The main aim of this study was to investigate the shape variation in the human ear canal and the effects of venting on the spatial design of hearing aids. The second aim was to determine the design feasibility of a multiple venting hearing aid and assess the flexibility of design provided. A statistical shape model based on principal component analysis was created from a dataset of 60 left and 49 right ears. The modal variations of these models were then examined to determine the narrowest portion of the ear canal likely to limit effective venting. Finally, 3D models of two hearing aid shells, one with multiple 0.4-mm vents and the other with a single large 3-mm vent were created. Results showed that more than 50% of the shape variation in the human ear canal can be described by the first three modes of the statistical shape model developed. The narrowest predicted variation of this model had a minimum area of 36.4mm 2, and the mean ear shape was found to have a minimum area of approximately 48mm 2. It is estimated that even with a conservative vent packing of 0.4, multiple venting equivalent to at least a single 2-mm vent is achievable. The predicted variation in the human ear canal provides adequate physical space for a feasible multiple vented hearing aid shell. Furthermore, as multiple small vents are able to fit in around other components in the hearing aid design, certain design flexibility is provided by this venting approach.

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.