Applied Acoustics 16 (1983) 245--255

V. L. Jordan, 1909-1982: A Biographical Memoire

Brian Day

Department of Architecture, University of Bristol, Bristol (Great Britain)

(Received: 17 November, 1982)

S U M M A R Y

Throughout his professional career, spanning nearly fiJty years, Vilhelm Jordan attempted to bring the methods and disciplines of scientific research to bear on the day-to-day practice of the acoustical consultant. The development of his practice from the Danish Radio Broadcasting House to the Sydney Opera House is traced, and his skill at informing professional judgement with scientific inquiry is exemplified. In discussing the application of the Schroeder integrated impulse theorem to early decay time measurements, a proposal is made for the revival of statistical description of random noise decays as a possible concert hall criterion.

This paper formed the text of a memorial address given at the Institute of Acoustics meeting held in Edinburgh, Scotland, in September, 1982.

INTRODUCTION

Vilhelm Lassen Jordan was born in Aalborg, in the north of the Danish peninsula of Jutland, in April, 1909. He died in Sydney, Australia, in February 1982, whilst attending a meeting to discuss further development of what was probably his most prestigious project, the Sydney Opera House complex. From the mid-1950s until his death he had been among the world's leading acoustical consultants. A list of his projects around the world is impressive both by its variety and extent. Although several recent

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Applied Acoustics 0003-682X/83/$03.00 ~ Applied Science Publishers Ltd, England, 1983. Printed in Great Britain

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projects remain incomplete at his death, his son and partner, Niels Jordan, is, happily, to continue the practice. There can be no doubt of Vilhelm Jordan's stature as a professional consultant, but in addition he had a strong background in academic studies and retained a lively and active interest in experimental and theoretical developments in room acoustics. This included a readiness to pass on his knowledge and wisdom as an occasional teacher whenever time allowed. In fact, his particular ability to incorporate research into his professional practice is an object lesson for any teacher concerned to enliven and reinforce the skills and

Fig. I. Vilhelm Lassen Jordan, 1909-1982.

V. L. Jordan, 1909-1982: a biographical memoire 247

judgement of a profession with the insight and enquiry of academic research.

Like most Danes, Vilhelm had a sense of fun and a distaste for formality that probably makes a formal memorial paper a highly inappropriate commemorat ion of the man. However, I am sure he would not begrudge us a celebration of his life, and a review of his work, with the opportunity to draw valuable lessons from his ability to combine the professional and academic aspects of his work.

TRAINING AND EARLY WORK, 1933-1945

He once explained to me that he had come to his profession almost by chance, although with some assistance from the forerunners of the Central Electricity Generating Board. After graduating from the Royal Technical University of Copenhagen in 1933 with a Master's Degree in Electrical Engineering he intended to make a career in power engineering and he came, at his own expense, to observe and study British power station practice. The power station engineers and their attitude to apprentice training were a great disappointment; so much so that, after some weeks, he abandoned for ever the world of generators and tea breaks and returned to Denmark. Soon after his return the opportunity arose to work instead at the Heinrich Hertz Institute for Electro-Acoustics in Berlin, under Erwin Meyer, and his career was begun.

He studied in Berlin until mid-1935, and then returned to the Technical University of Copenhagen to work with P. O. Pedersen on the problems of realising the acoustic scale model technique as a research and design tool. The time-scaling method using two-speed magnetic recording had been independently proposed by Lauridsen and Spandock, only a few years before, and Jordan's doctoral thesis, published in 1940 and entitled 'Elektroakustiske Undersogelser af Materialer og Modeller' describes his application of a wire recorder and a number of then novel devices to the problems of the selection of model materials, the measurement of acoustic parameters at scale speed and the generation and detection of high frequency test sounds. Reading his thesis is both a depressing and encouraging experience: depressing in that so many of the problems that he identifies and goes some way towards solving are still the subject of investigation, encouraging in that it exemplifies the possibility that what one writes today may still be useful in 40 years. For example, in spite of

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the language barrier, 1 find the account he gives of the theory of sound absorption mechanisms still one of the clearest available.

After obtaining his doctorate, Jordan took up a post with the Danish National Radio organisation. A new building was under construction in central Copenhagen the equivalent of London's Broadcasting House and he was given sole responsibility for the acoustic testing of all the studios as they came into being. Because of the war and the occupation the authorities were not anxious to complete the building, so that there was ample time available for testing the acoustics of the rooms as they were built. This experience was significant in reinforcing his strong preference for objective testing of projects, if possible during con- struction. In all his later work, physical measurements were not just an option--they were an essential part of the process, not only in refining the design of the building being tested, but also as a way of widening his own knowledge and skill for subsequent projects. This is, of course, a difficult thing to sell to a client--a large part of a professional's stock-in-trade is the reassurance of the customer that he has chosen the right expert. However, in an area like room acoustics where there are often uncertainties, it is the duty of the consultant to be frank about them where they exist so that realistic decisions can be made with a clear view of the risks involved, as well as the potential benefits.

Two specific experiences from the Radiohuset were reflected in Jordan's subsequent work. The first concerned the optimum shape of the curve representing the frequency dependence of reverberation time. In addition to the long standing preference for a rise in reverberation time at low frequencies, Jordan established, by jury tests on music broadcast from a variety of studios, that there was a distinct preference in these circumstances for a rise in reverberation time at moderately high frequencies also. Some of the studios were provided with variable absorption, and in the long period from about 1943 to 1945, while the opening of the building was being delayed, it was possible to carry out extensive tests of this effect. A number of recent reviews of acoustic criteria have re-established the relevance of some control of 'tonal balance' of this kind, but this would probably not use reverberation time as the control parameter any longer, as Jordan himself subsequently recognised.

The second novel insight he gained came from the problems with the main concert studio. This is a large concert hall with a stage for full

V. L. Jordan, 1909 1982: a biographical memoire 249

orchestra, but a small audience area seating only 800 people. The architect for the building was very keen to employ concrete shell construction for the roof so that the hall had a remarkably high ceiling for its plan size, with a strong concave curve and maximum height above the orchestra platform. The problems of focusing from the ceiling were investigated with a scale model and a system of imposed 'ripples' was designed to prevent a coherent reflection from this surface. Some work was also carried out on the suppression of low frequency resonances by means of Helmholtz absorbers built into the ceiling. These measures worked satisfactorily and the broadcast sound was reckoned to be excellent. However, soon after the opening of the hall, complaints began to be voiced by members of the orchestra concerning the ability to hear adequately the sound that was being produced overall, with consequent problems for ensemble and balance. This led to a prolonged series of investigations involving the measurement of the peak sound level produced by bursts of random noise of varying length, from which information about the development of the reverberant sound field could be obtained. It was discovered that the build-up of sound on the platform was much slower than in the audience area (a phenomenon that Jordan later referred to as 'inversion') and this was identified as arising from an absence of reflecting surfaces close to the musicians. Because of the small size of the audience, no overhead reflector had been provided, and the ceiling and side walls were too far away to reflect back to the orchestra enough early energy to aid ensemble. This was subsequently rectified in the mid-1950s by the provision of transparent, horizontal reflectors suspended halfway between the platform and the ceiling to direct some sound back down on to the orchestra. When the earlier glass sheets fell on to the stage some years later (fortunately the hall was empty) they were replaced (with perspex) at the players' insistence.

The consequence of this early experience with the problems of the development of the reverberant field was a continuing preoccupation with the refinement of criteria based on reverberation-like descriptions of room response, especially where these led to useful constraints on the form or construction of the main reflecting surfaces of the auditoria with which he was involved. It led, too, to a continuing concern with the problems of balance and ensemble for the orchestra and performers which was particularly valuable when he began his work on opera houses and music theatres.

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1945-1966

In 1945 Jordan established himself as an independent consultant, although continuing to work on the problems emerging at the Radiohuset. His first independent commission was for a multi-purpose hall in his home town, the Aalborghallen. Working from Copenhagen, he was also responsible for the Concert Hall at Turku in Finland and the Tivoli Concert Hall in the famous pleasure park in Copenhagen. The Aalborg hall is notable for its use of resonant absorbers to control low frequency reverberation time, the Turku hall has a +directed sound' philosophy, but still provides satisfactory conditions for the orchestra. The Tivoli hall was difficult for two reasons. In the first place its floor and ceiling were almost parallel, with a fan-shaped plan, and, secondly, there was a wish to provide a clear view into the hall from the gardens outside which led to a risk of noise penetration. The shape problems were overcome by the incorporation of small-scale serrations into the flat surfaces and the noise was excluded by deep double glazing.

In 1955 he moved his office from central Copenhagen to the village of Gevninge, just outside Roskilde, at the head of the Roskilde fjord. The house he occupied there had been the village school, and subsequently a riding school. The stable block was converted into a laboratory and office and provided the facility for his application of acoustic modelling techniques to all his subsequent major projects. This was the means by which he was able to bring into his professional practice as a consultant an element of investigative research which has often to be excluded from the process of design. Building design in particular suffers from the fact that each building has to serve as its own prototype. Innovation is an extremely risky affair and the foreknowledge of the performance of most aspects of a building is a matter for experience or skilled judgement. It is a crucial challenge for those who educate and train the professions to find ways by which the power of the scientific method and experimental inquiry can inform and expand the capabilities of professionals of all kinds. The way in which Vilhelm Jordan was able to integrate his laboratory studies into his consultant activity is, I think, a paradigm for the improvement of most kinds of professional practice.

The first building to benefit from the application of model studies at Gevninge was the New York State Theater. This is one of the three buildings that make up the Lincoln Center in New York City, the others being the Philharmonic Hall and the Metropolitan Opera House. Its

V. L. Jordan, 190~1982: a biographical memoire 251

prime function is to house ballet and large-scale drama, but it has been used extensively for operetta and 'musicals'. The concept of 'rise-time', which had been introduced as a result of the studies in the Radiohus Concert Studio, was replaced by 'steepness' which relates to the average slope of a curve showing the level variation with time as a sound field builds up in a reverberant space after a noise source comes on. The advent of reliable high-speed level recorders made it possible to record such curves even in tenth scale models, provided time scaling tape recorders were used, and the detailed design of the New York State Theater benefited from such studies. In particular, Jordan thought it important to achieve greater steepness in the orchestra and stage area than in the audience area. The general method for achieving this did not emerge immediately, but was found by trial and error in the model. The theatre was opened in 1965.

During this period Jordan also worked on radio and TV studio complexes in Sweden and Denmark. In the case of the office building for the Copenhagen television complex, his enthusiasm for design develop- ment testing led to the construction of a prototype pair of offices, on which lighting and solar control devices were tested, as well as the sound insulation properties of the construction. One of the main noise problems turned out to be aeolian tones generated by wind blowing over the large, vertical, external venetian blinds provided to act as a brise-soleil!

The work on the New York State Theater led to the project for the rebuilding (on an adjacent site) of the New York Metropolitan Opera House. The old 'Met' was much loved by the fiercely involved New York opera-going public, and the new building had to survive comparison with it, as well as seating many more auditors than a traditional house. The project might have been as great a trial of nerve as the Philharmonic Hall next door proved to be. Jordan's collaborator on the project was Cyril Harris. He again employed acoustic models as an aid in the design process, measuring rise time and steepness with random noise bursts, and echogram analysis using a spark source. One aspect that was studied intensively on this project was the influence of reverberation in the stage house on the acoustics of the auditorium. This involved modelling the fly tower above the stage; even at one-tenth scale this occupied the full height of the laboratory. Another aspect that was investigated in the model was the influence of vertical baffles hung beneath the balcony soffits on growth and decay processes for reverberant sound. At this stage the tendency in the work was to aim for a high temporal diffusion in the echogram in the

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audience areas, with many small reflections, rather than a few large ones.

By the mid-1960s the emphasis on the use of the development of the reverberant sound field was supplemented by an interest in the early part of the decay process. This was as a result partly of the publication of the Bell Telephone work that showed that the earlier part of the decay (first 15 dB) correlated best with subjective perception of reverberation, when this was tested in matching experiments between bi-sloped decays and linear decays. Jordan began to place increasing emphasis on ~early decay time' (EDT), which was measured at first by simply using a narrower range potentiometer in a level recorder and drawing an eye-averaged slope through the first 10dB of the decay. Because of the consequent enlargement of the fluctuations due to the use of random noise excitation, the variation between repeated measurements at the same location (which occurs in any determination of reverberation time) is greatly increased and, in order to obtain meaningful values, it was necessary to take an average of a great many separate determinations of the initial slope. This was a tedious process, but rather more convincing than the same process applied to the growth curve for steepness determination.

The publication by Schroeder in 1966 of the theorem relating the average random noise decay envelope to the integral of the time-reversed and squared impulse response provided a more rapid technique for the determination of the early decay time. Then, with the publication of the complementarity theorem, showing that the ~build-up' and 'decay' processes for random noise were essentially linked, the same theorem apparently removed the need to study both steepness and EDT. It may be that such formal relationships reduce the scope for multiple criteria. The facts of the physical response of an auditorium can be uniquely and completely specified in either the frequency or time domain, using impulse or noise excitation. However, the human perceptual process does not use more than a tiny fraction of the detail available in a full description and the trick in devising summary criteria is to find one which correlated best with the perceived qualities of the space. So, although 'steepness' and EDT (and clarity and frequency irregularity for that matter) all start from the same basic physical data, they may each have a relevance to one or other of the separate perceptions that can be made about the acoustic character of a space. Different facets of the physical response may be perceived by different processes, so different criteria are needed.

A small aside might be interpolated here, concerning a possible new

V. L. Jordan, 1909-1982. a biographical" memoire 253

criterion. Although the integrated impulse response procedure provides a means for simplifying the extraction of a value for the average properties of the random noise decay curve, it essentially ignores the significance of the variation between decays as a significant variable. Consider two rooms with the same reverberation time, but one having a 'dense', the other a 'sparse', echogram. It seems likely that if a space has an echogram consisting of a few well spaced but strong reflections (i.e. lacking in temporal diffusion), a series of individual random noise decay envelopes will show much more variation than a series in a room possessing a 'dense' echogram, even if it has the same overall decay time. Perhaps one could conceive an extension of the EDT criterion to include a measure of the variability of the decay curve for successive noise bursts. It seems likely that this would have the important property of giving a criterion which would distinguish between two rooms with identical reverberation times but very different volumes. There can be no doubt that there is a perceptual difference which is not necessarily accompanied by a difference in any of the established criteria. Further development of the integrated impulse theorem might produce a theoretical basis.

It was about the time that the work on the New York Met was being completed that I first came to know Vilhelm. In 1965 he was persuaded by Peter Lord to spend some time at the University of Salford as a lecturer on our mid-career post-graduate diploma course in acoustics. He was, by the way, an amusing and patient lecturer and also enjoyed taking part in laboratory teaching. After his second visit I was fortunate in being given leave of absence from my teaching post at the University to spend 6 months working in the Gevninge laboratory on the development of the model technique and the application of the Schroeder theorem to EDT measurements. We also attempted to make speech and music recordings in the models without the sophisticated equipment since available. I took my young family with me and we were made to feel so welcome that we have all looked upon Denmark as our 'second nation' ever since. There is a Danish word, hygge, which is untranslatable but encompasses concepts like 'warmth', 'homely' and 'friendship'. No one that has experienced the Jordan family hospitality can have any doubt about its meaning.

THE SYDNEY OPERA HOUSE AND LATER

So far I have said nothing of the Sydney Opera House. Jordan was part of the team, led by the Danish architect J6rn Utzon, that won the original

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completion. There is an apocryphal story that the original shells which form the roof and effectively won the competition with a few preliminary sketches, were actually generated by Utzon as he thought about a series of parabolic reflectors for directing sound from stage to audience. True or not, there is no doubt that Utzon was able to draw an intense commitment from his consultants, who were prepared to go to enormous pains to make the architect's 'visions' into a working reality. There must be doubt about the intrinsic worth of architecture that is designed this way, depending on one's philosophical view of architectural aesthetics, but there can be no doubt that the completion of the building represented a tour-de-jorce for all those involved in its realisation. Jordan tells something of the history of the project in his recent book,* from which it is clear that his own contribution, and that of the long series of acoustic model studies, had a very significant impact on the eventually satisfactory outcome of what became a long running drama, especially after Utzon's resignation. It seems to me that there are sufficient challenges in fitting the 'natural' constraints on a building, without imposing artificial ones in the form of quixotic decisions by a capricious architect; however, there can be no doubt about the achievement represented by the completion of the building, which is certainly Jordan's 'masterwork'.

Although the involvement with the Sydney project began in 1957, it was not completed in its first stage until 1974. During that period he also worked on concert halls for Oslo and Reykjavik and theatres in London and Managua, as well as the New York theatres. Since 1974, he and Neils Jordan were involved in ten different projects, most of which are still in progress. His book published in 1980, papers in Applied Acoustics and an invited paper given at the Institute of Acoustics Spring Meeting in 1980 displayed his continued involvement with the development of the science of auditorium acoustics, and the search for usable design criteria and guidance. To the end of his life he kept abreast of the newest thinking in academic research and sought to apply it in his professional practice, although with a healthy scepticism about over-complicated approaches.

One of Edinburgh's native sons, the historian Edward Gibbon, tells us, in The Decline and Fall of the Roman Empire, of the book written by the Emperor Constantine Porphorygenitus for his son, on the art of being an Emperor. Apparently it included a section on the arts of war and military

* Acoustical Design o[Concert Halls and Theatres, Applied Science Publishers, London, 1980.

V. L. Jordan, 1909-1982: a biographical memoire 255

tactics. Gibbon did not think a lot of formal learning, and in the following passage explains why:

'The general theory (of military tactics) is dictated by reason, but the merit, as well as the difficulty, consists in the application.

The discipline of a soldier is formed by exercise rather than study: the talents of a commander are appropriated to those calm, though rapid, minds which nature produces to decide the fate of armies and nations: the former is the habit of a life, the latter the glance of a moment, and the battles won by the lessons of tactics may be numbered with the epic poems created from the rules of criticism.'

It seems to me that that might well be written of most professions. But we cannot any longer reject cleverness based on theoretical knowledge in favour of wisdom based on experience, because the world is developing too fast. Vilhelm Jordan represented an example of how the fusion could be brought about, between predictive calculation and judgement, and between the spirit of sceptical scientific enquiry and resolute decision taking.