Sound deadening material inside shroud?

[Dr. Kralenstein]

Would it help at all to stuff some sound deadening foam or fabric in the open area of the shroud, especially with a big vented air stripper?

I know the expansion area in front of the muzzle makes most of the difference, but im making an air stripper that will be dumping the initial blast backwards into the shroud and making chambers in the rear section of the shroud for the air to foil through.

Would putting felt or something in those chambers reduce the DBs any more than just venting the air into those chambers?

 

[lbc_PSI]

Was considering trying the same with my RTI shroud project. You could create layers with felt an another material and have different elevations. I was thinking of alternating between a layer of felt and sorbathane…

 

[subscriber]

Adding a "non-reflective" material to the last inch or so of the rear of the shroud should help. Else, a very effective air stripper can send a bolus of air rearwards, only to have that pressure wave reflect off the hard flat surface, and come crashing back past the muzzle, so the forward baffles have to deal with it a split second later.

Don't fill the rear of the shroud with material, or it won't have any expansion volume left. But, certainly cushion the rearmost section of that volume. The more open the foam or fiber, the longer it can be without taking up too much volume. Two questions are, what would hold that material in place, so it does not partially creep forwards; and would it matter? To avoid material creep, consider a shaped rear shroud support bushing:

Another way is to make the rear shroud support cone shaped, rather than flat. Making the forward "ring" of the cone at barrel OD uses up less total air space, but the idea is the same as with fibrous material. To reduce the abruptness of the air running into the rear of the shroud, and to soften the rebound.

Experimenting with material will help, as the "best material" and configuration depends on the rest of the system.

 

[Star7]

I have not tried it but would double down on the recommendation to not fill the rear of the shroud. In addition to the need for volume, the velocity of the air at the muzzle is likely to start fluffing the material up and causing clipping of the pellet. I want to try something like this on my FWB P700. Even though it is a feeble Olympic rifle, it has a bit of a bark.

 

[Franklink]

Dunno bout shroud, but the quietest moderator that I've ever tested has a felt like material wrapped around the innards.

Doesn't look like much, no cones nor air strippers, but it hushes better than anything else I've laid hands on.

Photo is just prior to cleaning it. That's about 6 years worth of buildup.

 

[Airgunmann]

Back when I was big into car stereos if the box wasnt big enough we would stuff them with poly fill which for some makes it seem like there is more space in the box which also changed the tone It is just the pillow fill that you can get at like Walmart I'd give it a shot I vented a couple of my shrouds in the back which makes it a tad more noisy by the shooter and is quieter at the muzzle my thought was that way it has to use the whole shroud and it isnt air locked part way back

 

[Airgunmann]

Was considering trying the same with my RTI shroud project. You could create layers with felt an another material and have different elevations. I was thinking of alternating between a layer of felt and sorbathane…

I did the exact same thing on the impact I sold had a copper tube that just went the barrel ran the entire length of the shroud rapped felt around it till the shroud fit snug used o rings or rubber bands to keep the felt tight and vented the rear of the shroud and put it back together and yes it did help

 

[Clifton]

Huggett shrouds look to have something in the front to reduce sound and they work. Similar to their Snipe.

 

[Dr. Kralenstein]

Dunno bout shroud, but the quietest moderator that I've ever tested has a felt like material wrapped around the innards.

View attachment 432542

Doesn't look like much, no cones nor air strippers, but it hushes better than anything else I've laid hands on.

Photo is just prior to cleaning it. That's about 6 years worth of buildup.

This is similar to what I'm thinking. I'm not wanting to stuff it full per se, just a layer of felt or something like that's inside this mod, or a DonnyFL.

 

[Vetmx]

I pin a cone baffle about an inch in front of the muzzle, then this is what I pack into a shroud that has the room. Yes, it helps. Sometimes I don’t even need a mod. Except with a .30. They just move too much air.

 

[AlanMcD]

STO sells something specifically for this purpose. I decided to try it on my Sidewinder shroud and I think it helped with the sound level. They sell different sizes for not much cost: https://www.silentthunderordnance.com/air/shroud-damper

 

[Dr. Kralenstein]

I pin a cone baffle about an inch in front of the muzzle, then this is what I pack into a shroud that has the room. Yes, it helps. Sometimes I don’t even need a mod. Except with a .30. They just move too much air.

View attachment 432642

I'm thinking something very similar to that. Just something line the wall of the rear most section. I'm going to put a rubber flat washer at the end to stop the bounce as Subscriber suggested, and a section of foam with some screen or mesh to hold it. I'm going to have roughly 20 inches of open shroud behind the air stripper which will be 3" or so long before it's end cap. That will have slots cut down the sides to blast out of, and then a couple inches of expansion area ahead of the stripper before a couple more washer baffles.

 

[Vetmx]

Just a little warning that I’m dealing with right now. I decided to try a short barrel in a long shroud with a .30. I’m having trouble getting the short 500mm .30 to be more pleasing to the ears. I just can’t stand giant cans on my guns. They just look tacky. I pulled the shroud that I had packed (active shroud), and installed a shroud with nothing in it. But a bunch of dead space. My accuracy went to crap. The gun sounded as good as the active shroud but shoots poorly. When I’m done typing this, I’m going back to the active shroud with a can to see if the guns stellar accuracy returns. Maybe I have another issue that popped up and it was nothing other than a coincidence. The dead space in the accuracy killer is 5”.

 

[subscriber]

Vetmx,

The air is likely passing the pellet in the empty shroud, and buffeting it. Having at least one air stripper near the barrel muzzle may make all the difference. That air stripper needs a space to delay some of the air. Either reflex, or a simple primary blast chamber ahead of the muzzle.

Of course, you may have upset the barrel harmonic also.

 

[Vetmx]

Guns accuracy back to normal. It just didn’t like that much empty shroud.

 

[Vetmx]

Vetmx,

The air is likely passing the pellet in the empty shroud, and buffeting it. Having at least one air stripper near the barrel muzzle may make all the difference. That air stripper needs a space to delay some of the air. Either reflex, or a simple primary blast chamber ahead of the muzzle.

Of course, you may have upset the barrel harmonic also.

This would be my guess too. Bad things are happening in that big chamber with the mega blast from a .30.

 

[LDP]

Guns accuracy back to normal. It just didn’t like that much empty shroud.

You would get better results if you could add some baffles in the dead space to control the air flow so it doesnt disrupt the pellet. I would take a guess the short barrel and extra long shroud would be very quiet set up correctly with excellent accuracy. The baffles could be very simple flat washers with a thin wall tube that fits the ID of the shroud to space the baffles.

 

[Motorhead]

Somewhat a point a lot of LDC & especially shroud manufacturers miss ... is that similar to a PING one gets from air tubes of unregulated PCP's, So does the Shroud behind an air stripper Ping. LDC cans pending baffles & material can is made from can also resonate radially off the cans walls adding sound heard having nothing to do with muzzle POP exiting out with projectile.

I've taken apart many a production LDC's and left scratching my head on what they were thinking in the designs capture and processing of a high amplitude sound pulse ? Indeed not all LDC's are equal in this regard.

 

[Vetmx]

You would get better results if you could add some baffles in the dead space to control the air flow so it doesnt disrupt the pellet. I would take a guess the short barrel and extra long shroud would be very quiet set up correctly with excellent accuracy. The baffles could be very simple flat washers with a thin wall tube that fits the ID of the shroud to space the baffles.

That’s what I’m back to. I took the shroud I had packed (active) off the gun just to test a shroud with 5” of dead space. I never tested a shroud with any more than an inch or so of dead space. I finally did and it’s a no go.

 

[Ca_Varminter]

Somewhat a point a lot of LDC & especially shroud manufacturers miss ... is that similar to a PING one gets from air tubes of unregulated PCP's, So does the Shroud behind an air stripper Ping. LDC cans pending baffles & material can is made from can also resonate radially off the cans walls adding sound heard having nothing to do with muzzle POP exiting out with projectile.

I've taken apart many a production LDC's and left scratching my head on what they were thinking in the designs capture and processing of a high amplitude sound pulse ? Indeed not all LDC's are equal in this regard.

When I constructing a shroud... Front and Rear supports and 2 intermediate support disks.... This keeps the ping resonance down...

Then fill the front void with K-baffles.....