Multiple drivers in a line formation, I've heard the big Montana's years ago, very impressive, huge, heavy speaker, they were interesting because, they have the woofers and mid woofers on the top and the bottom of the huge cabinets, with the tweeters in the middle and dual mid-range's above and below those, very effiecent too! Pipedreams also come to mind, with like 30 mids and 40 tweeters in a column.
My big beef with line array's is all the crossovers, all that internal wiring and all the drivers, messes with the sound. I'll toot the horn of 'less is better', in fact, no cones at all, just a thin membrane of plastic to cover 80hz on up is just magic
. Big DOH on that from me eh??