Im thinking of adding another 15" and another 500wrms to my setup. Box will be about 7 cubes before sub displacement. Right now i have my 2 15"s in a sealed box facing up. Im not really happy with the output as far as the higher bass notes (70-100hz and such) but the lows bang out pretty good. Basically what im wondering is would it be better for me to build a slantback box or keep a up facing box? With my last setup (2 mtx 7500 12s in slantback) the high notes were alot louder and sounded better in the cabin too. Is there any optimum angle to slant the face at?