Wave effects and pressure distribution in the ear canal near the tympanic membrane

The complicated geometry of the human tympanic membrane and adjoining portion of ear canal can be expected to affect the flow of acoustic energy into the middle ear at frequencies greater than 10 kHz. To explore the implications of this geometry we have studied the acoustical behavior of a series of experimental cavities with shapes chosen to characterize the various acoustical factors that could be anticipated. The presence of the eardrum was simulated by the inclusion of a plastic or paper film of appropriate size and location. Preliminary experiments indicate that the penetration of the incident acoustic wave into the wedge‐shaped volume representing the final 10 mm of ear canal is strongly frequency‐dependent, and that between 10 and 20 kHz the apparent plane of reflection moves inward by approximately 6 mm. Measurements of sound pressure distribution in this region indicate that pressure variations greater than 15 dB can be expected across the human tympanic membrane at 15 kHz. Existing theoretical models will need to be modified if they are to be relevant above 10 kHz.