[quote author=djdj  link=1129093914/15#27 date=1129601683]I'm thinking 2 Imperial SO boxes with 15" V-max's. How much more would I notice over the standard dual-15" box? [/quote]

Absolutely heaps!

Typical Car 15" 87dB/1watt
Typical sensitivity of basshorn with 40hz cutoff,and 600L volume : 101-106dB/watt

+ Better quality.

[quote author=djdj  link=1129093914/30#31 date=1131061588]Thank you for the input! I ended up building the dual 15" standard bass-reflex box. Haven't finished it yet though. What would I expect with 2 Cerwin-Vega V-Max's in a regular Imperial? If it would level a building thats what I'm looking for! [/quote]

If the imperial is designed for an 18", the two CV15"s you have wont quite be the right cone area for the horn,but it should still be very effective!

The imperial will be way more efficient than the bass reflex.
Bass reflex with this woofer - probably about 90dB/1watt/1metre
Basshorn - 100dB atleast,typically 105dB/1watt/1metre.

Mike.e