Nick, I've been thinking about your design. It looks like when the front driver is moving foward, the side driver is moving backward (relative to the magnets) so air is being gathered up like taking a breath where both lungs are expanding. Then on the reverse travel they would be pushing air out of the cab through both the front and side vents like exhaling. The side driver is facing in so you lose most of the highs and upper mids that come from the dust cap are of the speaker. I think that this would result in a roughly 3db boost from 500hz on down. If you were using the faital driver you would have a low/lowmid boost with a flat upper mid and treble. If using a driver like the 3012ho which has a boost in the mids and a big boost in the upper mids, you would have a flatter response up to around 1khz and then a relative 3db bump at 2.5khz which, actually should sound pretty good. A fatter sound than would be expected with both drivers firing forward. Your design would probably give a bigger, fatter sound at lower volumes than a super 12.