Spectral analysis of hearing protector impulsive insertion loss

Abstract

Objective: To characterise the performance of hearing protection devices (HPDs) in impulsive-noise conditions and to compare various protection metrics between impulsive and steady-state noise sources with different characteristics. Design: HPDs were measured per the impulsive test methods of ANSI/ASA S12.42-2010. Protectors were measured with impulses generated by both an acoustic shock tube and an AR-15 rifle. The measured data were analysed for impulse peak insertion loss (IPIL) and impulsive spectral insertion loss (ISIL). These impulsive measurements were compared to insertion loss measured with steady-state noise and with real-ear attenuation at threshold (REAT). Study sample: Tested HPDs included a foam earplug, a level-dependent earplug and an electronic sound-restoration earmuff. Results: IPIL for a given protector varied between measurements with the two impulse noise sources, but ISIL agreed between the two sources. The level-dependent earplug demonstrated level-dependent effects both in IPIL and ISIL. Steady-state insertion loss and REAT measurements tended to provide a conservative estimate of the impulsively-measured attenuation. Conclusions: Measurements of IPIL depend strongly on the source used to measure them, especially for HPDs with less attenuation at low frequencies. ISIL provides an alternative measurement of impulse protection and appears to be a more complete description of an HPD’s performance.

Key Words:

• Hearing protection
• impulse noise
• insertion loss
• spectral analysis

Acknowledgements

The authors thank Amir Khan and Taichi Murata from the National Institute for Occupational Safety and Health for their assistance with data collection for this study. The authors also thank Jeff Hamer for the use of his shooting range and his assistance with data collection. Portions of this research were presented at the 2016 Annual Conference of the National Hearing Conservation Association in San Diego, California.

Disclaimer

The findings and conclusions in this report are those of the authors and do not represent any official policy of 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 CDC or NIOSH.

Declaration of interest

Cameron Fackler, Elliott Berger and Michael Stergar are employed by 3M, the manufacturer of the hearing protectors studied in this work. 3M, E-A-R, Classic, Combat Arms, TacticalPro and the colour yellow for earplugs are trademarks of 3M Company, used under licence in Canada. PELTOR is a trademark of 3M Svenska AB, used under licence in Canada.