Normal function of the middle ear and its measurement.

Some principles underlying acoustic impedance measurements in the ear canal and their evaluation are reviewed. The following topics are included: some methods of measurement, useful frequency range, the middle-ear system, impedance characteristics of normal and some pathological ears, and the relation between the impedance and tympanometric results. Advantages and disadvantages of measurements with an acoustic bridge and parallel probe tubes are contrasted and the same is done for tympanometry versus static impedance measurements. The relation between tympanograms and static impedance data referred to the tympanic membrane is illustrated by means of a semihypothetical example. The example suggests that a probe frequency around 700 Hz is more informative in tympanometry than a probe frequency of 220 Hz.