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Sound levels of various firearms

Discussion in 'General Gun Discussions' started by Richard.Howe, Dec 19, 2005.

  1. Richard.Howe

    Richard.Howe Active Member

    Dec 23, 2003
    Interesting data from http://www.freehearingtest.com/hia_gunfirenoise.shtml

    For context -- an increase of 10 dB is roughly a doubling of the sound level, since dB's are measured on a logarithmic scale.

    Not sure if I understand all this data -- like

    - a 9mm is louder than a 45 ACP?
    - .308 and 30-30 noise levels are virtually identical?
    - 2" more barrel in a 12ga creates a drop of about 5-1/2 dB?
    - a 30-'06 in an 18" bbl is as damaging to the ears as a .357 revo?
    - .223 and .25ACP are about the same?
    - Were these tests indoors or out, and at what distance from the firearm?

    Still interesting nonetheless...definitely a reminder about the cumulative effect of all those "just this once" moments in the woods...

    Merry Christmas!
  2. Mr_Moore

    Mr_Moore member

    Sep 25, 2005
    Interesting data. Thanks for the post.
  3. Double Naught Spy

    Double Naught Spy Sus Venator

    Dec 24, 2002
    Forestburg, Texas
    Rich, you missed somethings very important. A 3 dB increase in the level of continuous noise doubles the sound power {pressure}, however experimentation has determined that the frequency response of the human ear results in a perceived doubling of loudness with every 10 dB increase (from http://en.wikipedia.org/wiki/Decibel). In other words, a 10dB increase that produces a doubling of the perceived sound level (twice a loud) is actually more than 8 times the amount of sound pressure. It is not the loudness that causes damage per se, but the pressure.

    Indoor noises are louder can can cause more problems because the sound reflected back from walls, floors, ceilings essentially expands the duration of the event, as with gunshot noise, with the person actually hearing the report several times in very quick succession, reflected sound pressures decreasing with time of distance traveled. So with a single 150 db gunshot report indoors, the first many reflections of the sound that make it back to the shooter may all still be substantial enough to cause hearing damage. So a single report results in several insults via the reflected sound.

    You mentioned the cumulative aspect, but presented nothing to sugstantiate it. Hearing damage is cumulative. While those with auditory exclusion during high stress events don't report hearing gunshots they fired or having the sensation of ringing ears afterward, they still suffered hearing damage. They will have suffered physical damage. This is because the hair cell's hair-like stereocilia get damaged or broken by loud noise. These aid in hearing and once damaged do not repair or regenerate.

    You said you didn't understand the information you provided and wondered about things like inside v. outside, distance from firearm, and how different calibers can be louder than would be expected. This brings up several interesting points. The testing was probably outside so as to record just the singular event. As for distance, who knows? While distance is important, the pressure of sound decreasing with distance from the sounds, sounds are also directional. Shooting a Barrett 82A1 is not a bad experience for the shooter as the shooter is directly behind the source of the noise that the broadcast forward and then to the sides via the muzzle brake. From a position either side of the shooter by a foot or two, the sound is perceived as much louder and the pressure wave washing over the observer can be strongly felt and can be quite uncomfortable. Simply put, the shooter is in the position that receives the least amount of sound.

    So how can small calibers have more sound than larger calibers? There are a whole host of reasons why. First, the size of the caliber isn't critical. We assume that bigger calibers will produce more noise, but this is not necessarily true. Things such as barrel length, powder speed, muzzle brakes, etc. all influence what sound is projected. For example, a shorter barrel may allow for the bullet to be gone long before the powder is finished burning and you get a goodly amount of the powder burning outside of the gun and generating noise outside of the gun which then produces more noise than would be the case for the same caliber, cartridge, load fired from a longer barrel in which the entire amount of powder is burned internally.

    Rifles usually have slower powder than pistols. This means that the sound is generated over a longer period of time, hence the potential for more hearing damage because of the extended duration of the sound event.

    So, a .25 acp and .223 round can have comparable sound levels? Maybe so. The sound levels reported do not include the aspect of duration. The .25acp with a short barrel and fast burning powder will no doubt be loud as much of the sound will be generated outside of the barrel. .223 with slower burning powder may reach a comparable level and not louder in part because the powder is burned over a longer period of time and much inside the barrel.

    Now, a suppressor works by providing a place for those expanding gasses (and sound) exiting the end of the barrel to expand into an enclosed structure with baffles than then essentially release the gasses and sound at a reduced pressure, thereby lowering the report noise.
  4. Father Knows Best

    Father Knows Best Senior Member

    Apr 14, 2005
    Minneapolis, MN, USA
    That makes sense to me. Remember that sound is just a pressure wave, and the measurements given are for the peak of the wave. The peak will decrease with lower pressure and increasing distance from the measuring point. The higher the pressure, and the closer to the measuring point, the higher the measured sound pressure level, which may or may not be perceived as "louder" to the human ear.

    Thus, a 9mm round may well be louder than a .45ACP, as the .45ACP is typically a rather low pressure round. That's also why the .357 magnum is quite a bit louder than the 9mm -- much higher pressure. The .30-'06 out of an 18" barrel is as loud as a .357 magnum revolver because you start with a rifle round that is very high pressure compared even to a magnum pistol round, but give it 18" of barrel to bleed down before generating the pressure wave.

    Longer barrel lengths will reduce peak sound pressure by increasing the distance from the shooter's ears, and also by giving the pressure a chance to drop a little more before exiting the barrel.

    Keep in mind that perceived loudness may not match these figures. It is quite possible for you to perceive a particular cartridge/firearm combo as louder than another, even if the peak sound pressure is lower. That's because peak sound pressure does not measure the shape/duration of the wave. It can be a sharp crack, or a drawnout boom, or somewhere in between.
  5. hso

    hso Moderator Staff Member

    Jan 3, 2003
    0 hrs east of TN
    For further reading

    I would have expected the following conditions to have been used for gathering the data in the Krammer study.

    The noise dosimeter would have been positioned at one of two locations. Either at a fixed distance from the barrel off to the side or behind or at what would have been the location of the ear of the shooter.

    The measurements may or may not have been made outside, although it is most probable that they would have been made outside to set the same condiditions for both pistol and rifle shooting.

    Several shots from each gun/caliber would have been made and an average taken to get the SPLs (sound pressure levels).

    To reemphsise what's been said - A 3 dB increase in noise roughly doubles the energy of the noise. All hearing damage is cumulative. Keep adding it up and eventually you will notice a permanent hearing loss (says the little fat man with permanent ringing in his ears). The fact that you didn't "hear" a gunshot due to auditory exclusion does not reduce the damage to your ears and does not prevent any hearing loss.

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