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Old 09-04-2018, 02:24 AM   #1
1tonne   1tonne is offline
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How to make the quietest AEG ever

After years of trying to make the quietest AEG ever, I now have the knowledge to make the quietest AEG ever. This rifle will be quieter than the Mk23 Socom pistol which is renowned for stealth.

There are 5 areas of sound that you want to lessen. First the sound signature of the rifle (Length of sound), next is the squelching sound (Gearbox Noise), you also want to get rid of the spring sound (Twang), stock vibration and lastly is the muzzle sound (piston slap noise exiting barrel).
Of these 5 areas, the hardest one to eliminate is the squelching sound from the gearbox. So concentrate most of your time on this one. You may even want to take this into account when purchasing a rifle. Gearbox's that have a motor cage are the easiest to reduce the squelching sound as the motor should be trapped in the correct position all the time. Gearbox's like the V2 in the M4 are a lot harder to reduce sound as the motor can move a little putting the alignment off as it is not secured in a cage.

To make the quietest AEG there are 24 points you will need to work on. Here they are:

1. Air seal - When you have a good air seal you can use a weaker spring because you do not have as much waisted gas. The areas to check are O-ring seal, Cylinder to cylinder head, air nozzle to cylinder nozzle, air nozzle to hopup bucking and lastly, hopup bucking to barrel. Most of these can be fixed rather simply. The hardest is the seal between the air nozzle and the bucking. To seal this properly, check out number 13.

2. Spring — Thread on three little bits (about 10mm long) of heat shrink to your spring at each third and shrink them. This will help stop vibration and get rid of some of the twang sound.

3. Barrel Bore size — The tighter the bore, the easier to get higher fps which means you can use a weaker spring. A weaker spring means less stress in the gearbox. Less stress means less squelching noise.

4. High Speed Ratio Gears - The quicker the sound is the less your ear will be able to register it. So if you use a high speed gear ratio of at least 14:1 or less (I used 13:1) the rifle will be very snappy. Also these types of ratios have less squelching sound. (NOTE: High torque motors go well with high speed gears)

5. Use a LONEX Spiral Bevel & Pinion Gear Set. These gears have curved teeth that allow for better meshing of the pinion to bevel gears if your motor is slightly at the wrong angle. This is common in V2 gearboxes as the motor is not in a motor cage. The gear set still can help with sound even when the gearbox has a motor cage


6. Piston Weight — Make your piston as light as possible by drilling holes in it (this is called Swiss Cheezing your piston). This will make it easier for the sector gear to pull it back and it will also fire forward faster meaning less squelching and higher fps as well as a faster cycle.

7. Cylinder head cushion — Use Sorbathane as a dampener on your cylinder head.This will lessen the piston slapping sound.

8. Choose a cylinder that is smooth on the inside. Some cylinders have ridges that are designed to help keep the cylinder lubricated. The issue with these ridges is that they create more noise as the O-ring goes over them. So a smooth cylinder is better.

9. Use extra thick lubricant on gears - Thicker means it stays on- Less friction which means less squelching noise.

10. Use bearings instead of bushings - Bearings make for an easier cycle. The easier the cycle the less squelching noise from your gearbox.

11. Use gears that have in built bearings - Makes for easier cycle

12. Shim correctly — Lessens the gearbox squelch sound

13. Use an air nozzle that is about 1-1.5mm longer than normal or sand the front of the tappet plate so that the air nozzle moves further forward than normal (Some tappet plates like SRC are designed to make your air nozzle go further into the bucking). This will mean that the air nozzle will go into the bucking too far. So you need to shim inside the gearbox in front of the tappet plate. This will pull the air nozzle back to the correct position. When shimming, use a thin piece of Sorbathane. This will absorb the slamming sound that happens when the tappet plate hits the front of the receiver. When shimmed correctly, this will also increase your fps.

14. Use the biggest battery possible (I use 11.1v lipo) - Lessens gearbox sound signature. You do need to be careful though as sometimes this can create more high pitch squelching from the gears

15. Use the correct cylinder to barrel ratio - This is one of the most important, if not the most important thing to do when making your rifle quiet. If you use the correct ratio, then you are making your rifle the most efficient that it can be which means you do not need such a large spring to get your desired fps. Also, there will be no extra air being pushed out of the barrel that carries the sound of the piston slapping.

Here are the correct Ratios to make your rifle quiet:
BB weight------- Ratio
0.2gm------------2.13:1
0.23gm----------2.15:1
0.25gm----------2.18:1
0.28gm----------2.20:1
0.30gm----------2.23:1
0.32gm----------2.31:1
0.36gm----------2.43:1
0.40gm----------2.61:1
0.43gm----------2.68:1
0.45gm----------2.76:1

For all the information you need to know about cylinder to barrel ratios, read this thread that I wrote (It is a must read): https://www.airsoftsniperforum.com/...at-barrel-length-goes-what-bb-weight-aeg.html

16. The longer the inner barrel the quieter — A longer barrel will produce higher fps so you can use a weaker spring (Less gearbox stress). The disadvantage is that it can make the rifle too long especially once you add a silencer. So make sure the rifle is of a gameable length. A bullpup can be good in this instance as the inner barrel can run from the back of the rifle where the magazine is to the front.

17. Use a silencer - A Silencer is a really important part of making a quiet rifle as it captures the excess sound that is travelling behind the bb. Without a silencer your rifle will be a lot louder. This is expected though as the perfect ratio will have just enough air to push the bb out of the inner barrel. Even though the bb is out of the barrel and there is no excess air pushing the sound out of the barrel, there is still has a negative pressure at the rear of it of the bb. This negative pressure may drag the excess sound behind it. This excess sound can easily be captured by a silencer. So an airsoft silencer can really work if done correctly.

18. Silencer Length - Different silencer lengths can have different effects on the sound that comes out of the end. A silencer can be too short or even too long. So experiment with different silencer lengths or use a shorter outer barrel so that the inner barrel sticks into the silencer more. This will have the same effect as using a short silencer. For more on this check out: https://www.airsoftsniperforum.com/4...tml#post390637
I originally used a silencer that was 243mm long and it made the rifle louder. I now have one that is only 173mm in length.

19. Silencer Muzzle Hole Diameter - A normal airsoft silencer muzzle hole is about 12mm in diameter. If you put washers that have an 8mm hole between each piece of foam, the muzzle sound should be more trapped inside the silencer in each little compartment. You do need to be careful that the bb does not skim one of the washers as this will make noise and also make the gun inaccurate. If done with the other mods in this thread, your muzzle noise can be reduced that much that it is barely audible ear with your ear close to the muzzle. But be careful as you will need to experiment. On the odd occasion, modifying a silencer like this can increase the sound.

20. Try different materials in the silencer. Different materials will reduced the sound different amounts. Also try the material compressed into the silencer and then not compressed. Different rifle setups will produce different sound waves that need to be reduced in different ways. So experimenting is key here.
In my AUG, I used a white fluffy material that is used for sound deadening in buildings. I rolled is up around a spring to keep the fluff away from the bb.

21. Use Dynamat Sound Deadening - Put Dynamat sound deadening in as many places as possible. In an M4, there is not many places to use it as the M4 has very limited space. On an AUG, you can wrap the gearbox in it and put it on the inside walls of the stock.

22. Fill empty spaces - Fill any empty spaces in the rifle, especially the receiver with sound deadening foam or fluff. Loose, random fibres are the best way to kill sound fast. In an M4, there is not many places to use it as the M4 has very limited space. On an AUG, you put it between the gearbox and the stock walls.

23. Semi Auto - Use semi auto as it gives a shorter sound signature.

24. Motors can also add a lot to noise. A motor with an unbalanced armature or a slight bend in the shaft will vibrate more. This will make noise between the pinion and bevel gear as it will not have a consistent meshing

After making this rifle I told my son to stand outside for 5 minutes and face in a certain direction. I did not tell him why or that I was going to shoot to the side of him. I just told him to stand there and wait. Anyway, I was only about 10 meters behind him and I shot to the side of him making sure I missed. He didn't move. It took about 4 more shots before he realised I was shooting beside him. Very, Very quiet.

Here is what my rifle has:
-Army Armament Styre AUG
-SHS Ultra high Torque motor
-Super Shooter 13:1 gears
-M100 Spring (Producing 350fps) (Heat shrinked)
-Full Cylinder: Ratio = 2.18:1 for 0.25gm bb's
-Barrel: Action Army 425mm x 6.01mm
-Air Nozzle =Stock (24.75mm)
-G&G Green bucking
-Sorbathane on cylinder head
-Piston: G&G Polycarbonate with a single metal tooth (Swiss cheesed)
-Piston head: G&G Plastic with Foam Plug
-Bearings: Can’t remember the brand
-Silencer: 173mm x 40mm with foam inside (Round washers with 8mm hole inside)
-11.1v Lipo
-Dynamat on gearbox and inner stock

NOTE 1: To test if the sound is coming from your muzzle, put the receiver between 2 pillows with the muzzle sticking out and fire it with the desired bb weight. If you want to test the gearbox noise, just put a thick rag over the end of the muzzle and then cover it with the pillows and fire with the desired weight.

NOTE 2: I tested the sound in a similar way to how a lot of other rifles are tested. This is with the decibel meter 1 meter to the left of the barrel, at a height of 1.6m (standing shot) and the microphone pointed straight up at 90 degrees to the direction of travel of the bullet (to eliminate projectile pressure). (Thanks Zero Roaster)
So I measured the sound of my quiet rifle (an AUG) and I also measured a couple of other rifles too. A G&G CM16 (a gun that everyone know what it sounds like) and also a short barrel Ares Amoeba. This is a short stubby loud gun.

So:
Quiet AUG = 72.93dB (78.2dB without silencer)
Quiet M4 = 78.53dB
Mk23 Socom = 79.43dB
G&G CM16 = 85.2dB
Short Ares Amoeba = 87dB
.177 air rifle = 88-90dB (Taken off another website)

Check out this video: (If you can't see the video on YouTube type in "1Tonne Airsoft")
https://
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Last edited by 1tonne; 07-05-2019 at 10:34 PM.
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Old 09-04-2018, 04:09 AM   #2
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If you reduce the exit hole on the silencer to about 8mm (I fitted a 11mm to 14mm adapter) it will further quieten the muzzle noise.
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Old 09-04-2018, 04:30 AM   #3
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A halfway house is just to kill the high frequency sounds i.e. piston slap and muzzle blast. It is very difficult to determine the direction of low frequency noise, if you've ever heard a ships foghorn in fog at sea you'll know what I mean. So even if the shot is heard, they'll be unable to pin point the direction it came from. It's also the reason why you usually have only 1 bass speaker with your TV sound system.
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Old 09-04-2018, 11:03 AM   #4
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Cool! Is this where we get into the discussion about soundwave propagation and reflection vs. refraction or absorption? I have the lamda key on my calculator all queud up and ready to go...
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Old 09-04-2018, 11:52 AM   #5
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African or European sound?
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Old 09-04-2018, 01:49 PM   #6
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Quote:
Originally Posted by Tired Gun View Post
African or European sound?
Oh wow...this is going to be good...

Now, does sound go backwards if you cross the equator?
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Old 09-04-2018, 01:49 PM   #7
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American sound only. All other sounds are inferior
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Old 09-04-2018, 02:02 PM   #8
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Interesting you say that yet all the premium audio houses and research is European.
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Old 09-04-2018, 02:07 PM   #9
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inferior i say. Their premium sound is just american basic sound. lol
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Old 09-04-2018, 03:17 PM   #10
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Just added a note at the bottom:
NOTE: To test if the sound is coming from your muzzle, put the receiver of the rifle between 2 pillows with the muzzle sticking out and fire it with the desired bb weight. If you want to test the gearbox noise, just put a thick rag over the end of the muzzle and then cover it with the pillows and fire with the desired weight.
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Old 09-06-2018, 07:32 PM   #11
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Door stops make very effective silencer aperture reducers, the rubber further kills the high frequencies. Just drill out the center hole to ~8mm. Much cheaper than buying an adapter. All I get now is a muffled 'wump'. Shooting with it the gearbox now sounds louder.
They also make very good barrel spacers.


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Old 09-07-2018, 10:17 AM   #12
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In a most Canadian fashion, hockey pucks are much the same. Fantastic barrel spacer material, but not so optimal on noise reduction. That said, material from a furnace filter (also very Canadian) has fantastic dampening qualities...depending on the type of filter of course.
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Old 09-07-2018, 05:03 PM   #13
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I put in a 14.8v lipo to speed the cycle time up which lessens the sound signature.
Firstly it made the rifle double cycle in semi auto and it also lost fps on the second shot as the cycle was too fast. Anyway, I put in a spring that was about 10fps more and this slowed the motor down just enough that is now shoots single shots on semi auto. Full auto also works OK now too but I aim to use this gun more as a silent Socom rifle and so I will mainly be using semi auto.
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Old 09-07-2018, 05:11 PM   #14
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I just did one more alteration that has brought the muzzle volume down 1dB. So it is now around 87dB. All I did was make up a washer to fit in the silencer that has only an 8mm opening for the bb to pass through. (I will add this mod to the first post. PS Thanks to "Tired Gun").
I also did a side be side listening test of the Mk23 Socom and the quiet M4. The result when listening to the 2 guns is that the Socom still sounds a little quieter even though it is registering about 5-6dB more on the decibel meter. I presume the reason for this is that the sound coming from the Socom is a deeper sound than the M4. Lower frequency noises from what I have been told (Thanks Tired Gun) are harder to hear or distinguish while the M4 gearbox has a higher frequency.
Now the Socom also does not have a gearbox and so the only noise is the muzzle sound. I just tested the Socom muzzle sound on the dB meter came out as 92-93dB at 20cm away.
Since there are 2 areas that make noise on the M4 I decided to test both the muzzle sound and then the gearbox sound. With the muzzle 20cm away from the dB meter, it registered at 87dB. I then held the receiver over the dB meter about 20cm away and it registered at 91dB. So both the muzzle and gearbox sound register quieter than the Socom.
So even though the M4 is registering as a quieter rifle, the Socom is the harder one to hear. In game both guns will be very stealthy though and should be a lot of fun. I can hardly wait until the next game.
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Old 09-07-2018, 09:55 PM   #15
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Give the door stop reducer a try. I just ran a quick comparison test of it against the adapter I was using before. The door stop is 4dB quieter.
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