Guilhem Viallet

Axisymmetric versus three-dimensional finite element models for predicting the attenuation of earplugs in rigid walled ear canals.

The axisymmetric hypothesis of the earplug-ear canal system geometry is commonly used. The validity of this hypothesis is investigated numerically in the case of a simplified configuration where the system is embedded in a rigid baffle and for fixed boundary conditions on the earplug lateral walls. This investigation is discussed for both individual and averaged insertion loss predictions of molded silicon earplugs. The insertion losses of 15 earplug-ear canal systems with realistic geometries are calculated using three-dimensional (3D) finite element models and compared with the insertion losses provided by two-dimensional equivalent axisymmetric finite element models using 6 different geometry reconstruction methods [all the models are solved using COMSOL Multiphysics (COMSOL, Sweden)]. These methods are then compared in order to find the most reliable ones in terms of insertion loss predictions in this simplified configuration. Two methods have emerged: The usage of a variable cross section (with the same area values as the 3D case) or the usage of a constant cross section (with the same length and volume as the 3D case).

A finite element model to predict the sound attenuation of earplugs in an acoustical test fixture

Acoustical test fixtures (ATFs) are currently used to measure the attenuation of the earplugs. Several authors pointed out that the presence of an artificial skin layer inside the cylindrical ear canal of the ATFs strongly influenced the attenuation measurements. In this paper, this role is investigated via a 2D axisymmetric finite element model of a silicon earplug coupled to an artificial skin. The model is solved using COMSOL Multiphysics (COMSOL(®), Sweden) and validated experimentally. The model is exploited thereafter to better understand the role of each part of the earplug/ear canal system and how the energy circulates within the domains. This is investigated by calculating power balances and by representing the mechanical and acoustical fluxes in the system. The important dissipative role of the artificial skin is underlined and its contribution as a sound transmission pathway is quantified. In addition, the influence of both the earplug and the artificial skin parameters is assessed via sensitivities analyses performed on the model.

Influence of the external ear tissue domains on the sound attenuation of an earplug predicted by a finite element model

Earplugs are a widespread solution to prevent the problem of hearing loss in the workplace environment, but they do not always perform as desired. Using a model of the ear canal occluded by an earplug could be helpful to perform sensitivity analyses (geometry and materials of the earplug) and to better understand the role of the earplug. The human external ear is a complex system made up of different tissues with a 3D geometry. In practice, it is reduced to a 2D cylindrical geometry for the acoustical tests fixtures. The purpose of this study is to compare the insertion loss predicted by a 3D complex finite element model of the ear canal surrounded by different tissue domains (skin, soft tissue, and bone) and occluded by a silicon earplug versus a 2D axisymmetric model of the same system. In both models, some investigations are made in order to verify if the models could be simplified by replacing the tissue domains by mechanical impedances. These investigations are made to reduce the complexity of the mo...

Comparison of a 3 dimension model versus a 2 dimension-axisymmetric finite element model of an occluded ear canal

Due to low cost and simplicity, earplugs are a widespread solution to prevent the problem of hearing loss in the workplace environment. In practice, earplugs often perceived are being uncomfortable and/or do not always perform as desired. The attenuation, based on a laboratory measurement, is often overestimated compared to in situ measurements. The use of a model of an occluded ear canal can help to build an individual measurement system of the attenuation and to develop an earplug with optimized attenuation. It is established that the unoccluded auditory canal can be approximated by a cylinder to predict the interior pressure field up to 6 kHz. A remaining question is whether this approximation holds true for an occluded ear. First, a simplified 2-D-axisymmetric finite element model of an ear canal coupled to a cylindrical earplug is developed. Special emphasis is on the coupling between the earplug and the lateral walls of the auditory canal. Second, a 3-D model of a real ear canal coupled to a cylindr...