Low Frequency Phase Calibration for a Circular Microphone Array

Previous work has indicated that a limitation on the low frequency performance of a circular microphone array for holographic sound field recording is phase mismatch between the microphones in the array. At low frequencies these variations become more significant than at mid-range and high frequencies because the high order phase mode responses are lower in amplitude. This paper investigates the possibility of performing a "self" calibration of a microphone array. The basis of the calibration is to estimate the location of one or more sources using mid-range frequencies and to use this source location information to perform correction to the array at low frequencies. This of course implies that the calibration is performed in a relatively anechoic environment, since multipath effects at widely differing frequencies are uncorrelated. Initial results confirm that a significant improvement in the array response is possible using this approach.