Help! could any one calculate optimum spacing for me?

Les Ismore · Post by **Les Ismore** » Fri Oct 22, 2004 3:53 pm

Hi,
Well I've framed up a room within a room control room work space (20' x 10') in my house and I somewhat foolishly decided to try to float the walls off of the floor as I was concerned about transmission thru the floor to the other wall system. My capenter talked me into putting 1" polystyrene foam under the 2x4 studs and swore that it would support the weight. I had a hard time swallowing that and after I researched it (stupidly after the fact) I feel that my intuition was correct. This stuff is not going to be able to support the weight long term.

So I have ordered (and just picked up) 1" x 4" x 4" heavey rubber blocks to place under the studs (which are already framed in) at intervals, leaving the polystyrene in between to dampen vibration (somewhat I hope). I will cut out spaces for the rubber blocks and hammer them into place without redoing the walls.

Could anyone here possibly calculate the optimal spacing of the rubber blocks for me? I am self taught and only finished grade 7 in school so I don't speak algebra. Hell I can't even spell algebra.

The construction is 2x4 spruce studs on 16" centers. The walls are 7'2" high, the room is 20' long and 10 feet wide. I'm planning on drywalling it with 5/8" drywall and there is a space of only about 1/2 an inch between the inner and outer walls. There will be fiberglass insulation (R12) in between the studs.

I was going to place the rubber blocks under every vertical stud, but I am concerned about possible resonant frequency amplification from MSM. I could easily place them further apart if it would be advantageous. The main idea of the rubber blocks at this point is to keep the room from settling as there are very small tolerances in some spots and if it sags it could short out to the outer room. I would leave the foam in between.

Or does this make any difference?

If I could go back a week I would just put the stupid thing on the ground but it is all framed now and I just want to make the best of the situation.

Any help you could provide in this regard is greatly appreciated.
Cheers, Les Ismore

knightfly · Post by **knightfly** » Sat Oct 23, 2004 9:55 am

There are several variables (damned algebra again) that will make this difficult if not impossible to figure; if you leave the foam in place, it will contribute to the support of the wall (how much - good question) and so detract from the mass supported by the rubber (no mention of what KIND of rubber, durometer (hardness), etc - rubber behaves differently depending on whether you CONSTRAIN its sidewall movement (it gets stiffer) so the foam being left alongside could also change THAT -

If you remove the foam between rubber blocks, all you have for support is the span capability of the flat 2x4 wall plate, plus whatever stiffness is contributed by the wall panel - since you mentioned MSM, I'm assuming you know about double vs. triple or quadruple leaf walls, right?

4" x 4" surface area makes it necessary to space blocks even further apart for the same amount of compression; doing that would leave the wall plate unsupported under probably at least 3/4 of your rubber blocks, which would weaken the frame.

If the ceiling will NOT be supported by these walls, you can get close to the right weight by just adding up the individual panel weights that will be part of the wall, plus the weight of the framing. If you have enough specs on the rubber, you should tnen be able to figure the total surface area of rubber needed to get around 15% compression of the rubber; however, if you leave the foam in place then all bets are off.

The foam won't do anything to help seal the wall; this needs to be done by caulking around the edges of each layer of wallboard, after leaving 3/16 to 1/4" gap at intersections of different wall sections, ceiling, etc -

If you don't know the specs of the rubber, my first recommendation would be to give it back and get something with a pedigree; also, if it's anything other than EPDM rubber, you may be looking at less than 10 year life; will you be finished with your room forever by then? If not, look for EPDM or Sylomer.

Paul Woodlock has been working on this aspect of his studio for some time now, and can explain better than I how you need to handle all the elastomer stuff; generally though, I think you're in a really shaky area on this - too many variables, and not enough answers yet... Steve

Les Ismore · Post by **Les Ismore** » Sat Oct 23, 2004 4:45 pm

Very interesting points Steve. I was going for the rubber blocks basically because of several people I know used hockey pucks to float the walls with good results. Plus I'm a Canadian. Anything to do with hockey must be good eh?

The density of this rubber is slightly softer than a hockey puck. Somewhere between a hockey puck and a tire, closer to the hockey puck side. The folks who used the pucks were spacing them in between the studs it seems.
As far as the question of my knowledge of single dual and triple leaf systems, I am just learning (a bit late) from your site and others. I am quite amazed to find that if I remove the layer of gyprock on the inside of the outer wall I will improve the sound transmission loss. That really is not what I expected. Do I have that right? If so I guess this is truly a case of Les Is more.

The walls will be supporting the ceiling and I guess I will go 2 layers of gyp.
I used 16" centers which I am seeing now might have been better a bit wider. The problem is that we were wanting to not damage the house too much so that if we wanted to tear the studio out and turn it into a suite we wouldnt have to completely rebuild the place. hmmm
I built a pretty nice studio back in 87 and ran it for 14 years. That one we used 25 tons of concrete blocks and it worked pretty well, but this one is just a little control room work space so I can work at home and not drive my wife nuts. (or more nuts as the case may be)
Anyway I really don't want to tear down and start over as I can't afford that, but I would like to maximize the good and minimize the bad. (a freind I used to work a lot with said that "mixing is easy, just turn up the good and turn down the bad")
Do you think it would be worth the hassle to tear out the gyp on the inside of the outer wall to keep it from being a 3 leaf system? Am I speaking about this correctly?
Right now I have an outer wall of 2x6's with 5/8 gyp on both sides that I suspect does not contain insulation. Then my new wall is on the inside of that (with 1/2" gap between) with 2x4 studs and 2 layers of 5/8 gyp on the inside only (and insulation).
I could possibly tear it out by reaching in between the studs of the inside wall's framing. It would be pretty messy, but then I could insulate the outside wall as well and then I would have a 2 leaf system, right?
my head hurts.

knightfly · Post by **knightfly** » Sun Oct 24, 2004 9:55 am

Yes it would be a pain, yes you need to do it, and yes it will help - a LOT at lower frequencies. the third leaf may actually IMPROVE the TL at mid range and above, but since "bottom is the bitch", that's where the effort needs to be; the rest will usually just "fall into place" - Steve

Les Ismore · Post by **Les Ismore** » Mon Oct 25, 2004 1:39 pm

Ok Steve, you talked me into it. I'm going to remove the gyp on the inside of the original wall in the house. The wife won't let me rip it out on the outside wall or the ceiling though (in case we tear out the studio), but that shouldn't be too much of a problem as it's my bedroom upstairs and the outside was pretty quite from the studio room already with no soundproofing. We do have an (right now empty) suite downstairs accross the house from the studio, so minimizing the bass towards that side would definately be a good plan if we ever want to rent it out. (I'd prefer not to rent it out)
Hears an idea I would like to ask you about. We spaced the stud centers on the walls at 16", and I've been reading hear about making the spacing as large as possible to lower the frequency of the walls. I was thinking of cutting 2" strips of Donacona (a absorbant particle board) and running them down every second stud and then screwing the gyp to every second stud, thereby making the effective spacing for the gyp 32" while still having the strength of the 16" centers to hold up the roof. Do you think that's a good idea?
Talking about the roof, it is 2x4s laid sideways on 1 foot centers. I am concerned about it holding the weight up. I could do the same thing there, but that ceiling is going to be pretty heavy and I don't know if it would hold the weight without it every foot. I am going to go 2 x 5/8 gyp on walls and ceiling.
On the rubber block point, you were saying take out the polystyrene foam altogether. It won't be hurting anything there, so why do you think I should remove it?

knightfly · Post by **knightfly** » Mon Oct 25, 2004 6:04 pm

Trying to get a few hours sack time, just a couple things; first, can you do a sketch or two and label things enough to illustrate some of the questions you have? I've been buried so long I really need others to do more of the "legwork" so I can save some time...

Second, the reason I suggested removing the poly is because it WILL hurt; with that in place, the REAL spring material can't do the same job, won't have as much compression, may be constrained horizontally (not good)

I'll try to get more time on this, but I've seen your posts on other sites and you will probably get more useful info from Paul and Eric over at studiotips on this; Eric is an actual acoustician (I'm not) and Paul has been obsessing about this one area for over a year now - I feel both of them are better qualified than I on this (and other) subjects. Not that I don't want to help, but I think you'll get more thorough answers from them at this time... Steve