John Sayers' Recording Studio Design Forum

I'm a construction contractor in new york city who specializes in soundproofing. so in this topic you could say that i am discussing some of the "anomalies" of the "room " within a "room" design. I have dozens of recording studio builds under my belt that are this design, and i admit some of my earlier builds have triple leafs and the isolation is still good, well good enough to keep the studios running without any noise complaints. So the obvious reason why double leaf is more money is when you are building a sound isolation "room" within your existing "room" one would have to DEMO the existing walls(the third leaf). So this cost money and in most cases the landlords in nyc will make you take the new room apart before you move out. In new york studios and people move a lot, at least the low budget builds do like most of the discussions in this forum are about. For me this is a typical situation, to avoid the demo process (if and when i have to) (the cheapest thing to do is to just add lots of absorption to existing walls) I fill the cavity with blow in cellulose insulation and add another layer of drywall with greenglue to existing walls. it's expensive but very effective if you don't have the option of demo. BUT (of course) not as effective as demoing the walls to get the double leaf and hand filling both cavities with 3 inch thick thermafiber rockwool insulation. If you are going to demo existing walls it would be only if your design is a room within a room or if you plan on using furring channel with resilient channels. If you don't use those designs then find a local contractor who specializes in BLOW CELLULOSE who wouldn't have to demo the existing walls to fill them up. typically it should only cost around $3 sqft for the blown cellulose and keep in mind that the blown cellulose is adding around 3-4 lbs per sqft to your wall and is the highest rated insulation on the market.

Please feel free to add comments to this.ideas, new technology, ect... thank you for your time.

perhaps your statements might be more credible if you pointed us to the studios you have completed.
Otherwise I'm inclined to consider this spamming for cellulose insulation.

spamming for cellulose was not the intention nor did i display any number or business name that would gain me business. this is a forum and i will respect it so. If you think i crossed the line then do what you got to do. The triple leaf effect is an issue that I thought needed to be discussed further. So to break the question down further creating a room within the existing room works better when you demo existing walls, floors and ceiling. But if you don't have the option to demo you create a triple leaf effect with most standard room designs like resilient channel and room withing room. There isn't much left to do but to build onto the existing wall and treat the inside of the existing wall cavity with blown cellulose. so would you suggest demolishing all the existing walls to start your pro-isolation room as the #1 way to go? what would you could only add more layers to existing walls? sorry if this question has been answered already. and thank you for your time.

If it really is a "pro" room, which is what you postulate in your hypothetical situation, then yes, that's exactly what I'd suggest! And even if it is just an average home studio, I'd still suggest that course of action, if low frequency isolation is important (and when is it NOT important?!).

In any event, you do not need to demolish the entire wall: careful removal of the sheet rock from the side of the wall that will face the cavity, is all that is required. Said "carefully-removed-sheetrock" can then be used to beef up the other side of that wall, from within, between the studs. Then you can proceed to build the inner leaf, on its own studs. And if you ever DO need to demolish your entire studio (a major and rather expensive undertaking in any case) due to moving to a new location, then all you need to do is put new sheetrock back on those original studs right where the original sheetrock was, then tape, mud and paint. Presto! Right back the way it was. Not a huge expense, and not even very complicated, compared with demolishing the rest of the studio first.

So I don't even see what the problem is!

On the other hand, if you blow in cellulose and then have to demolish the studio later, you are now stuck with an even bigger problem: getting all that cellulose out, disposing if it, cleaning up the original sheetrock, and re-painting it anyway. If I have to choose between cleaning up all that cellulose, and hammering up a couple of sheets of sheetrock, I think I'll take the hammer-and-sheetrock solution any day!

If you absolutely cannot touch the existing walls due to some warped rental contract, then you have no choice but to build a three leaf wall, in which case you would compensate for the reduced low frequency isolation by leaving a much wider air gap, and making the third layer far more massive than you would have otherwise. You'd do the math and see how much wider you'd need to make the gap, and how many extra layers of sheetrock you need to get the necessary mass, in order to drive down the resonant frequency of the MSMSM wall to the same point where it would have been with a simple MSM wall, and attain the same isolation.

That's what I'd do. Others might have a different opinion.


- Stuart -

Stuart,

I think you say a lot of similar things than Andy. You just pick out one sentence.
Andy states that a double leaf is more efficient than a triple leaf.
He states if a double leaf isn't possible, that you just maximize the isolation of the existing double leaf system (additional panels and Green Glue + absorption).
Since you can't add other absorption than blow-in absorption (in existing wall without demounting), he refers rather explicit to cellulose. Andy probably has no experience with other blow-in absorption (insulation). He does however assigns it some superior properties which are not substantiated and likely of less importance compared to whatever other good absorption in the cavity (whether blow-in or not).

From a practical approach it seems that the OP gives a good summary, but probably overestimates the double leaf properties he suggests (and blow-in is only possible when the cavity was still empty, but any absorption versus empty will have a significant impact).
In function of MSM however, a 1-sided improvement (see picture) by tripling a 1/2 inch gypsum board (77.3 Hz) gives him +/- the same MSM as 1/2", 4" cavity, 3/2", 8" cavity, 1/2" (79.4 Hz) and significant lower, if rather than the center leaf, the third leaf is made heavier: as 1/2", 4" cavity, 1/2", 8" cavity, 3/2" (101.6 Hz)

You state that you still need a third wall, when you're not allowed to demount the inner side of the existing wall, with a large cavity and more mass on the inner enclosure (third leaf).
You suggest: Do the math. That's easier written than done isn't it? (The above and picture is theoretical, are rather complex quadratic equations, and triple leaf systems can behave rather strange, often not bothering too much about simple theories)



If you know the math you should know that it's indeed still best to do what the OP suggests by improving (adding mass) that (future inner) wall of the existing double leaf system, rather than adding more mass to that 3rd leaf of the inner enclosure (better is both, but the inner leaf of the existing wall is significant more efficient in function of MSM).

Thanks for the chart and sorry for asking questions when the answers are already there in the math. I just though if there is any more besides the math to be said on this subject you guys would be the ones to ask. which leads me to my last question on this topic.

Instead of demolishing sometimes antique plaster and ornate trim molding, "I drill some holes" in the existing walls to relieve the spring sound pressure created by the triple leaf?

Don't be sorry for whatever, certainly not for asking questions.
You should be more careful however in making explicit statements about specific products, unless you can substantiate them.

It is indeed possible to shortcut the air volume by making one-sided holes in the existing wall. That's a matter of investigating how much (law of inertia), which % free opening, en how large the closed parts should maximum be. And preventing to cause an additional, not meant Helmholtz effect.
I even think that with a bit of fantasy you can make this as such that the structural stability of the existing wall is preserved.

If I should make a NON-calculated rough guess (hence don't take this as an axiom) I gues that between 15 and 25 % could do the job.
If you hope to do this with a couple of holes on top and bottom, forget it. It wil just act as if you increased the cavity of the existing wall a bit, by weakening the airspring.

thanks everyone for your response to my "kinda" "hypothetical" but "common" issue i've run across with soundproofing in NYC. I'm using this forum to clarify the importance of demolishing the hard pre-existing drywall or plaster surface if you plan on doing a professional sound isolation room using "standard designs". I will take everyone's advice as "advanced credible evidence" for confused people who don't understand what needs to be done to achieve their goal. Thank you for you time and have a great day.

Does anyone have data that shows a triple leaf makes the LF worse?

Yep:





And if you want the theory behind it, with abundant examples and numerous real laboratory tests, then the best I can recommend is the 1973 Wyle report:

http://www.box.net/shared/jcaoavdc8g

It might be old, but it is still very, very valid. And very interesting reading.


- Stuart -

Thanks a great deal for taking the time to digs those up.

Let me re-phrase. Has anyone seen data where an existing double leaf was made triple and LF was worse than before?

Yep, but I don't remember where. It was either on Gearslutz or Studiotips, where someone who was in the process of building their studio reported accidentally creating a third leaf when they placed a sheet of plywood or drywall close to the outside of a finished two-leaf wall while loud music was playing on the other side, and discovered that reality is exactly as theory predicts. I'll see if I can find that, but I seem to recall a figure of at least a 6 dB drop in isolation being quoted.

- Stuart -

Just for accuracy, here is the place where I got that second graph from. It's a thread on Studiotips by Brian Dayton, and another one by Eric Desart which does a great job of analyzing the factors involved in 2-vs-3 leaf.

http://forum.studiotips.com/viewtopic.php?t=2142

http://forum.studiotips.com/viewtopic.php?t=2144


( The first graph came from the Wyle report. )

And thanks once again! We all have heard the ills of triple leaves and the advantage of double. No question on the data. I don't believe inserting a third leaf makes LF worse than before

You might also find this page (from Bob Golds) interesting:

http://www.bobgolds.com/WallCharts/Quad ... eafSTC.htm

And this one, from Green Glue:

http://www.greengluecompany.com/underst ... leLeaf.php


Just a few of the interesting links I have filed away on 3-leaf vs. 2-leaf! But I still can't find the one I'm looking for!


- Stuart -