Effect of external ear canal occlusion on acoustic pressure gain at the tympanic membrane

Hearing loss is classified into two primary types: sensorineural and conductive. The less problematic type is conductive hearing loss, which arises from issues or blockages in the outer or middle ear. The most frequent cause of it in the outer ear is an excessive amount of earwax (cerumen) in the ear canal.

In this work, a three-dimensional finite element (FE) model was used to examine the effect of ear canal occlusion with earwax under different settings on the acoustic pressure gain at the tympanic membrane (TM).

The effects of full and partial ear canal occlusion with earwax have been investigated using Comsol Multiphysics FE simulation software. The software used the finite element method to solve the model equations, accounting for a variable ear canal cross-sectional area. A lumped-element acoustic impedance is used to mimic the boundary between the downstream hearing system and the tympanic membrane.

The model results are consistent with those presented by other experimental studies. The results show that the acoustic pressure gain at the TM increases with the distance from the earwax layer. Similarly, an increase in the thickness of this layer in a fully occluded ear canal significantly increases the pressure-gain difference at the TM. As the occlusion percentage rises, the gain decreases, and the resonance frequencies shift to lower values. At up to 60% occlusion, there is no significant effect on gain. Considerable gain difference occurs with 95% occlusion. There is a significant phase difference between the 95% occlusion case and the fully open (no occlusion) case, which will affect the quality of sound reaching the TM and, consequently, the entire hearing process.

The model presented in this study provides deep insight into the effect of earwax on hearing quality and can be used in other settings.