Sonotube durability

[trc]

My brother-in-law and I are planning a sub for him using the Dayton RS HF 15" driver and a BASH amp. He wants it ported, which means a cabinet volume somewhere in the 10.5-11.0 cu. ft. range. That would be a very heavy box in MDF, especially since I would use at least two layers of 3/4" board. I've shown him the sonotube designs, and I like them myself, but his main concern with them is how well the cardboard will hold up over time. Does anyone have experience with either their durability or lack of it?

Here are a couple of questions that come to mind in this area:
* How difficult is it to move these subs without denting the sides?
* How strong are the sides against things that kids might throw at them?

Thanks.
trc

[ThomasW]

Yes an impact can 'bruise' the sides of the tube. It's strength is dealing with pressure from the inside not an impact from the outside. They're certainly not fragile per say but care should be exercised.

Covering it with a layer of carpet offers a nice layer of protection.

However a barrier consisting of barbed wire or better yet concertina wire is the most effective deterrent for pets and small children....:wink:

[noah katz]

"since I would use at least two layers of 3/4" board"

Way overkill. I built my sub, 2' x 2' x 5' with a single layer of cross-braced (no H-braces) 3/4" ply and it's very "quiet". The long sides have 4 X-braces each, the ends one in the middle.

But I'm all for Sonotube, there's no other way to get that weight/structural efficiency.

[trc]

the ends one in the middle.

Are you saying that you used an X-shaped brace that went from one end to the other? Wouldn't that interfere with the crossing X braces?

You used plywood, but my brother-in-law wants to use MDF for a smoother finish without paying the money for a veneered ply. Will the MDF really be stiff enough with just the one layer? I suppose it depends on how much bracing there is.

Thanks for the replies.

[ThomasW]

MDF is quite flexible compared to ply...if you want to use single layer MDF, plan on double the number of braces used for ply

[trc]

OK, that's kind of what I was expecting. Just wanted confirmation. Thanks.

[slayer]

There is no such thing as "overkill" in the DIY realm.

[Brandon B]

A geometric property of the circle is that it encloses the most area with the least perimeter of any 2-D shape. Therefore deforming a circle in any manner decreases its area. Since a subwoofer operates generally by pressurizing the interior, no amount of pressure will deform the circular shape, as that would only further increase the pressure. So unless your sub is so powerfull that it will literally rip the sonotube apart, the additional layer might damp resonance but will not strengthen it.

Now if you went with some 1/2" wall PVC sewer pipe . . .

BB

[noah katz]

"the ends one in the middle."

Sorry, s/b "the ends, one in the middle", which is still klutzy.

Any, they're all X-braces to opposite panels.

Hi Brandon,

"no amount of pressure will deform the circular shape"

That's not technically true, but for our purposes can be considered so.

All structures deform under load, it's just a question of how much and what the shape of the deformation is.

As the woofer pressurizes and rarifies the air in the box, the forces are resolved into forces into circumferential and axial forces, and the diameter of the Sonotube increases and decreases, as well as the height, albeit very slightly.

Nitpicky, but I didn't want anyone to generalize to a mistaken idea, like I used to.

[Brandon B]

Make that positive internal pressure, and it's true, barring the tube actually ripping or stretching.

BB