Re: 223 Noise Questions
All you dedicated ear plug, muff and/or suppressor users, have you ever read this: (scroll to bottom for commentary)
Original Research—Otology and Neurotology
Comparison of Muzzle Suppression and
Ear-Level Hearing Protection in
Firearm Use
Otolaryngology–
Head and Neck Surgery
144(6) 950–953
. American Academy of
Otolaryngology—Head and Neck
Surgery Foundation 2011
Reprints and permission:
sagepub.com/journalsPermissions.nav
DOI: 10.1177/0194599811398872
http://otojournal.org
Matthew Parker Branch, MD1
No sponsorships or competing interests have been disclosed for this article.
Abstract
Objective. To compare noise reduction of commercially available
ear-level hearing protection (muffs/inserts) to that of
firearm muzzle suppressors.
Setting. Experimental sound measurements under consistent
environmental conditions.
Subjects. None.
Study Design and Methods. Muzzle suppressors for 2
pistol and 2 rifle calibers were tested using the Bruel &
Kjaer 2209 sound meter and Bruel & Kjaer 4136
microphone calibrated with the Bruel & Kjaer Pistonphone
using Military-Standard 1474D placement protocol. Five
shots were recorded unsuppressed and 10 shots
suppressed under consistent environmental conditions.
Sound reduction was then compared with the real-world
noise reduction rate of the best available ear-level
protectors.
Results. All suppressors offered significantly greater noise
reduction than ear-level protection, usually greater than
50% better. Noise reduction of all ear-level protectors is
unable to reduce the impulse pressure below 140 dB for
certain common firearms, an international standard for prevention
of sensorineural hearing loss.
Conclusion. Modern muzzle-level suppression is vastly superior
to ear-level protection and the only available form of
suppression capable of making certain sporting arms safe
for hearing. The inadequacy of standard hearing protectors
with certain common firearms is not recognized by most
hearing professionals or their patients and should affect
the way hearing professionals counsel patients and the
public.
Keywords
tinnitus, sensorineural hearing loss, noise-induced hearing
loss, firearm suppression, hearing protection
Received September 15, 2010; revised December 20, 2010; accepted
January 11, 2011.
Noise-
induced inner ear injury is a substantial cause
of preventable disability in the United States.
Approximately 15% of Americans between the ages
of 20 and 69 years—or 26 million Americans—have hearing
loss that may have been caused in part by exposure to
loud sounds or noise at work or in leisure activities.
1
Subjective tinnitus affects approximately 50 million
Americans (12%-15% of the adult population)
2-4
and often
accompanies sensorineural hearing loss in patients with
a history of loud noise exposure.
5-9
Recreational use of firearms is a significant cause of
noise and related ear injury in America.
10
There are approximately
more than 250 million privately owned firearms in
the United States,
11,12
and the number increases about 4.5
million per year.
13
This rate of increase rose by 14%
for 2007-2008.14 Unlike industrial exposure, hearing protection
during recreational firearm use is not regulated or
enforced. This represents one of the largest neglected areas
of advocacy for prevention of ear injury.
Ear-level hearing protection is poorly understood by
patients and hearing specialists alike. Far from being a panacea,
ear-level protection rarely, if ever, confers the level of
protection or noise reduction ratio (NRR) advertised. NRRs
are determined using laboratory tests in continuous noise (not
impulse sounds such as gunfire) and are not useful for determining
the actual level of protection achieved by a given
individual in a particular environment.
15
How much protection is afforded by ear-level protection?
The National Institute of Occupational Safety and Health
(NIOSH) recommends that earmuffs be considered to have
25% less NRR than stated and formable earplugs 50%
less.
16
The most common commercially available ear
protection has an advertised NRR of 19 to 25 dB. The highest
rated NRR are 31 dB and are less common. The
Occupational Safety and Health Administration sets 140 dB
1
Private practice in otolaryngology, Corsicana, Texas, USA
This article was presented at the 2010 AAO-HNSF Annual Meeting & OTO
EXPO; September 26-29, 2010; Boston, Massachusetts.
Corresponding Author:
Matthew Parker Branch, MD, 400 Hospital Drive, Suite 115, Corsicana, TX
75110
Email:
[email protected]
as the safe threshold for single-impulse sound exposure.
Using the adjusted NRR levels, most hearing protection
(NRR 19-25 dB) is unable to make hearing safe a firearm
producing an impulse sound louder than 149.5 to 154 dB.
The best available ear-level protection (earmuffs, NRR 31
dB) is unable to make hearing safe any firearm louder than
163 dB under the best of conditions. According to Berger
et al,
16
even these adjusted figures are likely unrealistic.
This review of 20 published studies demonstrated far
worse performance than the corrected NRR suggests: the
laboratory NRRs consistently overestimated the real-world
NRRs by 140% to 2000% (Figures 1 and 2).
16
It is unlikely,
however, that most consumers of hearing protection have
any idea what the NRR is of the products they purchase or
what level of protection is necessary to make their particular
firearm safe for hearing.
Hiram Maxim first introduced and marketed muzzle suppressors
in the 1920s in the United States. These devices
either attach to the muzzle (by way of threading the barrel
or by proprietary quick attachment mechanisms) or are integrated
into the barrel. Muzzle suppressors allow the heated
gases from the barrel to expand into a series of chambers or
baffles, cooling and slowing the gas’s exit from the barrel.
The result is a shorter, quieter sound signature. The basic
design of suppressors has changed little over the years, but
modern design and manufacturing have improved their
sound reduction effectiveness. Unlike ear-level protection,
muzzle suppressors are relatively easy to use in a consistent,
repeatable fashion. They confer protection for the shooter
and bystanders alike and allow interpersonal conversation
and situational awareness of sounds not afforded by earlevel
devices. They are also legal in most states, although
their ownership and transfer are regulated by the Bureau of
Alcohol, Tobacco, Firearms and Explosives (BATF&E) and
requires a $200 tax and somewhat lengthy process for registration,
delaying use of the device for weeks or months
from the time of purchase. Importantly, it is relatively
simple to demonstrate their actual noise reduction capability
compared with ear-level devices.
Study Design
We hypothesized that modern muzzle suppression has
a demonstrable superiority to ear-level protection due to
the unpredictable protection of ear devices and improbability
of one-size-fits-all products. We tested common
pistol and rifle calibers with and without muzzle suppression
using strict military/industrial standard sound measurement
for impulse noise. We recorded the impulse noise
in decibels and compared the sound levels with and without
suppression. We then compared the average noise
reduction of the suppressors to likely NRR levels of earlevel
products.
Methods
The tests were conducted using the Bruel & Kjaer (B&K)
2209 sound meter with a B&K 4136 microphone calibrated
with the B&K 4220 Pistonphone. Calibration was checked
after the tests to verify there were no shifts in calibration
during the tests. All equipment has been certified and tested
so that it can be traced back to the National Institute of
Standards and Technology’s standards. The meter and
weapon are also placed in accordance with Military-
Standard 1474D protocol. Five shots were fired to establish
the unsuppressed level, and then 10 shots were fired with
the suppressor attached.
17
For the pistol tests, we used 9 mm and 45 ACP semiautomatic
pistols (Table 1). These are very popular sporting
rounds as well as common military standard calibers. The
rifle tests were performed with a semiautomatic 5.56 mm/
223 caliber round, as is used in the AR-15 style civilian
rifle and the NATO military M16/M4 carbine rifle, and a
bolt-action 7.62 3 51 mm/308 caliber rifle, also a common
sporting round and NATO military standard round.
The suppressors used are commercially available and
legally obtained by way of the standard BATF&E registration
process for civilian ownership. No institutional review
or ethics committee approval was deemed necessary or
sought for this study.
Figure 2. Noise reduction ratio (NRR) hearing protection provides
in the real world: earplugs.
Figure 1. Noise reduction ratio (NRR) hearing protection provides
in the real world: earmuffs.
Branch 951
Results
The average unsuppressed sound levels for the 9 mm pistol
at military standard recording distance (1 m to the left of
the muzzle) was 160.5 dB and 157.7 dB at the ear of
the shooter. The average suppressed levels were 127.4 dB
and 129.6 dB, respectively (difference of 33.1 dB and
28.1 dB).
The average unsuppressed sound levels for the 45 ACP
pistol at military standard recording distance and the shooter’
s ear was 162.5 dB. The average suppressed levels were
131.8 dB and 128.5 dB, respectively (difference of 30.7 dB
and 33.9 dB, respectively). The suppressor for the 45 ACP
is also designed to function wet (filled with 10 mL of water
for additional noise reduction). The average wet suppressed
level was 121 dB (difference of 41.5 dB).
The average unsuppressed sound levels for the 5.56 mm/
223 caliber semiautomatic rifle at the military standard
recording distance was 164 dB and 155 dB at the shooter’s
ear. The average suppressed levels were 137.4 dB and 134.2
dB, respectively (difference of 26.6 dB and 29.8 dB,
respectively).
The average unsuppressed sound levels for the boltaction
7.62 3 51 mm/308 caliber rifle at the military standard
recording distance was 165.7 dB and 157.2 dB at the
ear. The average suppressed sound levels were 138.9 dB
and 131.2 dB, respectively (difference of 26.8 dB and 26
dB, respectively). See Figures 3 and 4.
Discussion
The consistency of hearing protection use with recreational firearms
is dismal.
18
We know that hearing compliance programs
in industry rely on routine, supervised use of ear-level devices
and periodic audiometric screening to assess effectiveness. No
such programs exist for the recreational shooter. As the NIOSH
Web site explains, the best hearing protection is the one the
worker will wear.
16
But how do we motivate shooters to be
compliant, especially in light of the data regarding the poor
effectiveness of ear-level devices? Even compliant use of dual
ear protection (plugs and muffs) over time leads to degradation
of hearing.
19
Practical limitations of ear-level devices are
myriad. Poor fit, migration of device due to activity or sweat,
incorrect use, pain, heat, and loss of communication top the list.
Because of their use at the source of noise production,
muzzle suppressors are much more effective at reducing
noise. This facilitates communication and situational awareness,
which can improve safety when operating firearms.
Suppressors can easily and reliably be removed and transferred
between multiple weapons of like caliber and reattached
in a way that ensures proper fit and function. With
suppression levels from 26 dB to 41 dB that are reliable and
reduce impulse noise below 140 dB, all of the devices in
Table 1. Firearms (Caliber, Manufacturer), Ammunition, and Suppressors Used
Caliber Manufacturer Ammunition Suppressor
Pistol 9 mm Sig Sauer P226, Exeter, NH Remington UMC 147 gr ball, Lonoke, AK Advanced Armament Ti-Rant,
Norcross, GA
45 ACP Glock 21, Smyrna, GA Remington UMC 230 gr ball, Lonoke, AK HTG Cycle-2, Boise, ID
Rifle 5.56 mm/223 Colt M4 16 inch barrel,
Hartford, CT
M855 NATO 62 gr steel core
penetrator, Independence, MO
Gemtech G5, Eagle, ID
7.62 3 51 mm/308 Remington Model 700,
Madison, NC
Remington 168 gr BTHP MK, Lonoke, AK HTG M-30, Boise, ID
Figure 3. Firearm/suppressor attenuation compared with realworld
earmuff attenuation. EAR indicates at the shooter’s ear;
MLT-STD, military-standard.
Figure 4. Firearm/suppressor attenuation compared with realworld
earplug attenuation. EAR indicates at the shooter’s ear; MLT-
STD, military-standard.
952 Otolaryngology–Head and Neck Surgery 144(6)
our study are ‘‘hearing safe.’’ However, weapon-suppressor
combinations producing sound levels 130 dB or less (9 mm
and 45 ACP wet) are much more comfortable to shoot without
any hearing protection at all. In fact, the sound level of
the 9 mm pistol’s slide closing without any shot fired measured
124 dB. To our knowledge, this is the first time the efficiency
of muzzle suppressors has been properly tested and
compared with ear-level protection in any medical journal.
Conclusion
The muzzle-level suppressors studied on these weapons and
calibers reduced sound levels well below the likely noise
reduction of either earplugs or earmuffs.
Acknowledgments
The author thanks John Titsworth Jr, founder/owner of Silencer
Research, LLC and SilencerResearch.com, for providing firearms,
ammunition, suppressors, sound-testing equipment, and expertise
in the performance of the testing described in this article.
Author Contributions
Matthew Parker Branch, original concept, experimental design
and execution, research, writing, editing entire text, final approval.
Disclosures
Competing interests: None.
Sponsorships: None.
Funding source: None.
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Branch 953
PM me your email and I will email you the original article.
This research, however limited, shows how ineffective user-mounted ear protection is. Seems that one of the biggest reasons is the transmission of sound through facial or cranial bone. Muffs are better than plugs, but we all know that. This serves to begin to quantify how much.
R
