Performance of Sound Restoration Hearing Protectors in Impulsive Noise William J. Murphy, Ph.D. Commander, U.S. Public Health Service National Institute for Occupational Safety and Health Hearing Loss Prevention Section William J. Murphy, Ph.D. Commander, U.S. Public Health Service National Institute for Occupational Safety and Health Hearing Loss Prevention Section The contents of this presentation are the opinions of the author and do not represent any official policy of the National Institute for Occupational Safety and Health

Research Questions 1. Do sound restoration hearing protection devices provide sufficient attenuation for impulsive noise? 2. What is the typical attenuation performance for an electroacoustic hearing protection device? 1. Do sound restoration hearing protection devices provide sufficient attenuation for impulsive noise? 2. What is the typical attenuation performance for an electroacoustic hearing protection device?

Methods !Generate impulsive signals with gunshots and an acoustic shock tube !Digitally Sampled protected and unprotected signals  ¼” B&K 4136 microphone outside HPD  ISL mannequin with 4165 B&K ½” under HPD !Generate impulsive signals with gunshots and an acoustic shock tube !Digitally Sampled protected and unprotected signals  ¼” B&K 4136 microphone outside HPD  ISL mannequin with 4165 B&K ½” under HPD

ISL Mannequin Measurements Bruel & Kjaer 4136 ¼” microphone 4165 ½” B&K microphone 4157 B&K ear simulator Head Acoustics pinna and ear canal Isolated housing for 4157 assembly

Gunshot Impulses !Twelve weapons Five shots per condition  Smith & Wesson 586 and 686 pistols  0.45 Colt 1991A1, Para-ordinance pistols  0.40 Glock 22 and 27 pistols  9mm Pocket 9 and Sig Sauer P228 pistols  12 gauge Remington 870 & shotguns  Colt AR-15 & Heckler Koch G38 !Twelve weapons Five shots per condition  Smith & Wesson 586 and 686 pistols  0.45 Colt 1991A1, Para-ordinance pistols  0.40 Glock 22 and 27 pistols  9mm Pocket 9 and Sig Sauer P228 pistols  12 gauge Remington 870 & shotguns  Colt AR-15 & Heckler Koch G38

Shock Tube Impulses !Several Peak levels  150, 160 &170 dB !Five shots per HPD 200 kHz !Several Peak levels  150, 160 &170 dB !Five shots per HPD 200 kHz

Hearing Protection Devices !Six sound restoration earmuffs  Bilsom Targo and 707 Impact II  Peltor Tactical 6s and Tactical 7s  Howard Leight Leightning and Thunder with ProEars !Two electroacoustic earplugs  Electronic Shooters Protection Elite 6Hearing aid with compression circuit  CEP USA 203 Talk-through System !Six sound restoration earmuffs  Bilsom Targo and 707 Impact II  Peltor Tactical 6s and Tactical 7s  Howard Leight Leightning and Thunder with ProEars !Two electroacoustic earplugs  Electronic Shooters Protection Elite 6Hearing aid with compression circuit  CEP USA 203 Talk-through System

Hearing Protection Devices !Passive Earplugs  EAR Classic, Hifi, UltraTech, Combat Arms  Bilsom 555, 555NST !Nonlinear Earplugs  Combat Arms with ISL Cartridge  Bilsom 655 with ISL Cartridge  North Sonic Ear Valvs !Two electroacoustic earplugs  Electronic Shooters Protection Elite 6Hearing aid with compression circuit  CEP USA 203 Talk-through System !Passive Earplugs  EAR Classic, Hifi, UltraTech, Combat Arms  Bilsom 555, 555NST !Nonlinear Earplugs  Combat Arms with ISL Cartridge  Bilsom 655 with ISL Cartridge  North Sonic Ear Valvs !Two electroacoustic earplugs  Electronic Shooters Protection Elite 6Hearing aid with compression circuit  CEP USA 203 Talk-through System

Impulse Analysis !~50 msec analysis window !Maximum Impulse Levels,  Unprotected & Protected !Peak Level Reduction  Unprotected – Protected !Third-octave Analysis of Attenuation  Unprotected – Protected !~50 msec analysis window !Maximum Impulse Levels,  Unprotected & Protected !Peak Level Reduction  Unprotected – Protected !Third-octave Analysis of Attenuation  Unprotected – Protected

167 dB 136 dB

Auditory Hazard Assessment Model !Proposed Model to determine exposure criteria for U.S. Army !Mathematical model of the auditory periphery  Estimates the basilar membrane velocity  Estimates impulsive stress on the BM  Yields Auditory Risk Units !Developed from modeling animal exposures !Proposed Model to determine exposure criteria for U.S. Army !Mathematical model of the auditory periphery  Estimates the basilar membrane velocity  Estimates impulsive stress on the BM  Yields Auditory Risk Units !Developed from modeling animal exposures

Ft Collins Indoor Range

Ft Collins Indoor, Outdoor; USAARL

Conclusions !Simple Relationship for Impulsive Risk  Verified by AHAAH model  ARUs = 1.80x10-7 * exp (0.1295*Peak Protected SPL)  Number of Shots per Day = 500 / ARU !Simple Relationship for Impulsive Risk  Verified by AHAAH model  ARUs = 1.80x10-7 * exp (0.1295*Peak Protected SPL)  Number of Shots per Day = 500 / ARU

Conclusions !Electroacoustic/Sound restoration HPDs yield consistent peak reduction with respect to volume setting. !Recommend dual protection for gunshot exposure !Recommend pairing Electroacoustic muff with passive earplug to get below the 130 dB peak level of single protector. !Electroacoustic/Sound restoration HPDs yield consistent peak reduction with respect to volume setting. !Recommend dual protection for gunshot exposure !Recommend pairing Electroacoustic muff with passive earplug to get below the 130 dB peak level of single protector.

Acknowledgements !Gunshot data collection MAJ Mark Little (US Army), CAPT Randy L. Tubbs (NIOSH) Ft. Collins Police Services Department !Acoustic Shock Tube data collection LCDR David Byrne & LT Ed Zechman (NIOSH), Ken Madsen, Adrian Houtsma & William Ahroon US Army Aeromedical Research Laboratories !Gunshot data collection MAJ Mark Little (US Army), CAPT Randy L. Tubbs (NIOSH) Ft. Collins Police Services Department !Acoustic Shock Tube data collection LCDR David Byrne & LT Ed Zechman (NIOSH), Ken Madsen, Adrian Houtsma & William Ahroon US Army Aeromedical Research Laboratories