Taming the bark of an Avenger

[subscriber]

I think a good LDC works like a good recoil pad.   Comfort increases as the peak force is reduced.  This is achieved by stretching the time constant, rather than reducing the average force applied to your shoulder.  The ramp in force also matters; such that a ramping push is more comfortable than a slap or a punch.  A high peak force can hurt.  A high average force, just pushes us back.  No magic is involved.

Yes, I realize that suppressors can and do act to reduce recoil, so my analogy is not perfect.  My point is that it does not hurt if your wife step on your bare foot with a bare foot, for over a second.  Compared to stepping on your bare foot with stiletto heals, for a fraction of a second.   In the latter case, peak contact pressure is what we notice, rather than force.   Sensory inputs below a certain level are easily ignored, even if they are applied for a "long time". 

Any sound that starts and ends abruptly (especially with an audible echo - because that suggests the sound source is close) instinctively triggers our "what was that?" response; that then has us listening actively for more clues.  We want to know if there is a predator near us, heavy enough to snap twigs on the ground.  We want to avoid triggering that instinctive response in people nearby, by modifying the sounds we produce.

[JimD]

I'm not sure filtering the holes in the shroud does a lot.  I've seen it recommended before and came up with an idea to do it with things I had on hand so I did it and tested it.  I used a hair curler wrapped in plastic felt with another small piece of plastic felt inside.  All at the end of the shroud where the holes are.  That isn't a magic eraser as is sometimes recommended or cotton fiber but it's what I had readily available.

I took 4 measurements to the side of the muzzle and 4 to the side of the vent holes.  If I throw out the highest reading of both sets and average the remaining 3 then the muzzle got .8 db quieter and the vent area 3 db quieter.  If I just use all the measurements the muzzle got 1.7 db noiser and the vent area 1.4 quieter.  The "no free lunch" theory would suggest using all the measurements. 

No big change in any event.  It did seem to make the vent area closer to the muzzle in sound level (regardless of which sets of data I use). 

I don't see where it hurts anything so I left it this way.  I am not worried about lead dust because I think that happens when the pellet rubs the barrel and is unlikely to come backwards.  Even if it does, it would be very small in amount.  After a few hundred shots maybe I'll look at the felt.  Maybe it's a good idea from this standpoint. 

[subscriber]

Thanks, Jim

[WhatUPSbox?]

Bob, interesting that you aren't seeing a drop off with range. There may still be something in the Android recording. The fact that the low volume metronome generates a constant response may not apply to a high amplitude sound where some auto leveling may be applied. If you still have access to an iPad, maybe try recording directly into Audacity on the iPad. It will add some walking but maybe also add an analog meter reading at a couple of the distances.

For checking the Android recorder, you could create a sequence of tones at different amplitudes in Audacity, play it back through your PC and see if the Android recorded file  shows the correct amplitudes when measured back in Audacity.

[TorqueMaster]

Bob, interesting that you aren't seeing a drop off with range. There may still be something in the Android recording. The fact that the low volume metronome generates a constant response may not apply to a high amplitude sound where some auto leveling may be applied. If you still have access to an iPad, maybe try recording directly into Audacity on the iPad. It will add some walking but maybe also add an analog meter reading at a couple of the distances.

For checking the Android recorder, you could create a sequence of tones at different amplitudes in Audacity, play it back through your PC and see if the Android recorded file  shows the correct amplitudes when measured back in Audacity.

Stan,

You are right, some sort of additional verification that the Android gain is not changing would be a good idea.  Unfortunately, I have very limited access to the iPad.  I intend to test the frequency response of the Android/mic at some point, can do multiple volume levels as well, and see if it's still auto-gaining.

[subscriber]

If the instrument's sensitivity to different sound frequency bands is non-linear, might not the measured sound readings change with distance, simply because of that non-linearity and the natural drop-off in high frequency component with distance?

In a nutshell, when you multiply two non-linear factors the resultant output can create a "bathtub curve", or be "lumpy".

Is there a sound meter that is made for measuring gunshot sound levels, that is not disqualified by an interested party, and yet costs no more than $100?  I bought this one because that is what Pyramyd Air used at the time:  www.amazon.com/gp/product/B000EWY67W

[TorqueMaster]

Mother nature allowed some  more testing, which I followed up with a bit of analysis.  Did another 100 to 3 feet walk-up test with the mic pointed at the muzzle.  It clipped first at about 50', then didn't, then clipped again round 25', then didn't...  I chose 75' to try testing various LDCs.

Averaged 3 shots for each LDC, except where issues arose...more on that later.  Compared against the stock avenger.  The db values are calculated from the recordings, in Audacity.  Tried multiple sample window, 50ms, 125ms, and 300ms, as expected longer times gave lower db numbers, but the change in db between LDCs was almost constant, regardless of window size.  I'm calling this "max" -- the db average over the sample window.  Used 125ms.  I also recorded the peak value of the sounds-- this is the instantaneous peak (recorded at 44kHz, it samples every 0.000023 seconds....) Calling this "peak."  Ambient sound level was measured at 45db, and in Audacity, ambient level was around -55db on a -60 to 0db scale.  From that, 0db in Audacity should be 100db.  Obviously there's a lot of room for error here.  The numeric value of peak may not be correct, but again, the relative value should be. 

LDC          Peak db    Max db relative to Stock
Stock          99        --
No Cap        99       +1 (did not clip but seems wrong-- seems louder)
Plume         96        -5
Sponge        88       -9
Dig Felt *      90       -9
Felt **        83        -8    (whistling is not good....)
Buckrail       92         -7
Maxi ***    79          -17 (yowza!)
AirStripOnly 97         -4

The asterisks:
*Digital Felt -- Only used 2 readings, the third was way higher.  No damage is seen, unclear what caused it.
**Felt -- Only used 1 reading.  It was already damaged during assembly, and the 2nd and 3rd shot read way higher.   Obvious pellet damage showing,  probably from the 1st shot...
***Maxi -- Only used 1 reading.  2nd and 3rd were way higher, it has minor pellet damage.  That first shot didn't stand out while shooting as crazy quiet as the recording shows, but I have no reason to suspect the recording is wrong.

Takeaway -- I hate the bulky size but the maxi seems a clear winner.  Needs reprinting and retesting.  All of them in the -5 to -9 range are "quiet enough" in my book.  I think I like the Sponge Digital Felt sound best.

Attaching audio file -- 3 shots each of Stock, NoCap, Plume, Sponge, DigFelt, Felt, Buckrail, Maxi, AirStripOnly
Attaching pic of Minor but apparently fatal Maxi damage.

[subscriber]

Thanks, Bob

Your recordings make it clear that there is more to "best" than peak sound level.

I assume that the damage to fatso (maxi) was due to clipping.  All of my earlier designs had a nominal 7 mm ID.  Then after you reported the actual diameter as being 0.25 mm smaller than nominal, I bumped that to 7.2 mm.

It may be, longer term that the bore should be made a little larger; and / or that it should step up towards the LDC muzzle to account for angular error.  Else, a single wobbly pellet may start a cascade failure...

[TorqueMaster]

Thanks, Bob

Your recordings make it clear that there is more to "best" than peak sound level.

I assume that the damage to fatso (maxi) was due to clipping.  All of my earlier designs had a nominal 7 mm ID.  Then after you reported the actual diameter as being 0.25 mm smaller than nominal, I bumped that to 7.2 mm.

It may be, longer term that the bore should be made a little larger; and / or that it should step up towards the LDC muzzle to account for angular error.  Else, a single wobbly pellet may start a cascade failure...

Yes, damage looks to be from a pellet hit.  Could be the pellet/plastic shard blocked the muzzle and made it sound quieter than it normally would be...?  It was one of the one-piece prints, so the only alignment issue should be slop at the barrel/ldc interface.  It was one of the left-hand thread ones, but I had it cross-threaded in, seated firmly, and secured with tape.  A slightly wider bore, or tapering wider could makes sense.  Also some minimal test prints to make sure the barrel is fit -- not loose -- into the LDC, might be in order.  I have never noticed any resistance, nor rattling, but that sizing is somewhat critical.  Dealing with plastic, one rogue pellet could trash the LDC -- hard to imagine it could tumble very much in that 8 or so inches after leaving the barrel, though.

It just occurred to me -- I can measure the prints, all I need to know is the 22 barrel OD,

[subscriber]

I was just going to ask you to measure the Barrel OD and the socket ID so that the fit can be optimized.  I am still using dimensions provided by someone on GTA, over what feels like a year ago

The shroud ID was given me as 22.5 mm.  My design in-shroud part has an OD of 22.4 mm.   If there is opportunity to make this tighter, without actual interference, that would be good too.

With some shrouds the thread (or a burr at the end of the thread) are the tightest spot.  So, a jam might be possible there, with "guts" that would be a snug fit in the rest of the shroud.

[subscriber]

CAD diameter for Avenger barrel socket = 11.28 mm

What does the print measure?  Two places at 90 degrees, in case the print is not round.

What OD is the actual barrel?

Thanks, Bob

[subscriber]

As a general aside, Bob has agreed to order the famous Benelliboym1 Avenger in-shroud LDC, and to test it as a benchmark.   To facilitate this, and to show appreciation for Bob's more than generous contribution to this thread, I used paypal to credit him the cost of that LDC.

[jjohnsonlta]

I am using his LCD's on both my Origin and Beeman 1358. I am real happy with the results from both of these on my two guns.

[JimD]

I don't remember the details of the Maxi design but I used one I made for awhile that was much larger in diameter than my Tanto.  Even with the DonnyFL adapter - which moves the moderator out about an inch, I could not fill with the moderator on the gun.  Taking it on and off led to wear in the threads and the start of pellet clipping.  I know you guys were addressing this so maybe it isn't an issue with the Maxi.  There also may be a better foster fitting to use.  My fill set has a micro bore hose in line with the foster and it does not get out of the way easily.  A right angle foster would be a lot easier with a larger moderator. 

Thanks for testing the one I'm using.  I'm really interested in your results. 

[buddyb]

I just received my Moderator from Buck Rail and wow, it does a great job of quieting my Avenger. 

Great product so far and the price is right.

[buddyb]

Buck Rail LCD

[swingin]

May I ask is this his new model or is it the all plastic model of which I have.

[buddyb]

This is the one that fits over the barrel as well, not sure if its the new or old but I just ordered it Monday.

[TorqueMaster]

I was just going to ask you to measure the Barrel OD and the socket ID so that the fit can be optimized.  I am still using dimensions provided by someone on GTA, over what feels like a year ago

The shroud ID was given me as 22.5 mm.  My design in-shroud part has an OD of 22.4 mm.   If there is opportunity to make this tighter, without actual interference, that would be good too.

With some shrouds the thread (or a burr at the end of the thread) are the tightest spot.  So, a jam might be possible there, with "guts" that would be a snug fit in the rest of the shroud.

Inside of shroud (threads) measures 23.05mm at widest.  At least 23.00 all the way around.  No burrs noticed.  I don't think my calipers measure deep enough to get to the unthreaded part of tube.  I had shroud off today but didn't think to measure the unthreaded end.  I'll try to remember next time.

The .22 barrel is  11.00-11.02mm OD  The ID of the printed part of air stripper that goes around the barrel measures 11.07mm and is a perfect fit.  Slides on with just slight force, and rotates easily once on.  Would not change that dimension at all.

[TorqueMaster]

I don't remember the details of the Maxi design but I used one I made for awhile that was much larger in diameter than my Tanto.  Even with the DonnyFL adapter - which moves the moderator out about an inch, I could not fill with the moderator on the gun.  Taking it on and off led to wear in the threads and the start of pellet clipping.  I know you guys were addressing this so maybe it isn't an issue with the Maxi.  There also may be a better foster fitting to use.  My fill set has a micro bore hose in line with the foster and it does not get out of the way easily.  A right angle foster would be a lot easier with a larger moderator. 

Thanks for testing the one I'm using.  I'm really interested in your results.

The Maxi aka Fatso measures 2" OD and 4.2"long.  Weighs a ton -- don't remember the exact number but feels like half a pound.  I've been wondering if there is a more correlation between weight of the LDC and reduction, rather than the complexity of the design...as long as the basic cone shapes are in there.  Sadly the precision of my testing my not reveal much more than that.

This Fatso had bad threads, so I may have bumped it, messed up it's bore alignment and whammo, useless hunk of plastic.  Unless I was bench shooting and had to have the quietest report possible...I would not want that weight on my gun.

I got the beneliboym and hopefully will test soon.  It does not look like much compared to the internal/externals I've been testing...if it even comes close to matching them, it is an amazing reduction using very little material.  Only weighs 15g ... basically half an ounce!