Re: Carrie Underwood Sub Woofer Array
Having an empty rear area is needed, yes, otherwise the reflections from that rear surface will arrive too soon in time - IE, before the array as a whole can cancel them out. I'm assuming there is a minimum distance based on total array distance to get the time to line up right.
However, not sure about side surfaces being bad. Imagine a tube of subs, where it was not only a pair of parallel subs firing in, but two parallel rows. One pair firing at each other top/bottom, the other pair at each other side/side. As long as the rear was to free space, it would essentially be a big bass cannon, would it not?
If the space under the stage was rigid and had no air leaks, other than plenty of space out the rear - it should work fine. However, how many stages just happen to be constructed like this? 
