I currently have a box with about 1.4 cubic feet total inner volume(not counting sub displacement). It's a shared air space for 2 12" subs.(RF Punch Z, i think, the 150rms/400max model). These subs reccomend 1-1.5 for a sealed box. does that mean I need a 2-3cubic foot box for it to work properly? How much efficiency am i losing because of this setup?