Hello troyd,
For the record, the driver used on Axiom's EP400 is 8 inches in diameter, not 10 inches.
For larger rooms, you'd be better off getting two EP500s, which would deliver greater overall output in the big space as well as higher maximum sound pressure levels.
The EP400 was designed to produce very deep bass in smaller rooms from a smaller box with the same DSP control as the EP500. The 400 has a much smaller enclosure than the 500 so it's ideal for customers who don't want the bulk of a 500, yet still want the deep bass extension without having to fill a big room.
The trade-off in subwoofer design (as Casey01 has correctly noted) is that if you make the box smaller, it takes more power to get deep bass extension and you also give up maximum output. The 400's driver is smaller so it has to "work" harder (with greater excursion) than the 12-inch driver of an EP500, hence it can't produce the same maximum SPLs as an EP500.
Regards,
