It has been a long haul trying to get the studio finished. Demolition started in January 2008, but due to Chris' health, things did not progress as fast as we'd liked. Our plan has also moved from a large tracking room with an addition off the back for the control room, to adding the control room with in the existing tracking room, and finally, to a single tracking/control space that can be adjusted to needs. The first thing was to isolate the room from the outside environment. That meant using the room within a room concept and isolating the new room walls.
There was lots of backer rod and silicone caulk used.
Notice the putty pad covering the electrical box in the photo on the right. All boxes were covered with Firestop Putty Pads. The real test as to how well these things isolate came while staining some house trim in this room. One wall is shared with a bedroom which has three outlet boxes. I could actually see light from behind the boxes when the drywall was removed on the studio side. The Putty Pads on the outlet boxes in that room sealed so well, none of the fumes from the stain were detected in the bedroom at all.
If the fumes couldn't get through, sound shouldn't either.
These things are definitely worth the cost.