mtx 9500 enclosure

I am planning on building my first vented enclosure for a MTX 9500 12 inch sub.  I am not familiar with all the box building programs out there so I called MTX with the area that I have to work with.  I have a total of 3 cubic feet internal space and wanted to tune the enclosure to around 40 Hz.  MTX said that with an internal space of 3 cubes, I need a slot that has a 30 square inch opening by 16.5 inches long.  Does anyone have any experience with this sub and do these demensions sound correct?  Any other information on buiding an enclosure for this sub would be helpful, thanks.

As far as port area yes, that sounds right at 30 sq.in. of port area, but to find or figure tune you need to find your net volume. To find your NET, NET is gross internal, minus port volume, driver displacement and any internal bracing. Once you find net. Then you can use the site calculator to verify your tune is correct by entering you net, port height, width and tuning frequency to verify the length of the port is correct.