Guns, decibels, and math?

November 7, 2021 9:48 AM

Asking for DH: The neighbors are (legally) shooting guns on their property. DH wants to know this: What is the dB at the source if it is 150 dB at 100 yards away. Thank you.
posted by manageyourexpectations to Grab Bag (7 answers total)

Best answer: Approximately 209db. Source
posted by sacrifix at 9:54 AM on November 7, 2021 [2 favorites]

Do you know what they are shooting? It might be easier to figure the dB based on type of gun, caliber, etc. than based on distance (which might be affected by terrain and other factors). There is different information on the web about types of guns and dBs - here's a chart, for example.
posted by Mid at 9:57 AM on November 7, 2021 [1 favorite]

Response by poster: To answer Mid's question: We do not know with any certainty what they are shooting with or at. Thank you for the chart.
posted by manageyourexpectations at 10:06 AM on November 7, 2021

Best answer: Note that the 209 db calculation is only correct in a spherical chicken sense. Environmental factors (absorbers/reflectors) can have a significant effect thereby increasing or decreasing that number. And measuring correct db levels is difficult. If the 150db number is coming from a phone app it's suspect. No regular firearm is going to be 200+ at the source, that is in the artillery range.

PS: if you are friendly with your neighbours and if suppressors are legal where you live you might want suggest they invest in one. A suppressor won't eliminate the noise like in movies but it will drop sound levels by 20-30db which is a significant difference.
posted by Mitheral at 10:16 AM on November 7, 2021 [5 favorites]

Handgun/pistol (one-hand) or, shotgun/rifle (two-hands)?
posted by kschang at 10:45 AM on November 7, 2021

Depending on what direction you are in relation to the shooting, there can be a big increase in sound if they are shooting a large-bore rifle with a muzzle-break. This article is looking at sound measurements both to the side and behind the firearm, comparing muzzle breaks, to give a sense of how much impact that can have on the noise.

Anecdotally, I packed up and left an outdoor shooting range once after a guy showed up and started shooting some magnum caliber with a muzzle break. Even wearing ear protection and being around 50 feet away, it was painfully loud.
posted by Dip Flash at 10:58 AM on November 7, 2021 [1 favorite]

→ Approximately 209db. Source

I think you might be mixing up sound pressure level (= what we normally think of as "sound level") and sound power level (= a theoretical power output extrapolated back to the source as a point). Both are expressed in dB (though with different "re" subscripts) and are both often called SPLs.

Propagation is also difficult, and the measurement of impulsive sounds is a whole lot different from continuous community noise.
posted by scruss at 1:45 PM on November 7, 2021 [1 favorite]