Don't remember where, but I've heard to get these flat, they'd want an enclosure the size of a McMansion :laugh:RE XXX18. You want low, 54mm of one way linear. They don't make subs with more excursion than that one period.
But the real question is, how much power you got?
The same guy who sells the motors also sell baskets and all the soft parts you'd need to build them.I see a guy on ebay selling 400 oz subwoofer motors, where could i find good 18 or 21" subwoofer baskets if i were to get two motors?