Page 46 - Spring 2006

Recollections of Paul Sabine and the Harvard Underwater Sound Lab.
Laymon Miller
I worked with Paul Sabine, ASA President 1935-37, quite extensively more than 60 years ago! I was 23 and he was 63 when we first met. We were brought together by Ted Hunt’s Underwater Sound Lab at Harvard University (HUSL). I had already been there about eight months when Paul arrived in June 1942 from the Riverbank Acoustical Laboratory in Geneva, Illinois. We were sur- rounded by much younger people in those days, and we considered anyone over 40 “old age.” So, by our definition, Paul Sabine fell into that “old age” category. But, he was spry and witty, and he certainly didn’t deserve that descrip- tion. In fact, his grasp of our problems and his technical know-how soon convinced us that we were very wrong in our first judgments of him based on age alone.
Our World War II objective was to devise an acoustic homing torpedo for US Navy pilots: to be air-dropped and to search for an enemy submarine known or suspected to be in the area. The project was given jointly to our Harvard Lab and to Bell Labs, and we were directed to work togeth- er cooperatively but competitively, which we did. The pro- gram was very successful but we will not go into any oper- ational details here.
One significant requirement of that program was to research and design transducers that would be carried by the torpedo and which, hopefully, could “hear” the sounds made by the enemy target and steer in on those sounds. We were all novices and had little to go on. Fairly early in our work, we realized that we needed a facility for measur- ing the characteristics of any transducers that we might attempt to build. “Hydrophones” (like underwater micro- phones) were the transducers used for “listening only,” and “Projectors” were transducers that could both transmit sound and receive sound (such as sending and receiving the popular “ping” of the ship-borne or submarine-borne sonar system). That need for a measurement facility ulti- mately led to the building of a “Calibration Station” on a barge floating in the Charles River and to the acquisition of a “Fur-lined Tank” for indoor use. The Calibration Station was fitted with all the necessary equipment to measure the frequency response and the directivity pat- terns of our transducers in a relatively “free field” (free of strong reflections and interferences that would alter the data). Due to our heavy work load, we eventually had to build and instrument a second calibration station on Spy Pond in North Cambridge, alongside Route 2. Yet, we needed simpler and faster routines for measuring some of the other important characteristics of our transducers.
Hence, the “fur-lined tank” became a necessity. No, it really wasn’t fur-lined. That was just the popular term that we used to describe its function. Its exterior was a steel tank about 5 ft x 8 ft in floor area and about 5 ft tall, with some hoisting gear at the top to lower and raise transduc- ers inside. There was a large rubber tank inside the metal tank, and the space between the rubber and steel walls was
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filled with viscous castor oil. The wall of the rubber tank was 2 in. thick, and it was made of “ρc (rho c)” rubber, which was a special formulation that very nearly matched the acoustic characteristics of water: the Greek letter ρ is the density of the rubber and c is the velocity of sound in the rubber. The product of ρc for the rubber lining very nearly equaled that of water. Because of its good sound absorbing characteristic, castor oil was used to fill the space (about 8 to 12 inches wide) between the metal tank and the Úc rubber tank. The chamber inside the rubber tank was then filled with ordinary water. The significant feature of this tank was that it provided a water load (somewhat approximating a water “free-field”) to a trans- ducer; the rubber and castor oil allowed sound to pass through these materials and to be dissipated without any noticeable reflection of sound back into the test chamber where it might influence the test results. Essentially, it was an anechoic chamber for testing in water. However, it was not large enough nor reliable enough to allow directivity measurements of a transducer. It served adequately for measuring the frequency response of a transducer and determining its efficiency of operation, as we were experi- menting with various transducer designs.
So, it was into this situation that Paul Sabine was placed in June 1942. With his known background at the Riverbank Acoustical Laboratories and acknowledged expertise in calibration work, it was an obvious decision to have him in charge of that tank and all the measurements that would be made using it. He came to be known as our “King of the Tank.” The tank was located where it could be equally accessible for both the torpedo and the sonar groups. From time to time, Paul had Bob Payne, Jim Faran, John King, Johnny Reitz, Ellen Gallishaw, and Mrs. Margaret Mason as his helpers at the tank. Paul Kendig, Rensler McDowell, and I made occasional measurements there, too. When desired, confirming tests could be made at our calibration stations on the Charles River or on Spy Pond to check on sensitivity and directivity in a more nearly “free field.” Some very effective (and novel) trans- ducers had their earliest tests in the tank.
Paul Sabine’s first wife, Mabel, mother of Hale Sabine, died in 1929 and Paul married Cornelia in 1938. Paul and Cornelia became good friends of my wife Lucy and me outside of lab work. Paul was so modest he never told us of his very thorough background in acoustics nor of his deep involvement with the Riverbank Acoustical Laboratories in Geneva, Illinois. Of course, we knew of Wallace Clement Sabine by reputation, but Paul did not stress his relationship with Wallace. About the only thing that Paul ever said about himself was that he had been the Acoustical Consultant for Radio City Music Hall in New York City. I do not remember that he ever mentioned that he had been the President of the Acoustical Society only a
44 Acoustics Today, April 2006