I have a Hummer H3 with dual Sundown sa-12D4's running off a Hifonics BRZ1700.1 with 145 amp alt, big 3, 0 gauge, 8 gauge power wire for the speaker wire. I have them in a box with dimensions 38x21.25x14; .75 mdf. The port is 12.5x4.5x31.5 long. I have made the port longer and shorter and can't seem to get it to peak around 34hz. It sounds like it is peaking around 38 or so to me. I have built many single sub boxes, and all of them end up being just about perfect, but I can't seem to get this dual box to sound correctly. I have made 3 different boxes trying to get my box hitting the lows well, but can't seem to do it. Could somebody please help me to get the right port length for 34hz peak. I have the subs facing up and the port facing towards the right side of the vehicle. Any help will be appreciated.