In my old listening room (a basement in a condo), I bought some rubberized sound deadening material. This is normally used to wrap around ducts to shield them from noise. I used it to insulate the shared joists where I thought sound might leak into adjacent units. I had some left over so I peeled my flimsy hollow door apart and put a sheet in inside. This provided a lot of isolation and damping.
soundproof a door
My listening room has a hollow body bi-fold door that I can't replace with a swing door. My door opens into the living room where my wife watches TV. She frequently complains that my music is too loud. What can I do to deaden that door without hanging drapes or some other lousy attempt? I'm stumped. Frankly, I'm surprised this isn't more of a problem for you all.