Silencers on aegs?

[ikarma70]

Hi all, do silencers really work on AEG's?

 

Atb

Andy

[TacMaster]

Not really. The sound of the gearbox doesn't just come out of the barrel, and the motor is usually inside an AEG's pistol grip. While there are low noise builds, they need a lot of work to get right.

Suppressors are mainly just for looks on AEGs.

 

Although they are very useful on gas NBB weapons. I used to have a gas sniper rifle that was completely silent with a suppressor attached, aside from the sound of the valve knocker hitting the magazine.

[Monty]

Nope, just for looks.

[team flex]

And hpa guns. But to an aeg it will change the sound with the foam. Not necessarily make it quieter

[NH Shooter]

I'm currently making up one for a mk23... Should be only the slightest of clicks... Which is the whole issue... Too many moving parts in aegs...

[Samurai]

As usual, I argue.

The AEG's loudest sound is from it's gears. As TacMaster said, it is not easy to build one with low noise, but it is sure possible.

Then the next loudest can be the sound of piston hitting the piston head. This snapping sound comes from the barrel. With proper barrel length and piston head, it can be lowered, and then if you install a suppressor, this snap is transformed into a thud, that sounds much quieter.

[Josh95]

also, by adding a silencer it means if you want to you can add a longer barrel which may increase range

[Chock]

Silencers work by muffling the muzzle blast and sonic boom of firearms, and since AEGS have neither of these issues, a silencer would not suppress the noise of an AEG. A suppressor could silence a GBB weapon to some degree, since they do have gas escaping out of the barrel, but the noise of a GBB isn't that loud anyway. Theoretically a silencer may affect range and accuracy (a tiny bit) since the BB is protected from crosswinds for a little bit more time before emerging from the gun, but barrel length itself does not affect a BB gun much anyway, since an airsoft barrel is neither rifled nor able to build up more pressure behind the projectile to increase its muzzle velocity as is the case with a firearm, since an airsoft BB is essentially 'batted' out of the gun, although with a GBB, there may be some small effect, since it is launched by a build up of gas.

[team flex]

worth talking to ian, he knows about this thing as I believe thats what he works in (sound of some description, not firearms) and in the quick questions thread he drew a diagram of how silencers work, you can go and have a look if you want...

[Ian_Gere]

Weeeeeell, it's a complex subject, but the simple answer is... sort of

 

As has been said, the majority of the sound which an AEG generates does not come from the muzzle but radiates directly out through the sides of the receiver, but there is a both a shock wave and compression wave which travel down the barrel (the former at the speed of sound, the latter at whatever speed the air expands and mainly blocked behind the BB {hence the way dry firing sounds different to loaded firing}). Unfortunately the usual ways of dealing with these phenomena are mutually exclusive: the shock wave is best muffled by something absorbtive, the more and the denser the better, so rock wool is a big fav in sound studio design; but the compression wave, the deep bass thump produced by releasing compressed air, is best dealt with by enclosed expansion chambers with openings as small as possible... but if those chambers are full of foam, for eg, the air cannot expand into them without compressing the closed cells of the foam - if the foam is open cell then it should allow expansion more easily, however the substance of the foam is still taking up volume and volume is the crucial factor... since the more the air expands within a chamber, the less pressure is available to exit into the next chamber, and so on.

 

Something else to bear in mind is the actual length of the waveforms involved and the size of suppressors - wavelength is calculated by the formula lambda = speed of sound / frequency so, if you think about the ports in your hifi speakers, they are tuned to increase the output of the bass around 50-60Hz which you hear in music as the 'umph' of the kick drum, which is a handy comparison since it is made by a similar process of air being compressed inside a large drum escaping through a small port directly into a mic...

 

343m/s / 50Hz = 6.86m

 

...thus you can immediately see that even a long suppressor, say 250mm, full of foam is 3/5ths of fuck all compared to the wavelengths of the bandwidth carrying the majority of the energy in the sound. Still, when you think about the bandwidth of consonants in speech, 5-6KHz, which compares nicely with the obvious crack produced by piston head on cylinder head, 6.86-5.72cm, it's a different story.

 

There is also a phenomenon known as Helmholz Resonance, which has to do with air moving in/around chambers with specific volumes compared to aperture size (usually but not necessarily tubes) which affects us because a tubular suppressor has a resonant frequency and if this is excited out of phase with sound moving through air around the tube, it cancels out a portion of the bandwidth of similar frequency. In some real steel suppressors (and BMW exhausts) this effect is calculated mathematically, but for us it's really just a case of trial and error.

 

And having mentioned phase, we must also consider the effect of sound bouncing around inside the suppressor: obviously for longer wavelengths this matters not at all, but for wavelengths short enough to fit within the dimensions of the tube, some of those frequencies will reflect off the walls of the tube, plus any internal barriers, and combine with the sound emerging from the muzzle out of phase, although some of those reflections will also be in phase, so as well as reducing the amplitude/'volume' of some frequencies, it will boost others. But when you consider the complexity of how sound bounces around inside a tube, you'll not be surprised to learn that the net effect is to generally reduce the amplitude of the higher frequencies, with just a few which emerge unscathed/boosted in an effect which is known as 'comb filtering'.

 

A complicating factor is that, in the UK, it is illegal to manufacture a device intended to reduce the report of a firearm, which greatly reduces our choice of materials, because whatever we build must fail immediately if you were to fit it to the muzzle of an actual firearm and fire it. On top of that, when the BB leaves the barrel, due to hop up, it has a tendency to rise slightly which means that the gap down the centre of the suppressor must be wider than would be ideal for the expansion chamber theory because, although we could experiment to find exactly how high a 6.08mm hole in each internal barrier should be, in comparison to a straight line from the centre of the barrel, this would only work clamped to a bench - out in the field when it's subject to slight imperfections of horizontal level and involuntary body movements, given the best circumstances, and wholesale bobbing about when firing whilst running, for eg, the BB's hit the internal barriers (I've tried it).

 

IMO the best design to go with, which most people could make easily enough, is one which uses foam barriers, glued to the internal walls of the tube to form separate expansion chambers, each of which should be a different length to give you a better spread of Helmholtz Resonance. This allows the foam to flex and spring back so that its mechanical springiness will have a slight effect on frequencies lower than those which its thickness would tend to suggest (this is a phenomenon well understood in studio design where you try to leave a space between your rock wool and the solid wall behind). You can, and if possible should, use barriers with tighter holes than are generally provided through the foam rings in stock suppressors and a denser foam is desirable also. This is a very simplified diagram of the design:

The effect is to dampen the upper frequencies of the sound which emerges from the muzzle. This change of note is of slightly more significance than the simple slight reduction of overall volume, because bass frequencies are more difficult for us to locate than higher frequencies, due to the distance between our ears being much less than the wavelength of bass frequencies. So, if you also fit ICS helical gears, for eg, and shim them well, Kanzen or Modify Ceramic bearings, Teflon grease, and either Sorbothane pads to the piston head and/or cylinder head, so called 'silent' piston head and cylinder head set, or a Lees Precision Engineering air brake piston head, you can significantly reduce the sound an AEG makes and also make it more difficult for the opposition to know which bush you are firing from...

 

At some point I really should get round to writing this info up as a proper guide, but I also have an idea in mind based on a particular type of real steel suppressor which may be a fair bit more effective than the above design, but I just haven't been arsed to try it out yet...

 

Oh yeah, and before I forget, James... I know it bugs the arse off you, but let's have it right - if you do nothing else to a gun other than fit a longer internal barrel, then, so long as the barrel is of at least the same quality as that which you replaced, you will get slightly more FPS, no reduction in hop stability, and therefore slightly more range. That doesn't mean that a different gun with a shorter barrel might not have better range, or that you cannot get that increase in range in another way than replacing the barrel, but there we are, all things hop-wise being equal, more FPS = more range, and longer barrels do allow the expansion of air behind the BB to accelerate the BB for longer...

 

Edit to add: that diagram is actually incorrect with respect to the position of the BB, because the shock wave, the sound which bounces around inside the tube, arrives well ahead of the BB, not behind it. But trying to draw it that way was just complicating the issue.

Edited October 30, 2014 by Ian_Gere
correction

[team flex]

I told you he knew what he was talking about

[Ian_Gere]

I told you he knew what he was talking about

[joshcowin]

Their was an article in ai mag last month and their was a test to show that foam silencers do work,not loads but they do

[Spatch]

Anyone who has owned a G&G ump will know that the suppressor does actually work but it is one of the very few that do

[Samurai]

Well then, let's hear it!

The first gun is my G3. It was originally built to be silent but I had to replace the motor and the bushings, so it's not that silent as it could be.

The second is a mostly standard boyi pdw.

The suppressor has foam inside.

[Lozart]

Interesting vid. Definite change in the tone of the muzzle noise but I'm not sure it's any quieter.

[straffham]

Anyone who has owned a G&G ump will know that the suppressor does actually work but it is one of the very few that do

I have an old DE UMP, silencer def makes a difference giving a soft thud instead of a sharp crack, and it certainly seems quiter. Not found they do as much on M4 or AK variant AEGs though.

[Samurai]

Interesting vid. Definite change in the tone of the muzzle noise but I'm not sure it's any quieter.

I've edited the audio in audacity and put the first gun's unsuppressed and suppressed shots next to each other.

On the boyi it seems that all the sound, including the piston head hitting the cylinder head radiates from the gun, and not from the barrel. The G3 has a thick, soft bumper there, and I think that's the reason for the difference.