Hi and welcome!! You will need to "box out" the ducts with a frame that is equal to the isolation your getting from the ceiling assembly. Essentially you "trace" around the ducts with your ceiling assembly, making sure to keep adequate clearance around them to avoid them physically touching. This can be done a few ways. If you detail your ceiling and wall construction I can probably be more specific. I highly recommend "Build it like the Pros" by Rod Gervias. Aside from a wonderful general reference, it covers maintaining isolation around beams and ducts specifically, and includes drawings.

Was there any final solution to this? I’m in a similar situation. Building a studio in the basement. 15ftW x 19ft L. I have the HVAC main supply and return branch for the entire basement and first floor running the length of my space. This branches off into one supply vent for the studio, one supply and one return for upstairs rooms. Three ducts in total. 
 

I’m unsure on how to deal with these in the ceiling. 
 

My plan for the rest of the ceiling is this. 
 

I have 80” of total height. From concrete floor to underside of open joists. I plan to fasten two layers of 5/8” drywall directly to underside of the subfloor. With all edges caulked with OSI Quad. Then, an R-19 insulated fiberglass air gap, then two additional layers of 5/8” drywall fainted to furring strips. Also caulked. Then, all sprayed black and treated with acoustic absorption foam. Based on the dimensions of my space. 
 

any tips on how to handle these three ducts would be greatly appreciated!!

 

thanks,

 

shotgunn

Hi,

If you don't have Rod Gervias book "home studio build it like the pros" then definitely grab, it since you'll need all the information in it to have a successful build.

For the ducts, you just "box them out", ie you build around them.

If the ducts are going to supply HVAC to the studio then you'll need special consideration for how they physically touch the studio walls/ceiling, and also consideration for mitigating the airborne noise traveling thru them. Your studio will be air tight, you need to have ventilation and fresh air in it.

Couple notes on the rest of your post.

You don't need special caulking, standard non-hardening silicone, butyl, or big stretch (brand), caulking is fine. It just needs to be non-hardening. "Acoustic" branded caulking is a waste of money and not superior to the standard stuff.

Don't forget to use backer rod in addition to caulking!!!!

Also, you cannot attach the studios inner ceiling drywall to standard furring. This will not add any isolation, and will dramatically reduce your isolation relative to an isolation clip/hat channel based ceiling.  Pac International makes "Risc-1" clips, there's also kinetics "isomax"clips, and whisper clips. 

These decoupling your inner drywall from the ceiling joists, giving you a "room in room" type system which is required for studio level isolation. Do not use Resilient channel since it's not effective for low frequencies.