideas, and then you had to start making instruments. Did you have to market them, or people knew that you were making them, and they came and said, I have to buy one, two, or three?

Brüel:

No, I think the level recorder was rather simple because the analyzer was there already, and that was a good thing. Then you need the level recorder, but then before the war you could buy the Neumann level recorder from Germany. It was terribly expensive, but you could get it, and Siemens didn’t want to make it anymore. It should also be a different thing because it was wearing itself out in no time. It was a little too heavy, but there we got the idea to make the present one, and that may be a little funny story, because Viggo and I had decided that we would never touch a thing if we could not make at least 75 items of it. That was again the mix-up, because I said 50, he said 100. Then we came to the level recorder, and Viggo had found out that you could maybe sell 50. He counted some of the universities around the world. And I said you could sell 150, and he said no, we have to agree, 75. And so, yes, we have to agree, but do you mind that I do it myself in Sweden, which is what I did. So, I made the first up there, really, against his will. But come back to say how clever you are in imagining you can sell, that is, he said, 75 and I say 150. We sold 25,000. (laugh) You can see what market analysis is worth.

Peppin:

Was that the thing that really launched Brüel & Kjær? The graphic level recorder?

Brüel:

Yes, it was.

Peppin:

Because you sold so many?

Brüel:

Yes. And it was a good thing and a different thing, and you could make them, and there was a need for it.

Peppin:

Did you do the manufacturing, or did you send it out?

Brüel:

We did the manufacturing, except for the prototype up there and the production. And Viggo come over, and he saw Professor Campbell, and he had the idea to put the feedback in it, and then it was really special.

Peppin:

So, then what made you go into other things, like meters and stuff?

Brüel:

Oh, we had already made, very early, an ammeter and tubes with a copper rectifier with parabolic characteristics. And that was a quite good thing, too, and we sold them like hot cakes. And we made some [inaudible].

Peppin:

Here in the States?

Brüel:

Yes, that was later. We already made them at that time, then we made microphones, but that was [sold?].

Peppin:

When was that, about?

Brüel:

Oh, I started that already in Sweden.

Peppin:

You were doing everything in Sweden?

Brüel:

Oh, yes. It was very fun at that time.

Peppin:

So, when you started to make the graphic level recorder, the company really started to grow at that time.

Brüel:

Yes, it did.

Peppin:

When was that, about 1950?

Brüel:

It started already in ‘49, and then it grows fairly fast after that.

Peppin:

What things do you think in the early years were notable for you at Brüel & Kjær? Did you have some landmarks?

Brüel:

Yes. First of all, we were spread all over the world because, more or less, Leo put us over here [the U.S.], so that came very fast. In Germany we had many good friends. Professor Meyer, those people there. We were always university-connected. We always start there, with universities. In the technical part of it, the next thing was really the condenser microphone, because we were using the model based on the Western Electric 640 AA. All our customers bought it, and we also had a Danish manufacturer. And Dr. Schlegel made one more-or-less the same as Western Electric, except it was like… See, the membrane is coming up here, and the membrane is coming down here, and you have the electrode here. So, it was put in with friction here [Brüel points], and then of course you move the whole thing and stretched the microphone, and that’s the way we did it, too. Western Electric had a ring on the top where you get some screws in there, but most microphones had this peculiarity that it went more and more sensitive every year. Sometimes, if you have it in a drawer, it only drifted half a dB a year, but if you use it in the field it was up to two dB a year. Nobody could really explain that and tried to make it heavier and heavier. One day I was sitting at home, and I had a paper there, a pen there, and make the tension there, and I start to move it back and out comes the paper, and the whole thing was solved. Only a crystalline connection ― a crystalline connection you start by having a very thin housing and then put a membrane over by plating, put some wax in here and plated it, and that works very well. Then, you see, you can get away from all these thick heavy materials. So, then you could make small microphones, and we could make stable microphones because that was the whole thing.

Peppin:

When was that about?

Brüel:

That was in ‘55.

Peppin:

And that did it, too, that’s for sure. That’s pretty exciting.

Brüel:

And the most fantastic thing was no one copied that after 25 years.

Peppin:

In the United States your only competitor was General Radio?

Brüel:

Yes, on the instrument side, not in microphones. I just had a discussion here the other day with Alan Marsh and told him how the weighting curve was coming along. You can have it another time. It doesn’t belong so much to me, but it’s interesting what two people, Arnold Peterson and Leo Beranek, do as they sit over a cup of coffee and do a thing with weighting curve, which was wrong. And then that had influence, tremendous influence, on the whole world. Up to this day we have wrong weighting curves. We don’t have the [inaudible] between 2000 and 5000, which we need. What Zwicker is introducing ― Karl Kryter is introducing it ― and still we can’t get rid of the A curve.

Peppin:

And it really is incredible to think that people are reaffirming that A-weighting curve today without reevaluating its usefulness.

Brüel:

Yes.

Peppin:

It’s very interesting, what’s going on. I know what you mean.

Brüel:

And you know, I talked to those people, Leo and Arnold. We are very good friends. He’s still living, he’s living up here. He’s an old man, now.

Peppin:

Did you write a lot of books?

Brüel:

I wrote only one.

Peppin:

Only one book?

Brüel:

Yes, one for Chapman and Hall. That was in the ‘50s.

Peppin:

You must have done a lot of work on Brüel & Kjær technical reviews, too, on a lot of those technical papers.

Brüel:

Yes, yes.

Peppin:

I want to talk more about B&K, but there’s really just a couple of other things… But in Brüel & Kjær, the company really grew and became a renowned company for acoustics, probably still is, at least the name, anyway.

Brüel:

I hope so.

Peppin:

No question.

Brüel:

We’ll see if we can get it back.

Peppin:

And so, I guess it was in the ‘80s, did you want to sell, or did something happen to you that you wanted to leave?

Brüel:

What really happened, and that is no secret, is that Viggo and I were really running it, and there was no doubt about it, and there was no other influence. And we made a hell of a lot of money, and we had a decent living, so we were really rich, and rich in the way that we had no debts.

Peppin:

Oh, yes. I remember when I was working there, and it was a very good company.

Brüel:

What time was that?

Peppin:

About 1982.

Brüel:

It really was at the top at that time. We made a profit, at that time, about 100 million a year, after year, after year. But then we came to the time, at least Viggo thought, now we should try to find some people that could take over. And he was in a family that it was very natural that sons took over. He had a son, he was a good fellow, but he didn’t want to work for the company. But I didn’t like it, really, because he was not really in our field. And I had a son also there, very well educated. But I had a feeling he had no interest in playing around and things like that. He was an electronic engineer and had a good examination, but he was not really interested in the toys. Then it started also that we had a different opinion. We always had different opinions and we resolved them. But he had some other interest, and I also had some interest, and we also divided all the decisions. I take all the decisions with foreign people and all the decisions concerning the technical things, and he was looking into production and employment of people, and of course, also we put our nose into the other’s. And it worked very well, really. And sometimes, we always should have a decision when the problems came up: so we got in, and if we had different opinions we try to talk it through, and we didn’t go out the door until we had a decision.

Peppin:

It sounds like a good working relationship.

Brüel:

Sometimes when Viggo has an idea, he kept to it to the bitter end, so it could be a long way to try to persuade him. But really, we got things talked through. Very few times we had to flip a coin. But then, we had some problems.

Peppin:

You couldn’t agree what to do?

Brüel:

And I was traveling so much, and he employed my son, you see, when I was in China. And I was furious when I came home, to hear that. That doesn’t help. And then the younger generation with Viggo wanted to grow the company much more. It was 1000 at that time, but they wanted to go to 6000. They were convinced that they couldn’t do that with acoustics, so they went into ultrasonic and medical ultrasonic and also a completely wild collaboration with HP.

Peppin:

The VXI bus.

Brüel:

Yes, the VXI thing.

Peppin:

Yes, I remember they were hiring like crazy.

Brüel:

Yes, they used a lot of money to do that, and that went nowhere. And I said, okay, let us limit our products to low-frequency acoustics. Don’t go into gigahertz, which we had no knowledge about, no experience, not even people in Europe that knew something about it. It was all here in the USA, but that’s it.

Peppin:

But you still spent a lot of money on that company. You still had money.

Brüel:

Yes, we still had money, and then we sold it before it was exhausted.

Peppin:

Because you and Viggo said that, essentially, it was not working between you guys, and it would be better to get out and leave it to another company?

Brüel:

No, they were using so much money, the rest of it was frozen. And that was in tools and stocks and buildings, and so on, and so they had to go to the bank.

Peppin:

So, you always had your own money, and now you had to go the bank for it.

Brüel:

Yes, and I don’t like that. And at that time, we were running the company with a loss, of course, and that went on for about five years, when we lost about 100 million dollars a year so that the capital went down, and when it came down to the point where it was frozen, you had to go the bank and get it out.

Peppin:

So, this must have been a disheartening time. You must have been feeling bad about the whole company.

Brüel:

Yes, I was feeling bad, but it was a very short time, about two years ago, when I didn’t like it. I tried to go out myself, but they talked me into staying.

Peppin:

So, finally what happened?

Brüel:

What happened, the banks came and they said, “Oh, my dear, that can’t go on.” Then they advised us to sell, and our children (both Viggo’s and mine) were not interested in the technical things at all, so they said, “Hey, let us get the money.”

Peppin:

So, it went up for sale? It must have felt horrible, here your whole life being passed.

Brüel:

Yes, but on the other hand, you looked back to it and you had a wonderful time.

Peppin:

And you helped thousands of people.

Brüel:

Also that, yes, and it was a lovely time.

Peppin:

The total employment must have been ten or fifteen thousand people, total.

Brüel:

No, no.

Peppin:

I don’t mean at one time.

Brüel:

You mean when we were on top? Yes, when we come through, I don’t know, but we were rather stable there, 2,400 in Naerum, when we stopped, and 800 out on the payroll.

Peppin:

So, okay, when you sold it, there was another company, Brüel & Kjær, and you are out. What made you decide to go into Brüel Acoustics? Did you do it right away?

Brüel:

Right away. But I was very restricted. As to selling the shares, I couldn’t do anything. I had an agreement with Gunnar [Rasmussen] that we should try to do something, because he was kicked out.

Peppin:

A little before that, wasn’t it?

Brüel:

Yes, a little before that. I knew I was going out, but I had to sign this non-competitive contract, which lasted five years, but Gunnar didn’t want to wait for that, and I understand that also.

Peppin:

So, he went ahead on his own?

Brüel:

I could only deal with absorbers and room acoustics and things like that, which I did.

Peppin:

So, were you eagerly awaiting the time when the five years was up so you could get back on your own?

Brüel:

It is difficult to say. I was working and had a nice time, too, and I went around the universities that would all kind of dump these degrees on top of me. So, I had a good time, and then I had money. I had no economical problems.

Peppin:

From the Brüel & Kjær agreement plus your savings?

Brüel:

No, just the sale.

Peppin:

So, you had plenty of money because of the sale, and you don’t have to worry about that part? Then you did go back, so now you have another agreement with Brüel & Kjær?

Brüel:

Yes, but that’s just recently. But in the beginning, in the first beginning, when I sold the shares, the Germans were interested in having me help them making new things. Sure, so we got an agreement on that, that I should do it, but they wanted to be sure that I didn’t want out, too. So, in that agreement I had to show them, first, what I have done, and then they should decide if they want to have it or not, and, then of course, make an agreement on top of that. But the new manager that came there didn’t want to have anything to do with it. He told me straight away, “I don’t want to have you here at all, because I have the feeling that all the people are more loyal to you and not to me, so just for that reason I don’t want to have you.” So, that was it. And then he was threatening, too, you can really not do anything in instruments, but I don’t want to buy them from you in any case. That, maybe, I could have done, but I have enough to do with Brüel Acoustics.

Peppin:

Tell me about your airplane. When did you start flying?

Brüel:

I started flying, as I told you, in school time. I made this glider.

Peppin:

What about powered flight?

Brüel:

Oh, powered flights were much later. But I flew gliders, real gliders, that were towed up, just before the war, when I was at the university.

Peppin:

You bought your plane when you had money from Brüel & Kjær? When you were successful?

Brüel:

That was later. That was in the beginning of the ‘50s.

Peppin:

You were unique in that way, having your own plane and taking people around.

Brüel:

Yes, I flew around the whole of Europe, and that was fun.

Peppin:

Yes, that was pretty good. Are you still flying?

Brüel:

Yes, but I don’t take it out very much, because I can look over there and see, and it’s alright, but I cannot see sufficient what is going on there. So, they have given me a warning: we are going to take your license.

Peppin:

So, you have your plane for sale?

Brüel:

Two. I have two. I have a little [inaudible] one, which I can only fly in good weather, because there is no instrumentation, what you call a VFR plane. Then I have a Mooney 252, which is a beautiful plane and fully instrumented. You can fly in bad weather, and so on. Long distance, too.

Peppin:

Is there more about your professional life you want to talk about? I have some more things about personal stuff, but are there any more things about professional stuff you would like to share?

Brüel:

Yes, when you are going out from here, it comes up. But I don’t think so. So, are we pretty close to...?

Peppin:

Well, just a couple of things about family and personal interests and stuff, okay? What is your present marital status?

Brüel:

I am married and I have a son. I have married twice, and my first wife died [inaudible].

Peppin:

What was her name?

Brüel:

Her name was Drude, and there I had two children, now grown up: Niels and Marianne. [Niels?] is an architect living in England.

Peppin:

And then you remarried?

Brüel:

Yes, I remarried, and her name is Birgitte. We got married a little over 25 years ago. We had a silver wedding here the other day, but I have no time for it because I have to go down to Istanbul.

Peppin:

Does your wife work, or did she work?

Brüel:

No, no.

Peppin:

She stays at home? Your last marriage, did you get married in Denmark?

Brüel:

Yes, it was in Denmark. She was a Danish girl.

Peppin:

Where did you meet her?

Brüel:

I met her at another wedding party, no relation whatsoever before.

Peppin:

Anything special about your children you want to mention?

Brüel:

No, I think it’s going very normal and nicely.

Peppin:

So now, just your personal interest in things. Do you have any form of entertainment? Do you listen to music? Go to concerts, movies, or anything?

Brüel:

Not too much. I like music very much, mostly classical. Metal rock is not for me. (laughs) I have that happiness that our children [inaudible] fairly decent. So, they maybe like it, but we could put them into a basement and stay there.

Peppin:

How about reading, any reading?

Brüel:

Yes, I like to read from time to time. My wife is reading all the time.

Peppin:

Fiction kinds of books?

Brüel:

No, normal mystery. A few, mainly what other people have done, so biographies and what people have been through.

Peppin:

So, when you read, is it a lot of English or Danish books?

Brüel:

It is a lot of Danish, Swedish, and some English. And for a time it was German, because I know German pretty well from my school time.

Peppin:

How about any sports?

Brüel:

Sports, not really. I have been on skis, but not up in the competition.

Peppin:

Do you follow anything, maybe football, soccer?

Brüel:

I hate football.

Peppin:

A lot of people do.

Brüel:

I like cars. I have five old cars.

Peppin:

Oh? Classic cars?

Brüel:

Yes, classic cars. The best one is a Lancia Aurelia B20 and I bought it new, way back, and I am racing it, rallying it, twice a year, in Italy mainly.

Peppin:

Do you live in Italy part of the year or all of the year?

Brüel:

No, my cars are there. But I have a [inaudible].

Peppin:

About those cars, did you restore any of them? Or did you buy them?

Brüel:

I restore them. Other people restore them for me. I have good help. I have good friends in that area helping out.

Peppin:

When people are into that, they are really into classic cars, getting the tires right, the upholstery, all of that.

Brüel:

Yes, yes, but when you come over you can see it, and the plane is also old stuff.

Peppin:

A biplane?

Brüel:

No, it is a monoplane, but for two people and fully automatic. About my interests, I am interested in designs, industrial design.

Peppin:

Did you design all that new stuff for Brüel Acoustics, the impedance tube and all? That’s beautiful.

Brüel:

That has always been my responsibility, and I do it also now… quite interesting how it started. I was also one of the foundation starters of the Danish Industrial Foundation, which gives out prizes every year. That’s 50 years ago.

Peppin:

Well, the new things that I saw ― I think it was at the Inter-Noise in Liverpool ― what you showed me, the impedance tube and the RASTI meter, I think it was. Those designs are just gorgeous. I’ve never seen anything like that for instruments. They are like Bang & Olufsen is for the home design. It’s really nice.

Brüel:

Yes, I hope so. I like the [inaudible] car. I like that Aurelia, it is very nice looking. I like the little airplane, really made by an Italian, the most beautiful plane in this world. And the funniest thing is that in New York, they have a design laboratory. (It’s not called a design laboratory.) They have an exhibition, some old airplanes, the old Beech [inaudible]. Also my Aurelia is the same as the model in the same museum. I like these beautiful things. Look at my wife, she is beautiful, too.

Peppin:

So, what are your plans for the future? What are you going to be doing in the next five or ten years?

Brüel:

Oh, ten years? I would like to finish what I am doing now.

Peppin:

Which is the design?

Brüel:

… try to get those promoted. By the way, I hope I can get some agreement with Norsonics.

Peppin:

Yes, it would be good. They are doing okay as well.

Brüel:

And also with Brüel & Kjær, but, as far as I can see, Brüel & Kjær is moving away from that direction. Norsonics is moving in that direction. They are certainly not competing ― or they are not competing three years from now.

Peppin:

Are you talking with them? (Norsonics)

Brüel:

Yeah, that’s my idea. No, I am not talking with them, but I can see how well the possibility is. But then they go towards vibration and have more or less given up the building acoustics and noise damage. That is coming up now.

Peppin:

Well, they may go back to it.

Brüel:

And another thing is also, in Bangkok, we have a joint venture, making very effective sound boxes, for a decent price.

[The interview transcription concludes at this point; the audio continues along a similarly conversational track for a short period before also concluding.]