box to small?

Hey guys ive got  some problems i think my math is off on the size of my box. Ok my measurments (outside dimensions) are 42" long X 10" deep X 13.75" high. The port is a slot port 12.25" tall X 2" wide X 17" long with a power accoustic mofo stuff in it, so what im getting is 2.3 cubic feet tuned to 35 Htz. is this correct for this sub, i forgot to add in displacement of sub, so basically my question is with the displacment of the mofo is my box correct?First major build for myself in the process

Well the way im figuring you have 2.44 GROSS cubic foot. To figure NET we subtract your port, bracing and driver displacement from this to find the tune. The calculator on the site figures tune based on NET airspace. GROSS = 2.44 (Based on your outside dimensions and .75 material). - Port volume .24 - driver displacement .16 (guess based on a similar style, mounting depth and sized subwoofer). - Bracing .08 (figuring port wall as i figure it is run). = NET of 1.96 cu.ft. That puts you at an Fb= 40Hz maybe a bit higher if you have additional bracing I have not figured.