Hello thxgoon,
I read this tread now and I just want to inform you that I am building a sub project for the same reasons. My room is the same dimension 20 x 30 and need 2 subs with EQ to get optimal results.
http://www.hometheatershack.com/foru...-radiator.html
I think that 18" subs are the best but are to big to get the right WAF in my house (Whife Acceptance Factor) so I go with 12" drivers with passive radiators. I will put more info on my tread in the next week.
Did you complete your project ?