Interesting Sound Measurements

[WhatUPSbox?]

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.

[subscriber]

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:

[WhatUPSbox?]

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.

[JimD]

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

[WhatUPSbox?]

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.

[JimD]

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. 

[WhatUPSbox?]

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.

[JimD]

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. 

[subscriber]

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.

[subscriber]

For background noise, how does one encourage woodpeckers to adopt your yard?

[WhatUPSbox?]

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.

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.

[WhatUPSbox?]

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.

[Hawkeye51]

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.  😁 👌

[JimD]

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.   

[subscriber]

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.





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/

[subscriber]

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?

[subscriber]

What can we learn form commercial shooting ranges sound mitigation methods?  And from academics?


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://www.soundproofcow.com/soundproof-a-space-restaurant-office/gun-firing-range-soundproofing/

https://www.soundfighter.com/sound-attenuated-shooting-range/

https://www.controlnoise.com/treatment/gun-range/
https://www.controlnoise.com/product/qbo-blankets/
https://www.controlnoise.com/product/pyramids/

https://www.quietstone.co.uk/applications/shooting-range/

https://acousticalsolutions.com/soundproofing-a-gun-range/
https://acousticalsolutions.com/product/aqfa-10-absorber-sound-blanket/

https://www.soundproofingamerica.com/soundproofing/soundproofing-an-indoor-shooting-range/

[WhatUPSbox?]

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.

[subscriber]

Mouse traps make a nice crisp snapping sound when "dry fired". 

[WhatUPSbox?]

Jim, Did you figure out if Gypsy responds to the foam target impact?