Controlled environment for reciprocity calibration of laboratory standard microphones and measurement of sensitivity pressure correction

The operation of an environmental chamber for high-precision calibration of laboratory standard microphones and acoustical measurements is described. The nominal ranges for the environmental control system are: temperature fr om -10 degrees C to 50 degrees C; pressure from 80 kPa to 110 kPa; and rela tive humidity (RH) from 10 % to 90 %. The estimated uncertainties (expanded , with 95 % confidence level) of the pressure, temperature and humidity mea surements were 20 Pa, 0.05 degrees C and 5 % RH, respectively. The sensitiv ity pressure correction for Bruel & Kjaer type 4160 laboratory standard mic rophones varies with frequency. Over the barometric pressure range 94 kPa t o 106 kPa, the sensitivity of B&K 4160 laboratory standard microphones chan ges by approximately 0.2 dB at 1 kHz and 0.35 dB at 10 kHz. An empirical eq uation for this microphone sensitivity pressure correction for the B&K 4160 microphone has been developed.