B
bpape
Acoustic Designer - GIK
Do not do a double ceiling if both are hard surfaces. That can actually increase the issues with isolation.
If you want to spend some time (and money), build the 'real' ceiling at the dimension you've decided on. Then below that, build an angled ceiling (low in front, high in back with at least 1" per foot of taper - more is better) but have the visible ceiling be alternating 4" and 6" slats, 3/4" thick with 1-2" of 703 above it. Gaps to be varying from 1/8" to 1/2". This gives you an angled ceiling in terms of mids and highs and a nice broadband variable slotted Helmholz absorber for bass frequencies as the entire ceiling.
Bryan
If you want to spend some time (and money), build the 'real' ceiling at the dimension you've decided on. Then below that, build an angled ceiling (low in front, high in back with at least 1" per foot of taper - more is better) but have the visible ceiling be alternating 4" and 6" slats, 3/4" thick with 1-2" of 703 above it. Gaps to be varying from 1/8" to 1/2". This gives you an angled ceiling in terms of mids and highs and a nice broadband variable slotted Helmholz absorber for bass frequencies as the entire ceiling.
Bryan