Interview with Peter Walker - THE AUDIO AMATEUR'S EDITOR





TAA: What do you consider to be the important goals of a good audio reproduction system what ought a good audio reproduction system to do?


Peter Walker: 

Well, perhaps this reflects my age (which is 60), but I am still in favor of documentary type reproduction- an orchestra plays on a stage or in some auditorium and we try to get a real, believable picture of it. This is becoming out of date, of course. It's now thought that a completely new type of sound should be produced. I can't argue against this. I can't say there's anything wrong with this. Perhaps if Bach were around now he'd do the same thing, hit you on the head and do all sorts of things to produce an effect. But my own personal preference, my own goal, is to create a true sound picture of some acoustic event which is taking place somewhere else. The argument against that is that it had to be produced in a concert hall at one time, because there was no other means. But why should one stick to the concert hall? I stick to that, but that's just personal prejudice.

Peter Walker mit ESL57 Elektrostat
Peter Walker's interview with "The Audio Amateur"



You don't like to sit in the middle of the orchestra, then?


Peter Walker: 

I sit in the middle of the orchestra twice a week, in the local group, playing the flute with the trombones and French horns behind me. And very nice it is too, but, no, I don't like sitting in the middle of the orchestra. I don't think one likes sounds from behind one particularly, I think you want to turn and face it. An alarm calls from behind.



Well, does that mean you're not taken with some forms of four channel? With quadrophony or whatever?


Peter Walker:

I think there are two faults with it. One is that in a concert hall you have the reverberation all around you, but all the reverberation from the back comes from a whole lot of sources that are not coherent with one another; if you sat in the Albert Hall and all the back reverberation was brought into two coherent channels, from two points, you wouldn't like it at all. All four channel must do this. This is one failure.


Reg Williamson: May I interject something? Okay, Peter, as an engineer I say to you, "Right,it's now economically possible to give you two extra channels, what would you do with them?"


PW: My view is that the extra double band ought to give you better signal-to-noise. I would certainly try to use it to give a better picture up front. think if I took this room, or my listening room at home, and could hack out the end wall and hack out a similar area in the concert hall, attach the two together so that there was the Festival Hall (of London) and there was the orchestra, I'd be very pleased with that, certainly very much better than l've ever heard in any high fidelity reproduction arrangement.


RW: This is an extension of the open window concept?


PW: Yes--it's got to be a fairly wide open window, maybe 180 degrees wide, but I don't think it necessarily has to be 360 degrees.


RW: But you have said, you know, you'd use the extra channels to increase the bandwidth and signal-to-noise ratio. But surely the two channels in existing communications media are already adequate? So we are going to give you two extra channels, what would you do with them?


PW: Well, you might do better with four speakers up at the front. One of the engineers at the French radio did this a few years ago. He has four channels, and a special microphone arrangement. It was written up, but I've never heard it.
He said this was a great improvement over stereo I think it was two speakers fairly well back and then two out here, with a four microphone arrangement. I can well believe that this would give you a better picture of what's going on in front.


TAA: Do you think quadrophony has a future?

PW: No, I don't think it has a future. I think we probably could be very sensible and reject it in spite of tremendous publicity. A lot of people have said, "This is not what we want." I don't think the multiplicity of systems or the trouble of trying to get four loudspeakers into a room are the reasons although they must have something to do with it. It's just that you don't need these sounds in the back, they're not musically very interesting.

TAA: Have you heard what would be called ambient sound where you're not aware of the back 'speakers, where you have a matrix system to derive the ambience from a stereo disc, for example?

PW: I've heard most of the demonstrations; I've never heard a good demonstration of four channel. Usually, though, if the back loudspeakers are audible at all, you don't like it. If it's not audible it's very little different from having them off altogether, except for big cathedral stuff. After having had it for a year, most people with four channel and musical ears eventually pack it up, and go back to two channels.

TAA: What area of audio reproduction is, in your opinion, most in need of work?

PW: The loudspeaker in the room combination. I think you can do loudspeakers fairly close up to a person and get very good reproduction, then you put them in a room, so far from the floor, albeit pretty near a wall, near corners, and a lot of this gets ruined. We'd like to get over that. It's a difficult thing to do.

TAA: You're not planning to market high-fidelity rooms, are you?

PW: No, I don't think you can alter the room very much, that's not very practical. Various people are trying. They say: well, you've got this transfer function through the room, you can put all this in a computer and suck it out first. It's very difficult to do, but that's what one would like to do. I think you'd like to get the first arrival sound from the loudspeaker to your ears and no reflections for at least ten milliseconds. Then I think you could get a good picture. I think it's these early reflections that become confusing.

TAA: Is the path to that goal, then, with headphones perhaps?

PW: There is, I think, possibly a future in headphones if the material is recorded through an artificial pinna. (The shape of the outer ear.)

TAA: A dummy head?

PW: Yes. Then to do it properly I think you've got to use the pinna of an actual person--there's a lot of difference between the pinnas of people and according to Schroeder's theories, if it was recorded on a dummy head with your own pinna, or with microphones in your own eardrums, then it can be very good. But if it's somebody else's pinna you lose all these little decays from these little reflections. There's a good article in America by Gardner. Even filling in a little gap in your ear with wax stops a lot of your up and down capabilities because you have lived with that shape for a long time.

TAA: You'd have to have a casting of your own ears, in other words, to make good "beadphone" recordings.

PW: Well, it's impossible to make records that way, because a variety of people have got to listen to them! There might be a future there, or there might be a future for some sort of close-up loudspeaker.

TAA: Such as?

PW: Oh a loudspeaker embedded in the walls of a room, such that there were no reflections. If you could produce a strip loudspeaker strictly out of a corner, then there would be no reflections because all the frequencies would be within a quarter wavelength of all its images, then you've got rid of the reflections of the room. That should be extremely good but difficult to do.

TAA: That sounds like it might be related to the early days when we all talked about infinite baffles and mounting speakers in the walls.

PW: Yes, but you can't put a loudspeaker in a corner. You can make a bass loudspeaker that goes in a corner and up to a couple of hundred Hertz all is well, but then we come to some frequencies where there's a critical distance from the wall and this is where the interference occurs. This acts as a comb filter, which puts nasty tones on.

TAA: Well, do you see anything in speaker development that is promising?

PW: Oh, that's a difficult question! I personally like to work on electrostatic loudspeakers because you've designed out a lot of the defects that are present with non-electrostatic loudspeakers. But they bring in a lot of other problems and maybe we're going to get rid of those as well. I'm not saying that this is a perfect way, but it's one way of doing things.

TAA: So you like the answer that you're getting from the electrostatic?

PW: So far, yes I think that in the next generation one could do better still.
TAA: Your electrostatic is now almost 25 years old and you're still making essentially the same device?

PW: Yes. We could make a better one but it would be too difficult to manufacture, to make them producible. It's very easy to have two people stretching skins round and make one sample sound very good. But these days you've got to make a thing that you can set up in production and off they come out at the end of the line all the same without any variation. They've got to be reliable, they've got to last, the plastic mustn't shrink, it mustn't spark, or break down. They're the difficult problems.

TAA: Surely the new plastics have helped, though?

PW: Not in the last 20 years. For plastic diaphragms, you've got to have something that's very stable and the only stable diaphragms have a high Young's modulus, which means they don't stretch very much. This makes it very difficult to mount because whatever you mount them on must not stretch very much. If the mounting moves with temperature and humidity, then the resonances move. That's the difficulty about this, there's no elastic material that is stable, that I know of. The more elastic they are, the less stable they become. It's just the way of the world.

RW: When you originally designed the first ESL unit, did you envisage its use in a stereo system?

PW: It was designed as a mono device. After we made about 500 or 600, then stereo came in, and it was modified to give a better horizontal directivity because of the interferences on stereo.

RW: Are you satisfied with it as a component in a stereo system now, or not?

PW: Oh no. No, we think our loudspeaker very poor, but we think that the others are even poorer! But not all of them, no. The others have really improved their loudspeakers a tremendous amount in the last 21 years. When we first brought out ours people said, "It's a dreadful thing, it shows up all the buzzes on the records, the sensitivity's way below anything else, and it has no bass." We don't get these complaints now because all the others have become low sen-sitivity, all the others have got extended frequency range which shows up the tracing distortion and the buzzes. And all the others now sound more like ours!
That sounds awfully arrogant, but they've got very much closer. You can now put a good moving coil loudspeaker and an electrostatic side by side and there's much less difference now than there was 20 years ago. Our ESLs are thought more of now than they were 20 years ago.

RW: It's a fair comment, anyway, that the ESL was for a long time regarded as the standard to aim for, wasn't it?

PW: Not in the early days, it wasn't-most people didn't like it. Well, the engineers and loudspeaker designers simply said, "there's something nice about this,“  but the public didn't like it. It hadn't got the bass, the fullness of the big corner concrete horns that went woof in the night, you know--it hadn't got these things.
It couldn't shake the windows, which was the criterion in those days. Well, it wasn't very good at that, you see. No, it's thought of more highly now than it was ten years ago, by the general public.

TAA: For people who would like to use your speakers as mid-range and high-end reproducers- do you make suggestions about what they might add for moving-coil supplement below 100Hz, say?

PW: We try to keep out of it. Two or three people have made good attempts at this, adding woofers. It's not that easy to do. Initially it's quite im-pressive, but to try to give this a homogenous sound is difficult. Another thing people do is to use two of our panels, one above the other. This is quite reasonable because it is really a strip source, you can extend the strip source without deteriorating anything. All you do is add 6dB at the bottom end and 3dB everywhere else. It gives you a louder sound, a more impressive sound. That's all right. Adding woofers has never been very good.
TAA: Even with electronic crossovers and separate amplifiers?

PW: Well, one recording company, when they first started using our speakers said, woofers." A great big woofer was added, and they went with this for about five years. Finally, their recording engineer said, „We prefer it with a full range on the electrostatics for our quality monitoring. All right, so the bass doesn't get quite so far down but the whole sound of tympani and things is more natural. We'll accept this compromise as opposed to the other. Neither are right, nothing's perfect."
So its not been easy to do. Adding woofers has not been done very much in this country, anyway. Its been done quite a bit in America, and perhaps successfully. People tend to overdo it here. They say, "When the cello plays, we have to turn the woofer off." Well, that's wrong. If it's right, it should be on full time, speech and everything, but if one has to turn it off when the man announces, something's wrong with it. If it doesn't reproduce speech properly, something's amiss.

TAA: 'Have you any opinions you'd share on the relative merits of distortion tests, such as har. monic, two-tone IM, transient IM, or slew rate limiting, as clues to amplifier quality?

PW: An amplifier should, within its limits of voltage and rate of change of voltage, (which is slew rate limiting) if you keep within those two it should be very much better than any program material. These are the things that are measured at .01 per cent or .05 per cent. But what is listened to is usually a program with 2 or 3 per cent distortion in the first place. That's the least you can get on records, tapes, and such things.
Listening tests are usually not done in this region of .01 percent distortion. I'm quite convinced within that range the amplifier is just as perfect as you like to make it.
It's quite possible to put 50 amplifiers in cascade, each one into a load, potted down into the next one, and to listen to the 50th one or to listen to the first one, and the sound will be virtually the same. So I think you can make an amplifier just as good as you like, and no more different than a piece of wire. But where they vary, when these tests are done, are a whole lot of areas. To start with, you can compare one amplifier with a bass cutoff of 20 Hz. and another one that goes right down to DC. If you've got a program with a bit of fluffing going on at 5 Hz or so, the speaker cone in one case will be moving, and in the other case it won't be moving, so the sound from the speaker will be different.
This isn't really a condemnation of the amplifier, it's that they shouldn't have this 5 Hz. stuff there in the first place. So if you compare an amplifier with a straight wire, you've really got to make the straight wire have the same bandwidth as the amplifier, and the same terminating impedance as the amplifier. Once you do all these things, then the amps will be just as good as the straight wire. The peripheral effects are what get people into trouble.
You can see why you find these differences in amplifiers. You can always find them. If people test two amplifiers and say, "These sound different,“  there's no magic in it. Spend two days, maybe a whole week in the lab, and you find out exactly why they're different and you can write the whole thing down in purely practical, physical terms. This is why these two sound different, and the cause is usually peripheral effects. It is not really a case of good or bad amplifiers, it's that the termination impedances are wrong, or something of that sort.

TAA: How do you relate the merits of listening tests to instrument tests?

PW: We designed our valve (tube) amplifier, manufactured it, and put it on the market, and never actually listened to it. In fact, the same applies to the 303 and the 405. People say, „Well that's disgusting, you ought to have listened to it." However, we do a certain amount of listening tests, but they are for specific things. We listen to the differential distortion--does a certain thing matter? You've got to have a listening test to sort out whether it matters. You've got to do tests to sort out whether rumble is likely to overload pickup inputs, or whether very high frequency stuff coming out of the pickup due to record scratch is going to disturb the control unit. But we aren't sitting down listening to Beethoven's Fifth and saying, "That amplifier sounds better, let's change a resistor or two. Oh yes, that's now better still." We never sit down and listen to a music record through an amplifier in the design stage. We listen to tunny noises, tunny distortions, and see whether these things are going to matter, to get a subjective assessment. But we don't actually listen to program material at all.

TAA: How do you feel about bandwidth? Should an amplifier be limited to say, 20H. to 20kHz?

PW: All that concerns the customer is that the reproduction from 20 to 20kllz. or 21kHz or whatever the current argument is, has to be right.
Anything outside that doesn't matter, provided it doesn't interfere with what's coming out in the audio range. If an amplifier should do tricks at 50kHz. that produces something at 1kHz.,. of course the 50kHz. matters, but only from that point of view. Provided what you've got up there is not producing trouble in the audio range, then it doesn't matter. It's best to get rid of it, it gets rid of the problems.
Once you go all through the control unit, all through any amplifier design, what you've got below 20Hz, you should get rid of as conveniently as you can. Once you get above 20kHz., get rid of it as conveniently as you can. You must have tairly wide bandwidth because of the teed-back problems, but otherwise, try to get rid of extra bandwidth. From the customer's point of vIew, it helps not one bit.

TAA: some people like sputting up the signal with electronic crossovers. Do you see problems in that?

PW: It would cost more money! Provided you're not overloading, there are no advantages. If you've got three amplifiers covering three ranges, then you can run into overload with less trouble, because the bass can overload and it won't in-termodulate the high. Theretore we can get away with more distortion audibly successtully. It you're saying that an amplifier should never run into clipping, then using three amplifiers is no better than one amplifier. One amplifier with three times the power would be rather better, because at least the power can come in any part of the frequency range. So a hundred Watt amplifier covering the lot would be better than three 30 Watt ampliters, middle, bass, and treble. Because if all the signal comes in the middle, which it can do, then you're only limited to 30 Watts- -the other amplifiers are sitting idly by and you'd like them to come along to the middle one's aid, and they can't do that.

TAA: How did you first get interested in audio? What brought you into it?

PW: I've always liked music, I've always liked the technical thing. I can remember the first BBC broadcast in 1922 when I was six years old, everyone down the street was building crystal sets. What we built in the days when it wasn't too complicated.

TAA: A cat's whisker?

PW: With a potentiometer, a cat's whisker and a pair of headphones, you could get into it. The poor amateur today has got an awful job to get into it, with today's much high technology. I was born in that era when it was very much easier. One liked music, and one liked a challenge to make things sound better. I still like audio because it is a good technical challenge and it has this aesthetic appeal at the end: you've got the music. This is the reward for all the work done, it has the right balance of science and art. But it you were making nails, there's no great satistaction about sticking a nail into the wall. After you've done it, it hasn't got this aesthetic appeal that music has at the end of it all.

TAA: Do you like making things with your hands?

PW: Not very good at that these days- too impatient. I used to like it. But one's patience disappears.

TAA: Who were the audio people who influenced you?

PW: Paul Voigt was the maker of the first loudspeaker that sounded different and so much better than anything else I had listened to. What one had heard in previous days was a radiogram which was all wooly, and I suddenly, just almost by accident, heard this Voigt corner horn playing the Nutcracker Suite. Of course, there was record scratch, there was everything else, but you were also aware that a live, real-sounding orchestra was behind all that. It didn't sound like reproduced music. You compared it with the real thing instead of comparing it with the radiogram. And that sparked off my interest in audio.

TAA: And you went to concerts a good deal?

PW: Well, I used to play in a dance band in those days, which I quite enjoyed doing.

TAA: And you're still playing in an orchestra?

PW: Yes, amateur entertainment keeps your mind off the electronics a bit!

TAA: Did Voigt's speaker lead to you getting into manufacturing?

PW: No, I didn't start with manufacturing, that was after. I worked for a firm selling amplifiers. I sold an amplifier one day for thirty Pounds, and I thought, Well, I dunno, the parts here can only cost five Pounds, I could buy these parts, put it together one day and sell it the next day and make twenty-five Pounds, couldn't I? Very much better than the less than two Pounds per week I was getting at the time. So I handed in my notice and started. That was doing public address, though. I was installing a couple of loudspeakers and a microphone in a dance hall or cinema which was never very lucrative. We struggled with that for a number of years. The difficulty there was that you'd got to produce the maximum number of Watts for the minimum number of Pounds, and if people wanted a really good job they'd go to the big names like EMI or Standard Telephone.
Everything had to be tendered (bid for). People would either take the cheapest, and the cheapest bloke always lost money anyway, or they took the most well-known, which we weren't. We were in the middle.
We started in high fidelity before the war. But Paul Voigt, when he was in England, was making a much better loudspeaker than anybody else, but two a week was his maximum sale. It cost thirty five Pounds, which I suppose in present-day terms would be about six hundred Pounds. It was very expensive. But he couldn't do it on his own because there was no high fidelity market. You've got to have a lot of people making things, to get the advantage of the group advertising. In 1937 or *38 I made a high fidelity amplifier, push-pull, 25 Watt, triode, direct-coupled, with feedback. Oh yes, very good. But you couldn't really sell these things, partly because the records in those days were 78 with a lot of scratch. People said, "What's all that hiss, frying bacon noise?"
The BBC was very good. For speakers we had the Voigt, there was also an infinite baffle speaker in those days, in fact before the war, we had an acoustic suspension speaker in the Audiom 8. It had a fundamental resonance in free air of 16 Hz., and was stuck in a three cubic foot box which forced it to 50 Hz. It was an acoustic suspension speaker, and that was around in 1937 or so. But again, there wasn't a big sale for this because there wasn't a high fidelity market.

TAA: Nobody knew what good reproduced sound was.

PW: Nobody knew what it was at that time anyway. You might sell half a one a week, or one every two weeks. That's the best you could do.

TAA: What happened during the war?

PW: Well, there was no high fidelity then. We made radio coils for the army wireless.

TAA: But after the war hi-fi began to develop?

PW: I went into hi-fi as a sideline ' till the public learned to like it. You made a set for yourself, you sold these to a few engineers, about five or six a week, that sort of thing. Then of course hi-fi came in, mainly with the LP record, and since we were already in the business one could get pushed up with it doing the right thing by luck at the right moment. This is really what most of these things are about, aren't they?

TAA: You were at the right place at the right time.

PW: Absolutely, it was pure luck.

TAA: Goldmark came out with the LP in the summer of '48, I think.

PW: About then, yes. Things started to take off, and it has become bigger and bigger. It's now big business, which is not always good.

TAA: You're making some of your original products, aren't you regarded as rather a con-servative?

PW: We don't produce a new product every six months or even 12 months, no. Only two reasons for producing a new model: either you did it wrong the first time or there's been a fundamental improvement in the science. Fundamental improvements in the science come very infrequently.

TAA: You don't believe in breakthroughs, then?

PW: Well, there aren't that many breakthroughs. There are a few, yes. The transistor was a breakthrough, stereo records were a breakthrough, yes, the invention of the tape recorder was a breakthrough. Oh yes, there've been some minor ones as well, but they don't come out every six months.
But if you take the sound which was produced 25 years ago it isn't that much worse than what we produce now. We recently had a party of Japanese coming in and put on a demonstration for them of equipment that was over 20 years old.
The whole lot of it, including the records, was surprisingly good. It wasn't stereo, of course. The only thing that was wrong with it was that it was mono. It was extremely good otherwise. Perhaps the signal-to-noise was not quite as good as one can do these days, but the realism and naturalness were all there.
We used a Ferranti pickup. An excellent device.
It was made between '50 and '55, I'm not quite sure of the exact date so we played that, on a good mono record, through our prototype electrostatic speaker. But I believe you've been able to make amplifiers as good as you want, certainly for 30 years.

Mike Albinson: (Walker's Engineering assistant) If you want a subject fraught with idiocies, at the moment there's this craze that valve (tube) amplifiers are better, and that Quad II valve amplifiers are now the best, in terms of reproduction. Read through the technical press of about twelve years ago and you will learn that transistors are much better than valves and the valve amplifier is dead on its feet. Now today it is having a grand revival!
It's fashion- -there's no reality to it. A modern transistor amplifier is better on any count you care to mention than the Quad II was, with the possible exception, that if you must go and overdrive the thing, then the valve amplifier does show marginal differences. There have been a few bad transistor amplifiers. It's easier to make a bad However yarn hide the valveadplite, me phies; hum or something, but usually it was reasonably linear.

TAA: It is much more forgiving, too.

PW: Much more forgiving, yes- much easier.

TAA: Do you think Quad will be making a 200 Watt per channel amp?

PW: We can if we want to, but that means loudspeakers have got to get even less sensitive. You've still got to get rid of the heat off the speech coil, and in some of them, don't forget, the speech coil resistance doubles in value even with the heat we have at the moment. Think what that does to the termination of the crossover network. That's exactly the same as sticking another eight Ohms into the speaker lead, for a single speaker. So the damping factor has gone from infinity down to one, hasn't it? So it's getting very near the limits unless you use a lot of units, and multiple units have directivity problems. Making louder loudspeakers is hitting the limits at the moment.

TAA: What's the origin of the Quad name?

PW: It just came about by a quirk. One Amplifier we made was a QA12P, which was a Quality Amplifier 12 Watts with Preamp. People used to get it the wrong way round: "Can I have one of your 12AXPYs?" you know. So when the next one came along, we said, "We may as well make it make a word, they'll remember that," so QUAD's been stuck to it--Quality Amplifier for Domestic Use. So it was Acoustical Manufacturing Company quite a mouthful that is--type QUAD. So people called it "Quad,' and then they started to call us the Quad Company. And we really thought we ought to change our name from Acoustical to Quad, but we didn't do so. Perhaps it is just as well with all this four channel around.
Award - Peter Walker with Prince Philip
Award: Peter Walker with Prince Philip