Sound Testing A Dozen LDCs

[subscriber]

I suggest playing something neutral and soothing like this in the background...  cranked to 11 to mask the report.
Trust me... they won't mind the airgun.

I like drum solos for that.  Who is going to notice a few added pops and clicks? 

[Jshooter71]

 

[Earl]

Below are some decibel readings using my iphone 7 with the Decibel X app. and averaging 5 shots inside my den.
Benjamin Marauder shooting JSB 10.34 grain at 782 fps, 76.6 decibels at 6 feet left of the muzzle, 91.4 decibels at the shooter's ear.
Crosman Challenger shooting JSB 8.44 grain at 603 fps, 86.7 decibels at 6 feet left of the muzzle, 90.5 decibels at the shooter's ear.
Beeman P17 shooting RWS R10 7.0 grain at 398 fps, 88.8 decibels at 6 feet left of the muzzle, 100.9 decibels at the shooter's ear.
The Marauder sounds like a dull thud at the shooter's ear.
The P17 is a sharp crack at the shooter's ear.
The Decibel X app. gave consistent readings. Example: 76.6, 76.9, 77.1, 75.8, 77.0

Earl, thanks for your helpful input! Are any (or every) of the guns moderated at all? I know the mrod has baffles in the shroud, correct?

Also curious how you were able to get the slightly different dB readings between the muzzle and the ear. That would be a definite improvement on testing protocols, did you need to use two phones?

The guns were not moderated.  The mrod has the stock baffles in the shroud.
I put the iphone 6 feet left of the muzzle like you did.
Then I shot 5 shots and averaged them.
Then I  put the iphone even with the shooter's ear and shot 5 shots and averaged them.
I used the same iphone for all measurements.

[mrbulk]

Took Maxine out with the Tanto and my cell phone playing music was much louder.
For you poor folks living in an urban setting I suggest playing something neutral and soothing like this in the background...  cranked to 11 to mask the report.
Trust me... they won't mind the airgun.

Capital idea, Scott. I also sometimes wait for the neighbor's gardener to show up with his gas weedwacker and leaf blower.

[mrbulk]

Below are some decibel readings using my iphone 7 with the Decibel X app. and averaging 5 shots inside my den.
Benjamin Marauder shooting JSB 10.34 grain at 782 fps, 76.6 decibels at 6 feet left of the muzzle, 91.4 decibels at the shooter's ear.
Crosman Challenger shooting JSB 8.44 grain at 603 fps, 86.7 decibels at 6 feet left of the muzzle, 90.5 decibels at the shooter's ear.
Beeman P17 shooting RWS R10 7.0 grain at 398 fps, 88.8 decibels at 6 feet left of the muzzle, 100.9 decibels at the shooter's ear.
The Marauder sounds like a dull thud at the shooter's ear.
The P17 is a sharp crack at the shooter's ear.
The Decibel X app. gave consistent readings. Example: 76.6, 76.9, 77.1, 75.8, 77.0

Earl, thanks for your helpful input! Are any (or every) of the guns moderated at all? I know the mrod has baffles in the shroud, correct?

Also curious how you were able to get the slightly different dB readings between the muzzle and the ear. That would be a definite improvement on testing protocols, did you need to use two phones?

The guns were not moderated.  The mrod has the stock baffles in the shroud.
I put the iphone 6 feet left of the muzzle like you did.
Then I shot 5 shots and averaged them.
Then I  put the iphone even with the shooter's ear and shot 5 shots and averaged them.
I used the same iphone for all measurements.

Thanks. Very interesting that the gun metered louder when closer toward the back (behind the muzzle). I wonder if the noise of the action contributed to the max reading. I always figured the closer to the muzzle blast the louder the report would register. interesting twist to this, especially the P17.

[subscriber]

"Breech loud" pneumatics may have a leaky breech O-ring.  Lay a strip of toilet paper over the breech and see if that moves when you shoot.  A bad leak will rip the paper.  It can also sound like it wants to rip your ear drums...

[subscriber]

Radiated sound intensity drops off with the square of the distance from the source (just like light from a bulb).  Higher frequency sound waves are absorbed more by objects (even air molecules, over distance) than low frequencies (hence mostly the thump-thump of distant party music can be heard).  So, it is entirely possible for a professional peak sound meter to measure one gun or configuration as louder near the muzzle than another; then for the quieter one to sound louder 25 yards away.  It has to do with the mix of frequencies in the report.

It is not just loudness of audible sound that matters, but its propensity to grab attention - to make your perk up and actively listen; especially if the sound is repeated at short intervals.  Some sounds "stick out" above ambient sounds more than others.  I think that prey animals are instinctively programed to pay attention to the sound of snapping twigs.  That sounds signals a large animal moving closer - something that needs immediate attention, in case it is a predator. 

Predators (including humans) are also attuned to snapping noises, because it signals a large potential meal.  So, a sharp snap is much more attentions grabbing for its measurable loudness than a longer "shoo", that starts (and ends) with a ramp, rather than silent to full intensity in an instant. 

Repetitive sounds also grab attention out of proportion to their actual loudness.  Hence, we may miss a single knock on the door, but not four knocks, repeated in quick succession.  With airguns; the report, followed by the sound of the pellet smacking the target can be such an attention grabbing signal.  As can just the fact that the same unnatural double-sound repeats every so many seconds.

Better for your airgun to sound like a sneeze with an echo, than someone sneaking around in the backyard, stepping on twigs.

[JungleShooter]

Subscriber,

Thank you for this much needed
🔶 psychology of gun shot silencing! 🔶

We can measure all we want, but the dB numbers are only one dimension, and hiding sound from quarry or quarrelers (i.e., neighbors) has more than one dimension!


I'll probably end up writing a short guide to silencers, and I'd like to quote you, if I may!

Matthias

[subscriber]

Go ahead, Matthias,

I am glad what I suggested makes enough sense to include in your guide. 

If I were to write an airgun moderator guide, I would include an introduction; possibly including some of the thoughts I brain dumped below (feel free to include as much or as little of the text below as you like):


The standard microphone placement for measuring muzzle report intensity was first determined with and for firearms.  While that is still useful for airguns, the mission and purpose of suppression are different, with some overlap:

The obvious purpose of sound suppression with firearms is hearing preservation for the person shooting the gun.  Hence the multitude of devices that still allow sound levels of 130 dB - just considered "hearing safe".   Now, one would think that the microphone standard placement should then be located nearer the shooter's ear (and it is catching on as a second data point).  The problem with that, from a suppressor manufacturer's perspective is that they have no control over barrel length and action type.  This matters because not only are shorter barrel rifles much louder, the suppressor muzzle being even 6" closer to the shooters ear will have the mic capture much higher sound pressure (some examples of dB to distance are given below).  Also; self loading firearms have more "pop" at the breech than manually operated ones.  Higher dB scores without cross platform understanding can cost sales.  Hence mic placement relative to the muzzle as industry standard. 

Depending on the exact mission, suppressing of the sound source location and direction from the target's perspective might be more important than a firearm being rendered hearing safe.   A consideration important to hunters is the avoidance of spooking other game animals.  At the bottom of the list, is making ranges quieter for competitors and neighboring properties. 

Large bore high power airguns share many of the above goals because, unshrouded, they are very loud.  Low power, small caliber and shrouded airguns are mostly hearing safe to the shooter, out of the box. Adding a LDC to them, is done to mute their sound signature further, so as not to annoy family members or neighbors. And, generally not to draw attention.

As such, microphone (objective) and ear (subjective) placement when comparing LDCs on low power, small caliber shrouded airguns needs to have their usefulness ranking weighted more heavily towards measurements obtained at 10, 20, 30+ yards from the muzzle.  Both off to the side; and almost directly in front of the muzzle (with safe backstop considerations in place).  This is in addition to the standard mic placement near the muzzle.  The point is to recognize that because LDC goals may be different, appropriate measurement methods and standards can and should be different.

I think that any system of airgun report measurement can be very useful, providing it can be explained and repeated.  I see airguns test videos by "reputable evaluators" where the microphone sometimes seems 3 feet from the muzzle, and sometimes closer to 4 feet.   Often placed on a hard table where there is no regard for the effect of reflected sound.   Meanwhile, the actual difference in sound pressure at 3 and 4 feet from the muzzle would actually measure 78% higher at 3 feet than 4, for the same shot.  So, if you are going to measure sound at 20 yards, and have a one foot variation in mic placement, the error would be only 5%.

Now, all I need is a good editor....

[Bob Pratl]

Subscriber, thanks for your great explanation as it cleared up a lot of questions that I had.
I all makes a lot more sense.

[Mole2017]

Took Maxine out with the Tanto and my cell phone playing music was much louder.
For you poor folks living in an urban setting I suggest playing something neutral and soothing like this in the background...  cranked to 11 to mask the report.
Trust me... they won't mind the airgun.

Isn't that the track they used in one of the Star Trek movies? I can see Kirk in his chair smiling as I start listening to it. "Is that classical music?" asks Bones (I think)?

[Earl]

Below are some decibel readings using my iphone 7 with the Decibel X app. and averaging 5 shots inside my den.
Benjamin Marauder shooting JSB 10.34 grain at 782 fps, 76.6 decibels at 6 feet left of the muzzle, 91.4 decibels at the shooter's ear.
Crosman Challenger shooting JSB 8.44 grain at 603 fps, 86.7 decibels at 6 feet left of the muzzle, 90.5 decibels at the shooter's ear.
Beeman P17 shooting RWS R10 7.0 grain at 398 fps, 88.8 decibels at 6 feet left of the muzzle, 100.9 decibels at the shooter's ear.
The Marauder sounds like a dull thud at the shooter's ear.
The P17 is a sharp crack at the shooter's ear.
The Decibel X app. gave consistent readings. Example: 76.6, 76.9, 77.1, 75.8, 77.0

Earl, thanks for your helpful input! Are any (or every) of the guns moderated at all? I know the mrod has baffles in the shroud, correct?

Also curious how you were able to get the slightly different dB readings between the muzzle and the ear. That would be a definite improvement on testing protocols, did you need to use two phones?

The guns were not moderated.  The mrod has the stock baffles in the shroud.
I put the iphone 6 feet left of the muzzle like you did.
Then I shot 5 shots and averaged them.
Then I  put the iphone even with the shooter's ear and shot 5 shots and averaged them.
I used the same iphone for all measurements.

Thanks. Very interesting that the gun metered louder when closer toward the back (behind the muzzle). I wonder if the noise of the action contributed to the max reading. I always figured the closer to the muzzle blast the louder the report would register. interesting twist to this, especially the P17.

Please note:
The low readings are 6 feet from the muzzle to the side.
The shooter's ear was 3 feet from the muzzle to the rear on the rifles and 2 feet for the pistol.
Closer to the muzzle gives more decibels.

[JungleShooter]

Peter / subscriber,

your profound understanding of they physics of much of airgunning is a huge benefit to our AG community.
Thanks for sharing it! 


❌ If there is enough interest — couldn't we establish a silencer test standard?

❌ And couldn't we publish the results for all to see — webpages are cheap?


🔸We already have the general idea of where to place the sound meter — adapted to the purpose of an AG silencer. ✔️

🔸We already have a specs table of most commercial silencers. ✔️

🔸We already have a bunch of people interested in this. ✔️

🔸We already have the precedent of an airgunner (STO) receiving test samples on loan from fellow airgunners. We could do the same. ✔️

🔸I'm outside the US, so I can't do the testing.
But I can offer $50 toward a higher quality sound measuring device.
And I can offer to do some of the writing. Peter, you do good writing yourself!
And we could even publish the results in a scientific journal, or an airgun magazine, if we're so inclined.



🔶 We can ask the manufacturers for sponsorship — no strings attached.
However, I doubt if they are going to establish the test standards....
So, if we, the users, aren't going to do it, who will?! 


Who joins up?! 😄 

Matthias

[Earl]

Walmart has a decibel meter on sale for $18.03 (List $54.09).
https://www.walmart.com/ip/BENETECH-Noise-Meter-Sound-Decibel-Meter-Digital-Mini-Pressure-Level-Meter-Audio-Measurement-30-130dBA-MAX-MIN-Hold-Auto-Backlight-Batteries-included/719174741

I am happy with the free iphone app "Decibel X".
The "Decibel X" app seems to give consistent readings and is free and easy to use.
https://apps.apple.com/us/app/decibel-x-db-sound-level-meter/id448155923

Someone please compare the Digital X app to their sound meter and tell us if the readings are the same.

[Insanity]

One thing that using a cellphone mic is that it may have some built in sound reduction built in.

[Mole2017]

One thing that using a cellphone mic is that it may have some built in sound reduction built in.

When I did some testing of my PCP with and without its shroud and another LDC I had on hand, the limits of the microphone soon came up in two areas:

• Frequency response:
     The microphone I was using, a USB AT2020, has a pretty solid cut-off at 20kHz. That was likely a physical limit (the analog versions of this mic have the same limit), but the internal electronics had a limit not very far above that. It's a nice microphone, but when I looked at the data, it made me wonder: is there more to see or hear (if my ears were that good)? More to the point, is my shroud or this LDC shrieking at frequencies I can't hear but that my game or the neighbor's dogs might be able to hear? Perhaps of no consequence, but now I wanted to know.
• Accuracy:
     Most microphones don't have a constant sensitivity across the entire frequency range of the measurement. The At2020 differs by only 3 dB from 200 Hz to 10kHz. It's a small difference, but not every mic you pick up is so nicely behaved, and that can affect how well you compare measurements done with other microphones. The mics in phones are specially designed for a pleasant voice measurement--and who knows what the electronics do to it after that.

Research on the problem lead to "measurement microphones"--microphones with very flat frequency response characteristics across the whole input range. Some of these microphones are "flat" clear out to 50kHz. We can't hear that, but the audiophiles swear they can hear the difference in stuff recorded by a 40kHz capable Earthworks SR40V and "lesser" 20kHz capable microphones. Apparently, in addition to high frequency response, in the better mic there is an more accurate representation of the sound being measured due to the lack of subtle phase shifts or time delays at different frequencies across the spectrum.

Anyway, that has put me on another project: acquire an SR40V and a high quality USB recording interface (i.e. high sample rate) and repeat my test to see what I see in the data. The SR40V is not as specialized as a mic like the Earthworks M50 (50kHz capable), but it is almost as good out to 40kHz and a really good mic to have if a person thought they wanted to own a good mic. The interface can sample at 192kHz, easily digitizing whatever the microphone is "hearing". The goodies arrive this week and I hope to repeat the measurements and post a separate thread about it. (Yes, yes, I could have purchased a lot of air rifle toys for the money, but it actually wasn't my money. I did some work for a friend and he was willing to do the shopping for me...)

Yeah, absolutely accurate measurements that can be shared between folks for comparison with other measurements is not easily done. And sound is that much harder because so much depends on the equipment too. You can calibrate a scale or caliper with a calibration weight or gage block and you're good. But calibrating a microphone...yikes. Back-to-back measurements like those presented here are about the best you can do, and even then you have to make sure you set everything up the same each time.

[subscriber]

Matthias,

I appreciate your abundant energy and "unbridled enthusiasm".  I still have the latter, but my energy went walkabout...

I agree to the extent that I am willing to gift this sound meter to the effort:
 www.amazon.com/gp/product/B000EWY67W/]www.amazon.com/gp/product/B000EWY67W
It is the one that appears in the Pyramyd Air test videos.  That is why I bought it.  Not junk, and not super expensive.

As we are raining on Charlie's parade here, I think he should be the recipient of the sound meter (if he wants it).  He is also a long way towards testing LDCs, in a way that makes sense to him (and by background conversation, makes sense to me).

I am full of ideas and opinions; and can express them reasonably clearly.  That does not make me "right" about this topic.  I think that the people doing the actual testing should be free to develop airgun LDC test methods that suit them. 

Only after they are happy with their results would we consider such a method for standardization.  Such standards should be accepted because they make sense - if they make sense.  Sure, I could write a test procedure, but it would need to be considered a place holder.  A starting point.  Not "law".  I think my philosophical posts above actually go far enough (and too far, considering the reason why this thread was started).

I happen to know that Charlie is benchmarking LDCs for his own purposes - for him to share or not.  The fact that he has been gracious enough to share his results might not indicate that he thinks his evaluation methods are inadequate, or need to be standardized.   

I think that a separate thread could be started about standardizing airgun LDC test standards.  Travis, the GTA forum Administrator started such a thread a few months ago.  Why not coordinate with him? 

As for publishing anything related to "LDCs" in a scientific journal; I disagree on two counts:
1. Airgun LDCs fly under the radar. The more we publish about them outside the airgun community, the more likely they are to get unwanted attention.
2. Exactly what defines the gold standard "mouse fart quiet" LDC, is highly subjective.  Meticulous calibrated instrumented measurements are unlikely to settle any disputes.  We may (will) find some LDCs measure "louder", but sound quieter than others.  Other than that paradox being interesting to PhD types, it does not help one make a better purchase decision. 


I think that consolidating the results and methods used by people who publish clear tables of useful information, such as yourself is a great idea.  That could be a section on this forum.  It could have limited access.  For instance, on some forums, non-members cannot see imbedded images.  They have to join and log in first.  On others forums, sections may politely inform a viewer of their lack of credentials to access that part of the forum.  If a standard test method should develop amongst the people that do all the work and incur all the expense, then that would be good and right.  I might have an opinion about their test methods, but that is all it is.  They don't have to follow it.

I will close by expressing this opinion:  If a person can spend over $1000 on a dozen LDCs for comparative testing, then the same person can spend $100 on a reasonably accurate and appropriate dB meter.  Using cell phone apps would be cheaping out, and the results would be much less meaningful than comparative ear measurements.  It would be a bit like a guy spending $200k on a new Ferrari, then running low octane gas in it to save money...

[mrbulk]

Hey Sub, ask me no questions and I'll tell you no lies...