Instability of the voltage transfer function for an MR103 microphone in a coupler calibration technique

MR103 microphones are commonly used laboratory standard microphones in Japan. When the pressure sensitivity of MR103 is calibrated by using a coupler calibration technique, higher accuracy is difficult to achieve due to deviations in the measured voltage transfer function. These deviations are peculiar to MR103, but not to B&K4160, which is also a commonly used laboratory standard microphone throughout the world. Such deviations occur even when the measurements are done consecutively under the same measurement conditions, such as polarization voltage, temperature, and static pressure. tudy experimentally and theoretically considered one of the possible reasons for this deviation. The results reveal that (a) this deviation can be explained by changes in the microphone’s parameters, such as the distance between a microphone’s membrane and back-plate, and the tension of the membrane, (b) grease used to prevent leakage of gas and sound out of the coupler might be one of the reasons for this deviation, and (c) insertion of polished sapphire spacers between the microphones and the coupler might help diminish this deviation.