when the outer leaf is a double leaf....

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when the outer leaf is a double leaf....

Postby princeplanet » Mon Oct 22, 2018 12:31 pm

OK, so I own an office I'm converting to a studio and I need to attenuate 110 dB rock drums so the neighbour through the party wall doesn't want to kill me. Making it inaudible can't happen, so I'll settle for doing the very best I can and try not to be too annoying too often...

First thing I need to do is to make the outer leaf nice and dense as well as air tight. It's currently a normal double leaf wall clad on either side with 13mm plaster. So I want to strip off the plaster on my side and "beef up" between the studs so I get a 50+ kg per m2 density. However, after I strip off some plaster, I immediately notice a problem (see attachment).
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How the heck do I beef up between these studs when they are metal studs (harder to fit stuff b/n than wood studs) ? Even worse, I'm stuck with all the wires that belong to the office wall on the other side. I was hoping to place 50mm compressed strawboard in between wooden studs, but now that is not an option. After considering some options I came up with these:

1/. I can try to fit compressed cement sheet behind the wires up against the back plaster, maybe 2 or 3 layers where I can. Power points and cables to my side can be ripped out, but cables to the other side must remain, and I suppose I could "box around" these power points t in order to keep a consistent density (and air tightness) throughout the wall. It's messy because the studs themselves then become weak spots and will need U shaped steel plate or MLV to wrap around the front of the studs to seal them against the compressed sheets. Then there is the problem of getting inside the steel studs with the filling material with screws from the other side obstructing. Do i take to the screws with bolt cutters (fortunately the plaster is also glued) so I can wedge in the filling layers?

2/. Second option might be to simply leave the wall intact, maybe blow in some cellulose through some holes to get the cavity resonance down, and just add 3 layers of something to the outside of this double leaf wall, hoping this cladding will be massive enough to mitigate the resonance problem caused by the cavity, particularly if the cavity is filled with something blown in.

3/. Third option is to have my inner leaf (the room that goes inside the outer room) built 1 metre away from the outer leaf wall, whether I change the outer wall to conditions #1 or #2 or even not at all. In the event I left the outer leaf "as is" in this instance, I'm interested to know how deleterious this double outer leaf would be with respect to low freq T/L. Isn't there some maxim that indicates that the triple leaf effect is minimal in the event that the 3rd leaf is far enough away from the other pair?

I'll include another diagram of the proposed build for a clearer picture of where this is all headed.

Screen Shot 2018-10-22 at 1.53.44 pm.png
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Please help! I'm finding it difficult to look up the answer to this one.....
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