You can build a very well isolated room at a reasonable cost if you follow the following basic, tried and true methodology.
I agree, although there's probably room for debate about "reasonable cost"....
Resilient Channel (RC-1) ... Id be concerned about using it.
Used it for the walls (but not the ceiling) and was quite happy with the results, although it's hard to work with. None of the edges can be in hard contact with the floor/ceiling, so you need some kind of gasket and/or caulking all around.
Know that there is no data that supports that any other insulation (including the acoustic labeled, and recycled cotton) works better.
Really? That's a pretty strong claim... It's been a while, but I seem to remember some very real data on that.
Also, foam (open or closed cell) is superior for thermal, but distinctly worse for acoustic.
That's for sure! We have closed cell foam insulation in our current house and it is just about worthless for absorbing sound. "Transparency" might be great for some things, but not walls - especially when the neighbor's dogs get going at four in the morning.
#3 Add mass. Nothing better than standard 5/8 TypeX. Great mass at 70+ pounds a board, and cheap at $7 a sheet. Use two layers. Only mud and tape the final layer.
What we did for the innermost surface, which worked VERY well, was a layer of 5/8" and a layer of 1/2", with a layer of roll roofing material sandwiched between them (and this was hung on RC-1, on a separate frame). I don't remember the exact details, but using two layers of the same thickness is similar to having a square room - certain frequencies will be much less affected than by two different thicknesses. Also, any transition between two layers of significantly different material (hence drywall/roll-roof/drywall) creates a "shearing" effect (similar to light bending when you look at something underwater) which drains off some of the sound energy. That's part of the reason modern armor uses laminates instead of mass. Not 100% I'm remembering all the physics right, but as I said it worked very well for me.
#4 Consider damping these drywall panels with one of several field-applied damping compounds. Some work better than others, and independent lab data shows you get what you pay for here.
Too much "damping" is not necessarily a great idea. It might help with soundproofing, but it can suck the life out of whatever you're doing in the room. We had a very "damped" (bordering on anechoic) control room which allowed for very precise monitoring and mixing, but it wasn't a "pleasant listening environment". The outermost section of wall in the main tracking room was the layers described above, which gave it (combined with some careful dimensions) a very nice acoustic warmth. You want the room to sound good when you're in it!
After that, youd turn your attention to the ventilation, lights and doors. All of these are flanking paths for sound to get out of the formidable room you just built. They can be dealt with fairly easily, but youll want to design this in.
Yeah, that's something you really need to plan from the start, although I'm not sure about "easily". It took me almost a year (spare time) just to get through the R&D before I started building. Also, if you're doing multiple rooms, you'll want to have some ways to get signal (line, mic, speaker....) between rooms.
Anyhow, again IMHO this can be done, but not for a couple grand and a few weekends. I could be wrong, but unless someone has specific experience with building a similar room and can provide the room dimensions, the amount of time required, the total material cost, and some decent before/after SPL numbers, I'm disinclined to believe otherwise.
OTOH, one factor to consider is just how much you need to reduce the noise level. Probably the first thing you need to do is buy or borrow an SPL meter and find out how loud it gets when you're playing, both inside the room and outside (bedroom, nursery, ...), focusing on low frequency stuff (the hardest to control). Then start turning down things down until the volume outside the room is acceptable, and measure again. That will give you an idea of how much noise reduction you need.
One other possible idea is to set up a tactile transducer (like
http://www.thebuttkicker.com/) for practicing. In theory, you'd be able to "feel" the low frequency while reducing your low-freq SPL. If that works for you (and your drummer?), it might make it much easier to get "enough" soundproofing without spending way more than a few K$. Although I haven't tried it yet for bass, I have used these in my home theater setup and it worked very well (even with the sub turned down).
