Here is the deal, I have roughly about 6 cubic feet I can give for a box. Right now I have 2 audiopipe txx 15's that are rated at 1000rms in a 1.5ft sealed enclosure each ( I know the box is small). I want to run 2 15" subs ported in a 3.0ft box for each but is that enough space? I love low notes and spl pressure so im looking for a new setup. I've talked to Tod at digital designs and he said go with 1 DD 9518g in a 5ft box ported. THis is for a daily sub with good quality but i do want some pressure. Would it be The subwoofer will be in my trunk and not in a wall behind the seat. Another question, does anyone know the power rating on a fully loaded 18" btl? The DD9518g is gonna run me about $750. I don't want to spend no more than that for an 18". Im running a hifonics colossus xx version. Its 1600 x 2 at 1ohm or 3200 x 1 at 2ohms. If there is any suggestions on any other subs or setups that sounds good for my space and power, please feel free to spread some knowledge. Thank U!