Ceiling design, treating duct work above?

Are there any good references for construction below ducts in the ceiling (between a framed ceiling and the floor joists above) in terms of minimizing the transmission of noise from the room INTO the ducts?

I know that I've seen it mentioned here and there in dedicated threads, but was curious if there was a reference, or any "best practices" approach.

I think I've seen replacing flex ducting with rigid, and then wrapping that and building a MDF shell around it? Or is this really only a concern when running HVAC through soffits IN the room?

I hope my post makes sense. I'm probably going to have to cut my losses and deal with a 8' ceiling, and have to deal with the 1' loss in height due to dropped ducts. I appreciate everybody's comments in my other thread! It's been eye opening, that's for sure.

Hey, Big,
Thanks for your thoughts!

I was planning on double 5/8 drywall and Green Glue on an isolated framed ceiling OR clips and hat track. I just wasn't sure beyond that - in addition to filling open joists with insulation, if there was something else that was practical. I'm still not sold on the flex ducting that everybody uses, I still like the old school metal duct-work! I've seen some of the acoustical flex duct though - looks pretty substantial.

Thanks for the tips on ducts open to the theater. I feel like that's a can of worms in itself - but I think I have the basics. I think that I've seen a soffit that you built with a very nicely layered approach that I liked as well.

For the theater, I was planning on the largest ducts that I can fit in the joist bays, and using linear diffuser/slot vents to try to maximize the surface area of the vents. I know it's hard to do HVAC WELL unless you invest some planning in it. I've read some of Dennis' posts as well on the importance of it. I have a CEDIA spec that makes some really good general HVAC recommendations as well (pretty much standardizing what most people strive for in building on here anyway). I'll post a build thread when I get closer to it - so that I can get some feedback.