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Moderator Comparison Spread Sheet

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OldSpook

OldSpook

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I have seen a number of studies which conclude the most significant discriminant in the performance of moderators as sound reducing devices is the physical volume. I am not saying those studies are correct but I am inclined to go with their conclusions. Clearly there are other considerations but they all pretty much boil down to information necessary to compute their volume so...

I recently had a requirement for a replacement moderator for my Condor and decided to calculate the physical volumes / price for all of Donny FLs offerings as I am partial to his work.

The image below is the product of that spread sheet and the ss itself is attached as a file. You could add whatever other vendors products you wanted and compare them. One could add a weight column to that data if desired. I can't think of any other information that would be comparative and readily available to include.

donny-fl.1651261921.jpg


download.png
View attachment donnyfl-silencers.1651261932.ods


 
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once you get past sumo though they can start to be impractical .. i could get an endcap and put an emperor with extender on my mrod lol .. the rifle is gonna be about 7ft long though, where you goin with that lol ... other gun noise factors generally come into play once any moderator is installed, so getting the muzzle blast super quiet starts to mean less unless those are handled first ..
 
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Physical volume is not the only factor, shape is a large contributor. Generally, longer tubes allow for more air to be stripped as long as there's enough diameter to hold the volume so the pressure is significantly lower and the air exits slowly. Only enough diameter is needed for the maximum pressure/volume combination, after that the excess diameter isn't useful.

However, each expansion chamber is also important as shown by the Fatboy 2.0, which while it's a great looking can isn't that quiet. (It is versatile and takes out a lot of the sharpness of the sound, so there's that.)

Of course, if you're running a long-barrel Texan with Emperor V3 and Extender that puts a lot of weight on the shooter to support and is a bugger to carry in the brush. An Emperor on a small ,22 bullpup can be a lot to carry, so you have to really want "mouse fart quiet" to choose an Emperor over a Sumo--BUT the Emperor does get results.

I'll attach my own personal chart, but be forewarned the colors, bold, etc. were for a previous purpose and are no longer valid for my needs, much less yours I'm guessing. Also, huge sound reductions can be gained simply by pushing less air, and these charts don't reflect that, nor that the larger the caliber the more air that escapes and the louder it will be.

moderators.1651265473.png



 
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Volume certainly helps, but if the volume isn't shaped in a way that spreads-out the shockwave, it does not do very much. Probably the most ideal moderator would have fantasitically intricate wormy-curly asymmetrical pathways that force the flow to be turbulent and completely flattens the shockwave. Exactly how small you can get such a thing and make it "quiet-enough" is an interesting puzzle that has not been solved yet. 
 
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Friends, you are reminding me that I need another column in my Silencer Specs Table...! 😄 VOLUME!!
Click to expand...

That would be cool, you'll need a genuine sound meter to capture the actual difference in performance, Smartphone mics need not apply. Think something like a calibrated Bruel & Kjaer meter.

But it will get complicated quickly because, as @WI_Hedgehog points out, simply pushing less or more air will produce different results in different moderators.
 
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As @WI_Hedgehog points out, simply pushing less or more air will produce different results in different moderators.
Click to expand...



Yeah, and it's not necessarily just the increase of muzzle energy ("more air") that increases the loudness of the gun — because HOW the gun is TUNED to achieve that particular muzzle energy is also a big factor. 



Here is what I learned from Bob Sterne (resident tech writer over at www.GatewayToAirguns.org and some time HardAir Magazine):



Assuming always the same muzzle energy (ME):

🔸 The most quiet tune is the one with a higher regulator setpoint which allows only short sips of air (regulated by the HST) to achive that ME. (This tune would be less than 5% of muzzle velocity [MV] below the "knee" of the velocity curve. This tune is somewhat prone to larger muzzle velocity variations.)

🔸 The loudest tune, at the same power, is the one where the hammer opens the valve for a long time so that there is air flowing through the valve until the pellet has left the barrel — this tune allows for a very low regulator setpoint at this particular power.

🔸 The "regular" or "medium" tune is one that uses a medium time to open the valve, and a medium regulator setpoint, somewhere between 2% and 5% below the velocity curve's "knee." This is the most effective tune and the one with the smallest MV variation.



🔶 ➔ Tune according to your preferences. If silence is a priority over muzzle velocity spread and power, tune to produce tiny sips of very high pressure air — they are the quietest.



Matthias


 
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...

Assuming always the same muzzle energy (ME):
...
Click to expand...

Yeah, it would be nice if it was simple.

Still, there should be some value in comparing moderator efficiency on specific guns with specific tunes.

Unless the difference is only a couple three dB between them all. But I suspect it would be a decent way to sort out the crappy ones from the decent ones.
 
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3dB is a doubling of acoustic power. Our perception is different, where a 10dB difference is perceived as twice as loud.
Click to expand...





Jason, 😊

your profound and extensive airgunderstanding is always an inspiration to me, and a great help to literally THOUSANDS. 

Thank you that you keep sharing your airgunderstanding here and at other forums. 👍🏼

Matthias


 
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3dB is a doubling of acoustic power. Our perception is different, where a 10dB difference is perceived as twice as loud.
Click to expand...

Ok, thanks for the correction. I appreciate it. One thing I am sure of is the fact that 6 decibels represents a doubling/ halving of range. That is to say if you are hearing a thing at 50 yards and 60 dBs. Then if you increase the power to 66 dBs and move to 100 yards you will hear it at the same level.
 
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So now that we have that we can establish a "poor man's" test procedure to estimate how far our shot can be heard above the noise floor. Mind you I am going to cheat on the math a bit. It's a short cut but it's close enough. Exact solution in note at bottom. The cheat will work well enough given the limitations of our test setup and you can do it with pencil and paper at the bench.

First we measure the noise floor. It would be good to do that in a number of places using multiple microphones but the operative adjective here is "poor man's". We will be using an application on our cell phone. There are plenty some are better than others and naturally cell phone mics are not as linear as high end test equipment but in keeping with our budget... we will endeavor to persevere...

  1. So establish a noise floor by placing the cell phone running the sound meter application where you intend to measure the noise level of your shots. You will want it to be a few yards from your shooting position. I suggest 10 yards (or meters if you are going to do your math in meters). Let it run for a few minutes and note the average noise level. We will call this the "noise floor". The noise floor is the level below which detection of the sound of your shots is unlikely (not impossible).
  2. Shoot several shots at your target while running your sound meter. Note the peak noise level measured during each shot.
  3. Average the peak noise levels.
  4. Now subtract the "Noise Floor" value from that average. For example your "noise floor" average is 65 dB and the average of your shots is 82 dB. Subtracting 65 from 82 dB you get 17 dB difference.

    Now you have all your data.

    Remember that for each 6 dB the distance doubles. If you divide 6 into 17 you get 2.83. We need to double our range ABOUT 2.83 times. There is a way to do the math exactly using powers of two but here is a heuristic which will give you a good enough answer.
    • Double 10yards is 20 yards; subtract 6 from 17 = 11; 2.83 -1 = 1.83
    • Double 20 yards is 40 yards, subtract 6 from 11 = 5; 1.83 - 1 = .83
    • Double 40 yards is 80 yards TIMES 0.83 = 66.4 yards and that's your answer.

    The range at which your shots drop into the noise floor is about 66 yards from the muzzle. The exact answer is 71.27 yards. Clearly there is no way we can be that precise under these conditions and using the tools we have.

    If you don't want to do it with pencil and paper you can just use the spread sheet I will link in a different thread. The spread sheet uses standard deviation to calculate the distance +/- 1 standard deviation. Playing with it will give you an idea of just how hard it is to actually measure sounds in the field. That first decibel of standard deviation is a whole lot of distance.

    https://www.airgunnation.com/topic/spread-sheet-maximum-detectable-range-of-a-sound/#post-1254294

    ;)

    NOTE: The numbers I used in the above example are notional. IOW I just picked them out of my ...
    NOTE: The exact formula is: Sensor Distance * (2^((Average of Shots - Noise Floor Average) / 6))
 
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As @WI_Hedgehog points out, simply pushing less or more air will produce different results in different moderators.
Click to expand...



Yeah, and it's not necessarily just the increase of muzzle energy ("more air") that increases the loudness of the gun — because HOW the gun is TUNED to achieve that particular muzzle energy is also a big factor. 



Here is what I learned from Bob Sterne (resident tech writer over at www.GatewayToAirguns.org and some time HardAir Magazine):



Assuming always the same muzzle energy (ME):

🔸 The most quiet tune is the one with a higher regulator setpoint which allows only short sips of air (regulated by the HST) to achive that ME. (This tune would be less than 5% of muzzle velocity [MV] below the "knee" of the velocity curve. This tune is somewhat prone to larger muzzle velocity variations.)

🔸 The loudest tune, at the same power, is the one where the hammer opens the valve for a long time so that there is air flowing through the valve until the pellet has left the barrel — this tune allows for a very low regulator setpoint at this particular power.

🔸 The "regular" or "medium" tune is one that uses a medium time to open the valve, and a medium regulator setpoint, somewhere between 2% and 5% below the velocity curve's "knee." This is the most effective tune and the one with the smallest MV variation.



🔶 ➔ Tune according to your preferences. If silence is a priority over muzzle velocity spread and power, tune to produce tiny sips of very high pressure air — they are the quietest.



Matthias

Click to expand...

Great info - THANK YOU!
 
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