Far-field criterion for spherical microphone arrays and directional sources

A planar wavefront assumption facilitates significant simplifications in microphone array processing algorithms because information on the distance of the source is not required. This assumption was studied and formulated for spherical microphone arrays and point sources, but has not been studied yet for directional sources, which represent realistic sources such as musical instruments. A far-field criterion for directional sources is proposed in this paper, and the accuracy of a plane-wave approximation at a spherical microphone array is shown to depend on parameters of the acoustic configuration, such as the distance between the source and the microphone array and the source directivity.