An Investigation about the Effect of Diffusivity of Sound Field for Reciprocity Calibration of Measurement Microphones in Diffuse-field

The primary calibration of measurement microphones is usually performed by the reciprocity technique. In this technique the microphone sensitivity is commonly calculated from the electrical transfer impedance and the acoustic transfer impedance between three microphones connected acoustically in pair-wise combinations. In diffuse-field, the acoustic transfer impedance is determined from the measurement of chamber reverberation time. This paper presents an investigation about the effect of diffusivity of the sound field in the measurement of the chamber reverberation time for reciprocity calibration. The microphones were connected acoustically by a small reverberation chamber and to improve the diffusivity two types of diffusers were tested: hanging panels diffusers and boundary diffusers. The reverberation time was measured using the integrated impulse response method in thirty two source-receiver configurations. The microphone sensitivities were calculated and the results point differences up to 0.2 dB in higher frequencies.