LOCAL ACTIVE CONTROL OF DIFFRACTED DIFFUSE SOUND FIELDS

The average spatial extent of the zone of quiet created by a local act ive control system in a diffuse enclosed sound field has been investig ated using computer simulation and measured experimentally. The second ary source is modeled as a rigid sphere with a pulsating segment and i ts diffracting effect on a diffuse primary pressure field has been sim ulated. The diffraction effects of a hypothetical listener's head, mod eled as rigid sphere, on both the primary and secondary acoustic field s have also been calculated using a least-squares calculation for the amplitudes of a set of spherical harmonics. The size of the average zo ne of quiet is observed to increase slightly as a result of diffractio n of the secondary field by the rigid sphere. The calculations give a good prediction of the average zones of quiet measured experimentally, both with and without a diffracting sphere present. (C) 1995 Acoustic al Society of America.