Active techniques for the suppression and reproduction of sound fields

Abstract

The active suppression of unwanted sound and the reproduction of a desired sound field are very similar problems. Recent work on the active control of sound has successfully used multichannel adaptive filters in the feed-forward control of periodic and quasiperiodic low-frequency sound in aircraft [S. J. Elliott et al., J. Sound Vib. 128, 355–357] and automobiles [S. J. Elliott et al., Proc. Inter Noise '88 2, 987–990 (1988)]. The essence of the approach can be extended to deal with temporally random sound fields generated by multiple primary sources. The necessary extension of the existing theory will be described and some practical applications of the technique will be discussed. The same theory will also be shown to provide an appropriate framework for dealing with problems in multichannel sound reproduction. In particular, the formulation of the problem allows the specification of the optimal inverse filters that give the minimum mean-square error in reproducing a sound field recorded at multiple points. Some experimental results will be presented from the implementation of this approach in the two-channel case by Hamada et al. [Proc. IEEE Workshop on Applications of Signal Processing to Audio and Electroacoustics (1989)].