Institute of Acoustics Rayleigh Gold Medal Address: 1976

Journal of Sound and Vibration (1977) 50(2), 163482

INSTITUTE

OF ACOUSTICS RAYLEIGH GOLD MEDAL ADDRESS : 1976t P. H. PARKIN

Building Research Station, Garston, Watford WD2 7JR, England

(Received 17 June

1976)

In March 1940 I received a letter headed, simply, “Admiralty, S.W.1” and which started impressively “Sir, I am commanded by My Lords Commissioners of the Admiralty to inform you that they have sanctioned your appointment . . .” and which ended impressively “I am, Sir, Your obedient Servant”. The part in the middle was not so impressive because it was offering me a job as a Temporary Experimental Assistant grade III at a fixed salary of ;f230 per year. (I had a London degree. Comparing notes later with colleagues it appeared that if I had had an Oxford degree I would have been offered ten pounds a year more. I do not know what I would have been offered if I had had a Cambridge degree.) At that time I was halfway through my Ph.D. on the dielectric strength of air at high frequencies. My college had been evacuated and we few Ph.D. students had the buildings to ourselves and seemed cut off from the momentous events taking place in the world. I was very glad to go to the Admiralty, and this appointment was to prove my first introduction to acoustics. These opening remarks illustrate the type of address I am giving. My first thought when I heard that I was to receive the medal was, what can I talk about? It is some years since I have done much work on noise or sound insulation; I could attempt a learned review of room acoustics but I am not much good at reviews, nor very learned. So I decided to describe some of the more-1 hope-amusing minor events which have occurred incidentally to my work since I received that letter in 1940, and to touch briefly on the changes I have seen in this field since then. This lecture may be a little on the light and anecdotal side, but this does not mean that I do not deeply appreciate the honour the Institute has paid me. We are all familiar with the lecturer who says I have done this or that when he means he and his colleagues have done it: when he says we have found this or that one is not sure whether he is referring to himself and his colleagues or to the whole human race. Throughout this address I have tried to avoid this, but it will be impossible for me to acknowledge individually the help I have had from many colleagues over the years. But at the start I must thank those colleagues of mine who have worked with me in the Acoustics Section at the Building Research Station for at least 15 years, namely, Messrs Fuller, Heppell, Morgan, Purkis, Pursell, Scholes and Stacy. When referring to individuals I will give them the titles they had at the time, and-as Anthony Powell has put it-will “use that excellent masculine invocation of surname, before an irresponsible bandying of first name smothered all subtleties of relationship” (from Books do Furnish a Room). t The 1976 Rayleigh Gold Medal Address was delivered at the Annual Spring Meeting of the Institute of Acoustics, 12-15 April 1976, in Liverpool, and is being published in the Proceedings of the Institute of Acoustics. In continuation of the tradition established for the original Rayleigh Gold Medal Addresses of the former British Acoustical Society, it also is being published here in the Journal of Sound and Vibration, by arrangement with the Institute of Acoustics, to make it available to a wider audience. 163

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Returning to 1940. I was posted to the Minesweeping Division of HMS Vernon at Portsmouth which was headed by Dr E. C. Bullard, F.R.S. This Division had been responsible for the success in sweeping the German magnetic mine and at the time I joined-as a very junior member-the main problems of magnetic sweeping had been solved. However, a few weeks later the German acoustic mine appeared and this raised a large number of new sweeping problems. At that time I was on more or less routine magnetic measurements at Southampton and it was obvious to me that I was in danger of being left there and of missing all the excitement. So I managed to get an interview with Dr Bullard. It was obvious that he was very doubtful whether to take me on or not, but by rather exaggerating how much I knew about CROs he was finally persuaded. The war was of course a vast tragedy for millions of people, but I was lucky to have six years of extremely interesting work, and to work successively under three very clever people, Dr Bullard already mentioned, Dr K. Roberts, F.R.S., and lastly Mr Alan Pickles, who as you know played a large part in founding the Acoustics Group of the Physical Society after the war.

Figure 1. Air-sea rescue float.

This brings me to my first piece of advice to young men, and women : choose carefully the people you work for. The best sort are clever and hardworking; the next best are clever and lazy; then come the stupid and lazy ones, and worst of all are the stupid and hardworking. As I have just said, I was lucky to work for three clever and hardworking men. Those were my “Salad days, When I was green in judgment”, but they were undoubtedly the most formative of my life, when I learnt more than I had ever done before or have done since. Of course wartime conditions were very different from peacetime conditions. In 1941 the acoustic range at Portsmouth for measuring noise from ships was destroyed by bombing, and we were able to build a new range at Innellan on the Clyde within a few months. By present-day standards that now seems a fantastic achievement, although at the time it seemed rather slow. Tht first article I ever published [2]t describes this range and the second [3] described another range at Falmouth which was built later in the war mainly for measurements concerning the sweeping of pressure mines. Figure 1 shows the air-sea rescue float which was moored in Falmouth Bay and which was used to join the permanent two miles long cables t Numbers in square brackets refer to publications listed in the Chronological the paper.

Bibliography at the end of

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8.25knots

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of mtor

Figure 2. Contours of pressure change of a large motor vessel.

from the shore to the temporary cables going to the measuring units, and Figure 2 shows a typical ship’s pressure signature. Of this period I just want to mention two pieces of work, the first of which was the explosive sweep Mark I. Perhaps I should explain that acoustic mines have about the right sensitivity to explode under a normal ship, and are swept by a mine-sweeper making a very much louder noise so that the mines explode safely ahead of the sweeper. The next step by the enemy is then to introduce a percentage of insensitive mines which explode under the sweepers. So the next counter-move is to make a very much louder noise still and by this stage the only way to make a loud enough noise is to use explosives (this description is a considerable simplification). One loud bang is no good, because acoustic mines contain circuitry to stop them all exploding when the first one explodes. It is necessary to make a loud enough noise for a few seconds, and thus the explosive sweep Mark I came into being, which consisted simply of fitting fourteen hand grenades, with their safety pins removed, into a tube. They were then all pushed through the tube over the ship’s side into the water and exploded consecutively making a loud and long enough noise to sweep the insensitive mines at a safe distance. A very simple device, but effective, and I understand that it was used extensively during and after the war, the consumption of hand-grenades perhaps running into the millions. The second piece of work concerned a tunnel under the English Channel. At one time during the war it was thought possible that the Germans might dig, undetected by eye, a tunnel under the Channel thereby providing a rapid road for their tanks, provided that their aircraft could hold a small area of south east England where the tunnel emerged plus the “embarkation” point on the French coast. I was sent to investigate possible methods of detecting such tunnelling activity. A bomb disposal squad used various tunnelling equipment in the part of the Channel tunnel near Dover that had been started many years before the war, and I tested out various detection methods to see how far away the operations could be heard. We found that only six listening posts would give adequate coverage but it was by then decided that the Germans would not be building such a tunnel so the listening network was never set up. I suppose that-of the wartime work-one could say in modern research organizational terms that Hitler was our customer! At the end of the war I could have stayed in the Admiralty, but I had already spent six years of my young life helping to win one war, and did not want to spend the rest of my life getting ready for the next one. Also, I did not particularly want to continue in research, and had some rather more exotic ideas in mind. But at that time it was not easy for people of my age to get a job, largely because most jobs were reserved, quite correctly of course, for men who had held the jobs before the war and were being demobilized. I applied for a large number of jobs, and eventually was very pleased to hear that Pickles was going to B.R.S. and that I could go and work there, a move I have not regretted.

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Mr Allen had already been there some time, and there was a sound transmission laboratory, and three blocks of flats for sound insulation studies were being built, named Bagenal, Rayleigh and Sabine Houses, the initials thus being B.R.S. Up till then N.P.L. had made the actual measurements, but from 1946 onwards we undertook this ourselves. We started a large survey of the sound insulation of houses and flats, which has been fully reported, but I just want to mention that the standard in this country for sound insulation between dwellings was really set in 1667 when after the Great Fire of London it was laid down that houses must have party walls of brick or stone of various thicknesses (depending on the height of the building). Thus until quite recent times all party walls provided a reasonable sound insulation. Floors present a rather different picture and I was astonished to discover what elaborate measures had been taken to get good sound insulation in floors between tenements in Glasgow built about the middle of the last century (see Figure 3(a)). It should be realized that these elaborate structures were used in buildings deficient by modern standards in many things such as running cold and hot water. In later times party floors had fallen to about 30 dB insulation compared with the 50 dB insulation in the old buildings (see Figure 3(b)). Of this low insulation, Mr Bagenal once remarked : “Not only can you hear babies being born, you

Thick lath and plaster I% in x 2111 Battens

(branders)

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LIImx 3 m Jalsts Split pugging boords

6m Ash pugging

Figure 3. (a) 1850 floor ; (b) 1950 floor.

can hear them being conceived”. Many years ago Mr Allen used to live in a flat with this type of floor and in fact it had the lowest insulation of any of the 464 forms of construction measured by B.R.S. and described in Research Paper No. 33 [45]. No wonder he has always taken a keen interest in sound insulation. In these early years for me at B.R.S., the U.K. government was pursuing a policy of letting research contracts to German Universities to help them re-establish themselves. I was concerned with contracts on sound insulation with Giittingen University, and its then very distinguished Director was the first recipient of the Rayleigh Medal, Professor Erwin Meyer. Another distinguished name was Professor Lothar Cremer and through these contracts Professor Cremer’s attention was first directed towards sound insulation, which led, as we all know, to big advances in that subject. The B.R.S. did some collaborative research with Meyer eventually leading to a joint paper [12]. Meyer told me once about Hitler’s plan for his proposed Palace of Nazis. Immediately at the end of the war I had been with a team investigating the state of electroacoustics in Germany [l], and we had heard rumours of an 8 million cubic metre hall (about 100 times the volume of the Royal Albert Hall). Hitler’s instructions to the architects laid down that the hall was to be twice as big as the Palace of the Soviets, it had to last 1000 years, the ruins had to look beautiful and the whole of the interior had to be lined with marble. This resulted, Meyer told me, in a reverberation time of one and a half minutes. Meyer’s solution to this would have been to perforate the marble.

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Figure 4. (a) Mobile laboratory

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on board ship; (b) mobile laboratory

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in Holland.

I have calculated that it would have taken about 10 000 man years to drill the holes in the marble. Many other foreign contacts rapidly developed in this period: with the U.S.A., particularly with Professors Bolt and Beranek; with Denmark (Professor Ingerslev); Holland (Professor Kosten and his colleagues); and France (Professor Canac) and with many others. One result of these informal European collaborations was a standard European method of measuring sound insulation [4], a standard method which is still in force today although-in my opinion -it sadly needs improving. Our contacts with the Dutch were particularly close and we visited

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Delft several times, taking our mobile laboratory with us (see Figure 4). as we had also taken it to Gbttingen. Many years later this co-operation continued when Delft and we were designing our anechoic chambers (those status symbols). My one-time colleague Stacy visited Holland to discuss the design with Dr van den Eijk who was to meet Stacy at the airport. As they had not met before Stacy wrote and asked him how he would recognize him and van den Eijk told him not to worry about this. When Stacy arrived at the airport there was van den Eijk clasping a 4 foot anechoic chamber wedge to his bosom. It was on one of the earlier visits to Gbttingen that I met Haas and heard about his now famous work on speech delays. It was I who proposed the term Haas effect to the B.S.I., on the grounds that Haas was the first to quantify this effect: i.e., the apparent direction of the source being determined by the first arriving sound. There was some feeling, particularly in the U.S.A., about calling it this because the effect had been noticed many years earlier [57]. But I still hold that it is correct to name effects after the first person to quantify them, as Haas was, My only regret is that I now think it should have been called the Haas/Meyer effect. I have often wondered why the ear and brain act in this way. Perhaps it was a development which took place in our cave dwelling days; when the sabre-toothed tiger roared at the entrance of your cave it was literally vital to know where the tiger was and not be confused by the subsequent echoes in the cave. All those who could not distinguish between the first arriving sound and the echoes did not survive. We were to employ the Haas effect in the speech reinforcement system we were then working on for St Paul’s Cathedral [18]. (We had prepared for this work by previous experiments in the L.C.C. open-air theatre at Finsbury Park, in Harringay.Arena during performances of “Rose Marie on Ice”, and in the Coliseum Theatre during the run of “Kiss me Kate”.) Dr Brtiel, last year’s recipient of the Rayleigh Medal, was to visit us at St Paul’s one evening, but was late and got locked out. Nothing daunted, he climbed over the high spiked railings round the Cathedral and found us. One can see why his firm has been so successful. The St Paul’s system received a lot of publicity and I had a letter from Professor Meyer which said : “As you perhaps remember I am a permanent subscriber of the Daily Telegraph, which I get only one day later as the date of the issue. Today I discovered your nice picture

Figure 5. Mobile laboratory on site for the Royal Festival Hall.

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Figure 6. Measuring sound insulation on the Royal Festival Hall roof.

showing you firing a pistol shot in St Paul’s Cathedral. I congratulate you, for in the normal issue of this paper I find at this place only photographs of Princess Elizabeth, Mr Churchill or of persons of a similar rank! Apparently Acoustics is a science highly estimated now in your country”. Also during this period we undertook to be responsible for the sound insulation of the South Bank Concert Hall, i.e., the Royal Festival Hall, against the noise from the trains over Hungerford Bridge and from the underground trains which passed directly underneath the site. We measured the noise from the Hungerford Bridge trains in 1948 (see Figure 5) and the insulation of the Hall was designed accordingly. When we re-measured the noise in 1951 when the Hall was completed we found it had dropped by about 20 dB and this was because in 1948 the rails had been corrugated-apparently a well-known railway phenomenon-and by 1951 new rails had been laid. We were lucky: it could have happened the other way round. As it was, the sound insulation of the Hall was adequate (see Figure 6) and, as someone remarked at the time, we successfully stopped train drivers on Hungerford Bridge hearing snatches of Beethoven as they passed by. I was luckier still with the noise from the underground trains. We had measured the vibrations in the ground and then hopelessly miscalculated the amount of the noise that such amplitudes of vibration were likely to produce in the auditoria. (I do not think that even today there is any reliable way of calculating such radiation.) What is now Queen Elizabeth Hall adjacent to the Festival Hall was at that time planned to go underneath the Fesitval Hall, i.e., just above the tube trains. The pillars which support the Festival Hall auditorium are in fact separate concentric constructions so that the inner parts carry the weight of the Festival Hall and the outer parts were to carry the weight of the Queen Elizabeth Hall. This was to give adequate sound insulation between the two auditoria. In the event, it was decided that there was not time to design and build the Elizabeth Hall there, and if you now go into the basement of the Festival Hall where the Elizabeth Hall might have been, the noise from the tube trains gets up to about 60 dB(A). If the Hall had been built there, that would have been a short sharp end to my career in acoustics. I mentioned earlier the speed with which things could be done in the war, but the construction of the Festival Hall was no less remarkable (see Figure 7). Design work started in 1948 and the Hall opened in May 1951, and this in spite of all the shortages of materials resulting

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lb)

Figure 7. (a)

Royal Festival Hall site in 1948; Royal Festival Hall (b) in 1950 and (c:) in 1951.

from the war. Great credit goes to Mr Robert Matthew, Dr Leslie Martin, Mr Peter Moro and Mr Edwin Williams, backed as they were by the Architect’s Department of the London County Council. Of them, one could say as the German proverb has it-“Mit Ihnen kann

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man Pferde stehlen”. (With them one can steal horses.) Both the Colston Hall, Bristol, and the Free Trade Hall, Manchester, were re-built during the same period. It was about this time that the famous firm of Bolt, Beranek and Newman was formed. There was some question of Mr Allen and me being associated with them but this did not go ahead. If we had joined them then today I would have been either rich or dead, probably dead, because I doubt if I could have stood the strain over the years of such a high-powered and successful organization. I have always been bad at theory; this might be due to bad teaching or more likely to a natural inaptitude for mathematics. I must be the first recipient of the Rayleigh Medal who cannot easily get past Chapter I in the Theory of Sound. Of necessity this means that I have always adopted an essentially practical approach to all research, and have tried to make a virtue of it. I like to quote Leonardo de Vinci who said “. . . those sciences are vain and full of errors which are not borne from experiment, the mother of all certainty”. Impressed as I am by elegant theories, one must remember that they are not always right. During the war, theory very much underestimated the effect of the swell in the English Channel on the pressure mines laid by the Germans, as was discovered when an actual mine was recovered and tested by me in the Channel. (Incidentally, having discovered this I then spent all day trying to get through to Pickles in Edinburgh on a secret line, but eventually had to use a public call-box. I mention this as an advantage of working with clever people: Pickles quickly understood what I was trying to tell him in a very guarded language.) In more recent times, I notice that some theoretical work has predicted noise reductions by barriers (in the open air) of more than 100 dB. Noise is not a new problem. There are many references to it in the past. For example, in about A.D. 110 Juvenal wrote (translated by Peter Green, Penguin Classics 1967) : “Insomnia causes more deaths amongst Roman invalids than any other factor.. I How much sleep, I ask you, can one get in lodgings here? Unbroken nights-and this is the root of the trouble-

Are a rich man’s privilege. The waggons thundering past Through these narrow twisting streets, the oaths of draymen Caught in traffic jams--these alone would suffice To jolt the doziest sea-cow of an Emperor into Permanent wakefulness.” However, modern noise problems must be worse than they have ever been in the past. Even if one agrees, as I do, with Mr Attlee that the invention of the internal combustion engine was the greatest disaster to befall mankind, there is no doubt that it has given a great impetus to research into noise, and without the jet engine there would not be an I.S.V.R. Whatever the reasons, there has undoubtedly been an enormous expansion in the U.K. of the number of people researching into noise. A Special Correspondent writing in The Times in 1955 said [31] “It is doubtful if more than one dozen scientists (excluding otologists) are engaged in this country, whereas in America there are some 500 . . .“. Looking back I think that the figure of about one dozen was probably a bit of an under-estimate. Nevertheless any discussion about numbers today would be about how many hundreds are working on the subject, not about how many tens. And there has been a big increase in the number of journals: Acustica, and the Journal of Sound and Vibration and Applied Acoustics in the U.K., the first issues of all these three journals being distinguished by a paper by us, as in fact was the first issue of Noise Control. One of the biggest changes over the years I have seen in the subject has been in instrumentation. When I first started at B.R.S. condenser microphones were extremely rare and had to be bought at enormous cost from the U.S.A., and certainly could not be used in the rough and tumble of field work. Moving-coil microphones were the most commonly used but-by

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modem standards--their frequency response was far from flat and you either had to have them calibrated at N.P.L. or do it yourself, e.g., by reciprocity. Further, you had to design and build your own measuring amplifiers. Nowadays there is a complete range of sophisticated equipment. We at B.R.S. had one of the first six B & K level recorders ever made, and the first one in the U.K. This range of new equipment has undoubtedly been an enormous advance but perhaps not all gain and I do have two slight reservations. The first is that in the days when you had to calibrate your own microphones and build your own amplifiers then this acted as a sort of high-pass competence filter and weeded out at least some of the more incompetent people, whereas nowadays anyone with the money can buy this beautiful modern equipment and may proceed to get wrong answers at high speed. The second reservation is that some people at least tend to trust too much the infallibility of their instruments. I always insist that when making measurements people should not just trust the meter, digitalized or not, but should always either listen to what they are measuring or should look at the wave-form, thereby ensuring that they are not perhaps measuring hum or crackle with great accuracy. Another big change has been the rise of the dB(A). In the first edition of the book Acoustics, Noise and Buildings, by Parkin and Humphreys [34] it said (in 1958) about the sound level meter-“Because of the severe limitations of this simple type of apparatus the ‘A’ and ‘B’ responses are tending to go out of use”. Later we altered this to-“. . . if the ‘A’ weighting response is used, for all loudness levels, then for several types of noise the reading of the meter can be converted into loudness . . . with accuracy sufficient for most practical purposes . . .“. Brought up as I was on sones and phons (of various types, e.g., Zwikker, or Stephens) I was astonished to find how useful dB(A)‘s could be [49] (not however used as originally intended) and their simplicity did make it much more practicable to frame various regulations in a form which could be used by the non-specialist, compared with the previous labours of frequency analysis and re-combination into phons, or at least loudness units of some sort. There are some fields where the dB(A) can not easily be used and with the capabilities of the modern computer the simplification of the dB(A) is not so important, and indeed no doubt we are moving away from it in research and back towards more complicated-but now handleable-techniques which can allow for all the frequency-dependent factors. dB(A)‘s have been very useful, and so have the techniques of describing the variation of dB(A) with time, e.g., L1,,, or Leq, a type of system first proposed I believe by van den Eijk. (I would give the reference except for my resolution to indulge myself and give nothing but references to work published by me, or rather to work in which I have had a hand, and to include in the references everything I can ever remember publishing.) During the war we used to say that underwater acoustics would be easy if you did not have to keep the water out; nowadays we say that building acoustics would be easy if you did not have the subjective problems. There is a grain of truth in both these statements for it is still very much a problem how to relate subjective results to the objective measurements: in other words to decide what effects noise is having on people. If one is concerned with what I might call straightforward physiological effects, e.g., the loudness of pure tones, then accurate laboratory tests on the requisite number of people are obviously satisfactory. Similarly one can measure in the laboratory the effects of noise on the performance of tasks, but even this has already become more complicated than might appear at first sight. But it is when we come to the situations where passions might be aroused, e.g., the noise from next door, that we get into serious difficulties about assessing the effects. My own belief is that these situations cannot be judged in the laboratory by using panels of listeners, however carefully selected. I suspect that what you are really measuring is how good people are at imagining themselves to be in the “real” situation: e.g., how good they are at imagining they are in bed at home trying to get to sleep with a noisy television or radio next door. Noise is an additional stress on top of all the other stresses of life. As Bagenal once remarked, we walk down a street assaulted by a

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thousand primitive calls to action. So what does one do? I have always gone for the social survey approach but have always made the reservation that the answers are merely what people said when asked these questions, and are not necessarily the truth. And of course there are so many variables in the real life situation which will affect people’s reaction to noise. The panel in the laboratory measures the wrong thing very accurately, while the social survey technique measures the correct thing very inaccurately. Even so, surveys of this kind can only be a help towards making the decisions that have to be made. For example, the survey we did of the opinions of people living in three blocks of flats with different degrees of sound insulation (averages roughly 50,45 and 40 dB) showed that the people living in the flats with the lowest value of sound insulation were least disturbed by noise from their neighbours and a whole appendix in the report [38] had to be devoted to explaining this odd result. (Their imperturbability seemed to be due to their having moved from very much worse conditions, albeit some years before, and also that the density of occupation was much higher.) While on the subject of social surveys, before the three major concert halls were built after the war, i.e., the Festival Hall, the Colston Hall and the Free Trade Hall (there was to be a fourth, the rebuilt Queen’s Hall [30]), we sent a questionnaire to as many professional listeners, e.g., music critics, as we could find. As we have always found with questionnaires, the response was good, and Liverpool Philharmonic was generally thought to be the best of the then existing British Halls. We did get one rude answer, which said-in part-“The best recommendation I can give in the matter of concert-halls is that your department should close down as soon as possible: the free life of England may again flourish and will be able to express itself in music; until which time we shall continue to be dependent upon music made in Germany and performed by Jews”. When it comes to a question of making laws or regulations or recommendations, then measurements and social surveys are a help, but a limited help, because there are usually so many other factors involved in any noise problem, e.g., cost; someone has to make a judgment, and who should this be? It seems to me that the Wilson Committee was an excellent idea. The experienced people on that Committee made various recommendations in the light of the evidence presented to them so there was a set of authoritative recommendations on which administrators and the like could act. If the Wilson Committee could meet every few years to review their recommendations each time then we would have a reasonably stable set of recommendations to act upon. Ideally one would have a graph of noise levels, or whatever it may be, for each type of situation against likely human reactions to them so that those responsible for making recommendations can decide where to draw the official line. We tried to do this on standards of sound insulation between flats where we said [28] that Grade I would mean that noise from neighbours was negligible, Grade II (5 dB lower insulation) would mean that noise from the neighbours would be the worst single feature about life in the flats and that lower than Grade II the authorities could expect very serious complaints and deputations. The choice was thus put formally to the authorities concerned, but as far as I know nobody ever opted for anything less than Grade I, or if they did they never spoke about it. Whatever laws or regulations are made, certainly where building design or town planning or similar problems are concerned, the regulations must not be so complicated or call for such complicated measurements that those responsible just give up. This has happened in the past. Yet on the other hand the regulations should not be so loose, nor have such wide tolerances, that they are ineffective. There is plenty of scope for future work here. As I have already mentioned, ideally one would have a graduated system. For example, when we worked on the insulation of houses against aircraft noise, our original suggestion was that those worst affected would get 100 percent grants for insulating their houses, and the percentage granted would be less for houses further away, but this was just too complicated to administer. I want to give two examples of the rather unexpected happening in real life noise problems,

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which would not have shown up in a laboratory situation. The first example concerns the effect of aircraft noise on schools. Obviously teachers would be likely to raise their voices as aircraft passed and this could have been assessed in the laboratory situation (although even then it would not have been known how much they could raise their voices during a day without getting too tired). The unexpected factor in the real life situation was that from experience the teachers knew what sort of aircraft was approaching, and how loud it was likely to get. If it was a comparatively quiet type, they knew that even when at its loudest they would still be able to talk above it, so they continued to teach. If they knew it was a loud type, they knew they would eventually have to stop teaching no matter how loud they shouted, so they stopped teaching almost as soon as they heard it coming. So in effect the louder the aircraft type, the quieter the level at which the teacher stopped. This would not have shown up in a laboratory situation, and certainly standard intelligibility tests would have meant very little. The second example concerns experiments about the introduction of background noise using loudspeakers into an open plan office [72]. One of the noises tried was a tape of office noise, doctored so that it was fairly uniform in level and so that practically no speech was intelligible. Listening to this noise at the weekend in the empty office I thought that at last we had found the noise which stood a good chance of working: i.e., of being loud enough to mask conversations in the office without being a distraction. I was completely wrong. Nearly all of the occupants of the office regarded this noise as an alien office suddenly put over their heads, and reacted violently against it. In fact the dissatisfaction with the noise climate in the office went up to a record 80 percent. I mentioned earlier aircraft noise and schools. One good idea I had was the acoustic window: i.e., a window which shuts itself automatically whenever the noise goes above a certain level (see Figure 8). The conventional way of insulating schools against aircraft noise is to install double windows and artificial ventilation. These permanently closed double windows mean that the school is virtually sealed off from all outside noises, and some noise from outside is desirable, for psychological reasons as well as providing a reasonable background noise. Also, if the classrooms face south or west they really need full airconditioning if they are not going to get too hot in summer, and this is expensive, particularly if it has to be installed in existing buildings. So we thought that a window which shut automatically would get over the insulation problem, and would be a lot cheaper. We installed one

Figure 8. Acoustic window.

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experimentally in a school near Heathrow. The teacher had an overriding control (the window did not have to be open just because it was quiet outside) and could also control how far the window did open in quiet periods (which make up most of the day even near Heathrow). It took a week or two for the staff and pupils to get used to it but after that it worked very successfully. It received a lot of publicity at the time, and we had over five hundred enquiries from people thinking of trying one. Yet it has been a complete flop, not a single one having been installed after our original experimental one (which is still there after ten years, opening and shutting, and requiring little maintenance). I do not know why this has been. We were unfortunate in the arrangements we made to get the window made commercially, and in fact there never was one for sale. Nevertheless, one would have thought that somebody would have made them. I still think it is a good idea. For some years we worked on sound propagation in the open-air, starting with vertical propagation using an aircraft flying over B.R.S. at various heights [26], then going on to oblique propagation using a helicopter flying along the Thames and recording the noise levels at various roof-top sites [36]. Later we worked on horizontal propagation at Radlett Airfield [48] and at Hatfield [50,52] with help from the firms which owned these airfields, and making our own local meteorological measurements. The only noise source loud enough to measure propagation over useful distances is a jet engine, and we bought a Swift aircraft (Figure 9) from the appropriate Ministry for a nominal sum, although our idea of what was nominal differed by a factor of ten from the Ministry’s idea. These horizontal propagation trials showed up the ground effect, which at first we did not believe, thinking there was something wrong with the measurements, but by listening to the jet noise at a distance one could plainly hear the gap in the spectrum. In those days our research programme was less formally planned than it is now, and the broader range of topics looked at, if only very superficially, did help with another part of B.R.S.‘s functions, which is to give as much advice as possible to enquirers, and even today when there are so many consultants in the field, B.R.S. in matters of noise, sound insulation and acoustics still answers in one month about two hundred telephone enquiries. The many other subjects B.R.S. deals with are often a help when replying to enquiries and my own favourite reply-illustrating this multi-disciplinary approach-concerns how to reduce noise made by rain in tropical countries on corrugated iron roofs. The answer, as I remember

Figure 9. “Swift” jet aircraft for propagation measurements.

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it, was that the best way was to place thatch over the top of the corrugated iron but then one had trouble with birds, particularly owls, nesting between the thatch and the corrugated iron and making as much noise as the rain. The birds could be driven out by banging on the inside of the roof and could be shot as they flew out but you had to remember that they were sliding down the roof before they took off and were thus flying at a greater speed than was usual and you had to allow for this when aiming. On the more formal research side it was always di,fficult to decide what to do, and such decisions are no easier today. During the war I remember Dr Bullard remarking that any fool could have an idea. I was a little hurt at the time but 1 can now see exactly what he meant. The problems are: how much effort is it worth putting into your good idea; how long should you continue if the preliminary results are reasonably promising but not overwhelmingly so; are you following the right path or should you turn off this way or that way, etc., etc. And then when the work is done, where do you publish it? Obviously, anything you publish in such respectable journals as the Journal of Sound and Vibration or Applied Acoustics is vital for your scientific reputation and when it comes to getting jobs in Universities or the Scientific Civil Service. However, with applied research-which is what I have done all my life-it is important to get it actually applied and thus one must publish in the journals most likely to be read by the people, e.g., architects, who might apply your work, even though these journals -highly respectable as they will be in their own fields-do not carry the same weight in one’s Curriculum Vitae. I suppose the ideal solution is to publish in both areas. One point about publishing in these other types of journals is that the Editor is likely to alter your English without consulting you. This is very irritating if, as I have to do, you have worked hard to get your English reasonably clear and simple (I write naturally in a verbose way), or if you have put in little bits which you think will interest or amuse your readers. In an article in the Wireless World [18] about the speech reinforcement system in St Paul’s Cathedral (which was the first to use loudspeaker columns and time delays based on Haas), Mr P. Taylor and I had originally written a rather elegant-we thought-first two or three paragraphs describing the Cathedral and Wren’s thought about acoustics, only to have it shortened to “Though the 17th-century architect, Sir Christopher Wren, showed some interest in acoustics and sound insulation . . .“, and, more recently where I had written in the Architects' Journal [66] about assisted resonance that the use of it might give you “two halls for the price of l-1 “, it was altered to “two halls for perhaps only 10 per cent more than the price of one”. Your title might also be altered. One article [47] I wrote about assisted resonance and acoustics for the New Scientist had its title altered-without consulting me-to “Warming up the Royal Festival Hall”. This was classified by B.R.S. Library under heating research. Further, with applied research it is gratifying to get your work applied although this means a lot of unappreciated work. I can claim that quite a lot in the Wilson Committee report was based on B.R.S. work, but this is no help to the author in any citation index. One of my failings has always been, and still is, an inclination to put off writing up work for as long as possible, in some cases never getting round to writing it up at all. I have already mentioned the propagation work we did some years ago. Also at that time we were working on the directivity of the noise emitted by jet aircraft in flight (see Figure 10). We had various jet aircraft flying low over a row of microphones. One minor technical trick we used which I have not seen reported elsewhere was to feed the microphone signal first to a level recorder and then feed the signal from the slider of the level recorder to the tape recorder. In this way the signal-to-noise ratio of the tape recorder is increased by the value of the level recorder potentiometer, say 50 dB. I very much regret not publishing all that work, and I really should have published something on the acoustics of the Colston Hall, the Fairfield Hall and the Belgrade Theatre, on loudspeakers in Salisbury Cathedral (Figure 1l), on trying to break windows at sub-sonic frequencies, on noise in schools, on the sound insulation of the Royal Festival Hall,

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on the vibration isolation of the Planetarium and on several other items that still rest in the lab files. Another such item was the use of Helmholtz resonators by Mr Hugh Creighton in the Queen Elizabeth Hall (Figure 12) and Purcell Room to control the low frequency reverberation time. I mention this last item to show that even the very best scientists are not always good at foretelling the future. In 1859, Helmholtz met the King of Bavaria, and writing to his wife about it Helmholtz said : “The King hoped that I would make some acoustic discoveries that would benefit the architecture of public halls; but I could hold out small prospect ofthat”. So another piece of advice to young people is for goodness sake get your work written-up before you go on to the next-and obviously more interesting-item of work.

Figure 10. Sound pressurelevelsin 37-75 Hz band under largejet aircraft flyingat 185feet.

Figure 11. Mobile laboratory

at Salisbury Cathedral.

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Figure 12. Helmholtz resonators in Queen Elizabeth Hall. I have given advice to the young, now for some advice to those placed in authority over them, and I think all managers should be made to read the Preface to the Book of Common Prayer, and I will quote a small part of it : “It hath [ever] been wisdom . . . to keep the mean between the two extremes, of too much stiffness in refusing, and of too mucheasiness in admitting any variation.. . For, as on the one side common experience sheweth, that where a change hath been made of things advisedly established (no evident necessity so requiring) sundry inconveniences have thereupon ensued; and those many times more and greater than the evils, that were intended to be remedied by such change: So on the other side,-[such things as are] in their own nature indifferent, and alterable, and so acknowledged; it is but reasonable, that upon weighty and important considerations, according to the various exigency of times and occasions, such changes and alterations should be made therein, as to those that are in place of Authority should from time to time seem either necessary or expedient.” That could serve as a text for any future Wilson Committee, and the final draft of it was

ratified in 1662 by the Upper House of Convocation meeting in the Jerusalem Chamber of Westminster Abbey, where the Sound Advisory Panel for the Abbey now meets, although I doubt if any of our prose will be quoted in three hundred years time. However, this Advisory Panel, which was set up by the Abbey to give advice on any acoustical problems in the Abbey but particularly the loudspeaker system (see Figure 13), has provided me with several days of what Bagenal once called one of the major pleasures of life, i.e., discussions among experts. I have today said little about the acoustics of auditoria (for anyone interested I can recommend the 1976 Fairey lecture at Southampton [73]) but before concluding I will mention one more matter. I have said earlier how difficult it is to get reliable subjective assessments of noise, and it is even worse when dealing with the acoustics of auditoria. Someone engaged in research should have no opinions of his own, but in practice you are forced to make judgments if anything is to get done. One can ask acousticians for their views on auditoria, and speaking the same language,

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13. Loudspeakers in Westminster Abbey.

the results can be very useful, but one limitation is that acousticians hear several things that no professional musician or ordinary concert-goer would ever notice. I tend to put my faith in the ordinary concert-goers, not only because they are the ones who pay to go in, but because there does seem to be a tendency to get consistent answers from them. Mr E. M. Forster remarked once “there is no such person as the average-concert-goer and no-one can speak in his name”. In spite of this stricture I still think that their collective opinions are useful. But in my more cynical moments I sometimes feel that the acoustics of auditoria are more a matter of public relations than anything else. One awful warning of the difficulties of assessing the acoustics of concert halls is shown in what happened in the Royal Albert Hall in the 1890’s. In his book The Royal Albert Hd (Hamish Hamilton, 1958) Mr R. W. Clark says: “Inside the Hall, things were hardly happier. The Electrophone Company, which operated a system by which subscribers could dial on an apparatus rather like a telephone and then listen to the events taking place in any of certain theatres and halls, installed their apparatus in 1896, paying the Corporation f50 a year for the privilege. Yet what their subscribers heard was still subject to the persistent echo which during the 1890’s had one of its periodic resurgences of notoriety. To cope with it, Wentworth Cole [the Manager] had wires stretched across the Hall and a length of rabbit netting suspended from each wire. ‘There does not appear any doubt that these wires have proved effective in diminishing in a marked degree, if not altogether getting rid of the echo, and in effect bringing the sound of instruments, and of the voice, markedly nearer to the listener.‘, he later reported. ‘The opinion of the Honorary Stewards and others who have been constantly at the Hall on nearly every occasion it has been used for the last twenty years, and have listened to music from different parts of the building, has been invited, with the result that the almost unanimous opinion is that a great benefit to the acoustic properties of the building has resulted.“’ The awful warning is not the mere fact of trying the wires; they-if anything at all is certain about the acoustics of auditoria-could not possibly have had any effect, but is the “almost

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Figure 14. Diffusers (“flying saucers”) for the Royal Albert Hall being tested in the B.R.S. anechoic

chamber.

unanimous opinion” about the improvement. These wires disappeared at some later, unknown date. The so-called “flying saucers” (Figure 14) have had a similar opinion reaction, this time justified. I have dealt lightly with a fair number of matters, and I want to conclude with some final advice to young people who want to get anything done : advice not from me but from a great engineer, Isambard Kingdom Brunel : “I would only impress upon you one principle of action which I have always found very successful, which is to stick obstinately to one plan, until I believe it wrong, and to devote all my scheming to that one plan, and, on the same principle, to stick to one method and push that to the utmost limits before I allow myself to wander into others; in fact to use a simile, to stick to the one point of attack, however defended, and if the force first brought up is not sufficient, to bring ten times as much, but never to try to back upon another point in the hope of finding it easier”.

ACKNOWLEDGMENT This paper is published by permission of the Director ment of the Department of the Environment.

CHRONOLOGICAL

of the Building

Research

Establish-

BIBLIOGRAPHY

British Intelligence Objectives Sub-Committees Final Report No. 980, circa 1946. Electroacoustics in Germany, Part 1. P. H. PARKIN 1946 Journal of the Royal Naval Scientific Service 1,237-242. Innellan acoustic range. P. H. PARKIN 1947 Journal of the Royal Naval Scientific Service 2,79-84. The Falmouth range. P. H. PARKIN(on behalf of Committee) 1949 The Physical Society, Acoustics Group Symposium, 3&M. Provisional code for field and laboratory measurements of airborne and impact sound insulation. 5. P. H. PARKIN and H. R. HUMPHREYS1949 The Physical Society, Acoustics Group Symposium 109-l 19. Sound insulation between flats. 6. P. H. PARKIN 1949 Nature 163,122-124. Concert hall acoustics.

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7. P. H. PARKIN and H. R. HUMPHREYS1949 and 1950 Oil Engine and Gas Turbine 17, 225-227, 260-261, 296-297. Quietened oil engined plant. 8. P. H. PARKIN 1950 The Builder 178, 396-398. Transmission of sound in buildings. 9. P. H. PARKINand W. E. SCHOLES1950 Colloque Internationald’Acoustique Architecturale, 51-55. Influence de la ‘pente’ de la courbe d’isolement d’une cloison sur la reduction de niveau du discours et de la musique. 10. P. H. PARK~Nand H. R. HUMPHREYS1950 Journal of the Royal Institute of British Architects 57, 392-395. Measurements of sound insulation in houses and flats. 11. P. H. PARKINand W. E. SCHOLE~195 1 Wireless World 57,445O. Recent developments in speech reinforcement systems. 12. E. MEYER,P. H. PARKIN,H. OBERSTand H. J. PURKIS1951 Acustica 1,17-28. A tentative method for the measurement of indirect sound transmission in buildings. 13. P. H. PARKIN and W. A. ALLEN 1951 Building Research Congress, Part I, 15-20. The acoustic design of concert halls-with special reference to the Royal Festival Hall. 14. P. H. PARKIN 1951 Nature 168,264269. Acoustics of the Royal Festival Hall, London. 15. W. A. ALLENand P. H. PARKIN1951The Architectural Review 109,377-384.Acoustics and sound exclusion (of the Royal Festival Hall). 16. P. H. PARKINand H. J. PURKIS 1951 Acustica 2,81-82. Sound absorption of wood panels for the Royal Festival Hall. 17. P. H. PARKIN1953 Journal of Scientific Znstruments 29,8-l 1. The design of electronic laboratories. 18. P. H. PARKINand P. H. TAYLOR1952 Wireless World 58, 54-57 and 109-l 11. Speech reinforcement in St Paul’s Cathedral. 19. P. H. PARKIN,W. E. SCHOLE~and A. G. DERBYSHIRE 1952 Acustica 2,97-100. The reverberation times of ten British concert-halls. 20. P. H. PARKIN 1952 Journal of the Acoustical Society of America 24, 542-543. American and European standard methods for measurement of sound transmission in buildings. 21. P. H. PARKIN 1952 Nature 169,214216. Speech reinforcement in St Paul’s Cathedral, London. 22. H. J. PURKISand P. H. PARKIN 1952 Acustica 2,237-241. Indirect sound transmission with joist and solid floors. 23. P. H. PARKINand W. A. ALLEN 1953 Nature 172,1-5. Acoustic design of auditoria. 24. P. H. PARKIN,W. A. ALLEN,H. J. PURKISand W. E. SCHOLES1953 Acustica 3,1-21. The acoustics of the Royal Festival Hall, London. (Also Journal of the Acoustical Society of America 25, 246-259.) 25. P. H. PARKIN 1953 First International Congress on Acoustics, Electra-Acoustics 87-89. The application of the Haas effect to speech reinforcement systems. 26. P. H. PARKINand W. E. SCHOLES1954 Journalof the AcousticalSocietyof America 26,1021-1023. Air-to-ground sound propagation. 27. P. H. PARKIN and H. J. PURKIS 1954 Acustica 4,439-4&I Noise levels underneath some civilian aircraft shortly after take-off. 28. P. H. PARKINand E. F. STACY1954 Journalof the Royal Institute of British Architects 61,372-376. Recent research on sound insulation in houses and flats. 29. P. H. PARKIN and E. E. STACY1955 Noise Control 1, 40-45 and 90-91. Quieting of apartments and houses. 30. P. H. PARKIN 1955 (letter in) Report of the Committee to Consider a New Queen’s Hall. London: Her Majesty’s Stationery Office. 31. A Special Correspondent 1955 (24 and 25 October). The Times. The curse of noise. 32. P. H. PARKM 1955 Technique 9,22-23. The use of the Muirhead-Pametrada Wave Analyser in noise measurements. 33. P. H. PARK~N1957 Acustica 7,57-58. Loudness of common noises. 34. P. H. PARKIN and H. R. HUMPHREYS1958 Acoustics, Noise and Buildings. London: Faber and Faber; first edition. 35. P. H. PARKIN 1958 in Electronic Engineers’Reference Book. Measurement and analysis of noise; and, planning of public address systems. London: Heywood and Company. 36. P. H. PARKINand W. E. SCHOLES1958 Acustica 8,99-102. Oblique air-to-ground sound propagation over buildings. 37. P. H. PARKIN 1958 Engineer 205,463464. New mobile laboratory. 38. P. G. GRAY, ANN CARTWRIGHTand P. H. PARKIN 1958 Noise in Three Groups of Flats with Different Floor Insulations. London: Her Majesty’s Stationery Office. 39. E. J. EVANSand P. H. PARKIN 1958 Acustica 8,117-l 18. Sound absorption of a stone wall. 40. P. H. PARKIN 1959 New Scientist 6,1335-1337. The problem of noise.

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P. L-LPARKIN 1959 Engineering lgg678-680. Heliport noises may be a public nuisance. P. H. PARKIN 1960 Insulation Review 4, 14-17. Control of noise in buildings. P. H. PARKIN 1961 NPL Noise Symposium. Propagation of sound in air. P. H. PARKIN 1961 Znsulution Review 5, 12-14. Sound insulation of buildings against external noise. P. H. PARKIN, H. J. PURKIS and W. E. SCHOLES1961 National Building Studies Research Paper No. 33. Field measurements of sound insulation between dwellings. London: Her Majesty’s Stationery Office. P. H. PARKIN 1964 Journal of Sound and Vibration 1, 336337. Assisted resonance for concert halls: a technical statement by the Building Research Station. P. H. PARKINand K. MORGAN1964 New Scientist 23,278-280. “Warming up” the Royal Festival Hall. P. H. PARKIN and W. E. SCHOLES1964 Journal of Sound and Vibration 1, 1-13. The horizontal propagation of sound from a jet engine close to the ground, at Radlett. P. H. PARKIN1965 Journal of Sound and Vibration 2, 86-88. On the accuracy of simple weighting networks for loudness estimates of some urban noises. (Letter to the Editor.) P. H. PARKINand W. E. SCHOLES1965 Journal of Soundand Vibration 2,353-374. The horizontal propagation of sound from a jet engine close to the ground, at Hatfield. P. H. PARK~Nand K. MORGAN1965 Journal of Soundand Vibration 2,74-85. “Assisted resonance” in the Royal Festival Hall, London. The effect of W. E. SCHOLE~and P. H. PARKIN 1967 Journal of Sound and Vibration 6,424442. small changes in source height on the propagation of sound over grassland. P. H. PARKIN 1968 (August) Engineering, 243-246. Engineering Outline 137: Acoustics of rooms for speech. P. H. PARKIN 1968 (February) Engineering, 307-3 10. Engineering Outline 113 : Sound insulation in buildings. W. E. SCHOLESand P. H. PARKIN 1968 Applied Acoustics 1, 3746. The insulation of houses against noise from aircraft in flight. P. H. PARKIN,H J. PURKIS,R. J. STEPHENSON and B. SCHLAFFENBERG 1968 London Noise Survey. London : Her Majesty’s Stationery Office. P. H. PARKIN1969 Journalof the AcousticalSociety of America 45,513. Comments on “Historical background of the Haas and/or Precedence Effect”. P. H. PARKIN 1969 in Windows and Environment. Part 4: Windows and sound. St. Helen’s: Pilkington Brothers Limited. P. H. PARKIN 1969 (Autumn) Building Research Station News, 10-12. Assisted resonance. P. H. PARKINand K. MORGAN1970 Journalof the Acoustical Society of America 481025-1035. “Assisted resonance” in the Royal Festival Hall, London, 1965-1969. P. H. PARKINand E. F. STACY1971 Journal of Sound and Vibration 19,277-286. The anechoic and reverberant rooms at the Building Research Station. P. H. PARKIN 1971 Science Journal7,56-60. The acoustics of the Royal Festival Hall. P. H. PARKIN and K. MORGAN 1971 Journal of Sound and Vibration 15, 127-141. “Assisted Resonance” in the Royal Festival Hall, London: 1965-1969. (Also published in the Journal of

the Acoustical Society of America.) 64. P. H. PARKIN 1972 Project, No. 19, 33-35. Acoustical “Warmth”. 65. P. H. PARKIN1972 Philosophical Transactions of the Royal Society, London 272,621-625.

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Acoustics of concert and multi-purpose halls. P. H. PARKIN 1974 The Architects’ Journal 160,297-300. Assisted resonance at the Central Hall, York University. P. H. PARKIN 1974 Journal of Sound and Vibration 32, 530. Pitch change during reverberant decay. P. H. PARKIN 1974 Spectrum. “Assisted resonance” for auditoria. E. C. KEIGHLEY,P. H. PARKINand M. WEST 1974 8th Znternational Congress on Acoustics 2,642. Noise climate in landscaped offices, M. WESTand P. H. PARKIN1975 Applied Acoustics 8,43-66. The effect of furniture and boundary conditions on the sound attenuation in a landscaped office: Part I. (Part II to be published.) P. H. PARKIN1975 in Auditorium Acoustics, 169-179. Assisted resonance. London: Allied Science Publishers Limited. E. C. KEIGHLEYand P. H. PARKIN 1977 (to be published). Subjective response to sound conditioning in a landscaped office. P. H. PARKM (to be published) 1977 Fairey Lecture: The acoustics of auditoria.