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Old January 26, 2016, 01:17 PM   #1
Skans
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silencer function question...

I am interested in knowing where the blast sound emanates from on a suppressed firearm. For example, I believe on average a decent 9mm suppressor will still have about 125db coming from it. Does anyone know what percentage of this noise comes straight out of the muzzle as opposed to resonating from the suppressor walls? Has anyone ever measured the amount of noise that radiates from the body of the suppressor itself (excluding what comes out of the muzzle end)?
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Old January 26, 2016, 02:14 PM   #2
T. O'Heir
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All muzzle blast emanates from the air moved out by the passing bullet and gasses going back into place after the bullet and the gases pass. A suppressor acts just like a car muffler by breaking up and absorbing that air disruption.
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Old January 26, 2016, 07:59 PM   #3
Machineguntony
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Lemme see if I understand your questions correctly...

The percentage of sound coming from the muzzle is simply calculated. If a completely unsuppressed firearm has 150 decibels, but the same suppressed firearm has 120 decibels, 30 of which is converted to heat energy via the silencer, then it 20% of the energy from the muzzle blast has been converted to heat energy.

You asked for the percentage of energy conversion. This is different from calculating the percentage of reduction in noise. Decibel ratings are logarithmic, not linear. This means that 200 decibels is 1000 times louder than 100 decibels; i.e., 200 decibels is NOT 100% louder than 100 decibels.

There are five sources of noise when operating a gun: action noise, bullet impact noise, muzzle blast, sonic signature, operator noise (wiki says there are three, but I've always been taught there are the five mentioned).

With a silencer, if I understand your question correctly, you are also asking if there can be noise directly emanating from the body of the suppressor. I would hypothesize yes, there can be noise emanating from the body of the suppressor. So, that would be a sixth source of noise, however minimal the noise. To clarify, you aren't talking about the nose from the front/exhaust/muzzle of the suppressor, rather, you're talking about from the suppressor body itself. If you want to get really technical, then the noise source would come from the expanding gas hitting the walls/cylinder and baffles, thereby creating noise. The analogy which I would state is that the gas is like a baseball bat, and the baffles and cylinder are like a plank of wood. When the baseball bat hits the plank of wood, there is sound created. Similarly, when the expanding gas hits the cylinder and baffles, there is also sound created.

How much is this noise? I can't imagine a way to manually or directly measure this, as the sound would be too minimal, compared to the muzzle blast, to manually or directly measure. You would have to extrapolate such data based on various known variables; variables which I don't have.

I hope someone can extrapolate the answer for us.
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Old January 26, 2016, 11:02 PM   #4
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Quote:
The analogy which I would state is that the gas is like a baseball bat, and the baffles and cylinder are like a plank of wood. When the baseball bat hits the plank of wood, there is sound created. Similarly, when the expanding gas hits the cylinder and baffles, there is also sound created.
I don't think the baseball bat and plank of wood are the best analogy. I think a fluid in a pipe (air, steam, powder gas, water -a bit of a special case, because it is non-complressible- , etc.)

Think of a pipe with (open) valves inline, bends, "Y"s and "T", connections, all things that change the straight open flow of the fluid. The act similar to the baffles in a silencer. They distort the flow, created eddies, vortexes, backpressure, things that slow down the flow over a pure straight pipe (the bore). Sound is created at each of these points, BUT it is a small amount, tiny, compared to the sound at the open end of the pipe where the fluid exits.

I spent several decades working in the nuclear chemical industry. WE do pipes and fluids (among other things). You can take an experienced operator (or pipefitter for that matter) walk them alongside a fluid line, blindfolded. They can tell by ear, where the pipe makes a 90, or where a valve is, by the difference in the sound of the moving fluid.

So, yes, there is sound created by the powder gas contacting and flowing through the baffles and body of the silencer. Due to the sound levels and the extremely short duration, it is not detectable by the human ear.

Hope this helps.
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Old January 27, 2016, 09:19 AM   #5
Skans
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Quote:
To clarify, you aren't talking about the nose from the front/exhaust/muzzle of the suppressor, rather, you're talking about from the suppressor body itself.
That is correct, you understand exactly what I'm talking about.

Quote:
I can't imagine a way to manually or directly measure this, as the sound would be too minimal, compared to the muzzle blast, to manually or directly measure.
If the muzzle end of the suppressor was attached and sealed to a large sound-proof chamber so that all muzzle blast noise could be eliminated, then the remaining noise emanating from the silencer body itself could be easily quantified. I would think this information would be crucial in developing better silencers. It would tell the designer where to concentrate their efforts in attempting to lower the db's with modifications.

Quote:
So, yes, there is sound created by the powder gas contacting and flowing through the baffles and body of the silencer. Due to the sound levels and the extremely short duration, it is not detectable by the human ear.
This is what I have a hard time reconciling. If the silencer, through it's baffling system stops and converts a large portion of the energy coming from the gun's muzzle into heat, or also changing the sound signature, wouldn't all of that converted energy be "sound" coming from the silencer itself?

Last edited by Skans; January 27, 2016 at 09:26 AM.
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Old February 6, 2016, 11:02 PM   #6
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Noise coming from the suppressor itself would have to be the result of vibrations of the external surface of the suppressor--yes/no/maybe??? This would be outside my area of knowledge.
I've fired a rimfire pistol while cupping the suppressor in my non-firing hand and didn't notice any significant vibrations emanating from the tube.
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Old February 6, 2016, 11:26 PM   #7
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Noise coming from the suppressor itself would have to be the result of vibrations of the external surface of the suppressor--yes/no/maybe???
Maybe not vibrations, but at least some sort of motion of the external surface of the suppressor. Noise is ultimately the motion of air molecules and that motion doesn't start spontaneously.

For the suppressor to radiate noise from its surface, the surface would have to move in order to create motion in the surrounding air molecules. Either it would have to vibrate/resonate, or perhaps expand abruptly as the firearm discharges.

I've fired a suppressed gun that was so quiet that the hammer drop and the noise of the bullet impacting downrange were louder than the discharge noise. If the silencer was radiating any noise as a result of the discharge, it wasn't enough to worry about. I'd try to work on masking the noise of the hammer fall before looking at anything else.

It's also worth remembering that some suppressed pistols have latches that prevent the action from cycling. That's because the noise of the pistol cycling can be louder than the noise of the discharge. What's the benefit of trying to reduce the firing noise even more if the noise of the action cycling is already louder than the sound of the suppressed shot?
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Old February 7, 2016, 11:59 AM   #8
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"It's also worth remembering that some suppressed pistols have latches that prevent the action from cycling. That's because the noise of the pistol cycling can be louder than the noise of the discharge. What's the benefit of trying to reduce the firing noise even more if the noise of the action cycling is already louder than the sound of the suppressed shot?"

FWIW
I've used the thumb of the support hand to hold the bolt closed on my muffled 22/45. I only do this with subsonic ammo as the HV kind of hurts my thumb. Doing this does make the set-up just a little quieter since it stops the cycling noise and keeps the breach sealed.
Long ago and far away the folks I worked for had an old suppressed High Standard HD-M in the arms room that had the safety modified to hold the slide closed. The only safety was the half cock but really, the guys using the weapon didn't have a problem with that. The plan was for only one shot to be fired anyway but that shot needed to be as quiet as possible.
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Old February 8, 2016, 01:20 AM   #9
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Quote:
Originally Posted by Mobuck
I've used the thumb of the support hand to hold the bolt closed on my muffled 22/45.
I've also done this on my silenced Glock 19. Due to the locked-breech action, it takes about the same amount of pressure as doing it on a MkIII.
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