I am using WinISD to design a vented box for my LANZAR OPTI1533d. I am stuck between 4 - 5 cubic feet after sub displacement and tuned 35 - 40 hz. I want to get as loud and deep as possible and still sound good. Tuning it at 40 seems like the sweet spot as far as loudness goes. 35 seems like the lowest it likes to be tuned before it starts to go crazy. I don't want to bottom out early. What do you guys think?