I am building out my home theater in my basement in addition to two other rooms.
My plan at this point is to take all precautions to "sound proof" the theater room to keep other noises from the house out and my enjoyment and volume levels in.
To achieve this I plan to use double 5/8" drywall on the walls and ceilings with green glue between layers and double wall construction with double drywall on both sides for walls common to other rooms. My ceiling will also be separate joists supported by the wall and mounted in between the existing joists. This will ensure my ceiling is not mechanically attached to the 1st floor floor.
My question revolves around 3 of the theater wall. Three of the walls are concrete foundation. The fourth wall is common to a kids playroom and the rest of the basement. This fourth wall will take all measure to keep sound in.
Do the other three walls need to have double drywall 5/8" thick, or could those just be 1/2" single layer drywall since behind the drywall is insulation, pink foam board, and concrete foundation?
Is there a sonic benefit to using double drywall on all walls for theater room performance?
It's obvious you done some research but I'm surprised you haven't learned about flanking paths. Yes all four walls need the treatment. And as I've read having all walls with the same impedance helps in room calibration. Not that I can tell the difference with my ears.
I was really hoping the 3 walls with single layer drywall and one wall with double drywall would not impact the potential calibration or sonic performance of the room as it would save some good money.
I am familiar with sound flanking and have it addressed in multiple ways. First, the concrete slab happens to have a control joint completely through the floor under the wall which divides the theater from the rest of the basement. The other three walls are concrete with no other common wall.
I am installed pink foam board on top of the concrete floor with 3/4" tongue and groove OSB on top of that. I plan to fully cut the OSB also under the dividing wall so there will be no horizontal trasmission path.
The exterior walls will also have a break in them at the wall junction so sound cannot be transmitted through them from room to room.
The ceiling is independent of the first floor and only supported by the walls in the theater room so there is no transmission through that to the first floor or adjoining rooms.
The theater walls are also not attached to the current basement ceiling joists and will be free standing from the floor.
For the supply ducts, I plan to bring those into a soffit and then using duct board or just plywood build a plenum with a convuluted path for about 8 feet prior to exiting the soffit through a vent.
The cold air return will be in the corner and I plan to build a box from duct board with a torturous airflow pathe internally to prevent transmission of sound out. Both plenums will be substantially oversized so the flow path has minimal effect on airflow rate.
I think I have my bases covered, but if you see any avenue I haven't addressed yet, let me know.
First "density" change means nothing in this context. Second, concrete is an excellent transmitter of sound albeit high mass. You will have serious flanking paths from the back side of the single sheet of drywall to the face of the concrete foundation wall. I second the advice to contact the Soundproofing Company. You'll be getting "sound" advice from honest people who actually know what they are talking about. Good luck on your project and have fun doing it!
Regardless of sound isolation it's worth knowing that a single sheet of drywall has a tendency to keep on making sound after the bass note that energized it has stopped. DD with GG is nice and damped. Result = better bass.
Also worth knowing is that DD on Isoclips works as a pretty good bass trap <60Hz.
Acoustic Frontiers: design and creation of high performance listening rooms, home theaters and project studios for discerning audio/video enthusiasts.