(5/6/19 update) Moderator Design, Testing, and Evaluation (the big test)

Forums PCP Airguns (5/6/19 update) Moderator Design, Testing, and Evaluation (the big test)

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    Hawkeye51
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    Member

    STO

    First, congratulations on generating such a fascinating read, ( 4 pages in one gulp) I just discovered the thread today. I know nothing about the technical aspects of sound or measuring it. However being in the medical field, I do understand the the need for accurate and repeatable data accumulation and measurement .

    I also have an appreciation for how widely varied the human senses can be from one individual to another, e.g.  "Stan Lee's Superhumans".  We can have an individual anomaly that makes us more or less sensitive to various frequencies and or overall decibels etc. etc.. I realize that the following suggestion completely goes against my original statement, but since this is such a unique opportunity to compare a myriad of Moderators, from basic to exotic (cheap / expensive) why not add a totally non scientific catagory of "perceived efficiency"?  The NBC show "The Voice" comes to mind, where a helper or two blindly listens to the different Moderators and subjectivity give them a grade. This part of the testing could be done after all of the data is accumulated and fashioned like an eye exam ( "a" or "b" ).

    I'm extremely interested in the scientific results of the testing,  but think this would add an extra element of "fun" to the results. Wishing you the best, and looking forward to seeing how your design compares to the rest of the pack. 

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    STO
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    So for everyone who has loaned me moderators to test, thank you so very much. The last of them I'm waiting for is scheduled to be delivered today. From there it is just a waiting game for suitable weather conditions. As far as when that might be, the short term forecast says too windy and with various precipitation events. Looking towards the end of the week it looks like I might have a window of opportunity there, however at least in New England any forecast more than 48 hours out is…… well lets just be polite and call such forecasts tentative. ;) 

    It is my plan to do the testing, run all the numbers to make sure everything looks good and there are no screwups which need to be redone, and then when everything looks good ship everyone their moderators back. It may subsequently take me a couple weeks to write everything up and organize it with photos and get it into a vaguely coherent post, but I'd like to have everyone's moderators on their way back to them before even starting the writeup. 

    And that is pretty much the news as it stands. 

     

    Hawkeye51

    …..I realize that the following suggestion completely goes against my original statement, but since this is such a unique opportunity to compare a myriad of Moderators, from basic to exotic (cheap / expensive) why not add a totally non scientific catagory of "perceived efficiency"? …..

     

    So I'm afraid I'm not going to get together a cohort of blind monks to subjectively test moderators, however I do have every intention of adding my subjective observations on the subject as a simple supplement to the hard numbers. And not just sound profiles, but the designs and fit and finish of the moderators. The whole 9 yards basically. So long as I have them, why the heck not? I hope that will be sufficient. ;) 

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    Hawkeye51
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    I'm sure the "cohort of blind monks" will be glad to know that they are off the hook, never the less, I'm wishing you the best. 

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    STO
    Participant
    Member

    First off is an immense thank you to the half dozen or so trusting souls who sent me, a total stranger, what I have to imagine is well over a grand worth of airgun moderators. You guys are the heroes of this story as far as I'm concerned. Don't be shy to sound off if you want to take some public karma, but out of respect for your privacy and a potential desire to avoid any backlash I've intentionally avoided publicly naming any of you.

    So I want to preface this with a dozen different points before diving into the meat of things. I also want to summarize the test protocol, add a few important caveats, and generally reiterate a few things. Feel free to skip this section if you just want the results, but if you have questions you might want to revisit this section before asking because I might just have already covered it. ;)

    One of my best friends is SUPER into this, and when he heard that I was getting together other moderators he insisted on getting involved. I think it was something more along the lines of “your design sucks, you have no idea what you're doing, I can beat you at this.” The two of us spent a weekend in an incredibly crappy and hastily thrown together anechoic chamber (which really wasn't) rapid-prototyping, testing, eating cold pizza, arguing, tweaking designs, accusing the other of stealing ideas, rinse, repeat, etc., ad nauseum. By the time the weekend was over we'd both eaten some humble pie, learned a lot, tipped a few sacred cows (both our own and other people's), and improved moderator performance beyond what either of us had thought possible. (and it was a lot compared to my previous design) All of this was still done within my original 35x120mm envelope, which is cursedly small in terms of trying to cram things in, but means revisions can be cracked out much faster than a larger design…… and believe me, I know, because after this was done, for the sake of humor, I scaled the design up just to see what'd happen. It doesn't really stand to reason that a good small design would scale to a big one, but at least some of the principles you'd assume would be maintained….. right?

    Next bullet point I want to make is that nobody has paid me a penny to test any of these designs, nor were any of them sent by the manufacturer, at least not to my knowledge. I also don't have a bone to pick with any company that manufacturers moderators. My subjective qualitative observations on cans, both sound and manufacturer design/quality, are based nothing other than my own eyeballs and earballs. Take them for what little they're worth, which is to say the deranged ramblings of some random guy on the internets.

    Accuracy vs. precision is something that came up in an unfortunately contentious manner in another thread. Without intending to upset anyone, this discussion helped me put my finger on something I wanted to say about the test equipment I'm using to do this work. To define the two terms with an analogy, an accurate gun is one which will put the rounds around the bullseye, while a precise one may put the rounds nowhere near the point of aim, but it puts them all together in a close group. The reason why the numbers I list aren't in decibels is because I can measure the sound with a good level of precision, however I'm unsure of the accuracy therefore do not want to mislead by claiming the center of the target is somewhere that it is not. Each data sampling is actually done on multiple simultaneous pickups. You can see these as different colors in each image. This acts as a check on every single shot, if the two pickups disagree (rare) something clearly went wrong and I just repeat that shot. And there are multiple shots taken (five) for each test. In this way every shot is double-checked, and is an average of an average. All this, plus a little knowledge of the system, gives me a good confidence interval on the precision of the data recorded.

    The subjective ear is a tricky thing. I can empirically say which moderator is louder or quieter at it's peak, and this is the standard in the firearm suppressor industry, however this alone is NOT a strictly accurate reflection of how a person will perceive the loudness of the moderator or firearm suppressor for that matter. Particularly at close range, moderators with a lower peak but which produce more noise subsequent may sound louder. Different frequencies will also sound louder, and which frequencies these are will vary between people. This is part of why I feel it is so important to post an image of the sound profile, it gives a more complete glimpse into what the moderator is doing. To the greatest extent reasonable I've striven to blind myself while doing this testing, so I can write my thoughts on how I think each moderator sounded before diving into the numbers and sound profiles. It is an imperfect way of doing things, but I also consider my subjective observations to be secondary to the hard data.

    Something brought up by another member is frequency, and that this frequency will change with moderator volume. Each vertical line represents a millisecond, so you're all welcome to do a little napkin math and see how you think the predominant frequency changes between moderators. I've not correlated any of this to perception, so what exactly it means is hard to say. Obviously there are multiple frequencies going on here, and the visible snapshot is quite short.

    I expect, but have no data to support, that there may be differing relative performance between moderators on different hosts. Why? Because of the differing nature of the volume of air and sound they produce. A very small sound-damping focused moderator may perform very well on a low output target gun, better than a really really big high power moderator. But you wouldn't expect that tiny moderator to still be better if you put it on an Airforce Texan right? What is important here is that both moderators will be louder than before, but their relative positions of which is less loud will likely have changed. At this point it is purely a thought experiment, because I don't have a vastly more powerful airgun to test. It is also worth noting though that all the moderators here are made for small-bore use (being defined as sub-100 foot pounds and .30 caliber or less) and most attach via 1/2-20UNF. My host, an FX Crown, is running about 32 foot pounds in this test. This puts it in roughly the same power class as almost all use cases for these moderators. Even if we take the “extreme” end of the spectrum, such as an FX Wildcat II .30 cal with its 700mm barrel, that only puts out 69 foot pounds (ref. Utah Airguns' product listing). Or, put another way, if you look at a Utah Airguns caliber chart on the FX ImpactX page, you'll see the comparative shot count between 22, 25, and 30 caliber. The 30s seem to run about half the shot count of the 22s, suggesting twice the air consumption. I would therefore put those in roughly the same ballpark, as opposed to “big bores” which may output an order of magnitude greater air. Looking at the forums we mostly seem to be shooting 22s and 25s, which are maybe 25% different in terms of air consumption, not really that dissimilar and so I would expect to perform reasonably similar on these moderators, assuming an otherwise comparable host/mount. (most airguns are shrouded these days) I hope that reasoning makes sense to people, and to be clear I do NOT have test data to prove it, these are just my meandering thoughts on the subject.

    Aesthetic nitpicking is something I'm going to do for some of these moderators, not because I believe in it, but because some people really care about these things. I personally tend to be pretty happy with form follows function, and would rather get performance over beauty, however I can also very much understand why you want your 250$ moderator to look perfectly at home on your 2500$ Daystate. To that end, I go through and nitpick finishing of both the internals and externals of some of these designs. Please don't think I'm innately this anal-retentive about these moderators, as I could largely care less, but for those who want to know, I strive to answer. If you don't like the aesthetic nitpicks, I'm actually inclined to agree with you, so just skip the first paragraph of every section.


    The test protocol. The muzzle of the moderator is exactly parallel to the pickup, and separated by exactly one meter. The milspec protocol for firearm suppressors is 1.6 meters off the ground, however given the depth of the snow in Maine at the moment, I did 1.6 meters above the surface of the snow, and an indeterminate amount (several additional feet) above the ground itself. Two pickups were used, next to each other and equidistant from the moderator, and each test was five test shots. The results are an average of that, so ten datapoints. I hand select each sound profile (image) which I feel is representative of the moderator's overall performance. The host gun is an FX Crown .22 regulated to 135 bar and shooting JSB 18.13grain pellets at about 890fps for a total of 33 foot pounds. All tests were done with the shroud fully retracted, excluding the shroud-only test. The nearest solid surface in front which will reflect sound directly back is about 80 meters away, and so will not reflect sound within the capture time-frame. Note that a lot of a moderator's sound comes out through its muzzle, and so if you shoot with a reflective surface in front of you (such as shooting indoors) moderators will sound much much louder.

    Each moderator comment has three sections. The first are aesthetic observations/nitpicks. Second is my SUBJECTIVE thoughts on what it sounded like. While testing I had a friend taking data, so these are blinded because I don't know what numbers are being produced. Then third is a brief discussion of what the sound meter said, and how that relates to how I feel the moderator sounds.

    Stock FX Shroud (extended)
    Sound – 288

    What can I say about the design? It looks like the stock FX, because it is. TypeII ano, and kinda goofy looking when extended in my opinion.

    As far as the subjective ear goes, what can I say? It sounds relatively loud and hollow. Amusingly it isn't the most unpleasant sounding thing here. That dubious award goes to the moderator possibly from Wolf Airguns. (no branding or ID on the tube) If I were guessing, I'd guess the unknown brand moderator cuts the peak considerably as compared to just the extended shroud, however the subsequent and significant noise that moderator makes causes it to sound worse than the stock shroud. It is hard to say though because the separation of time between the two tests fuzzes your memory.

    Looking at the test data, I’ve seen this before. It is loud, but drains quickly. You’ll notice I’ve added a new, longer, perspective so you can get a better idea of sound taper to ambient. This shroud is loud, but at least it quickly drains.

     

    DonnyFL

    So I actually had the pleasure of testing three of his cans and Tanto, an FX, and a Sumo. The amount of excitement, and dare I say hype, around this brand is impressive. Based on the offers of loans I got, at least in the US I think Donny outsells the competition by at least a factor of ten to one. Doing a little research, aside from sound attenuation, I hear a lot of complimentary things said about the quality of his machining. To be clear I'd never touched one before this test, so all these things are second hand reports from forum members. Because these moderators are all virtually identical in terms of design and construction, I'm going to do just one overview/nitpick of the design and finish.

    That prefaced, I'm about to tip a sacred cow: I don't think his machine processes or finish is exceptional. The machined aluminum itself looks quite simple, and optimized for manufacture, which is fantastic particularly if it offers great sound attenuation. The minimization of parts count and assembly time, and the ability to work well with looser tolerances, are both big wins and these designs happen to have that. That said, I promised nitpicking and I intend to deliver. The little nitpicks are things like uneven depthing and radiusing on the aesthetic body slots (I assume the radiusing is done incidentally as part of the blasting process), the bores of the Tanto and FX look like straight extrusion, the ano looks like a type II to me rather than a more premium type III, the rear-caps have five faces rather than six so you can't grab it with a wrench, the tubes and ends don't align perfectly, and finally the designs themselves are very heavy (this may help with sound attenuation).

    The big one that surprised me though was what I found inside the Sumo, which was major chowdering on half the length the inside of the main tube's bore. Maybe the boring bar wasn't stiff enough, or the tool head was dulling and gumming up, who knows, but either way it is pretty ugly and it is underneath the anodizing so it was clearly shipped that way. To be clear it is not visible when in use and doesn't affect the the shooting experience of the moderator in any way so this definitely still falls under the category of nitpick, but it is still there. Anyway the sum of all these things is I would say they are reasonably made, the machining and finishing are neither rave-worthy nor something I'd knock them for. And if this paragraph doesn't get some angry comments, I don't know what would. Truly no ill will is intended though, these are just my observations having a whopping total of 3 Donnys on hand to compare with the other major brands.

    Cores on all three are also the same, plus or minus can diameter obviously. They are a monocore with a wrap of what appears to be stainless steel mesh held with masking tape and then a wrap of felt also held with masking tape. Simple and, if third party accounts are anything to go on, highly effective. Worth noting is that the two small cans use a black felt while the Sumo uses a tan felt.

    Donny FX

    Sound – 73.2
    Mass (grams) – 135.5
    Volume (mm^3) – 118,941
    Length (mm) – 126.5
    Diameter (mm) – 34.6
    Exit OD (mm) – 8.0

    This thing sounded great, surprisingly great. It is quiet and “clean” sounding. It is quite heavy though, despite its small size, and you notice this in how it changes your gun's balance, handling, and POI. This additional mass could possibly help it damp sound though.

    In terms of peak, it beat the mean and beat the median. That said the trace doesn’t look quite how I’d have expected, as I was expecting a cleaner peak and faster drain from such a simple design. I can see why people like these though. The big surprise upset here was that the peak was higher than the Tanto. That said I wouldn’t call it a big upset, because the difference is within margin of error.

     

    Donny Tanto

    Sound – 71.2
    Mass (grams) – 100.0
    Volume (mm^3) – 94,324
    Length (mm) – 126.6
    Diameter (mm) – 30.8
    Exit OD (mm) – 7.2

    This sounded louder than the FX, more “pop” to it, which is exactly what you'd expect. To what extent I hear that vs. I hear what I expect is unclear, thus data. Again this one is a chunky little bugger, having some real gravity to it despite being so small.

    If I were a betting man, I’d say it is that smaller muzzle bore that gave this smaller design comparable performance to the FX. I stand by what I said though of it sounding a whisker louder, and some of the noise on the trace supports that. Let me put it this way, cash in hand choice between the two, I’d pay the ~25$ premium for the FX because I still think it sounds a little better.

    Donny Sumo

    Sound – 108
    Mass (grams) – 187.5
    Volume (mm^3) – 209,393
    Length (mm) – 165.8
    Diameter (mm) – 40.1
    Exit OD (mm) – 8.0

    This one was a big surprise. Given the performance of the Donny FX I was expecting hammer slap to be all I heard. That is not what happened, it actually sounded as loud or louder to my ear than the DonnyFX. It also lacked that “clean” sound of the FX, picking up just a hint of an odd metallic sort of sound. I'll mention this sound a couple times, as this is not the only moderator which has it, but I'm guessing it is resonance inside the moderator. My buddy and I talked a lot about what analogy best describes it. I think the best description is like a high tension steel cable failing, where you have both an air “hiss” and that metallic resonance. He thinks it sounds a bit more like a tennis racquet. Either way it is kind of a hiss-twang kind of thing, and I want to be clear there sounds like just a hint of it in this moderator.

    This is a bigger upset, being a lot louder than, not just the other two Donny designs, but was actually the third loudest moderator here. You can see the peak is quite high, however the subsequent dip is quick, which is probably why it sounds much quieter than it actually is. It looks to me, on the trace, like it produces sound for a fairly long time though, not tapering to ambient even by the end of the trace, which I would expect to be the moderator resonating, which is also not exactly fantastic. It is hard to say why exactly this is worse, however both hearing it and measuring it I’m confident in the result. Just because something is unexpected doesn’t mean you can discount it.

    Donny Emperor

    Sound – 81.0
    Mass (grams) – 436.6
    Volume (mm^3) – 536,804
    Length (mm) – 266
    Diameter (mm) – 50.69
    Exit OD (mm) – 8.55

    THIS MODERATOR WAS TESTED ON 6.1019, SEPARATE FROM THE REST OF THE MODERATORS TESTED HERE

    The first thing that jumped out at me about this wasn't the size, it was the weight. In fact it was so heavy, I had to pull the core out and weigh it in parts as it was maxing out my scale. For those who don't speak metric, that is a whisker shy of a pound. It also is the only thing I've yet tested which is heavier than the Clague, and although it has a larger bounding volume it is a little shorter. Internally this, and the Ronin, differ from the other Donnys I've handled in that, instead of three chambers of varying sizes and two baffles, these have multiple chambers of identical size and far more of them. The Emperor also now has wire mesh around the outside of the felt as well, and it is held closed with zip-ties rather than the usual black masking tape. There also appears to now be not-insubstantial space between the outside of the core-wrap and the tube, effectively creating a permeable barrier between the inner core and an outer chamber of sorts. It may seem like a small detail, but this could have a substantial impact on ultimate performance, causing these designs to perform much better than their diameter would suggest. Fit and finish is otherwise identical to the other Donnys, as described above.

    Before I leap into testing, I want to note that this Emperor was marketed and sold for .22/.25, but Donny said these came out a little on the snug side for .25 so really it is best as a .22 can. This is probably because, with a couple stacked tolerances and such a long mod to amplify any tolerance issues, you want that size exit hole to quite large to reliably clear a .22 pellet. The point I'm trying to get at though is that this was very much NOT made for .30.

    My initial reaction to this design was surprise, and in a good way. Given all my testing with large diameter designs, I was expecting this to be much much louder than it actually sounded. Maybe it sounded a bit like a Huggett Belita but without the ring of the Huggett? What I'm getting at is, if you didn't know it was an enormous moderator, you'd never guess it by listening to it. It didn't seem to have that sound of very high peak and low subsequent sound you (or rather I) expect from a large diameter can. Another thing I want to note here is that the muzzle is substantially farther from the shooter's ear than with other designs, and the face is much wider, so it is possible some sound attenuation to the shooters ear occurs based simply on the form factor. Put another way, this can moves the “muzzle” of your gun almost a foot further away from your ear than no moderator, and then casts a significant shadow. Given that your muzzle may have only been two feet away from your ear to start with, this is likely not inconsequential.

    So how did it actually do? Not bad really. Again I was expecting armageddon, something up in the Clague range of mid hundreds. To be below 100 was great, in fact this design was almost as good as normal sized moderators. Looking at the traces, there is clearly less residual sound than many other smaller designs, but it isn't dead silent either. It is enough that, if you were to measure with an unsuitable sound meter or a phone, you might get erroneous numbers suggesting it is quieter than say a 0dB. Given this design's length and weight I can't exactly call this result great, being almost as good as a design a quarter its mass, but it sure is a heck of a lot better than I'd have guessed.

    Donny Ronin

    Sound – 103.6
    Mass (grams) – 267.7
    Volume (mm^3) – 325,562
    Length (mm) – 160.5
    Diameter (mm) – 50.82
    Exit OD (mm) – 8.11

    THIS MODERATOR WAS TESTED ON 6.10.19, SEPARATE FROM THE REST OF THE MODERATORS TESTED HERE

    I covered above, on the Emperor, the internal and aesthetic observations of these two. Beyond that, they are largely similar to the other Donny designs I've tested from an aesthetic perspective and are covered in greater detail above.

    I also want to note that this design was sold for .22/.25, not .30. I too would expect this exit OD to be too tight for .30.

    My subjective impression on how this design sounded was “peaky,” that is to say producing a peak which is much higher than you'd expect given its draining sound. That isn't to say it sounded quiet, because it really didn't, but having passed my initial surprise given the performance of the Emperor I guess this sounded neither luxuriously quiet nor ostentatiously loud. It definitely has the kind of sound delivery which would make it hard for an untrained ear to judge how loud it actually is, if that makes any kind of sense. I do worry I've listened to too many moderators at this point, and so my subjective impressions are starting to diverge substantially form what a lay-person would perceive, however this is why hard data exists.

    Well, for those who say this sounded quieter than the Sumo, I believe them because it is….. barely. We're probably within margin of error here, but on a previous day the Sumo averaged 108 and the Ronin averaged 103.6. Of course both of these are substantially louder than smaller diameter designs, but there it is. I suspect, although could easily be wrong as I have been so many times before, the design alterations of the Ronin will give it a further edge over the Sumo on higher flow guns.

    As a small aside to these two Donny tests, I expect someone will point out that, while these designs may have been bored for small-calibers, they were intended for higher power air handling. To this end I screwed them to my Crown .30 (80 foot pounds) and ran some dry-fire shots through them. The results were erratic, but far from flattering, producing the highest peak of the session at 220. I wouldn't read into that though, because I also ran a couple other designs dry for the purposes of comparison and discovered that dryfires cause moderators to behave very strangely. In short, a dryfire test of a given moderator may or may not be representative of its performance with projectile, and you'll have no way of knowing until you test it properly. :/

    0dB

    Sound – 63
    Mass (grams) – 145.4
    Volume (mm^3) – 133,871
    Length (mm) – 167.5
    Diameter (mm) – 31.9
    Exit OD (mm) – 9.5

    If I were going to pick a moderator for most visual appeal, it'd be this one. Nice matte black finishing, some good stylistic flairs, etc. I don't think it looks particularly good on the Crown specifically, both because the diameter is too small and because the tapered rear face looks dorky unless put on a shroud or barrel with a smaller diameter, but it does seem to have some nice eye appeal. In terms of how well the caps align with the tube, I'd say this can is second only to the Huggett, however you can see some tool/work piece deflection at the tips of the aesthetic slotting particularly at the front of the can. The whole thing also appears to have been carefully and thoroughly blasted. This external beauty though is contrasted with the core, which isn't as nicely finished, and it appears to have basically the machined equivalent of hair curlers and washer baffles. Clever on the outside, but a well-worn path in terms of design on the inside. While there are clearly points for bespoke tooling to grab and unthread it, it isn't my can and I didn't want to force it or risk marring it so left it at that. In that regard you could almost consider it a Hugget clone, as the stylistic similarities both inside and out are pretty apparent.

    Given the sound of the Huggett, I was expecting this to sound similar. It didn't, it sounded louder than the Huggett to me, louder than the DonnyFX too. But it sounded as quiet or quieter than many of the moderators here. My subjective ear puts this somewhere at the good end of the pack, but not the best.

    This design was technically the quietest of any moderator here, beating the Donny Tanto (second best) by about 8 points. That said, the victory may be a bit hollow given that it did it by being 50% heavier, 25% longer, and with 30% greater volume. It also didn’t sound great, to my or my buddy’s ear, so the fact that it won startled both of us. Hell he was recording all the data and even he didn’t see this coming. You can see on the trace why too, because it produces a lot of noise after the peak. It just so happens that the peak is quite low. I think we’ll see this story repeated, and it isn’t an indictment of any design lowest is lowest and peak probably carries across distance better than subsequent lower noise, it is just worth noting that this is my explanation (excuse) why I didn’t see this coming despite having listened to it.

    TKO

    Sound – 81.6
    Mass (grams) – 73.1
    Volume (mm^3) – 88,984
    Length (mm) – 167.6
    Diameter (mm) – 26.0
    Exit OD (mm) – 7.7

    There is no branding on this moderator, and its owner didn't recall its brand, but it sure looks like a TKO from the outside. Same size, same look. While it looks like carbon fiber, I believe it is actually an aluminum tube with a faux carbon wrap on it. Ends appear to be delrin, as do the baffles. All this matches TKO to my knowledge. Fit and finish is not what you'd call great externally, and while this moderator has clearly been loved hard for a couple years, the fake carbon wrap and coarse machine marks on the delrin end I'd say put this moderator in not so great standing from an appearances perspective. It also appears to be held together by solely glue, which I discovered accidentally when giving it a gentle test to see if the end was threaded in. Oops. :( This is easily the skinniest moderator here, which I believe is done intentionally to clear iron sights. Internally the baffles appear to be a simple slightly conical design. It is small and light though, so I could imagine this being the moderator of choice for things like pistols where thin and light are what you want. In that regard it is the only thing tested here which is really suitable for the application, and I give it extra points for being so very light weight. A lot of sacrifices are worthwhile to shed weight, and this appears to make the most of them, or at least a lot of them. There is a real purity of purpose about this can's design, and I really really like that. The baffles look like a mini lathe with an auto feeder could crank them out all day long. The aluminum tube looks thin and light, and the faux carbon wrap may help dampen its vibration. Ease of assembly cuts manufacturing cost, and it doesn't get much easier than glue. Thus as a package it really really works, from a design/assembly perspective.

    I'm torn regarding what to say about this little moderator. It is the smallest, lightest, and least expensive commercial design tested here. It'd have every right then to be the loudest, but it sure doesn't sound it. Far from it actually. It isn't whisper quiet, that is for sure, but I would also place it somewhere at the louder end of the middle of the pack. I guess the best thing I can say about it is that it is surprisingly not loud, all things considered.

    This design had every right to be the loudest, and it just wasn’t. It does an excellent job cutting the peak, given its size, and just continues making noise afterward. I don’t know how much more could be expected from this little thing, and there was nothing else like it here to test. I’ll be curious to see how it stacks up in the length vs. attenuation comparison.

    Wolf Airguns? -the big one

    Sound – 89.8
    Mass (grams) – 296.9
    Volume (mm^3) – 325,927
    Length (mm) – 253
    Diameter (mm) – 40.5
    Exit OD (mm) – 8.0

    Again no branding here, but this looks like a Wolf Airguns K-baffle moderator of some form. To be brutally honest, this thing looks and feels and is built a lot like a .22 caliber PB silencer and I will be relieved to get it back to its owner. It is just aluminum K-baffles in a big tube. That said the quality of finishing and machining is perfectly adequate. Neither exciting nor anything to complain about. The tool paths are clearly visible on the baffles, however this uneven surface can reduce sound signature, so I wouldn't fault it there. This thing is also HEAVY. It is easily the biggest moderator here in terms of weight and length. The finish appears to be some kind of powder coat, which does a nice job of making it look good while hiding the tooling marks on the outside. The rear mating face was clearly machined post-powder-coat, presumably in order to maximize alignment precision. I'm not sure exactly how abusive to felt moderators some of the higher pressure big bores are, however if I owned such a gun which frayed felt cores, a moderator with an architecture more like this might be the ticket because it looks like it can eat just about anything an airgun can throw at it.

    This was the second loudest moderator here, to my ear, and it had that metallic sound I mentioned above in spades. Not good. The weight also caused considerable POI shift.

    I learned this the hard way myself, back when I started this project: firearm silencer designs make really lousy airgun moderators. Such is the case here as well. What would you expect given K-baffles with no cross jetting?

    Wolf Airguns? -the smaller one

    Sound – 114.8
    Mass (grams) – 179.3
    Volume (mm^3) – 111,857
    Length (mm) – 153.1
    Diameter (mm) – 30.5
    Exit OD (mm) – 6.8

    Again no idea what this is, but it is full of some pretty basic aluminum conical baffles. Same F&F as the other, minus the powder coat. Everything fits nicely and looks like it has been made to a reasonable standard of quality. Worth noting here is that the exit OD may be factory, however the exit “crown” pretty clearly is not, having been badly chowdered by what looks like a handheld drill with a multi-flute countersink bit. The only noteworthy from a design perspective is that this is the smallest exit OD of any moderator sampled here, which is probably why the muzzle end has been futzed with. And still there is something I can't quite put my finger on which I really like about this moderator. For some reason its appearance and proportions and feel just seem pleasing to me. Then again I'm just some crazy guy on the internet right?

    Contrasting the appearance was the sound. This thing brought to a head all the discussions regarding the “metallic sound” we're getting from some moderators. This one had it so loudly I finally put my finger on “snapping steel high tension cable” as my favorite description. It really has that metallic almost “twang” plus the whipping sound of the cable flying through the air. Other descriptions are a tennis raquet, punching metal, a sheet of steel being flexed and making that “twang” sound, and so on. It also sounded louder than the stock shroud, maybe not in peak, but certainly in terms of total sound. What can I say, this moderator is unequivocally the worst sounding one I have EVER heard.

    So the peak wasn’t exactly low, but you can see clearly why I called this the worst sounding moderator of this test. Despite having a similar design to the TKO, it seems like someone sank a lot of testing into the TKO and not so much into this. The thing lights up like a tuning fork, and is the only moderator in this entire test which keeps making loads of noise well past the end of the trace. This design is just a loser, no two ways about it. Disappointing really, because I kinda liked how it looked.

    Neil Clague

    Talk about a name, Neil was in this game before it was cool and is still one of the most storied brands. The two moderators I have of his were made model specific, like all his designs. One was for a .25 caliber marauder, the other for a .30 caliber FX impact. These moderators have been through a couple owners, and show some signs of use. It is also worth noting that another Clague owner I've chatted with had insisted that his designs were simply empty tubes. That was a bit surprising to me, but these Clagues are clearly not empty tubes.

    Clague Marauder .25

    Sound – NA
    Mass (grams) – 143.7
    Volume (mm^3) – 150,585
    Length (mm) – 189.6
    Diameter (mm) – 31.8
    Exit OD (mm) – 7.0

    The .25 caliber Marauder moderator I actually didn't test. Why? Four reasons. One was due to the performance of the other moderator, which we'll get to. The second is what I discovered when I peeked down the core: it was full of rust. The baffles themselves look like maybe freeze plugs to me, and they're covered in rust. Third is that there is nothing here internally which appears unusual or special. By this point you're probably tired of me saying “hair curlers and washer baffles,” and in a twist there are no hair curlers. The baffles are flat with holes in them, and they appear to be spaced with what looks like a machined white plastic which I'm guessing (wildly) is PVC given its surface finish. Fourth is that the threaded end appears to utilize a male thread unique to the mrod shroud, and taking the time to fabricate said thread adapter didn't sound like the most fun I've ever had with my pants on. For now I'll pass on this one. I will say that a .25 caliber pellet (6.35mm), the intended payload of this moderator, is awfully close to its 7mm exit hole and even closer to its 6.87mm entry hole. As far as external fit and finish goes, this moderator has been quite beat up, but looks like aluminum which was painted black once upon a time. It also appears to have had hidden seams, that is to say was finished on the lathe as one piece, so from a cap-fitment perspective looks great.

    Clague FX Impact .30

    Sound – 152.6
    Mass (grams) – 325 (maxed out precision scale, used hanging scale which is less precise)
    Volume (mm^3) – 493,214
    Length (mm) – 276
    Diameter (mm) – 47.7
    Exit OD (mm) – 9.6

    The .30 cal FX Impact moderator is big, and I mean BIG. It is easily the largest here, and is the second heaviest despite its carbon tube. This is probably in part because the end caps are quite large and solid aluminum chunks. The whole thing looks like it was finished on the lathe, which creates that seamless look of the other moderator. Before it was unceremoniously drilled and then taped back up, I bet this thing had some serious presence, particularly in the sun to light up that carbon. In that regard, despite the weathering and ELU modification, it looks great. The core is, again, hair curlers and washer baffles. In this case it looks like a tan colored foam held back by cross drilled alu. cylinders. Said alu. cylinders do not appear to be deburred and look like they were drilled by hand as the spacing is uneven. The baffles look all the world like freeze plugs to me. They could just as easily be something else, but the punchline is that they are effectively flat dividers. I should note a couple things about this can, I am at least the third owner, and I do mean owner because the previous owners all were so dissatisfied with this can's performance it was given away multiple times, eventually to me. One of the previous owners, who I'm told is an airsmith of quite some repute, tried venting the carbon tube in a variety of locations to improve performance, which allegedly it didn't, and so taped it back up.

    Even given the warnings of the previous owner, I was shocked by how loud this thing was. It is not quiet, and I don't mean not quiet given its volume, it is just flat out not quiet. I'm guessing this was the second or third loudest moderator here, which is quite something given its size and weight. There was an accompanying very large POI shift downward. I guess you could say I'm just not a fan here.

    It was the loudest, it was the heaviest, it had the largest volume by a huge margin (well 2.6 times the average, and 30% more than the second largest), and it was the longest. While not included in the test results, I did try wrapping the outside of the tube in a sound barrier material to ensure the sealed holes weren't leaking sound, and they aren't, so this moderator kinda just has to own its performance or lack thereof. I’m staggered. Not only did this result shock me, it shook some of the very foundations of what I believed to be true regarding moderator performance. I just don’t know what else to say.

    Huggett Belita

    Sound – 75
    Mass (grams) – 97.2
    Volume (mm^3) – 90,648
    Length (mm) – 120.1
    Diameter (mm) – 31
    Exit OD (mm) – 7.0

    So I don't know how much these bad boys go for in the UK, however stateside I believe I'm correct in saying that they are the most expensive commercial moderators available. This tiny little Belita will set you back 170 'murican pesos. Given the prices, steeply increasing with size, I was expecting some combination of space magic and fairy dust inside this can, or at least something complex and difficult to machine anyway. You can certainly burn a lot of money doing complex surface machining on a CNC. I was surprised when I popped it open to discover felt, hair curlers, and washer baffles. Don't get me wrong, it was all very nicely machined inside and out, in terms of precision of machining I'd definitely give the Huggett the highest score of any moderator here as all parts including the caps fit and align flawlessly with the tube, but it is just flat faced discs, felt, stainless steel mesh, and alu. hair curlers. I don't mean to be crass, it is all very nicely made even where nobody is going to be looking, but it also isn't exactly unusual or unique in there. Again maybe these bad boys are more affordable over in the UK, and the machining is very nice, but at the end of the day it is an old and simple architecture with a shiny type II anodizing on the outside. I don't know, I guess I just expected more somehow? The similarity between this moderator and the 0dB also really jumped out at me. I don't know what kind of history exists between these companies, so I don't want to cast shade on anyone here, so I'll just say they appear remarkably similar. For what it is worth, I really like the form factor of this moderator, it is just nicely proportioned.

    Subjectively, this moderator sounded pretty quiet, surprisingly so given its size. I'd definitely put it at the better end of the pack performance-wise. It didn't have an entirely pleasant sound though, it had that dreaded resonance I've mentioned before. It is subtle, but it is definitely there.

    So I’m actually going to go out and say that I’m pleasantly surprised by how well this little bugger did. It is tiny, the shortest design here and despite its simple architecture it worked in cutting the peak quite well. That said, look at the trace; it is still resonating (or at least appears to be) quite significantly at the end of the trace. I think this is part of why this moderator just doesn’t quite sound as nice as it could and should. An updated architecture with better damping might be easy for Huggett to implement, and could make a good design even better.

     

    *Trident Ramus

    THIS MODERATOR WAS TESTED ON 4.15.19, SEPARATE FROM THE REST OF THE MODERATORS TESTED HERE. I did test a number of other designs which were tested on this day, and they were all within a few points of where they were before, however in the interest of full disclosure I wanted to put this in.

    Sound – 92.6
    Mass (grams) – 113.1
    Volume (mm^3) – 158,814
    Length (mm) – 160
    Diameter (mm) – 35.55
    Exit OD (mm) – 6.87

    So I know, when I initially did this writeup, that I thought the 0dB was most visually appealing. I FULLY rescind that, this is without a shadow of a doubt my favorite production moderator from an aesthetic standpoint. The the aesthetic slots cut up to the edges of the ports end perfectly consistently. You can just barely make out where the ball-nose endmill cut its path around the little indents at the muzzle end of the tube, that and some of the faintest lines where the exterior of the tube was turned down to size are the only machine marks, and they are tiny. Cap alignment appears as good as the Hugget. And, also importantly, there are 6 of those body flats on the main tube, so if necessary it could be gripped by a soft-jawed vice or wrench for loosening/tightening the front cap. The sheen is a little higher than anything else seen in this test, if I were guessing it'd say it may have been bead blasted or media tumbled rather than sandblasted like Donny's. (note, I don't have a citation, but I recall reading somewhere that Donny sandblasts prior to ano and I have no reason to disbelieve it, but without citation such a claim should be viewed skeptically) Internally I do have one more nitpick: the core is .51mm shorter than its alloted space in the tube. Essentially the core is 3D printed, not via FDM, but by the looks of it via a 3D Systems MultiJet printer. I suspect this is how the price is kept so modest despite a very intricate design would would be very challenging to machine. This core is then wrapped in felt. The tolerance discrepancy is totally aesthetic, as the aforementioned felt keeps it from rattling around. This core is what then makes up the muzzle exit OD specification, as the aluminum tube merely is a pressure vessel and has the attachment threading for your rifle. It is a very clever design, all in all. I'd also add that, out of all the commercial moderators tested, if I were walking, cash in hand to buy one, it'd probably be this one. The two big selling points for me are the innovative core design and the light weight. The fact that it looks cool is just a bonus.

    For the subjective ear I'd say it sounds higher frequency than the typical hair-curlers and washer baffles designs. It is slight, but is noticeable. I don't know if this will show up on the trace, or I'll look like a fool, but there it is. I'm guessing the air handlers toward the distal end which swirl the air are the cause for this. It also sounds a little “puffy” if that makes sense, like the event is slightly more sustained. I'm not sure if that is why it sounds slightly louder, the frequency and duration, or if it is because it peaks louder.

    Well there it is, a peak of 92.6. I was genuinely surprised it was that high. Given how it sounded to my ear, I wasn't expecting it to meter like a mouse-fart, but I wasn't expecting it to be quite that high either. Looking at the trace, I'm genuinely not quite sure what to make of it. The ramp-down after the peak is quite interesting, as initially (for ~1ms) it is a VERY clean ~7kHz. And it is like that on all the traces. It also, to my subjective eye, seems unusually symmetric, as if the moderator really is converting half a sound wave into a full sound wave and then propagating it. I genuinely have no idea what to make of it.


    So I wanted to add a bit of a break in here, because this is the phase of the exercise where I post test results of “my” designs. As I noted in the introduction, a buddy of mine helped me immensely. (he would say I stole some of his ideas, in a good natured way) If it weren't for our friendly competition over who can make the quieter design, my test results below would be CONSIDERABLY higher. Just look at my other tests from earlier. Going into this, I really had no idea how I'd stack up, and the answer is without his help and encouragement I'd have been somewhere in the middle of the pack. So a big thank you to him. Ben if you're reading this, bugger off you stole my best ideas! :P Humor aside though, I really can't thank you enough, and if it weren't for our rapid-prototyping and massive associated pile of discarded experimental cores, none of this would have happened. Having someone to bounce ideas off of, or borrow ideas from, and the ability to turn complex CAD geometries into physical objects so quickly made this possible.

    Also a thanks to all the space monkeys out there who jumped on my crazy ideas and tested a core and provided me with feedback. Your collective feedback was contradictory and confusing, and your support was very much appreciated. :) You know who you are and if you have one of these early cores, I'm going to make a limited time offer: you can send it in and for the cost of return shipping I'll re-core it with this new design in 1/2-20UNF which I can say with absolute confidence is much quieter.

    Ultimately I tested three designs. The only one with real development behind it is the small 35x120mm design. The longer design is just a lengthened version of that, basically an answer to the question “what would you do if you weren't so length constrained?” The largest design is again a scaling up and recycling of ideas from the smallest design, with a few other completely experimental twists thrown in. It answers the question of what I'd like to try now without length or diameter constraints, but like the smaller OD “long” design it simply hasn't been optimized. It is kind of an odd duck too, as I have a sneaking suspicion that, despite being the size of a big bore can, it is at least closer to optimized for small bore performance. Going in I didn't really know how all of these would measure up, but also didn't have time to tweak and optimize them, so I just kinda hoped the smallest design's principles scale, and went for it. More data, more better right? Whats the worst that could happen?

    Levitas

    Sound – 60.4
    Mass (grams) – 48.1
    Volume (mm^3) – 116,308
    Length (mm) – 120.2
    Diameter (mm) – 35.1
    Exit OD (mm) – 8.4

    Credit to BobO for this one, he said I couldn't just call everything a gas diode I needed a name, and now that there are three different sizes in a myriad of different flavors I do see his point. So the smallest I named Levitas, latin for lightness or fleetness of foot. It represents my core principles when approaching this project which were to keep everything as small and nimble and light weight as possible. A lot of subtle tweaking and revision brought the last (rev.4) gas diode design forward to this. The same basic principle remains of use an air stripper to first pull turbulence away from the pellet, then delay the air with a gas diode, and then damp the sound produced. The locations and proportions changed though, and in a quest for ever more volume the dual walled tube system was abandoned. Looking at the scope, it is clear the gas diodes are noisy, they make a lot of sound doing what they do, and so the relative split of sound damping to flow delaying also changed. I think this is part of why the rev.4 design sounded louder than it actually was: it produced a lower peak, but noise afterward for a longer time period. Put all together and it is a nice quiet package. There are also some tweaks to aid in assembly, which became necessary as my buddy and I ripped through core designs. Anything to speed the turnaround. :P The core itself is 3D printed, but unlike previous revisions (and the experimental cores) which used ABS, this was done in 20% high modulus carbon fiber reinforced nylon. Why? Better strength, better solvent resistance, and quite frankly because it just looks sexier. I had special stainless steel thread inserts I'd been using with the ABS 1/2-20UNF core designs, because the ABS really needed the reinforcement, but the carbon nylon just doesn't need them, and yanking that shaves 6% off the mass right there. As far as the skeletal section on the end, just like with previous designs, those struts and trusses are there to hold sound damping material. It doesn't really show up in CAD, so you'll have to take my word for it that it is there. You could say it is my take on hair curlers and washer baffles. :P

    I'm not sure I'm a good critique of my own fit and finish, because I obviously made all the design decisions and also know exactly how it was done, but I'll give it a go. Externally the carbon tube looks like a carbon tube that has been post-machined so it isn't ribbed for her pleasure like some of the carbon products you see out there in the airgun world, and has been clear-coated to protect the carbon. (that ribbing is the result of the mandrel wrapping, part of the manufacturing process) The silvered engraving is nice, but isn't perfect; tooling marks are visible in it if you look closely. Ends have an unusual look and texture, and are completely basic being flat and square without embellishment. Cap alignment with the tube is adequate but not exceptional. It all has a machined finish. Disassembly holes (for disassembly tools) are on the rear face only and have been functionally, but not aesthetically, deburred. There is also a visible seam on the rear face between the rear cap and the core. Unlike externally, where everything is machined-finish, internally print lines are clearly visible. It is hard to see what exactly is going on inside by looking down the tube, but it sort of appears to have four closely spaced baffles at one end, and then a ladder-like structure through the rest of the can. The bore path itself looks clean though, which it should because it was reamed to final dimension once the whole can had been assembled. I'm not sure if this critique is fair, but I hope it is a good description at least.

    As far as how I think it sounds, I'm obviously biased so you shouldn't listen to a word I say. That said, I think it sounds very quiet, particularly for its size and weight. Nice tone, no resonance. Kind of a puff followed by a quiet hiss of the air draining. Of all the moderators tested today, I'd guess this is among the quieter designs. With your head down on the rifle's comb, hammer slap is definitely the predominant sound, and the reg filling is very noticeable too.

    The trace looks pretty good to me here. The peak has been effectively blunted and, unlike in previous gas diode designs, I’ve incorporated enough sound damping that the noise from the diode isn’t overwhelming. It steadily and in a reasonable time frame tapers to background. I think some of this is also changing materials with non-homogeneous mass distribution and which are innately damped, so even if made in the form of a literal tuning fork, they won’t resonate.

    Pilum

    Sound – 51.8
    Mass (grams) – 62.9
    Volume (mm^3) – 161,883
    Length (mm) – 167.3
    Diameter (mm) – 35.1
    Exit OD (mm) – 8.4

    I nicknamed this design Pilum, after the long skinny javelin the Romans used to such great effect. So I had a choice when designing this: one gas diode or two. If I were running a ballsier and more powerful gun, 100 foot pounds or so, I think two would have been the better choice. As it stands though the peak is effectively blunted in my design by just one, and in the super short Levitas, so I used the extra space for more sound damping. I wanted that sound profile to drop off as quickly from the peak as possible in this form factor. I guess you guys are the judges of whether or not that was effective.

    Design and finish are identical to the Levitas, minus the engraving. Again this design is the same, just more.

    Sound wise maybe this sounded a little better than the Levitas? Hard to say really, and I wonder if I'm not just fooling myself because I'm expecting it to be better. The “puff” sounded about the same, but maybe a little less sound from the moderator draining pressure after? Because I know this design so intimately I really feel like I’m fooling myself thinking it is quieter, and it just might not be. If it is quieter, it certainly isn’t a night and day difference. Hammer slap and the reg filling are the predominant sounds either way.

    Looking at the Pilum and Levitas traces back to back, it is clear the primary advantage is in sound damping not in peak. Yeah okay sure whatever, the average peak was about ten points lower, but it should have been more. The quicker taper to background is nice though. This design might have benefited from a little less sound damping in exchange for another gas diode module. Or maybe just a sound divider somewhere down in the damping. As I learned competing against Ben, with moderators the devil really is in the details, and while this design is better than the Levitas it isn’t “enough” better given its increased length, mass, and volume. I took a guess at the length scaling and got it wrong, essentially. Further tuning and refinement will be required, I’m just not satisfied this design is living up to its potential capabilities.

    Mus

    Sound – 103.6
    Mass (grams) – 111.0
    Volume (mm^3) – 321,428
    Length (mm) – 162.4
    Diameter (mm) – 50.2
    Exit OD (mm) – 8.4

    I named this design Mus, latin for “mouse,” half as a joke because this was meant as my go-for-broke HUGE design and half because I was sincerely hoping that, at this size, the thing would be absolute mouse-fart quiet. And for those who shoot indoors, there is a big difference between an outdoor mouse fart and an indoor mouse fart. I was hoping for the latter. Also I have a confession: I'm a Cheaty McCheaterface with the mass on this one. Why? I didn't have any carbon tube in this size on hand, so I 3D printed the tube and core from ABS. This makes it lighter than a proper carbon fiber tube and carbon fiber reinforced nylon core, but more delicate as the core design relies on the stronger carbon nylon and a 1mm walled ABS tube isn't going to win any awards for durability either. Basically it is fine for testing in this configuration, as it can easily hold the pressures, but ignore the mass number because it isn't representative of anything you'd actually want on the end of your airgun under normal circumstances unless perhaps you were a strictly benchrest shooter. This is a weird design in that, as I said before, is big-bore sized but is probably much more optimal for small bore airguns. The real changes here, aside from scaling everything up, are in the sound damping area. I have some crazy theories about sound penetration and variable density foam, and just kind of ran with them. I have no idea if they made things better or worse.

    As far as fit and finish goes, this design is BY FAR the worst moderator seen here. Cap to tube alignment isn't even a metric, as it isn't even pretending to have it. The cap color is white while the tube is gray, which hideously clashes, and the whole thing has an air of delicacy without any poise or sophistication. Flashing is clearly visible everywhere, as are the uncleaned remains of supports. The choice of white also means every single smudge of dirt or lead or grease or whatever clearly shows up on the surface, and can't easily be cleaned. Basically it looks like a hastily made and very ugly prototype, which funny enough is exactly what it is.

    To my subjective ear, this actually a fair bit louder than the Pilum and Levitas, at least in terms of the initial peak or “puff.” The subsequent pressure draining sound was quieter. I'm pretty disappointed. I was hoping for the mechanical action to be the only audible sound or at least for it to be much quieter, but it definitely wasn't. I guess this is what happens if you're a goof like me and think that these things should just scale. Oh well. :/

    Talk about eating humble pie, that peak was nothing short of a disaster. Clearly the gas diode didn’t even pretend to scale, and so did a downright abysmal job of stomping down that peak. Clearly more development is necessary, although I’m vaguely curious how this would perform on a big bore. I don’t have any evidence for it, however I have the sneaking suspicion that the air output from a shrouded .22 caliber Crown just isn’t great enough to saturate the diode and make it work. Thus it behaves like oddly shaped conical baffles, rather than as a diode. This may not be the case if considerably more air were put through it, and it is the only poorly performing big design tested here which has a plausible mechanic which could make it actually quieter if put on a more powerful host. The sound damping also clearly worked, however it is unclear if it did that due to sheer volume or if the variable density foam actually helped.


    Discussion

    So that is a lot of information I just threw at you, and a lot of lines to scroll through to compare all these different moderators. Let me start with a convenient chart which puts all the important data together in one place.

    So lets talk about this quickly before moving on, and just point out some general trends. Most obvious, I put the highest and lowest values for every category in bold. This makes it pretty stark that the Clague was the clear loser in this test, it was the worst for all four categories. Largest and smallest volume, to be fair, aren’t necessarily a “best” and “worst” category, but while being smallest is arguably an excuse for being loudest largest would be reason to be quietest or at least among the quietest. A few other honorable mentions to make here, the Huggett Belita was the shortest by just a whisker, and was below the median peak sound, which I think is a solid accomplishment. I’d give Huggett a round of applause for that one, because again the Huggett and TKO have every excuse to be the loudest designs here and they just aren’t.

    Lets move to some data visualizations that’ll make trends and comparisons easier though shall we?

    So maybe this will ring a bit ironic to some people, as I’ve bucked the bullpup trend in my preference for the Crown, however I’m more opposed to moderator length and mass than I am to moderator diameter (volume). So in an effort to visualize this, and compare longer and shorter designs on a level playing field, I generated the above chart. Please note the the trend line was not statistically generated. That is a fancy way to say I eyeballed it to show the trend I’m trying to highlight, while excluding all the noise in the data in the top right hand side of the chart. The short version is that the “ultimate” moderator would be in the bottom left hand corner of the chart, producing 0dB (punny, I know) with zero added length to the rifle.

    Realistically what we see is a good cluster of the Hugget, smaller Donnys, and 0dB. From this metric, you’d say they’re all good competitors for each other as they’re in about the same performance class. Now you could tilt that line to make the 0dB and Pilum look relatively worse and the Belita look better, but honestly I’d say there isn’t really enough data here in a cluster to really fit a solid trend line. So it is just a guess either way. I confess, I’m very happy with the Levitas here, as this chart clearly shows it is doing what I wanted which is being short and quiet.

    As I said above, length and mass are my two big things I look at when I want to build a moderator. And it is a real prickly pear because sound damps mass, and length makes it easier to make a moderator quieter. Again the hypothetical optimal here is to be in the bottom left hand corner, zero mass and no sound, and the more bottom-lefty-ish your design the better. Again I inserted a general non-statistically generated trend line to try and highlight the performance of “the pack.” I don’t want to kick the Clague here every time, so I’ll say it once and be done: in almost every chart, the Clague is going to be off in the bad corner. Now lets move on.

    So the pack, as I’m referring to them, here show the trend I expected. More mass, more quieter. :P The TKO finally found itself in the game here too, as this metric doesn’t penalize its small diameter as necessarily harshly. My opinion is that this is the most important chart shown here, because it clearly clusters the good commercial designs along an axis where users can make decisions between sound attenuation and “size.” It is worth noting that the Sumo is in this unexpected never never land, way off the performance curve. I’ve said it before, and I’ll say it again, I think the Sumo is optimized for eating the air from more powerful guns. That said, I genuinely don’t know if this test were performed on a more powerful rifle it’d be on the curve. It might well be. It might also not be, it is very possible that its sound attenuation vs. mass will still leave it an outlier. Without data I just don’t know.

    I’m tooting my own horn here, to put it mildly, but again this chart is showing me pulling off PRECISELY what I aimed to do, which is make moderators stupidly light weight and reasonably quiet. The Pilum and Levitas broke the trend, but on the good side of the line and by a significant margin. The Mus not so much, that is off in the “what was I thinking” rhubarb. I’ve given all my excuses before, so no need to revisit them, but I do have an idea for twin nested gas diodes, basically a gas diode inside a gas diode, so such a large design could saturate at least one diode irrespective of power output.

    Ask people about airgun moderator design and you’ll invariably get a bunch of people telling you that the primary factor is expansion volume, and design architecture is secondary. Hell I even believed it. Clearly not though. Again better designs are toward the lower left hand corner. The non-statistically-generated trend line here was the one I am actually most uncertain about. It could easily change slope, making the Pilum and 0dB look better or worse. More data would be better.

    Before everyone jumps on me urinating on the sacred monument of airgun moderator faith, which is to say expansion volume, let me be clear that not only is there a trend, there are potentially two trends here. The obvious trend line I placed at the bottom clearly shows performance improvement with volume. Lets then address the elephant in the room: why did ALL the big designs do badly? Well you could almost fit another trend line up there around the Wolf, Sumo, and Mus. If it weren’t for the Mus, you could make the claim that the cluster represents volume without good sound damping.

    The Levitas is, once again, clearly doing what I want it to be doing, which is to say clearly below the pack for sound attenuation vs. volume. Where I’m less happy is the Pilum, which I alluded to in its section god knows how many paragraphs above. Looking at the Levitas alone, I was certain it wasn’t performing up to its potential, and now this chart shows that in start contrast. If you draw a line between the Levitas and Pilum, the slope will be considerably steeper than that of the pack’s. Thus it doesn’t appear to be operating at its potential. Yeah, sure, I didn’t optimize it I just winged it, but that is just an excuse.

    So this chart is a little silly, because obviously diameters can vary wildly thus any correlation between mass and length would be loose at best. Note the two trend lines, for one I locked the intercept to the origin, and the other I did not. Amusingly the former has a higher Rsquared, and you might say “makes more sense” because a zero length moderator you’d expect to have zero mass. On the flip side of that coin though, at zero length, you’d still expect to have the mass of the mount and cap though no? The second trend line suggests that these features have negative mass, because a zero mass design should have a hypothetical length of 98mm. WE HAVE SUCCESSFULLY DISCOVERED ANTIMATER!

    This is the less silly version of the former chart, the plot of mass vs. volume. It is important to note why there are two trend lines here as well: moderators are essentially cylinders, so their volume should increase exponentially with their surface area. You can judge for yourself here though. In this case more optimized designs are above the curve, you’re looking to be in the top left hand corner where you have great volume and no mass.

    Notable standouts here are the Clague .25 and .30s, the Sumo, and the TKO. I’m just thrilled I finally have something positive I can say about the Clague .30, which is that its volume to mass ratio appears to be ahead of the trend. There isn’t much out there in right field to compare it with, but a win is a win and that is a good thing. Also surprising to me was the Sumo, which really feels like a brick in the hand and on the gun, but by this it seems to be either hanging with or slightly ahead of the pack.

    So remember when, on the Mus, I said I was a Cheaty McCheaterface? Well you would think this is the chart that clearly shows that, that it is curve-breakingly light for its volume. But it appears that I was wrong. While writing this, and staring at the chart, I noticed that the Pilum, Levitas, and Mus all line up. So I scratched an eyeballed trend-line on the chart, and this was the result. Given that the relationship shouldn’t be linear, this suggests the Mus might not even be ahead of the curve, it might be on it or even behind due to increased core mass. Hard to say. It gives me some hope though that I might be able to build something in this size class which has about the same mass as a DonnyFX or 0dB.

     

    Future avenues of inquiry which most interest me are twofold: first I have a great interest in eccentric bore designs. While an integral moderator core upgrade for the Edgun Leshiy would be a very fun project and catches my eye, in general the ability to sling most of a moderator’s volume out of the scope path offers advantages and allows much larger moderator volumes without detriment. Second I’m very interested in moderator development on more powerful rifles. While an integrally shrouded .22 at around 30 foot pounds (or considerably less) is probably the largest use case scenario for a moderator (guessing) and is exclusively what I shoot (minus Baikal target pistol), these slug guns and big bores have started catching my eye. Something suited for the 100+ foot pound range that isn’t absolutely enormous and is very quiet would also be a very interesting and fun challenge. In both cases I don’t own the gun, and it is somewhat ridiculous to purchase a gun just to play around designing a moderator for it, but it isn’t out of the realm of possibility. I am just some deranged guy on the internet after all right?


    Whew, what a read. Believe me, it took much MUCH longer to write. Thank you again everyone who loaned me moderators to test. Those should be shipping out Monday, I'll send you all tracking numbers when I have them. And for everyone, I hope you all enjoyed reading this, and that it provides useful information and insight. If your favorite brand didn't do well, my apologies, no offense anywhere or against anyone was intended. 

    • This reply was modified 1 month ago by STO.
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    spysir
    Participant
    Member

    Thanks for sharing all the effort.   All the scientific info seems pretty well matched to all the just shooters information from attending shoots and all the common brands/cans , does seem like I would like to see ( not hear, eh ?) a bit more of the advanced design loike the "mus"

     

    John

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    Tomiboy
    Participant
    Member

    I'd really like to see some results with 25 and especially 30 caliber

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    Clifton
    Participant
    Member

    Much appreciated. You are unbelievably generous to spend the time to write this and share.

     

     

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    Shelby78
    Participant
    Member

    I would like to say thank you. I have been waiting a long time for someone to do something like this. In doing these tests it shows some interesting things and raises even more questions. It almost seems that there's actually a point where volume can hurt performance at a certain ft pound level. Kinda like too big of carb on a certain size engine. I would also be interested to see how more power weather it be ft pounds or bore size plays into designs with more volume.

    Other things i noticed is that you can have a quieter can with a bigger bore hole. Smaller doesn't always mean quieter. Then there tube venting… How big of role does that play and could it benefit your designs? It is almost more Confusing now than without the data lol. Thanks again for a excellent read!

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    Macros
    Participant
    Member

    What a read!

    Among the best posts I've read on any forum ever 🙌💪🙏🏻

    Something looong overdue, but you can see why. The amount of work must have been incredible, even before the thesis that is this writeup 😄

    Only issue is I now NEED at least two Levitas and maybe a Pilum 😆 

    Thank you for all the effort!

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    Revoman
    Participant
    Member

    All a very interesting read, no matter how long.  Your approach is excellent and your analysis of all are also very good.  Enjoyable read would be a good synopsis in my view.

    This however begs the question;  Since you have 'pioneered' the sound deadening analysis of air driven rifles and your Pilum design appears to have won as far as sound deadening, are you going to start manufacturing same?

    mike

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    STO
    Participant
    Member

    As far as all the kind comments go, I'm not quite sure how to respond to them, but I really do appreciate them. So thank you. :) 

     

    Shelby78

    I would like to say thank you. I have been waiting a long time for someone to do something like this. In doing these tests it shows some interesting things and raises even more questions. It almost seems that there's actually a point where volume can hurt performance at a certain ft pound level. Kinda like too big of carb on a certain size engine. I would also be interested to see how more power weather it be ft pounds or bore size plays into designs with more volume.

    Other things i noticed is that you can have a quieter can with a bigger bore hole. Smaller doesn't always mean quieter. Then there tube venting… How big of role does that play and could it benefit your designs? It is almost more Confusing now than without the data lol. Thanks again for a excellent read!

    Picture a tree. You start at the bottom, thinking you understand things reasonably well and there is just one path upward. Every single experiment, every tweak, every measurement, all of them cause the tree to fork from one branch to ten. And I'm not sure I'm in the canopy yet. :P Your questions are good, but are just a tiny fraction of the number I've now amassed. Running them all down would be the work a lifetime, maybe tends of lifetimes. I'm somewhere at the bottom of the bell on the Dunnign-Kruger curve. That said, let me try to answer what little I can. 

    So I hypothesize that it isn't volume hurting performance per se, but rather a failure of optimization for that large volume. As you dump more and more air, that "wasted space" may hurt you less and less or at least may become less and less wasted as you simply require more expansion volume. This is all strictly hypothetical, but I just can't see a mechanism whereby a larger moderator optimized for a smallbore application would necessarily be handicapped. With a few exceptions, the commercial designs here were all some variation on the hair curlers and washer baffles theme, even the Donnys are really just (to my eyes) a clever monocore and manufacturing-optimized adaptation of that concept. Saying that design architecture doesn't scale I think has some limited basis of support in the data. The Mus though I think failed by another mechanic. If you look at the trace, aside from the peak, it is reasonably quiet. This suggests a failure of the flow-stopping elements, not the sound damping elements.

    I tried some tube venting in my experiments, you'll note that was part of the game with the earlier revs. I vented forward, away from the shooter's ear, rather than laterally. Same concept, different execution, the punchline is you have more drain speed than your exit OD would allow. You'll note that I ultimately abandoned it, because the space it required wasn't worth its cost. In the case of the Huggett and 0dB it may do something, but I am doubtful. Hindsight 20/20 I should have just thrown some masking tape across those vents and tested it again, but really they all run the same basic design so the fact that they all cluster on the same trend line suggests to me the vents in this case aren't doing a whole lot. On the Donny though, I'm kind of dubious though that they do anything. The whole event is there and gone just so damn fast, how much air could they possibly drain? So a quick measure on a DonnyFX I have sitting on my desk says the vent holes are ~1mm in diameter and there are 5 of them. That means you have 3.95 square milimeters of vent. The exit OD is 8mm, so that is 50.27 square milimeters of direct venting area. Now compound that with the fact that Donny puts his vent holes at the front of the can, what looks like (eyeballing) in the last chamber, the same chamber as the exit, so the two will be venting simultaneously, rather than the other designs which could in theory allow venting before the pressure gets to the muzzle. My conclusion then? This is pure speculation, but I'm guessign Donny tested venting and found it didn't help and may have even hurt. (possibly in aesthetic ways, like allowing fuzz to start blowing out the holes) So he put them where they could do the least harm, in the last chamber, and made them super super small so that people who say "but I want a moderator which is vented" get what they ask for as well as what they actually want. (a quiet moderator) Just guessing though. Again, I'm at the bottom of the Dunning-Kruger curve here. 

     

    Revoman

    All a very interesting read, no matter how long.  Your approach is excellent and your analysis of all are also very good.  Enjoyable read would be a good synopsis in my view.

    This however begs the question;  Since you have 'pioneered' the sound deadening analysis of air driven rifles and your Pilum design appears to have won as far as sound deadening, are you going to start manufacturing same?

    mike

    This is not a for-sale thread. This sort of question should be asked via PM. :) 

     

    Tomiboy

    I'd really like to see some results with 25 and especially 30 caliber

    I figured somebody would say that, if not outright ask for a bigbore test. Forgive me for being blunt, but the thing is I don't own a rifle in either of those calibers, and I don't care to. There was a race up the calibers as people quested for greater sectional density and kinetic energy. As pellet (and slug) design caught up, we've watched a race back down the calibers. Even the old .20 appears to be getting new life these days. 

    Regarding .30, I can actually shoot Lapua match grade rimfire suppressed, which has better ballistics and more kinetic energy, at a lower cost per round than the JSB 30s. About 20% lower actually. And that lower cost is before you even factor in air. So while it may have worked out for competitions at one point, and it may be a godsend to those who can't own guns, I'm not in either of those boats. 

    Regarding .25, I'm personally less opposed, but I also see less benefit/difference from .22. I don't see a convincing advantage that it is in a different performance league accuracy-wise (look at EBR for example), I still think the pellets are overpriced, meanwhile the air consumption is only ~20-25% greater than .22. (https://utahairguns.com/fx-crown/ scroll down to the chart where you get shots per fill) which suggests to me anyway that the outcomes on the same rifle wouldn't really be radically different. 

    The simple reality is that I do these experiments because they are interesting to me. It sounds narcissistic, but this isn't just an afternoon for the good of the community, a lot of time and effort goes into this. I have empty tins of JSB 18.13s where not a single round was used for target shooting, the entirety of them were wasted into a test backstop at close range to develop moderators. I've got more pet projects, and questions about moderator design, than I know what to do with. I also have comparatively little free time. So if it isn't fun, I'm just not feeling an overwhelming desire to run out and spend ~1.5K on a rifle with a good consistent regulator and world class accuracy just to answer someone's question about what'll happen if you dump 25% or 50% more air into these moderators with a larger diameter pellet. I don't mean to insult people who love .25s and .30s, they are great guns I'm sure, and the question itself does have some merit, but it just doesn't interest me and is not an easy/accessible/cheap test to perform. 

    The question in this vein which does perk my ears up is what changes when for a moderator on a proper big bore, something with an order of magnitude greater air consumption. How does that change things? I've been patiently waiting for the "perfect" big bore to be developed, particularly one that is suitable for moderator development, and I have high hopes it'll come along soon, maybe in the next couple years hopefully. :) 

     

     

    I hope all that makes sense and is reasonable. Again apologies to everyone for the questions I don't have the answer to, but believe me there are more questions than answers here by far. I also don't mean to start a caliber debate, I'm just stating my personal preferences and reasoning behind it. The name of the game here is fun, this is a hobby after all, and so we should do what we love. If it isn't fun, they call it work and they either pay you for or your wife tells you to do it. :P 

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    steve-l
    Participant
    Member

    Wow. You spent a great deal of time doing this testing and for that a great big "Thank You" is in order. I am curious why you did not test velocity loss. I think it is relative to effectiveness. I have made many silencers of many designs over 50 years and in my experience the most effective silencers not only attenuated sound but also bullet/pellet speed. In my experience the more sound reduction, the more speed attenuation. I contend that this speed loss is due to the flow resistance caused by the silencer to the air column in front of the pellet.

    I also commend you for pointing out the sound of resonance or ringing of the tube if you like. A lot of that is material choice and mechanical design. Lately I have used 3 equally spaced compression studs that compress the whole assembly together. My baffles precisely fit the inside bore of the outer tube, but are not attached to it. The baffles instead are held in place by individual aluminum compression tubes that the studs run through. I also use a few Belleville washers  stacked with the tubes to take up any small differences in length. This design offers very large compression forces on the assembly, which appears to reduce resonance very well.

    Your theory of a gas diode is also very good, but it is a difficult shape to achieve. I think an inverted cone baffle accomplishes the same thing by intercepting the escaping air as it tries to race around the speeding pellet, but just as importantly, the space that this air is being deflected into is in effect an expansion chamber and any containing chamber will have a natural resonance frequency.  (the Helmholtz principle) For this reason I never use equal spacing in the moderator. The first chamber is always the largest with each succeeding chamber being progressively smaller and each baffle is also an inverted cone as well as the back surface of the forward end cap. Each one is effectively a gas diode.

    These individual chambers reduce the driving air pressure, induce turbulence dissipating energy and each chamber has a different resonance frequency. I also believe that the inverted cone deflects the escaping air from influencing the pellet's path increasing accuracy as well. I have no way of proving that, but it makes sense to me. I would very much like to have had you include my latest silencer in your testing, but sending it from Europe and back might have been problematic. After all we are considered terrorists lately.

    One thing I would like to mention is that my silencer greatly reduces the gun's report without a pellet, but with a pellet there is a definite pitch change to the report, not greatly louder, but certainly sharper. I suspect it is simply pellet noise, but I am not certain. If you like, I will send all my dimensions and its overall weight. I made this silencer for my .25 Crown.

     

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    Papy_Yosh
    Participant
    Member

    That is a really good and detailed study. Well done on that job. Thank you for your time and for sharing your findings

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    STO
    Participant
    Member

    Thank you everyone for your kind words and support. :) 

    So Tom from Ramus sent me a Trident to test. I put its test results up in the original "big test" post, simply so that everyone can find it. I realize I may at some point have to just split that off into its own "big test" thread, but for now I guess I'll keep simply adding to that post in an effort to make it hard to find, but easy to access as it is all in one place. :P 

    I have to say, I really really like the Trident's design. I had wanted very badly to test it, because the design is just so unique and interesting. Unlike everything else here, which is basically a whose-who of conventional airgun moderator design, this thing walks its own path internally. It was sent to me by Tom, who works for Ramus, and without solicitation reached out to me to make his moderator part of this test. He told me the four primary priorities were, in order: accuracy must be unaffected or improved, light weight is paramount, one size (presumably aluminum tube/cap?) fits all calibers up to .357, and that it must not be able to function on a firearm. So how do these claims measure up? Well in terms of accuracy, I shot groups back to back against another moderator (Pilum) and after 5 groups of 5 rounds each I could find no significant accuracy difference between the two designs. The disadvantage of shooting at that range is wind, which will throw little .22s around quite a lot, however the advantage is that any destabilization caused by the moderator will become very apparent. I did also move inside to an approximately 15 yard range, and at that range both moderators simply put one round after another into the same hole. So I will concur with the first mission statement of accuracy unaffected. In terms of weight, the best point of comparison is the mass to volume graph. Obviously smaller moderators will be lighter, so this compares them on a relatively level playing field. The Trident is one of only five moderators which are clearly above both trend lines, so it is definitely ahead of the curve when it comes to mass. Put another way, it is flat out over 16% lighter than the much smaller DonnyFX. Regarding 1 size fits all calibers, the aluminum front cap has an ID of 9.22mm, so it can pass a .357” projectile. The core however can not, and is clearly marked .22. I assume this design mandate allows for interchangeable cores. It would be very clever actually, if the cores were modestly priced and readily available on the after-market, to make such a design so one could easily change between calibers. The core's exit OD is 6.87mm. That is significantly smaller than the industry average, the second smallest (at the time of writing) sampled here. Never the less, with accuracy unaffected, I guess if it works and improves sound attenuation why not? Anyway the punchline is I really like this design. 

     

     

     

    The other thing I've been doing, which I didn't update in the above post, is tweaking the Pilum and Mus. 

     

    This produced an average peak of 57, which the astute will note is higher than the earlier test. Funny enough, it was 5 points higher than that same older rev. Pilum tested on this day. It is still an improvement though in my opinion, and the reason is that it is an almost negligible reduction in sound attenuation on relatively low-flow systems like my Crown with its massive shroud, however it appears to have considerably improved air-handling on higher flow systems. The problem with testing there, and why I don't have better results, is I've been running it on a shroud-less Diana Stormrider and that has two major shortcomings: 1) being unregulated every single shot is different, so direct comparisons are impossible and 2) the hammer slap ACTUALLY louder than the moderator. 

    I realize everyone these days puts a moderator on their gun and says "all you hear is hammer slap," however that probably has a lot more to do with your head being right next to the hammer than anything else. If you look at the measurements taken in previous posts, it clearly isn't the case…… except here:

    You might reasonably ask how I know that is the hammer slap. Two reasons. The first is timing. Second, and more importantly, it is because the hammer slap remains unchanged no matter WHAT you put on the muzzle. You can become desperate, as I did, and apply a moderator which has no exit hole whatsoever and dry-fire into it….. hammer slap remains. So yeah, learning new things every day, like why you can totally buy a Diana Stormrider, but you probably shouldn't. 

     

     

     

    I also had another very notable failure with the Mus. Building on my earlier Stormrider-induced observation that the gas diode in it was simply too large to saturate properly and start acting like a diode, I tried compounding it by filling its inner chamber with regular conical baffles. That also didn't work. So here I am with another failure and another wild hypothesis to try and fix it. This time though, this time I think I'll crack it. :P All this work with the Pilum though is making me reconsider my dimensions for the Mus. Might keep the OD/ID the same, but increase the length a bit. I have a whole bunch of different ideas about where to go with it. Ultimately though just two goals remain: 1) make it effective on small bore designs and 2) get my hands on an actual big bore design and confirm efficacy on that as well. 

    The only other noteworthy thing is I've split off a second thread devoted specifically to the Leshiy. It is such an odd combination of eccentric bore and high air volume in a small caliber with a constrained space it is turning into its own unique and separate challenge. So that, for the curious, can be found here:
    https://www.airgunnation.com/topic/muzzling-the-leshiy-a-silencer-story/#post-479892

    And if you suffered through this much of my writing, I'm shocked, impressed, and a little worried about your alcohol consumption. :P I hope people find something interesting in all this. I do the design and testing for my own amusement, certainly, but it is for you guys that I write it up and share it. :) 

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    airgunfans
    Participant
    Member

    I have also been experimenting with DIY moderators on my Huben K1.  Up to now the only thing I have found is that volume does not affect quietness much. I have made two moderators, both are of the same length ( about 200 mm ) but one has an internal diameter of 72mm while the other is 38 mm,  both have 3-chamber design with simple washer baffle between chambers. The much fatter one is only very slightly quieter, the reduction definitely does not justify the huge amount of additional volume ( and weight ).  This is in line with the test result of the OP.

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    STO
    Participant
    Member

    You know I've been working on a good hypothesis for this phenomenon, because some people observe huge gains from larger moderators and some don't. If we ignore the possibility that they're simply psyching themselves out, that is to say hearing what they want to hear, what is left? My best guess is that much larger diameter moderators tend become more effective when you have a much larger volume of air to contend with. They are worse at sound damping, flat out, because of the greater distances between the damping surfaces and because they now have more hard surfaces to reflect around on, but with sufficient air volume to contend with that expansion volume becomes useful enough that they overtake their smaller diameter brethren. It is just a hypothesis though. It does give some creedence to @mendopellet though who, unusually, covered his baffle surfaces in felt as well as the inside of the tube. https://www.airgunnation.com/topic/fx-crown-bespoke-moderator-tesla-gas-diode/page/2/#post-386063

    This seems to at least casually fit with the Huben which is both very air efficient (for its power level) and has a shroud to further spread out that pressure. 

     

    It is all just a hypothesis though. I'd like to break it, by making the Mus properly properly quiet if I can. Otherwise the only room for improvement is length, and there is a limit to how long you really want your moderator to be….. 

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    ackuric
    Participant
    Member

    I've said it before, and I will say it again, length is by far superior than any other silencing method, unless you get into some very advanced technology (think particle physics). First off, moderator length creates more distance between the release of HPA and your ear. Secondly it allows more time (air travels at well over 1000 FPS, or 1 foot per MS.) to occur from the time air begins to enter said device to when it exits.

     

    I don't expect any well design moderator to be far superior to another provided similar length / OD…I think these tests have displayed that quite well with the provided data…and I am sure anyone that used their good ol 'ears' (which is what matters, its what observes the sound to OUR perception, not these sound monitoring devices..) would conclude the same.

     

    -Matt

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    airgunfans
    Participant
    Member

    Hi STO, I noticed that in all your design including the LIM which uses simple conical baffles, the largest chamber is always at the front.  This is opposite to common designs having the largest chamber located close to the exit of the barrel . Is there any reason for that ?

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    STO
    Participant
    Member

    airgunfans

    Hi STO, I noticed that in all your design including the LIM which uses simple conical baffles, the largest chamber is always at the front.  This is opposite to common designs having the largest chamber located close to the exit of the barrel . Is there any reason for that ?

    So it isn't exactly opposite the common hair-curlers-and-washer-baffles designs, but yes it is a bit unusual. Let me explain. 

    So one of the common designs like a Donny or Hugget or 0dB or Clague, they also have a large front chamber, however without tuning what they really have is the exact same internal architecture repeated throughout the can. Yes yes, the middle chamber on all these designs tends to be smaller while the first and last larger, but you see what I'm getting at. Their designs work by having a couple choke points, usually two, for flow and then the rest of the design is just expansion area (empty space) and damping material (felt/foam). 

    Coming from the opposite direction, and with experience working on firearm silencers, I started with the opposite strategy which was all baffles (choke points for flow). I made some advances optimizing that architecture, but the designs sounded louder than what they metered because the sound they produced was more sustained. So I started introducing sound damping materials into the front of the moderator to try and mute the sound that the baffles make slowing down air. 

    This three stage strategy of stripping turbulence off the pellet with a blast baffle, delaying flow with some sort of baffle/gas diode design, and then damp the sound worked and worked well….. the question became a matter of ratios. Given a finite amount of space in which to work, how much volume do you give to your blast chamber, your baffle section, and your sound damping section? I determined it experimentally, and on my .22 caliber FX Crown attached to the front of the shroud. This is probably why it favors more sound damping, the "open section at the front," as opposed to more baffles: there is a lot of reflex volume in that shroud in which the baffle end can hold pressure in and slowly release it, so there is a much greater need for large sound damping volume than large blast chamber volume. 

     

    As you can see above, I have been doing some tests on higher flow systems, and the results lead to a few tweaks to optimize the Pilum for better performance under those conditions, but until I get my hands on a system which is regulated and produces significantly higher power I won't be able to generate a design fully optimized for those conditions. I suspect that ratio of sound damping to flow delaying will change, but until I try it I really can't say by how much. My experiments with the Leshiy have been informing my thinking on the subject, because there you have a gun producing most of the power of a full sized airgun with a barrel half the length or less and you have VERY little space in which to suppress it. As you can clearly see, the ratio of baffle to sound damping is rather different than on my Crown. ;) 
    https://www.airgunnation.com/topic/muzzling-the-leshiy-a-silencer-story/#post-482262

    I hope that answers your question. :) 

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    bucketboy
    Participant
    Member

    Great write up thanks.

    i am very great full that I had the foresight to make a sandwich and a cup of coffee before  I started reading this.

     

    Bb

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