Leo L. Beranek, the Oldest Living Graduate of the Harvard Physics Department, Background and Days at Harvard, 1936 to 1946

September 26, 2014

Leo Beranek was born 100 years ago in September 1914 in Solon, Iowa. His accomplishments over his long life are well known. This note describes his work at Harvard as a graduate student and faculty instructor from 1936 to his departure in 1946. Most of the information is taken from material he wrote in preparation for his autobiography Riding the Waves. The title is apt: Leo makes waves, the kind that sweep away old ways of thinking and leave space for creative solutions. He is not only brilliant at finding practical solutions, he has a gift for finding, encouraging, and motivating smart people into intensely creative teams.

Leo came from a farm background with seemingly unlimited energy and a fascination for things mechanical and electrical. During his sophomore year in high school Leo took a correspondence course in radio, followed by an evening apprenticeship with a local radio repair expert. By his senior year he was operating his own radio repair business and playing in a local dance band. He saved enough money to pay his first year's tuition at Iowa's Cornell College. While carrying a full course load at Cornell College in Iowa he ran a radio repair service and did house wiring, as well as playing in a college dance band. Thinking about graduate school in radio, he, by chance, changed a flat tire for a passing motorist, a former instructor at the Cruft Laboratory and then president of Browning Laboratories in Winchester, MA. Browning encouraged the young wizard to apply to Harvard - something Leo had never considered. He was accepted and given a full scholarship, arriving at Cruft in 1936.

In his second and third years Leo was a half-time paid assistant to the acoustics Professor Frederic V. Hunt. With Hunt he helped develop the first light-weight phonograph pickup that made possible the long playing (33⅓ rpm) phonograph record, and was co-author with Hunt of a paper on room acoustics. As a fourth year graduate student in 1939-40 he received the honor of a Parker Traveling Fellowship. His plan was to complete his D.Sc. on the measurement of acoustic impedance of materials in that year. Hunt was dubious but Beranek proceeded to invent, build the apparatus for the resonance-tube measurement method, and make measurements on many commercially available materials. His thesis was ready for binding in April of 1940, and he was granted the title of "Instructor in Physics and Communication Engineering."

That summer President Roosevelt established the National Research Defense Committee (NDRC), which contacted Karl Compton (MIT's president) about the urgent need to study pilot fatigue (possibly due to excessive noise) in bombers over Europe. The B17 was so noisy that the only communication method possible between pilots and gunners was Morse code. Compton gave the job to Philip Morse, who (having heard Leo at an Acoustical Society meeting) wanted Beranek as his right hand man. At Harvard, Hunt blew his top. Compton decided the only possible solution was for a joint Harvard-MIT laboratory with Beranek as director. Beranek prepared a budget of $4000 for an assistant and some equipment, but the military captain in charge of the project, F. R. Dent, was horrified, saying "This is a high priority project and needs a budget at least 10 times larger." They also needed psychological research into the effects of noise on psycho-motor efficiency of pilots, and Harvard psychology professor Stanley S. Stevens was selected to lead with a similar budget. Space was given to Beranek in Cruft. His project was named "Research on Sound Control," later renamed "Electro-Acoustic Laboratory." Stevens extensively remodeled the basement under Memorial Hall for the "Psycho-Acoustic Laboratory."

Beranek was in his element. He took an extended trip by air to major airframe builders, as well as to manufacturers of sound absorbing materials. He also started recruiting the brightest graduate students he could find from around the country, with skills in physics, mathematics, and electronics. Beranek found the best sound measuring and recording equipment available, with converters to run it on military aircraft. Beranek helped Stevens set up a room with loudspeakers capable of duplicating the measured noise, and invented a light-weight sound-absorbing material for use in aircraft. It quickly became clear that reducing the noise in the plane was impossible - better interphone equipment was needed.

In April of 1941 Beranek proposed that Steven's new chamber be used to determine whether the major problem for pilot-gunner communication was the oxygen-mask microphones or the headphones. Using conscientious objectors as subjects, they found it was the headphones. By early 1942 they knew that all the military headphones had almost no response above 1.2kHz. Beranek assembled test equipment and searched the nation for any product that had adequate response, finding only one (from Western Electric) suitable for high altitude communication; it became the aviation standard in 1941. Because that phone was too thick for ground military metal helmets, Leo personally redesigned the magnet structure to reduce it from 1" to 3/8", and it was rushed into production by two manufacturers. The lab also invented the kapok-filled donut that sealed the phone to the ear. But the manufacturers needed calibrated microphones to verify the performance, which Beranek proceeded to find and calibrate. In late 1943 the Electro-Acoustic Lab found that the human voice decreases dramatically at low atmospheric pressure, requiring more amplification at high altitude flight.

In the summer of 1942 the US Army ground forces required a means of evaluating high-power loudspeaker systems, ostensibly for communicating with troops. (Beranek's memoir does not comment on this - but the project was a cover for developing the loudspeakers used by the top-secret "Ghost Army" - a division of inflatable rubber tanks and wire-recorder driven loudspeakers that could look and sound like an armored battalion. It effectively drew enemy forces away from strategic positions, and then vanished overnight.) A large, sound absorbent and highly isolated space was needed. With characteristic speed (and the use of a resonance duct) Beranek found that wedges of fiberglass were the best way to make fully sound absorbing walls; he found a manufacturer and installed 19,000 48-inch-long wedges in a new building next to Lyman Labs, with three-foot thick walls of concrete. He named the space an "anechoic chamber," a name now in universal use. At Harvard it was just "Beranek's Box."

By this time the work at the lab on noise and speech intelligibility was winding down, but Beranek was as busy as usual. The Command Information Center (CIC) on a ship is where all available information is brought together, including the plotting from a radar screen the course and speed of incoming aircraft. If they are identified as foe, coordinates are given to aim the guns. But kamikaze bombers came in too fast for manual plotting, and the best (but still not effective) defense was a marine with rifle. Harvard was contracted with a project named "Study of CIC Requirements" in November of 1943 - with Beranek as the head. Yost and Beranek went to sea on the shakedown of a heavy cruiser, along with eight Dictaphone voice recorders which inscribed all CIC communications in wax. His recommendations were complete in February of 1945, the most important of which was that a land-based CIC simulator laboratory be set up for training CIC crews, equipped with the latest radar equipment. Beranek staffed the facility (housed at Beavertail, in Rhode Island) with seven psychologists, thirteen physicists, four operations personnel and four consultants. But the latest radar equipment could only be supplied to ships, so the Navy commissioned the facility as a ship - the "USS Beavertail," making Beranek effectively the only non-commissioned captain of a Navy ship. Its Harvard name was "Systems Research Laboratory." Recommendations from the facility were taken seriously. Some thought that introducing the Navy to systems research was the most important long-term result of the two laboratories' work.

At its peak there were almost 100 personnel in the Electro Acoustics Laboratory, and its expenditures approached a rate of a million dollars per year. With work winding down at the end of the war, Beranek sought and was granted a Guggenheim fellowship to continue work on acoustic impedance of materials. In 1946 he was given the title of "Director of Research in Acoustic Materials." During this time he was led by Hunt to believe he was in line for promotion to an "Associate Professorship in Physics and Communication Engineering," but at the last minute the tenure slot was given to Edward Purcell -- a good choice in Beranek's opinion, as Purcell won the Nobel Prize the next year. Leo looked for another position, tentatively accepting an offer from Notre Dame. Just a day later Compton called offering him a tenured Associate Professorship at MIT, accepted immediately by Beranek.

His Harvard story ends here. Within two years Hunt had disposed of the reports, patent models, and nearly all of the equipment of the Electro-Acoustic Laboratory on Acoustics. Beranek went on to form many new creative teams, who continue to produce many of the things we now take for granted.

Following his love of music Beranek personally dove into the morass of mythology and opinion that constitutes concert hall architecture, writing the classic book Music, Acoustics, and Architecture (Wiley, 1962). But real understanding of this field remained elusive until his Concert Halls and Opera Houses (Springer, 2004). His early mentor Hunt continued teaching; I took his courses in 1964 and '65, and even considered switching my field to acoustics, which Hunt advised against. (That was good advice. I gained both an excellent mentor and a friend in my work with Robert Pound.) Beranek's Box was still functional. Paul Horowitz and I used it to characterize condenser microphones we made in the Jefferson shop. Two years later Hunt died, and acoustics at Harvard died with him. Harvard got a grant to destroy the anechoic chamber in 1967.

Beranek continues his passion and activity in concert hall acoustics. He has been an inspiration to me, and my mentor in my efforts to understand the remarkable human ability to understand speech and appreciate music in the presence of reverberation and noise. Leo has embraced this work with gusto, giving talks and writing papers all over the world. Far from resting on his well-deserved honors, he continues making waves.

David Griesinger, PhD (Physics) 1976

Recent papers by Beranek:

  • "Analysis of Sabine and Eyring equations and their application to concert hall audience and chair absorption," J. Acoust. Soc. Am. 120 (3): 1399-1410 (September 2006)
  • "Mean-free-paths in concert and chamber music halls and the correct method for calibrating dodecahedral sound sources," J. Acoust. Soc. Am. 135 (1): 223-230 (January 2014).