Okay, I remeasured the area in the basement where the home theatre is planned, without worrying about the Golden Ratio.
ceiling height, assume finished height is 7'11 (95") with double drywall - assuming finish flooring (carpet) is zero height.
Room width: there are some cold air return plenums that start to intrude around 15', that would drop the ceiling height by 8". If I can box in soffits around this, I can widen the room by that boxed in amount. (E.g. 2' soffit would enable a 17' wide room.)
Room length is constrained by a gas shutoff valve at 21.5 (that must be accessible).
So how does this sound? (haha
H=95" (7'11"), W=17' (w/2' soffits on each side), L=21.25'
I still need to find the guidelines for seating, viewing angles, etc.
Does one have to have the electronics (speakers, projector, etc) selected before designing a room including where the speakers are located?