Standard Moderator

[OldSpook]

The Standard Range
The test range is laid out like this diagram:

The diagram is as I drew it into my notebook. The bench is on the left side of the diagram and the backstop is on the right side. The microphone is located at the top between the two triangles. It is placed on a concrete slab (a brick would do as well) which elevates it about 3 inches above the grass. There are two microphones on the phone I am using so I made two wind mufflers by printing gyroid infill cubes which fit on the ends of the camera. These perform well. Today there was gusty wind blowing with peak speeds around 20 mph. I don't hear any wind noise in the audio so they must be working.

I chose a 25 yard distance because I can easily duplicate the range in nearly any grassy space in just a few minutes with a 50 foot tape and some stakes. I chose to put the camera close to the ground because it was easier than making a stand and the grass tends to hold down echos coming off the ground. The size of the test range will help to ensure that the recording device does not experience "clipping" by being overloaded with the noise we are trying to measure. The microphone is located equidistant from the bench and the backstop because that simplifies the calculations when solving for muzzle velocity and when comparing the sound of the shot to the sound of the pellet striking the backstop (or whatever I put at that spot).

This is probably the final configuration of this range as it is nearly perfect for my purposes.

The Standard Moderator
Today I tested a "Standard 17" moderator design. I call this moderator the "Standard" because it is the design I build whenever I want to test some new theory. It is standardized and I am using the same test rifles with the same power levels, tunes, and projectiles in all my tests. I do this in the hope that I can achieve reproducible results from one day to the next. That will allow me to save data between tests and compare them later. In the end that will mean less repetition in the data collection effort.

The specifications of this moderator:
DIameter: ~1.2 inches; 30mm
Length: ~5 inches; 125mm
Weight: 59 grams; 2.00 oz.
Thread: EZTap 1/2 x 20 UNF


CONSTRUCTION DETAILS REMOVED IN KEEPING WITH THE CONCERNS OF MANAGEMENT




When I test I record the test session with my phone and then analyze the test in Audacity software.
I recorded the entire session and have removed all of the dead air. The remaining file contains all of the data which interests us for this test. Here it is:

Here is the comparison of the audio without and with the moderator.

Here is the Audacity graphic of the two shots which are being repeated in the above clip.


Analysis of these two shots shows that the moderator reduces the report of the bare rifle by 3.6 dB.

Using the audio data from the last three shots heard in the top audio clip we can calculate the average velocity over the range for that rifle and pellet. This image shows the start and end times for the shot and impact noises for one of those shots. Strelok confirms this corresponds to a muzzle velocity of about 860 fps which equates to about 18 foot pounds.



This is a nice little moderator. It was inspired by a desire to improve on the Weirauch/Huggette "hair curler" design.

I'm happy with the design.

 

[EmptyTin_Tim]

Very cool stuff, and also very scientific. Its a lot of fun to experiment with different designs and see hard data you can actually compare everything to. You make that from scratch?
I've only used Fusion 360 so far but it's been great. Is open scad easy to use?
I had a question though, if it is only 5 " long why not FDM print the whole thing as one piece? Stand it up on end. The carbon fiber outside looks really nice but you could still add that like a sleeve on the outside if you wanted.

 

[OldSpook]

Very cool stuff, and also very scientific. Its a lot of fun to experiment with different designs and see hard data you can actually compare everything to. You make that from scratch?
I've only used Fusion 360 so far but it's been great. Is open scad easy to use?
I had a question though, if it is only 5 " long why not FDM print the whole thing as one piece? Stand it up on end. The carbon fiber outside looks really nice but you could still add that like a sleeve on the outside if you wanted.

I do the resin print for aesthetics. Carbon fiber is lighter and stronger than PETG.

Introducing carbon fiber tubing into the design creates a lot of problems. I had to design a special tool to ensure the end caps were lined up parallel to the tube axis when I glued them on.

It's hard to get a good glue that works with carbon fiber and has enough pot life to let you do a clean glue up that's attractive.

In short I am designing a moderator with three requirements. It has to be accurate. It has to be quiet enough. It has to be easy on the eye.

I have hit those goals.

 

[Scroooface]

If you need an unbiased opinion, I'll gladly accept the challenge of testing one of those bad boys out

 

[OldSpook]

If you need an unbiased opinion, I'll gladly accept the challenge of testing one of those bad boys out

Thanks for the offer! This design is out of the testing phase. I am currently building inventory. You should start seeing them in the classifieds in small quantities soon.

 

[Firewalker]

I'm using both the MIL-STD 1474D (considered the military standard for measuring sound. Following these standards, place the microphone 1 meter to the left of the muzzle and 1.6 meters above the ground, with the microphone pointing upward, at a 90 degree angle to the bore. All testing needs to be completed away from any reflecting surfaces, as to not negatively affect the audio readings) and one of my own design, 10m directly in front of the bore and 2 inches below the flight path of the round.

I do this to see what someone standing next to me hears and what prey may hear from the gun.

Keep in mind, these are subsonic shots only.

 

[bigHUN]

...It's hard to get a good glue that works with carbon fiber and has enough pot life to let you do a clean glue up that's attractive...

You can use arrow building hot melt glue = re-useable, a cigarette lighter heat is good enough to soften it for removing or install, at ambient temperature holds really strong...

 

[OldSpook]

I'm using both the MIL-STD 1474D (considered the military standard for measuring sound. Following these standards, place the microphone 1 meter to the left of the muzzle and 1.6 meters above the ground, with the microphone pointing upward, at a 90 degree angle to the bore. All testing needs to be completed away from any reflecting surfaces, as to not negatively affect the audio readings) and one of my own design, 10m directly in front of the bore and 2 inches below the flight path of the round.

I do this to see what someone standing next to me hears and what prey may hear from the gun.

Keep in mind, these are subsonic shots only.

I did not even research the MIL standards because I knew I would not be able to meet the hardware requirements and the physical requirement of no nearby reflectors. I also don't have a hardware timing setup so I spend a lot of time calculating event times based upon flight time and other identifiable audio events. I can identify reflectors in the audio stream usually. The audio we want occurs during the first 20 ms of the shot cycle, usually starting around 7ms into the shot cycle and completing within about 10ms. If I can identify any echos occurring during that time, I can remove the offending object from the range. Of course the easy answer would be to set up the range in the middle of a 1 acre field of grass.

I've done some testing (as a lark) to discover what the gun sounds like down range. I posted that in another thread. My setup places the microphone about 1 meter below the muzzle 12.5 yards in front of it and 6.25 yards to the left on a line perpendicular to the line of fire. That creates an angle between the line of fire and the microphone of 30 degrees. That gives me significant audio information about all events which happen on the whole range and satisfies my need for information regarding "other identifiable audio events".

Yes supersonic is bad.

 

[OldSpook]

You can use arrow building hot melt glue = re-useable, a cigarette lighter heat is good enough to soften it for removing or install, at ambient temperature holds really strong...

I had not thought of that! Thanks, I might give it a try. My only concern (been thinking on it all afternoon) is for cold temps. I've used hot melt a lot when building arrows and never had trouble with it except in very cold conditions or when I buried a field point a couple of inches into a 2 by 4. Strong stuff!

 

[IMADMAN]

You can use arrow building hot melt glue = re-useable, a cigarette lighter heat is good enough to soften it for removing or install, at ambient temperature holds really strong...

I’d say + 1 to this. Just make sure it’s the correct type. I recently bought a stick locally since I wanted to redo some arrow inserts as well as replacing a fishing rod tip. The shop I bought it from swears that it is correct, even though it looked exactly like the ones used in basic glue guns, (clear in color) It was worthless. The one I used prior was amber in color and I used a candle stick to get it to melt.

 

[JungleShooter]

Old Spook,

this is AWESOME!
▪ A repeatable set-up.
▪ Sound approach and method.
▪ Always looking to improve.

Excellent work.

Thank you for contributing to our sport and our community.


Cheers from Peru,

Matthias

 

[bigHUN]

...I buried a field point a couple of inches into a 2 by 4. Strong stuff!

I’d say + 1 to this. Just make sure it’s the correct type.

I've been dealing with lancasterarchery and built my competition arrow shafts diy probably well over twenty years. Those thin CF shafts that cost $500 a dozen when finally assembled ....
Look for a flexible and rubbery - softer on touch hot melt, not for hard sticks like Bohning.
I know very well what that means hitting a 2x4 target frame .... better that shaft just brake it off right away.

 

[OldSpook]

I’d say + 1 to this. Just make sure it’s the correct type. I recently bought a stick locally since I wanted to redo some arrow inserts as well as replacing a fishing rod tip. The shop I bought it from swears that it is correct, even though it looked exactly like the ones used in basic glue guns, (clear in color) It was worthless. The one I used prior was amber in color and I used a candle stick to get it to melt.

If that works, it is another argument in the coffin of the "intended use" issue. Hot glue surely will not work on PBs

 

[OldSpook]

This will be my last post regarding the construction of air gun moderators on this forum. This is per the wishes of forum management. I can only speculate as to what might have motivated that choice and that would be counterproductive.

I am still interested in testing moderators and I would be open to test any moderator anyone ships to me and return that when I am finished with it I'll pay shipping on my end. I have developed a test which I think can be used to compare apples to apples.

I have a request in to management to check and make sure that would be acceptable before I start doing it.

If you're interested give me a thumbs up I'll contact you.