Beamforming performance of circular microphone array on spherical platform near bottom boundary

Spherical microphone arrays have been extensively studied for multimedia applications by both academic and industrial communities. General assumption of such study is based upon a planar wave traveling in free space model. However, in practical applications, acoustic wave reflections from boundary of a confined environment such as rooms or nearby furniture´s carrying the array may degrade array performance significantly. In this paper, we present an approach for beamforming and direction of arrival (DOA) estimation using circular microphone array mounted on the equator of a sphere near a bottom boundary where the bottom reflection is dominant over other reflection, which corresponds to the applications such as spherical microphone array set on table or floor. We examine impact of reverberation to the beamforming performance and propose an algorithm to improve the microphone array performance. We first introduce an acoustic spherical scattering model to provide a theoretical background. The boundary reflection model is subsequently developed based on two-path ray theory. We further propose an approach using corrected steering vector to improve the beamforming performance to compensate mismatch of plane wave assumption in free space that the normal beam-forming is based upon. The effectiveness of the proposed approach is evaluated by numerical simulations.