If i were to get two 12 ixls and push them with a sundown 1200d, would they be louder than if i were to just purchase one and put the full 1200 watts to it? Also this may be a dumb question but a friend of mine's dad is gonna build me a box, and if i were to make 1 cut out on one side, later on could i add another cut out to the other side? Its gonna be a sealed box but i was wondering if that would mess the frequencies up and stuff. thanks

2 12's sealed woud probably be louder than 1 sealed...and no it wont mess with any in the box if it sealed but make sure its big enough for 2 12's

Cone area would win out, plus you wouldn't be stressing the drivers out.

Of the IXL's I have had 1-10", 1-12", 1-15", 2-12". All on the same amp. All the single driver systems were seeing ~1200rms, And the 2-12's 900rms combined and the dual 12's are louder.