Upper and lower room corners are quite problematic since they produce very high sound pressures, actually much higher than the average sound pressure in the room when music is playing.
Geoffkait
Don't sit with your head in the corner. Problem solved. ;)
Seriously though, another nod to ATS Acoustics. Well built, fairly priced and quick. I built a couple DIY pieces with ok results. After purchasing a couple panels from ATS, I won't build any more. By the time you run around getting supplies, building and cleaning up, it seemed more cost effective to buy ready made pieces. And they looked better too.