ok i have a box that i want to build and the dimensions are L= 21in. W= 32in. H1=14in. H2=7in. and i tryd to calculate the volume and got 4.0833333 cubic feet outer volume. and then i went to this website http://www.eatel.net/~amptech/elecdisc/caraudio.htm to do the inner volume and it came out as 2.7 cubic feet internal. and i am using 3/4 mdf. if some one could help that would be great because i dont think this is right.