fixin Wrote:Silencer co. carries some good looking stuff, make sure whatever can you go with to hunt down decibel data on it outside of manufacturer spec. There is no single set standard on decibel testing, more a conglomerate of ways to test. Recently the military picked up a 6 inches from the right ear test that I personally like. That for me is best case scenario for testing a can since it is next to the shooter's ear as opposed to anywhere else. My first thread on here was asking for decibel data for the Q LLC. Trashpanda and nobody had any data on it, so by the looks I'll be guinea pigging it once my form 4 shoots back to me.
fixin,
There has been a handful of suppressor studies over the years including the World Health Organisation that has informed the US military's current standard for severe noise exposure Damage Risk Criteria (DRC). The current standard is MIL-STD 1474-E which was promulgated in 2015. Prior to that has been 1474-D since 1997. The previous 1997 standard assumed that all sound above 140db (peak impulse) would be mitigated by people using hearing protection. This is why manufacturers have labelled some of their suppressors as 'hearing safe' if the sound is below 140 at wherever they place the microphone near the gun. As you might imagine peak db levels vary widely depending on where the mike is around the gun, but also the type of action. For example, Lobarinas and his colleagues in 2016 conducted a study to find out what db reduction you would have with a suppressed semi auto AR15 using 223 and 300BLK. They found the db reduction varied depending on what ear you were recording. The left ear recorded on average (it varied because they tested more than one suppressor) a 20-30db reduction while the right ear which was more exposed to the ejection port was less at about 10-18db.
Getting back to the formal studies and standards finding a clear quantifiable link between sound pressure and what hearing damage results is imprecise. We end up with models which get massaged in subsequent studies. The current MIL-STD1474 uses an electroacoustic model designed by Price and Kalb (1991) called the Auditory Hazard Assessment Algorithm for Humans (AHAAH). The model attempts to predict the total energy received by the cochlea which causes temporary and permanent damage. Predicting hearing damage is further confounded by how we test for sound around a firearm. I've already mentioned how sound varies greatly depending on where you put the mike but also what you are measuring. Audiologists are prone to measuring with an array of microphones, averaging the pressure and then attempting to remove any reflections from things like floors, walls and in shooting scenario's, tables and benches. Manufacturers however tend to source a quality mike and test for pinpoint sound at points, for example, 2metres a right angles to the muzzle. Some academics do the same, so there is a lack of convention across the world in this area. I hope by all this I have created a sense that it depends on standards and definitions. What is for certain, and I keep stressing this on the forum is that no suppressor is hearing safe. I know in the US you guys go to a lot of expense and effort to get these things and they do mitigate sound but please don't be tempted into thinking you can use them without also using ear protection. If you think that kind of defeats the purpose and effort of getting one then good luck in your old age when that bus you didn't hear ends up bowling you over, or the telephone that never rings (high frequencies suffer the most).
A good read that concludes external ear protection should be worn when using suppressors has just been published in the Journal of Audiology by Murphy et al (2018). These guys are from the Hearing Loss prevention team at the National Institute for Occ health and Safety in Cinncinati. They focus on the two main sounds generated by a firearm; the sonic-boom and the muzzle blast. The sonic boom is called the N-Curve due to the nature of its pressure over time. It looks like the letter 'N' on a graph. The point being is that suppressors can do nothing to mitigate the sonic crack. Peak sound pressure recorded by Rasmussen's 2009 study had the sonic boom N-Wave at 172db while the muzzle blast was 175db. If you are firing subsonic ammo that of course eliminates the N-Curve and you are left with the muzzle blast.
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Murphy's team placed 10 microphones around the shooter and recorded the noise reduction using Gemtec HVT-QM (.308), a G5 (.223) and Outback IID (.22) suppressors on two bolt guns; a Savage, a Rem 700, and a Ruger Charger .22 handgun.
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Here is their paper's conclusion;
[INDENT]Conclusions
The measurements described in this paper are in general agreement with those reported previously. The suppressors reduced exposures at the ear between 17 and 26 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions Figure 8. Sound power as a function of the one-third octave bands after the N-wave was extracted. The N-wave contributed substantially to the energy measured at the microphones in the front half of the hemisphere in Study 2. Firearm suppressors and auditory risk reduction S39 observed for the instructor’s position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB LAeq,8h. Although these results imply a substantial risk reduction, the limited numbers of firearms, suppressors and environmental conditions evaluated in this study are insufficient to consider any combination of gun and suppressor ‘hearing safe'. Thus, hearing protection should be worn whenever firing a gun. For more energetic firearms when target shooting double protection is warranted for the unsuppressed gun and single protection is needed for a suppressed gun.[/INDENT]
These guys make the point that they conducted the test in the open and above the ground. If you shoot in a blind, or under a roof, or inside CQB the surface reflections increase the hazard.
My overall point is there are a bunch of suppressor studies going on all the time in controlled environments that inform institutions and standards. While there is little consensus of how firearm sound should be measured there is consensus that high-power centrefire suppressed firearms are not hearing safe. They do however reduce the damage and help those around you, and won't scare game as much. Plus setting aside any tactical reasons to use them they are simply good fun to shoot. Ironically, if you don't use ear protection with a suppressor you will end up more deaf than if you didn't have the suppressor and wore the usual ear protection.
References.
Lobarinas, E., Scott, R., Spankovich, C. and Le Prell, C. G. (2016). Differential Effects of Suppressors on Hazardous Sound Pressure Levels Generated by AR-15 Rifles: Considerations for Recreational Shooters, Law Enforcement, and the Military. International Journal of Audiology 55 (1): S59–S71.
Murphy, W. J., Flamme, G. A., Campbell, A. R., Zechmann, E. L., Tasko, S. M., Lankford, J. E., Meinke, D. K., Finan, D. S. & Stewart, M. (2018). The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition, International Journal of Audiology, 57
up1, S28-S41, DOI: 10.1080/14992027.2017.1407459Link: https://doi.org/10.1080/14992027.2017.1407459
Price, G. R. and Kalb, J. (1991). Insights into Hazard from Intense Impulses from a Mathematical-model of the Ear. Journal of the Acoustical Society of America 90 (1): 219–227.
Rasmussen, P., Flamme, G. A., Stewart, M., Meinke, D. K. and Lankford. J. E. (2009). Measuring Recreational Firearm Noise. Sound & Vibration 43 (8): 14–18.