A finite element model to study the earplug contribution to the objective occlusion effect

Abstract

The use of earplugs is commonly associated with an amplification of low frequency physiological noises in the earcanal referred to as the occlusion effect. In the literature, the type of earplug has been shown to significantly influence the occlusion effect in particular when inserted deeply enough. However, few studies have investigated the physical mechanisms that rule the earplug contribution. Their understanding is necessary to ultimately act on the earplug to reduce the occlusion effect. Classical lumped element models usually simplify the earplug as an impedance connected to the earcanal cavity. Intricate couplings of the earplug with the earcanal wall and the earcanal cavity are thus neglected. Finite element models can account for these couplings and thus make it possible to study the earplug contribution. In this work, the physical mechanisms that explain the earplug contribution to the objective occlusion effect are investigated. For this purpose, a 2-D axi-symmetric finite element model of an outer ear is used. Two types of earplug (foam and silicone) as well as two insertion depths (medium and deep) are considered. The earplug influence is interpreted in terms of volume velocity imposed to the earcanal cavity and related to its mechanical properties and its insertion depth.