In-ear and on-body measurements of impulse-noise exposure

Accurate quantification of noise exposure in military environments is challenging due to movement of listeners and noise sources, spectral and temporal noise characteristics, and varied use of hearing protection. This study evaluates a wearable recording device designed to measure on-body and in-ear noise exposure, specifically in an environment with significant impulse noise resulting from firearms. A commercial audio recorder was augmented to obtain simultaneous measurements inside the ear canal behind an integrated hearing protector, and near the outer ear. Validation measurements, conducted with an acoustic test fixture and shock tube, indicated high impulse peak insertion loss with a proper fit of the integrated hearing protector. The recording devices were worn by five subjects during a live-fire data collection at Marine Corps Base Quantico where Marines fired semi-automatic rifles. The field test demonstrated the successful measurement of high-level impulse waveforms with the on-body and in-ear recording system. Dual channels allowed for instantaneous fit estimates for the hearing protection component, and the device worked as intended in terms of hearing protection and noise dosimetry. Accurate measurements of noise exposure and hearing protector fit should improve the ability to model and assess the risks of noise-induced hearing loss.