Evaluation of Non-Spherical Scattering Bodies for Ambisonic Microphone Arrays

Paper in proceeding, 2022

The XMA was recently presented, which is a higher-order ambisonic microphone array with a non-spherical scattering body. The approach is compatible with the also recently presented equatorial microphone array so that also XMAs can be designed with the microphones distributed solely on a circumferential contour around the scattering body. This greatly reduces the required number of microphones compared to classical spherical microphone arrays that require the microphones to be distributed over the entire surface of the scatterer. The equatorial XMA has so far only been evaluated as a head-mounted array, i.e. with a human head as the baffle. Other form factors of a range of sizes are also of practical relevance, particularly those form factors of 360 cameras as these are capable of capturing a complete panoramic audio-visual experience from a first-person view when combined with an equatorial XMA. We present a set of simulations based on which we identify what spherical harmonic orders can be obtained with what accuracy for a set of convex scattering body geometries that are of relevance in the given context. We demonstrate that the shape of the body is not very critical, and even corners are possible. The main limitation is that small bodies do not allow for extracting higher orders at low frequencies.