Hi there "cprescott1972", and Welcome!
Soundproofing is important but not super critical.
OK, but how much do you need? There are equations and tables and charts for figuring out how to build your walls, but they are all based on the number of decibels of isolation that you need. So you should first measure that.
Planning on building the wall at an angle to avoid reflective flutter etc.
That's not necessary. Flutter echo can be dealt with in several ways, with the treatment that you will need anyway, plus angling the wall wastes space. You only need angled walls if you are doing something like an RFZ design concept.
My initial question is whether it's worth tearing out the interior drywall to replace the R-13 standard pink insulation with something heavier like rock wool,
Why do you think you'll need heavier insulation? It's not the weight or the density as such that matters, but rather the density according to the type of insulation, and the type of application. Mineral wool insulation needs one density, and fiberglass needs another. Ceiling clouds need one density, and bass traps need another. Etc. It depends on what you want to do, and also on your budget, the available space, your building skills, etc.
Pretty sure it's currently standard 1/2" sheet rock over the insulation and exterior stucco. Looking into the first steps in the new construction.
Depending on how much isolation you need, you will very likely need to remove that drywall, regardless of what you decide to do with the insulation. 1/2" drywall on the same studs as the outer leaf is not going to give you any useful isolation. So you'll probably need to take that off, and build new framing all around the room, an inch or so away from the existing walls, as your inner leaf, then put a couple of layers of 5/8" drywall on only one side of that new framing.
The door opens inward so doing a double door wouldn't work without some obvious and strange exterior second door framing. Anyone else dealt with this issue?
Exactly as you say, and as I mentioned above: you will need to build another frame inside the existing shell, and that frame will carry your second door. The easiest solution to the inward-opening problem of the existing door, is simply to reverse the sense of that door so it opnes outwards.
- Stuart -
