2X4 Vs 4X4, 24" OC Question

From what I am starting to understand, 24" OC stud construction helps extend TL to lower frequencies for a given wall assembly vs. 16" OC, and I believe this is due to the larger bay size allowing more of the panel's original resonant frequency (say given a 4' X 8' sheet) to vibrate unimpinged. If i'm mistaken, please correct me here. Recently I've been reading that for fully decoupled wall systems (i.e. Double Stud), having increased stiffness, (such as using wood instead of steel studs) also helps also improve TL in the low end. If this is true, wouldn't using 4"X4"'s be better than 2"X4"'s given the same wall system depth and general stud spacing? If so, I would consider this in a build I'm planning for. Brainditch

cost is one factor. a wider structural member contacting the drywall though causes more transfer into the frame as well as shortening the span of the drywall raising the resonant frequency of the assembly. if you need more stiffness - go with a 2x6 instead of 2x4.

"If this is true, wouldn't using 4"X4"'s be better than 2"X4"'s given the same wall system depth and general stud spacing?" no...and for at least the same reasons Glenn mentioned. Stiffness (read 4X4) versus flexibility of the assembly.

Thanks for the responses, folks. So if some of the contact area of the stud's edge were removed (as in a chamfered edge), would this possibly improve the low Hz TL? Brainditch

No it would not. Not that we have proof, but there is a good chance it is "too much sugar for a dime". Stick with the basics, do not try to re-invent the wheel...

I appreciate your point xspace, however in builds like the one I'm pursuing, sweat equity is easier to apply than space (at a premium since it is a garage conversion). Because I'm handy with power tools, running the relatively few studs I need through a tablesaw to achieve a chamfered edge, and being a little more careful with DW application (chalk line marking every stud location) might be worth it if: 1. It results in a few more psi of holding pressure at the screw edge (if this is part of what makes up the "assembly stiffness" mechanism). 2. If it results in a few Hz lower bay resonance. It probably won't do much for either of the above conditions because of the relatively small percentage change, but I'm keen to understand the underlying mechanism better. For example, even if unaffordable, would changing stud mass and rigidity, such as by using Structural Strut as a stud material yield much improvement? We may never know because the published studies were focused around more commonly available materials and methods in service to the general construction industry. I freely admit that we as a community of studio builders and private studio owners have benefitted tremendously from such inquiries, yet I continue to attempt deeper exploration of the salient points, because there may be cases where going to such lengths may be useful or necessary. Brainditch

The problem is that different parts of the spectrum are affected differently by different factors. Mass rules in some parts, rigidity in others, flexibility in others, material resonance in others, coincidence in others, etc. Whatever you do to improve one aspect is going to have an effect on another aspect, and it might not always be what you expected. So like Brien said, it's not a good idea to try to re-invent the wheel, unless you also happen to own an acoustic testing facility where you can try out all possible variations and see what affects what, and by how much. Instead, the better idea is to go with the know factors: Calculate your MSM resonance based on your materials and design, and if you don't like the number you get then: 1) Increase your mass on one or both leaves, 2) increase the air gap between them, 3) fill the air gap more completely with insulation, 4) all of the above. There are no more options. All of those will drive down your MSM resonance, and increase your isolation. If space is an issue and you cannot increase air gap, then increase mass. If you can't even afford the extra 5/8" of another layer of drywall, then switch to a higher density material, such as fiber cement which has twice the density, so you can get twice as much mas in the same thickness. Or if that still isn't good enough, then think about steel plate, or even something really exotic like lead sheeting. All of those have already been researched, and are known to work. Beveling stud edges hasn't, as far as I know, and even if it does have some effect my guess is that it will be minimal, and nowhere near as effective as slapping on another layer of drywall, or maybe some Green Glue between layers. I'd go with what is known to work, and has already been tested. - Stuart -