Double-wall construction PLUS resilient channel? Worth it?

[jazzman]

Has anyone here gone through the trouble of putting resilient channel on one side of a double wall (2x4 stud framing) that's resting on foam or neoprene? Was it worth it?

I once asked an acoustician this question and he thought it was overkill and not worth it since the foam theoretically isolates the two walls from one another already. But I want the best isolation I can get if it would actually help more than just, say, 1 dB.

Lee

[knightfly]

Lee, from what I've read (have NOT tried it myself) if you're using WOOD studs you'll see about 2-3 dB difference - reason being, you've just lowered the inertia of the wall panel from the entire weight of the stud frame AND the panel(s) to just the weight of the drywall, so it softens the "spring" by about 1/3.

If you're using metal studs, you'll probably get about half as much improvement since the metal studs have less inertia already, and provide about half to 2/3 as much isolation by themselves as the RC does when placed on wood studs.

All the above are "SWAG's" - If I were doing it, I'd use the RC if the studs were wood, and flip a coin if they were steel... Steve

[jazzman]

Thanks, Steve. But your answer raises a new question. How much does the stiffness of the wall contribute to its ability to keep sound from being transmitted? I've put a couple of firestops (parallel to the floor) between each vertical stud in order to stiffen the entire structure to reduce vibration as quickly as possible. And it certainly helps. When I bang on a section of wall that has the fire stops, it doesn't "ring" very much at all. Without the fire stops, the wall resounds noticeably longer.

Now if I put the gypsum panels on springy resilient channel, won't they vibrate more since the stud framing and Liquid Nails construction adhesive will no longer damp the motion of the panels?

I'd be curious where you read about the effect of resilient channel on one side of a double stud wall. Any chance you remember? I'd be happy to look it up.

And thanks again!

Lee

[knightfly]

Not sure where I read that - could have been here

http://groups.yahoo.com/group/acoustics/

or in the Master Handbook of Acoustics by Everest, or I might have "interpolated" it from other reading.

In my mind, it makes sense from the standpoint of decoupling the two leaves of a mass-spring-mass wall system.

By stiffening the wall with firestops, all you do is change the resonant frequency to a lower one (which isn't bad, usually) the same basic thing can be accomplished by adding more mass, such as an extra layer of wallboard. Now, if you make that extra mass less coupled to the rest of the wall system (by adding RC), you have the advantage of stopping more sound (more mass) added to the decoupling between leaves (less sympathetic vibration) so should see an increase in TL through the total wall.

That last paragraph was total interpolation from the last 15 years of study, so don't bother asking where I read it - I didn't. By the same token, I may be assuming here.

The problem with going "out of the box" on wall construction is that it's nearly impossible to build and test half a dozen different wall construction methods (at least for an individual) since the accuracy of the tests will be largely dependent on the "test bed" - by that, I mean that you would have to first build other walls that were an order of magnitude greater performance than the ones to be tested, then build each type of wall flawlessly between those superior walls, test thoroughly, tear it down, build the next test wall, etc - doing that by yourself would keep you from ever completing the studio you started out to build.

I don't know about you, but after contemplating the proper ways of soundproofing, etc, I'm already tired of this shit and just want someone else to build me a free studio so I can get back to playing/composing/recording... Steve