Improved Technique for Detailed Measurements of the Middle Ear Impedance

Abstract

An apparatus is described for measurement of the acoustic impedance of the middle ear at the tympanic membrane which offers a possibility of studying the fine structure of the middle ear impedance. The method makes use of a constant current sound source mechanically fixed to a microphone probe indicator. Both the sound generator and the sound receiver microphone are coupled to a tube which is inserted into the ear. This unit can be fixed directly to the subject''s head, thereby eliminating the effect of the subject''s movements on the measurements. The results of measurements on 8 normal subjects are presented, in part as impedance, in part as admittance measured at 50 cps intervals from 200 to 2000 cps. The individual spread of data proved to be very great and appreciably greater than the difference between the 2 ears of a single individual.