Double leaf insulation

Hi, I am currently constructing my studio and i am looking for a bit of advice. My live room is 18' * 14' , i am building a stud wall 4" inside the brick wall(also 4" thick). The stud wall is being made with 4' * 2' which is completly decopled from the walls and sitting on a floating floor. My question is A- Should I put plaster board on both sides of the partition wall or just on the room side? B - What density of rockwool should I use? C - Should I fill the 4" air gap with mineral wool or leave it empty? Thanks for your time Peter

Just the room side, otherwise you have 3-leaf wall which will pass bass MORE - use anywhere from 2 to 3 PCF (32 to 48 kG/m^3), and make sure the batts are slightly oversize; fit them into stud cavities so they press against the plasterboard for damping. Filling the rest of the wall cavity can add a couple dB of isolation, but if you have ANY moisture problems it's usually better to leave that space open... Steve