After searching for answers on the internet, I figured it would be best to just post on this forum and ask the question.
I have a new 1.5 stroy house that I built on time constraints so I was not able to do all the cool soundproofing featuers I wanted. I have a room on the second floor that is designated to be the future home theater. It has no windows, and has three of its four walls facing empty attic space. All four walls are 4" walls insulated with blown cellulose. The door to the main house is a solid core interior door with gaskets (but no threshold). The walls facing into the attic are covered with Blue 3/4" XPS foamboard for extra insulation. I sealed all cracks and gaps with caulk for air-tightness. The cieling of this room and of the first floor has about 22" of insulation which is a combo of fiberglass and cellulose. The floor is carpet with an 8lb pad with a 1.5" toungue and groove plywood subfloor.
I would have loved to put in clips, two layers of sheetrock with green glue, etc, etc. However, to get in the house in time, we had to simplify and move on. Now I am looking for ways to upgrade this room without breaking the bank.
I have a crappy little all-in-one theater system in there now and mostly just play music for my kid to hop around too. Overall, the amount of sound that leaks from this room is reasonable. The insulation in the walls and solid door do a good job for starters.
I think that having 3 of the walls reverb into the attic helps since the attic has so much insulation in it.
So I am trying to figure out what to do next:
Maximum: Tear out trim and carpets and add another level of sheetrock with green glue all around. Under the carpet add another sheet of plywood (or soundproofing board) with green glue, then re-carpet. Add sill to door.
Minimum: upgrade just the one wall that faces the living areas of the house. Let the other three walls reverb into the insulated attic. Pull up carpet and drop some MLV underneath and lay it back down.
I have also considered adding layers to the attic side of the three walls. I called green glue to see if I could add a sheet of plywood over the XPS but they said it was not recommended.
Any thoughts on my approach in this particular case? I would like to start small and work up big, unless going small is not worth the effort.
Thanks for all your help.