An Experimental Study on Multiple Acoustic Venting for Hearing Aid Applications

Providing adequate relief from the occlusion effect while avoiding gain-limiting acoustic feedback continues to be a major issue in hearing aid design and fitting. Traditionally fitting of a parallel vent is often seen as a trade-off of occlusion performance for increased feedback effects. This paper explores the possibility of using multiple small acoustic vent paths in hearing aid design and provides an understanding of varying vent number and size on acoustic transmission through a vent system. The sound transmission properties of multi-vented samples have been tested in a custom 2 cc coupler. Results show, with increasing vent number and vent diameter there is an upward shift in vent associated resonance. Decreasing vent number decreases the magnitude of the vent resonances observed. In general, smaller vents require greater area to exhibit similar low frequency transmission properties but are less prone to vent associated Helmholtz resonances. High frequency attenuation important for feedback performance is found to be dependent on total vent area but not on the size of the vents used. We would expect multiple vented earmoulds to have similar feedback performance to traditional single vented samples with the same area of venting. Occlusion performance may be poorer than a single large vent, however multiple acoustic venting may provide greater design flexibility with regard to space in the ear canal.