Abstract: The acoustic impedance of the ear is a function of frequency. With the change of test frequency, tympanograms taken from normal human ears show characteristic variations both in shape and in magnitude. The low-frequency (220-500Hz) tympanograms possess essentially a pinnacle shape, with the peak of maximum compliance pointing to the direction of decreased impedance. For test frequencies in the range of 1000-1300 Hz tympanogram become inverted (V-shaped), and, in opposite to that for the low frequency ones, the peak of maximum compliance represents at the same time the maximum impedance. Transitional forms are found for test frequencies of 630 and 800 Hz and are characterized by the frequent appearance of double peaks. When test frequency increases from 1300 to 2000 Hz tympanogram, after passing the similar transitional forms, changes back to its pinnacle shape again, thus completing a cycle of evolution. The magnitude of the tympanogram, which represents the range of dynamic compliance shift of the middle ear during tympanometry, decreases systematically as the test frequency increases.
Variations in shape of the tympanograms are interpreted in the light of the nonmonotonic impedance-compliance correlation. This non-monotonic complication is due to the presence of acoustic inductance in the measured over-all impedance, although it does not change significantly during tympanometry.