It would be real nice to have a way on the ipad app to have 2 identical speakers in one box and also have 2 identical vents. Simple check boxes with number of drivers and number of vents. It is very common to design large bass reflex subwoofer with multiple drivers. 2 12 inch drivers is the same piston area as 1 18 inch. The 12 inch drivers have better transient response because of the lower cone mass to move however. And then you can use a stereo amp, one channel driving each speaker. Single voice coil 12 inch drivers also have a much greater selection than a dual voice coil 18 inch.
It would also be nice to have this program and some of your others for the Macintosh platform.