PCP Moderators - larger internal volume vs felt/sound deadening material

[ackuric]

Dispersion of air released over time = perceived sound...the less air dispersed over a longer period of time (ie: like a very small leak from your pcp or tank) will be the quietest, a balloon popping loudest...



With how compressed air works...it becomes a very tight 'Parcel' moving through the barrel, the objective of the LDC is to 'break up' that singular Parcel into many smaller Parcels, which the means to the end has been thoroughly discussed by myself and others.



Reducing pressure isn't the main objective, although it certainly doesn't hurt...so volume is not key its just part of the equation in terms of creating distance for air to travel and become disrupted/broken apart along the way. Baffling does the disturbing of air the best. Overall LDC Length and Length/distance from baffle bore to LDC wall (tube radius..) creates the largest paths for air to travel and is priority over everything else...but generally severely limited/reduced in capacity due mainly to practical purposes...but you'll see some of the finest LDC's are VERY large in OD (1.5" +) and 6" or longer for this very reason, they don't use intricate complex baffling designs or even many baffles at all..because that comes second to the OD / length.


Keeping the overall baffle / exit bore sizing as close to barrel bore OD +1.5-3mm is fairly critical as that itself impedes air flow..so sizing your LDC for your caliber is critical in maximum sound reduction.

HTH,

-Matt

 

[Kinetic45]

Question: I use a conical air stripper/ muzzle brake to keep the air released from the muzzle from overtaking the pellet or slug and disturbing it's flight. I always wondered why a combined air stripper cone and first expansion chamber would not be more efficient to keep from changes to trajectory and to slow the air down... but what you see is an 'empty' expansion chamber with perhaps some wall lining then either baffles (and even the cone shaped K style are usually spaced fairly far forward leaving an empty 1st chamber) or more liner as you are describing previously here.



Also, one of the quietest big bore rifles I have (a .357 BTW) uses the barrel tension nut which is vented back into the internal empty volume between the CF shroud n barrel OD and has a relatively small 3d printed ''dispersion - many chambered" baffled can in front to do the rest. (it really IS a LDC and has to be cleaned every 300 or so pellets, haha)

 

[J.M.M.]

So after much experimentation, research, and a little dumb luck, I seem to have caught a unicorn, in that, to my naked ear, at least, the report from my wood FlashPup QE, is at least 50-60 percent quieter. I used to not be able to detect the valve ping over the muzzle blast, until i was down in the mid yellow range on my manometer, now, it is the loudest sound when I fire, at 2000psi, where my gun shoots hardest, followed by the muffled thump of the bullet striking the target (im testing in a small closed space, with a target only a couple yards away, bare walls, and a wool blanket folded about 6 layers deep over the wood planks im using for the target, for context.). I achieved this by starting with the 3d printed 10 stage baffle replacement, popular on ebay, which actually did very little to quiet my FP wood, just changed its tone a bit, so I cut it in half with a hacksaw, and sanded it down just enough so that if i wrapped a thin piece of felt (1mm) around it, it would fit tightly in the QE tube, and with the felt cut so it would extend from the shroud nut to the first couple baffles, I used the tight fit to anchor the (now) 5 baffle core in the front of the QE shroud, taking up the front half, with the rear half as an expansion and dampening chamber. Then i stuck a rubber washer that had an OD just a bit bigger than the QE shroud, and pushed it in the front, which made it conical due to being slightly over sized, with sub millimeter clearance on the ID. Oh- little more context, my hammer spring is adjusted about 7 turns CCW from all the way CW. Now, if you stand outside the door to my workshop room, you cant even hear it despite the horrible reverb off the bare walls. IDK what a decible meter would read, but in context to the other sounds the report from the muzzle completely drowned out the others, now it is the quietest of them.

 

[J.M.M.]

So after much experimentation, research, and a little dumb luck, I seem to have caught a unicorn, in that, to my naked ear, at least, the report from my wood FlashPup QE, is at least 50-60 percent quieter. I used to not be able to detect the valve ping over the muzzle blast, until i was down in the mid yellow range on my manometer, now, it is the loudest sound when I fire, at 2000psi, where my gun shoots hardest, followed by the muffled thump of the bullet striking the target (im testing in a small closed space, with a target only a couple yards away, bare walls, and a wool blanket folded about 6 layers deep over the wood planks im using for the target, for context.). I achieved this by starting with the 3d printed 10 stage baffle replacement, popular on ebay, which actually did very little to quiet my FP wood, just changed its tone a bit, so I cut it in half with a hacksaw, and sanded it down just enough so that if i wrapped a thin piece of felt (1mm) around it, it would fit tightly in the QE tube, and with the felt cut so it would extend from the shroud nut to the first couple baffles, I used the tight fit to anchor the (now) 5 baffle core in the front of the QE shroud, taking up the front half, with the rear half as an expansion and dampening chamber. Then i stuck a rubber washer that had an OD just a bit bigger than the QE shroud, and pushed it in the front, which made it conical due to being slightly over sized, with sub millimeter clearance on the ID. Oh- little more context, my hammer spring is adjusted about 7 turns CCW from all the way CW. Now, if you stand outside the door to my workshop room, you cant even hear it despite the horrible reverb off the bare walls. IDK what a decible meter would read, but in context to the other sounds the report from the muzzle completely drowned out the others, now it is the quietest of them.

REVISION

I may have overestimated the percentage in my exitement, but in context to the other sounds, that part is accurate, to my naked ear at least. My next adventure is to make a second shroud which will be a simple expansion chamber, fitting over the flared section of the QE shroud, and extending 6 inches past it, and the whole can lined with felt, with a couple felt wrapped cone baffles in the front, and either fiberglass or scotch brite as diffuser/dampening material in the space around the QE shroud, venting out of 4 small holes toward the rear. I have never heard of anyone using a shroud over a shroud, closest I can find is using a LDC on the end of the QE shroud with an adaptor, but can't find a single thing on anybody trying to actually use an over barrel type shroud system, over another shroud system, so should be an interesting experiment, and looks like it will cost me under 4$ at Lowes, for the parts. I'd love to hear any ideas or commentary, its forums like this that I used to figure out what I have got right thus far, I'm still a noob, got my first PCP only a couple months ago, and now I'm completely hooked. These guns are a tinkerers dream! The FlashPup was my first PCP but will not be my last, next will be the Blitz, followed by a big bore. Anyway thanks to all for their posts and comments, I have learned so much in such a short time (but still a drop in the bucket compared to all you veteran Airgunners out there).

 

[bucketboy]

Willie, either you don't read my posts which thoroughly explain the most effective methods of reducing sound, or you disagree...



I'll reiterate briefly...



Length (imagine a place where air can go and never be released due to its length being infinite like a loop. Your HPA reservoir can simulate this condition, because the air is infinitely moving around inside of it when filled until released...given enough time (eternity) the air will eventually be equal to atmospheric and no sound would be noted during that process..)



There is absolutely NO quieter method than the above, that theory and logic is full proof. If you simulated an LDC with the exact length of your pellets trajectory, that would be the most efficient ldc...although this is not practical, there is no argument against it lol.



Another interesting factor is distance from BORE, the WIDER the tube, and larger the distance from bore to ldc wall, means greater time spent inside traversing that distance there and back...which ultimately results in a slower release of air..that is more important than the volume inside your ldc, the LENGTH / distance air has to travel when diverted...



LENGTH/TIME are the largest factors, keeping the distances air has to travel at its maximum (very wide ldcs perform best not JUST because of volume but distance from bore to wall and back, provided you can divert the air to the wall...



-Matt

I am sorry but this is flawed science.

Of course an infinitely long moderator would have 0dB but a very long mod with a Dia only slightly bigger than the pellet would be almost as loud as it would be without a mod, as would a very short mod with massive Dia and volume.

The is no magic formula for airgun mods, what work well on one gun may only be average on another. for example a large Donny on a high powered pcp might be very effective but on a low powered pcp it really isn’t very good, a shorter mod with baffles and wading will definitely work better.



If your rationale is correct, then this shroud/mod

would be significantly quieter than this 

Same gun, same calibre same velocity, yet the smaller mod is a vastly superior at noise suppression. I have no reason to lie, the gun was mine and I made both mods. 







Bb

 

[KratosTM]

Enjoyed reading this, but I myself am more interested in how the volume, felt, length, etc. effects the ACCURACY of the pellet/slug.
I have a Ronin on my AEA Challenger Pro .25 cal, and I would love to know if removing all the felt and screen would actually help the accuracy of my slugs.

 

[PBuffa]

Wow, lots of information and experience here guys.

Thanks for sharing. Based on the information gleaned here, I decided to go with the felt wrap on the forward 1/3 of the Emperor and leave the back 2/3 empty in order to maximize volume. The felt is just to lower the pitch of moderator.

Wonder how that auto sound deadening mat would work. Thin but ver effective in vehicles ….

 

[GaryD]

I'm trying to compare two moderators and based on these discussions, it's likely the one with larger volume snd length would perform better. They are both modular and use aluminum cone type baffles. The "Impulse Air IA-1350" measures (1.35" x 5.125") AND the DonnyFL Yokozuna measures (1.6" x 7.48"). The Impulse Air appears to have a first large open chamber and then 4 equally sized baffles all within 5.125". The DonnyFL has the first large empty chamber and then 3 equally sized baffles, all within 7.48" and also a larger diameter. They also sell additional individual baffles to increase the length. I have not found a Head-to-Head test on YT of these two moderators on the same rifle. I'm looking to use this on an Evanix Max Air II Semi-Auto (.25) Bullpup. Thoughts?

 

[Stubbers]

I'm trying to compare two moderators and based on these discussions, it's likely the one with larger volume snd length would perform better. They are both modular and use aluminum cone type baffles. The "Impulse Air IA-1350" measures (1.35" x 5.125") AND the DonnyFL Yokozuna measures (1.6" x 7.48"). The Impulse Air appears to have a first large open chamber and then 4 equally sized baffles all within 5.125". The DonnyFL has the first large empty chamber and then 3 equally sized baffles, all within 7.48" and also a larger diameter. They also sell additional individual baffles to increase the length. I have not found a Head-to-Head test on YT of these two moderators on the same rifle. I'm looking to use this on an Evanix Max Air II Semi-Auto (.25) Bullpup. Thoughts?

The Yokozuna should perform better, although with airgun moderators there is a great amount of diminishing returns with increased length/volume, so how much better depends on several factors but all things being equal from the gun, probably marginally so. I can't entirely speak as to the math behind that law applied to moderators, but in my experience, the impact at the target starts to overcome the muzzle report in best case scenarios.

Tune refinement generally achieves better results than variables within the moderator design provided the moderator is of adequate length (5"+) and outer diameter (1"+), and bore diameter (1-2mm over rifles bore diameter). Moderators lined with felt or similar sound gentler to my ears where as carbon/steel walled moderators can have more ping within the tube itself.

There really is no ground breaking designs that I have heard about in the moderator game for pcp's...likewise if there were these design factors should be transferable to airgun counter parts and make news on that front, but the technology there is pretty dated, standardized and well known. Just my 2c.

The quietest airgun is going to be the largest caliber available in your arsenal shooting at the slowest velocity applicable to get the projectile on target, due to the barrel volume itself working as a moderator to diminish the pressure evacuating the muzzle at the end of the shot, akin to having a 6" barrel with a 20" moderator attached. Using the barrel itself as a 'moderator' in very low power tunes is most efficient because the pressure slowly reduces over the barrel length remaining after the valve has closed, minimizing any 'pop' made within a typical moderator, where as a tune that uses nearly half to full barrel length will have a larger pop present within the attached moderator due to the sudden exchange of high pressure into a low pressure/atmospheric chamber. Comparable to popping a balloon vs letting the balloon deflate out of the same orifice you filled it with.

-Matt

 

[GaryD]

Thank you Matt!