second wall inside a room alway done wrong?

every time I see someone build a second wall inside a room they put sheetrock on both sides. After reading the facts it seems they would have better results if they uses 2 layers on the room side and left a larger air gap between. Am I missing something?

You are abslutely correct and everyone you see building three leaf assemblies on purpose is wrong.

sharward wrote:

You are abslutely correct and everyone you see building three leaf assemblies on purpose is wrong.

For music purposes it's better to have 2 leaf indeed. Since low frequentie isolation is wors on 3 (or more) leaf walls. Mid/high, however, benefits from such structures. So it kinda depends. But overall 2 leaf should be used (atleast for this forum's sake => building studios that is) By removing the plane(s) from the air-cavity and re attaching them on the outer side of the frame, the mass will be the same but the spring (air) will be bigger. (and it'll take a few inches of extra space but hell)

Don't recall seeing this in Rod's book so ... When building a 2 leaf double wall assembly is there a minimum effective air space depth or volume within the assembly? __________ lee

Bare minimum, assuming 2x4 framing (actually 1½" x 3½") would be about ½" between frames, which yields an air gap of 7½". That's because you measure the air gap from backside of drywall of wall A to backside of drywall of wall B. More gap is better, especially at low frequencies. My understanding is that there is somewhat of a diminishing return after about 12". That's not to say larger isn't better, but it becomes much more expensive square-footage-wise, and probably cost prohibitively so. In my project I'm running about 12" around my perimeter, with close to 8" in one area and about two feet in the area between the doors. Steve (Knightfly) has plans someday to build his dream facility on his property, which would have a 36" walkable air gap all around the perimeter of the building. Yeah. That's right. Be jealous. We all are! --Keith :mrgreen:

Thanks Keith. We're working on a major remodel and I get part of the basement to play with. Attaining adequate isolation in the ceiling assembly will be the challenging spot. There are a couple of I should have a SketchUp plan with appropriate descriptive content for posting later this week. In the meantime, here are a couple of "the studio goes here" pics. _________ lee

Does this three leaf assembly theory still apply if the inside wall is floating? What is the point of floating the walls (or the whole room for that matter), if it's not going to make a difference because it's still a three or four leaf assembly?

Does this three leaf assembly theory still apply if the inside wall is floating?

YES

What is the point of floating the walls (or the whole room for that matter), if it's not going to make a difference because it's still a three or four leaf assembly?

Not sure where you came from thinking wise with that question. (Don't worry I've spent days going off on simpler things then like OC measurement.) Point is, we avoid three or four leaf assemblies the best we can. The main part of our construction should be 2 leaf. Even just a... let's say a piece of paper floating inside air space of MAM (like paper vapor barrier on insulation) will make 3 leaf and hurt isolation. Any thing solid creating another air space, even if it's not tightly sealed will cause the 3 leaf iso loss. BUT sometimes we can not avoid 3 (or 4) leaf so we then beef as much as we can the Mass we are building to try and compensate. Even Sharward has a complete 3 leaf wall in his build, and he is (maybe overkill) compensating for it. There are many threads on this forum debating the 3 leaf thing and MAM as described/posted by the "more experienced, well read forum members" always wins. :wink: Marc

Oh OK, I think I have it now. So the "floating" walls or floor doesn't avoid the three leaf short comings, but helps to compensate as much as possible?

Ebony, welcome; can you please visit here http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3231 To start, we need you to update your profile to include what city you're in, or at least a state. See the link for more. It will also take you to a few other links that may explain things a bit better for you. If not, keep buggin' us :wink: and I'll cover the reasons for leaves, floating, resilient mounts, mass, etc, once more (or maybe remember the link I can't find ATM)... Steve