Noise Reduction Ratings of Active Noise Cancellation Headsets William J. Murphy 1 , Hilary L. Gallagher 2 , Richard L. McKinley 2 1 National Institute for Occupational Safety and Health Division of Applied Research and Technology Engineering and Physical Hazards Branch Hearing Loss Prevention Team 2 U.S. Air Force Research Laboratory Battlespace Acoustics Branch Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Products mentioned in this presentation are not endorsed by CDC/NIOSH or US Air Force Presentation to the National Hearing Conservation Association, San Antonio TX, February 25, 2017
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Noise Reduction Ratings of
Active Noise Cancellation Headsets
William J. Murphy1,
Hilary L. Gallagher2, Richard L. McKinley2
1National Institute for Occupational Safety and Health
Division of Applied Research and Technology
Engineering and Physical Hazards Branch
Hearing Loss Prevention Team2U.S. Air Force Research Laboratory
Battlespace Acoustics Branch
Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily
represent the views of the National Institute for Occupational Safety and Health.
Products mentioned in this presentation are not endorsed by CDC/NIOSH or US Air Force
Presentation to the National Hearing Conservation Association, San Antonio TX, February 25, 2017
Efforts to Revise Standards
• 2003: EPA Public Meeting – Washington
• 2004: Planning Meeting – San Diego
• 2005-2006: Interlaboratory Study
• 2007: ANSI S12.68 NRSA Rating Standard
• 2008: ANSI S12.6-2008 Testing Standard
• 2010: ANSI S12.42-2010
ANR & Impulse Testing Standard
• 2015: MIL-STD 1474E Dept. of Defense
Design Criteria Standard Noise Limits
Types of Protectors Covered
• EPA – 1978 40 CFR 211 B
– Earplugs, Earmuffs, Canal Caps
• DoD MIL-STD 1474E
– Passive Hearing Protectors
– Active Noise Cancellation (ANC)
• Earmuffs & Earplugs
– Level Dependent HPDs
• Nonlinear Filters
• Sound Restoration
Current Noise Reduction Rating
• NRR – ANSI S3.19
– Experimenter Fit Data
• 98% protection factor
• Small standard deviations (<3 dB)
Performance Rating for Active HPD’s
• Passive component – ANSI S12.6 / S12.68
– Experimenter-Trained Fit, Real Ear Attenuation at Threshold (REAT)
• Active component – ANSI S12.42
– Microphone in Real Ear (MIRE) modified Active Noise Reduction devices
• Measure with ANR turned ON and OFF
– Passive REAT + Active MIRE
• Performance rating determined with ANSI S12.68
Performance Rating for Active HPD’s
• Active component – MIRE Testing Muffs
– Miniature microphone centered in ear canal
• Measure with the muff turned OFF
• Measure with the muff turned ON
• The difference in the octave band measurements will be
used to estimate the Active component.
Performance Rating for Active HPD’s
• Active component – MIRE Testing Plugs
– Need to be tested on a mannequin.
• Measure with the plug turned OFF
• Measure with the plug turned ON
• The difference in the octave band measurements will be
used to estimate the Active component.
Combining REAT & MIRE data
Corrections for Bone Conduction
Differences ANSI and ISO ratings
• ANSI required that the same subjects be used
with REAT and MIRE measurements
– ISO proposed that different subjects could be
allowed, but the latest draft (11/9/2016) seems to
have required the same subjects be used.
• ANSI required 5 samples of the protectors to
be tested in a counterbalanced order over 10
or 20 subjects.
– ISO has proposed 4 samples of the headsets be
counterbalanced across 16 subjects
Active Noise Cancellation Headsets
Bose A20 Pilot DNCXL PA1779T
Sennheiser HMEC250 Telex Stratus HeliXT
Methods
• 10 Subjects at WPAFB (IRB: F-WR-2007-0008-H)
– 5 Male, 5 Female
– Hearing Threshold Levels ≤15 dB
• Real Ear Attenuation at Threshold
– Two trials for occluded and unoccluded conditions
• Microphone In Real Ear
– Three placements of headsets
– Measured with Active Noise Control On and Off
– Measured with 1/3rd Octave Bands 100 to 10,000 Hz
Analysis Methods
• All Calculations done with MATLAB
• Determined Noise Reduction Statistic for A-
weighting (NRSA) and NRS Graphical (NRSG)
• Determined NRSA and NRSG for Active and
Passive Conditions
• Four example spectra used to check
– Estimated Protection Levels
– Estimated Exposure Levels
NRSA Active and Passive Ratings
Bose A20 NRSG Ratings
Pilot PA1779T NRSG Ratings
Sennheiser HMEC250 NRSG Ratings
Telex HeliXT NRSG Ratings
Four Example Noise Spectra
NRSA, NRSG, Oct. Band Protection Levels
0 20 40
0
10
20
30
40
Octave Band Protection Level (dB)
NR
SA P
rote
ctio
n L
eve
l (d
B)
r2 = 0.720
0 20 40
0
10
20
30
40
r2 = 0.986
Octave Band Protection Level (dB)
NR
SG
Pro
tectio
n L
eve
l (d
B)
0 20 40
0
10
20
30
40
r2 = 0.744
NRSG
Protection Level (dB)
NR
SA P
rote
ctio
n L
eve
l (d
B)
NRSA, NRSG & Oct. Band Exposures
70 80 90 100
Octave Band Exposure Level (dB)
65
70
75
80
85
90
95
100
105
NR
SA E
xpo
su
re L
eve
l (d
B)
r2 = 0.721
70 80 90 100
Octave Band Exposure Level (dB)
65
70
75
80
85
90
95
100
105
NR
SG
Exp
osure
Leve
l (d
B)
r2 = 0.892
70 80 90 100
NRSG
Exposure Level (dB)
65
70
75
80
85
90
95
100
105
NR
SA E
xpo
su
re L
eve
l (d
B)
r2 = 0.844
Conclusions
• The ANSI S12.6 + S12.42 methods provide for
adequate input data to the S12.68 rating standard
• The NRSA may be appropriate for a typical
industrial noise LC-LA ~ -1 to 5 dB
• The NRSG provides a better estimate of exposure
than NRSA
• The NRSG is a good approximation of the octave
band method
Questions?
William J. Murphy, PhD
(513) 533-8125
Hearing Loss Prevention Team
Our research is sound.
Hilary L. Gallagher
(937) 255-2203
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