From what I've learned from competitors using these (and being around them some myself), they're nearly siamese twins of the Memphis HPO series subs and I'm inclined to agree....And IMO that's a very good thing...
As was mentioned, on paper the specs are meager, but w/Memphis (and these) subs, their mechanical limits allow them to do much more damage than the xmax would lead you to believe....The old Memphis PR series is a good example...
Of course, the above statement in now way implies IA cloned that particular Memphis series...Just that the mechanics, specs and performance are neck and neck.
The best part is that the 187 is about 1/2 the price of the similarly performing Memphis subs....