Vibroacoustic simulations of asymmetric tapered duct mimicking cochlear hydrodynamics

Upon excitation by two pure-tone closely spaced in frequency, the cochlea produces intermodulation distortion tones which can be measured at the ear canal as otoacoustic emissions (OAE). Although OAEs have been widely used in auditory diagnosis, their mechanism of generation and backward propagation are not well-understood. It is known that sound stimulation elicits two types of intracochlear pressure waves: the fluid-borne compression wave, which travels at the speed of sound and the fluid-structure coupled traveling wave, which propagates significantly slowly, especially as it approaches the best place. However, compression wave excitation of the cochlear structures, such as the basilar membrane (BM), has been questioned on the basis of the classical Peterson-Bogert model. This question has significant implications for identifying the mechanism of backward propagation of OAE. To address this question, vibroacoustic simulations are performed in this study in symmetric and asymmetric tapered ducts mimicking the passive human cochlea with the objective of clarifying how compression wave can excite the BM. The two ducts are separated by BM without restricting its number of radial modes. The details of compression wave excitation of the BM are shown up to very high frequencies, and insights on this interaction are brought out.