Suppressors A question about suppressor noise properties.

[Tburkes]

I've heard that as a can gets hotter from continuous shooting that the sound suppression properties go down, that it gets louder to the shooter, to the point that it will get so loud that the sound will make your ears ring.

My question is...why does this happen?

 

[bachelorjack]

Re: A question about suppressor noise properties.

I don't think I've experienced this.

As you get past the first shot the oxygen in the can is exhausted and suppression gets better. These louder first shots are known as First Round Pop or FRP.

One of the things I have experienced is cans that are marginal in suppression sound quieter for a few shots. If you keep shooting them the hearing damage and exposure increases and they appear to sound worse. Suppression is the same, just perceived suppression decreases. The proper sound testing meter will show this.

Is this maybe what you're referring to?

 

[Tburkes]

Re: A question about suppressor noise properties.

No sir, not what I'm referring to.

I had delivered some prototype suppressor heat shields to a company that is affiliated with one of the more well known suppressor companies. I was told that they had all kinds of fancy equipment to measure heat buildup, etc.

They did some of the testing and I was told the the covers held up pretty well, except that they held so much heat in that the can could not dissipate it fast enough. This caused two things to happen, 1 the can seized up on the barrel, and 2, as the can got hotter the sound got louder, to the point that it was causing ears to ring, basically it sounded like their wasn't a can on any more.

I don't understand how this happens.

 

[Conqueror]

Re: A question about suppressor noise properties.

Perhaps thermal expansion of the metal causes a small amount of widening of the baffle aperture, such that the cans don't contain the gas as well. That's the only explanation I can come up with. I haven't noticed this to be a significant problem in the past, and I don't know that anyone has really studied it.

 

[Ranb]

Re: A question about suppressor noise properties.

A silencer lowers noise by acting as a heat sink and expansion volume. Heat it up enough and it is no longer an effective heat sink. My guesses are free.

Ranb

 

[Bacarrat]

Re: A question about suppressor noise properties.

Interesting. I didn't really notice a huge sound difference this weekend when I proceded to do a couple mag dumps out of a suppressed M16. I will have to keep this in mind next time.

 

[KYS]

Re: A question about suppressor noise properties.

Ive put quite a few rounds downrange on a 308 bolt gun wearing a TAB cover. It got hot enough to where you couldnt grab it for about 3 hours I never noticed it getting louder. and yes I had my earmuffs off.

 

[bachelorjack]

Re: A question about suppressor noise properties.

Zero ideas here. Know what they were made out of and what platform they were on?

 

[Tburkes]

Re: A question about suppressor noise properties.

Also, I'm pretty sure this was in shooting .223 rapid fire, not any of the .30 cal or larger rounds.

This was in testing the heat shields that we're working on. The covers held up pretty well, it was the problem of holding too much heat in that caused the seizing up and louder than normal sound.

 

[PLeighton]

Re: A question about suppressor noise properties.

That is one of the reason that the Knights QDSS-NT4 has the outer cover with the holes in it.

It acts as a heat sink.
This allows it to stand up to the ridiculous abuse that is required for the SOCOM contract.

The relationship between heat and suppression levels can best be illustrated by the use of cooling mediums in pistol caliber sound suppressors.
(Wet vs. Dry suppression levels.)
The hotter the gas the louder the report.

Hope that helps a little bit Tony.
I don't know the science of it, but I will poke around if I have time and see if I can come across some additional info.

 

[divejay]

Re: A question about suppressor noise properties.

interesting reading tag!

 

[RollingThunder51]

Re: A question about suppressor noise properties.

Thermal pathing and efficient dispersion is the largest challenge within a well designed suppressor. It has many factors and consequences. As properly pointed out already, full auto becomes the most challenging especially if the suppression is to be better than the "good enough" cans contracted currently in large quantities. These cans are designed not to provide ultimate low level full auto sound suppression, but rather good enough suppression for FA wailing and the means to survive the resulting heat.

As to the perf wrap on the can above, it is there to address one of the mysteries of quick detach...fast on but Waaaaahuuunga! hot to come off. The phrase should really be "QA/WTFD." As any good engineer would tell you, if you were to add a perf layer for heat sink, your standoffs would need to be a much higher percent of surface contact and you wouldn't perf from 10-2 o'clock to avoid the operator aiming through heat mirage.

Thurkes, no wrapping for FA applications. But...there is another way. PM me again.

 

[Zak Smith]

Re: A question about suppressor noise properties.

When I have an array of long-range steel in front of me, I like to pull the trigger a lot. So I'll often keep firing using a TAB cover until I start to smell/feel heat - woops - and then pull the cover back and let it cool. I have not noticed heat-related decreases in suppression, but I haven't metered it either.

 

[Tburkes]

Re: A question about suppressor noise properties.

HaaaHaa, you're walking on the ragged edge aren't you.

If you fall over just get ahold of me and we'll get it sorted out.

 

[308sako]

Re: A question about suppressor noise properties.

deleted in protest!

 

[Zak Smith]

Re: A question about suppressor noise properties.

Yeah on the other hand something very hot has a higher rate of cooling due to the larger difference in temperature (ie, rate of heat energy transfer is usually proportional to "delta T").

 

[Stealth-X]

Re: A question about suppressor noise properties.

I agree with RanB and 308Sako.

My understanding is that a suppressor works in 3 ways.

1. It gives the gas a volume to expand into, thus lowering it's pressure.

2. It slows the gas and releases it more slowly so there is more of a hiss than an explosion, or another way to think about it is the same sound is spread over a longer period of time, and thus sounds quieter (or something like that.)

3. Lastly, the can absorbs heat from the gas. If I had to guess why this helps, I would have to say that hot gas expands, so cooler gas expands less and would also have less pressure. I think you would have to get the can VERY hot for the heat to significantly/noticeably reduce the effectiveness because the other two functions of a can are more important and still working (slowing the gas and allowing for gas expansion).

In the end, we're trying to take energy from the gas and turn it into something besides sound. Nearly all of the 'sound energy' taken from the gas is turned into heat. For this to stop working, the can would have to be very close to or higher in temperature than the gases expanding behind the bullet.

I'm not a physicist though, so this is mostly intuitive. If I'm wrong, I'd love to hear the reality of the situation.

Regards,
Nate

 

[Boomholzer]

Re: A question about suppressor noise properties.

here is my angle with about the same conclusions as the above post......

Without going into the different mechanisms in how a suppressor works, I'll guess with the following:

Thermo laws 1 and 2 are a good start.
#1 conservation of energy (it has to be accounted for)
#2 entropy (given the same shit happening over time, it's all going even out)

Energy into the suppressor is:
1) hot gas at velocity
2) the projectile (M & V): BUT the projectile passes through, often with MORE velocity so we can ignore #2.

#1 normally a rifle shot (w/o suppressor) creates a significant blast and report. The suppressor obviously reduces this. In return, the suppressor does not buldge, explode, dig holes, or have any other mechamism to transfer gas velocity energy except to create heat. Conservation of energy is conserved in that the reduced report and blast turns into heat.

Back to thermo law #2:
There likely is a critical temperature where the suppressor itself and the trapped gas inside becomes more equal to or hotter then the new injected gas from firing a bullet, thus greatly reducing it's efficiency or ability to change gas velocity into heat.
This could be a linear change with temp, but the effects are largely unheard with supersonic ammo untill the report greatly exceeds the sonic crack.....But, I doubt it.

A "mental picture" may be that the gas velocity is always lowered mechancially due to the suppressor's volume and the baffles. These features are constants regardless of heat. However, if you ignore that and think about the basics, it makes sense.

 

[TOPO-sniper]

Re: A question about suppressor noise properties.

Its been awhile since I had thermodynamics and don't feel like hunting down the textbook, but to cause a substantial decrease in supression I would guess the thermal wrap possibly allowed the f/a supressor to reach yeild temperature for some component of the can. That componant yields/deforms and the sound suppression goes down.

TB, did they disassemble the can after the test?

 

[Zak Smith]

Re: A question about suppressor noise properties.

I can't give full details, but we have tested one of our original can designs to destruction on an M240. To the ear, the suppression level was roughly constant even through mild internal damage, and only got really noticeably louder when there was catastrophic internal damage and ultimately a tube failure.

 

[Tburkes]

Re: A question about suppressor noise properties.

The company that did the testing did not tell me whether or not took the can, cans apart after the testing.

From what I remember of the conversation it went something like this, as we kept shooting and the can got hotter and hotter the noise suppression got less and less to the point that the shooters ears started ringing and it was uncomfortable to be around and noise protection was needed.

I was told that the cans heated up so much that they started to seize up on the barrel, or quick connect, or whatever it was they were using to connect the can to the barrel.

They were supposed to send the covers back to me with picture documentation, and some kind of paper work as well, documenting the test.

I never got anything back from them, despite repeated calls to them.

From what I was told the covers held up pretty well, but since I never got them back I can't say for sure.

 

[breezernate]

Re: A question about suppressor noise properties.

Higher temperature gas means higher pressure gas.

Higher pressure gasses exiting the muzzle mean more noise.

Simple.

Nate

 

[Outsydlooknin75]

Re: A question about suppressor noise properties.

A TAB cover on an AAC m4-1000 and 2 30 round mag dumps is enough to cook the finish on the can. Did it do any damage other than just basically fubar the finish, NOPE. It did take a while to cool back down though. We stuck a little meat thermometer between the can and the wrap and watched it spin like a hellicopter, I dont know the actual temp but it was hot.

But with that being said I need to order a cover for my 1000 since I have it on a bolt gun and wont be letting loose 60 round dumps although it is possible with just 2 mags.

 

[HPLLC]

Re: A question about suppressor noise properties.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RollingThunder51</div><div class="ubbcode-body">
As to the perf wrap on the can above, it is there to address one of the mysteries of quick detach...fast on but Waaaaahuuunga! hot to come off. The phrase should really be "QA/WTFD." As any good engineer would tell you, if you were to add a perf layer for heat sink, your standoffs would need to be a much higher percent of surface contact and you wouldn't perf from 10-2 o'clock to avoid the operator aiming through heat mirage.

Thurkes, no wrapping for FA applications. But...there is another way. PM me again.

</div></div>

That's not accurate- the girdle gets extremely hot quickly and wasn't designed to allow the hot suppressor to be removed.

The Perforated girdle was added because the test required to be passed was resulting in weld failures. <cracked or holing through of welds. The addition of the girldle allowed the suppressor to pass the required torture testing without failures.

This probably has a lot to do with 625 inconel deriving a lot of its strength from cold reduction. So tube drawn over mandrel is strong. Once fusion resistance spot welded, the 625 inconel is brought to the molten temperature and cooled- possibly resulting in strength properties more like cast 625 inconel- which are approximately = to 316L SS.

So the engineered properties of the component designed with .035" wall 65,000KSI yield tube, are now compromised.

Adding the girdle does effectively increase cooling, and also lowers maximum operating temperature, which increases the useful strength of the welds to the extent that the welds do not fail under the original torture test parameters.

The actual engineering reason for not perforating the 4 sections I don't know. It probably accomplishes two things:
A provides a surface to put ATF data on.
B adjusts the weight of the component for a combination of heat sink, and cooling surface area capability.

IE more holes = more surface area for cooling, however, more weight equals greater capacity for short run heating offset- AKA there may well be a more balanced engineering relationship than meets the eye involved in the design of the product.

 

[Killer Spade 13]

Re: A question about suppressor noise properties.

OK, I read the post that states that when the first round is fired through the suppressor, "oxygen in the can is exhausted " which results is quieter subsequent shots.

I don't quite follow this.

The expanding gasses are vented through the suppressor and would, for a very short period of time, create a vacuum inside the suppressor body which would be filled with incoming fresh air.

How can the oxygen level inside the suppressor be reduced when, after the gasses an round have exited the suppressor body, it is refilled with ambient air at the ambient air pressure?

 

[softcock]

Re: A question about suppressor noise properties.

The second shot is always the quietest in a pistol w/dry Can & real easy to hear the difference with your ear .
Also the second shot . The Can aready filled solid with smoke ( artificial environment introduced ) + ( lack of Oxygen ) from the muzzle blast .
.

>..." <span style="font-style: italic">How can the oxygen level inside the suppressor be reduced when, after the gasses an round have exited the suppressor body, it is refilled with ambient air at the ambient air pressure</span> ? ".

The Can is Not re-filled with fresh ambient air . It is packed full of smoke.
Shoot a shot & then take your Can off & blow it out . It packed full .
.

 

[biffj]

Re: A question about suppressor noise properties.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Killer Spade 13</div><div class="ubbcode-body">
I don't quite follow this.

The expanding gasses are vented through the suppressor and would, for a very short period of time, create a vacuum inside the suppressor body which would be filled with incoming fresh air.

How can the oxygen level inside the suppressor be reduced when, after the gasses an round have exited the suppressor body, it is refilled with ambient air at the ambient air pressure? </div></div>


Actually no vacuum is created, the can vents down to equalize pressure with the ambient surroundings. Once there, thats it, no further venting drops the pressure below ambient so no new clean air is sucked into the can. Once you blow out the initial clean gas the can contains a goodly amount of burned powder gasses and not much oxygen. I don't know if thats the real reason for first round pop but since blowing any non combustion supporting gas into the can seems to get rid of it the explanation seems sound.

Frank

 

[We own the Night]

Well that's close but actually it's a little more complicated, as you shoot the barrel and suppressor heat up. As the heat up the ambient air inside chambers begins to drop in air pressure because higher temperature air has lower air density and colder air has higher density. When the exploding gases leave the barrel and enter the suppressor baffles, they are expanding at incredible speed, the pop or cracked we here is the reaction of those hot games when they come into contact with the cooler ambient air, that is the crack or pop we hear, and also it can be the supersonic bullet breaking sound barrier, this is why most suppressors are used with subsonic ammo that does not break sound barrier...it's not that there is no oxygen in the tube, it's that the rapidly expanding explosion is starved of the element needed to create a stronger shock wave - so the baffles compartmentalize the ambient oxygen and prevent the whole mass of oxygen from exploding at the same time...If you just had one big open chamber it would be much louder, muzzle breaks and flash hides work in similar way..

Sent from my SM-N900T using Tapatalk