How Distance Affects the Sound of a Gunshot

I live near a military base and a wood, and I regularly hear both the training of the soldiers and shooting from hunters. So is it reasonable to assume one would hear a hunting rifle shot from about a distance of 100/200m when inside a house? A friend of mine says no, claiming shots aren‘t that loud and wouldn‘t be overheard. I think otherwise, but perhaps I overimagine?

So, this is actually a shockingly complex topic, and I’ll try to keep it somewhat simple, but there are a lot of factors that seriously skew these numbers.

If there was no environment, and just natural atmospheric fall off, 200m from a high power rifle going off would still potentially be loud enough to cause pain. And you could still hear the rifle going off at a kilometer, at roughly the volume of a conversation. (It works out to around ~40 decibels, so, audible but not especially loud.)

The only time you’re likely to encounter something like this is if a shooter is firing out over a valley. (Worth noting is that atmospheric humidity will heavily affect sound propagation. If I remember correctly, low humidity will reduce sound propagation, while high humidity will increase it. However, I don’t know exactly how much this affects, and I could be remembering this backwards.) However, the valley example is somewhat artificial, because in any real space, the valley’s terrain will affect propagation.

Related to this, sound transmits very well across hard surfaces. So if you’re in an urban environment, sound will echo off the buildings, down the roads, and it will travel farther (or, more accurately, it will retain volume over longer distances.) This is also true for sound traveling across bodies of water. It will be easier to hear a rifle being fired from across a lake, than within a dense forest, closer to the shooter. In fact, using the example above, that rifle shot would still be ~85 decibels after a kilometer over open water.

Then there is the inverse, foliage, and even just grassy meadows will dramatically reduce the propagation of sound. A properly constructed outside range can make use of earthen berms. On their own, these will significantly reduce the perceived volume of a gunshot. Just breaking line of sight between the gunshot and the listener will significantly reduce the sound transmitted to them. So, with grassy berms shielding an outside range, you could easily drop that 127dB rifle shot down to ~85dB at 200m. Add some dense trees around the range, and might be able to drop it low enough that it would be extremely hard to hear over ambient noise in a residential dwelling at those ranges.

I’m not sure exactly how much noise absorption you’re getting from the woods, but it would not surprise me if you can hear hunters taking shots. Especially if the terrain is (mostly) flat, and you have an effective line of sight on the shooters (even if you can’t actually see them.) Similarly, if you have windows open, that’s not going to mitigate the sound of a gunshot.

As for the military range, it’s entirely possible you can hear that as well, depending on how the range is constructed, and the exact terrain between you and them. If they’re on the other side of a river, you could absolutely hear that over the water.

That said, it sounds, from your description, like the shots are fairly quiet (under 40dB), which, yeah, that’s absolutely plausible at those ranges.

-Starke

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