Interesting Sound Measurements

[JimD]

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

 

[mann]

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

[AlanMcD]

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.

[JimD]

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. 

[mann]

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

[JimD]

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

[AlanMcD]

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  ).

[Ribbonstone]

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.

[jjohnsonlta]

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.
 

[Doug Wall]

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.

[JimD]

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

[subscriber]

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.

[jjohnsonlta]

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.

[WhatUPSbox?]

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 

[kbstingwing]

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.

[Greg_E]

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.

[subscriber]

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.   

[soupyyy]

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

[Tomygun1]

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.

[PikeP]

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...