Hey Jack,
Here's a link to some pics of the studio I recently constructed in my home:
http://www.vsplanet.com/ubbthreads/ubbthreads.php?ubb=showflat&Main=44097&Number=408842#Post408842 Bottom line - took a long, long time to build and there were a myriad of issues that I encountered, some as a result of ignorance, some due to poor planning and others just 'cause that's what happens when you do this kind of thing. In the end, I learned a lot about sound (pressure, dampening, materials, etc) and will certainly be better equiped the next time around (which hopefully is not too soon). The heavy/limp-mass rule is definitely one to follow, as is the variance in air pressures between walls as sound travels best when it is subject to only one pressure level. As such, the more air-tight the better but you might want to consider A/C options as it gets hot and stuffy rather quickly in an air-tight room, and even moreso in an airtight vocal booth.
I did the room inside a room concept with a floating floor, basically. First thing I did was cut the concrete slab all along the perimeter of the room (not something your wife would likely approve of as the concrete dust is brutal). I then vapour-barriered the floor to deal with moisture issues. Next laid a cheap carpet over the concrete slab and installed Dri-core sub-floor over that. Laminate flooring over a thick underpad was the final floor covering but I did add extra padding under the drum kit.
I filled the exisiting room walls with soundblock insulation, vapour barrier, a layer of 5/8" gyproc, resilient channel strips over that and another 5/8" layer of gyproc. Left about a 3 to 4 inch gap between the existing walls and then did the staggered stud wall application with 2x6 plates and 2x4 stringers in the room inside the room walls and ceiling. All plates and stringers were fastened with 4" screws and every joint was connected with sill gasket foam in between. 3 more layers of 5/8" gyproc, soundblock insulation, vapour barrier and resilient channel on the inside room walls and used PL400 adhesive on the outside of the wall between the gyproc and studs. All plugs, switches and outlets were installed with sealed plastic boxes and the vapour barrier and any conceivable cracks were applied and filled with acoustic calking. As I mentioned previously, a sound wave has a difficult time maintaining it's amplitude when travelling through 2 or more air spaces with varying degrees of pressure. As such, making things air-tight is a big priority.
I used a knock-down stucco finish on the last drywall layer which offers meager sound diffusion in and of itself (Home Depot). It has a 3-door entrance system to gain access to the room with rubber gasket as a door seal. Some of the biggest issues I had to deal with were an outside window and the existing HVAC system as you have touched on in your post (which is basically a 2-way noise conduit). Air conditioning mini-split systems at first appear ideal for studios as all of the noisy stuff is installed outdoors and the actual cooling element is on the inside. However they don't bring in any fresh air and are a bit on the pricey side.
Incidentally, I have no heater in the studio. It's so well insulated that during times when the door is open, the warm air remains long enough to keep things comfortable. It's also a great bomb shelter. Try to anticipate as much of your wiring needs ahead of time as possible and consider putting in a few 'forget-me-nots' (pvc pipe from the control station to the booth within the walls just in case you miss something). Lots more things to consider but I'm on my way out to vote right now (picking a new Prime Monster today here in the GWN).
Anyway, good luck with your new studio. I'm sure you'll get lots of other suggestions and advice. Feel free to PM me if you have any specific questions about what I've tried to describe above.
Cheers,
7thSAM
post edited by The_7th_Samurai - 2008/10/14 19:01:52