Numerical study of the broadband vibro-acoustic response of an earmuff

In this paper, the vibro-acoustic response of a passive earmuff in a broadband frequency range (100 Hz to 5 kHz) is investigated using a finite element analysis. Firstly, the study focuses on the vibro-acoustic response of the cup and the back-plate regardless of the comfort cushion contribution. Secondly, emphasis is put on the foam-filled comfort cushion which is the trickiest component to model because of its physical complexity. This multiphasic cushion is modeled in a simplified way as an equivalent solid, either isotropic or transverse isotropic in order to take into account the added transverse stiffness due to the bulging of the cushion polymeric sheath. The accuracy of these models is investigated by comparing the simulated insertion loss (IL) to measurement data. The IL predicted with the isotropic cushion model is highly underestimated between 500 Hz and 2.5 kHz due to the presence of an unrealistic mode of transverse deformation. It is found that (i) neglecting the acoustic excitation on the cushion' external flanks of the isotropic model or (ii) using the transverse isotropic cushion model significantly improves the simulated IL.