"Once made a dual delta 12 lf with dual beta 8 and single apt 80 that sounded pretty darn good. [Made for a church.] Perhaps this Great Plains driver is in another league?"
This sounds like a good speaker, and not too expensive either.

I was thinking about attempting to build an OB speaker with a pair of JBL 2118J eight inch woofers per side in an MTM configuration, running them from 100Hz and up. Using a B&C DE250 with DSS ENG 90-1" waveguide on one side of the JBL woofers. And a horn super tweeter mounted on the same plane as the DE250 waveguide combo on the opposite side of the woofers in a diamond configuration.
The sub 100Hz would be covered by an active U baffle subwoofer system.
I am not quite sure if I would be better served as far as speed and integration is concerned. If I used two 12" sub drivers over a single 15" in the U baffle. I guess I will figure it out down the road.

Norris