noob needs help

[unrated 10+ year member]

hey everyone, im so confused here, ports are driving me crazy, but i dont understand slot port, im designing a box for 2 15" Rs dual 2 ohm dual chamber box, each chamber is 4 cubes, i would like it tuned to around 32hz, i was gonna put 2 4" x 13" long ports, but i would rather put in a slot port, but i do not understand the square inches or any of it, 3.5" deep x 13"wide , how long do i hafta make that port, heres a sketchup of what i am trying to make

http://img405.imageshack.us/my.php?image=box1yt4.jpg

http://img443.imageshack.us/my.php?image=boxfrontix9.jpg

http://img476.imageshack.us/my.php?image=boxtopys0.jpg

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[iceteebone 5,000+ posts]

there is a big long formula you can do to work it out or you can use this calculator http://www.carstereo.com/help/Articles.cfm?id=31 be sure to check slot and it will factor in end corection. also when figuring out how long, go down the center

 

[96civ 10+ year member]

Lv = [((1.84*10^8)*Av)/(1728*Vb*((Fb/.159)^2))] - .823sqrt(Av)

it's kind of sad that I have that memorized now.

where;

Lv = length of port (down the middle as iceteebone posted)

Av = port area

Vb = net volume

Fb = tuning frequency