When I play with your figures in WinISD I find the RL-P18 D2 model with the 2 ohm coils in series for 4 ohms total and 750 watts per channel from the EP2500 seems to give the most reasonable results (with my limited knowledge).
Much more power than that and the excursion and velocity seem to get a bit too large.
If I use a 550 liter box (19.423 cu.ft) with a 16Hz tune and a 21.27" single flanged 8" port combined with 4 ohms driven from a EP2500 (750watts) I get the following results. Having two boxes would be 6dB more SPL output I suppose.
SPL
blaser RL-P18 D2 series SPL.jpg
EXCURSION
Goes a bit over Xmax at full power. Don't think that's greater than Xmech though.
Includes a 1st order 10Hz electronics rolloff filter.
blaser RL-P18 D2 series EXCURSION.jpg
AIR VELOCITY
Exceeds the 17 m/sec 5% rule, but is only 7.5% max at full power.
blaser RL-P18 D2 series AIR VELOCITY.jpg
I played with the box a bit with a front vent.
Seems like a big box. I'm not too use to using BoxNotes, so it was an experiment for learning.
Don't know if it's realistic. Seems correct.
The only box resonance that seems a concern is a quarter wave one at 86Hz. I wonder how important these resonances are. Takes a lot of playing around to minimize them and still get a sane box.
Anyone else use this program?
blaser RL-P18 D2 series BOX.png
brucek