I need to build a nice enlosure 4.5 cubes to 8.0 cubes for my Fi 18" BTL N2. Problem is, I don't know how to build a box and tune it to 35 hertz. I've got a Mazda 3 sedan so my room to play in my trunk is 30 width, 36 depth, and 18 height. Can anyone help me design a box with a round or slit...