Développement d’une oreille artificielle simplifiée et réaliste pour quantifier l’effet d’occlusion objectif

Abstract

In Quebec, approximately 360,000 workers are exposed daily to noise levels that could damage their hearing health. The use of earplugs is sometimes the only solution to reduce the workers’ exposure to these dangerous noises. However, their use is often associated with multiple discomforts which reduce the quality and the wearing time, thus rendering them ineffective. This dissertation is primarily concerned with the occlusion effect, an acoustic discomfort associated with the increased perception of internal sounds (such as one's own voice) when the ears are occluded. The purpose of this memoir is to improve the simulation and measurement tools of the objective occlusion effect, an indicator generally associated with the experienced acoustic discomfort. The objective indicator of the occlusion effect (OE) is therefore defined as the difference in sound pressure at a given point in the earcanal between the occluded and open earcanal. Indeed, the existing artificial ears do not allow an accurate limitation of the main effects observed on groups of participants (e.g., effect of earplug type and the insertion depth) and the models used to design these ears have not yet been validated. The development of this type of tool is essential to be able to design more comfortable earplugs. This master's work therefore aims to develop an artificial ear prototype (POA for “prototype d’oreille artificielle” in French) dedicated to the objective quantification of the occlusion effect. This POA must be simple in terms of its geometry and anatomy, but realistic enough to be able to properly reproduce the vibration field on the walls of the earcanal. The POA is designed to have a cylindrical earcanal of constant section integrated in a parallelepiped matrix reproducing the surrounding tissues and to be excited perpendicular to the earcanal directly on the soft tissues using a test bench dedicated to the characterization of acoustic materials (QMA bench). The POA is first designed using initial digital tools. It is then manufactured and evaluated experimentally against data extracted from the literature. Evaluation of the POA determined that the main known effects observed on the OE (i.e., earplug type and insertion depth) are correctly reproduced for a foam earplug, but less so for a more rigid silicone earplug. A validation phase is then carried out. In the case of a simple occlusion device made at the entrance of the earcanal, the simulations of the OE are quite close to the measurements carried out on the manufactured POA, and this mainly when the soft tissues are designed as a quasi-incompressible viscoelastic solid. For earplugs type occlusion devices (foam and silicone), the measurement/calculation comparison is less satisfactory. Several factors could explain these differences, including: the mechanical properties of earplugs and the contact between the skin and the earplug, which are poorly understood and poorly modeled. This prototype of an artificial ear takes a step forward in the development of the tools dedicated to improving the comfort (and therefore the effectiveness) of earplugs, thus reducing the risk of deafness for workers.

Date	9 Dec 2021
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Olivier Doutres (Supervisor) & Franck Sgard (Co-supervisor)