In standard Bass Reflex design one uses 1/2 Vb to calculate each duct.

I admit to being kicked-out of MENSA, so how do I proceed?

Note: I want to build "Konus Audio Essence" style enclosures (only ones with sufficient WAF) for my EV 12TRXB's (3.8 ft^3 as per PiAlign) and think dual down-firing ducts will provide optimimum 'balance' -- not to mention looking way-better than one little duct positioned assymetrically on the front. (Severe WAF deduction.) ; )