Wayne Parham Messages: 18789 Registered: January 2001
Illuminati (33rd Degree)
Don't put the mains on top of flanking subs because that defeats the purpose. They need to be a few feet behind, below and beside the mains. Each flanking subs needs to be between the main speaker it's flanking and the nearest boundaries, in all three dimensions. So they're usually slightly behind, to the outside and just below the mains, which are on stands.
Constant directivity cornerhorns are an excellent option when the room has the right corners to support them. You're right - they don't need flanking subs - because the problem solved by flanking subs doesn't exist in constant directivity cornerhorns. They are acoustically close to the nearest boundaries, so there is no self-interference notch from them. I still recommend multisubs though, just the more distant variety, designed to increase extension and smooth the lowest frequency room modes.