Wall Spacing

Hey guys just wondering what is a decent gap space between the outer and inner leaf frames to achieve isolation. I was thinking about going with 4-5 inches, or should I increase this if I can? Thanks, Ian viewtopic.php?f=1&t=11508&start=30

It's the distance between the inside surface of the outer leaf, and the outside surface of the inner leaf that counts, not so much the distance between frames (although obviously, the two are related!) With air gaps, bigger is better. Less than 4" between the leaves is not really recommended, 8" is great, even more if you can spare the space. Somewhere I have a document with graphs of isolation vs. air gap, but I can't seem to find it right now! - Stuart -

Thanks Stuart, I'm about ready to tape out the walls on the floor, im using double stud walls as you suggested but do to the outer shape of the control room area (outer leafs) my inner leafs will differ in space while keeping symmetry. Could this be an issue? For instance my inner leaf wall facing the live room will be spaced 5" from the outer, another wall will be 6" apart from its outer leaf - while its adjacent (but non parallel) will be spaced 4."

Probably Ro or Andre or another real expert can comment on that with authority, but to my way of thinking, it isn't an issue. It just means that some walls will have better isolation than others. And of course, you can splay your walls, too (angle them) so that the gap varies: That is actually a good thing, I think, since it would reduce flutter inside the wall itself. If you do splay them, then the smallest gap is the weakest point, and it only gets better from there. So keep your smallest gap to at least 4", and it should be fine.

If that's the only option, than it's not an issue. 1 inch more or less doesn't make a world of difference. A 1" gap will work too, but bigger is better (hmmm...never mind) As long as the walls are trully separated you're already in the save zone. :blah:

Hello, Forgive me if this is a hijack, but this thread is very close to an answer I was looking for: what I'm gathering is that I build a two-leaf room, and if I splay the walls then the gaps between walls will not be constant - and that's OK, right? Preferrable even? - Josh

Doesn't matter as long as your shortest gap is big enough to consider a gap (huh? ofcourse!) Bigger gap is better isolation, so yeah it's a relative good thing

That's good to know, because as it stands I'll have from 1" to 12" in between the insides of the leaves of the two walls, varying based on the geometry if the inside walls of course. There's been an argument around here about this subject. My partner wants to add a layer of soundboard to the inside of the outer leaf because he's paranoid about this double wall thing not working when the air space gets up to a foot at some points. Completely understandable, you only want to have to do the work once, right? But I have Rod's book which explains the double wall system and why it works, and I've done a lot of searching here and on other forums and I keep coming up with the advice that "the more air space, the better". I do plan on putting some insulation inside the walls for dampening.

My partner wants to add a layer of soundboard to the inside of the outer leaf because he's paranoid about this double wall thing not working when the air space gets up to a foot at some points.

And why does your partner think that "sound board" would make any difference in any case? On what principle of physics does he base his hunch that sound board works better over a larger air gap than drywall? Besides, your partner seems to have it backwards: an MSM wall doesn't work well when the gap is too SMALL, and works BETTER when the gap is large. Your 1 inch minimum gap is going to be your week point, not your 12 inch gap! If you can, you should increase that 1 inch gap to at lest 3 or 4 inches. the improvement you will get is well worth it. You might want to get him to look at the graph below, which comes from a detailed paper published by the BBC acoustic research department, several years ago. Basically, if you want more isolation, then use a larger air gap. More is better, always. And that statement is based on real world physics and laboratory tests, not on "paranoid hunches"! :)

... and I keep coming up with the advice that "the more air space, the better".

Yup! That's because you keep coming up with advice based on science, not "feelings". :)

I do plan on putting some insulation inside the walls for dampening.

Once again, "YUP"! You certainly do want to do that! It should gain you around 10 dB of isolation. I'm attaching a second graph from a real paper about real acoustics, that shows what a difference insulation makes on total isolation. Quote from yet another research paper: "Adding a sound absorptive material inside the cavity of a single stud partition (wood with resilient furrings or steel) or a staggered wood stud partition increases the STC rating by 5 to 9 points depending on the type of sound absorptive material used. For double stud partitions, an increase of 10 to 13 points was obtained depending on the amount of glass fiber insulation added to the cavity." - Stuart -

For some reason, my partner thinks Celotex is a miraculous cure-all sound blocker. He totally got sold on it by someone, and that's fine. He's doing the best he can with what he's got, just like I am! It just means I have to try harder to get my point across. I'm not expert either, but I do spend a lot of time researching this stuff and trying to get solid data rather than taking what I want at my convenience and "winging" the rest. Thanks to the wealth of resources and advice available I can actually begin to understand the logic behind how the construction principles work... and it all really seems illogical on the surface! Anyhow, the graphs are great! The second one especially, but does it mention density of the fiberglass? I plan on using rockwool against the inside wall, and regular batt insulation to fill in the cavity (without connecting the walls together of course). Would this be overkill at all?

For some reason, my partner thinks Celotex is a miraculous cure-all sound blocker. He totally got sold on it by someone, and that's fine. He's doing the best he can with what he's got, just like I am! It just means I have to try harder to get my point across. I'm not expert either, but I do spend a lot of time researching this stuff and trying to get solid data rather than taking what I want at my convenience and "winging" the rest. Thanks to the wealth of resources and advice available I can actually begin to understand the logic behind how the construction principles work... and it all really seems illogical on the surface! Anyhow, the graphs are great! The second one especially, but does it mention density of the fiberglass? I plan on using rockwool against the inside wall, and regular batt insulation to fill in the cavity (without connecting the walls together of course). Would this be overkill at all?

Here is part of the reason your friend thinks it is so wonderful, soundstop celotex that is: http://www.soundstop.net/demo/Default.aspx Also, I inquired about this very thing from Jeff Cooper earlier this year. His reply was that of one still in support of this method. "We still find it very effective to use sound deadening board as an interstitial material between layers of drywall" /end This idea has been around for a long time, and professionals still employ this in their design. There is a difference in the detail that may go into a full blown structure specifically for audio and the builds that we are involved in. So mass is what we lean on lacking the history and confidence to explore other options.

I've seen that before... and I can understand why we've used it in our wall layering. I'm beginning to really understand that all of these materials work together, not as inherently wonderful sound isolaters but to create an effective system. That being said, I don't agree that if we ever need any kind of foxhole soundproofing to just "throw a piece of Celotex on it to knock the sound down", which in this case would create a third leaf. I don't know if it would hurt so much being one layer of Celotex, which is pretty light stuff, but I certainly don't think it would help enough to risk finding out.

If I understand the function of celotex as it applies to this instance, it is particle damping, which is not a mistake or an error. http://www.roush.com/LinkClick.aspx?fil ... 12&mid=920 Greenglue is aimed at this very area. I looked over your posts and I do not see the three leaf you refer to. Sheetrock, celotex and another sheetrock, is not a three leaf. It is just different layers of the same leaf. I'm not pushing one or the other understand. I'm saying that there are things going on and just because we may not know of it, or cannot wrap our collective head around it and accept it for what it is, does not mean that it is an incorrect method. Only that we do not understand it as of yet.

Hey, no problem! I appreciate the input - I'm pretty sure that w're on the same page, I'm just talking about a different set of circumstances. I haven't gotten into it because A) I don't have a graphic image of our design, and it's tough to explain and B) I should start another thread if I were to do so! But the short of it is that we built two rooms attached to each other, one is a single wall, staggered stud, the other is the double wall config. The issue pertaining to this thread is that my partner was concerned that the amount of air space between the sheeting on the outside of the staggered stud wall (on 2x6) to the inside wall would come to almost a foot in some places based on the geometry of the room, and he wanted to put a layer of Celotex on the inside face of the staggered stud wall. My thought was that this would be a third leaf... instead we should leave the air space and use insulation to dampen. Of course, you may have completely understood this, and you're saying that the sheet of Celotex would act as a dampener rather than a solid leaf... is this true? If so, sorry for launching into detail! And I definitely appreciate your philosophy - my experience is limited, and I don't know all of what's available nor the options I have at hand. Good stuff! -Josh

If I understand the function of celotex as it applies to this instance, it is particle damping, which is not a mistake or an error. http://www.roush.com/LinkClick.aspx?fil ... 12&mid=920 Greenglue is aimed at this very area.

Ummmm..... So you are saying that Celotex soundbord is actually a viscoelastic damping material, just like Green Glue, and works in the exact same way? So, how come Celotex does not make that claim for their product? I can't see palce place where they claim that it is a viscoelastic polymer. Or are you saying that Green Glue is actually a particle damper? How come Green Glue company does not make that claim for their product? I'm looking at their technical data, and not finding any claim that it is a particle damper.... I'm having a hard time figuring our what you were trying to say here, since neither manufacturer makes any such claims about their products, and viscoelastic damping is not the same as particle damping anyway.... And why did you talk about particle damping, then link to paper about viscoelastic damping? I'm also having a hard time figuring out how anything you said there is applicable to the original question of how Celotex soundboard would prevent the isolation characteristics of an MSM wall getting worse if the air gap is wider than 12 inches. That was the original claim: That if you have an air gap of greater than 12 inches in an MSM wall, then adding a layer of Celotex will prevent the isolation from getting worse due to the large gap. It's REALLY hard to see how soundboard would stop that from happening, since it was not going to happen anyway, and in fact the exact opposite is true! An MSM wall gets BETTER isolation with large gaps, not worse. Nobody questioned whether soundboard is a useful treatment or not, so I can't see why you are defending it so vehemently: The issue was not whether soundboard works as advertised, nor whether anyone recommends it, but rather whether it works to prevent a "problem" that doesn't even exist! :) - Stuart -

rockstar_josh wrote:

Of course, you may have completely understood this, and you're saying that the sheet of Celotex would act as a dampener rather than a solid leaf... is this true? If so, sorry for launching into detail! And I definitely appreciate your philosophy - my experience is limited, and I don't know all of what's available nor the options I have at hand. Good stuff! -Josh

You guys, or one of you, are concerned for having too large an airspace, and you shouldn't be concerned. You mention there has been an argument on airspace on this site. Most agree that larger is better, materials depending and up to a certain distance. What I am saying is that you still have a lot of reading to do before both you and your friend can build with some assurance that what you are doing is the correct thing. It was unclear how your walls are being loaded and the confusion you guys had then add the whole hijack thing.

pardon me for buttin' in... but I think that a quick bit of ASCII physics :roll: may clear this up... 1) 1St Room Space 2) Gypsum #1 3) 2x6 Stud Frame 4) VaRiAbLe Air gap 5) Staggard Stud Frame 6) Gypsum #2 7) 2nd Room Space If I've read this correctly, this is what I understand your construction looks like.... And, your partner wants to put celotex between either 4) and 5) or in the stud bays at the 5) and 6) points. If he is thinking that the 4/5 is the right position, he will indeed be creating a rather limp, but effective triple leaf assembly. If he's thinking the 5/6 junction, then yeeah... I spose' celotex would be OK... but I'm willing to bet that you can add gypsum far cheaper than celotex... and additionally... again, if I'm right in the construction... you can loose the studs on the 4) side of the staggard stud wall... as they aren't doing you any good. If I'm mis-reading what you've described, just ignore my post...

Yeah, you're 95% there. Only one staggered stud wall, because I'm attaching to a room that was built that way. Thanks for trying! I'm outta here, because I didn't mean to hijack a thread but it has happened.