How We Test
At Stephen Katz & Associates we specialize in the measurement and analysis of anything that generates high-peak sound pressure levels, especially from fast rising impulses. This can include firearms, pile drivers, pneumatic tools, machinery, etc.
Our philosophy is to high-speed, precision audio record all our data for post analysis. With high-speed low-noise recording you can always go back and re-measure or measure other and/or new parameters. A key feature is that all filtering is done post recording, not altering the response time of the original signal. Types and weights of filters can be changed at will. A major benefit is that you can listen to any track.
We record our data at 192k/24 bits. This equates to a sample every five and one-half microseconds (5.5µs) with a dynamic range greater than one-hundred and thirty dB (≥130dB). The wide dynamic range, along with low-noise converters and instrumentation microphones allows us to do measurement and analysis not available with traditional type-one sound level meters. The 192k/24bit format is ubiquitous and is ready exchangeable, and played back on most computers.
Shooting Range Microphone Placement Along with stand-mounted microphones, in the spirit of MIL-STD-1474D which recommends, “transducers shall be located at the center of each operator or crewmember’s probable head location,” Stephen Katz developed the Personal Mounted Microphone (PMM).
Photo 1 below shows the Personal Mounted Microphone (PMM) in use (PCB 378C01) as well as pressure sensors (PCB 106B) mounted by the left and right temples to measure the pressures heard at each ear as well as pressures from adjacent shooters. The shooter also wears a pressure sensor on their sternum.
Things We Measure Below are examples of Stephen Katz & Associates small arms measurement technology. Included are illustrations of: Peak Level, Pressure and Pressure-Time, Suppressor measurement comparison, before and after, Reverberation Time (RT60), the effect of canopies and angled baffles on the peak level, and outdoor measurement technology, where our technology separated gunshot noise from the background noise.
Peak Level, Pressure and Pressure-Time
Figure 1 below shows an Energy Pressure/Time History, measured in decibels, of two-rounds (2) fired on a Barrett M82, .50 BMG rifle as measured with a Personal Mounted Microphone and recorded at 192k/24 bits. The first shot measured a peak level of 178.8 dB SPL with a pressure of 1482 Psi, a duration of 1.7 seconds with a pressure time (Psi(t)) of 2447. The second shot measured peak level 179.6 dB SPL with a pressure of 1541 Psi, a duration of 1.8 seconds with a Psi(t) of 2742.
Psi is defined as 1 pound of force per square inch. 1 pound per square inch (psi) equals to 6894.76 Pascals.
(Psi(t) is the integer of the area under the peak pressure curve (in Pa), divided by 6894.8, times the total event duration in seconds with the formula (psi (t) = Zn ( ∫ ƒ (x) dx/6894.76 (sec))))
Figure 2 below shows a comparison of an M4 5.56, unsuppressed and suppressed. It can be seen that the peak level of the M4 5.56, unsuppressed, is 165.5 dB SPL compared to the same firearm, same shooter, same location, microphone, etc. the peak level is 145.5 dB SPL, a reduction of 20 dB SPL. Comparatively, the pressure of the unsuppressed firearm was 199 psi, suppressed the pressure was 92 psi. It is possible to expand the time history to get an even better picture of how the suppressor is reacting. What is interesting is that peak level reflected back to the shooter from the bullet trap was approximately the same level. Quantitative and qualitative testing of suppressors should be done in a space acoustically treated with materials capable of absorbing high-pressures, and the space should not have a reflective bullet trap.
Figure 3 shows the comparative Reverberation Time (RT60) between an acoustically untreated and acoustically treated twenty-five yard (25yd), seven-lane shooting range. Reverberation time in a shooting range is not simple to measure. Typical sound meters, that can measure reverberation time, typically do not have high-speed detectors, and the critical capability to individually synchronize each 1/3rd octave (there is a 20 millisecond time shift between 50 Hz and 20,000 Hz (f=1/t), and their one size fits all RT60 algorithms do take into account the strong reflections off of the bullet trap. For a Range Proof of Performance, and Certificates of Acceptance, Stephen Katz & Associates averages the Reverberation Time (RT60) from multiple shooting positions using Personal Mounted Microphones as well as fixed point microphones.
The Effect of Canopies and Angled Baffles
Figure 4 shows the effect of angled surfaces, an outdoor shooting range canopy, on the overblast pressure, aka muzzle blast from an M4, 5.56 rifle, and the same rifle, same shooter, same microphone, etc., standing in front of the canopy. It can be seen in the pressure time history of the amplitude waveform expressed linearly in Pascals, that the primary peak level observed under the canopy is 158.5 dB which compares closely to the 157.4 dB measured in front of the canopy. But then, four and one-half milliseconds later (4.5 ms) there is a second, much louder peak of 162.0 dB. This secondary, higher peak can be eliminated with proper acoustic treatment designed for high-pressure absorption.
Figure 5 below is an example of how Stephen Katz & Associates high-speed measurement technology, in a windy, outdoor setting, was able to find, isolate, separate, and measure the peak level of distant gunfire separated from the background noise. The example shows a peak level of 95.0 dB SPL. The reverberation of the distant gunfire noise can also be clearly seen.
At Stephen Katz & Associates we relish the challenge of measuring and analyzing anything that generates high-peak sound pressure levels, in fact anything related to sound and noise.
“If it’s about sound, we are there…”
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