Investigation of the variability in earplugs sound attenuation measurements using a finite element model

Several studies report that an important range of attenuation can be observed in the measurement of earplugs (EP) sound attenuation. This important range of attenuation can be attributed to several intricate factors; the most commonly cited being the earplug insertion depth, the presence of leakages, the inter-subject ear canal (EC) geometrical variations, and the dynamical properties of the human EC tissues. The purpose of this work is to investigate the effect of these individual factors on the insertion loss (IL). Firstly, a finite element model of the EC surrounded by human external tissues and occluded by two types of EPs (foam and custom molded) is developed to predict the IL. Secondly, comparisons between attenuation measurement on human subjects and IL predicted by the model are carried out to validate the model. Thirdly, the effect of the aforementioned factors is quantified using the proposed model in order to explain the variability observed in the attenuation measurement on human subjects. It is found that the presence of leakages and the EP insertion depth are mainly responsible for the variability of the predicted EPs IL at frequencies