Abstract

A system and method of measuring the linear and nonlinear power-based responses of the ear uses a small probe assembly containing a sound source and microphone inserted into the ear. The linear power-based responses, or transfer functions, measured by the system include reflectance, admittance and impedance calculated in the time and frequency domains. A calibration procedure is based upon measured pressure responses in one or more calibration waveguides, and upon a model of the transfer function of each of the calibration waveguides that incorporates viscothermal losses. The linear transfer functions and the measured pressure responses in the ear may be combined to calculate sound power absorbed by the ear. The system is further able to measure the corresponding nonlinear power-based response of the ear by measuring any of the above transfer functions at different levels of the acoustic stimulus. These are used to calculate the nonlinear power absorbed by the ear when combined with the measured pressure responses in the ear at each stimulus level. A differential nonlinear transfer function of the ear and differential power absorbed by the ear are calculated based upon the level-dependent measurements of the transfer functions and the absorbed power. By delivering changes in static pressure applied to the ear via an additional probe tube in the probe assembly, the system is able to measure the dependence on static pressure of any of these linear and nonlinear power-based functions. The system is particularly useful in testing the auditory response of the human ear, with applications to the detection and diagnosis of abnormalities in the external, middle and inner ear of humans ranging in age from neonates to adults, as well as to the better understanding of the threshold audibility function in normal and hearing-impaired humans.

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