Thanks for the link Mike. I found another interesting link these folks cater to bands such as the Red Hot Chili Peppers.
Here is their take on horn loading... http://ratsound.com/concept.htmTheir Rat Trap Five speaker seems like a real winner, I wish I could hear a pair of them. Here is a link to their system configuration page , it kind of shows what it takes to fill a given area with sound... http://ratsound.com/sysconfig.htm
The pic is 24 of their Rat Trap Five speakers used at a Pearl Jam concert.