The soundfield microphone utilizes an array of microphones to derive various components of the sound field to be recorded or measured. Given that at high frequencies the response varies with the angle of incidence, it may be argued that any angle of incidence is as important as another, and thus it is important to achieve a calibration that achieves an optimum perceived response characteristic. Gerzon noted that ‚ÄúAbove a limiting frequency F Àú c/(pi r) [. . .] it is found best to equalise the nominal omni and figure-of-eight outputs for an approximately flat response to homogeneous random sound fields.‚Äù In practice, however, soundfield microphones have been calibrated to realize a flat axial response. The present work explores the theoretical ramifications of using a diffuse-field equalization target as opposed to a free-field equalization target and provides two practical examples of diffuse-field equalization of tetrahedral microphone arrays.
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