the box is 11.5 cubes tuned to 31 hertz and yes im now running 6 1500s numbers went up a little 154.2 headrest 155.4 windshield 156.6 floor this is meca style or fcbc style im going to try a 11.5 cube box at 35 hertz with a larger port ......the internal space is 11.5 with port its 13.1 cubes