Active noise control in finite length ducts

Trinder, M. C.J. and Nelson, P. A. (1983) Active noise control in finite length ducts. Journal of Sound and Vibration, 89 (1), 95-105. (doi:10.1016/0022-460X(83)90913-6).

Record type: Article

Abstract

A simple technique for the active control of sound in ducts, initially suggested by Olson and May [1], is investigated in detail. A simple, "virtual earth" principle, feedback loop is used to drive the sound pressure to a minimum at a microphone placed close to a loudspeaker in the duct wall. This produces a reflection of downstream travelling plane waves. A detailed investigation of the loudspeaker near field has enabled the optimum position of the microphone to be identified. The system is shown to be especially effective at the frequencies of the longitudinal duct resonances, where the acoustic response of the duct produces a high loop gain. Results are presented which show a reduction of up to 20 dB in the amplitude of low frequency broadband noise at a position downstream of the cancelling source.

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Published date: 8 July 1983

Additional Information: Funding Information: The authors gratefully acknowledge the assistance of Professor G. B. B. Chaplin, suggested this topic of research, and Mr 0. Jones for many helpful discussions. M. C. J. Trinder also acknowledges the support of an SERC Case Award. The authors are grateful to Sound Attenuators Limited for permission to publish work.