A few comments here: Standard fiberglass (R-19 in a ceiling and R-13 in a wall) will work as well as any specialized insulation. There is certainly no need to pay a premium for insulation unless you're looking to avoid fiberglass,...
The fiberboard materials really don't add / do much. They are too dense to adequately decouple, and are also too dense to provide much absorption.Mineral fiber will perform as well as standard fiberglass in a wall or ceiling cavity.Not...
There are a lot of good, prudent things that we know work, but no one has ever said why from a physics standpoint.
I just hope that long post made some sense. Thanks for allowing me to post that. So often we get caught up in fancy...
The separate ceiling is a method of decoupling. Like double stud walls or staggered walls. Resilient clips are also a means to decouple.
So for a ceiling you could assemble a floating ceiling with separate joists as Wayne pointed...
I would personally use a sheet or two of 5/8" drywall. MDF is denser, but drywall is so much easier to work with and cheaper.
You will not get the isolation regardless. You just can't layer in enough mass. But the mass will help.
The low frequencies is where it all either happens or it doesn't. The quiet rock is a bit expensive for what you get. Or what you could get with other techniques and materials.
