The calibration of ear-probe microphones can increase the precision of calibrating stimulus levels in situ and of measuring acoustic responses from the ear. This paper proposes a methodology to measure the sensitivity of an ear-probe microphone, requiring only an acoustic coupler and a calibrated reference microphone. The input impedance of the coupler is measured, enabled by a preliminary acoustic Thevenin calibration of the ear probe, and the plane-wave transfer impedance of the coupler is calculated analytically. Using these two quantities, the pressure transfer function between the reference microphone and the ear-probe microphone is estimated. This enables estimating the sensitivity of the ear-probe microphone. The proposed and an existing method were compared, resulting in substantially similar ear-probe microphone sensitivities. The proposed method is practically feasible in producing reliable measurements of sound pressure in the ear canal and calibrating stimulus levels in a clinical setting.
Nørgaard, K. R., Fernandez Grande, E., & Laugesen, S. (2018). A coupler-based calibration method for ear-probe microphones. Journal of the Acoustical Society of America, 144(4), 2294–2299. https://doi.org/10.1121/1.5064283