Triple leaf effect?

[alexbel]

Hi there,

we are trying to soundproof our basement ceiling from living room upstairs. This is what the builder came up with:
"The drywaller has recommended a layer of Donna Conna (a sound proofing board), then resilient board and then the layer of 5/8" drywall." They meant resilient channel, not resilient board. There will also be Safe ‘ n ‘ Sound batts to fill the cavities between floor joists.

Just wanted to ask if we could be creating a triple leaf effect? I don't understand it very well.

Thanks!

[gullfo]

the donnaconna board (ala celotex, homasote, etc) is not really very dense so 1) why use it? 2) is it strong enough? as a general approach - if your subfloor above is clear (or can be cleared) of nails etc, then apply 2x 16mm type-x drywall between joists to that to increase the mass. then use isolation clips and hat channel to suspend the ceiling (with something like Kinetics Noise spring units you can get very close to the joists) with 2x 16mm drywall + green glue or add a 3rd layer of drywall. fill the cavity with the safe-n-sound.

[alexbel]

Hi gullfo, thanks for the input. I think the option you described would be too expensive for us.
Our original configuration was just the safe n sound, resilient channel, and 5/8th drywall. The donnaconna was the only suggestion by the drywaller to improve the STC rating of the assembly. We had not found much good information about donnaconna and came across the triple leaf effect(which I think would happen if we used the donnaconna) which actually lowers the STC rating. I'm still not sure if the donnaconna layer would create a triple leaf effect, but I think even if doesn't, the benefit of it would be minimal.

[John Sayers]

What Gulfo said is correct. Double layer of 16mm fire-rated drywall/plaster. But it depends on what you want to do past that stage.
Make sure the space is totally sealed as sound is air pressure and you want to seal the sound in this sealed box.

Then you build your studio inside this box with no connection to the outer box except via the floor.
Float the wall frames on rubber to 1. isolate the inner frame from the floor, 2. seal the connection between frame and concrete/timber floor.

You then have two airtight rooms and the maximum sound isolation.

cheers
john