Transmission of high-amplitude sound through leakages of ill-fitting earplugs

Exposure to high sound pressure levels (SPL) is a leading cause of noiseinduced hearing loss, and earplugs are a primary means of protection. The effectiveness of earplug protection depends on the seal formed in the ear canal. An ill-fitting earplug leaves air gaps that leak sound and degrade attenuation. The acoustics of these leak paths and their dissipation mechanisms under high-amplitude sound remain poorly characterized. This study quantifies sound transmission through modeled earplug leakage with rigid-wall idealization and identifies the governing dissipation mechanisms by combining impedance-tube experiments and direct numerical simulation (DNS). The methods were first verified against stand-alone slit resonators and orifices, for which extensive published data are available, and then used to measure the transmission loss (TL) and acoustic power absorption coefficient of modeled earplug–canal configurations over 1–5 kHz at overall incident SPLs of 120–150 dB. Leakage from an ill-fitting silicone rubber earplug reduced its TL by approximately 18 dB relative to a sealed configuration at an overall incident sound pressure levels (OISPL) of 120 dB, and the leakage-path TL increased with SPL, indicating a nonlinear attenuation mechanism. DNS resolved the SPL-dependent mechanism, showing that incident acoustic energy is converted into vortical kinetic energy at the leak edges at an OISPL of 150 dB, more strongly at lower frequencies. These findings show that this nonlinear mechanism activates under modeled leakage and identify the leak path as the dominant SPLdependent transmission route in ill-fitting, non-absorbing earplugs, underscoring the importance of seal integrity in high-SPL environments.