Interesting Sound Measurements

[JimD]

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. 

[WhatUPSbox?]

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.

[subscriber]

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

[JimD]

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.

[WhatUPSbox?]

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.

[jjohnsonlta]

 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.

[JimD]

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

[jjohnsonlta]

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.

[AKM]

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.

[JimD]

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.

[JimD]

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.

[JimD]

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.

[WhatUPSbox?]

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?).

[JimD]

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. 

[WhatUPSbox?]

To evaluate the effectiveness of just the trap, in different directions, the mousetrap as the noise source approach might give you additional information.

[WhatUPSbox?]

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. 

[WhatUPSbox?]

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.

[jsk68]

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.




blackholetarget.com

[WhatUPSbox?]

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?

[jsk68]

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.