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

Abstract

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
• in-ear noise dosimetry
• hearing protection
• personal attenuation rating
• wearer-induced disturbance

Acknowledgment

The authors would like to acknowledge the financial support received from the Natural Sciences and Engineering Research Council (NSERC) through the NSERC-EERS Industrial Research Chair in In-Ear Technology (CRITIAS), as well as for technical support provided by EERS Global Technologies Inc. The authors would also like to thank the Centre for Interdisciplinary Research in Music Media and Technology (CIRMMT) for project funding opportunities. The first author is grateful to the Institut de recherche Robert-Sauvé en santé et sécurité du travail (IRSST) for the financial support received during his doctoral program and to the École nationale du meuble et d’ébénisterie (ENME) and its students for their participation in the field data collection.

Disclosure statement

No potential conflict of interest was reported by the author(s).