Pennsylvania Firearm Owners Association
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  1. #1
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    Default Attenuation levels: anyone measured ?

    I took a sound level meter to the range to measure the level of attenuation achieved with my suppressor (actually, I had to take it several times until I eventually caught a day/time with having the whole range to myself - works better that way, with no other gunfire in the background).

    I was measuring an OPS Inc. Model 12 on a High Standard AR15 with a 20" barrel.

    I positioned the sound level meter on a tripod, near my head (when shooting) and on the opposite side of the buttstock, and had it pointed in the direction of the muzzle. I measured 104dB without the suppressor and 86 dB with.

    On the Ops Inc website, under the specification listing for the Model 12, they indicate 40dB of sound attenuation, but there is no description of instrument placement for that measurement.


    Anyone else make similar measurements ?

  2. #2
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    Default Re: Attenuation levels: anyone measured ?

    did you use the same load/ammo the mfg did when testing? if so, i would be pretty pissed off.
    FJB

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    Default Re: Attenuation levels: anyone measured ?

    There are variables for measuring sound, temperature, humidity, altitude, etc.

    That's why some supressor manufactures don't like to post information on their products noise level reduction.

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    Default Re: Attenuation levels: anyone measured ?

    Most likely it was measured 90* from the muzzle, so your placement was off.


    The fact that it only regestered 104 rather than 140 without the surpressor is telling. Ammo shouldnt matter that much. Also the type of meter and the scale used will matter.

    .

  5. #5
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    Default Re: Attenuation levels: anyone measured ?

    Noise meters aren't so good at measuring impulse noise. 104 dB unsuppressed is way off, it should be at least 140 dB. Decibels are a log scale so 40 dB is a big error.

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    Default Re: Attenuation levels: anyone measured ?

    Quote Originally Posted by bogey1 View Post
    did you use the same load/ammo the mfg did when testing? if so, i would be pretty pissed off.

    That's just it, they don't provide any information about what ammo was used or where they placed the sound measuring instruments, so I just guessed at most parameters when making my measurements.

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    Default Re: Attenuation levels: anyone measured ?

    Quote Originally Posted by Kramer View Post
    There are variables for measuring sound, temperature, humidity, altitude, etc.

    That's why some supressor manufactures don't like to post information on their products noise level reduction.
    I see your point, but temp, humidity and altitude all factor into the speed of sound, but not significantly into attenuation...especially over such short distances (of 3 to 4 feet).
    Last edited by ticker; August 26th, 2010 at 09:39 PM.

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    Default Re: Attenuation levels: anyone measured ?

    Quote Originally Posted by RaisedByWolves View Post
    Most likely it was measured 90* from the muzzle, so your placement was off.


    The fact that it only regestered 104 rather than 140 without the surpressor is telling. Ammo shouldnt matter that much. Also the type of meter and the scale used will matter.

    .
    That makes a lof sense that they likely measured some distance perpendicular to, or possibly slightly forward of, the muzzle. Intuitively, I would expect it to be quite a bit louder out close to the muzzle, but I was ultimately more interested in quantifying the levels reaching my ears while I'm shooting.
    The scale used was A-weighting (500 to 10kHz, the range of greatest sensitivity for human hearing). I'm sure the meter is not optimized for impulse response, but it can be set to monitor peak or average levels - I had it set for peak monitoring, which should catch transients.
    Last edited by ticker; August 26th, 2010 at 09:41 PM.

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    Default Re: Attenuation levels: anyone measured ?

    Quote Originally Posted by Philbert View Post
    Noise meters aren't so good at measuring impulse noise. 104 dB unsuppressed is way off, it should be at least 140 dB. Decibels are a log scale so 40 dB is a big error.
    No argument there...I was expecting something north of 120dB, even measured back at the buttstock. But then placement makes all the difference in the world.
    As you probably know, sound intensity falls off according to the inverse square law, so specification of distance from the source is critical. However, if we consider it in the framework of relative sound levels, and keeping the sound meter in the same position for both open muzzle and suppressed, it seems like the difference should line up closer to the company's advertised 40dB of attenuation, instead of the 18dB that I measured.

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    Default Re: Attenuation levels: anyone measured ?

    Quote Originally Posted by ticker View Post
    No argument there...I was expecting something north of 120dB, even measured back at the buttstock. But then placement makes all the difference in the world.
    As you probably know, sound intensity falls off according to the inverse square law, so specification of distance from the source is critical. However, if we consider it in the framework of relative sound levels, and keeping the sound meter in the same position for both open muzzle and suppressed, it seems like the difference should line up closer to the company's advertised 40dB of attenuation, instead of the 18dB that I measured.
    The measurements I've seen have been 1m from the muzzle, directly perpendicular to the muzzle.

    But I reckon the manufacturers probably rigged everything to their advantage, position included. Or maybe they looked only at a particular frequency.

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