Mones E. Hawley
Jack Faucett Assoc., 4550 Montgomery Ave., Bethesda, MD 20814
Speech communication in noisy aircraft was recognized as a problem as early as World War I. The problem persisted throughout World War II, particularly between aircrew members with both talker and listener in loud noise. In 1947 the U.S. Air Force awarded RCA a contract to develop a high-intelligibility speech communications system for use in aircraft. The systems were tested in 120-dB sound pressure levels of synthesized propeller and jet noise. Dr. Harry Olson at RCA had invented an active noise-canceling system using loudspeakers for use in industrial work places. Elvin Simshauser and Mones Hawley of RCA invented a noise-canceling headset---a negative hearing aid---for interphone use in aircraft and other noisy military environments. A microphone on the outside of an earcap monitored the ambient noise near the user's ear. The signal from the microphone was fed into a filtering and phase-shifting device that matched the attenuation and phase shift of the earcap. The resulting signal had its phase reversed and introduced into the earphone in the ear cap. The sound pressure level from the noise environment under the ear cap was reduced by 10 dB in the demonstration system. When the speech communication signal was superimposed on the signal from the noise-cancellation device, intelligibility was much improved.