Objective: To properly measure the effective noise exposure level of workers with hearing protection devices (HPD), the use of in-ear noise dosimeters (IEND) is increasing. Commercial IENDs typically feature one in-ear microphone that captures all noises inside the ear and do not discriminate the residual noise in the earcanal from wearer-induced disturbances (WID) to calculate the in-ear sound pressure levels (SPL). A method to alleviate this particular issue with IENDs and calculate the hearing protection level on-site is therefore proposed.
Design: The sound captured by an outer-ear microphone is filtered with the modelled HPD transfer function to estimate the in-ear SPL, this way part of the WIDs mostly captured by the in-ear microphone can be rejected from the SPL. The level of protection provided by the earplugs can then be estimated from the difference between in-ear and outer-ear SPLs. The proposed method is validated by comparing the outcome of the proposed WID rejection method to a reference method.
Study sample: The detailed methods are assessed on audio recordings from 16 industrial workers monitored for up to 4 days.
Results: The merits of the proposed WID rejection approach are discussed in terms of residual SPL and hearing protection level estimation accuracy.
Conclusions: Based on the findings, a method to integrate the proposed WID rejection algorithm in future IENDs is suggested.
Keywords: Noise exposure; hearing protection; in-ear noise dosimetry; personal attenuation rating; wearer-induced disturbance.