An Experimental Technique for Determining Middle Ear Impedance

Abstract

A two-microphone technique was used to determine the middle ear impedance of a live subject. the procedure involved the application of standing wave tube theory and the assumption that the ear canal behaves like an homogeneous cylinder with plane acoustic wave propagation up to a certain frequency-2 kHz for the current analysis. During experimentation the subject lay on a bench with his head braced against a wooden fixture. Acoustic pressures were recorded from the ear canal by the use of a spectrum analyser and probe microphones with flexible tips. Resultant impedance curves show middle ear natural frequencies at 831 Hz and 1, 970 Hz with high levels of damping. the reactive impedance curves show the influence of stiffness and ossicular mass on middle ear sound transmission. An advantage of the approach is that using features of the recorded data it is possible to calculate the effective probe tip to eardrum distance required for the calculation of middle ear impedance. the two-microphone technique appears to be a promising tool for assessing healthy and diseased middle ear function.

Key Words:

• multiple probe measurements
• higher frequency analysis