Coincident microphone simulation covering three dimensional space and yielding various directional outputs

Claim 1

A microphone assembly for providing outputs corresponding to at least zero order and first order harmonics equivalent to the outputs which would be obtained from a plurality of coincident microphones, the directional response curve of each coincident microphone being a respective spherical harmonic, said microphone assembly comprising at least four microphone units mutually disposed at the integration points of an integration rule for the surface of a sphere, as hereinbefore defined, matrix means having a respective combining means for each desired spherical harmonic including a first combining means for said zero order harmonics and a second combining means for said first order harmonics, means for applying the output of each microphone unit to said combining means with a gain proportional to the weight of said integration rule corresponding to the integration point at which said microphone unit is located and a further gain equal to the magnitude of said spherical harmonic in the direction of maximum response of said microphone unit, first equalisation means connected to said first combining means for applying an equalisation to the output thereof and a second equalisation means connected to said second combining means for applying an equalisation to the output thereof, the equalisation being such that all outputs of each said equalisation means have substantially the same frequency response to sounds from all directions up to a limiting frequency and are substantially identical to the outputs obtained from a plurality of coincident microphones.