Abstract
Tympanometry was performed on twenty-two ears of twelve normal hearing subjects with the stapedius muscle in the relaxed state and again with the muscle contracted during exposure to 98 dB SPL 1000 Hz narrow band noise. Components of acoustic admittance were calculated and converted into their reciprocal acoustic impedance parameters. The changes in acoustic admittance and acoustic impedance and their respective components were analyzed and compared with earlier data obtained by other investigators. The results confirm that the major change in the acoustic impedance is a consequence of a stiffening of the middle ear with a small resistance increase using a 220 Hz probe tone and decrease using a 660 Hz probe tone. This method is shown to be a satisfactory procedure to derive and display dynamic changes in the transmission characteristics of the middle ear associated with the acoustic reflex.