i'm gonna be using a 12" brahma and i want a ported box. what i came up with is internal dimensions of 34.5 wide 12.5 tall 12.5 deep (36 14 14 external made out of 3/4 mdf) for the port i came up with 2 wide 12.5 tall and 19 deep giving me 30 hz tunning. the sub displacement is .15 and i came up with a final total of 2.59 cubes tunned to 30 hz. is this accurate? is it actually tuned to 30 hz?