If you plan to have double layer of wall, is good to have air gap to really prevent sound from passing through. Never use aluminium type of frame, it will vibrate. There is almost no way to sound proof 100%. Is how much you can reduce

You have to build a room within a room.

For the walls inside the room, I did it similar to this:



Difference is that I'm not using R13 fiberglass, but rather Rockwool 38kg/m3.

What I learned is that I shouldn't have used double 5/8" gypsum wall because it made the walls too stiff, especially for a small room (18' x 13' ft) which created too much room gain for the low frequency response.

ALWAYS use wood framing btw, never aluminum. Low frequency will vibrate the hell out of aluminum frames.