GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: JimD on March 08, 2022, 01:47:24 PM
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I was messing around with my P35 this morning and decided to measure it's sound output at 15 feet. I started this on my shooting bench on the side porch of my house but also did a few from the back porch. Results:
105 db - 4 baffle/curler combinations and shot a 2 inch swinging target 20 yards from the sound pressure meter
79.7 db - also 4 baffle/curler combination but shot into lake 30 yards from meter
82.8 db - 4 combos but shot into ground about 20 yards from meter
87.6 db - 4 combos shot pellet trap filled with shreaded rubber 25 yards from gun, 20 yards from meter
85.5 db - 4 combos shot into pellet trap at 33 yards from gun, 28 from meter
85.1 db - no projectile
77.4 db - 4 combos into lake (again)
86.3 db - 4 combos into lake from back porch. Lake is about 22 yards from gun, 17 yards from meter
78.6 db - 4 combos into lake from back porch but shot lake about 200 yards from gun.
76db - 3 combos from side porch into lake about 30 yards from meter
74.9db - 4 combos from side porch into lake about 30 yards from meter
81.9db - 4 combos from side porch into ground about 20 yards from meter
I set my meter to fast and max when I do these measurements. I'm trying to get the peak noise level.
I measured lower should levels with 4 baffle/curler combinations previously and seemed to get a little lower readings after the meter sat off for a few minutes while I was changing the shroud. So these measurements may not be repeatable, even by me. What I think they clearly show, however, is the noise of the pellet hitting the target can easily be louder than this gun. I've never tried to record the sound when I shoot a squirrel, it would be interesting to know how loud that is. It seems a little quieter than shooting the pellet trap. I left the gun with 3 baffle/curler combinations in it. It seems the gun will be quieter than the pellet impact so there is not much point trying to make it quieter.
Jim
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I've done a few sound measurements my self and it seems to measure the smack of the target than the gun meaning hitting the target is louder than the gun also dry firing is louder to from some of my testing
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Practically every PCP out there fires off a different amount of air when dry fired, as compared to firing a projectile - it is the nature of how the valves work with different levels of restriction in the barrel. Some let out more, and some let out less.
But even if the amount of air released is exactly the same in the two conditions, the one with the projectile will be quieter - this is because the projectile has acquired some of the energy from the air charge, and all that energy would be vented to the air (with much of it being sound energy) without the projectile in the barrel. If the shot without the pellet is quieter or similar to the shot with the projectile, then that is a sure sign that the valve is releasing less air without the projectile raising the pressure in the barrel.
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I will probably try a different sort of pellet trap to see if it is quieter. Aaron Cantrell recomends a box filled with old clothes. I have some jeans I need to get rid of so when I get a suitable size cardboard box I'll probably try it. I would not want to use cardboard long term, I'm thinking of welding something up out of metal, but it would work for a trial. I wonder how long it would hold up, however. I used a pellet trap by Crosman for awhile with my Prod and it had a fabric curtain over the metal back plate. That seemed to get shot to threads pretty quickly. But the only way I see to know for sure is to try it.
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I'm using a box made of 3/4 in ply wood I had left over from a project it's 18 inches long filled with rubber mulch works very well even stopping big bore 457 texan 350 gr at 850 fps
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Mark,
My current pellet trap is made of 3/4 plywood and has a sheet metal inside back that was the back of a plastic Crosman trap my kids gave me. It works but filled with mulch it is heavy and I used scrap interior plywood I had laying around so it is not able to stand up to rain. It is only a little bigger than my 8.5x11 targets so the edges of the plywood get impacted sometimes. If it was bigger or the target smaller this would not happen. I think a wood box works fine, I just did a quick and dirty on mine.
I'm thinking a slightly larger trap of 16 gauge steel, probably with a 1/8 angle iron frame in front, would take impacts better and, with paint, survive outside better. Not sure if I will fill it with mulch or clothes until the rain stops and I get a test done.
Jim
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I find that the rubber mulch itself is very quiet - the only problem is retaining it on the side with something that we can shoot through that is quiet. I too built a wooden box and placed a steel plate in the bottom as a safety. Sometimes I hear pellets hit the bottom having tunneled through after 8-10 high powered shots in the same spot, so it is good to have in place. The acoustic challenge is that I use cardboard to shoot through, and as that gets chewed up I add duct tape: the cardboard can be quite loud, and the duct tape is a bit quieter, but the best is the second or third shot through the same hole into the rubber mulch. Even with the target 20 yards away I can hear the difference in sound level coming back to me.
Anyone have any recommendations that are quieter? The quietest result is from shooting straight down into the mulch in the box, but that is not practical (although I imagine it could lead to some very accurate long range groups, if done from the top of a building ;) ).
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Have to replace it often, but basic egg crate foam as your front face, then the box of mulch. Gets shot up and leaks mulch pretty quickly...less quickly if you hang the new target a bit off center from the last one. Still have the noise of holing the paper target, but that’s about it.
Have often wondered at being picky about the shroud/LDC performance, then go out and shoot metal targets.
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I use a plastic tote filled with rags. I screw a piece of cardboard to it or just stick my targets on it to hold self adhesive targets. Cleaned it the other day and got 4 lbs of pellets out. It does make some noise shooting it because of pellet going through plastic of tote. Never had one go completely through both sides because loose rag fill stops them.
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If you're shooting from a porch, you're getting inaccurate readings. The sound reflections from the side of the house will mess you up. You really need to shoot a good distance (several yards) from any surface that will reflect sound.
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Doug,
That's why I shot some from my back porch too. It did not affect my readings significantly as you can see in the initial data. I agree it can make a difference but did not seem to this time. Side porch means walls are within 3 feet of the gun, back porch means walls are more than 6 feet away. I put the meter on a window sill on the side porch but had it out in the lawn on a chair from the back porch.
I got a break in the rain and tried a cardboard box with an old pair of jeans inside and got essentially the same reading as my normal pellet trap which has cardboard on the front, 88 and 87.5 db for the two shots I measured (at 25 yards from the gun, 22 yards from the meter).
I agree with the comment already made that it is the cardboard. Mulch is OK, at least you can't tell a difference with the noise of the cardboard. Duck taping it instead of replacing it when it gets shot up is interesting, that would let me by lazier too - another advantage. I'll probably try that when this one gets pretty shot up. Could just rip a hole and tape over it now, I guess. Eventually I think it would have to be replaced, I think. I could also put jean fabric over the mulch after removing the cardboard but I think the mulch would bulge out too much. Same thing will probably happen with taped up cardboard.
I haven't measured it yet but the smaller "know your limits" swinging targets are noticably quieter than the biggest one (2 inch). I was shooting a pellet I had pushed through the barrel when I had it off the gun and wasn't sure how accurate it would be. When I miss it hits a large oak tree and I've previously measured that at about the sound level of the pellet trap. I like the slap the pellet makes on the bigger target but it is pretty noisy.
I think this data kind of substantiates "back yard friendly" can't mean much less than about 85 db. Whatever we shoot it seems to lead to about that level of noise so what the gun makes is only important when it's greater than that. I wouldn't mind finding a way to reduce the noise of the trap but until I do, I think my guns are quiet enough.
Jim
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I had a guy on this forum put in a lot of effort designing and making custom LDCs. At some point both his and my "best designs" all plateaued out at the same (unacceptably loud) level, only slightly quieter than where he started from. The fact that all configurations measured about the same suggested to me that he was measuring how loud his trap was (or saturating his meter).
His trap was in his closed garage, 10 feet in front of the muzzle. I told him to place the trap at least 25 yards away and make it out of soft material. Due to his specific situation, he could not shoot outside, so he persisted with testing in his garage.
So, I suggested he shield his meter from noise emanating from the trap by draping a shipping blanket, roof to floor, with a hole cut in it to shoot through. I even offered to ship a blanket to him. But, that was too much trouble for him, and he simply concluded that all LDCs are equally loud.
My suggested draped screen (if sufficient distance to the trap or soft backstop are not available) is very simple. In case it is not obvious, the sketch below might help.
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https://www.youtube.com/watch?v=LqcsmlrV_mM&t=1348s (https://www.youtube.com/watch?v=LqcsmlrV_mM&t=1348s)
This is a real interesting video with Dr Russ and Donnyfl. They talk about how he uses sound testing equipment costing thousands of dollars vs a Amazon or Ebay low buck sound meter in his testing. Worth watching.
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he uses sound testing equipment costing thousands of dollars
Great video, though Donny basically says he uses his wife's ears. I would not assign a cost to that ;)
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I found that air density, wind, moisture and temp affect sound, cold air seems to make it louder, wind makes it quieter, moisture makes it quieter, seems quieter at high elevation than at sea level according to the sound meter I have, but it is a cheap one from amazon, but seems to work well.
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A word about cotton stuffed traps... You definitely want dense clothing like denim. Lighter Wright stuff like shirts offer very little energy absorption. Also be very mindful that the projectile may leave a permanent cavity, subsequent shots will go deeper and deeper unless they hit previous projectiles. This can get unnerving when shooting higher powered guns. Rubber mulch seems to work better at removing the energy and filling the cavity and I'll probably be switching back to this because the cotton leaves me feeling uneasy. Or at least I need a steel plate in the bottom of my bucket, which I should do anyway.
The cotton is much nicer when you throw the projectile back in the lead pot to recycle. You also can get an idea how they might perform as a hunting round because they definite deform more than rubber mulch.
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The problem with peak sound pressure levels is that this measure is blind to the nature of the sound. This suggests that Donny's wife's opinion may in fact matter more than a very accurate sound pressure meter reading. If the sound bothers her, it does not matter what the meter says. Ditto for if she is not bothered by it.
If you want to prevent your neighbor from being upset, consider this: A series of loud vehicles rushing by on a nearby road may not warrant special attention; but even a lower level noise that sounds like a gunshot, just sounds like a gunshot further away, than the same sound when it is two or four times as loud. The goal is to make the sound level so low, or modify it so it does not trigger "gunshot" in the mind of anyone who hears it.
By stretching the sound out and making the leading edge much less of a square wave, the peak will naturally come down (a bit like a soft recoil pad lowers the peak recoil force of a 12 Gauge). However I contend that a pop-echo, followed by a thud of projectile impact immediately or shortly after, is so characteristic that it grabs attention, despite being quieter than the background noise. This is a bit like us easily ignoring the "rush" of traffic, while finding a loud conversation outside our window very distracting.
I am not suggesting that sound meters are useless. They can help figure out which strategies help reduce sound levels. The better meters would be able to separate the frequencies at which the noise peaks.
I am suggesting that subjective impressions ultimately matter more than measured values - unless your only goal is to guard against hearing damage. Don't just ask, "is this LDC quieter, but is it less attention grabbing?". If "attention grabbing" is hard to fathom, substitute "annoying". If I have a headache, most sounds are annoying at levels much lower than I would otherwise be able to ignore. So, even that is not a constant. Stay below the annoyance threshold of your nearest neighbor when they have a hangover, and that will probably be good most of the time for most others within earshot. :)
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I use a cheap sound meter and the number usually confirm what I am hearing. I can tell the difference between the HW30 and the RWS 34. It is harder to distinguish between the RWS 34 and the HW 95. In my testing anything below 85 dB is considered backyard friendly to my ear during the daytime. Anything lower than than 80 dB I can shoot inside the house on the kitchen table and non of my family member is bothered by the sound.
I will try and keep all my testing in the exactly same normal condition and it is a good idea to test with another un-mod popular air gun for reference. When I look at the LDC number on the QB78s at 75 dB it is way better than then the HW30. My ear confirmed this. I don't listen to rock heavy metal music so I know my ear is very good :)
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I have had some success in keeping the impact sound level low by placing my cardboard target stand in front of bails of straw. I say bails, plural, as often I will penetrate a single bail. Now that the bails have sat out all winter and are soggy I don’t expect to see anymore penetrations. It’s still surprising just how loud the impact can be hitting only cardboard but it’s good enough.
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Projectile impact is often times louder than the gun going off.
The less dense the object the projectile comes in contact with, the less the impact noise. A looser pile of clothes would be much quieter than a box packed densely with the same cloth for example.
Rubber mulch is nice, but when placed inside a cardboard box and filled densely, its generally quite loud, even at lower power levels.
Its about how the energy in the projectile is released, the velocity is brought to a halt immediately, a lot of that energy is converted into SOUND...
You surely don't here a projectile slap the ground when you let gravity take hold if it compared to the slap of a projectile moving 900 feet per second...
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The carboard face on a cloth trap makes about same noise as the same carboard in front of a rubber mulch trap. While that carboard slap can be loud, if the carboard is not full of holes already, it acts as a noise shield for whatever is inside the trap. Use that principle to shied the trap noise and keep most of it from reaching your ears; and especially your meter. Use two layers of cardboard with an inch gap between them; for example.
Floppy carboard makes a different noise to well braced cardboard. My point is to make your trap quieter, rather than prescribe how that must be done.
To state the obvious; your sound meter does not know the difference between the muzzle blast and the projectile slapping the trap. The meter simply captures the peak sound pressure. Even when you can discern the delay between the two sounds. The meter cannot. The problem is when we pay a lot for a meter, we assume the measurements of muzzle blast are trustworthy (because that is what we intend to capture), even when our ears tell us that the trap is the loudest sound.
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Here are some number to entertain you. Some t-shirt material and stainless steel scrubber makes for excellent pellet stopper at a reasonable fpe. Sound meter is about 1.5' in front and 1' to the side.
Not scientific in any way.
Just some cloth backing to the stainless steel scrubber - 80.8. 82.3
1" foam in front of scrubber - 87.0
1 layer duck tape - 100.3
standard 20lb paper - 93.0
cardboard Amazon box - 98.0
Costco paper towel folded 8 layers - 92.0
Lemon leave - 93.0
I am shooting the Nova Liberty .22 CPHP 14.3 at low power around 750 fps with an LDC and in my typical setup the meter would be 16' in between the quiet pellet trap and the muzzle and it register 78 dB.
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I've been working on other things and neglecting my shooting. But I plan to try substituting a layer of denim from an old pair of jeans for the cardboard layer on my pellet trap. I want to see how much that lets the shreaded rubber bulge out and how much it reduces noise. Your data suggests it will help. If it doesn't bulge too much I might even use it. Nothing magic about cardboard but it works and is cheap. But pellets hitting it make a fair bit of noise.
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Thanks for sharing your measurements, Peter
As usual, your test is sensible, and your data useful and well documented.
It seems that cardboard and paper are even louder than I imagined, even when placed in front of a "quiet" trap. Intuitively, I knew that the cardboard was forming a drum-skin of sorts. Even that is rather loud, if it is close to the meter. Thus the meter should be further away from the trap when one wants to measure muzzle blast - as you normally do. Every instance where you double the distance from the meter, the sound pressure should drop by a factor of four - assuming no hard surfaces nearby to reflect sound, and confuse the measurement.
As you normally have the meter midway between muzzle and trap, there is still the possibility that a loud trap may register louder than muzzle when shooting a quiet airgun. I am not suggesting your historical data is flawed, but it occurs to me that if you could move the trap further away while keeping your standard muzzle to meter distance, confidence in your data would improve further. Yes, I know that your yard is limited in size, so this comment may have to remain theoretical.
One way to remove my urge to move your trap further away would be for you to measure the muzzle blast the same way you measure your trap sound - as you described above. We assume that the muzzle is still much louder than the trap at 1.5 foot in front of the muzzle and 1 foot to the side. If you confirm that, then there is no doubt that by placing the meter in the middle, as is your method, you have never captured the trap as the peak sound over the muzzle.
It is easy for me to write a busy test plan for someone else to carry out, but if you should shoot the same Nova Liberty as you just did and measure that from 1.5 x 1 foot from the front of muzzle, perhaps you could do the same for the benchmark of quiet, the HW30 also. That would help calibrate the human ear.
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My swinging, energy absorbing quiet pellet trap. This time with the sound meter 1.5' in front and 1' to the side of the muzzle.
About 30 feet from muzzle to quiet pellet trap.
HW 30 .177, CPHP 7.9
95.6, 94.7, 94.8, average 95.0 dB
Nova Liberty .22 with LDC, CPHP 14.3
Low setting - 94.6, 94.2
High setting - 99.1, 98.6
* Nova Liberty .22 with LDC, shoot CPHP 14.3 at low power around 750 fps and in my typical setup the meter would be 16' in between the quiet pellet trap and the muzzle and it register 78 dB
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I initially noticed the "target is louder than the gun" effect working on a home made moderator. I was shooting into a large oak tree 25 yards away from the muzzle with the meter no more than 5 yards away. Nothing I did made the gun quieter and then I thought about shooting into the ground or lake further away.
My interest in the trap sound level is for avoiding attracting interest with my backyard shooting. I feel like the guns are quiet enough at 85 db or so or less. I need the trap to be quieter for it to make any difference my favorite gun is under 80 db.
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Peter,
I think your sound measurements and methods for airguns are of the most sensible and useful posted on this forum. You have gone on to provide data in response to the question about how loud your trap is.
I wanted to satisfy myself that placing your sound meter at 15 feet from both the trap and muzzle is not so close to the trap, that the trap might still be the loudest sound captured from a moderated airgun. So, I did a quick "regression study". It is based on your dB data for the 1.5 x 1 foot distance between your trap and meter.
Then, following the inverse square law for sound radiation, I attempted to calculate at what distance your 95 and 100 db trap sounds would drop to, or just below the values for muzzle blast you captured at 15 feet. In other words, I am asking if you are far enough from the trap so that the sound you capture is definitely muzzle blast and not trap noise.
Because you measured your trap noise from 1.5 feet in front of the trap, and 1 foot to the side (to avoiding shooting your meter), the effective distance between meter and trap adds complexity and uncertainty to my calculation. So, I used three distance as the baseline for your dB measurement: 2.5, 1.5 and 1 foot respectively:
The first table in the attachment below starts at 2.5 feet (30") from the trap because that is the diagonal distance from the center of the trap. The second table, 1.5 feet. Now, perhaps the sound radiates from the nearest outside surface of the trap, rather than its center - suggesting the effective distance is closer to 1 foot.
Results:
If the effective distance to the trap was 2.5 feet, then the same trap sounds measured at 15 feet would be about 79 and 84 dB for the HW30 and Nova Liberty respectively.
If the effective distance to the trap was 1.5 feet, then the same trap sounds measured at 15 feet would be about 75 and 80 dB for the HW30 and Nova Liberty respectively.
If the effective distance to the trap was 1 foot, then the same trap sounds measured at 15 feet would be about 71 and 76 dB for the HW30 and Nova Liberty respectively.
Conclusion:
1. As the lowest experimental LDCs on your Liberty has produced peak sound values of 77 dB at 15 feet, the effective distance between your latest trap sounds and meter was closer to 1 foot. And, you are right on the threshold where the trap and muzzle are equally loud to the meter, when that is placed equidistant between muzzle and trap at 15 feet. So, you may not be able to develop an LDC quieter than 77 db at 15 feet for your Liberty, because that is what the trap is producing at 15 feet with that airgun, pellet and tune.
2. Whereas, the 86 dB value captured at 15 feet from the bare muzzle of your HW30 means that the trap noise can be ignored at 15 feet. This assumes that trap noise is constant, which I doubt. It depends on the state of the trap and how many holes there are in the carboard around the location of any given pellet impact.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=197179.0;attach=394864;image)
Suggestion:
Don't change anything that would render your previous sound data obsolete. Keep the 15 foot muzzle to meter distance you have been using, with the one foot side offset. As the placement of your trap cannot be easily extended to much further, leave it where it is. As your trap is already "soft", trying to improve on that is likely to be difficult and time consuming.
A much simple confidence booster in keeping trap noise off your meter, is to shield the meter from trap noise by means of a carboard sheet attached to dowels, pushed into the ground. Place the cardboard so that the point of impact on the trap does not have line of sight "visibility" to the meter. In fact, none of the trap box should have line of sight to the meter. See simple sketch of that from a top view, below.
I suggest that the cardboard be placed midway between the meter and the trap, so that sound does not reflect off the cardboard front face and add to the sound it "sees" from the muzzle. If the carboard were a shipping blanket then there would be no reflected sound to be concerned about. If plywood, then that might reflect sound more strongly than cardboard...
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=197179.0;attach=394866;image)
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That's some great analysis there . . . .
That leads to an idea that would be easy to try, and I will do it next time I do any sound testing, but others can as well:
Given that the trap has a flat surface that faces the shooter (as we all seem to do it), the sound most likely radiates out from the trap with a heavy directional bias - the peak sound pressure level is almost certainly radiated out perpendicular to the cardboard face of the trap. With that in mind, the idea is that if we rotate the trap about 45 degrees to one side, we should be able to reduce the sound pressure level that is radiated back down the line to the shooter and the sound meter. Then if we add the cardboard sound blocker in front of the target trap like in Subscriber's illustration, still perpendicular to the direction of the shot, we should really be cutting down the sound level heading back to the sound meter.
Of course all this is just about getting a better reading on the sound level of the gun - pellet impact sounds are still a very real world factor. If we do that on our shooting ranges, we are simply redirecting the sound to a different place. But if that new place is facing less sensitive neighbors, or neighbors that are much farther away from the trap, then it is a good thing out there too.
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Good point, Alan; about using directionality to help reduce the trap noise "pointing" towards the meter.
While such shenanigans seem not "real world", it will help prevent someone from giving up in disgust when their expensive LDC does not produce the expected low reading that they are convinced they can hear. Ditto for evaluating different LDC that all seems to produce about the same benefit, based on measurements. Whether these LDCs are bought, or under development; professional or commercial (vegetable, animal or mineral; from G+S :) ).
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I had not seen these comments about trapping the sound from the trap until just now but I did some more measurements this morning. My way of avoiding the impact masking the gun noise is just to shoot into a lake behind my trap. I try to make the impact close to 200 yards away. Still it seems like the noise sometimes comes back. Maybe I need a barrier in front of the meter.
I shot each of my three guns at least 3 times. The averages were:
AV Avenger, 25 caliber, with DonnyFL Tanto : 84.93 db
Prod (22 caliber tuned to 16-17 fpe) : 85.5 db
Prod with Buck Rail silencer : 76 db - note this is totally different from what I measured last time but my trap was making me think the silencer does not do much - it definitely does. Roughly a 10 db reduction is big and this moderator is not expensive nor does it require an adapter.
P35 (25 caliber tuned to about 32 fpe) : 79.7 db
P35 into trap with cardboard face : 88.3 db
P35 into trap with cloth (jeans) face : 88.4 db
So I learned the Buck Rail silencer works and that using a cloth face instead of cardboard doesn't make a difference. All my guns are quieter than the noise of their projectile hitting the trap. My main interest is in keeping the peace with my neighbors. I don't see any obvious way to quiet the trap but maybe I'll think of something or one of you will have an idea. My neighbors are not complaining so I guess I'll just keep shooting. I dug over 10 lbs of pellets out of my trap today.
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Thanks for the info, Jim
Where was the meter placed for these measurements?
I don't think impact noise from 200 yards away is going to bother your meter...
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I put the meter about 5 yards in front of the gun and a little to the side (on a window ledge). It was thus about 20 yards from the trap for the measurements - so the trap impact is significantly louder than the guns. 15 yards further from the meter and still noiser.
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I was testing some 3d printed add-ons the other day and was shooting over my meter and had a baffle strike and... shot my meter :P
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The new and improved quiet pellet trap for testing LDC. The main pellet trap is enclosed inside a box and surround by foams. There is a 7" space in front of the stainless scrubber surround by foam. Some interesting number with the different backing behind the sound meter.
Liberty .22 with LDC, CPHP 14.3, start 2900 PSI down to ~2750 PSI, power setting Low-750 fps. Sunday 3/20/22 9 AM quiet outside.
This is the order of test.
Brick backing - 81.8, 82.2, 80.8
Brick with foam - 80.5, 79.3, 80.1
No backing - 79.6, 79.2, 78.5 (surprised it is lower)
Wood 3/4" MDF - 80.5, 80.2, 80.4
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Interesting, Peter
So, sound from the muzzle that would have gone into "space" is reflected off the meter shield, onto the meter, making the reading higher?
A few days ago when I suggested the meter shield, the possibility of reflected sound occurred to me, but you have vindicated my prediction. That is why I suggested the screen be midway between the meter and the trap. Even so, the wavy foam should have been OK near the meter; but it was not.
Another forum member suggested the shield be angled so that sound hitting it would be reflected away from the meter. That should work for both muzzle and trap noise; although wavy foam is omnidirectional (and up close; a problem).
Your deep trap with the small hole should help reduce the total sound leaving the trap. Although what is able to leave would be rather directional.
Thank you for doing this work, and replacing speculation with actual data. I think a lot of people who would be happy with a given LDC, have been disappointed with their meter reading, because they were unaware of how sound behaves. But, since they trust the meter more than their ears, they end up less than happy with their LDC. You are providing information to help calibrate their measurements; and expectations.
As an aside, I suspect that sound measurement and perception work a little like earthquake measurement: The Richter scale is not just about peak amplitude. Duration and total damage potential also factor into it. We think that the sound meter simply reports the peak sound value, and that is it. I get the impression that sound exposure is cumulative, and that lots of sound, from more than one side, and / or for a longer duration can sound (and perhaps measure) louder. Perhaps two sound wave from the same source can meet to create a higher peak. The point is that measuring sound is not quite as simple as it seems it should be.
If my suggestion sound like nonsense, consider the muzzle blast of a .223 Remington rifle with a 16" barrel. Compare that with a 12 gauge bird shot load from a 28" barrel. Both are very loud close up. Yet the muzzle pressure of the smaller caliber is over half the peak chamber pressure of the larger caliber. The larger caliber noise "makes up for this" by projecting the sound from a much larger area "speaker" (muzzle). Now, we won't confuse the two calibers, but to state that one is much louder than the other would be a misstatement. One has a sharper sound, while the other has a "larger" sound.
What has the above got to do with airgun LDC sound measurement? Sound reflected off hard surfaces makes even lowly airgun report seem "larger" and more significant. To the ear, and apparently, to a meter. Not to mention that any sound that has a significant echo screams "gunshot" to anyone within earshot.
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Peter, Interesting results. I think anything firm that you put near the meter will just reflect the muzzle noise back to the meter.
It would be interesting to compare your new trap to the basic cardboard target hanging below it. Maybe put the meter 5 ft off to the right (if you can), even with the trap, and compare the two.
What is the close-out panel on the trap made of?
Here are a couple of links on soundproofing. I'm thinking in the direction of the box in a box approach with sand as the absorbing material. Now to see what scrap materials I have on hand.
Great work.
https://www.acoustiblok.co.uk/soundproofing-materials/ (https://www.acoustiblok.co.uk/soundproofing-materials/)
https://soundproofcentral.com/does-sand-absorb-sound/ (https://soundproofcentral.com/does-sand-absorb-sound/)
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The plan-view image below is my perception of how loud airgun muzzle blast sounds, with my ear placed relative to the (virtual) muzzle. To keep one aspect constant; the inner circle has a radius of one meter from the muzzle.
The muzzle is pointing up in the image. Red arrows indicate ISO standard hearing safe measurement meter placement.
Doubling of the line length in my image equals a doubling of perceived loudness. Something that would measure about 10 dB louder on a meter.
The outer profile in my image is demarcated by the line lengths that represent my perception of how loud the relative sound is, if I were to place my ear on the one meter radius, about someone firing an airgun. No, I have not placed my head in front of the muzzle, so there is a lot of speculation represented here.
The point is that muzzle blast is very directional; such that the apparent sound level increases sharply as your ear moves forward of perpendicular with the muzzle (if a muzzle brake is used on a firearm, the loudness to the side and rear do not drop off as sharply, compared to a bare muzzle).
Conversely, the further back from perpendicular with the muzzle at one meter the more rapidly apparent sound level drops off. Standing directly behind the shooter even at one meter from the muzzle is usually not loud at all with typical airguns. In that case, their body acts as a shield, in addition to the directionality aspect I am trying to "quantify".
Now, if we are shooting at our trap near a wall towards a neighbor's property, they are in fact subject to near maximum aspect of muzzle blast - less that screened off by the wall (a significant reduction). I mention this, because Peter's placement of his meter at one foot off bore axis is in fact trying (and succeeding) at capturing this. If we place the meter at 45 degrees off from the muzzle so it is just as far to the side as it is from the muzzle, the reading will be much lower than with the meter nearly in front of the muzzle. Unless that is where the ears are, that must not be offended such meter placement is a nice way of fooling ourselves that our airguns are less disturbing than they may actually be.
That said, I think that capturing reading all the way around the muzzle at some distance greater than the one meter I show in my image would be extremely useful data to have mapped out. I predict that house and property walls nearby will cause the shape of such a sound map to be distorted from the smooth semi-circular curve I suggest it is at one meter from the muzzle. Even having that degree of sound reflection objectively quantified would be very valuable. So, I am not going to "specify" the radius, but would suggest 15 feet so that it attaches neatly to Peter's existing data.
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There is a little reflected sound data in my initial data set. My normal shooting position is from the side porch of my house putting the house about 3 feet to the right of the gun for the first 8 yards of so if the pellet's flight. So I should see amplification. But I did not seem to. My other shooting position was from my back porch with no side wall closer than 5 or 6 yards away although the wall of the house was behind me. Maybe that is why the readings were about the same. If so, a wall to the side of the gun or a wall behind the gun has about the same effect on the readings I'm getting. When I measured from my back porch the meter was out in the yard with nothing around it about 15 feet in front of the gun. When I shoot from my side porch the meter is on a window sill 15 feet in front of the gun. I expected to see lower readings from the back porch but did not.
With respect to using sand to absorb the impact, I don't think it will make a difference if the target is still supported by cardboard. I tried cloth instead of rubber mulch and the readings were the same. I also tried cloth over the rubber mulch to support the target and got about the same readings. The cloth also did not support the rubber mulch well. I wonder if cardboard will support sand. If you had a big pile of sand so you did not have to support it and then suspended just a paper target in front of it, that would be interesting. I have not found it to be much quieter shooting into the yard, however.
So far my only successful way to keep the impact noise out of the measurement is to move the impact very far from the meter - like a couple hundred yards. Even if I shoot into water 30 yards or so from the meter it makes significant noise. I realize not everybody had the ability to safely shoot a couple hundred yards, however.
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Stan,
Here is the number for the same Amazon cardboard box with the new pellet trap box. It is definitely much better at containing the noise going out of the box. I keep the same distance so the number can be compared. I did put the front cover back on.
Swinging pellet trap - 98.0
New pellet trap - 88.7, 87.1
Here are some sound and dB number for some common items around the house.
https://youtu.be/Mi0ZbXzXKM8
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The sand suggestion was not to shoot into it as a backstop but to use it for deadening the walls of a sound trap in front of the target similar to what Peter is doing.
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Sorry, I misunderstood how you would use the sand.
I am interested in Peter's deep pellet trap idea with respect to sound off to the side. That is where my neighbors are. I might even try just taping cardboard around my trap or something and then measuring off to the sides. It would be nice to have lower noise from the trap in the path of the pellet but even if that were not achieved, less off to the sides would be helpful with respect to negative feedback from the neighborhood.
I tried putting a small, about 12x12 inch, piece of cardboard close behind my meter. It was angled and intended to reduce the noise from the trap. Didn't seem to do anything. May have been too small.
I volunteer at my church on Mondays and one of my projects there gave me another material to test. I was replacing some damaged ceiling tiles in the offices. I saved a scrap that cannot be used at church due to the damage. I don't have enough to try it on the sides of the trap but I'm planning to tape it over the cardboard backer and then taping the target to it. It may do nothing but might help to dampen the impact noise. The back side seems softer so maybe I'll put that facing the target. I have not purchased ceiling tiles but I think they are relatively inexpensive and might be another idea for the surround of a deep trap. They are supposed to reduce noise between floors of a building.
If I don't blast too many holes in it first I might also try it as a baffle behind my meter.
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Jim, I hope those ceiling tiles are not old enough to be from the asbestos acoustic tile days.
You guys inspired me to do some testing today. I tried three different trap configurations.
The first is my standard cardboard trap, filled with clothes, steel plate in the back. The front face is standard issue cereal box cardboard. (first image)
The second is a foam face trap with two layers of foam and clothes behind that (second image)
The third image is the muffler I put together yesterday to check out the sand idea I posted. It consists of two containers separated mostly by sand and some foam, The wood blocks are only at the top for centering. The core wire tube is wrapped in a shop towel (at least I thought she said it could be a shop towel) and some clothes. The third image shows it with the carboard trap clamped to the rear. The hole is about 3".
The shooting distance is 25ft and the soundmeter is 5ft from the target plane. I aimed the meter at the trap since that was what was of interest. Next to the meter you can see a small microphone (iMM-6) processed by a 96KHz USB sound ADC and captured by Audacity S/W (free) on a laptop. This second instrument collected a lot of data but I won't distract this thread.
I used a stock P-17 as my loud gun and a shrouded CP1 as the quiet gun. I was shooting Daisy wadcutters since I guessed those would have the loudest impacts.
The results from the meter (set on Fast, A, Max)
The foam was about 10db lower than the reference cardboard trap. If you put a sheet of printer paper in front of the foam the readings went back up almost to the cardboard levels
The muffler suppressed the cardboard trap by about 12 db for the louder P17 and more so for the CP1. I think the P-17 muzzle noise was limiting the reduction.
These numbers should be taken with a grain of salt. I'm still trying to figure out what the meter readings contain compared to the microphone results.
The foam is a viable trap if you can get it cheap/free. You could stencil/paint the bulls on the surface and the wadcutter pellets cut clean holes.
The muffler is a way to attenuate the noise from the trap front surface. You probably don't need all that I put into it (I had fun building it) in actual use, you could add a couple of LEDs to illuminate the recessed bull.
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Those traps look proper emanation diodes, Stan.
Makes me think of this one:
(https://bbts1.azureedge.net/images/p/full/2020/11/0b16818f-5ac5-4db0-82b3-4eb70162d324.jpg)
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How loud is shooting directly at a brick surface? Somehow I don't think the "tink" is all that loud, providing the pellet frag does not go somewhere it can cause harm. And, that no one minds the marks on the brick. So, sacrificial bricks would be required.
Perhaps a bad idea for lots of shots in the same location, as a pockmark could eventually act to direct pellet frag back towards the shooter or other fragile or living things.
It is over 40 years since I shot an airgun, using a face-brick wall as the ultimate backstop. From memory; it was not loud at all. Don't have any bricks around here, and cinderblock is not as robust, although it would probably be as quiet.
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Stan's measurement of paper over foam at around the level of cardboard convinced me shooting through acoustic tile will not be quieter. I don't think these tiles have asbestos but I haven't tested them. I tried putting a rectangular tube made of cardboard around my meter with the opening pointed to the gun away from the target. Didn't seem to help.
I did some measurements at 15 feet away from the trap to better match up with Peter's. The meter was on a drywall bucket in the yard for these measurements. Both in line with the gun and at right angles to that line, I measured about 88 db. That is just about the same as what I measure from my most common placement of the meter, 15 feet in front of the gun but 20 yards from the target. But in those measurements the meter is also up against a window of my house. So reflections off the house may negate the greater distance from the trap. At about 45 degrees to the trap (still 15 feet away) I measured 82, 75.7, and 73.5 db. Significantly lower. I didn't expect that.
I haven't shot any bricks yet but I have a bunch and probably will.
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Thread title is appropriate indeed.
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I went and did a little yard work and then decided to shoot a brick. I had not shot my P35 today so I used it. It likes 20.06 grain H&N FTTs and I have tuned it to shoot them at 850 fps or a little more. Not a very powerful 25 but it works great on squirrels. I placed three brick stacked on each other at 25 yards from my shooting bench. I put the sound meter 5 yards from my bench in it's normal spot up against my house. I measured 87.6 db, 86.3 db, and 86.4 db. That is 2-3 db less than I measured for pellets hitting the cardboard front of my pellet trap.
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Thanks Jim,
I suspect that the sound off a brick has a very high pitch to it. Something that dies off very rapidly with distance?
This, while a carboard box sounds like a drum.
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I googled for examples of things that are 85 db. It came back with heavy traffic when you are in your car, a food blender, a cinema, and a noisy restaurant. These examples go on for seconds to hours, not a fraction of a second like our pellet impacts. It is about where it is suggested hearing loss starts. But for our very brief exposure, I doubt it affects us. Now my swinging target at over 100db.....
The brick might be higher pitched, I'm not sure. It sounded different from the cardboard.
The distinctive cardboard strike is sometimes useful. I've recently managed to shoot a few small groups at 25 yards, 1/8 inch or so. It started to make me wonder if I missed or something when I couldn't see another hole through the scope. But I remembered hearing the pellet strike the cardboard.
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For your hanging target, I wonder if you were to glue a couple of layers of 3/4" plywood to the back side to suppress the ring (and maybe truckbed liner on the front). In the past, I've melted used pellets to fill a pellet tin (to use as a weight in the shop) but it might make a quiet target with pellets hitting the lead face. For some indoor testing I've used a short piece of pipe filled with LDPE bags and an end cap (idea borrowed from Lloyd Sykes). That would make a good hanging target. The bags are very efficient at stopping pellets.
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The next thing I want to do with the swinging target is to measure the sound of each of the 8 targets. I only measured the 2 inch which was over 100 db. But that is not a very challenging target so I could easily skip it. My impression is the others are not as noisy but I don't trust my impressions of sound level.
I appreciate the ideas of how to quiet it down. I just dug over 10 lbs of pellets out of my old trap and have a little melting furnace so I could cover the face of that plate with lead and see if it helps. It probably would. The sound is like a slap. Kind of a neat sound but loud. All my guns will move all these plates but none of them spin the 2 inch around. So lead on it would make the movement even less. I wonder how long a lead face would last. I make the swingers out of 1/4 inch rod and washers. I have to double or triple up the washers so they are thick enough to withstand the impact. I weld the hole closed on the washer. But i could leave the hole at least partially open to help the lead stay on. But it seems like the lead would still get beat up. But it could be melted down and reused.
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I think the lead would need to be contained in something (pipe cap?), otherwise it might just crack apart.
I looked at some of the microphone/Audacity data for the shots I took the other day. The basic geometry of the test is in the first image with some of the key distances. For each path I show the time estimate based on the speed of sound for most and on the pellet muzzle velocity for the pistol to target distance. I also calculate the difference from the arrival of the muzzle noise. The second image shows the Audacity plots for two of the shots, one facing the target and one facing the pistol. both are for the quiet foam target. For both shots, the first blip on the trace is the muzzle noise and it looks like the target blips show up at about the predicted time. The target facing trace has an extra blip which I'm guessing is the reflection off of the wall (the mic is facing the wall). By changing around the test geometry you can move these around. I don't know what the sampling time of the soundmeter is and this is hard to find online. I show .125 sec for reference since that is the time constant for the fast setting.
My takeaway is that for my configuration, everything takes place in around .060 sec and I imagine all three events (muzzle, wall bounce, and target) are all in the soundmeter measurement.
I think Jim's shoot into the lake 200 yards away is the way to go. Otherwise pointing the mike at what you want to emphasize may help.
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That is an outstanding analysis, and it is great to see the trace. It looks like if the trap were about 75 feet from the target, the sound from the trap would not make it into the trace for the pistol facing mic. Of course a faster pellet from a more powerful gun would change the timing, and it most likely would require even greater distances. Great work!
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I have another idea I may set up later today. It builds on Stan's successful reduction with a sort of muffler in front of the trap. I will shortly go pick up an order at Home Depot and do some other errands. While I am out I will buy a couple 16x16 concrete pavers. These will form the top and bottom of a little enclosure. The walls and back and maybe a front will be stacked brick. I plan to just literally stack things up on an old workmate in the yard at 25 yards from my bench. Without a front I don't expect it to change the sound near my bench where I put the meter. But I'm interested in what it does off the sides. Like at 90 and 45 degrees off to the side of a line between my bench and the target. I think it may give me a significant reduction. If so, I might build little structures like this at 25 and at 33 yards from my bench (33 yards is my back fence location). By stacking bricks in front to create a smaller opening, I may also be able to reduce noise coming back at me, for moderator testing. But I'm thinking of just ignoring that most of the time for convenience. I have several hundred recycled bricks waiting on me to find something useful to do with them. So my cost would just be the pavers and some mortar (and time). I might even be able to rig up a way to put swinging targets in there although I might need more depth.
It may not do much, of course. But it won't cost much to find out.
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Nice idea.
If you close off the front, one of these selfie lights mounted inside the front, running off of a USB powerbank could be a cheap way to light up the target. https://www.amazon.com/s?k=B091T6Z9ZY (https://www.amazon.com/s?k=B091T6Z9ZY) or even some solar powered garden lights where you separate the panel, leave it on the roof to charge and just cover it so the interior lights come on when it is time to shoot.
The other thought is to use 2 8X16 pavers for the top and leave enough of a gap to slide a target frame down. Kind of like an old slide viewer. That would make target changes easy.
Post some pictures.
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Another piece of information is how the ear responds to short sounds. I found the curve below that shows how much louder a short sound needs to be to sound as loud as a longer (or continuous) sound. Below .2 sec (200ms) the hearing starts to drop off and you need more db to sound the same. In the traces above, most of the combined noise takes place in less than .060s (60ms) so our hearing already needs an extra 3 db or so. The actual muzzle blast happens within 10-20 ms so that is an extra 10 db. Who knows how the soundmeter response relates to that.
Having someone off to the side listening is probably the best evaluation
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It stopped raining long enough I got some measurements. Unfortunately I don't see much benefit. I started measuring with my meter in my normal spot up against the house and 5 yards in front of the gun. I measured the same sound level there as 5 yards in front of the trap previously. My readings were 86.7, 87.5, 87.9. That is slightly lower than the 88+ I last measured but only slightly. I then measured at 90 degrees to the line of fire and 5 yards from the trap. I got 85.9, 86.1, and 86.9 db. I measured the same as in line previously so this is very slightly better but only slightly. Last I measured at 45 degrees to the line of fire and 5 yards from the trap. I got 85.9, 86.1, and 86.9 db. I got a couple lower readings before at 45 degrees but they look odd, these make more sense to me.
Then I tried blocking off all but the top row of bricks with more bricks in the front. So I had a 1 brick tall slit to shoot through. I got readings of 78.6, 83.2, 81.2, 77.1, and 82 db. I shot two extra times because I noticed a brick moved from the impacts and I wondered if that had an effect. I moved it back and got 77.1. But then I shot again and got 82 and the brick had not moved. These are a little better but shooting through a slit is not practical for a normal practice. These aren't low enough for moderator testing.
The fact that these are not sealed, not laid in mortar, is undoubtedly raising the sound due to leakage. But I doubt it is making an impact more than a few db. If I had gotten results like the slit ones for an open front, I would probably have made traps this way. But for a couple db it doesn't seem worth the effort. A longer tunnel would also undoubtedly help but it would also make seeing the target more difficult. I could put a light in there but I don't really want a really big trap in the back yard.
I left it set up. Maybe I'll think of something else. I haven't shot that accoustic tile yet. Probably have to at least do that.
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Well, you could stack the closeout bricks on edge and shoot through the holes. ;)
I think the bare brick interior just reflects the sound. Maybe try lining the interior with a few layers of your acoustic ceiling tiles. Depending on how pliable or crushable the acoustic tile is, you may be able to put it between the layers as a gasket of sorts.
I'm not sure if you have enough room on the 16X16 but I wonder if changing the stack to a chevron type would help break up the flat surface. Or cutting the bricks through the holes to create a shaped edge.
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Thanks for your effort, Jim
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Stan,
You seem to have specialized acoustic knowledge. Do you think it possible to make a trap that uses active noise cancellation? Or is that only something that can be applied at the ears of a specific person?
If noise cancellation works by overlaying the inverse of a sound wave in the right phase, then accidentally overlaying waves in the wrong way can make them louder, depending on just where you (or the meter) are positioned. AKA constructive and destructive superpositioning.
It would seem obvious that we should avoid constructive superpositioning, but how do we achieve that? More importantly, how to ensure that this applies to the neighbor across the wall?
If we stand in just the wrong place, might muzzle blast (or reflected report) superimposed on "trap slap" create an unusually high peak that we can hear (or measure) further away?
https://www.youtube.com/watch?v=gDpvJ2jLA5I (https://www.youtube.com/watch?v=gDpvJ2jLA5I)
https://courses.lumenlearning.com/boundless-physics/chapter/interactions-with-sound-waves/ (https://courses.lumenlearning.com/boundless-physics/chapter/interactions-with-sound-waves/)
https://www.acs.psu.edu/drussell/demos/superposition/superposition.html (https://www.acs.psu.edu/drussell/demos/superposition/superposition.html)
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No specialized knowledge, just a curiosity about the subject.
My understanding of noise cancellation (e.g. headphones) is that they need tonal content and some duration to be effective. They suppress the steady hum of the airplane engine but the screaming toddler, not so much. Unfortunately airgun shots are short and have a lot of frequency content.
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If there is no direct solution, look for an indirect solution:
If we can't reduce broad spectrum square wave muzzle report and trap-slap by means of noise cancellation, then perhaps we can drown it out with a noise everyone knows, but does not mind. Perhaps an endangered bird's call; or a dog's squeaky-toy. So, not cancelation as much as dazzle camouflage.
Even if the idea is stupid, it may offer some amusement value. In that instant where the mind relaxes, an idea may present itself:
https://www.youtube.com/watch?v=ynC3jDyCQh0 (https://www.youtube.com/watch?v=ynC3jDyCQh0)
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Well, for the last week there has been a woodpecker pounding on the neighbor's tree. I think he could mask one of the full auto BB guns.
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One reason I would like my trap to be a bit quieter is the Gypsy factor. When I shoot one of my air rifles a neighbors dog, Gypsy, starts barking. I know Gypsy's barking annoys another neighbor sometimes. She is a nice dog but her owners put her on their screened porch and she gets bored and barks if anything interesting happens. Gypsy is three houses away from me but it is pretty quiet where I live. I see background noise at 40-50 db on my meter.
I think creating noise that is not annoying that could mask the gun and impact has merit. We will all have our ACs on soon here and I know from previous measurements my compressor is around 70 db up close. Once the one at her house is running Gypsy may not hear me. I could turn on some music but I am pretty sure that could be more annoying instead of less. If I could time the birds making noise correctly it might work. Need to think about what noise to use. I get squirrels chattering at me sometimes too - but from a distance, they know better than to do that in my yard. A natural noise like this, played for a few seconds around the time of the shot, might work. I wonder if any noise at 85-90 db would be consistently inoffensive, however. I guess I could record my lawn mower and pretend I am mowing the lawn. I would need to measure but I think it is this loud.
Jim
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Are there similar noises she is familiar (bored) with? Maybe construction noise (circular saw, hammers, etc.)? Maybe spin up a saw a few times before shooting so she thinks it is that.
Sometimes falling water is used to mask noise. Waterhose falling into a tub from a few feet up maybe a quick test. If it works, medium sized fountain pumps can be had for around $25. Or you could use a recording (crashing waves on the lake?).
I would not give up on your trap improvements yet either.
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Well I confirmed a couple of Stan's tests today and learned two baffle/hair curler combinations in a long short configuration work better in my P35. I started with the latter and was pleased to find using one full curler and one half curler made the gun almost 7db less than 3 half curler/baffle combinations when the 3 were tightly packed. Packing was about 3 db of that so maybe 4 db for the short/long combination (worked better with the half curler closer to the barrel). But I digress.
I put the acoustic tile in the back and on one side (all I had tile for) and got 81.28 db. Then I remembered I had some scraps of seat cushion foam in the attic and cut a piece to go on the back of the trap. I cut down the acoustic tile from the back and moved it to the front. I got an average of 78.28 db. Then I tool the bricks and tile off the front of the trap and measured and average of 75.5 db. Then I put a copy paper target in front of the foam and measured 86.6 db.
I think the bottom line is shooting into bare foam is the best alternative to moving the pellet impact really far away from the sound meter. Stan already showed that, I just duplicated his result. If you can't let the pellet impact be far away while testing LDCs, shooting into a block of foam may work fine.
I have not made a final decision about making brick traps. There would be advantages but sound reduction is apparently not going to be very significant. I also learned a single layer of brick is not a great backstop. I busted one up today. I was using up some Benjamins my guns don't like. They are heavier than my normal FTTs. That was not a big surprise. I'd probably include a 2 inch thick paver in front of the brick if I make brick traps. I could angle it down to try and better contain the pellets as they fragment. I could put in a steel plate but I am pretty sure that would get loud. I might just make the brick trap big enough I could put my normal trap inside. It stops the pellets in rubber mulch. I think it would be easier to recover the pellets if I stop them in mulch. They spatter when they hit bricks.
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Those acoustic tiles look promising. If they are easy to score and snap into smaller pieces, maybe just cut them into 3-4" wide strips and stack them to make the walls and ceiling. May need some outside weather protection. If they are safe to cut (dust) you could even shape the inside edges to avoid flat walls. Looks like they are marked so you can find out what they are made of.
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I only had a scrap of a tile. I could just go buy one. But the foam was quieter, even with the front open. Until the target goes on it. The acoustic tile is not hard to cut, you just use a utility knife. You can score it and snap it or just make multiple passes and cut through it. But it won't withstand multiple hits in the same spot, it disintegrates. Foam looks like it might actually be less damaged by the pellet impact. But I'm sure it will also fall apart eventually. Big issue is the target sound.
I googled for ideas and saw a thread on AGN where they recommended wetting the target. I might try that. It may be hard to get it wet enough without getting it so wet it just falls apart. Might be able to get it to stay on foam (or possibly acoustic tile) by wetting it. Might be something to try tomorrow. I'll have to find a spray bottle. Probably have one somewhere.
If the wet target idea works, maybe a foam back and acoustic tile on the sides of the trap. Or maybe acoustic tile all around the inside and just plan on replacing the back. The acoustic tile doesn't like water, however.
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Jim,
I think that the brick trap is still going to be much quieter 90 degrees to the side of the trap, and behind the trap, compared to a cardboard box, for instance.
So, it is not just a matter of quieter towards you, but towards ears that might object.
What makes a noise is a sudden high force, applied to an object that can ring and act as a speaker membrane.
Bullet traps that are popular with some indoor ranges are steel spirals, where the bullet meets the spiral at a shallow angle initially. Then as the bullet slows by skidding along the shallow part of the spiral, the spiral tightens. Sure, this is mainly to keep bullet frag from being ejected from the trap, but may have application for a quiet airgun trap because of the shallow angle of incidence.
A square steel sheet cone fitted to the front of the spiral would also be useful. Even just using a square cone a slight angle to ensure projectiles rub along one side could be useful. If there is no friction along the sides, then the large impact at far end would still occur. The cone needs to be stiff enough to avoid it acting a speaker cone.
The cone and spiral need to be stiff, or stiffened. And housed in a shielded box, if required to reduce noise transmission towards the side and back.
The opposite of a quiet trap is a thin sheet metal box, where the pellet hits the back almost square on.
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For background noise, how does one encourage woodpeckers to adopt your yard?
https://www.youtube.com/watch?v=tGyLwj_OPQA (https://www.youtube.com/watch?v=tGyLwj_OPQA)
https://www.youtube.com/watch?v=F0v-CukKW5Y (https://www.youtube.com/watch?v=F0v-CukKW5Y)
https://www.youtube.com/watch?v=hNSxCLYKgys (https://www.youtube.com/watch?v=hNSxCLYKgys)
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Jim, I misunderstood and thought you had a bunch of the tile from church.
Here is an informative DIY video, including some of the more useful comments. https://www.youtube.com/watch?v=pABvTWSxOes (https://www.youtube.com/watch?v=pABvTWSxOes)
My takeaway is for the sound passing through the walls, you want to seal the enclosure (maybe just use dirt/mud as the mortar for the test). Inside the walls, floor, ceiling I think something soft and heavy: old bath towels, maybe around particle board for structure, or you could wrap them around a chicken wire frame like I did, or carpet. On the innermost surface, maybe some of the opencell foam to reduce reflections out the front. I think you'll end up with at least a half height enclosure in the front with similar soundproofing.
For the target surface, the foam works. The wadcutters I was shooting left clean holes (and cut out well formed foam Cheetos on the back side) The foam can be backed up by clothes, carpet?, some of your rubber mulch, and then a hardstop in front of the bricks, maybe some sheetmetal glued to particle board or something to absorb the drum.
Maybe you can refresh the foam surface with plugs of foam into the shot out section or just use lots of bull spots and replace the sheet as needed.
Just some ideas, tailor to what you have on hand.
I thought you might be able to reduce the reflection out front by stacking the bricks at an angle, but probably not worth the effort.
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This guy is 25 ft up and pounding on a soft palm trunk. Fortunately we are not in the part of the country where they store acorns by pounding them into house trim.
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Wouldn't it be interesting if we could record a report without a moderator, and create the negative wave, then using the trigger and a set delay, to "cancell" the report. We would see guns with built in chips that record, modify, amplify and play to achieve a "soft" report. I would love to have something like that in my basement range... It does get loud down there at times. 😁 👌
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Interesting thoughts, guys. I don't worry much about behind my trap because there is a couple hundred yards of lake there before the nearest neighbor. I'm pretty sure he likes me shooting into a trap instead of a target fastened to my fence (sometimes the pellets skip) but I don't think he can hear much. On the sides of me both neighbors have double lots but that still keeps them within 50 yards - so considerably closer. Gypsy is over 100 yards away and obviously still hears me so maybe if the guy across the cove has dog ears....
I also did not measure much reduction to the sides of my brick quasi trap. But I also agree the very crude construction is undoubtedly contributing to my results. With the enclosure sealed I am sure it would work better.
I got pretty good results with foam on the back of the enclosure and accoustic tile on the sides until I put up a target. Then I was back up to 86.6 db average. I didn't use my calculator but I think the results with a damp target today were no better (the readings were 83, 85.3, 87.9 and 87). I tried another idea similar to a comment by Stan and stuck little 1 inch red target dots onto the foam. They didn't stick well, the foam was wet, but they would stay in place long enough for me to shoot them. That was an obvious improvement, 70.3, 84.2, and 78.3 db. Just using a marker to put a dot on the foam would work at least as well I am sure.
So nothing I've tried or I've seen others do makes a normal paper target impact less than 80 db except possibly Stan's small hole with a sand dampened enclosure around the target setup (I don't remember what was in back). That's what got me thinking of closing off the front but my results yesterday with the front open were lower with foam on the back and tile on the walls. The "big deal" seems to be the impact occurring on a soft surface. I saw a video of a guy using fleece blankets and I watched the linked video with the towels. But if you put cloth in a cardboard box, it is just as loud as my trap with ground rubber and a cardboard front. Hitting paper or cardboard with a pellet makes a 80-90 db sound. More than my guns.
A longer "tunnel" for the target to sit in the back of might change this but it also may not. I think it would need acoutic tile or sound panels or possibly towels on the sides and I worry about them staying out in the weather. Old towels might actually be the most durable. I could rig up a small metal frame to hold them in place.
Right now I just put me pellet trap on a piece of pressure treated 4x4 with bricks around it to hold it up. It works but doesn't look nice. Building a proper brick column to hold the trap up was already on my "to-do" list. This would need to be bigger, I'm thinking of making it 16x16x16 inside so I can put my trap inside easily and line the walls if I want. So it would be 24x24 inches outside, roughly. That is not huge and I have the bricks. I could also fill it with sand and put my swinging targets in front of it so I don't damage the tree behind them now. That might bust the bricks up but I'd probably take that chance to save damage to the tree. So there is a decent chance I'll make this but largely for other reasons. I'm still not seeing results that lead me to be confident it will make my target shooting significantly quieter.
One thing that does work, however, and could be used for LDC testing is just shooting into foam. I saw something on line where a guy was using long straight pins to put jelly beans on a block of foam and shooting them. Small marshmellows should work the same way. Seems like an idea for plinking targets that would be quiet. But if I want to shoot targets it doesn't seem to matter if the target is on a block of foam or on a pellet trap, the noise level is about the same. My crude "tunnel" didn't change things either. I think it would if it was better constructed and long enough but I'm worried "long enough" is not a length I want to look at all the time. But maybe pushing the impact back a foot from the entrance like I am envisioning will be more significant than my crude experiment would suggest.
If I had a driveway culvert handy, I would make something where I could put a target at the back and measure sound. I'm thinking something dense like this and much longer would dampen the sound a lot better. Ideally I'd love to know the reduction with various lengths. But I see no practical way to gather that data. Maybe if I just had the culvert I could position the target at various distances from the entrance and get meaningful data that way. But at least right now I do not have the culvert.
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Jim,
I think that a deep trap with the inner walls having conical or angular faceted faces should help. Even if they are hard, as in Stan's brick trap image, imbedded below. Making those features from, or covering them with towel or foam would work better, but would get chewed up if hit regularly.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=197179.0;attach=395992;image)
Shooting tunnels that have a semi baffled shape are often made from used tires. These are usually near the gun muzzle, but placing them near the target could also work. Or something with a similar shape: https://www.shootersforum.com/threads/backyard-shooting-range-noise.23982/ (https://www.shootersforum.com/threads/backyard-shooting-range-noise.23982/)
(https://www.shootersforum.com/attachments/range-sound-suppressor-jpg.3274/)
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I realize that trap noise has risen to the top priority over muzzle report. Partly my doing :).
I also know that we don't use dry firing of PCPs to evaluate LDCs because that is louder than firing a projectile. However, would it be useful to dryfire a PCP for the purpose of mapping sound reflection in and around our shooting galleries, with certainty that we are not being affected by trap noise?
If such muzzle only mapping is useful, could it be assumed that the trap has a similar signature? One that is probably not as directional as muzzle report, but that might be contained or benignly reflected in a similar fashion?
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What can we learn form commercial shooting ranges sound mitigation methods? And from academics?
https://www.youtube.com/watch?v=Fd1D42dVxS0 (https://www.youtube.com/watch?v=Fd1D42dVxS0)
https://www.bu.edu/articles/2019/making-the-world-a-lot-quieter/ (https://www.bu.edu/articles/2019/making-the-world-a-lot-quieter/)
The metamaterial, ringing around the internal perimeter of the pipe’s mouth, worked like a mute button incarnate until the moment when Ghaffarivardavagh reached down and pulled it free. The lab suddenly echoed with the screeching of the loudspeaker’s tune.
“The moment we first placed and removed the silencer…was literally night and day,” says Jacob Nikolajczyk, who in addition to being a study coauthor and former undergraduate researcher in Zhang’s lab is a passionate vocal performer. “We had been seeing these sorts of results in our computer modeling for months—but it is one thing to see modeled sound pressure levels on a computer, and another to hear its impact yourself.”
By comparing sound levels with and without the metamaterial fastened in place, the team found that they could silence nearly all—94 percent to be exact—of the noise, making the sounds emanating from the loudspeaker imperceptible to the human ear.
https://en.wikipedia.org/wiki/Active_noise_control (https://en.wikipedia.org/wiki/Active_noise_control)
https://www.soundproofcow.com/soundproof-a-space-restaurant-office/gun-firing-range-soundproofing/ (https://www.soundproofcow.com/soundproof-a-space-restaurant-office/gun-firing-range-soundproofing/)
https://www.soundfighter.com/sound-attenuated-shooting-range/ (https://www.soundfighter.com/sound-attenuated-shooting-range/)
https://www.controlnoise.com/treatment/gun-range/ (https://www.controlnoise.com/treatment/gun-range/)
https://www.controlnoise.com/product/qbo-blankets/ (https://www.controlnoise.com/product/qbo-blankets/)
https://www.controlnoise.com/product/pyramids/ (https://www.controlnoise.com/product/pyramids/)
https://www.quietstone.co.uk/applications/shooting-range/ (https://www.quietstone.co.uk/applications/shooting-range/)
https://acousticalsolutions.com/soundproofing-a-gun-range/ (https://acousticalsolutions.com/soundproofing-a-gun-range/)
https://acousticalsolutions.com/product/aqfa-10-absorber-sound-blanket/ (https://acousticalsolutions.com/product/aqfa-10-absorber-sound-blanket/)
https://www.soundproofingamerica.com/soundproofing/soundproofing-an-indoor-shooting-range/ (https://www.soundproofingamerica.com/soundproofing/soundproofing-an-indoor-shooting-range/)
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In George's long CP2 and Titan hacking threads we used classic mouse spring traps as simulators for checking out some of the instrumentation. It may be useful here to isolate the performance of any target trap soundproofing from being combined with the muzzle blast.
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Mouse traps make a nice crisp snapping sound when "dry fired".
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Jim, Did you figure out if Gypsy responds to the foam target impact?
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She was quieter when I was shooting into the foam but her owners might have taken her on a walk or inside then too. She is a factor but not a controlling one in my mind. Dogs bark, I don't want to spend too much time worrying about why. I think sometimes it's me but it isn't always me. Her owners need to be the ones worrying more about her barking.
I looked at most of the linked items. I noticed that the city was getting complaints about noise levels that were mostly in the 80-90 db range, one may have been a little higher. So comparable to my trap impacts. The company got it into the 70s and at least they thought that was success. I would also like to get it under 80 db but I don't want that bad enough to spend a lot of money to get there. I also found it interesting that hanging up sound absorption blankets seems to have a large effect. Maybe a road culvert is not the right kind of tunnel. Maybe a light structure to support a towel or another sort of sound absorbing material is the right kind of tunnel. I don't want 25 yards of panels in my yard but if a light structure I could drape a towel over (or velcro it to) would help meaningfully that might work. I don't like the setup/tear down but it might be possible to keep it reasonable. I wouldn't have to use it all the time either. I don't normally shoot on weekends much because of boat traffic and neighbors being home. I could use the blanket during those times and other times I want to be quieter.
If I make my 16x16 inside brick structure I would put some sort of sound absorption in the front ahead of the trap. Possibly behind the trap and above and below too. Should be room for about a foot. I've seen stick on 1 inch thick panels on Amazon but I don't know how durable they would be only partially protected from the weather. But I could try it, they don't cost much more than a tin of pellets. We may also replace another room of acoustic ceiling tiles at church freeing up some old ones for me to use. If that is still over 80 db - and I'm thinking it probably will be - I could weld up a little cage of some small square tubing I have from a shipping crate and put a towel around that in front of the brick structure. That could give me more than another foot of a crude acoustic panel. Might work. I might need more than one layer of towel.
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Maybe you can build your brick pedestal with 2 or 3 sides and the drop in your sound proofed (towels or blankets over frame?) target with or without the trap. That way the soundproofing does not have to be weatherproof. If you do a front closeout, maybe it is partial height and you flip it get to the other bulls. May need a light but those are cheap and easy.
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Jim,
Set up some wind chimes that provide background sound to capture the attention of whoever is actively listening. If needs be, set up an oscillating fan to blow on them :)
https://www.youtube.com/watch?v=X7t--zPZdic (https://www.youtube.com/watch?v=X7t--zPZdic)
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The chimes made me smile. I may leave the base of the structure open either for storage or, if necessary, a boom box with a tape of a mower or maybe a circular saw or other loud tool. With a remote I could push the button to get the noise going and then shoot. But I'm not sure one type of fairly loud noise is that much better than another. If I really needed to hide the noise I would do this if I cannot dampen the noise. But what I'm doing is legal so if I get a complaint I'll deal with it. But I stopped doing much shooting with my Avenger when it was over 100 db. To me that is not reasonable even if it is legal. Now it's down in the low 80s with it's printed moderator.
I thought of a way to try my blanket idea. I put a couple fairly long boards from a pallet I tore up on top of my makeshift brick structure and weighted them down and draped a towel over the boards. So it surrounded the trap and extended about 24 inches in front of it on the top and two sides. That was not very effective. Averaged 86.3 db. I got 86.6 average without the towel. Then I pinned the bottom together at the end away from the trap. Couldn't do it close to the trap because the trap was helping support the blanket. That worked better. Average of 83 db.
So with all this better implemented, mortar on the bricks so they aren't leaking air, solid towel on 4 sides, sound suppression within the brick structure I can see it getting a little under 80 db. I don't need it much quieter because the guns are all either a little under or a little over 80 db. I think the quietest is 76 db. I might get there.
I've thought of putting a towel directly around the trap. I could but think it would be hard to have enough support for the towel, get the towel fairly well sealed to the trap, and not have the trap tip over from the towel and it's structure. I'm using an old small circuit breaker box I found in my shed for a trap. It's nice heavy steel and filled with rubber mulch it stops pellets fine even from my 48 fpe Avenger. The back gets dinged if the mulch settles too much but it still stops them. But it only weighs about 12 lbs. I think this could be done but I think it will be easier to have the brick tower support the towel.
I don't have to have a large 16x16x16 inside opening, however. I could have a light steel structure incorporated into the tower to support a towel and just set the trap on top of the tower under the towel. I'm a little worried that making a larger opening will tend to increase sound. Those shooting ranges certainly had large openings around the shooting, however, and still managed to block the sound with panels. I've also thought about using towels over a frame as the soundproofing inside a concrete and brick structure. If they were velco'd on or something they could be taken out and washed. They wouldn't fall apart quickly from weather.
I'm still leaning towards the concrete and brick structure partially because I have 3 grand kids and a larger back stop could be handy for them initially. I occasionally miss the trap too if I'm testing new projectiles. But I'm still thinking about it. Hitting the lake occasionally is not terrible.
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Well, if you are willing to go boombox, then a tape of a woodpecker is the logical choice. You could even go electronic and have your shot sound trigger a 5 sec clip of a woodpecker drum solo.
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Jim
Have you considered approaching your neighbors and telling them that you are an air gun hobbyist. You could explain that you target shoot into a pellet trap and there is no danger to them whatsoever that might cause concern. You could tell them that it's completely legal and you just giving them a heads up that they might hear you shooting. Tell them what they might hear is the pellet striking the target which is probably louder compared to your guns. Tell them the gun shoots a small projectile powered by compressed air unlike a regular gun that uses gun power.
Not sure but might be worth considering for your peace of mind while shooting and not being in a constant state of worry about the noise.
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Les,
Only one neighbor has mentioned it and she asked if I was using a nailgun or something. I told her I was shooting an air rifle and she said her husband does that sometimes. I know others are shooting pellet guns because I killed a couple squirrels that had 177 pellets under their skin where the wound had healed over. So I don't think it's a big deal, just trying to be neighborly.
I think I have decided to just make a simple brick column about a foot square and put a 16x16 concrete paver on top. Then I plan to make a skeleton structure with some small steel tubing that was part of the packaging of a gazebo I recently put up - so no cost. I plan to bolt the steel skeleton to the paver and use it to support towels over the trap. I was struggling, I think, with the idea that eliminating the brick enclosure around the trap was not helping with noise but it seems pretty obvious that is the case now. I need soft surfaces, not hard ones. The skeleton structure with towels might not work but the simple test I did yesterday makes me think it probably will. Might need two thicknesses of towels or something. I pin them together for a trial and sew them up if it works. I won't leave them up all the time and may not always use them but if I want to be quiet, it gives me a way to do it. This alternative doesn't give me everything a larger structure would but I think it will be useful without sticking out too much.
I appreciate everybody's thoughts. It will probably be a week before I get this made, depending some on what else comes up. I'll have to give the mortar a couple days to cure. I'll let you know either way if it works to reduce noise and by how much.
Jim
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Keep us posted on your results.
I currently use a large plastic tote filled with rags as a backstop. I screw a piece of cardboard to it that has my 3 in. stick on targets on it. The pellets do make a loud slap sound hitting the plastic tote. I think I am going to try out an idea with it. I have a piece of plastic netting that I will zip tie in place of the lid. That way I can turn it on it's side and shoot directly into the rags. I can take a piece of printer paper and stick some targets to it then tape that to the plastic netting to see how it compares noise wise. If it makes a big difference I'll let you know.
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I use a pile of depleted garden and potting soil. Every year we remove the old top soil from the garden and I pile to up for my back stop. Virtually silent and ricochet proof, looks like nothing more then a big compost pile.
The trick is finding silent targets. I use thin foam.
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No results yet but I'm getting close. Yesterday I laid up a few bricks for a post to support the trap and the sound suppression "hood". Today I welded up the little rectangular steel tubing I had to make a frame to supports towels which hopefully will suppress the sound of the impacts. I'll include a picture. Tomorrow it is supposed to rain here but I may work on wrapping the frame with towels and hopefully test it Friday.
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I didn't quite get the benefit I was seeking but I got some and I think these results are interesting too - surprised me.
For these measurements I was shooting my P35 in 25 caliber. I used Benjamin domed pellets because it doesn't like them much so they are expendable. They weigh 27.8 grains and I measured the velocity of 3 shots and it averaged just over 750 fps for almost 35 fpe.
With no towels on the frame, just the trap on the pedestal I measured an average of 86.2 db at my shooting bench.
With one white fluffy towel wrapped around the end of the cage with the trap inside I measured 88.1 at the bench and 82.7 db fifteen feet to the side of the trap on about a 90 degree angle - directly to the side. (the Bench is 25 yards from the trap so much further away)
With the white towel on the back of the cage and a beach towel over the front of the cage I measured an average of 83.23 db - at 15 feet to the side.
With four towels - doubled up towels - I measured 80.63 db on average. I also measured this configuration at the bench and got 87.43 db.
Then I measured doubled up towels on the back part where the trap is and nothing on the front closer to the shooting bench. I got an average of 80.53 db.
I thus believe my cage is too long. It is 40 inches long and I will probably shorten it to about half that. It is hard to wrap the beach towel around the front of the cage so I won't miss that. But both the one towel thick and the two towels thick results say the front towel(s) are not doing anything. That might be a little different if I measured other angles but I doubt it would be enough different I would want to mess with the additional towels.
I did have a few individual measurements under 80 db like I wanted but the average of 3 was always a bit over. I should probably do an uncovered 15 foot to the side test but I think the towels over the cage are dropping the sound 6-8 db. It is also easy to do, I just safety pin the towels on. So maybe this will be my new target shooting setup, at least when I am testing pellets or guns and firing a lot of shots. I might also try a doubled towel under the trap. I had a wash towel under it but it is too small to even cover the entire pedestal top.
I had a few measurements which didn't make sense and I am attributing to some guys doing tree work across the cover. I watched the meter go over 80 db when their chipper was pointed towards me and near the shoreline. They were around 200 yards away - must have been really noisy for them. The chain saw was not this loud, only the chipper was.
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OK, I think I finished with measurements - and got one average of 3 readings under 80 db! But first a couple of pictures of the setup:
First I measured sound at 15 feet from the trap, with two towels on the back and the meter at about 45 degrees to the line between the shooter and the trap. I got an average of 79.4 db. Then I took the towels off and measured the sound with the meter at 90 degrees. I got 86.3 db.
So it looks like I am decreasing the sound of the pellet hitting the trap by 6-7 db. I consider that not great but not terrible either. It gets the pellet impact noise pretty close to the gun noise.
Maybe a third towel would help but I am pretty sure the benefit will be less than I got for the second. Probably 2 db or less.
Sound at the shooters location is pretty much unchanged by this. I also learned that the benefit comes from sound absorption within 18-24 inches of the impact. I did not expect that. That makes if more convenient since the necessary "hood" can be significantly smaller.
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Jim, interesting results. I wonder if the towels are good to a point but may be a little permeable. Maybe leave them in place and put something heavier, more air tight on the outside (moving blanket?).
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I will probably try a third towel, possibly a moving blanket, but I've decided to reduce the "hood" length to about 18 inches. I was not seeing a benefit of the 40 inch version I initially tested and it was significantly more work to set up. So I cut it down last night and rewelded it. But if I reduce the sound of the trap only a few dbs, the gun will be louder. I might already be about there for my P35. Might have to use my Prod.
Cutting it down also eliminates the need to bolt it to the concrete slab to prevent it from tipping forward.
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To evaluate the effectiveness of just the trap, in different directions, the mousetrap as the noise source approach might give you additional information.
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Jim, you inspired me to take a shot at making a front sound enclosure. It also gave me a chance to use up some odds and ends in the garage.
The enclosure is 12" deep and 9" on the inside. That was the size particle board I had and I think it matches up with 1/2 sheet targets. I had a few berber carpet tiles (from way back when berber was a thing ::) ). I think I may end up with a towel on a wireframe on the inside but for now I'll test it as is.
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I did some tests with the basic sound box configuration attached to my usual target box (cereal box cardboard front face backed by clothes and a steel plate). I ran 3 test series with the soundmeter 6 ft to the side, in back and in front. In each case the mic was pointing at the target. I used my quietest airgun (shrouded CP1). 6 shot series, throw out high and low and average the remaining 4.
Soundmeter on side gave 6.5 db reduction.
Soundmeter in the back gave 3.2 db reduction but theses were already very low numbers for the bare box, apparently the clothes do a good job in that direction
Soundmeter in front gave a 3.5 db reduction. Not surprising that this is a modest reduction since the sound box is open and only 12 in deep. As was expected, shots placed closer to a wall were quieter than the middle.
For my use it is a good start for the basic particleboard and carpet design. Several upgrade paths exist.
Of course the usual caveats about soundmeter readings apply.
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I bought a foam archery target to use for a backstop, it's quiet and nothing I shoot gets close to going through it (700 fps .22) ...plus it's weatherproof. I figure you could always put a side panel off an old pc behind it if you wanted to be extra safe.
(http://)
blackholetarget.com
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Foam worked well when I tried it, but once I put even just a copy paper target in front of it the numbers went up.
Are those archery targets self healing when pellets hit them? Do you need to use pointed or domed pellets?
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They appear to be self healing, all the reviews I've read are for arrows of course but everything I've read claims they last extremely long, if that isn't enough they make an even stouter one for crossbows. I think for long term use I will cut a piece of plywood to size and attach it to the back side just to be safe.
The construction design is many sheets of 1/8in. foam stacked and compressed horizontally.
also all the prices I found online were pretty high I bought mine from a local store for $40.
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I was shooting wadcutters into shipping foam. It was very quiet but each shot cored out a clean foam worm. Your stacked foam is different but pointed or domed pellets may be better. I'll try those next time.
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This foam has a consistency more like a plastic card board it's fairly rigid, it was actually just an experiment, so far so good. I shoot a lot indoors and the clank of a metal trap just isn't an option.
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For completeness, I added the front cover plate (from post 41) to the sound box. It is plywood with thin foam on the inside and a 3 " entrance hole.
I repeated the tests with the CP1 and the soundmeter in front, facing the target. The results for the box with the front cover were about 13 db lower than either the plain paper box target or the open box without the cover.
I have some ideas to make the cover more practical, but that combination got me to below 75 db in each of the directions for my test configuration.