Component Characteristics for an Active Ear Defender

Abstract

Proposed methods of electronic noise reduction at a listerers ears have been described previously [J. Acoust. Soc. Am. 28, 773 (A) 1956)]. A headset incorporating electronic noise reduction has been termed an active ear defender. One method proposed uses a microphone under each earphone in a negative feedback arrangement. Another method makes use of a microphone located outside the earphone cushion to provide a canceling signal. The canceling arrangement is very sensitive to amplitude and phase errors. Examination of its electrical analog reveals that a surprisingly large band width is necessary because of the critical phase requirements. The band width required for the negative feedback arrangement is also large but amplitude and phase characteristics within the useful band are less critical. In this paper the microphone and earphone characteristics required for effective noise reduction are discussed. A negative feedback system is described which provides approximately 15 db of noise reduction from 100 to 200 cps. Component characteristics which will make possible greater amounts of noise reduction are discussed. (Work supported by U. S. Air Force and U. S. Army Signal Corps.)