LOCAL ACTIVE CONTROL OF DIFFRACTED DIFFUSE SOUND FIELDS

The average spatial extent of the zone of quiet created by a local active control system in a diffuse enclosed sound field has been investigated using computer simulation and measured experimentally. The secondary source is modeled as a rigid sphere with a pulsating segment and its diffracting effect on a diffuse primary pressure field has been simulated. The diffraction effects of a hypothetical listener's head, modeled as rigid sphere, on both the primary and secondary acoustic fields have also been calculated using a least-squares calculation for the amplitudes of a set of spherical harmonics. The size of the average zone of quiet is observed to increase slightly as a result of diffraction 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 Acoustical Society of America.