How to stiffen interior wall with subwoofers

[sargon19552003]

I want to stiffen an interior wall in which I plan to install subwoofers for a home theater. I would like advice on the best way to do it.

[RicodJour]

Stiffen? For what purpose? Stiffness would almost assuredly require additional wall depth to have any real difference. Is that something you're willing to live with? I'd just go with something like this:

R

[Bobk207]

As Rico mention, adding significant out of plane stiffness to a timber framed wall means adding depth (thickness) to the wall.

Without increasing wall depth (thickenss) you could opne up one side & sister heavy steel channels to the 3.5" dimension of the studs. An expensive & labor intensive effort

Alternatively you could open up the wall on both sides and sheath both sides with plywood; glue & staple, creating a very stiff plate structure.

when you say stiffen...how much do you desire to increase the stifness? +50%? 2x? 5x?

cheers Bob

[jloomis]

I would use channel iron from the store.......or bed frame used.........get some double sided foam tape, and put the channel on the wall stud with foam tape inbetween.........screw it down tite...... The channel from the store comes pre-drilled.......You could use small lags

[sargon19552003]

Hi Bob,

I should have stated that the wall in question is still under construction (no drywall up yet), so I can modify as I wish. It's 3 feet in front of an exterior wall. The idea is to effectively make an enormous speaker enclosure (infinite baffle). I want to stiffen the wall so that the force of the subwoofers (a pair of panels with 4 15" woofers each) doesn't make the wall move. I'm not sure how much stiffer it needs to be. Could I add, say, unistrut to the studs ( think that's what jloomis was talking about)? Or how about putting pairs of scissors trusses between the wall and the exterior wall where the subwoofer panels are? The exterior wall is stucco on the outside, and half of it has shear wall panels.

[RicodJour]

Easiest way to stiffen it would to put a couple intermediate braces from each stud to the outside wall at the third points vertically. Effectively you're shortening the unsupported stud length. Unsupported in this instance means laterally. That would give you the biggest improvement in stiffness. Since it's an enclosure, - a crawl/ access space - those braces shouldn't really interfere with anything.

Alternatively you could go with much deeper studs, say 2x8s, and use horizontal blocking at the third points vertically.

The first option would be stiffer and cheaper. I'd also consider sheathing the stud wall in 3/4" plywood.

R

[Bobk207]

This is the operative phrase.

[sargon19552003]

There are no specific listed requirements for the speaker drivers. They're actually designed for car audio, so the assumption is they would go into something like a trunk panel. What I plan to do is mount the drivers on a panel (4 to a panel) made of a triple layer of

3/4" plywood and MDF, then screw the panel into the studs over a cutout of the drywall. Based on what you said about a 2 x 8 wall being 10x stiffer than a 2 x 4 wall (10x stiffer sounds adequate), it sounds like the best approach will be to add extra wood so that it effectively doubles or triples the thickness of the studs.

[PeterD]

8x8's ?

I don't know if it is practical if those sub-woofers are any good at all. I think you'd need some massive wall to block the sound. (Is that what you are trying to do, avoid upsetting the neighbors, or are you afraid the sounds will break the plaster?)

Or are you seeing resonance problems with the walls?

A bit more information on what the problem is would help...

[sargon19552003]

I'm not concerned about the sound waves as such. My sole concern is the mechanical force applied by the woofers to the wall they're mounted on. I want to keep the wall from flexing too much.

[sargon19552003]

Sounds like the best approach to me. Thanks!