Alternatives to spherical microphone arrays: Hybrid geometries

We present a novel theory and design for constructing microphone arrays to extract spherical harmonic components from sound fields. The proposed non-spherical array structure provides a flexible and alternative design to the traditional spherical microphone arrays with lesser restriction on sensor locations. We use the properties of the associated Legendre functions and the spherical Bessel functions to develop a systematic approach to place circular microphone arrays in three dimensions for hybrid array geometries. As an illustration, we design and simulate a fifth order spherical harmonic decomposition array using 70 microphones to operate over a frequency band of an octave.