In my old 12 x 15 x 8 room
1. I had an 8ft wide vinly blind behind the listening position - it was only lowered about 15 inches - any lower made no difference
2. I had a sound absorbing panel on top of a book shelf to the right of the listening position - it improved clarity a lot - guess it stopped reflections between the top of the bookshelf and the ceiling
3. the floor was hardwood with a 5 x 8ft rug
In my new room I only have the panel on top of the bookshelf.
The new room is 16.5 x 40 x 8 ft with dropped sections taking it down to 7 ft
- the speaker are 8 ft from the wall behind them and 4.5 ft in from the sides
- there is around 24 ft of open space behind the listening position
The entire room is carpeted
I no longer hear any reflections
The image is huge and 3D.
I have also applied the vinyl blind treatment at a friends concrete condo with 11 ft ceilings - the improvements were very dramatic.
I would focus effort on curbing reflections in the upper level of the room
Regards - steve