(4/15/19 update) Moderator Design, Testing, and Evaluation (the big test)

Forums PCP Airguns (4/15/19 update) Moderator Design, Testing, and Evaluation (the big test)

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    ackuric
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    Welp, I tested a LDC with and without F1 felt. Its an LDC built 1:1 to a Donny FL style that has a mono-core that I can modify if desired, that screws into a tube. The monocore OD is .2" less than tube ID which allows me to wrap it with felt…

     

    DB meter showed insignificant change weighing in favor of the version without felt wrapped around the monocore…my ears noticed 0 difference as well.

     

    I won't contribute the insignificant difference to superiority as there is always slight shot to shot variation especially at my lower FPE tune, upwards of 4%…so if anything I will call it a 1:1 wash / tie. 

     

    The sound analyzer app I use is very sensitive to change and measures across many frequencies. There was literally next to no change between all.

     

    On another note, the smaller 3.5" telescoping moderator I built, full extended is 1" longer than the mono-core version but has MUCH less overall volume, and it again performs basically 1:1 with the 'donnyfl' version. When collapsed its 2" shorter and MUCH louder, registering 2-3~ db higher. 

     

    Look forward to seeing any updates you have on your Tesla Gas Diode or any other version you design STO.

     

    -Matt

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    ackuric
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    Test# 2.

     

    I put F1 felt into my 3.5" LDC's blast chamber which is nearly 1" OAL. There were no significant changes in favor of with or without to the ear or to my sound analyzer app. 

     

    I have yet to find a configuration that benefits from adding F1 Felt, either I am doing it wrong or its placebo effect on those who think it further dampens sound from our air guns.

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    STO
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    Yeah apologies for being slow. Excuses are lame, so I'll just say that I've been incredibly busy with things which are more demanding of my immediate attention than fun pet projects like this, and so it just hasn't been finished yet. I've got several designs done and mostly assembled, including some with F1 felt just for your FeltFanboy ;) where I can swap the felt for other materials and compare efficacy. It is my hope to get the testing done some time this week, as the forecast suggests the weather should hold. But for now, that is all I've got. :) 

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    Mendopellet
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    My felt is fraying ! LOL  I appreciate your findings very much!  As we spoke abt privately, I am about to start testing on this end as well. 

     

    I am most interested in finding out what causes the anomalies in moderators. To be clear, I once witnessed a 4" moderator on a FX Tarantula that made the gun "click" quiet. When you screwed on either of the much larger and longer, and highly regarded moderators, the gun became noticeably louder. WTF ?  And that is what I am hoping to figure out. Why some guns respond SO differently with different mods. I hope to be able to photograph the air blast from several muzzles, in super slow mo to see how differently the outward expanding cones of the air blast are from different barrels/crowns. 

     

    I never tried felt in a mono tube moderator. But in multi baffle, it did make noticeable differences.  I had a Royale 400 with factory moderator, in which I unscrewed the end cap with heat, and added felt.  All 4 or 5 people heard the bark change significantly. BUT, it may have been a frequency change difference we were noticing. Our ears become MUCH more sensitive in the vocal range, and it's first and third harmonics. When you removed the felt from the FX mod, it changed right back. Obviously more experimenting is in order!

    Feltfanboy has been knocked down in round 1 !  Will he answer the bell for round number 2 ??? LOL

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    ackuric
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    I am quiet certain that there is absolutely zero configuration with F1 Felt that will significantly change frequency or sound pressure. For there to be any significant changes my sound analyzer app would immediately recognize it. 

     

    For example:

    No moderator = 83.5~ DB

    Moderator retracted = 81.3 DB

    Moderator Extended = 78.8 DB

    The above configurations all have incredible sound difference. When I added felt in ANY config be it between baffles or around…there was literally no change shown on the results I got from the app, nor could my ear hear any notable changes :/ 

    YMMV

     

    Monocore vs stacked baffles is a silly argument its just how the baffles are configured, either independently or as one…they can be designed 1:1 and perform 1:1. You can cut a monocore in 3 pieces and it'll perform the same, or glue your stack of baffles together and they will perform the same… Monocore's use the same baffling principles as their counter-part. I have turned my marauder baffle stack into a monocore and it changes nothing. Further, I tested felt in both monocore and stacked baffle arrangements and saw the exact same results, which were absolutely zero change in sound pressure.

     

    -Matt

     

    • This reply was modified 4 months ago by ackuric.
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    ackuric
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    All it takes is a smart phone and a free app to compare one moderator to another, or compare any possible changes in configuration. Never trust your own ears…as it is VERY easy to convince yourself once 'modifying' something that it becomes better…its better to verify the truth than assume it.

    So far my data has only proven one thing…that both reducing the volume via the felt provided little to no change, and the felt itself provided little to no change…either the two cancel each other out, or NEITHER are significant enough to radically change sound pressure. I bet its the latter…I am sure if I run the same 3.5 inch moderator but one as wide as a bus, the rifle would STILL put out the same observable sound pressure. Why?

     

    Well IMO Because LENGTH and Baffle Efficiency are probably the two biggest factors. Air will find the path of least resistance in ANY direction it is allowed.  To radically change the sound, you need to radically change the duration the air stays inside via redirection (baffle efficiency) and length.

     

    The most quiet airgun will be one with a barrel long enough that utilizes ALL pressure released from the reservoir, or a moderator that replicates said event. I am sure there is a design such as the Tesla Gas Diode will hopefully break new ground with Baffle efficiency that allows much shorter length moderators that are as effective as the larger counterparts. If I could have my 3.5" retracted moderator as quiet as it is extended, well…that would be awesome. Felt is not the path to that, Baffle Efficiency is.

     

    On another note, most moderators I've come to know only reduce DB levels around 5~ db…+ or – 1~…its a common trend.  

     

    Example 1:

    (results in -5 db with rocker 1 AND sumo over stock…)

    Example 2:

    (results -5 db avg…)

    Example 3:

    My config…

     

    Its quiet interesting how -5 db seems to be a fairly set in stone marker for sound reduction on pcp's IMO. I don't see ANY hitting -10 to -15 db or anything remarkable…just an observation. 

    -Matt

    • This reply was modified 4 months ago by ackuric.
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    STO
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    ackuric

    All it takes is a smart phone and a free app to compare one moderator to another, or compare any possible changes in configuration. Never trust your own ears…as it is VERY easy to convince yourself once 'modifying' something that it becomes better…its better to verify the truth than assume it.

     

    So I've touched on this before: generally phone microphones and the associated apps can't/won't accurately measure or compare these sound impulses. If you're using that, your results may be wildly inaccurate. Obviously I can't test every possible phone or sound meter out there, but I've tested a couple phones and a couple inexpensive meters and they just don't produce good data. They will produce some numbers, all of them, however those numbers either vary wildly or are surprisingly consistent but don't accurately reflect SPL. Amusingly the typical failure mode is they report roughly the same dB readings despite dramatic changes in sound level. 

     

    • This reply was modified 4 months ago by STO.
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    Mendopellet
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    Uh … Matt, are you saying an empty tube is the exact same as a tube with baffles ?  

     

    I did read where you did state MOST moderators, not all of them, but neg 5 can not be the limit, or close. Because I once owned a 7" long by 7/8" OD that made a 27 fpe gun suddenly go "click" … stupid, stupid sound reduction. From LOUD to non existent. I would NEVER believe it, had I not witnessed it. I still have photos of the gun even

     

    THIS kind of crud is what I want to find out HOW it can possibly happen. I DO KNOW the internals of the moderator. But copying it EXACT would be the only way to find out, and I no longer have it. .

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    ackuric
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    Mendopellet

    Uh … Matt, are you saying an empty tube is the exact same as a tube with baffles ?  

     

    I did read where you did state MOST moderators, not all of them, but neg 5 can not be the limit, or close. Because I once owned a 7" long by 7/8" OD that made a 27 fpe gun suddenly go "click" … stupid, stupid sound reduction. From LOUD to non existent. I would NEVER believe it, had I not witnessed it. I still have photos of the gun even

     

    THIS kind of crud is what I want to find out HOW it can possibly happen. I DO KNOW the internals of the moderator. But copying it EXACT would be the only way to find out, and I no longer have it. .

     

    Uhm where did you gather I said an empty tube is as effective as one witth baffles? I have never said anything like this, not even slightly…
     

    I stated the two things that matter MOST…BAFFLE EFFICIENCY AND LENGTH more so than VOLUME or SOUND DAMPENING MATERIALS.

    I hear way too many people say that some magical moderator makes their rifle go 'click'…No offense, but either you have hearing issues, or are full of it….quiet is subjective but when a db reader hits 70+ DB's its not even remotely close to quiet or 'click, hammer noise only'…it infuriates me that some people seem to have serious hearing issues or opinions about whats quiet that varies EXTREMELY from the INDUSTRIES STANDARD…

     

    If you're going to make claims, use modern technology available to confirm your findings or beliefs or just keep them to yourself. IMO. For a rifle to just go 'click' from the sear? you would be registering at 40-50 db's…I've shot pellets at 150-200 FPS (3 fpe) that make more noise than that…

    • This reply was modified 4 months ago by ackuric.
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    ackuric
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    STO

    ackuric

    All it takes is a smart phone and a free app to compare one moderator to another, or compare any possible changes in configuration. Never trust your own ears…as it is VERY easy to convince yourself once 'modifying' something that it becomes better…its better to verify the truth than assume it.

     

    So I've touched on this before: generally phone microphones and the associated apps can't/won't accurately measure or compare these sound impulses. If you're using that, your results may be wildly inaccurate. Obviously I can't test every possible phone or sound meter out there, but I've tested a couple phones and a couple inexpensive meters and they just don't produce good data. They will produce some numbers, all of them, however those numbers either vary wildly or are surprisingly consistent but don't accurately reflect SPL. Amusingly the typical failure mode is they report roughly the same dB readings despite dramatic changes in sound level. 

     

     

    So let me get this right, its better to use my ears as an instrument to measure sound than a phone app that was designed to do such? Lol, because I am not dropping coin on a db meter…so short of my ears, what other option do I have? 

     

    I am only using my phone to cross compare one moderator to the next, not for base DB level…also the first video I posted was using a calibrated db meter…his results = -5~ db reduction with moderator/ldc….my results = -5~ db difference with phone app. I've seen about 3 other videos with use of DB meters over phone apps that had the same results…seems like a trend.

     

    As I stated much earlier, phone app's that measure sound levels are great for cross comparison…not for actual db readings. Feel free to download one (its free) and use it on your comparisons in the future as they are applicable to these tests just as any other db meter is…the true db reading may be off X% but the difference in data extrapolated between two moderators will not be off by that same %…SPL is very linear in the range we're testing…

     

    I'd rather you post DB measurements taken by phone than none at all…its easy as 1-2-3 and you'd be surprised how accurate they can be

     

    -Matt

    • This reply was modified 4 months ago by ackuric.
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    DHart
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    I agree with Matt in that there is good utility for the free with the smart phone apps.  While they may not give such precise and absolute readings as an expensive SPL meter can, they can serve well in comparing one moderator to another.  The app I have used gave readings of different cans that were relatively in line with my subjective hearing perception.  Not everyone needs to test with expensive professional instruments.

    • This reply was modified 4 months ago by DHart.
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    STO
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    So I did a little quicker and dirtier testing just to see where things are with these various design concepts, materials, etc. And, of course, see about felt. So 5 designs in all were tested, many of them with both felt and a rubber damper of the same shape/dimensions. I have a bit of a different take on precision, clearly, so I just want to highlight that these are all rough numbers. I didn't use the full distance and mic positioning protocol, the standard deviations are a little high, there was at least one significant baffle clip in one of the tests, some of the foam in some tests wasn't adequately constrained and was sucked into the path and spit out, the setup was too close to several solid objects including the house and the hard surface the rifle was rested on so there are potential sound reflection issues, and there was enough wind that some of the readings may have been skewed. In short, these are rough numbers at least by my standards. 

    As usual though each number is not converted to dB, and is an average of a whole series of different averages of different readings. Also, as usual, the same length carbon tube was used so that the OAL of all moderators was 120mm to keep things equal So here goes:

    Gas diode moderator – 119.2
    This is the same silver gas diode as in the original tests. Things meter differently depending on the day, so some standard to check progress is sensible. This was that. 

     

    Gas diodes + felt – 71.6
    Instead of the usual stack of 5 gas diodes, this uses the same flow-through concept but only two gas diodes to blunt the initial forward rush of gas. After that it uses damping materials which can be changed to test design efficacy. In this case felt (not shown) 

     

    Gas diodes + rubber – 66.4
    First blow to the felt. This damping rubber produced significantly better numbers than felt, and I'd expect it to have better long term durability as well. Both the felt and the rubber were cut with a laser, and while the rubber had to be cleaned once cut, it didn't smell nearly as bad as the felt. Burnt hair is smelly stuff. 

     

    Classic w/ rubber – 84*
    Another attempt at a classic baffle design at the back, with rubber and foam at the front. It suffered a number of problems in testing and was deemed unsuitable. For this reason the asterisk essentially means "this test was NFG and we know it." 

     

    RFD felt – 59.6
    This is a non-flow-through gas diode design, again with just a couple diodes at the back (pictured) and a felt stack at the front (not pictured) 

     

    RFD rubber – 47.6
    Same design as above, but now a rubber stack. This is the next blow to felt. 

     

    LIM felt – 61.2
    LIM stands for Less is More, the idea being that less stuff taking up space inside the moderator means more volume to eat that blast/sound. Again the rear stack is pictured, the front section where felt or rubber are stacked is not. 

     

    LIM rubber – 74
    This is the only test where the felt out-performed the rubber, however the SD on this test is very large, 18 in fact, so the error margin likely exceeds the difference, which is not true for the RFD design. 

     

    I'm really really big on precision, which is why I cage all of this in endless caveats. Taking the time to do truly proper testing is very time consuming, and so when I want to just go fast and get an idea of what directions to try going in next, I'll cut some corners. That was done here to roll out at least some useful results. Most notably that felt isn't turning into a huge win. In a way its a shame because F1 felt is comparatively inexpensive, but on the other hand it is a relief because felt does fray and break down so omitting it from future design work is one fewer failure mode. I do want to say though that this isn't a comprehensive indictment of felt. If you were to exclude the open cell foam we also used, it might have had a more significant effect. In our case though, it seems the felt just isn't worth it. It also stinks to high heaven when you cut it. 

    More testing to be done, however I might start at least partially moving away from the flow-through design given the RFD results. RFD, LIM, and classic were designed by a buddy of mine who "cheated" in a couple small ways like reducing the core hole diameter, and failing to fully constrain the foam, so I'm genuinely unsure of the performance jump between the gas diode – rubber and the RFD – rubber tests. *shrug* As always, I'll continue testing. 
     

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    STO
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    So another update. The designs and materials have been tweaked a bit from the pictures above excluding the rev.1 diode obviously. A fair bit of smaller scale fettling and informal testing went into optimizing these before putting a bow on everything so I could post it. I also wanted to do some quick back to back accuracy testing as I had, lets call it a hunch, about the rev.3 and LIM damping sections, as well as the LIM design outright. Pellets are just SOOOO sensitive to bad turbulence in there. 

    Also the numbers are supposed to be different. Different  pellets, no calibration, totally different atmospheric conditions. they're only meant to be relative performance within, not across, tests. Hence why I retested both the shroud and the OG gas diode: wanted a solid baseline for comparison. 

    If there was a theme for this series of tests it would be stopping air-flow at the back and then muffling the sound at the front. Different pressures and flows exist from the back of the moderator to the front, so it only makes sense the design should accommodate that. Seems to have worked as well. 

    ^Shroud extended – 199.6

     

     

    ^rev.1 gas diode – 138.2

     

    ^rev.2 gas diode – 112.0

     

     

    ^rev.3 gas diode – 100.6

     

     

    ^LIM – 91.2

     

     

    Shot some quick groups at 59 yards standing off a tripod (not as stable as prone off a bipod, but there is snow on the ground so……) just to make sure things are working and/or find out if they're not. 

    Stock shroud, and rev.2 diode are running great. The damper section on the rev.3 diode is still too aggressive and, while quieter as a result, the accuracy loss is NFG. LIM threw a flier all the way off the paper and was just generally an oversized group. This design develops too much turbulence around the pellet and just opens up the groups. 

     

    And that is where things stand for now. I've switched over to the rev.2 Tesla gas diode on my gun full time. I really thought I was approaching the performance limit for such a small package size with the rev.1 diode, but to my surprise I'm still able to find significant gains. Not quite sure where I'll go from here to improve performance, but there is always something to be found, some efficiency to be had. 

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    ackuric
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    I like your current revision, however..

    How do the above tests correspond to perceived sound and DB levels in comparison?? The above tests don't really give a good example of what the human ear is going to experience…which after-all is primary purpose to sound reduction… In every city I visit, they generally have sound ordinance measured in DB, which is a simple universal measurement of perceived sound, I highly recommend including it with your tests to be conclusive as to how perceived sound is altered…is it -5 db? -10 db? -2 db?…

     

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    Rich_B
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    Have you explored the Epsilon baffle design? I got to do a little playing around with a 1”X6” tubed suppressor of HTG manufacture when the guy that developed them was still here in the states. It worked very well with no accuracy loss on my air rifle. Just something you might be able to incorporate into your design. 

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    STO
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    Rich_B

    Have you explored the Epsilon baffle design? I got to do a little playing around with a 1”X6” tubed suppressor of HTG manufacture when the guy that developed them was still here in the states. It worked very well with no accuracy loss on my air rifle. Just something you might be able to incorporate into your design. 

    The epsilon baffle design. Holy crap. Talk about seeing ghosts. I haven't heard that name in….. maybe 15 years? Did you know Vais?

     

    I don't know how much of the history behind this you know or care about, but at bare minimum for the benefit of any forum members here who are curious, the design was cooked up by a crazy Greek guy named George Vais in the '00s, and it had at least some notoriety in its time. The chronology in the suppressor industry is a little weird because Brugger and Thomet were doing great research quietly for decades, but the industry in the United States was largely in the dark ages, barely crawled out of the primordial soup of stacked wipes by the '00s. Remember at this time most people still though silencers were completely illegal, it wasn't until AAC with their gurellia marketing and then later SCO and their successful campaigns that people realized it was just some paperwork and a 200$ tax to own. Anyway so back in these dark ages there wasn't much in the way of quality testing or design comprehension, and the epsilon baffle was a reasonably clever design in its time. It worked via cross-jetting and was at least somewhat optimized for manufacture. Top three designs in this legendary X-ray are his:

    So anyway he patented the design and made it under his company HTG, which he later sold and the new owners got involved in some legal entanglements and it went belly up. Looking into this now, it appears Black Rain Ordnance purchased the patents and still build some of his can designs. By today's standards they're quite outdated, but in at least some respects the epsilon baffle can be thought of as the conceptual predecessor to the clipped conical baffle which is lighter weight, more efficient, and now dominates the industry.

     

    Regarding using it in airguns, I haven't directly tried it however I think I have a pretty good idea of how it works. In essence it uses asymmetric flow at the mouth to generate a cross-jet which reduces flow rate. In this way it is a lot like the clip on a conical baffle, trying to create that asymmetry as pressure drains from one chamber to the next. You'll notice though that, in his designs, there are few baffles. This is because the lack of a conical rear face both increases necessary thickness for equivalent durability, and decreases effective gas expansion prior to meeting the next baffle. In firearms, aside from being unusually heavy, these cans were notable for their POI shift, which is not surprising given the design. I don't know why you wouldn't have seen these associated issues in your airgun, at bare minimum just from barrel sag. 

    I guess the punchline though is that, as far as performance goes, the clipped conical baffle has eclipsed the epsilon baffle in terms of performance in the firearms industry and I'd expect that to be mirrored when it comes to airguns. It is a page back, but I tested that design here:
    https://www.airgunnation.com/topic/fx-crown-bespoke-moderator-tesla-gas-diode/page/2/#post-381182

     

    I hope that answers your question. If I missed, or misunderstood, or otherwise posted something flat out incorrect please jump in and set the record straight.

     

     

     

     

    ackuric

    STO

    ackuric

    All it takes is a smart phone and a free app to compare one moderator to another, or compare any possible changes in configuration. Never trust your own ears…as it is VERY easy to convince yourself once 'modifying' something that it becomes better…its better to verify the truth than assume it.

     

    So I've touched on this before: generally phone microphones and the associated apps can't/won't accurately measure or compare these sound impulses. If you're using that, your results may be wildly inaccurate. Obviously I can't test every possible phone or sound meter out there, but I've tested a couple phones and a couple inexpensive meters and they just don't produce good data. They will produce some numbers, all of them, however those numbers either vary wildly or are surprisingly consistent but don't accurately reflect SPL. Amusingly the typical failure mode is they report roughly the same dB readings despite dramatic changes in sound level. 

     

     

    So let me get this right, its better to use my ears as an instrument to measure sound than a phone app that was designed to do such? Lol, because I am not dropping coin on a db meter…so short of my ears, what other option do I have? 

     

    I am only using my phone to cross compare one moderator to the next, not for base DB level…also the first video I posted was using a calibrated db meter…his results = -5~ db reduction with moderator/ldc….my results = -5~ db difference with phone app. I've seen about 3 other videos with use of DB meters over phone apps that had the same results…seems like a trend.

     

    As I stated much earlier, phone app's that measure sound levels are great for cross comparison…not for actual db readings. Feel free to download one (its free) and use it on your comparisons in the future as they are applicable to these tests just as any other db meter is…the true db reading may be off X% but the difference in data extrapolated between two moderators will not be off by that same %…SPL is very linear in the range we're testing…

     

    I'd rather you post DB measurements taken by phone than none at all…its easy as 1-2-3 and you'd be surprised how accurate they can be

     

    -Matt

    ackuric

    I like your current revision, however..

    How do the above tests correspond to perceived sound and DB levels in comparison?? The above tests don't really give a good example of what the human ear is going to experience…which after-all is primary purpose to sound reduction… In every city I visit, they generally have sound ordinance measured in DB, which is a simple universal measurement of perceived sound, I highly recommend including it with your tests to be conclusive as to how perceived sound is altered…is it -5 db? -10 db? -2 db?…

     

    I took some time to think about how to answer this question, given our previous chats on the subject, and formulate a thorough response.

     

    The issue regarding decibels specifically, so far as I can tell, is one of communication: how to communicate to a reader how much louder or quieter something is. This is actually a non-trivial challenge, not nearly so simple as throwing out some dB numbers. And this is for a couple reasons, which I will try to highlight before giving you the answer you may have been looking for. (dB numbers off a cell phone sound meter app)

     

    For a start, decibels are logarithmic, which is not how most people's minds work and also not how people's ears perceive SPL. For the benefit of someone reading this who doesn't already know, going from 100 to 120 decibels isn't 10% greater sound pressure level (SPL) but actually 100 times greater SPL. This also makes distance dissipation a bit more complicated, but the very rough rule of thumb is you cut 6dB off your reading every time you double the distance, or increase it by 6dB every time you halve the distance to the sound source. On top of that, how we perceive things also doesn't have a good correlation with decibels. Something which is ten times louder (+10dB) won't sound ten times louder, and tone messes with this even more as our ears have varying response both in general and from person to person, and this changes with age among other things.

     

    This makes things abstract, easy to understand but much more difficult to truly comprehend. I've been working with sound for years, and still if you say something is -5dB or -15dB I don't have a good mental benchmark of just how much and how different that will sound unless it is a firearm suppressor or airgun moderator. Contrast that with time or distance or temperature, where most people have a pretty good idea. If someone says it is 40 degrees Fahrenheit out for example, that probably gives you a pretty good guess how it will feel. When it comes to decibels, I suspect most people have little to no mental benchmark at all.

     

    Another major confounding issue is that a lot of people are using unsuitable equipment like phone apps to “measure” the “dB” reduction of a moderator. This means, whatever mental picture people have of sound attenuation as it relates to a given moderator in dB is almost certainly wrong, in both absolute and relative terms. Readings can vary wildly from phone to phone. You clearly disagree with this, so as part of typing this up I decided to again download the app and test a couple constant background sounds (running machinery) and continuous tones. These are the kinds of things an app might be suitable to measure, as opposed to impulse sound like an explosion or impact or “uncorking” sound. To compare against I have a pair of sound meters one of which (meter 2) has been calibrated in the last 6 months. This is all of them sitting next to each other with mics parallel, and some distance from the sound source so readings should be similar.

     

    Location 1
    app 42dB

    meter 1 59dB

    meter 2 62dB

     

    Location 2
    app 50db

    meter 1 60dB

    meter 2 61dB

     

    Constant tone 440Hz

    app 57dB

    meter 1 65dB

    meter 2 68dB

     

    Constant tone 26Hz

    app 32dB

    meter 1 OL

    meter 2 55dB

     

     

    So the last one was intentionally an oddball, and it shows. And, again, meter 2 has had a calibration within the last 6 months. That doesn't guarantee accuracy, but I certainly trust it a lot more than the phone app. I realize we've sparred on this subject before, but I just can't tell you how comprehensively wrong you are to think that you can accurately measure sound at all let alone an impulse sound with an app on your phone. This is the case both with absolute measurements, and relative comparisons between sound sources. Phone mics have a wide variety of things going on in the back end, some electronic some physical/mechanical, to try and make the sound they record pleasing and “clear” to the human ear, they're not about fidelity. A cell phone designed to measure this type of sound we generate with airguns would make for a really really bad phone. Just look at the 26Hz test as an example, that 32dB reading is 20dB off (two orders of magnitude) but it is actually worse than that, because 32dB is what the phone measured as background noise. It seems likely it was either unable to read or filtered that frequency because you wouldn't want it in conversation. So what was a very audible and consequential sound to my ear, it completely did not measure.

     

    The best analogy I can make here is that a phone is like a silvered mirror. Ever wonder why we use silver for mirrors, given that it reflects spectra imperfectly, instead of aluminum like you see in optical instruments? It is because silver will increase our perception of rosy cheeks and flesh tones so that we think we look prettier than the cold hard reality. Same thing is true of a phone, it is trying to transmit our voices, not every single distracting noise out there in optimum fidelity. You wouldn't want to own a phone which was good at recording, let alone measuring, the type of sound coming out of an airgun moderator. It would and should intentionally seek to filter these sorts of sounds.

     

    And of course your phone's mic/app is just COMPLETELY uncalibrated.

     

    So funny enough I've already tested these two sound meters and this app before on airgun moderators and discovered that none of them work for this application. I'm kind of a stickler for precision, as you may have noticed, so I'd rather give numbers I know are accurate but haven't been converted to dB for lack of calibration than throw out some “close enough” guestimate. While I had all three of these cheapy meters out though, and was recording data, I figured I'd make hay and just run them next to each other against my Crown. Here are the averages which make for rather comical results, numbers from left to right are as follows:
    rev.2 diode, shroud extended, and the delta (difference).

     

    app – 63.4, 77.6, 14.2

    meter 1 – 56.95, 71.7, 14.75

    meter 2 – 99.45, 104.7, 5.25

     

    Meter 1 was throwing crazy varying numbers with the moderator on, almost a 10dB range, so the similarity in delta to the app is purely coincidence. Drop one number out of the average, or take one additional sample, and that'd go away. As far as meter 2 goes, when measuring the Crown no matter how you configure things it tends to spit out numbers in that range. As an extreme example I can straight up put tape over the muzzle and dryfire it and you'll still get numbers around 100dB. They bear not real correlation to anything else, so I haven't the foggiest idea what it is actually reading or why, but sound is a tricky thing so it is just a mystery. *shrug*

     

    I guess if you still think that cell phone apps are a good way to measure moderator performance, you have the numbers you wanted. ;)

     

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    Bob_O
    Participant
    Member

    I have to agree with you STO, on cell phone apps not being good for measuring impulse sound levels.  Maybe not the apps fault, but rather the phone's/microphone's fault.

    The extent of my experience is from recording scope cam footage and 3rd person cam footage of my shooting, both with air guns and powder burners.

    Cases in point.

    I can use my FX Streamline 22 recorded by my phone, compact camera, GoPro and X-Sight, and it sounds like I'm using four different guns.

    Same with my FX Crown recorded by my phone, compact camera and GoPro.

    Same with my 6.5 Creedmoor recorded by my X-Sight, compact camera and GoPro.

    Phone apps are great for some things but obviously not for accurately measuring impulse sounds.

    You obviously know what you're talking about here.

    • This reply was modified 3 months ago by Bob_O.
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    Rich_B
    Participant
    Member

    I do know George. Still talk to him from time to time. I spent quite a bit of time in his shop with him in the last few months before he moved back to Greece. Learned a lot from the High Tech Greek.

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    STO
    Participant
    Member

    Thanks Bob. :) 

     

    Rich_B

    I do know George. Still talk to him from time to time. I spent quite a bit of time in his shop with him in the last few months before he moved back to Greece. Learned a lot from the High Tech Greek.

    Really now? Well that is cool. Browsing around I finally found his patent on the epsilon baffle:
    https://patents.google.com/patent/US20060123983

    How a baffle design is expected to work and how it actually works are often not exactly similar, however in this case it seems Vais and I have a pretty similar conception of how his design will function. I'm sure if you knew him, you also knew about the controversy that surrounded this design, so I won't get into it here. Suffice to say though, given a sound meter and another decade, I'm genuinely curious what he'd have cooked up by now. Dare I ask what he is currently up to in Greece? A lot of history has happened there in the last ~15 years? 

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    Rich_B
    Participant
    Member

    He’s mostly fishing, painting, and messing around with airguns. I’m hoping he got enough money to finish living his life out over there. Very good generous guy and more than willing to share his knowledge.  

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