Drum shells as sub enclosures?

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Can anyone comment on the drawbacks on using a Maple 10ply drum shell as an enclosure for a sonotube type sub. The drum shell has a wall thickness of .270"

I realize that real wood will potentially "color the sound", but thought I could get around this by using something like Cascades VB-1S PRO damping spray on the internal walls.

Any comments will be greatly appreciated.
 
johninCR said:
The strength of a circle for the pressure of a fluid can't be disputed. I have a big ported pcv sub and the walls are totally dead. I did have to go with 2" thick end caps to avoid the need for bracing and it's only 12" dia pipe.

You are right, there is no disputing the strength side of things. But I'm not sure this is the complete picture.

It has strength and stiffness, but lacks mass and thickness. I expect there will still be a fair amount of sound transmission.

I suspect that the advantages of sonotube being a cylinder, although correct, are often overstated.

The question I would ask is can you feel vibration of the enclosure? If the answer is yes then energy is being both absorbed and transmitted in and through the enclosure.
 
Paul,

That's what I'm saying, it's dead. I did have to strap it down to prevent movement from the mechanical operation of the woofer because it is so light, then there's no vibration on the cylinder walls. The only other sub I've built that comes close in that department is a well braced cube with 3/4" ply with a 1" outer layer of an extremely dense and heavy hardwood.

With the long wavelengths of a sub, I'm not sure there is sound on the inside. I think it's just pressure changes, one of those does the refrigerator light turn off kind of things.
 
That's a really intersting idea Basham.
How about using something like this for starters.
I would paint the inside with epoxy/fibreglass, fit plywood baffles to the front and back and mount the driver on the back. How cool is that!
 

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Hello all,
Thanks for the great comments.

"It has strength and stiffness, but lacks mass and thickness. I expect there will still be a fair amount of sound transmission."

Paul, this was my concern from the beggining. This is why I had intended to spray the interior with some type of damping material,
hoping to eleminate, or at least minimize, any sound transmission.

"The inside doesn't need anything for strength, so spend the time and effort bracing the 2 baffles, especially to each other."

John, what would be the reasoning in bracing the endcaps together, if they were at least 1.5' thick and attached securely to the walls?

Once again, thanks for your replys
 
The flat surface of the end caps, even at 1.5" thick must be braced or they will flex and those vibrations can be audible. An X shaped brace connecting both baffles with a cutout for the driver basket using 3/4" end caps would be far better than 1.5" or 2" end caps and no bracing. I realize it doesn't seem to make sense with a circle of such thin material being fine on it's own, but the circle is many times stronger and more rigid for the effects of the changing air pressure inside.
 
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Now if you used 2 drivers-one on each end, the baffles would have such big holes in them that any discussion of stiffness of the baffles would be almost irrelevent. Then if you had a solid wood brace between the magnets of the woofers it would be super solid.
The movement of the drivers in opposite directions cancels out almost all vibrations transmitted to the floor.

As has been said here already, with low frequencies, it's strength against flexing you are concerned with mostly. The walls resonant frequency (especially with those beautiful maple shells) is much higher than the frequencies you are reproducing, so no worries....
 
Paul, this was my concern from the beggining. This is why I had intended to spray the interior with some type of damping material,
hoping to eleminate, or at least minimize, any sound transmission.

Damping material absorbs above 100 Hz and has very little if any value here. Sound transmission is another thing altogether. This is reduced by vibration decoupling (box within a box), mass damping and having solid, thick, dense materials.

A very interesting experiment would be to construct a box with dual chambers - one for the front and rear radiation of the driver. Then when played, all that you would hear would be the contribution of the box to the sound. It would be interesting to see how much the level is attenuated in comparison to the output from the driver. It would be very interesting to see how a sonotube would compare to a well built box.

The movement of the drivers in opposite directions cancels out almost all vibrations transmitted to the floor.

They will prevent it moving around but vibration of the enclosure won't be cancelled out. Its a bit like a tug of war - the rope will still vibrate. Vibrations in a box will only be cancelled if you have waves moving towards each other where the -ve peak of one is superimposed with a +ve peak of the other. I don't think this will occur in a box set up in that way.
 
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