Cork as an acoustical ceiling block

Haven't tried it, but must ask: what part of the frequency spectrum are you trying to block? Most likely the bass is primarily what's getting through to above right now, and a layer of cork isn't going to do much of anything about the bass. Neither is anything else you just stick to the ceiling. To affect this part of the spectrum, you have to go with a decoupled secondary "wall" (actually the ceiling). This means either some fairly deep self-supporting beams (probably 6-8" minimum, more if the ceiling span is large), or else the special flexible decoupling studs that are made for just this purpose (although I don't honestly know if they are designed to withstand ceiling use), plus drywall. If you want to save vertical space, you should probably tear out the existing drywall on the ceiling and install the decoupled beams parallel to and in between the existing floor joists so that they hang an inch or so below the bottom of the joists, then reinstall the drywall attached only to the new beams. A major project but it will be very effective and you will only lose an inch of ceiling height.

Much of the sound travels through the structure (i.e. the joists). What you would like to do is separate the joists from the ceiling with a small air gap decoupled from the joists (we have designs just for this) and have a high mass ceiling attached to it of varying layers. You will lose about 3 inches of ceiling height doing this, but it is very effective. Cork isn't high mass enough. It will reduce mid band and high frequencies, but won't have much effect on the energy the subwoofer is delivering.

Whatever you use, MAKE SURE THAT IT'S FIRE-RETARDANT (or is treated with a fire retardant spray)! As the tragedy in Warwick, R.I. showed, some accoustic material can ignite and burn like napalm, while also spewing a variety of toxic fumes (phosgene which is similar to "Mustard Gas" of W.W.1, and cyanide). Enjoy, but be safe!

Thanks fellas. You've given me some greatideas.