Sensitivity measurement of a laboratory standard microphone by measuring the diaphragm vibration

Abstract

As a method to determine the sensitivity of a laboratory standard microphone, the reciprocity method is employed as an international standard (IEC61094-2). This method is highly reliable and achieves high precision. However, three microphones are essentially required for this method. This procedure is complicated and takes a long time due to many combinations of microphone pairs and couplers. To overcome these difficulties, a novel method based on the measurement of vibration on the surface of a microphone using a laser Doppler vibrometer is proposed. It aims to obtain the sensitivity of a laboratory standard microphone. To this end, the relationship between the surface velocity of the diaphragm centre and acoustic volume velocity induced by the vibration of the diaphragm surface is investigated, and an empirical model is developed by measuring the distribution of the surface velocity. This paper used an empirical model of a 1-in. laboratory standard microphone estimated with 6 samples. The estimated sensitivity using this model has a difference of about 0.1 dB from the results of the reciprocity method applied to samples not used for estimating the empirical model.