that alpine surround design is the way that you get great control and far excusion (the jbl gti's series surround is exactly like that). big surround has no control over higher bass frequencies
sealed and ported boxes are more accurate. bandpass is louder, but they have horrible group delay (sluggish sound) and you can't hear if you are over driving your woofer with bandpass.
a simple sealed box is easier to get accurate sound, but a properly designed (sometimes hard to make) port box is the way to go, as you can go up 8 to 10 db louder plus you can make it deeper than a sealed box
you will find that the jbl is louder than almost any speaker ever made. they had an old aura speaker that was most loudest accurate speaker but it was expensive. these new woofers that handle higher power (3000-5000 watts) they all sacrifice sensitivity (loudness) for that high power handling, meaning that the jbl will go louder and deeper with just 400 watts than those other woofers will when they are receiving 2000-3000 watts