Time-domain finite element model of level-dependent nonlinear filter earplug

Nonlinear filter earplugs are hearing protection devices that protect against high-level impulse noises while allowing communication and situational awareness. Unlike conventional passive protectors, these devices provide increasing attenuation with the impulse sound pressure level thanks to filters made of one or more small orifices. Their performances are usually assessed with experimental measurements requiring specific high-cost equipment. This study aims to develop a numerical model based on the time-domain finite element method to provide an alternative approach to evaluate these protectors’ performance. Thus, the modeled acoustic pressures in an acoustic test fixture’s ear canal occluded with a simplified nonlinear filter earplug were estimated. The simulations were performed using high-level impulse noises ranging from 116 to 171 dB-peak. The effects of equilibrium temperature and model limitations were also analyzed. The in-ear sound pressure levels and corresponding protector’s attenuation calculated with the numerical model were compared to previous experimental measurements, and good correspondence was found. Regarding the in-ear peak sound level, deviations comprised between 0.5 dB and 1.3 dB were computed. A change in equilibrium temperature did not induce significant variation in peak sound pressure levels. This study and its underlying observations pave the way for optimizing nonlinear filter characteristics and their integration into new hearing protection devices at lower costs.