(2/12/19 update) Moderator Design, Testing, and Evaluation

Forums PCP Airguns (2/12/19 update) Moderator Design, Testing, and Evaluation

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    STO
    Participant
    Member

    Good to hear. :) 

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    STO
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    Okay, so I finally have some tests on a 1/2-20UNF design. There is a real loss of physical volume and length, internally that is, going from a Crown shroud mount to a 1/2UNF. There are a couple older rev. moderators and prototypes out in the wild now, and I've gotten wildly conflicting reports back on how loud they sound relative to other moderators out there. The consensus seems to be that they take the bark off the airgun while being small and very light weight though, which is the point of this form factor. 

     

    Adapting the original concepts to a 1/2UNF universal application is more challenging than it sounds. The FX Crown's unique design, and unique associated moderator, was more than just a gas diode. The large thread allowed for significant flow to be tapped off from around the bore. Were size no constraint a blast chamber integral to the moderator could be used to fulfill the same function, however this is volumetrically inefficient when it comes to this level of sound attenuation. Further, the lack of a flow-through system along the perimeter will put additional load on the gas diodes as there is no alternate pressure relief, they simply have to eat it. This leads to one final concern, which is air stripping. Without the expectation of some sort of muzzle brake on the rifle to pull turbulent gas off the pellet near the muzzle, the moderator must now possess this as well.

    So, how to go about it? Well in this case I went with a three stage system. The first stage is, of course, the aforementioned blast baffle/air stripper. A symmetrical conical baffle designed to bear the brunt of the blast out of the airgun's muzzle, and cleanly strip that turbulent air off the pellet to maximize accuracy. Following that, the second stage, are two of a new and more efficient gas diode which stops or at least delays forward air flow. Unlike the rev.1 and rev.2 gas diodes, which were comparatively volumetrically wasteful, these waste much less of the precious internal space. They also offer cavernous flow-chambers, reflexing vastly more air. All in all, they are a massive design improvement, and I really couldn't be more pleased with them. The third stage is something incorporated all the way back in the rev.2 gas diodes, sound damping. Why should flow and sound in a moderator be the same from end to end? It wouldn't, not if the moderator is working properly anyway, so it stands to reason the design of the moderator itself should change from end to end to match this. Most moderators out there seem to either focus on flow disruption or sound damping, but my approach of first flow stopping then multi-layer sound damping appears to be more effective than either flow stopping or sound damping alone. The CAD images don't capture this sound damping structure well, showing just the skeleton around which is it installed, however it is built of high surface area foam, a new type of foam I’ve never before featured, and rubber. Again this is a combination of materials arrived at after much testing of different combinations and designs.

     

    Before we get to the test results, I also want to bring up something I’ve touched on before, which is peak sound vs. total sound. It is difficult to relate and difficult to quantify, this concept of total sound, because in essence you’re trying to put a number of a squishy human perception. I’ve done a series of experiments with RMS (root mean square), however so far these have not yielded good consistent data. You see there is more to a moderator than just the brief “uncorking” sound produced when the pellet exits and the maximum pressure wave gets out, there is also the sound of your moderator draining that pressure slowly over time. A bare muzzle may have a very high peak, but the subsequent drop back down to zero will be very rapid. Meanwhile a moderator design which effectively slows the flow of air out may have a very quiet peak however because the moderator spends a long time, relatively speaking, draining out all that air until it equalizes with ambient pressure, it may produce more total sound. How this relates to human perception of loudness is more complicated still, because both intensity and duration of sound will affect perception. At longer ranges though it seems the peak is what is most audible, and most likely to alert a prey animal or nosy neighbor. Thus quantifying this is next to impossible, which is why we associate a representative sound readout with each data sample. Below you can see an example in high tech MS-Paint, with the peak (what I measure) circled in purple, while the subsequent sound profile bracketed in teal.

    So enough foreplay, how about test results? I used the same protocol as always, with the moderator separated from the pickup by 1 meter, perpendicular to the muzzle. Excluding the Crown Shroud test, which was done with the shroud extended, all tests were done with the Crown shroud collapsed. I also pulled the old acoustic foam filled moderator out to once again provide fair comparison against a “typical” foam/felt filled moderator (your hair curlers and washer baffles) design of equivalent material, design, volume, etc.

     

     

    Shroud Extended – 214.4

    Been there, done that. It is loud. It is the baseline, it is what it is. I always insist on repeating the baselines because some days, some atmospheric conditions, god knows some moon phase just results in different numbers. So I always strive to meter the baseline/s so that the later data has good context.

     

     

    Rev.1 Gas Diode – 122.6

    Again, another baseline. The rev.2 is a major design improvement, but it is always good to see progress. Here we can also see one of the things which I strove to improve upon, which is the quantity of noise produced AFTER the peak.

     

     

     

    Foam Filled Moderator – 172.4

    Again, this is an open cell foam filled moderator, intended to be a test analogue for the common high surface area moderators out there which use felt or foam. Here we see a phenomenon I alluded to before, all the way back in the first tests. The sound just tapers faster on these sound damping, rather than flow-stopping, designs. So you get higher peak sounds, the moderator is definitively louder, however it empties that air more quickly and more quietly. We can see that in the image, the initial spike is quite high, but the subsequent taper is more rapid. One has to wonder if part of the reason why felt/foam baffle-less moderator designs are so popular because of this phenomenon: while they may technically be louder, particularly at close range some people may perceive them as quieter. Borrowing or purchasing a popular and highly regarded commercial moderator design, such as a Donny FL, might be a good idea both to get a better understanding of what sound profiles they produce but also to provide a baseline for comparison that other people can relate to.

     

     

     

    Rev.2 Gas Diode – 115.3

    Still doing comparisons and baselines, what can I say? The second lowest peak, and one of quietest total sound profiles of all the moderator designs tested today. Why? Well this moderator you'll recall is a combination of gas diodes and sound damping in the center, and with off-axis flow-through around the perimeter, again with sound damping toward the muzzle end. The result is a design which slows the initial blast, and effectively and quickly drains the pressure and quiets the resultant sound. Thus there is both a fairly mute peak, and good quick tapering of the remainder of the sound profile.

     

     

     

    Rev.4 Gas Diode (1/2-20UNF attachment) – 81.2

    So this is the culmination of all this testing, the moderator which this is all about. More efficient gas diodes and a sound damping system work together to bring the peak down to the lowest moderator yet tested. And I don't mean just in this round of tests, I mean of all time; this is the quietest airgun shot I’ve ever sampled. I was surprised and pleased, to say the least. Remember this moderator maintains the same overall length, 120mm, as the other designs which ALL were direct thread into the Crown shroud. Integrating a 1/2UNF thread mount means you now have to eat up precious length and volume inside the moderator for the threads, so I would have been exceptionally happy if it were able to simply match the rev.2 gas diode, beating it by a significant margin was an unexpected but pleasant surprise. You'll notice though that the peak is not much higher than the rest of the sound profile. Both of the previous gas diode designs (revs.1&2) had pickups around the perimeter, out of the bore axis, which tapped off gases from inside the Crown Shroud and likewise vented them out of line with the bore. This is more useful than you might think, as it allows you to place dampers directly between the sound source and the exit for at least some of the air. This isn't possible with a 1/2UNF mount, for obvious reasons. While such a design could hypothetically be integrated into the blast chamber, with the loss of volume and effective length it just wasn't feasible thus was omitted. Even still though, it is great performance by any standard, so I'm very happy with it. 

     

    I think my next step from here is getting my hands on a couple popular moderator designs from other manufacturers and getting some hard numbers on them. Maybe it is a harebrained idea, but anyone who has a moderator they want to loan for me to meter I'd like to get a couple together. All results will of course be published along with sound profiles here, and moderators returned to their owners after testing. 

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    Tomiboy
    Participant
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    Impressive!

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    Bob_O
    Participant
    Member

    😮

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    Macros
    Participant
    Member

    Wow, getting better and better. Sincerely hope I can get my hands on one of these one day 👍🏻

    I'd send you my silencers in a flash if I weren't half a world away. Hope you get plenty!

     

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    ackuric
    Participant
    Member

    I'll go the other way with it, send me your moderator, and I'll test it against several of mine using a universally accepted sound rating system…and then I'll send yours back. I cannot interpret any of your data, nor do I know what the 81.2 represents, 81.2 of what? I haven't seen someone dodge the Decibel system so much when it comes to sound suppression. 

     

    No one, and I mean no one, is more excited then I to see innovation, or progression in our industry…but there has to be some form of expression that removes any and all language barriers, and that is simply a Decibel rating…Rev2 seems to taper off much more aggressively on the above charts…yet it was much louder? I really am unable to both read the graph, and the number posted  below it to correlate any significant difference between the two.

     

    I  mean I hate to be THAT guy but…

    https://en.wikipedia.org/wiki/ITU-R_468_noise_weighting

    https://en.wikipedia.org/wiki/A-weighting

    https://en.wikipedia.org/wiki/Noise_calculation

    https://en.wikipedia.org/wiki/Acoustical_engineering

     

    Please use an INTERNATIONALLY accepted rating system…without that, I don't care if you invent a 1" silencer that is quieter than any 5" silencer on the market…I won't believe it till the above systems  are used…

    • This reply was modified 1 week ago by ackuric.
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    BlackICE
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    Any weighting system is a  reduction of the actual data. It would nice nice to have the raw data as a frequency spectrum or a calibrated digital capture of course calibration would be critical to set the DB level. Then one can run any type of weighting they want. In real life measuring sound to achieve the desired goal is very difficult thing. Do you want to measure in the middle of a desert and with nothing around? That would be a lot different than measuring with a cement building behind you and lush forest in front of you. In real life there are a lot of frequency-dependent reflections and absorptions by the environment that impacts the sound you and an observer may hear.

    I think STO's  raw waveform data is useful in comparison between his various runs. One can't make any conclusions on how loud they are relative to anything else but his own test. Nevertheless they are still useful for determining which design is quietest.

    • This reply was modified 1 week ago by BlackICE.
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    STO
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    ackuric

    I'll go the other way with it, send me your moderator, and I'll test it against several of mine using a universally accepted sound rating system…and then I'll send yours back. I cannot interpret any of your data, nor do I know what the 81.2 represents, 81.2 of what? I haven't seen someone dodge the Decibel system so much when it comes to sound suppression. 

     

    No one, and I mean no one, is more excited then I to see innovation, or progression in our industry…but there has to be some form of expression that removes any and all language barriers, and that is simply a Decibel rating…Rev2 seems to taper off much more aggressively on the above charts…yet it was much louder? I really am unable to both read the graph, and the number posted  below it to correlate any significant difference between the two.

     

    I  mean I hate to be THAT guy but…

    https://en.wikipedia.org/wiki/ITU-R_468_noise_weighting

    https://en.wikipedia.org/wiki/A-weighting

    https://en.wikipedia.org/wiki/Noise_calculation

    https://en.wikipedia.org/wiki/Acoustical_engineering

     

    Please use an INTERNATIONALLY accepted rating system…without that, I don't care if you invent a 1" silencer that is quieter than any 5" silencer on the market…I won't believe it till the above systems  are used…

    I'm sorry, were you not the one just a few posts ago extolling the virtues and accuracy of measuring moderators with your cell phone app? I even, rather reluctantly, provided you with the cell-phone app "data" in decibels after an explanation of why that doesn't work. You might want to refer back to this post where I provide the test results in "decibels" and both explain and show why your technique of measuring decibels is inaccurate: 
    https://www.airgunnation.com/topic/fx-crown-bespoke-moderator-tesla-gas-diode/page/3/#post-423262

    I see in the interim you've become a wikipedia expert on acoustical engineering, and I assume reversed your stance on the benefits of using a cell phone app instead of a sound meter? Tongue in cheek aside, if you're just here to be oppositional I would ask you to kindly leave the thread.  

     

     

     

     

    BlackICE

    Any weighting system is a  reduction of the actual data. It would nice nice to have the raw data as a frequency spectrum or a calibrated digital capture of course calibration would be critical to set the DB level. Then one can run any type of weighting they want. In real life measuring sound to achieve the desired goal is very difficult thing. Do you want to measure in the middle of a desert and with nothing around? That would be a lot different than measuring with a cement building behind you and lush forest in front of you. In real life there are a lot of frequency-dependent reflections and absorptions by the environment that impacts the sound you and an observer may hear.

    I think STO's  raw waveform data is useful in comparison between his various runs. One can't make any conclusions on how loud they are relative to anything else but his own test. Nevertheless they are still useful for determining which design is quietest.

    So I don't generally save these captures in full resolution, as you describe, as the files are quite large. There is no reason I can't though, if you wanted to have a look.  Each screencap of the capture is just one of multiple samples taken which I select by hand because it looks representative of the group. You're completely correct though that environment will significantly affect the results, making comparability even between perfectly calibrated meters used in identical protocols differ from day to day. This is why I always try to repeat the baselines, so people have something to compare against. The lack of a standardized testing protocol for airgun moderators, reliable/quality  instrumentation, the variability between airguns, and the outright lack of other other data further makes me question the value of trying to convert my numbers into decibels.

    On the off chance you haven't slogged through the last four pages to find my explanation of why I don't provide numbers in decibels, I'll give it again here:  

    This meter hasn't been calibrated recently enough to be convincingly accurate. So while I actually have decibel conversions for each test, I refuse to publish them because I would consider it bad data, and it is irresponsible to publish bad data. Results within test groups have good precision, just likely not good accuracy, so I can happily provide the raw numbers knowing that they are a good reflection of relative performance, just not absolute performance. It seems like the right thing to do. I hope that makes sense and seems reasonable.  

     

     

    Macros

    Wow, getting better and better. Sincerely hope I can get my hands on one of these one day 👍🏻

    I'd send you my silencers in a flash if I weren't half a world away. Hope you get plenty!

     

    Thanks mate, I hope so too! 

    • This reply was modified 1 week ago by STO.
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    Tomiboy
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    I'd send you one too, if I had one! My last Donnyfl sumo ended up going with the gun I sold when I gave up airguns. That lasted about 6 months and I'm back! LOL. I am waiting on one of these new ones. I was good with the Crown only one, but it would be nice to have one you could switch to different guns

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    STO
    Participant
    Member

    So I've already gotten a couple offers of loaner moderators. Thank you everyone who has offered so very very much. I believe I've now responded to everyone directly, however I want to post these instructions here as well just so (hopefully) I don't have a moderator show up without any information on it. 
     

    1) Ship with delivery confirmation and insurance so you know it arrives, and can make a claim if it doesn't. All moderators will be returned with a tracking number (which I'll PM you) and will be insured! 

    2) Label your moderator clearly. Put a piece of masking tape on the side and write your return addressforum handle (so I can get in touch with you, and give you return tracking info), and your moderator's value. (need a value to insure it for. Please be aware that if the worst does happen and an insurance claim is necessary, you'll need to show a product listing somewhere with an equivalent value) 

    3) Package your moderator safely and securely. 

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    STO
    Participant
    Member

    So it is good, before performing an experiment, is to generate some hypotheses which will be challenged. I thought I should do that here and now, so if I'm completely off base and look like an idiot there will be a record of it and we can all have a good laugh at my mistakes. :) Anyway, the following are my hastily written musings on the subject, apologies for any omissions, errors, or just being flat out wrong once the testing is done! :P

     

    I have seven real hypotheses surrounding this testing:

    Volume will be the primary determining factor of performance. Within a given can architecture this is obvious, but I expect this to transcend designs. Some will obviously be a bit more efficient and others a bit less efficient, but I don't think any design will be so much better it breaks the correlation. Put another way, across can designs, there will be a fairly high r value correlation between overall volume and how quiet the moderator is.

     

    Length will be a secondary factor. Again it seems obvious, the longer the distance the air has to travel, the more time and stuff can be put in the way of the wave front to dissipate it. I will be curious to see how this plays out.

     

    Mass will be a tertiary factor, possibly getting lost in the noise (pun intended) between different designs which use their mass more or less efficiently. Mass dampens sound, no two ways about it, but mass is also the enemy because nobody wants a big heavy stick at the end of their rifle to haul around and cause barrel droop/POI shift. Using that mass effectively I think is going to really separate the men from the boys so to speak.

     

    I think I'm going to eat some humble pie here. I think I'm going to discover that both several of my hypotheses are wrong and also that my moderators aren't as quiet as I hope they are. There are a few early designs and prototypes running around in the wild now, and I've received wildly varying feedback from users regarding how quiet they sound, some claiming they sound quieter than cans much much larger than they, others claiming (some on the identical can) that they are louder. So yes, in short, I'm expecting to eat some humble pie here. I realize this is possibly a once-in-a-lifetime opportunity to get a whole bunch of moderators together and test them all at once though, so I have no intention of squandering it. I'm working frantically to get all kinds of crazy experimental designs together to test, even roped in a couple buddies with an interest in the subject to help. Throw everything at the wall and see if anything sticks eh?

     

    I think there will be some level of disconnect between measured results and perceived performance. Part of this is just down to how the human ear adjusts to sounds, and is really really bad at telling if something is louder or quieter. And part of this is what I've been banging on about all this time that, particularly at close range, total sound profile and peak sound output are both factors in how loud something sounds.

     

    I think at greater distances, peak sound output will have a more noticeable impact on how loud the moderator is perceived as being. Stated another way, that loud initial pop I think will be what you primarily hear at a distance, and so will be more important. This will be true for whether you're trying not to scare game, or keep your nosy neighbors on their side of the fence.

     

    And finally, I think it is a bit inglorious to say, but I expect at least one person will be ticked off. Maybe they won't like my methods, maybe they will be upset that my results differ from theirs, maybe they will be unhappy that my tests don't cast their favorite moderator/brand in a great light, or maybe just just don't like the cut of my jib. Either way, I expect someone will be upset by this. :/

    Thats all for now. It is going to be a busy weekend for me. Lots of scrambling and prep work to do. And an IMMENSE thank you to everyone who offered up moderators for testing. As far as I'm concerned, you guys are the stars of this. All I'm doing is crunching numbers and playing with toys here. :)

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    Hepotter
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    Member

    It makes no difference if a silencer is so quiet that even a dog can't hear it…if my neighbors can't hear what I'm doing, then it's quiet enough.

    The science of sound moderation can result in the "paralysis of analysis"…

    All I want is enough "quiet" so I can have some backyard fun!  

     

     A video of my neighbor discussing noise, wildlife harassment, and doing shit she doesn't approve of.

     

     

    Regards to all,

    Kindly 'Ol Uncle Hoot  

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    bandg
    Participant
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    Others may have different needs.  

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    Zonk
    Participant
    Member

    Great neighbor Hoot, that's why my neighbors are all 1/2 mile away or farther.

    Zonk

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    Revoman
    Participant
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    I think she might be climaxing….

    I for one, have thoroughly enjoyed this thread and commend your efforts.  Thank you!

    • This reply was modified 4 days ago by Revoman.
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    Hepotter
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    Zonk

    Great neighbor Hoot, that's why my neighbors are all 1/2 mile away or farther.

    Zonk

    Zonk…as I recall, on the other forum you said it was the smell that drove them away!!!

    .

    Actually, I enjoy this thread, these people are way smarter than I am. 

    But, sometimes it's good to stir up the dust, to see which way the wind is blowing…makes folks sit up and pay attention.

     

    Regards,

    Kindly 'Ol Uncle Hoot   Back off bitches…you're crowding my roll…

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    MikeVV
    Participant
    Member

    Interesting read, but –

    Silencer = by definition of the word, yes

    Mitigator = by definition of the word, yes

    Muffler = by definition of the word, yes

    Damper = by definition of the word, yes

     

    But "moderator"…by definition…not so much..!

    How come folks feel the need to make up new definitions for existing words ?  Make up a new word to use with a different definition.

    Or…just use regularly used words to get a point across.

     

    Mike

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    STO
    Participant
    Member

    HOOT! Good to see you're alive and still kicking. Don't you dare change one bit! 

     

    Revoman

    I think she might be climaxing….

    I for one, have thoroughly enjoyed this thread and commend your efforts.  Thank you!

    Thanks mate. :) 

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    steve-l
    Participant
    Member

    STO, I don't mean to rain on your parade, but the following are things I have discovered over the years. It is possible to really limit this guns report, but you cannot limit the sound of these pellet's flight through the air nor limit the impact sound of the pellets striking its target and those are both loud.

     Complex internal designs often do nothing to limit the sound volume. In point of fact they can and do effect accuracy. Sometimes simplicity and symmetry is the best answer. I have designed many silencers and some didn't work at all. When an air rifle is fired there is a pressure differential between the front and back of the pellet. As the column of air in front of the pellet is accelerated down the barrel any resistance to this air column changes the front to back  differential pressure and hence the pellet velocity achieved. So part of the OP's testing regimen must be speed attenuation of the moderator. On my best design so far for my .25 Crown, I achieve 940 fps without the silencer using the JSB 25.39 pellet with a standard deviation of less than 5 fps. With the silencer mounted, the velocity drops to 900 fps with the same standard deviation of less than 5 fps.

    POI does usually change on the Crown. I think that is normal, but if the POI is repeatable, no matter the position of the shroud, then it is safe say that the cause is barrel droop and that simply is no problem. Just adjust your scope and don't even think about it anymore. On my best silencer my POI shifted down and right, but my accuracy and grouping never changed. It remained the same both with and without the silencer.

    If you experience a loss of accuracy, it is usually caused by turbulence. Once the pellet is free from the confines of the barrel, the existing pressure differential between the back and front of the pellet will cause the air behind the pellet to deflect around the pellet and try to out accelerate it. This is where baffle design becomes very important. The baffle(s) must deflect this accelerating air away from the intended pellet path and confine this air as long as possible and this must occur equally around the pellet. If this deflection is not equal, pellet deflection will occur and hence a loss of accuracy.

    Another old wives tale is the use of sound absorbing material INSIDE the silencer…..who cares? It is inside not outside. Now wrapping the OUTSIDE of the silencer with something, that makes more sense, as it would dampen any sound being emitted from silencer vibration,. I don't do it because it makes so little difference in sound, it isn't worth doing.

    • This reply was modified 3 days ago by steve-l.
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    STO
    Participant
    Member

    Hi steve-l

    You're not putting a pin in anything, at least nothing I'm doing. I appreciate you taking the time to give me your input. 

    As I'm sure you can attest, there is an immense amount of mythos, bad information, and bad test equipment out there in the airgun suppressor world. We all come at it with our experiences, biases, and prejudices, however being in the position of having at least adequate test equipment for comparison purposes I've chosen to intentionally ignore basically all of this well-intentioned advice. It gives me a fresher and more open perspective.

    That which is true will be borne out by testing, and the people who said it can take satisfaction in seeing themselves proven correct. That which is false will be demonstrated as such. Having a few airgun suppressors from various other companies showing up to be measured back to back will also, I hope, be an insightful look at what works and what doesn't. If you have a design you'd like to submit as well, I'd be happy to put it in the lineup. 

    Cheers mate! 

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