In-ear noise dosimetry under earplug: Method to exclude wearer-induced disturbances

Abstract While personal noise exposure assessments are necessary to prevent noise-induced hearing loss in the workplace, standard personal noise dosimeters are limited when measuring the noise exposure of individuals wearing hearing protection devices (HPD). To overcome the difficulties in assessing the attenuation provided by HPDs, continuous monitoring systems of an individual's noise exposure under the HPD show promise. However, these systems can be affected by the noise events induced by the wearer, though research has shown that the risk of hearing loss inherent to self-generated sounds (voice, swallowing, chewing) can be less than for external noise. This paper presents a low computational method to perform in-ear noise dosimetry under an earplug while excluding the noise contributions from the wearer. The method uses a dual-microphone earpiece able to take measurements both under the earplug and outside the ear. A comparison of the two microphones signals, through coherence calculations, provides sufficient information as to whether the protected noise levels originate mainly from the wearer or from external noise sources. Laboratory results collected on human test-subjects suggest that the proposed method is not only valid for a wide variety of self-generated sounds, it is efficient regardless of the amount of attenuation provided by the earplug. Further work involves validating the approach and parameters in occupational settings, and adapting this method to other types of HPDs such as earmuffs or dual hearing protection.