Side branch and parallel vent effects in real ears and in acoustical and electrical models.

The purpose of the project was to demonstrate and explain the acoustic effects of side branch and parallel vents in individual real ears. It was shown that parallel and side branch vents produce similar low frequency filtering effects and vent-associated reactance resonances. However, when the input system incorporates a side branch vent the sound pressure produced in the ear canal at frequencies above the vent-associated resonance is less than that produced when the input system is unvented. This effect is not seen when the input system is associated with a parallel vent. Data obtained in the real ear canals were compared to analogous measurements made using an acoustical model (the Zwislocki coupler) and an electrical model designed to simulate the hearing aid receiver, input tubing, earmold, ear canal, and eardrum. Both models yielded data very similar to the real ear results. The advantages of each model in predicting the effects of individual earmold vents are discussed.