Taming the bark of an Avenger

[subscriber]

Thanks for the measurements, Bob

[JimD]

Thanks for the explanation of Maxi, Bob.  That sounds something like the one moderator I made that worked, for awhile.  It's body was 2 inch PVC plumbing pipe - so over 2 inch diameter.  The center was a piece of aluminum pipe with 5/8 OD and 5/16 or 3/8 ID (don't remember which).  I threaded one end 1/2 UNF but the pipe was not machined and I don't have a metal lathe so my threads were not great.  I made 3 and only one was concentric enough to work - for a while and then it started clipping and I threw it away.  My theory is that taking it on and off for each fill wore out the threads in the soft aluminum and that led to the clipping.  The other two worked a little but clipped from day I.  They were three different lengths and their reduction followed the internal volume - larger was better.  My end pieces were discs of 3/4 plywood so they didn't shatter if they got clipped but the shot was way off, of course.  I tried a plastic brillo pad inside but did not see a change.  That's the only thing I did inside any of them.

I agree that the little inside-the-shroud thing I'm using is awfully simple looking.  I am very surprised it worked as well as it has for me.  Seems like the kind of thing AV should include - couldn't cost more than a buck or two to make in volume. 

[AKM]

I agree that the little inside-the-shroud thing I'm using is awfully simple looking.  I am very surprised it worked as well as it has for me.   

I have been watching this thread and all I can say is "Holly over thinking a simple solution Batman"

You’re working with a sudden blast of cool air not high pressure gas like a PB. The principles are different.
 
With air volume is key, the bigger the better coupled with the smallest diameter apertures possible. To accomplish this you need almost absolute concentricity between all the parts to avoid clipping (the hard part).

Moving the blast of cool air through all kinds of little complex passages may be counter productive

This is done with PD suppressors to cool down the hot gas which in turn helps to lower pressure. You get none of this benefit with a blast of cool air and you actually reduce the overall volume of you chambers/LDC.
 
You will be surprised how well simple cup baffles work when they are set up as described above. Just stack them until you get to where you want to be. The LDC might be longer and fatter then you like but the end result will speak for itself.

Good luck with the crazy complex designs. They are interesting as is this thread.

[Spin]

Water, alcohol, Vaseline have all been used as ablative or evaporative cooling agents in firearm suppressors.  As the air leaving a PCP muzzle is actually colder than ambient due to its rapid expansion, I don't think evaporation and the desire for more rapid cooling will have much more than a placebo effect.   

I am not a fan of adding moisture where it can condense in a barrel and cause corrosion either.

I think that an incompressible fluid would take up internal volume and might make a PCP LDC louder.  It might just alter the sound, without being helpful.

The value proposition being explored would include: quieter, smaller, shorter, lighter, cheaper, better grouping, and possibly easier to make.  Internal cleaning might be another factor.  I suspect that lead dust acts to damp structural vibration, even though in extremis, it reduces internal space.

     "I suspect that lead dust acts to damp structural vibration, even though in extremis, it reduces internal space."

A very adept observation and at face one I'm inclined to agree with.   

[TorqueMaster]

Took a timeout to utilize some unusually calm conditions to try to improve my 100 yard shooting with the 22 Avenger (lots of room for improvement, still experimenting) and to compete in the casual 50 foot match with my Daisy 853, and whoop @ss in the 30 yard match with my 177 Avenger.  Back to LDCs...

I did audio testing of the previously mentioned Ebay purchased LDC versus stock, and the "plume" style designed by subscriber.  Both are a big improvement over stock.  And to my ear, the plume style is much quieter / pleasant than the Ebay unit. The Ebay unit still has a bit of a "crack" in the discharge sound.   Analyzing the audio recording in Audacity for 125ms "max" rms readings, the plume averages 5 db less than stock, and the Ebay averages 4db less, so by the numbers, not a huge difference, but one I could notice. 

Attaching mp3 audio -- stock x3, plume x3, stock x3, Ebay x3, plume x3.

[subscriber]

Thanks, Bob

That is pretty impressive for the eBay unit, considering its small size.

Do you have visual traces for the recordings?  If so, the difference in shape may be instructive.

[JimD]

Interesting.  So on Bob's gun he's getting about the same results as one of Subscriber's designs (plume) but about half the benefit of others (with Maxi still better but probably not practical).  Still makes me wonder why it works better on my gun but I've seen other reports on moderators where they work differently (have different benefits) on different guns.  So I guess that is to be expected.  Maybe it's a little like why some pellets work better or worse on different guns. 

[TorqueMaster]

Thanks, Bob

That is pretty impressive for the eBay unit, considering its small size.

Do you have visual traces for the recordings?  If so, the difference in shape may be instructive.

I looked back at my previous post -- for starters I was happy to see that the plume was consistent in the 5db reduction from stock.  This testing method (so far) is repeatable.  Also noted that your air stripper only, just the internal part of the 2-piece systems, also got 4 db down, just like the Ebay unit.  Both are better than stock, but somehow the extra db from the plume, and even better from other styles, and more likely the waveform, make a big difference to my ears.

I can take some screenshots of waveforms and post them for all to see.  Audacity is free and open source for anyone who want to look at the sounds in detail.

[TorqueMaster]

Interesting.  So on Bob's gun he's getting about the same results as one of Subscriber's designs (plume) but about half the benefit of others (with Maxi still better but probably not practical).  Still makes me wonder why it works better on my gun but I've seen other reports on moderators where they work differently (have different benefits) on different guns.  So I guess that is to be expected.  Maybe it's a little like why some pellets work better or worse on different guns.

I can't argue with your logic -- maybe it's more with how the individual perceives it.  Also remember, my numbers and recordings are from downrange -- what the target hears, not the shooter.  When I get to that, it may show more what I'm hearing, why "1db" difference makes the plume, etal, much more pleasant.

AV can't really change the id of the shroud, nor the od, or we'd see different generations of parts that don't mix.  I.e., your shroud is likely the same thickness as mine, which is the single biggest reason I can think the ebay unit would work better in yours than mine.  Material could change...but unlikely.  My shroud is unthreaded on the receiver end, just one screw (barely) holds it to the boss.  Is yours like that or threaded, as I have read newer ones are?  Not that I see that making an audible difference, just looking for possibilities.

[TorqueMaster]

Images of sound files:
Stock, Plume, Ebay

[subscriber]

Thanks, Bob

It seems the area of those sound plots is different, rather than the peak amplitudes.  The latter surprises me.  Also that they all start as a "square wave" (flat, and very abrupt).   I was expecting the sound to taper up more for the quieter ones than stock.  The sound recordings are a more of a hiss for the LDCs, compared to a obvious slap at the start of the sound for the stock configuration.

I wonder how these three configurations would compare in sound, perpendicular to the muzzle, at whatever distance the readings don't clip?  In other words, closer to the standard method for measurements.   Although your system may clip at 1 meter to the side of the muzzle.  That said, I still think that the sound as a neighbor would hear it, is more important than at 1 meter.

Another measurement case would be at the shooter's ear.  What individual customers are probably basing their opinions on.

[JimD]

Bob,

I think your measurement of the ebay unit is more consistent with mine than I first thought.  You are measuring without holes in the shroud, right?  I have holes in mine but did a test with them taped over.  In that test I was in the low 90db range 1 meter ahead of the muzzle which is roughly 5 db (maybe a bit more) lower than the stock configuration (I don't have any stock measurements at 1 meter ahead of the muzzle). 

I get low to mid 80s with mine with 8 holes in the shroud.  Certainly possible you would not.  I wouldn't blame you for not wanting to permanently modify your shroud this way on the chance it makes that moderator work better.  Putting the holes in also makes it a bit noisier for me (i.e. measurements back at the hole area and 1 meter to the side were higher with the holes open than taped over).  I posted my results a page or so back in this thread.

I also understand your point about your measurements being down range.  My shooting bench is also quite close to my house and that undoubtedly affects the results some.  I also respect your right to pick the unit which sounds best to you regardless of the exact numbers. 

I like it better that a large part of the difference in our measurements seems to be the holes in the shroud.  It may not matter to anybody else but I like to have some understanding of "why". 

Jim

[subscriber]

I like it better that a large part of the difference in our measurements seems to be the holes in the shroud.  It may not matter to anybody else but I like to have some understanding of "why". 

Ugly sketch below:  If "A" represents the industry standard muzzle report measurement location, and "B" is where you are measuring, Jim; it seems to stand to reason that "C" will be louder with holes in the rear of the shroud and "B" would be quieter.

If you have 100 dollar bills on you, and you place 80 in you right pocket and 20 in your left pocket, then you still have 100 dollars.  You also only have 80 in your right pocket; and that is less than 100.  In other words, with holes in the rear of the shroud you have moved sound away from where you are measuring it, to where you are not measuring it.  If moving sound levels up to the rear and sides is valuable to to you, away from the muzzle then mission accomplished.

[TorqueMaster]

I have no holes in my shroud.  I think holes in the rear of the shroud, as subscriber diagrammed, is going to change where the sound comes out, but perhaps not the overall "quantity."  Taped over we should be similar downrange.  Untaped, downrange is quieter at the expense of the shooter's ears.

Also seems like area inside the shroud, around the barrel, behind the muzzle, is ripe for more sound reduction before being vented out the rear holes?  May be better than letting the pressure bounce around inside the shroud, maybe not...
This gets onto possible barrel/poi issues, which the Avenger has enough of already.  I've been having fits with consistent poi, and have convinced myself that removing and installing the ldc for pumping, careful as I am, causes the shroud to rotate, which affects barrel position.  There are aftermarket parts -- aluminum rather than plastic -- to secure the shroud at the receiver/barrel better.  I feel a 3D printed part, likely with imbedded metal female threaded inserts, would suffice.  On the list...

[TorqueMaster]

More images of LDC waveforms.  To illustrate that the waveforms vary some even with multiple shots through the same LDC.  I show this in db format, which should be more representative of how we hear, and linear, which oddly enough, seems to better show the differences I'm hearing....    Also zoomed in on the first of each type of waveform, all in 400ms interval, so you can see the rise, peak(s), fall, and duration better.  I think they are all named well enough to describe the contents:

[TorqueMaster]

And each type in db format zoomed in 400ms frame:
EDIT -- should point out that visible bulge/peak late on in the plume is the metronome "tick", not part of the discharge sound.

[subscriber]

Bob, your last three images (post number 414) are far closer to what I expect to see.  The amplitude and abruptness of the widest section of waveform matches how sharp and loud your recording sound. 

Stock starts wide, flat and abruptly.  eBay has a little flat section before tapering to max amplitude.  And Plume has the longest taper at the beginning to a flat area of maximum amplitude - so the most gentle ramp into max amplitude.

[WhatUPSbox?]

Bob, did you ever get a chance to do the shots with the moving blanket wrapped around the shroud? I wonder how much of the noise is generated by the shroud walls.

[TorqueMaster]

Bob, your last three images (post number 414) are far closer to what I expect to see.  The amplitude and abruptness of the widest section of waveform matches how sharp and loud your recording sound. 

Stock starts wide, flat and abruptly.  eBay has a little flat section before tapering to max amplitude.  And Plume has the longest taper at the beginning to a flat area of maximum amplitude - so the most gentle ramp into max amplitude.

Can you circle the parts you mean?  It makes sense that the highest vertical peak should be the loudest part -- the "crack" -- but playing it slow, it's the initial transition from zero to not zero that seems to be that sound. 

Further, when played slowly, all have a "metallic" sounding ping at the same time -- at 0.260 - 0.275ms from sound start -- the middle peak in all the linear waveforms  --  which I  would guess is the shroud "pinging" or the air tank "pinging."

I haven't tried the blanket wrap yet.   I think from the side and from the side wrapped are the next tests.  I'm less enthused now -- my vevor type electric pump just went t!ts up, so I'm hand pumping for a while.  It will be very interesting to know if the "ping" is from the tank or shroud (or both) if I can isolate it, so I'm still motivated.

Attached soundfile at one-tenth speed -- Stock, plume, ebay.  I feel like Jonesy in Hunt for Red October.  No magma displacements or whales humping heard as of yet...

[subscriber]

Bob,

I was suggesting that leading edge of the sound, and how tall that vertical "flat section" there is, correlates with how harsh the "slap" sound of the shot is.  That that "square wave" leading section has a large effect on how loud the sound seems to be.   Compare "A", "B" and "C" below, taken from your sound captures.

Note that when the sound captures are arranged with their "bodies" aligned the way I have below, the quieter eBay and Plume captures have a more gradual wedge on the front end; compared to stock.  The smaller the "point", the less of a slap to the sound.