Taming the bark of an Avenger

[subscriber]

Whatever sample length is used, it needs to be consistent.  The tools within Audacity can give a relative db reading based on any sample length...I'll be curious to see if those tools, when measuring the same sample length as a stand alone meter or app (set to say "fast" 125ms) show similar numbers.

The recordings (when not clipping) reveal the relative "peak" values, too, so both the meter/app and recording/Audacity can be compared and hopefully show similar numbers...that may be more dependent on the granularity of the samples that each method is using, though...

I think the sound recording at constant non-clipping recording level are very useful, despite not having numbers.

Consistent measurement strategy is important for meaningful comparisons.  A measurement that produces the same ranking as what one hears would be more useful than one that is "industry standard". 

I suspect that some people find meters that read lower, to flatter a particular product.  Yes, the larger companies go to great lengths to prove they are using the ISO test - rather than mimicking the human ear.  It is a bit like paying with reserve currency VS gold coin.  One is standard, while the other has real value

Other than "peak loudness", the question of how unpleasant and attention grabbing the sound is matters a great deal.  High fidelity sound recording can help with the latter.   The shape of the sound trace may be similarly helpful:

Other than a lower peak amplitude, how abruptly the sound starts probably has a large effect on "unpleasantness".   The total area suggests the energy contained in the sound.  A longer sound carries more energy, even if the peak is lower and starts with a long ramp, rather than a "wall".

The attached speculative sound traces suggest; bare muzzle; conventional LDC; and Benelliboym1 (A or B):

[Outer_Rondacker]

I made a support for the barrel to the shroud with an O-ring. I spun the thingivers internal with the drill press and use a dremel on a fixed arm to cut in a grove for a O-ring.

Jolly good.

It would be useful to post some pics and some specs, if you have them.

I would love to and will just as soon as I get my cameras back. They are all set up for time laps from one of the prints we did. Your design. I was going to put out the video and send you the link but life has gotten in the way.

[subscriber]

Looking forwards to the time lapse video!

[JimD]

Sorry, I did not notice the question about the design of the shroud to barrel spacer until a few minutes ago.  It is open.  It seals to the shroud with two O-rings and is secured to the barrel with a grub screw but the sides are open.  I'll include a couple pictures. 

While I had things apart I took a couple pictures of the in shroud moderator John gave me.  When I put it on my gun I did not expect to see a significant benefit.  It is quite simple with angled air deflectors.  I positioned the device about where it would be inside the shroud.

I also positioned my hand near the holes in the shroud while I took a couple shots yesterday and there is a noticable puff of air that comes out. 

I think the sound it makes with this device does seem to be elongated - last longer.

Another test that would be interesting would be to ask a neighbor some distance away to comment and/or record what they hear.  It's subjective but it is also pretty much the point. 

[subscriber]

Thanks, Jim

Do you have stuffing in the rear of the shroud?  What do the holes there look like?

[Mr.P]

This is a long and very interesting thread.  Very dense comments with lots to follow even in individual comments.

Would anyone be willing to create a quick TL/DR for those who would like to
 follow and/or contribute?

I was just wondering myself which of the few ideas I have would be worth posting here, and I don’t want to waste your time with unrelated ideas or things you’ve already discussed in detail.

For example, have you guys systematically tried varying chamber sizes?  I recently had an unusual experience (for me) trying to quiet down a .357 aea to a tolerable level.  I tried a variety of baffles and spacers and materials and was getting differences but only small differences (to my ear for what that’s worth).   On a whim I swapped the position of two chambers of different volume, and found rearranging chamber order to have a strong effect: there one spacer combination with just a couple of baffles that was an obvious auditory outlier to all the dozen other combinations I had tried.  I say “on a whim“ because I have been following what I thought was the proper way to sequence the chambers based on what I have read here and there.   since I wasn’t getting the results I wanted I just flipped it around for the heck of it and there was the quiet I was looking for.  In this case having the largest chamber at the end of the LDC and a smaller first and second chamber in front.

My experimentation was all practical just based on my ability to tolerate doing some shooting in my garage, but for my own tinkering in the future, I will be trying to optimize chamber size and arrangement first because it seemed to swamp the other variables I was trying out.

I don’t know if this comment is relevant to the thread or not - i know you all mentioned uneven chamber size at one point but I am not sure I saw any messing with the order the unequal chambers are arranged in. Worth a try if not. 

[JimD]

No stuffing, 8 holes evenly spaced #56 drill bit, .046 diameter.  4 holes are about an inch from the receiver end of the shroud and 4 are about 1.5 inches from the same end of the shroud. 

[subscriber]

No stuffing, 8 holes evenly spaced #56 drill bit, .046 diameter.  4 holes are about an inch from the receiver end of the shroud and 4 are about 1.5 inches from the same end of the shroud.

Thanks Jim

Can you measure or evaluate sound with the holes taped over, and open?  Tape wound around, so it does not  lift off.

Measurements opposite the muzzle and a meter away to the side; and a meter off to the side of the rear of the shroud?  Rather than me predict what I think will happen, a deliberate eval would be useful.

You could also eval or measure sound from further away, but I think the readings will merge pretty soon into the same average.   Any deliberate evaluation that produces repeatable results would be useful.

[subscriber]

Marco,

What do you mean by TL/DR?  Are you asking for a short summary?  I find "short" very difficult .  Here goes:

There are many contradictory recipes for effective LDCs.  I am trying to make sense of them by "looking at" lots of data.  For instance; the Marauder is the benchmark for quiet.  It uses multiple short fixed length conical baffles.  Weihrauch uses 3 large uneven chambers to equally good effect.  Neither of these approaches is the only, or best one.

How one ranks LDCs has a huge effect on which approach is "better".  I am open to more than one way - my only criteria are that it makes sense and does not violate the laws of physics - not on closer examination - even if it appears so on initial impression.

So, any data that provides a clear signal for "better" and "worse"; achieved by a single configuration change is useful. 

My goal is to develop better understanding.  My working conclusion (subject to change) is that there are several overlapping principles involved, where one or more might dominate for a given design.   Other designs depend on other principles to work equally well.

If you want more detail, that would violate the "summary" request.  Besides, I think I have probably stated my thoughts about this throughout the thread; as lucidly as I could at the time.   I know that the probability of someone reading a lot of text goes down, the longer it is.  One is either motivated to see if there are useful nuggets in there, or not.  I try to skim efficiently, if I don't have time.  Ditto; if I "already know" about something someone states in "too much detail".

If your garage testing produces clear advantages to a given configuration, that needs to be reversible and repeatable.  Else it could be due to the garage door being open when it is warm, and partially or completely closed when cold.  I state this as an example of an apparent system response to a deliberate variable; not as an expression of lack of confidence in your abilities.  Systems often respond to incidental variables.  It is easy to attribute such responses to the factor/s we changed deliberately.

How does one deal with test methods performed by multiple people?  I am not arrogant enough to demand a given test protocol.  I prefer to let people do what they can with what they have; providing the same setup is used for all comparisons.   If there are signals of trouble, then I politely ask the right questions and make suggestions to trouble shoot and improve the measurement system.  Having sound levels clip, was such an instance recently.  A too close loud trap, dominating the muzzle report is another obstacle to actively prevent.

[Mr.P]

That’s perfect.  So in addition to solving the particular problem for the original poster you all are just exploring various factors that might let one squeeze a little more out of a particular available space.

How about wet moderators?   I can think of lots of reasons why this is not a good way to go but I’m certainly curious about designs that use water for dampening.

[subscriber]

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.

[WhatUPSbox?]

I also positioned my hand near the holes in the shroud while I took a couple shots yesterday and there is a noticable puff of air that comes out. 

There have been several posts where people reported on what they cleaned out of their LDC/Shroud. There was no additional information on what the dust/gunk was made of (lead? mold release? other?) but venting towards the face may be something to avoid. It may be interesting to wrap the holes in a couple of layers of tissue paper and see if anything is captured after a tin or two of pellets. I'm guessing it is very pellet dependent.

[Bob Pratl]

There have been several posts where people reported on what they cleaned out of their LDC/Shroud. There was no additional information on what the dust/gunk was made of (lead? mold release? other?) but venting towards the face may be something to avoid. It may be interesting to wrap the holes in a couple of layers of tissue paper and see if anything is captured after a tin or two of pellets. I'm guessing it is very pellet dependent.

That's a very good point, a few years back there was a post on adding a piece of a 1" thick donut, cut from a Magic Eraser between
the barrel and shroud to cover the vent hole. This stopped a good percentage of the lead dust which could be seen after cleaning it.

[JimD]

I tested for sound with the holes taped over and untaped a few minutes ago.  My shooting bench is on a side porch of my house (gives me 8 yards more distance) so that was a bit of an issue with meter placement a meter to the side of the gun.  But I used a scrap 1x4 to support the meter and got some measurements.  I measured a meter to the left of the gun, about 5 or 6 feet from the house. 

With the holes untaped I got 84.3, 85.6 and 85.1 db ahead of the muzzle about 1 foot and about 1 meter to the side.

Back to the side of the vents in the shroud I measured 97.4, 87.3, and 86.9 db.

Then I put aluminum foil tape over the holes.  I wrapped it around but it was wrinkly when I started and got more so when I applied it.

I measured first to the left of the vent hole and got 85.1, 84.9, 85.2 db

Then I measured at the muzzle end - again about 1 foot forward of the muzzle and a meter to the side - and got 90.6, 95.4, 82.8, 82.8, and 91.6 db.

The 82.8 readings bothered me so I pressed the foil tape down before the last measurement - and it went back up.  So I think the tape started leaking.

Seems to indicate that at least with this moderator, the vent holes help the report at the muzzle but increase it slightly at the shooter. 

I had exactly the same holes in the shroud when I tried first the Tanto and later the larger moderator John sent.  But without testing I have no idea if it helped or hurt these more conventional moderators.

[Mr.P]

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.

Makes sense -  thanks for that explanation.

[Fate]

Saw this: https://www.airgun101.com/sub12-airgunners/video/gta-grip-review-zero-db-silencer-quiets-down-the-air-venturi-avenger-gta-airgun-review. and since it was about an Avenger thought it would be of interest here.

My own experience with a "barking" air rifle (.22 Huntsman Revere) and the 0 db Silencer in the video is that it's hard to believe in use. I have a much bigger and heavier moderator I'd been using and was skeptical about the use of the small and lightweight 0 db... but if anything it is quieter than my big moderator (Falx). DS chooses the 0 db for use in its advertising, which was why I decided to try it. It's incredibly light and small making it aesthetically attractive (to me) but its sound reduction is why it will stay on my rifle.

I haven't followed this thread religiously and my parsing of posts didn't show this moderator as having been tested with the Avenger but if it has, my apologies.

PS

The video is hosted by a website that says GTA, Gateway to Airguns.... and it has great video information. I have been unaware of this website after years here on GTA. My bad I guess for being ignorant of this part of GTA, but it should be "advertised" more IMHO. Seems it should have been mentioned in the first posts of this thread?

[TorqueMaster]

I expected to have more testing time today, but mother ... nature did not cooperate.  I set up the phone at 100' away, about 5' off the ground and maybe 2' to the right of the pellets' path, and shot towards my 300' target area.  Walking forward, took shots from roughly 100', 90', 80', etc, ... the last was from about 3 feet, not zero, from the phone.  Stock .22 Avenger, 14.3 CPHP roughly 900fps, no LDC.  The phone was providing a constant metronome sound to verify the recording was not changing gain.  The main point of this was to find a distance where the recording does not clip, and use that, or slightly further back, as a standard distance to use comparing LDCs to the stock Avenger.

Sooo..none of the shots caused audio clipping, not even from 3 feet away.  I had clipping before at 6 inches, and at 10'.  I think moving away from the previous location with concrete sidewalk and outbuildings, into a grassy area, made a difference.  I also had the phone mic pointed 90 to the pellet path (brain fart, I meant to point it at the muzzle, like before) so now I have multiple variables to deal with. 

I ran the audio through Audacity, to measure average sound levels of the shots compared to a constant background noise.  I tested with data windows from 50ms up to 300ms wide.  The shorter the window, the louder the average sound.  For instance, a 300ms sample read +39.4db (over background of 40-50db), and same shot, 50ms sample gave +46.9.  Expected results, and see no reason to choose one window size over another, except shorter windows exclude part of the discharge waveform.

I also compared the results of walking closer -- I ended up with 10 shots, so I was moving more like 11 feet each time -- sounds should get louder. Well...not really.  At every sample window size, the result is similar, so here's the values for 125ms "fast" window from 100, 89, 78, 67, 56, 45, 34, 23, 12, 3 feet:
43.0, 48.0, 48.1, 48.8, 47.5, 47.1, 47.5, 49.0, 48.8, 50.4.  It did generally get louder, but no idea why it dips in the middle.  Only one shot per distance, so I'll for sure need averaging to get believable results.  Also I expected a lot bigger db rise from 100 feet away to 3.  I got +7.4db, physics says, if I'm reading the chart right, it should be more like +30db!  Is grass and trees absorbing it all?

The metronome was rock solid on constant db values, no significant gain changes observed.

Of course it was starting to rain on me and my phone at this point, so no LDCs were compared at any range.

I may repeat the walk test for clipping with the mic facing the muzzle.  If the results do not change... I'll guess I'l choose the phone to be closer to the muzzle, since that's more convenient.  All I can think to do is get the gun back on a rest (same spot every shot) aiming at the same spot every shot, to eliminate all angular changes.  And let the testing begin...

Forum software goes brain dead if attachments are too big or wrong type.  Trying again, hopefully this post isn;t a dupe.  It iisn't allowing a 2.1Mb zip file.  2100kb.  Less than 3200kb.  I'll try just the .mpg here

[TorqueMaster]

Wav file in .zip ...maybe...

An Error Has Occurred!
Your attachment couldn't be saved. This might happen because it took too long to upload or the file is bigger than the server will allow.

Please consult your server administrator for more information.

[subscriber]

I tested for sound with the holes taped over and untaped a few minutes ago.

Thanks, Jim

It seems there is no "free lunch". 

I think that if you added about an inch long "slug" of loosely stuffed cotton wool at the rear of the shroud, the sound measured in both places as you did might come down slightly.  With no change between leaving the shroud holes open and taped over.  The purpose of the cotton wool would be to act as a poor pressure wave reflector.   It would also choke off the shroud holes, assuming they don't extend forward further than the wool.

[subscriber]

Bob,

Thanks again for your tremendous effort.

I can hear a change in your recorded sound file.  The shot sound is sharp and short initially; then becomes more rounded and longer later in the file.  This, while the metronome sounds the same. 

When you record sound from far away, the high frequency component is filtered out and the square wave slap at the start is more apparent, because more of that remains.  When you get closer, more of the high frequency component is captured because less of that sound has been absorbed by the air and the grass nearby. 

For sound recordings, with or without wave forms, capturing the whole shot event is useful.  For traditional peak sound measurements, a short window is better for reporting the peak.  Else, a lot of the end down taper of the sound is included in averaging over the sampling period.  As you numbers show, that reduces the peak value reported.  Very significantly.

As long as the widest part of the sound wave near the leading edge falls in a sampling period, the peak sound will be captured.  The fact that many more such samples occur and are discarded as the sound tapers off does not matter to an accurate peak sound pressure reading.  That is why it is industry standard to use a short sampling window.

An analogy of short window sound capture is having a motion sensing security camera running all day.  When you review footage, only the few second when an uninvited guest climbs over your wall are captured.  That is the "field of interest".  Averaging in the rests of the day suggests that nothing much of significance happened all day.  When something significant did happen, over a much shorter period.

See my attached sketch of shot sound sampling periods:  The fast sample "A" represents a standard peak sound pressure reading.   Sampling period "B"  may include the full event, but averaging over such a longer period reports an artificially low peak sound.

Now, that is not to say that longer sample period average readings don't have value.  I think they do tell us something about the total energy released.  But long average values should be supplemental.  Not replacements for short sample period measurements.

If you want to do something to reduce crime, you need to know the stats by ZIP code and block.  Averaging over county, state or country suppresses the data required for targeted action.   Sound measurement averaging over too long a period similarly represents a loss of resolution.  If the goal is to reduce the peak sound value to a more comfortable value that cannot be heard as far away.

I think your sound readings dropping off in the middle distance is a strange interaction between sound frequency sensitivity of your instrument, high frequency absorption of the surroundings, and the increase in both peak and average sound over a given sampling period.

Again; thank you for your perseverance.