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What affects the Tone of the gun?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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What affects the Tone of the gun?

Unread postAuthor: owmatooth » Fri Feb 19, 2010 8:08 pm

thanks for taking a second...

I'm new to this and couldn't see an answer while searching the forum, so I thought I'd throw my question out there.

I'm looking to change the tone of my shot. Essentially, I would like more of a boom of a cannon than the pop I'm getting now. I'm currently set up with a pneumatic gun, 20 inch long 2in pvc chamber and 24 inch barrel, again 2 in pvc. 3/4 in inline sprinkler valve.

I worked today on changing the barrel diameter at the end (widening it out) with no real change in tone, will a larger chamber make a difference?

Velocity isn't my main concern, it shoots anything just fine. I'm running the system at 60 to 80 psi and getting a change in volume, but not hearing additional base. I'm trying to think of it in the idea of a subwoofer, to lower the tone, but would love to not have to reinvent the wheel again. Thanks for your help. I've seen a bit on silencers, but I'm looking not so much for a louder noise, just more of a boom than a pop.

I've read the trick on the tape over the barrel bottom in the noisemakers thread, and while this sounds like it will be louder, how about some reverb?

anyway I ramble... :idea:
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Unread postAuthor: Insomniac » Fri Feb 19, 2010 8:24 pm

A shorter barrel may help, as well as higher pressures and perhaps a more powerful valve.

I do think you may struggle to get the loud, cannon-like boom you want out of a pneumatic. You would be much better off with a combustion, because while they can't compete with a good pneumatic as far as power is concerned, they produce one heck of a bang.
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Unread postAuthor: clemsonguy1125 » Fri Feb 19, 2010 8:37 pm

Um maybe a burst disk and i am sure higher pressures would work
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Unread postAuthor: owmatooth » Fri Feb 19, 2010 8:40 pm

But nothing about the diameter of the barrel? I was hoping some sort of a flare or extra wide barrel might do it. Along the lines of a megaphone...
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Unread postAuthor: clemsonguy1125 » Fri Feb 19, 2010 8:42 pm

owmatooth wrote:But nothing about the diameter of the barrel? I was hoping some sort of a flare or extra wide barrel might do it. Along the lines of a megaphone...

A funnel at the end of the barrel made my airsoft gun a bit louder
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Unread postAuthor: POLAND_SPUD » Fri Feb 19, 2010 8:44 pm

yeah higher pressures would help... above 300 psi everything is much louder than it should... though I normally prefer to keep chamber volume as close or smaller then the volume of the barrel for this reason
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Unread postAuthor: Marffy » Fri Feb 19, 2010 10:35 pm

You could buy a tuba and cut the horn of of it then epoxy it to your barrel. That could be expensive though.
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Unread postAuthor: starman » Fri Feb 19, 2010 11:31 pm

Bigger diameter, short barrels will give lower boom like sounds. Just about any way you cut it, pneumatics are going to have a breathy pop or crack character rather than a boom.

Go combustion, 3 or 4" dia (or larger), short barrel and a basic burst disk for much better boom sounds.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 20, 2010 12:41 am

The obvious answer is simple make a better gun :)

A 3/4" valve can at best only let through about 15% of the air that can flow through a 2" barrel. Get yourself a larger sprinkler or make a piston valve and you'll see the difference.

Alternatively, keeping the 3/4" and reducing the diameter of your barrel to 1/2"-1" should have a similar effect on noise. Otherwise the large barrel is simply acting as a silencer:

Extra barrel length = a suppressor

Extra ten inches or one full foot of barrel and bore length is able to act as a suppressor. Volume of the extended bore shall lessen the pressure of powder gasses emerging muzzle. Friction between rifled bore and the bullet slows down muzzle velocity; Q.E.D...

When using Standard Velocity .22 LR ammo, the bullet velocity is increasing to ca. 400 mm (16") distance from the chamber, but after passing this culmination point, is the velocity decreasing, because bore friction shall overcome the thrust of powder gasses, pushing the bullet towards gun muzzle.

Bore pressure is decreasing, because volume of the bore behind the bullet is expanding and temperature of gasses is declining. Barrel metal absorbs the heat, and rapid decrease of the bore pressure cools also powder gasses down. "Diesel Effect" can be reversed too..!
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Unread postAuthor: SpudBlaster15 » Sat Feb 20, 2010 3:01 am

If you don't want to change the dimensions of the launcher, a cone on the end of the barrel will increase the noise output in the downrange direction. Increasing the chamber pressure will obviously help, and there's some evidence to suggest that a muzzle brake may also increase the loudness.
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Unread postAuthor: jimmy101 » Sat Feb 20, 2010 1:16 pm

A bell at the end of a resonant pipe really just affects the directionality of the sound, it doesn't affect the frequency very much. The bell is also there to tune the impedance of the pipe, which is getting into fairly conplex accoustics, that in turn affects it's efficency but not its tone (much).

The gun makes sound when the ammo exits the barrel, kind of like the pop you get when opening a bottle of champaigne. The sound is related to a lot of things, the amount of air and it's pressure when the barrel uncorks and the gun resonating as a pipe with a single open end once it is uncorked, are two improtant parts of the sound. The uncorking pop is fairly short duration, the gun resonating lasts much longer. The longer the pipe the lower the resonant frequency. Double the length of the pipe and you cut the resonant frequency in half. (Picolos are very short and give a very high pitch, a digeroo (sp?) or tuba is very long and resonates at a very low tone.)

The energy in the resonant chamber also affects the pitch. At higher energies you get most of the sound in the overtones (integer multiples of the pipes natural resonant frequency). Blow into a picollo gently and you get the fundamental (native) resonant frequency. Blow harder and the tone jumps (without pasing through intermediate frequencies) to twice the fundamental frequency. Blow harder still and it jumps again. (All wind intruments behave the same way; saxaphones, flutes, tubas, trumpets...) In guns there is typically so much energy left in the pipe after the round exits the muzzle that the resonant frequency is a couple integer multiples of the expected resonant frequency given the gun's (pipe's) length.

The resonant frequency also depends on the speed of sound which in turn is very dependent on the temperature of the air in the pipe. When a gun "uncorks" the temperature of the air fluctuates pretty wildly. Pneumatics and combustions gun behave differently but in both cases you get fairly large swings in temperture that occur pretty quickly so the actual resnonant tone fluctuates about as fast as the sound wave actually oscillates.

That's probably a lot more than you actually wanted to know. :roll:
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Unread postAuthor: Brian the brain » Sat Feb 20, 2010 3:53 pm

I found that a very large chamber at relatively low pressure ( up to 5 bar or so) gives a very low boom.
I'm talking 13 liters of reservoir and a 2" porting valve.

The more volume ( of air) the more bass like it gets, the higher the pressure the higher the pitch.
Also, the shorter the barrel the louder it gets.

There are a lot of variables..
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Unread postAuthor: MrCrowley » Sat Feb 20, 2010 5:16 pm

Large diameter piston valves are also very loud at pressure as low as 80PSI. Though a burst disk advanced-combustion is probably better in terms of noise.
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Unread postAuthor: iknowmy3tables » Sat Feb 20, 2010 6:22 pm

so right bigger faster valve, bigger chamber, shorter barrel should help
however you have yet to hear the sound of an ear ringing spud gun, a really really big chamber helps, I knew a mate who took him basic spud gun knowledge and created a spud gun with two 10' 4"pvc pipes for a chamber attached to a 2" valve, the length of the barrel compensated for the slower valve and the result made your ear's ring
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Unread postAuthor: maverik94 » Sat Feb 20, 2010 8:45 pm

Yeah, you don't need a huge chamber for a really big bang. Once when shooting this gun, the breech cover cracked, and air ruched out of it right next to my ear. It left my ear ringing for about 15 minutes. That was at about 110 Psi by the way.
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