I have two 4.14cuft boxes (theyre actually one big box with a divider down the middle) so the entire box is about 8.28cuft. Anyway i have the subs inverted on the top of the box and its tuned to 36hz. What affect would there be if I added two more subs to the from of the box so there are two subs sharing the same 4.14cuft of airspace? I can post pics if I didnt explain it well enough.