If you're considering a bass reflex box, then the boxes should be approximately 24" x 16" x 10" - but this includes no offset due to the volume displaced by internal components and the thickness of the wood. I'd expect that your actual cabinet needs to be closer to 28" x 20" x 12".

If you're planning a cornerhorn, then the motor cabinet should be 32" x 16" x 8" - again, having no offset for volume. And again, I expect that your actual dimensions after including the displacement of all the parts inside will be something like 36" x 20" x 10".

Let us know how they sound.