Measurement of Impulse Peak Insertion Loss for Five Hearing Protectors.

Measurement of Impulse Peak Insertion Loss for Five Hearing Protectors.

William J. Murphy, Greg A. Flamme, Donald S. Finan, Amir Khan,

James E. Lankford, Deanna K. Meinke, Jacob Sondergaard, Michael Stewart

William J. Murphy, Greg A. Flamme, Donald S. Finan, Amir Khan,

James E. Lankford, Deanna K. Meinke, Jacob Sondergaard, Michael Stewart

The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and Health

and should not be construed to represent any agency determination or policy.

The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and Health

and should not be construed to represent any agency determination or policy.

2

Regulatory HistoryRegulatory HistoryCongress promulgated the Noise Control Act in 1972 giving the US Environmental Protection Agency (EPA) the authority to regulate Noise.

EPA promulgated the Hearing Protector Labeling Rule in Sept. 1979.

Applicable to passive hearing protection devices (HPDs) available at that time.

The Noise Reduction Rating (NRR) was designed to inform the consumer about the protective effects of an HPD.

Congress promulgated the Noise Control Act in 1972 giving the US Environmental Protection Agency (EPA) the authority to regulate Noise.

EPA promulgated the Hearing Protector Labeling Rule in Sept. 1979.

Applicable to passive hearing protection devices (HPDs) available at that time.

The Noise Reduction Rating (NRR) was designed to inform the consumer about the protective effects of an HPD.

3

The Problems with the NRR…The Problems with the NRR…Designed for Continuous Noise

Typical protectors exhibit nonlinear response at high levels >140 dB SPL

Nonlinear orifice protectors provide increased attenuation with increasing peak Sound Pressure Level (peak SPL).

Electronic Protectors are designed to limit output to levels below about 82 dB peak SPL.

Designed for Continuous Noise

Typical protectors exhibit nonlinear response at high levels >140 dB SPL

Nonlinear orifice protectors provide increased attenuation with increasing peak Sound Pressure Level (peak SPL).

Electronic Protectors are designed to limit output to levels below about 82 dB peak SPL.

4

Proposal: Impulse Noise ReductionProposal: Impulse Noise ReductionMeasure the Performance for protectors for levels from 130 to 170 peak SPL.

Measure performance over a range of levels (130-134), (148-152) and (166-170) dB.

Measure the device on an Acoustic Test Fixture (ATF) to limit human subject exposure.

Measure both Free-field and ATF waveforms and apply signal processing to the determine the impulse noise reduction rating.

Measure the Performance for protectors for levels from 130 to 170 peak SPL.

Measure performance over a range of levels (130-134), (148-152) and (166-170) dB.

Measure the device on an Acoustic Test Fixture (ATF) to limit human subject exposure.

Measure both Free-field and ATF waveforms and apply signal processing to the determine the impulse noise reduction rating.

5

Experimental ConfigurationExperimental Configuration

Measurement Equipment

Measurement Equipment

6 ISL Acoustic Test FixtureISL Acoustic Test Fixture

Blast ProbeBlast Probe

GRAS 40DP

GRAS 40DP

B&K 4136

B&K 4136

7

Colt AR-15 0.223 caliber rifleColt AR-15 0.223 caliber rifle

8

Theoretical BasisTheoretical BasisMeasure Unoccluded PATF(t) and PFF(t)

Measure Occluded P’OCC-ATF(t) and P’OCC-FF(t)

Compute Free-Field to ATF Transfer Function

HFF-ATF( f ) = PUNOCC-ATF( f )/ PFF( f )

Calculate Unoccluded ATF Pressure using the Free-Field Pressure P’FF(t)

P’UNOCC-ATF( f ) = HFF-ATF( f ) P’FF( f )

Compute Impulse Reduction in time domain

max(P’UNOCC-ATF) – max(POCC-ATF)

Measure Unoccluded PATF(t) and PFF(t)

Measure Occluded P’OCC-ATF(t) and P’OCC-FF(t)

Compute Free-Field to ATF Transfer Function

HFF-ATF( f ) = PUNOCC-ATF( f )/ PFF( f )

Calculate Unoccluded ATF Pressure using the Free-Field Pressure P’FF(t)

P’UNOCC-ATF( f ) = HFF-ATF( f ) P’FF( f )

Compute Impulse Reduction in time domain

max(P’UNOCC-ATF) – max(POCC-ATF)

Experimental DesignExperimental DesignThree peak pressure levels (AR-15 rifle) 130, 150, 170 dB at 1, 3, 20 metersFive models of hearing protectors

EAR Pod ExpressEtymotic EB1EAR Combat Arms Open (Nonlinear)EAR Combat Arms Closed (Linear)Bilsom 707

Five samples of each modelFive insertions of each sampleThree shots per insertion

Three peak pressure levels (AR-15 rifle) 130, 150, 170 dB at 1, 3, 20 metersFive models of hearing protectors

EAR Pod ExpressEtymotic EB1EAR Combat Arms Open (Nonlinear)EAR Combat Arms Closed (Linear)Bilsom 707

Five samples of each modelFive insertions of each sampleThree shots per insertion

9

10

11

12

13

14

15

16

ConclusionsConclusionsMultiple Samples were necessary

Some samples exhibited greater attenuation or more variability

Multiple levels are necessary to measure variability

The 150 dB prediction interval was accurate for three of the models, but under estimated 10 and 90 percentile range.

Measurements need to be confirmed with laboratory data.

Multiple Samples were necessary

Some samples exhibited greater attenuation or more variability

Multiple levels are necessary to measure variability

The 150 dB prediction interval was accurate for three of the models, but under estimated 10 and 90 percentile range.

Measurements need to be confirmed with laboratory data.

18

How IMPULSE Labels Might LookHow IMPULSE Labels Might Look

OPEN CLOSED

The Rudyard GangThe Rudyard GangThe Rudyard Gang

Amir Khan

Amir Khan

Jaco

b Son

derga

rd

Jaco

b Son

derga

rdGreg

Flamme

Greg Flam

meJa

mes Lan

kford

James

Lankfo

rdMich

ael S

tewart

Michae

l Stew

artDea

nna Mein

ke

Deanna M

einke

Donald

Finan

Donald

FinanWilli

am M

urphy

William

Murph

y

QUESTIONS?QUESTIONS?

20