Abstract
Pressure sensitivities of laboratory standard microphones are acoustic standards required for precise measurement in the audible frequency range. The National Metrology Institute of Japan (NMIJ) has developed a pressure calibration system that enabled absolute calibration of pressure sensitivities. In this study, we analyzed the measurement uncertainty of pressure sensitivities calibrated at NMIJ in detail by using the pressure sensitivity formula and examining every possible component that contributed to the uncertainty. The analysis revealed several dominant components, such as repeatability in the measurement of the voltage transfer function, cavity volume of the coupler, capillary tube correction factor, and instability of the microphone. Within a frequency range in which the expanded uncertainty was constant, the expanded uncertainty (coverage factor k=2) was 0.04 dB for Brüel & Kjær 4160, a type LS1P microphone, and 0.09 dB for Brüel & Kjær 4180, a type LS2aP microphone.
