**Figure 15.** Three-dimensional plot of a family of normal admittance magnitude tympanograms as a function of frequency. The tympanograms
are sliced at different frequencies to show (a) a low frequency at which the ear is stiffness dominated, (b) a frequency just
below middle-ear resonance, (c) resonant frequency, and (d) a frequency above resonance (taken from Lilly, 1984).