Acoustic impedance studies of the normal ear

Repeated measurements of the acoustic impedance at the eardrum were performed on 33 normal subjects. The data are analyzed from the standpoint of the development of criteria for the compliance and resistance parameters of normal impedance as well as ear canal volume measurements. The study also emphasizes the high reliability of repeated impedance measurements.

Effect of the acoustic reflex on the impedance at the eardrum

Seventeen ears of 12 subjects with normal hearing were tested in both a laboratory and a clinical setting to study impedance changes in normal human ears associated with the acoustic reflex. Compliance and resistance at the eardrum were measured with middle ear muscles relaxed and contracted by means of a contralateral noise stimulus, respectively.

The reflex induced impedance changes were compared to similar impedance data obtained by other investigators, and to typical otosclerotic impedance values. The reflex is shown to affect the impedance by a decrease in compliance and a slight decrease in resistance.