New Proposed Attic floor with plasterboard sandwich!

[R1R2]

Hello Newbie here ........Has any one tried laying a wooden subfloor , say 25mm exterior ply onto the new floor joists - then a plasterboard layer , and then the top machined t&g boarding- at 30mm thick.
I'm wanting to stop noise carrying through from the stereo etc , and general noise between floors.

 

[Static]

I wouldnt use plasterboard as a flooring layer, try looking for a soundproofing membrane or increase insulation between joists.

 

[Deluks]

That would increase your floor weight about 3 times, it's unlikely your floor was made with that load in mind, so could overload the floor joists.
You're on the right track though bt increasing the mass. Definitely lots of insulation between joists, and then 18mm ply all over (no gaps) plus the t&g, you might get away with.
Is the ceiling below directly attached to the same joists? If so then you will get structural sound transmission anyway if the stereo is particularly loud.