SSS.4 - Test Method and Results

The following are paramount for adherence to this standard:

Accurate pressure waveforms.

PEW-SOFT is an excellent tool for generating those. The Silencer Sound Standard combines PEW-SOFT data with empirically validated hearing damage models.

Many unsuppressed and suppressed firearms, in various calibers and with various silencers, were fired 1.6 m above the ground. Sound pressure was measured at the following locations:

1. Muzzle (1.0 m left of the muzzle, at 1.6 m muzzle-and-microphone elevation) - This is the “MIL-STD” muzzle location.

2. Ear (0.15 m right of the right ear, 1.6 m ear-and-microphone elevation) - This is the “MIL-STD” ear location. This was done with the shooter present; that is, the firearm was fired by a human with the human’s head 0.15 m from the microphone.

3. “Far Field” and “Non-Standard Muzzle” (2.0 m or 1.0 m right of the muzzle, at 1.6 m muzzle-and-microphone elevation) - These are “control” locations and this data is not currently published.

In general, five shots were fired in each weapon configuration, multiple times, over multiple test sessions. Tests have been conducted indoors and outdoors, and the effects of reflections, temperature, ambient noise, wind, and electromagnetic interference have all been studied and noted.

The PEW-SOFT system was used to acquire each waveform from each microphone location from each shot. The computation of the peak positive phase impulse for every shot was performed. Finally, Warned and Unwarned hearing damage risk analyses of each of the hundreds of waveforms was performed. Both Warned and Unwarned damage analyses are presented here in unmarked data-space, as the correlation mapping is PEW Science proprietary information.

The master data set, to date, is shown in the following four figures: Fig 16 ( Warned, Muzzle), Fig 17 (Warned, Ear), Fig 18 (Unwarned, Muzzle), and Fig 19 (Unwarned, Ear). Our P-i plots now have three dimensions; one for each metric of loudness. The contours on all plots are kept constant to visually illustrate ARU magnitude in a consistent fashion and how the simplified maximum peak sound pressure and impulse metrics influence the parameter.

Notice anything strange about the plots? Here are some things to keep in mind:

1. The slope from the low-risk areas of the plot (pink) to the high-risk areas (red) is non-linear. This is expected, based upon the nature of the human ear’s response to sound pressure and impulse (and should again highlight the usefulness of the logarithmic dB unit to you, visually).

2. There are peaks and valleys. There are a couple of reasons for this:

   • The generated meshes are quadratically interpolated views of the data set. As further testing is conducted, the data set will grow and some features will smooth, while other features may be more pronounced. This is a living data set and is being continuously updated.

   • Not all firearm/silencer combinations produce the same wave shape. It is anticipated that as the data set grows, P-i relationships for different weapon platforms may naturally evolve. One advantage of consistent measurement and waveform computation is evolving interpretations from the growing data set.

3. The wave shapes at the muzzle and ear are different. That’s why there are separate plots for muzzle and ear; it is dangerous to compare waveforms in the true “free field” (measured at the muzzle) to waveforms measured near a reflecting surface (the shooter’s head). Reflections induce wave amplification and time-phase changes that are unavoidable. Most data measured “at the ear” includes the shooter’s head as a nearby reflecting surface. Rather than create a mechanical pseudo-acoustic-transparent servo/rest system to fire the weapons and measure free field pressure 0.15 meters from a fictitious head position, this Standard maintains the shooter’s head in the test method for practicality.

SSS.4.1 - Hearing Damage Levels™

Below, the previously shown 3D ARU plots have been converted to allowable daily shot thresholds. The below plots contain real measured 5-shot averages and best-fit empirical P-i curves, each bounding a PEW Science Hearing Damage Level™ (HDL™). The plots in Fig 20 and Fig 21 illustrate how many times you can fire each silencer/host combination, per day, without sustaining permanent hearing damage, if the subject is located 1.0 m to the left of the muzzle or firing the weapon, respectively. The pressure [dB] and impulse [dB-ms] scales are kept constant between the figures. It is important to note that each HDL color region is shifted down and to the left in the ear plot, when compared to the muzzle plot. This again illustrates, visually, that measured peak pressures and impulses at the ear (0.15 m right of the shooter’s right ear with the shooter’s head present) have different wave-shapes than in the true free field (1.0 m left of the muzzle).

Hundreds of shots with hundreds of individual hearing damage model runs were used to develop the relationships seen on this page.

Note that some silencer/host combinations are much louder than others, at the muzzle, or at the ear, or both. Also note that just because a silencer “meters” louder (has a higher peak sound pressure), it may have a lower HDL threshold and therefore may be more “hearing safe” than a silencer that “meters” quieter!

As described earlier in the Hearing Effects portion of the Standard, multiple metrics are important and required for complete silencer sound signature characterization.

Using the plots in Fig 20 and Fig 21 to rate suppressed weapon system performance, while possible, is still complicated. This has been addressed:

See how this all fits together in the first ever empirically validated universal suppressed weapon sound rating system, developed by PEW Science. Head over to SSS.5 - Suppression Rating™ and check it out!