I am in the process right now of finishing my basement. The reason for doing the following is to keep the music from traveling through the floors and ductwork. Also would hope it has some acoustical benefits in the listening area.
I don't have an issue with walls because I used styrofoam building blocks as the frame for the poured concrete. I am taking a lot of time though with insulating the ceiling and around the duct work. After building a frame around duct work I put in 3-6 inches of insulation, depending upon the area available. I am then going to place 6 inches of insulation between the floor joists, being sure to overlap it with the insulation going up the sides of the duct work. The insulation will be flush with the bottom of the joists.
Before the drywall goes up the duct work and ceiling will be cover with soundboard (fiberboard). This should be a better solution than 2 layers of drywall. Also feel that the soundboard with isolate the drywall from the joists to possibly reduce resonance.
This may not be the best thing to do, but I felt it was a reasonable thing to try. Doing the work myself so I don't have to listen to a builder saying I'm crazy. Well, maybe I am, have to wait and see.
Jeff: Drywall standard construction turns out to be excellent. If the room dimensions are right then you can do a 2 or 3 layer buildup. If not, you are actually going to want to lose some bass energy, so stick to single layer in that case. As to the "egg crate" foam. Most of that is very low density and not as good as the higher density Sonex, or even better is Owens Corning 703 fiber board wrapped in fabric.
You might want to get a book on Acoustics--Alton Everest Master Handbook of Acoustics is a good start. Our website and in particular, the listening room may prove to be helpful. The simulator there is also pretty fun when modelling a room.
I just finished the drywall in my basement, and after consulting with several "experts", I did the following:
1-Had someone that was qualfied look at my floor plan to evaluate resonance points and head off bad room layout before it was set in stone.
2-Ran truly dedicated power for my stereo from panel.
3-Densly packed my floor joists/ceiling with fiberglass insulation.
4-Wrapped all water pipes in 1/8" neoprene rubber to kill any sounds of running water.
5-Lightly insulated walls with backed fiberglass insulation to kill any resonance inside walls
The only thing I wish I had done so far but didn't is install metal strips available at Hm Depot to decouple dry wall from the floor joists above. All told, I spent about $500 on insulation, $60 on rubber, $20 on electrical, and every ounce of patience I had on my "experts".
Packed fiberglass insulation or neoprene should quiet noisy ducts depending on the amount of space you have around them (Fiberglass takes 2-3 inches, neoprene <1").