Analysis of the high-frequency extension for spherical eigenbeamforming microphone arrays.

The em32 Eigenmike® spherical microphone array is constructed with 32 omnidirectional pressure microphones mounted on the surface of a 8.4-cm rigid spherical baffle. Beamforming is accomplished by the spherical harmonic decomposition eigenbeamformer and modal-beamformer concept. Due to the array size, geometry, and average element spacing, this approach yields fully controllable beampattern control up to approximately 8 kHz. Above this frequency, spatial/modal aliasing begins to interfere with beampattern control. However, professional audio applications require an operating bandwidth to much higher frequencies. One solution is to use a single microphone capsule that is closest to the main axis of the beampattern direction at higher frequencies. It will be shown that there are some problems to this solution. As an alternative implementation it is shown that using a small subset of microphone capsules at high frequencies allows one to smoothly transition the beampattern from eigenbeamformer processing to higher frequencies.