Method for protected noise exposure level assessment under an in-ear hearing protection device: a pilot study

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.