Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
If putting the mains on top of the woofers is all you can do, then you can't take advantage of modal smoothing using multiple sound sources. The mains and the subs will sum the same (either in phase or out of phase, depending on how they're connected). But bear in mind, if you're outdoors or in a very large space, this is exactly what you want. It's only indoors where room modes are a problem that can be mitigated using a multisub approach.
I must say that it seems inconceivable to be that flanking subs couldn't be employed due to space limitations. They're not far away - Just maybe two or three feet outside and behind the mains. If you are setup indoors and have the mains less than about eight feet from the wall behind them, then I'd definitely flank 'em with subs. Just put he subs a little bit behind the mains instead of directly underneath them.