Characterization of Cartilage Implication in Protected Hearing Perception During Direct Vibro-Acoustic Stimulation at Various Locations

In noisy environments, hearing protection is used to occlude the ear canal's external meatus to limit air conduction. However, acoustic waves travel through several pathways such as bones, cartilages, and soft tissues, which impact protections' effectiveness. Physical properties of cartilage, as well as soft tissues can generate airborne sound in the occluded ear. To assess the part of the cartilage which contribute to the limitation of hearing protection, Bekesy audiometries with electrodynamic transducers are performed. Four zones (ear tragus, scaphoid fossa, ear lobe, behind the concha) are excited by a pulsed signal sweeping from 125 Hz to 8 kHz. The frequency response tends to denote that the ear tragus has the best transducer-cartilage coupling efficiency. The occlusion outcome is also evaluated at the mastoid and ear tragus, showing cartilage ability to transmit sound, especially at low frequency. For higher frequencies, the contribution of cartilage decreases, and the involvement of direct air conduction from transducer acoustic radiation increases, prominently when the ear canal is not occluded. Nevertheless, considering the transducer-skin coupling effects evaluated with airborne radiation measure and the contribution to the hearing perception of the earlobe, composed mainly of skin and adipose tissue, this paper raises the question of the conduction of the sound in soft tissues, and in a first step, in the understanding of the pathway of the sound when the ear canal is occluded. (C) 2021 Elsevier Ltd. All rights reserved.