Enhanced finite-element model and acoustic test fixture to assess the objective occlusion effect induced by earplugs under bone-conducted stimulation

The occlusion effect refers to the increased perception, mainly at low frequencies, of bone-conducted sounds like physiological noises and one's own voice when one wears hearing protection devices. This phenomenon may lead to an acoustic discomfort and subsequently to less effective protection. It can be quantified by an objective indicator defined as the difference between the sound pressure level in the open and occluded earcanal. Several finite-element models based on truncated outer ears are available in the literature for predicting the objective occlusion effect but they suffer from several limitations mainly due to anatomical simplifications. In this paper, the occlusion effect of earplugs is assessed using an enhanced finite-element model and an augmented acoustic test fixture both based on the same real head geometry of a living participant. The finite-element head model is evaluated by comparing numerical results with various experimental data. The augmented acoustic test fixture is evaluated itself with respect to the participant. Using the finite-element model, the variability of the occlusion effect induced by the uncertainty on the stimulation position of the bone transducer, the position in the earcanal where the occlusion effect is assessed, and the uncertainty on the soft tissue Poisson's ratio is investigated.