Anyway, a friend of mine had a fairly propper studio built by a contractor after he researched for many months on his own for sound proofing/isolation. I did all the electrical as I'm an electrical contractor.
From his existing garage, he had the contractor build four double-studded 2X6 walls in new parts within the existing garage walls and the studs were off-set. There is several inches inbetween the new and existing walls... A [i:6e07921698]room with a room[/i:6e07921698]. The existing ceiling was more than 10 feet so a new ceiling was built below that on top of the new stud walls. The walls were heavily insulated and he bought special sound-proofing sheet rock.
All electrical boxes for outlets, switches and ceiling light boxes had a special putty that was wrapped around behind and I also layered in inside back of the boxes with this putty before I installed the devices, which was sold to him by the sound proofing company who he bought that multi-layer sound proof sheet rock from. This made all electrical boxes air tight.
Before painting he caulked all joints, corners, etc with a special caulking bought from the same company above. This cost him mind you!
This is as I understand (not being an expert) more or less sound proofing.
The only bad thing in the end that took away from [i:6e07921698]complete[/i:6e07921698] sound proofing is that the counter would not allow him to cover up the existing garage window, so the contractor built an opening from his new inner studio walls to the existing window, which is well over one foot deep. He will eventually either install a secondary window, or most likely build a sealed sound deadning cover over this opening. We talked about possibly building a sliding type cover that can be latched and sealed tight to the wall when in place.
Another bad thing was his studio door entrance is just an ordinary solid wood prehung door which leads to the remaining 5 feet of space on the side of the existing garage making basically a hallway leading into the house from the previous existing garage. We talked about him placing sound absorption materials on the studio inside of the door and/or the possibility of installing a second door in front of that door for a double-door. However he did seal the door so it's air tight. The only thing is, I believe air inbetween any layers of anything is important for maximum isolation.
All in all we can play a Marshall Stack on 10 and beat the acoustic drums like a red-headed step child and it's very minimal sound coming inside the house
Oh and above the old garage/new studio is a spare bedroom (two-story home) that his wife uses as a sewing/TV hang out room for her very own [i:6e07921698]space[/i:6e07921698]... Any sound that seeps in from his studio below is also minimal.
This is his just personal home studio and he works mostly alone. He has a day job and this is only his passionate hobby 8) It only get's loud if he's playing his drums for fun or record as well as his electric guitar.... or if he has a jam session.
PS, he had a nnew garage built in front of his existing garage.
Oh, and here's a link to his web site if you're interested in checking out his studio-build details. It's very nice!
http://www.duncanjp.com/