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

Abstract

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.

Keywords:

• Noise exposure
• noise dosimetry
• noise-induced hearing loss
• hearing protection
• auditory injury
• impulse noise

Acknowledgements

The authors gratefully acknowledge Mr. Kurt Yankaskas of ONR for sponsoring the multi-centre noise collection and Mr. John O’Donnell of USMC for his support at Quantico; Dr. Alan Wall of AFRL for coordinating the large collection and Dr. Kent Gee of BYU and Mr. Chucri Kardous of NIOSH for their feedback on early analysis; and Mr. Joe Lacirignola and Ms. Christine Weston of MIT LL for development of the in-ear and on-body noise dosimeter prototype. Portions of this work were shown in the following presentation: S. Davis, C. Smalt, W. Murphy, and C. Kardous, “In-ear and On-body Measurements of Impulse Noise Exposure,” 2018 Annual Meeting of the National Hearing Conservation Association, Orlando FL, February 2018. Approved for public release. Distribution is unlimited.

Disclosure statement

No potential conflict of interest was reported by the authors.

This material is based upon work supported by the Department of the Navy under Air Force Contract No. FA8702-15-D-0001 and Office of Naval Research. Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Department of the Navy. Furthermore, they do not represent any official policy of the U.S. Navy, the Centers for Disease Control and Prevention or the National Institute for Occupational Safety and Health. Mention of company names and products does not constitute endorsement by the USN, USAF, CDC, or NIOSH

Notes

1 IPIL values were not corrected for bone conduction.

2 A-duration is the time between the start of an impulse and the first zero crossing in pressure after the peak.

3 The Well-Fit PAR measurements were conducted near the end of the data collection, so there was no opportunity to notify the two low-PAR subjects and allow for HPD refittings. See Section 4 for further discussion.