Luckily I used to be a professional sound engineer
not that my work was directly related to gunshots, but I can check the box for this particular conversation.
The short of it is that you used the wrong tool for the job and got very inaccurate readings because of it. If someone were to rely on your information and make reasonable assumptions from that point, they would very likely end up with serious, permanent hearing damage.
I also searched the accuracy of the phone apps. Not that internet knowledge equals actual knowledge, or even accurate information, but the information I found stated that the phone apps were "fairly" accurate. I'm not trying to perform an OSHA study. Obviously, I'm not a professional sound technician.
Phone apps can be acceptably accurate, but only within their design parameters and their physical (and software) limitations. Same thing for cheaper dedicated sound meters (or even some of the more expensive ones). They are normally designed to measure sustained, environmental sounds that are not loud enough to cause immediate hearing damage. Measuring high dB short duration (impulse) sound levels is a pretty niche area and you have to get very specific meters in order to get even remotely accurate measurements.
The mics that phones use are designed to max out at 115-120 dB because a phone in its intended use (even as a video recording device) has absolutely no need to be able to accurately record, measure, and represent loud and quick sounds. Some might say that it is actually a good thing that the phone doesn’t accurately replicate a gunshot. The microphones and processors used to accurately measure gunshots are very specific, expensive, and require regular calibration. And frankly they are so specialized that they are a bad option if you want just general sound measurement.
The fact that all of your readings were almost exactly the same indicates that your phone was just maxing out and effectively showing “this is the highest number I can show, so this is what I will give even though the actual sound was louder”. Alternatively your phone was missing the initial gunshot because of the short duration and only picking up the lower dB but longer duration echos.
Technically speaking there is a way to take a phone’s (or any sound meter’s) design characteristics and maximum accurate dB level into account and calculate a specific distance where the sound level will be in line with what the meter can measure. It’s been a while since I ran the numbers, but for a gunshot at 168dB (1M from the muzzle) to be reasonably below 120dB so that it can be measured by a phone, you need to be something like 300-400 meters away. And that still doesn’t get into the phone not measuring impulse sounds correctly.
Tone and duration are also very important when considering the human perception of a sound, and these are things that are not well represented by just looking at a max dB number. That’s why you can have a finger snap next to your ear (higher frequency, shorter duration) feel like it is harsher than a car door closing (lower frequency, longer duration), but still get the same peak dB measurement.
I don’t want to get even further into the weeds with this (there can be a lot of math and science involved) but there is no way that a reading of 115dB is an accurate representation of an unsuppressed rifle at the shooter’s ear.
For my limited purposes, the phone apps seem to be able to give me adequate usable information. I'm just trying to get a general understanding of the sound levels behind the gun and in the general area of a shooting range.
I’ll try to use some more comparisons and standards to try to illustrate my point. I’ll be talking a bit about suppressors here because that’s where a lot of my personal research and experience has been.
OSHA standard for an impulse sound being hearing safe is 140dB, and that’s where a lot of suppressor manufactures start making the claim as well. I know from personal experience that suppressed shots in the mid 130dB range (most supersonic ammo) is bearable but uncomfortable without ear pro. It really only gets comfortable around the mid- to upper 120dB range (suppressed 9mm pistol, subsonic ammo).
As mentioned in my last post, we also have readings for various sounds like snapping (104dB) and an AR bolt closing (120dB). These readings are from a high quality, professional, calibrated setup.
If we compare to your numbers with a high of 115dB, that would be saying that a gunshot from an AR15 is quieter than the bolt closing on the same gun.
Additionally, if someone were to trust the 115dB reading, that would indicate that being behind a gun would be completely hearing safe, and maybe even moderately comfortable for someone and would NOT require hearing protection. We know that is not the case. Shooting a gun while not wearing hearing protection is absolutely and immediately damaging to hearing.
If the noise level is the same whether behind or in front of the gun (or relatively close), none of the usually available hearing protection would work; i.e. 168 decibels minus 30 NRR = 138 decibels. Hearing protection seems to be only as good as its passive rating. Your Peltor Tac 100s are only rated at 22 NRR. My Peltor Tac 6Ss are rated at 19 NRR. Your Swatcoms (at least the ones I looked up-Swatcom Active 8s) are rated at 18 NRRs. What I tested above had higher NRRs than either of those.
I think you’re assuming that hearing protection makes gunshots completely safe from a hearing loss perspective. Unfortunately they don’t. They are a significant help, but they don’t completely eliminate all hearing damage. In addition to your ear canal, sound can also resonate the bones around your ear drum which can result in hearing damage. For example, depending on the sound your jaw could resonate and impact the sounds you hear. That’s one reason I prefer over the ear hearing protection as opposed to just plugs. It doesn’t completely eliminate the issue, but it does help. That isn’t always reflected in NRR ratings either.
Not to make this a whole dissection of the NRR rating process, but the average NRR number doesn’t tell the whole story. You really need to look at the frequency specific ratings.
For example, using the Swatcoms (and yes, the Swatcom active 8 is the right one) the NRR is 19 (18 is close enough) but that is an average for the entire tested range including low frequency sounds which are very difficult to reduce.
If you look at the frequency range of the peak for small arms (around 900-1500 Hz) those same Swatcoms actually have a mean attenuation of 26-27dB. And for the record, I bought the Swatcoms for the compression (not cut) technology, their low profile, and their ability to fit under a hemet. Sound attenuation wasn’t the only consideration.
I don’t usually like to direct to other forums, but NFATalk has a lot of good suppressor reviews and they take the time to break out unsuppressed information as well. I’d recommend taking a look at their metering data.
