4th order bandpass

anyone who could explain how to figure porting and sizes for a fourth order bandpass please help me out. ive done alot of builds in my time but never attempted one of these..   any help or suggestions would be greatly appreciated.

I usually start with the sealed side optimized for the driver, then the ported side at about 1/2 that volume.  Tune the port for around 70 - 80Hz, model it with whatever software you use, and tweak it as needed.  Though I usually find that I prefer to port both chambers.  I am running one now with the larger chamber tuned to 30hz and the smaller to 70hz.  I like how these sound.  You can also port the low side through the interior wall to the high side if you want. But everyone likes different things. Treat it like its two seperate boxes.  Figure ports for each side of the box just like you would a single chaber box, only tuned to different frequencies.