Acoustical Society of America
Gold Medal Award - 1975

Leo Leroy Beranek

During the middle third of this century acoustics, one of the oldest members of the physics family, was rejuvenated by its marriage to the youthful science of electronics. The fruitfulness of that union was enhanced to no small degree by the skill, industry, and pertinacity, as matchmaker, of Leo Leroy Beranek.

Those three qualities had previously got Leo from a farm in eastern Iowa to nearby Cornell College, and from that obscure college to prestigious Cruft Laboratory at Harvard for graduate work. Of course there were assists from his parents, from a mathematics teacher at Cornell College, and from a correspondence course in radio repairing. His mother, before she died, had strengthened his resolve to go on to college. His father sold the farm and started a hardware store in Mount Vernon, Iowa. The store catered to the new craze for radio sets and, with his father's encouragement, plus the aid of a correspondence course, Leo built up a good business repairing the sets. By 1931, when he graduated from high school, he was sure he wanted to become a scientist.

The lucky breaks he got in the next five years were unique enough but probably were no more numerous than those taken advantage of by other ambitious youths. He drew out the money for his first year at Cornell College just one day before the Mount Vernon bank closed its doors in the Great Depression. His dedication to science was strengthened by the guidance and inspiration of his mathematics instructor, Elmer Moots, who took great interest in him. Lacking money to continue his third year, he managed to find a job with the rapidly growing Collins Radio Company in nearby Cedar Rapids, where he learned still more about electronics circuits and earned enough to return to college.

Playing drums in the local dance band and repairing radios took so much time that, though his grades in his science courses were tops, his grades in nonscience courses were not, so his chances for admission to graduate school were not bright. But, in the summer of 1935, he played good Samaritan to a passing tourist with a flat tire, who turned out to be Glenn Browning, of Browning Radio in Winchester, Mass. Learning about Leo's interest and ambitious, Browning suggested he write to E. L. Chaffee at Harvard. With assists from Moots and Browning, Harvard was persuaded to admit him and to grant him enough scholarship money so that, with his savings, he could survive during his first graduate year at Cruft Laboratory.

His next stroke of deserved luck was his appointment as half-time graduate assistant to F.V. Hunt for the academic years 1937–1939. Here he found himself at the forefront of the rapid progress of application of electronics to acoustics. The concepts embodied in the Newtonian equation for simple harmonic motion were coming full circle, from mass and spring to electric circuits back to vibration and sound, whence they had come. But knowledge and understanding had grown during the cycle. Mass had become inductance and was becoming inertance, and spring constant had become capacitance and thence compliance. Dynamic analogies were merging and sensitive instrumentalities were being created.

Beranek learned Hunt's meticulous experimental techniques and improved upon them. He also was active in the cooperation/competition between the Harvard group and the acoustics enthusiasts at MIT—R. D. Fay, R. H. Bolt, and P. M. Morse and their students. The concepts and the methods of measurement of acoustic impedance were being worked out and were being used to understand more about the behavior of sound in rooms and in ducts. Beranek's first published paper, this one with Hunt and D. Y. Maa, was on the "Analysis of Sound Decay in Rectangular Rooms." His third paper, in 1940 (the year he received his doctorate), was "Precision Measurement of Acoustic Impedance" and his fifth paper, also in 1940, was "Sound Absorption in Rectangular Ducts." During all this he found time to meet, woo, and marry Phyllis Knight, a fellow devotee of good music.

Leo came of age scientifically just in time to contribute materially to the war effort. Even before the National Defense Committee was completely organized, the Army, via the National Research Council, established two projects at Harvard to see what could be done about noise in military vehicles, particularly in aircraft. S. S. Stevens was put in charge of the group to investigate the physiological and psychological effects of the noise on personnel, and Beranek was put in charge of a group to measure the noise and to see how it could be controlled. The two groups made impressive contributions, many of which were implemented before the war's end.

They early determined that the biggest detriment of noise, in the military environment, was on communications. This was particularly important because the military microphones and headsets had not been fundamentally improved since the 1920s. So the two groups revised the military specifications for voice communication equipment, got the services to authorize the revision, and arranged for the desired equipment to be manufactured quickly and in quantity. Beranek's group then worked out a criterion of acceptability for background noise when communication is important and went on to study means of quieting airplane cabins to meet the criterion. They developed a multilayer sound-absorbing blanket, the analogue of a multistage electric filter, that cut down sound transmission through the cabin skin and yet was light enough to meet weight requirements.

In the course of these studies, Beranek designed and built the first anechoic chamber in which fiberglass wedges were used. In spite of the skepticism of several famous experts, the lining turned out to absorb considerably more than 99% of the incident sound, over a wide range of frequencies, as Beranek had predicted.

After VJ Day, Beranek was persuaded to come to MIT, to joint R. H. Bolt in setting up an acoustics laboratory. The joint effort prospered, attracting a long sequence of students and co-workers who have since become important figures in the world of acoustics. Here Leo perfected his armament of measurement techniques and wrote his first major book, Acoustic Measurements, a compendium of data, formulas, and instructions that still is a valued reference 25 years later. And he continued the development of standards, criteria, and their measurement, which was to be such an important part of his contribution to acoustics. For example, he developed, justified, and publicized the Noise Criterion curves for specifying allowed noise levels from ventilating systems and air-conditioning equipment.

The work of Beranek and his colleague Bolt in noise control and in auditorium acoustics suggested so many possibilities for application that, in 1948, the two formed a company that now is the famous firm of Bolt, Beranek and Newman; Leo was its president from 1953 to 1969. One of their first jobs was the design of a mammoth muffler for the NASA–Lewis Supersonic Wind Tunnel in Cleveland that brought the emitted noise down to a level that the surrounding community was willing to allow.

That success pushed Leo still farther from the academic life into one of applying his knowledge in practice. He did complete a book called Acoustics in 1954, but by that time he was spending most of his time at BBN, designing silencers for engine test cells and advising on other noise control problems. His book, Noise Reduction (1960) and the more recent Noise and Vibration Control (1971) demonstrate again his abilities as a collector of definitive data and a devisor of standard criteria.

The complementary aspect of the noise problem, the effects of noise on people, was not neglected either. Starting with his wartime work on the effects of noise on speech communication, Beranek went on to work out standards of "noise comfort," to show, for example, that a room can be too quiet for comfort. And this led naturally to an investigation of the design of auditoriums. Typically, it started with a series of measurements of the acoustical properties of the better-thought-of concert halls and opera houses of the world, plus a correlation of the results with the hall's design and construction. The results came out in 1962 in the book Music, Acoustics and Architecture, where he again dealt with criteria, their measurement, and how they can be achieved.

His work in these and other acoustical fields has received national and international recognition. He has been president of the Acoustical Society of America, the Audio Engineering Society, and the Institute of Noise Control Engineering, as well as of the Opera Company of Boston and the Cambridge Society for Early Music. He has been the recipient of the Biennial Award, the Wallace Clement Sabine Award, the Silver Medal of Le Groupement des Acousticiens de Langue Française, and the Gold Medal of the Audio Engineering Society. He and his wife have seen much of the world during his visits to lecture to consult on acoustical problems.

Recently his interests have extended beyond noise and music to television. He is now President of Boston Broadcasters, Inc., a company that, after a nine-year battle, took over ECVB-TV-5 in Boston. Most of Leo's time now goes into planning syndicated and local television programs rather than sound measurements, into worrying about Nielson ratings rather than noise criteria. Dare we hope that eventually there will appear a treatise on criteria for good TV programs, plus a summary on how they could be achieved? Philip M. Morse