[NickTF]

Oh, ok. I've made the attempt to make correlations in the past between different alignments and i'd say this much from what i've learned. You can compare a sealed box setup to an IB somewhat in output but the IB will become more effecient in lower frequencies due to no air spring. Also, because of no air spring the subs are in danger of over-excursion so some form of electrical limiting (eq, infrasonic filter, etc.) must be used if you are using enough power to hit your particular woofer's xmax and then some. Long story short, I'd think if you are happy with a sealed alignment using two 15s then you'd be happy with a IB alignment using the same drivers if you are able to prevent over excursion. Remember, the woofer recovers faster in an IB so you will miss some bloat and overhang associated with smaller sealed enclosures which some may call SPL.

Now, regarding ported/passive radiator alignments it seems to be a bit more tricky. I don't totally understand but at the system's tuning, atleast in a radiator setup, I believe you get the radiator's displacment capability which needs to be twice that of the active driver, but only at Fb and higher do you gain this displacement. Actually, in thinking while typing this it would seem the system is capable of displacing twice the amount of air as the active driver(s) (hence the requirement for twice the amount of radiator displacment of that of the active driver(s) in a passive radiator alignment) at Fb in ported or radiator alignments. Now I don't understand the exact relationship of how that diminishes as you get over Fb and i'm sure it's different for every alignment.

Long story short, if you want the most output for given amount of wattage, outside of a large horn enclosure, it seems a ported enclosure or passive radiator setup is for you!!!