AN EXPERIMENTAL-TECHNIQUE FOR DETERMINING MIDDLE-EAR IMPEDANCE

A two-microphone technique was used to determine the middle ear impeda nce of a live subject. The procedure involved the application of stand ing wave tube theory and the assumption that the ear canal behaves lik e an homogeneous cylinder with plane acoustic wave propagation up to a certain frequency-2 kHz for the current analysis. During experimentat ion the subject lay on a bench with his head braced against a wooden f ixture. Acoustic pressures were recorded from the ear canal by the use of a spectrum analyser and probe microphones with flexible tips. Resu ltant impedance curves show middle ear natural frequencies at 831 Hz a nd 1,970 Hz with high levels of damping. The reactive impedance curves show the influence of stiffness and ossicular mass on middle ear soun d 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 impeda nce. The two-microphone technique appears to be a promising tool for a ssessing healthy and diseased middle ear function.