Advantages of cartilage sound conduction in hearing aids

A cartilage conduction hearing aid has been developed for patients who cannot use conventional hearing aids owing to particular diseases of the external or middle ear. A user of such a hearing aid places the ring-shaped transducer gently at the entrance of the external auditory canal, so that it does not cause any feeling of discomfort. The cartilage conduction transducer vibrates the aural cartilage of the user, and the transmitted vibration generates sound in the external auditory canal, particularly in the low and middle-frequency ranges. In this regard, the cartilage conduction hearing aid has a different principle of sound transmission from conventional hearing aids. In this study, the performance and possible advantages of cartilage sound conduction in hearing aids were examined. This was achieved through two experiments focusing on important indicators: (i) the susceptibility toward acoustic feedback compared with air sound conduction and (ii) the ability of the user to realize sound directivity during binaural use of the cartilage conduction hearing aid. It was found that cartilage conduction was less susceptible to acoustic feedback than air conduction through an open-fitting earplug, even though both the cartilage conduction transducer and the open-fitting earplug keep the external auditory canal open. With respect to the second experiment, the binaural use of cartilage conduction transducers was found to facilitate subjective lateralization for users when examined using the interaural intensity difference (IID) cue. These results show that the cartilage conduction hearing aid has distinct advantages over the conventional air conduction hearing aid in terms of the robustness against the acoustic feedback and effective binaural use. Although the cartilage conduction hearing aid was once considered merely an expedient alternative for patients suffering from particular diseases, the advantages highlighted in the present study may attract patients with mild and moderate hearing loss, who are currently using air conduction hearing aids.