Geometric error estimation and compensation in compact spherical loudspeaker array calibration

Compact spherical loudspeaker arrays are nowadays investigated as sources for directional measurements and audio playback. Their microphone-based calibration is not trivial as it requires an elaborate measurement setup of highly accurate geometry. This contribution shows how measurements of accurate geometric alignment were obtained to the authors' best knowledge, and systematically discusses how possible inaccuracies affect the resulting spherical harmonic radiation patterns. Eventually, a method is developed to estimate geometric errors from the measured responses. This geometry estimation is verified by tests with intentional errors. Finally, results are successfully employed to make calibration measurements more robust against geometric errors of the setup. This is done by both time realignment of the responses compensating for radial errors and the correction of the angles in the spherical harmonic transform.