Make sonotube from old propane cylinder? - diyAudio
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Old 24th July 2004, 11:08 AM   #1
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Default Make sonotube from old propane cylinder?

I keep telling myself I gotta try out a sonotube type enclosure one of these days. The benefit that gets me going about it is because of it's cylindrical shape there is not the flexing (and therefore need of bracing) that you get with a conventional wooden box-shaped enclosure. No panel vibration = clean sound, more predictable frequency response & higher power handling.

Most people seem to make one of these things from a large diameter cardboard tube normally used by the construction industry for pouring concrete into to make supporting pillars for buildings etc. Anyway, I got to thinking about stuff and it seems to me that you could make a workable unit from an old propane cylinder. You still have the same advantages from the cylindrical shape of course, and the sealed end is already sealed (well, duh!) and it is a dome shape so it's rigidity is enormous! All you have to do once you have cut off the valve end at (maybe) the full diameter of the cylinder is weld on a circular flange to mount the driver. A certain amount of damping material to line the inside surfaces too.

The setup I want to try in particular is a 2-chamber, 2-port bandpass unit made from a large and small cylinder face-to-face with the driver at the junction of the two but I haven't decided whether to have the ports come out the side just near the driver, or at the extreme ends of the cylinders.

Depending on the frequency range pumped into the system, it might be useful to have a layer of carpet or similar wrapped around the outside to absorb any tendency ring, depending also on the thickness of the metal. Hmmm.....
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Old 24th July 2004, 11:16 AM   #2
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The safety aspects involved with cutting and welding a propane cylinder make that a very bad idea! A great way to loose a hand. Even an empty cylinder still conatins some propane, just not under pressure. When you cut that cylinder, the sparks you create have a very high chance of igniting that propane, and causing an explosion.
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Old 24th July 2004, 11:42 AM   #3
SY is offline SY  United States
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Default Paging Hank Hill!

I was unaware that the cylinders can't be flushed. Thanks for the warning. I wonder if it's possible to get new cylinders, i.e., ones that have never been filled with propane.
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Old 24th July 2004, 11:59 AM   #4
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Haha...hank hill...ya!

Instead of welding you could liquid nails an MDF flange. Boy, sounds like a future project Spheres 3....bigger and badder

So how do you purge the tank??

Heres a google response, but I think they mean purge in a different manner. Not emptying it.
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Old 24th July 2004, 12:20 PM   #5
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A used but empty propane cylinder can be safely cut with a torch or electric welded if completely filled with water, but being a machinist myself I think it is not the way to go. Besides being a lot more work there is one reason here that still applies that causes people almost exclusively to never make HiFi speaker cabinets out of steel. If you don't know, rap the cylinder with your knuckles to find out.

They don't make church bells out of sonotube for the same reason. One of these materialsd rings like a bell and the other doesn't, least that's my story and I'm sticking to it!
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Old 24th July 2004, 01:30 PM   #6
dnsey is offline dnsey  United Kingdom
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Here in the UK, at least, propane bottles are owned by the gas companies, and are only hired to the end user as a part of the deal when buying gas.
The comanies don't take kindly to having their bottles hacked about - I knew someone who used one as an air receiver, and was fined heavily!
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Old 24th July 2004, 01:35 PM   #7
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Propane is heavier than air. Even though the propane tank seems to be empty there can be residual propane laying in the bottom of the tank. The only way to empty the tank of propane completely is to displace the propane with some other medium. The easiest would be water. Beware, as you fill the tank with water you are forcing the residual propane gas out of the tank. Do not do this anywhere near an ignition source. Once the tank has been completely filled with water, it can be emptied and cut.
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Old 24th July 2004, 04:07 PM   #8
Variac is offline Variac  United States
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I liked the beer keg idea better....
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Old 24th July 2004, 04:26 PM   #9
markp is offline markp  United States
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You ever bang to tanks together by accident? What did it sound like? Get used to it as the speaker will have the same sort of ring to it. The reason sonotube is used instead of metal is that it is selfdamped, i.e. no ringing. Besides that, being a circle the sonotube is very rigid when it comes to pressure changes. Thats why it is used for a concrete form, if it was square it would bulge under the pressure of the concrete inside. If you really have a problem with the sonotube then go get some thick walled pvc sewer pipe. It works very well and can be cut and glued easily.
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Old 24th July 2004, 04:48 PM   #10
Variac is offline Variac  United States
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I'm sure he is planning to coat the tanks inside with some sort of tarlike substance. Ever bang two tanks together with a bitumin layer on the inside of them? Well, probably not, but I don't think there is going to be much ringing.... Also using them as enclosures isn't really the same thing as banging them together.

They will have a great advantage on lower notes in that the walls practically won't flex at all.

The high end Krell speakers are made from very thick welded aluminum plate. While they wouldn't ever ring as well a single piece shape the would certainly ring if not damped and banged together. I guess they ARE damped because they are reputed to sound very good.
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