In our last house we did double drywall on the ceiling - and I think we did one layer of normal drywall and one layer of soundboard. We also used some pretty dense bluejean insulation. It worked really, really well. Someone could be blasting a movie downstairs, with explosions and everything, and the sound would be coming up through the stairwell, but not through the floor. I'm a big fan of layering different types of materials (ie., normal drywall and soundboard), so that when one material starts resonating, the other material will dampen it because they have different resonant frequencies. When I build speakers, I layer mdf and plywood together with flexible glue to do the same thing.
Last edited by brew; 10-16-2012 at 02:54 PM.