Good to know stoti, 4.5" is a tiny length to try to achieve results comparable to larger ldc's, but still within average for factory lengths. I am sure its right in line with the Tanto in terms of sound reduction.
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PCP Moderators - larger internal volume vs felt/sound deadening material
- Thread starter frank320
- Start date
I’m running a donnyfl tanto on my 22 cal streamline and I’m very impressed with how it does, yes my sumo is quieter on it but not much. In fact my tanto stays on it because I get less barrel droop and honestly I feel it shoots better with it. But for an experiment I took the silencer section and tube off of my r5m long, it’s pushing 34grn edgun s 860fps. Dear lord is it loud without it! Then I installed the moderator adapter and sumo, to the shooter with the ping it was no quieter then the factory mod. I honestly think a lot depends on the gun and how hard you are pushing it. I’ve thought of dropping to 800fps just for more shots and less noise but my pellet impact on both guns is much louder then the gun.
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Generally the gun is always louder than the pellet hitting the target, the target hit is only perceived because its bouncing off target which is straight line of sight right back to you...where as the muzzle blast is directed away from you, either way I have tested and proven this. Especially if you measure DIRECTLY @ the muzzle versus DIRECTLY @ target. Its crazy how we perceive sound by the human ear...
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Keep in mind all your doing is giving the expanding air a place to slow down before it hits the outside air. The more surface area the better
That's the whole in the simplest terms. It's the method that gets complicated, air like water when accelerated can be hard, the felt liner is a soft " bumper" that helps reduce the sound of the air hitting the sides of the moderator. It is surface area that plays an interesting part the more places you give air to "scrub" against and and slow down the better. Think about it this way a rubber ball thrown against a solid wall compared to one thrown against a foam or soft wall which one would bounce back with more energy and which one would bounce back with less noise.
deflection is the key to silence(the best mods keeps deflecting the air against that surface at angles slowing it down) in the same manner as a water stream hitting the wall straight on would mushroom uncontrollable compared to that same stream hitting the wall angled.
Think about it this way you plan on going out to the lake for a boating trip your getting the boat ready at the launch under the trees it's a little windy but not too bad, you get the boat out in the middle of the lake and holy crap that wind just doubled it's speed ???? Why because the surface area for the wind to scrub against was cut in half, no trees to slow it down... There is a huge amount of volume but nothing inside that volume of space to deflect and slow the wind down.
The felt also I think plays another important part.....it is flammable.... Therefore the device is an airgun moderator not a firearm silencer.
The more materials used inside that would limit the usability of the device to airgun only the better
Yes you need volume to work with but it is the surface area inside that volume of space and what you do with the air that makes it quiet and tames the beast
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Good thoughts but the surface area logic is flawed. Imagine a tube stacked with baffles with .001" spacing throughout the entire tube, that is nearly maximum surface area...yet you would yield poor performance compared to properly spaced baffles...just saying, its not quite as simple as 'more surface area more better'. FWIW.
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Agreed, you need the volume (space) for the air to scrub into the LDC otherwise it would just pass on through
Check this out
https://youtu.be/7pOXunRYJIw
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I'm sorry Willie, you are just wrong. I suggest you make a few dozen and test your theory yourself. Volume is the key, sealed baffling within the moderator volume also helps by breaking down the total volume into individual expansion chambers. Placing any form of sound absorbing material inside the moderator does nothing to reduce sound. I invite you to make a few and test yourself.
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Aha ? And why becomes my cars silencer louder and louder when the insulating wool into silencer burns out with the time ?
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The sound of the discharge of the air rifle is due to the rapid expansion of propellant gas into the atmosphere. Powder burners benefit from baffles and heat absorbent materials as steel wool ect which allows the gas to cool and REDUCE in volume prior to ejection into the atmosphere. The baffles slow the ejection of the gas so it cools more and reduces in volume. Air gun gas cools slightly as it expands down the barrel and reduces in pressure, more so in the Ldc expansion chamber, reducing the volume of pressurized air ejected. But there is very little heat in air stored in the air bottle so heat absorbing materials as metal wools are almost useless to the air gunner. The baffles may in a small way slow the ejection of air gun propellant slightly changing the tone and perceived sound volume. Think of an inflated balloon. Pop it with a pin and the gas under pressure is released all at once. Pierce the balloon before inflation, place a small piece of tape on the hole, inflate the balloon, peel the tape off and no loud noise, the air volume is released slowly not allowing the rapid expansion of the gas. One other factor, your personal hearing. I have hearing loss and it greatly effects what I think I heard. Many frequencies are lost to me and I do not truly perceive the concussion of the gas ejection. My perceived understanding of the sound of a shot has been attained by questioning the scientists I worked with and around in my previous years of employment, reading to help me understand them, some experimentation. The best explanation was the one about balloons. I am not degreed in sound transmission but I had a good physics teacher. This is probably too long of an explanation for that I apologize. GBGUNNER
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Great thread. On a similar note, given a full shot cycle, from shooting to hitting the target, 3 separate sources of sound is made:
1) From the rifle - hammer hitting the valve, muzzle report, gases expanding, etc...
2) Sound of the pellet/bullet whizzing thru the air towards the target
3) Sound of the pellet/bullet hitting the target
Number 1) and 3) we can control using moderators, shooting into a muffler box, using a mulch target backstop, etc...
But 2), at this stage, we can't control. As an example, for my FX Impact X, the sound of the pellet/bullet whizzing thru the air is louder than the shot itself if shot into a soft backstop. As per mentioned by ackuric, one has to stand downrange to appreciate how the sounds of the shot differs from the shooter's perspective. And believe me, 2) the sound of the pellet/bullet "whizzing" thru the air is loud and significant.
Ideas for reducing 2)'s signature?
1) From the rifle - hammer hitting the valve, muzzle report, gases expanding, etc...
2) Sound of the pellet/bullet whizzing thru the air towards the target
3) Sound of the pellet/bullet hitting the target
Number 1) and 3) we can control using moderators, shooting into a muffler box, using a mulch target backstop, etc...
But 2), at this stage, we can't control. As an example, for my FX Impact X, the sound of the pellet/bullet whizzing thru the air is louder than the shot itself if shot into a soft backstop. As per mentioned by ackuric, one has to stand downrange to appreciate how the sounds of the shot differs from the shooter's perspective. And believe me, 2) the sound of the pellet/bullet "whizzing" thru the air is loud and significant.
Ideas for reducing 2)'s signature?
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frank320, very slow moving pellets 
The sound of the pellet deflecting air is speed dependent, where 1 fps would be absolutely silent and 900 fps sounds a lot like a bullet moving through the air or a tiny flying plane. Just the nature of something beating up the air as it passes through and the harmonic frequency it creates by deflecting said air. Kudos!
The sound of the pellet deflecting air is speed dependent, where 1 fps would be absolutely silent and 900 fps sounds a lot like a bullet moving through the air or a tiny flying plane. Just the nature of something beating up the air as it passes through and the harmonic frequency it creates by deflecting said air. Kudos!
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I wonder if a slug would be quieter due to the shape and increases bc? My neighbor hears my 25 flying and hitting when I shoot, they also said my22 they just hear it hit. I’m shooting along their driveway slightly angled away from them into a large field. I might order some slugs and see if the higher bc cuts down on the #2 sound.
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Just went out for a quick test. Shooting a .30 Impact 700mm at 100 fpe. Measuring with a Meterk MK09 about 2 feet left and forward of the muzzle.
Ronin with Uni BF1 filter foam. 1 layer fills the area between the baffle and outer shell. = 109.8 db
Everything removed from the Ronin including the screen. = 110.9 db
With the suppressor empty there was a good size plume from the muzzle.
With the Uni foam a plume wasn't noticeable.
Ronin with Uni BF1 filter foam. 1 layer fills the area between the baffle and outer shell. = 109.8 db
Everything removed from the Ronin including the screen. = 110.9 db
With the suppressor empty there was a good size plume from the muzzle.
With the Uni foam a plume wasn't noticeable.
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Steve I'm not saying that the felt is the main sound mod but it does play a role in changing the frequency of the sound and does assist with giving more surface area for the air to scrub against. Materials like this cannot be used in a firearm LDC because they would burn up or come apart in the much higher pressures
Sound frequency plays a very important part of the both the shooters and spectator comfort level
Changing the frequency or tone of the sound can and does change how "loud" the shot sounds even if the volume of the device in question isn't changed.
And while air is not sound---air impacting the sides of a chamber does make sound.
Shoot an .45 Texan or .357 Bulldog with or without an LDC and you will get an ear full of that fine example. Those bottles (and yes the spring n valve) are loud I've actually shot the .45 Texan with one of most respected and well known air rifle LDC on the market at the the trigger I could not even tell the difference because of the sound of the bottle at my ear, those around me however said there was a huge difference in the sound.
If it was just about internal volume then you could stick your barrel inside a drill pipe pull the trigger and no sound..... it don't work.... In fact it rung like a bell (What was really bad is I still missed the critter
)
Yes absolutely you need enough volume of space to work with, I agree with you that the baffles and brakes are what does the Lions share of knocking the sound down within that volume. But considering car manufacturers use sound deadening materials as a cover over items like antanaas, wipers and other wind struck parts I can't see your logic on saying felt will not effect the sound of the LDC
An interesting statement made in the video is that the length of the LDC effects the sound more than the width of the device.
Sound frequency plays a very important part of the both the shooters and spectator comfort level
Changing the frequency or tone of the sound can and does change how "loud" the shot sounds even if the volume of the device in question isn't changed.
And while air is not sound---air impacting the sides of a chamber does make sound.
Shoot an .45 Texan or .357 Bulldog with or without an LDC and you will get an ear full of that fine example. Those bottles (and yes the spring n valve) are loud I've actually shot the .45 Texan with one of most respected and well known air rifle LDC on the market at the the trigger I could not even tell the difference because of the sound of the bottle at my ear, those around me however said there was a huge difference in the sound.
If it was just about internal volume then you could stick your barrel inside a drill pipe pull the trigger and no sound..... it don't work.... In fact it rung like a bell (What was really bad is I still missed the critter
) Yes absolutely you need enough volume of space to work with, I agree with you that the baffles and brakes are what does the Lions share of knocking the sound down within that volume. But considering car manufacturers use sound deadening materials as a cover over items like antanaas, wipers and other wind struck parts I can't see your logic on saying felt will not effect the sound of the LDC
An interesting statement made in the video is that the length of the LDC effects the sound more than the width of the device.
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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'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
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A balloon is only a few psi over Atmospheric and generates upwards of 120+ db when popped, due to the suddenness of air slightly above atmosphere coming in contact with atmospheric air.
So in a nutshell, it doesn't matter how much volume you have to obtain pressure equalization with atmospheric if you don't divert the air in an attempt to slowly release the gases over time opposed to all at once. So therefore...
Length/Distance air travels (includes diversion from baffle) > Baffle Efficiency > Volume
So in a nutshell, it doesn't matter how much volume you have to obtain pressure equalization with atmospheric if you don't divert the air in an attempt to slowly release the gases over time opposed to all at once. So therefore...
Length/Distance air travels (includes diversion from baffle) > Baffle Efficiency > Volume
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Another note, air speed is measured in RMS, so the RMS speed of sound @ atmopsheric is 1125 FPS.
That means there are air molecules traveling + and - that, by quite large margins. Without an LDC the air is all held back in speed by the pellet (most the time), so it will all exit at near identical speed (@ near pellet speed in the same direction but likely still 1125 fps chaotically (unidirectionally) + or - some) creating a fairly loud POP.
Toss on an LDC, (properly designed) and air becomes diverted, its still moving 1125 FPS or greater, but in many directions, from LDC wall to bore its a bunch of air molecules dancing like a bunch of drunken hippies bouncing around each other, and walls...the more times you can get the air to bounce, be it off a wall or themselves, the longer line they create at the exit. If that doesn't paint a clear picture for you to how to design the most effective ldc (largest acceptable OD + length + quality baffle with tight tolerance to bore = done) then IDK what else to say.
-Matt
That means there are air molecules traveling + and - that, by quite large margins. Without an LDC the air is all held back in speed by the pellet (most the time), so it will all exit at near identical speed (@ near pellet speed in the same direction but likely still 1125 fps chaotically (unidirectionally) + or - some) creating a fairly loud POP.
Toss on an LDC, (properly designed) and air becomes diverted, its still moving 1125 FPS or greater, but in many directions, from LDC wall to bore its a bunch of air molecules dancing like a bunch of drunken hippies bouncing around each other, and walls...the more times you can get the air to bounce, be it off a wall or themselves, the longer line they create at the exit. If that doesn't paint a clear picture for you to how to design the most effective ldc (largest acceptable OD + length + quality baffle with tight tolerance to bore = done) then IDK what else to say.
-Matt
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Wilie,
You are correct, packing material will change the sound signature, but not the sound volume. You can use packing material successfully in a PB...... I did, but it doesn't do poop for the sound volume. As stated, in my experience it's volume that counts. good baffling helps, but good reverse cone baffling will also pull down some pellet speed as well. I lose 40ft/sec with an 8" LDC on my Crown in .25. Please also note that FX and other manufacturers must believe the same, as their shrouds rely on only volume to do the job.
You are correct, packing material will change the sound signature, but not the sound volume. You can use packing material successfully in a PB...... I did, but it doesn't do poop for the sound volume. As stated, in my experience it's volume that counts. good baffling helps, but good reverse cone baffling will also pull down some pellet speed as well. I lose 40ft/sec with an 8" LDC on my Crown in .25. Please also note that FX and other manufacturers must believe the same, as their shrouds rely on only volume to do the job.
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Really interesting discussion. Really good points made by everyone but bottom line is I need to find out what material or materials I need to make my guns quiet, quieter than a mouse fart. Has anyone heard a mouse fart, my point exactly.
I have used felt (what donnyfl) uses, I used plumber's felt (thicker material & fire retardant), I used high density foam (memory foam), and uni foam (pre-filter for my dirt bike) and what I have found out is that it depends on what gun I used it on because there is a difference with different material for different guns shooting at different speeds. It's a lot of trial and error but bottom line is as long as my neighbors don't hear me, it's all good.
Aloha
I have used felt (what donnyfl) uses, I used plumber's felt (thicker material & fire retardant), I used high density foam (memory foam), and uni foam (pre-filter for my dirt bike) and what I have found out is that it depends on what gun I used it on because there is a difference with different material for different guns shooting at different speeds. It's a lot of trial and error but bottom line is as long as my neighbors don't hear me, it's all good.
Aloha
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