# Simple lightweight muffler

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#### poormansairforce

##### Well-Known Member
So we got the muffler built for my son's go kart with a Predator 212 and it works pretty well. I know this isn't an airplane but it will carry over and since this was being discussed on another thread I thought I would start a new thread rather than take away from that thread.

Note: This is a brand new engine so he is not running it very hard.

#### pictsidhe

##### Well-Known Member
Interesting baffle. If you bleed energy from a sound wave travelling down a pipe, the first hole will leak more energy than subsequent holes as the wave will decrease in energy as it passes holes. You can balance it by increasing the size of later holes, or using more. The maths and physics to calculate it is a bit nasty, but nothing wrong with taking a guess, probably faster to make test pipes..

#### poormansairforce

##### Well-Known Member
Interesting baffle. If you bleed energy from a sound wave travelling down a pipe, the first hole will leak more energy than subsequent holes as the wave will decrease in energy as it passes holes. You can balance it by increasing the size of later holes, or using more. The maths and physics to calculate it is a bit nasty, but nothing wrong with taking a guess, probably faster to make test pipes..
I thought about doing that but didn't feel like rechucking 4 different times. That's an improvement for the next time. For the time being I wanted to see the benefits of staggering the holes.

#### pictsidhe

##### Well-Known Member
It's easier to do something like 2 holes, 3 holes, 5 holes, 8 holes.

#### TFF

##### Well-Known Member
Doing can within a can within a can, reversing direction, can make it quiet that all you will hear is the clutch shoes ringing the housing. Maybe a little steel wool packing in the last can. 10 oz to 16 oz to 24 oz. reversing and expanding is how many people get smaller squirrel cage blowers to run pipe organs without the whoosh sounds or quiet air compressors in small shops. A friend and I made a different than standard race pipe for our race cart. It mostly was a smaller diameter than the regular; I think limited to 18" long. It made a lot more torque but did limit the RPM. we were spinning 5 hp briggs 6000 rpm.

#### poormansairforce

##### Well-Known Member
Doing can within a can within a can, reversing direction, can make it quiet that all you will hear is the clutch shoes ringing the housing. Maybe a little steel wool packing in the last can. 10 oz to 16 oz to 24 oz. reversing and expanding is how many people get smaller squirrel cage blowers to run pipe organs without the whoosh sounds or quiet air compressors in small shops. A friend and I made a different than standard race pipe for our race cart. It mostly was a smaller diameter than the regular; I think limited to 18" long. It made a lot more torque but did limit the RPM. we were spinning 5 hp briggs 6000 rpm.
Agreed. An extra can was in the plans if it was too loud but he has been running it around the house and it is not any louder that the GY6 with it's heavy muffler. It's been sitting for 2 years so he is 30 lbs heavier and he said it has more get up and go in the mid range for sure. It handled 2 people better than before so we are good. The top speed still needs to be determined but that's not as important to him.

The pipe organ operations are an interesting idea. Thanks for that.

#### poormansairforce

##### Well-Known Member
It's easier to do something like 2 holes, 3 holes, 5 holes, 8 holes.
I had thought about different size holes but I didn't think about adding holes as I went from end to end. I was too focused on creating different path lengths I guess. Bummer! Oh well, it works.

#### Himat

##### Well-Known Member
Interesting baffle. If you bleed energy from a sound wave travelling down a pipe, the first hole will leak more energy than subsequent holes as the wave will decrease in energy as it passes holes. You can balance it by increasing the size of later holes, or using more. The maths and physics to calculate it is a bit nasty, but nothing wrong with taking a guess, probably faster to make test pipes..
Looking at it as an energy distribution that will be the answer, yes the first holes bleed of most of the sound energy. The impedance of the ports, or load of the holes in other words, are then not taken into account. Even if the holes are the same diameter and area, the impedance may change with placement relative the ends, walls, geometry and other aspects of the tubes involved. In this example the second row of ports may bleed of just as much energy as the first, but maybe at a different frequency due to the spacing.

I do find this a fine example of an easy built, light and cost effective silencer/muffler.

#### pictsidhe

##### Well-Known Member
Looking at it as an energy distribution that will be the answer, yes the first holes bleed of most of the sound energy. The impedance of the ports, or load of the holes in other words, are then not taken into account. Even if the holes are the same diameter and area, the impedance may change with placement relative the ends, walls, geometry and other aspects of the tubes involved. In this example the second row of ports may bleed of just as much energy as the first, but maybe at a different frequency due to the spacing.

I do find this a fine example of an easy built, light and cost effective silencer/muffler.
"is a bit nasty"

#### choppergirl

##### Banned
If you aim the exhaust pipe straight up, the sound wave will not have anything to hit (short of the air molecules itself) to bounce back to the listener and your noise level will be substantially reduced.

So why aren't all exhaust pipes aimed straight up? Rain. Rain going down them right into the cylinder head which leads to rust, hydrolock, etc.

However, when not in use, like an airplane parked in a hanger, or not flying, exhaust pipes pointing straight up could be capped (with a cap that perhaps slides or screws on) to keep out the rain

I discovered this phenomenon when playing around with the idea of designing silencers.

A blank gunshot shot straight up is deathly quiet.

A gunshot shot at the ground at a 45 degree angle, will hit the ground, and bounce upward into space away from the shooter at another 45 degree angle, and also be very quiet to the shooter.

However, a gun shot, shot down range in a forest level, produces a lot of noise, as every tree reflects sound back to the shooter.

A gun shot shot in an open field down range, will be mostly quiet, until the sound wave hits something down range and bounces back to the shooter.

Therefore, my design was to design a silencer that allowed the bullet to go straight forward down range, but the baffle "rings" would be at a 45 degree angle and bounce the sound straight upwards through vertical pipes from the silencer unit. Outdoors, it would work to silence most of the sound by directing it upwards, but indoors, with a ceiling overhead, it would not produce the same leveling of silencing power as the ceiling would reflect the sound back downwards.

Most gun shots however, occur outdoors, so it would be a very effective silencer for the most part, as long as you were not shooting with a canopy of trees overhead.

I've never seen any silencer design do any such thing, attempt to reflect the gunshot sound wave and expanding gases "upwards", so I considered my silencer idea and design rather unique.

~

When I angle my own plane exhaust, I plan to aim it straight up, or perhaps straight up and rearward pointing up and backwards away from the pilot seat. Cover it up when the engine is not flying, as a habit or checklist item, just in the same way you might do other things when you are done flying, like parking the prop at the right angle, draining the gas, etc. You definitel don't want water go down into your cylinder head, as I've seen small engines where that has happened going down the air intake manifold (when the air filter box unit was taken off and left off, and the engine left to the mercy of the elements) and rusted them tight.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
My tractor exhaust is straight up with a rain guard flapper.
Just make sure the exhaust fumes doesn't hit the pilot.

#### akwrencher

##### Well-Known Member
HBA Supporter
My first Comercial fishing boat had a worn out muffler on an old Jimmy diesel, pointing up. Could hear it from miles away until I replaced it. After that, only the noise from the engine was screaming in my ear. Straight pipes are straight pipes, unless turboed.

#### poormansairforce

##### Well-Known Member
A blank gunshot shot straight up is deathly quiet.
I have several 12 gauge shotguns and and a 7mm rifle. If you stood anywhere around me when I shoot it straight up you will not be saying that it is "deathly quiet"!

It will help but you still have a pressure wave impacting the atmosphere sending a wave in all directions. Go to a tractor pull with the alkys having straight pipes pointing up. We need to either lower the peak pulse by stringing it into many small ones that arrive at different intervals or use a negative/positive cancellation.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
VW Beetles have two 8" long silencers clamped on the tailpipe end. I just tried one on my V-twin, it really absorbs the sharp pop.

#### pictsidhe

##### Well-Known Member
A regular gunshot has the bullet/shot to bounce the wave off. I've never used blanks, so can't comment on how big the effect is.
Saying that, sound is directional. The problem with tailpipes pointing up is that the small wavefront will encourage diffraction. You will get a few dB reduction, but not 'deathly silence'. A megaphone pointed up would help, but that's bulky, draggy and a rain magnet.
A simple compromise could be an upward kinked tailpipe with a small drain hole.

#### Armilite

##### Well-Known Member
A regular gunshot has the bullet/shot to bounce the wave off. I've never used blanks, so can't comment on how big the effect is.
Saying that, sound is directional. The problem with tailpipes pointing up is that the small wavefront will encourage diffraction. You will get a few dB reduction, but not 'deathly silence'. A megaphone pointed up would help, but that's bulky, draggy and a rain magnet.
A simple compromise could be an upward kinked tailpipe with a small drain hole.
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With a Gun Shot, you have the Sound of the Hammer & Firing Pin Striking the Primmer, the Bolt if Semi/Full Auto, the Hot Gas following the Bullet that hits the Cooler Atmospheric Air, and then the Sonic Crack if the Bullet is traveling roughly over 1150fps, and if it hits a Target Close by, the Sound of Bullet Impact. If Shooting towards the Woods and Shooting Normal Ammo that Sonic Crack can also echo back towards you. Take one of them DB Aps for your Smart Phone. Dry Fire you Gun to get the DB Reading of the Hammmer & Firing Pin. If Semi Auto, pull Slide Back and let go to get that DB Reading. Then Shoot some Normal Rounds and get that DB Reading, then Shoot some Subsonic Rounds and get that DB Reading. If, you live in a State where Suppressors are Leagal, you can also Test their DB Data. Last I new, All 50 States but 6 they are Legal in, but you have to check your State, County, City, Laws. The same goes for Machineguns.

A Muffler and a Suppressor are very similar, they Absorb Heat, and Slow the Hot Gas down to give it Time to Cool, before it exits the Muffler or Suppressor. Each Gun and Motor is different.

This guy puts out some Nice Video Reviews. Here is a 300 black out Suppressed.

A Pistol

See Through Suppressor.

What some Suppressors look like inside and what your Typical Mufflers looks like inside. They Both do the same Thing, Absorb Heat, and Slow the Hot Gases down, giving them Time to Cool. If you Noticed, on the Suppressor, you don't see any Hot Flash come out the end. Fire needs Oxygen to Burn. So with a Suppressor you not only lower your Sound Signature, you lower your Flash Signature.

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