Modeling Intracochlear and Ear Canal Distortion Product (2f1–f2)

Responses of a mechanical model of the peripheral auditory system are calculated for two-tone stimuli with primary frequencies chosen so that the frequency of the cubic difference tone (2f₁-f₂) is maintained constant for all pairs used. The comprehensive model explicitly includes linear characterizations of the earphone driver, acoustic coupler, and middle ear, and a passive cochlear model with nonlinear damping of the cochlear partition motion. The amplitude and phase plots of the (2f₁-f₂) distortion signal, determined both in the ear canal and at the (2f₁-f₂) characteristic place, show rapid variations with f₁, and quite different patterns depending on the stimulus level. These plots, as well as plots showing the spatial distribution of primary and distortion signals along the cochlea for six selected f₁ values, are interpretable as showing interactions between multiple propagating waves at the distortion product frequency.