My first studio construction - appreciate your help

[Hashbrown]

I do understand all the theory behind what we're doing here. You can see by when I joined that I've been reading and re-reading this stuff for quite awhile. I agree that possibly I'll have an issue using this softer neoprene along the whole bottom plate of the wall. The question is how far off am I, and how much should I actually use? I've done lots of searching on this forum, and this seems to be the point where things always just trail off, it's never really been answered. I'm hoping this can help many others who get stuck once you really get down to the details.

Like you said, we need to get the calculations and not take guesses, but then you go on to say that there is no way to know the compression rate of the neoprene unless we know the size of the puck. And then the only way to really know is go get this test done on my particular durometer. Well besides yourself, I haven’t' heard of anyone on this board doing that, so how did everyone else figure out the spacing when floating their floors/walls? Seems to me everyone is guessing.
Sorry, a little frustrated that I keep getting warned not to guess, without any info on how NOT to guess.

Anyway I did calculate the weight of the wall. I'll compare to your example for clarity. The wall is about 735lbs, and about 6.3 linear feet. So let's say 116 lbs/ft, translates to 2.76 lbs/sq inch. Like you said, no way that's going to compress a 1x1" piece of durometer (we think).
So to compare to your tests, you used a piece of neoprene that was 5.25 sq inches. And averaging 1st and 2nd dry results, I'm going to say you'd need about 500lbs to get you 10% compression, or around 95 lbs per sq inch.

Well let's see if I can take a stab at this. So if the weight of my wall is 735 lbs, divide that by 95 lbs, it means I should only use 7.75 sq inches of neoprene along my 6.3 ft wall to get the right compression?

Well that's at 60 duro, mine is 40 duro, considerably softer, but how much? If duro is a linear measurement, then it is 1.5X softer. So instead of 95lbs/sq inch, we'd need 63 lbs/sq inch to get our 10% compression. So at 40duro I'd need around 10 sq inches of neoprene along the whole wall plate in order to get proper compression.

Ok, do those calculations and assumptions seem reasonable? I'm guessing I've got some errors in there somewhere.
Here is another disconnect for me; throughout the forum you see folks floating floors on 50 duro neoprene under 2x4's. When you calculate the average load on that floor I can't imagine you'd ever get enough weight to compress those pucks, unless you used really tiny pucks spaced about 8 ft apart. And then you'd be more worried about the floor sagging that 1/2 inch between the pucks and touching the subfloor anyway. So does this technique really even hold up(uh, no pun intended)?

I really do appreciate you taking time out of your own work to consider and respond to my posts!

[knightfly]

I'm getting kinda lost here too; are you trying to float a single frame wall (RC one side) on neoprene, or is this a 2-framed wall?

Part of the problem with what you're doing is lack of information - few suppliers even KNOW what their materials will do. EAR composites

http://www.earsc.com/HOME/engineering/index.asp?SID=6

is one of the few.

Also, I'm not physicist enough to guide you through the complex math required to figure out what a WALL will do when floated; this gets into SHEAR properties instead of relatively simple compression. From what little I know on this, it's much easier to make things WORSE instead of better. This will be the case if you choose a material/thickness that comes close to the resonance of the entire wall, so that your "floater" material actually AMPLIFIES wall movement instead of cushioning it.

As to figuring weight for purposes of VERTICAL deflection, this also gets tricky when using a continuous piece of rubber; all commonly available materials like this will ONLY work when allowed to "squish out" - IOW, they're not constrained sideways. When you use a continuous strip, you constrain the "squish" in the longitudinal dimension, changing the performance/compression of the material.

This is why I posted the method I did in the REFERENCE section for testing your OWN materials; this is the only way I know of you can actually get it right because the cross-sectional area of your pucks will SERIOUSLY affect the amount of compression per unit area, using the exact same material.

Add to this the fact that you're using at least one wall that's only a single frame, and bedding walls in cushion material becomes an excercise in futility.

Personally, I'd just bed your walls in either sill seal or 2 layers of 30# building felt for purposes of Thermal Break (concrete, moisture, condensation) and, where using separate frames for each leaf, use NO RC. For your single frame wall (between you and utilities) the RC will improve mid-high frequency perfomance, so will be important to help block most machine noise. It's not important acoustically which side of the wall the RC goes on, just don't "short it out" with wrong screw placement. (REFERENCE section, first thread)

HTH... Steve

[sharward]

Hey Hashbrown,

I feel your pain, brother.

I wouldn't say that nobody does the math. Paul Woodlock surely did the math. But I agree, it is rare. A lot of people guess and crapshoot. And when they announce that's what they're doing, people like Steve and me will speak up.

There are no easy answers when it comes to float vs. not float. I battled it for months myself, big time.

Pretty much like Steve said -- floating is hard to do right, easy to do wrong, and doing it wrong is worse than not doing it at all.

I appreciate that you "get it" in terms of knowing the general direction to go with your calculations. If something is "wrong," you generally know what direction to move in to make it "more right." The problem is, "more right" is only "slightly less wrong" and there is a very small margin of "actual rightness," and anything outside of "actual rightness" is "distinct wrongness." Bottom line, it's impossible to find that sweet spot without a clear map. Unfortunately, the universal map you're seeking doesn't exist -- it actually needs to be custom drawn.

This is why I have no faith in the Auralex U-boats. Here's why. (I realize we're not talking about U-boats here, but the same principle applies.)

--Keith

[Hashbrown]

Thanks for the consideration guys! Steve, I am creating a single-frame wall, rc on one side and floated on neoprene. My whole purpose for floating the wall was to de-couple from the floor. I could probably achieve much the same results from using the RC alone, but thought I would create less margin of error by employing both methods.

I know I've read your thread on testing neoprene. Just searched for it recently and couldn't find it again. Must be buried somewhere in Aaron's monster thread?

I should say that I'm not going to use RC but furring channel mounted with RSIC clips(Kinetics).

Keith - Yeah I know Paul measures! That guy is intense! I started following his diary when it was still under 20 pages i think

You know I spent 6 months compiling info that I learned here into a cheat sheet, and read about so many other people's mistakes, and then I blow it myself, argh!

Well, I'm going to see how well I can salvage this, I think i might be able to get portions of the neoprene removed from under the wall. Fortunately this wall isn't my biggest concern, it's the ceiling. The living room is right upstairs, so I've really got to put the most effort there. I'll double-check that strategy with you guys later, but it's pretty straight ahead, same methods most are using around here.

So I know my previous post is bit dense, but can you guys check to see if my calculations, or at least my appraoch to them is correct? I'd like to kow if I now have an understanding of this.

Thanks.