I'm just curious about what the trade off would be if you had used a 4" fullrange driver instead of the Tang Band & the supertweeter... I've seen a number of OB designs with just a 4" Fostex fullrange and Eminence 15" bass...

EDIT: Looks like that design is an older Martin J King design as well:

http://www.quarter-wave.com/OBs/OB_Design.pdf