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Many manufacturers
provide a number that is supposed to represent the sound
reduction capability, in decibels, of a particular
suppressor model. However, a sound suppressor may provide
significantly different results when used on different types
of firearms, or when firing different ammunition. This is
why SureFire provides sound level readings for particular
firearms using particular ammunition with a particular
suppressor model, utilizing SureFire's
How Suppressors Work
A sound suppressor
is basically a metal tube with interior chambers separated
by metal walls called baffles. Running through the
center of the baffles is a passageway for the bullet.
Suppressors "suppress" sound primarily by confining,
cooling, and extending the release time of firearm discharge
gases, all of which occurs in a fraction of a second.
 While
this fundamental design is inherent in all modern
suppressors, there are many possible modifications to it
that can dramatically affect sound reduction capabilities.
It should be noted
that sound reduction capability is not the only crucial
factor in suppressor design. Ease of attachment/detachment
to a firearm, solidity of attachment, weight, size,
suppressor durability, and firearm accuracy are also
extremely important. Achieving optimum results in all of
these areas is a complex and time-consuming engineering
feat.
Also, it should be
noted that a particular sound suppressor can produce
different results depending on the type of firearm it is
attached to, the particular ammunition used, the temperature
of the suppressor, local atmospheric conditions such as
barometric pressure, air temperature, and humidity.
Human Sound
Perception
Human perception
of a gunshot sound depends on the sound's intensity,
duration, frequency distribution, distance of the listener
from the firearm, position of the listener with respect to
the firearm, and the listener's hearing abilities. Human
ears are most sensitive to sound frequencies of middle A and
its higher harmonics (between 2 and 4 kHz).
Unit of Sound
Measurement
The standard unit
of measurement of sound intensity, which humans perceive as
loudness, is the bel, named for Alexander Graham
Bell. However, for most measurement purposes the bel is too
large, so the decibel (1/10 bel) is more commonly
used. Decibel is abbreviated as dB. The decibel scale is
logarithmic, which means that a small difference in
logarithmic scale value actually means a great difference in
intensity. For example, a noise source measuring 70 dB is 10
times as loud as a source measuring 60 dB and 100 times as
loud as a source reading 50 dB.
Measuring
Suppressor Effectiveness
The measured
results of a sound suppressor's effectiveness in reducing
the perceived loudness of a firearm discharge can vary
tremendously, depending upon the equipment used to measure
the sound, the position of microphones, the immediate
environment in which sound is being measured (such as hard
surfaces versus sound-absorbent surfaces), ambient
atmospheric conditions such as temperature and humidity, the
suppressor's condition (wet or dry, hot or cold), length of
the firearm's barrel, and the ammunition used.
Because they
utilize the same basic design, modern sound suppressors of
similar size and weight generally provide similar sound
reduction — about 30 decibels. Where they differ is in
durability, repeatability, convenience of attachment,
solidity of attachment, and the effects on firearm accuracy.
SureFire suppressors outperform all others in each of these
areas.
SureFire Sound
Measurement Methodology
SureFire has
developed a standardized suppressor test and measurement
protocol intended to provide unambiguous and reliable
acoustic performance data. This protocol incorporates
state-of-the-art instrumentation and meticulous measurement
practices. A minimum of two measurement locations are
required to characterize the suppressor, or family of
suppressors, in terms of sound attenuation:
ERP — Ear
Reference Position, representing what the shooter hears.
TRP — Threat
Reference Position, representing what the target hears.
For the ERP, the
microphone is placed eight inches from the shooter's left
ear, perpendicular to the bullet trajectory. Left side is
used to avoid signal input from ejection port.
For the TRP, the
microphone is placed two meters to one side of the line of
fire and 50 meters downrange. ERP and TRP are illustrated in
Figure 1.
 Data
Acquisition/Signal Processing
ERP and TRP data, both with and
without suppressor, must be collected simultaneously and in
parallel for each test condition, meaning the two
microphones (ERP and TRP) must both feed into the same
measurement device. This requires a minimum of two
channels of data acquisition and simultaneous signal
processing and analysis of the two input signals. |
