How to tune this box

lilrob Silver Member Username: Extrmndor3 Chicago, Ill Us Post Number: 144 Registered: Feb-06	Posted on Thursday, March 23, 2006 - 22:00 GMT i just made a box but i dont know how to make the port so this is the picture the sub is an 18 inch re audio sx :
Lewass Silver Member Username: Lewass Boomfield Hills, MI USA Post Number: 400 Registered: Jan-06	Posted on Friday, March 24, 2006 - 16:07 GMT http://www.accelerator-pedal.com/ported-box.asp?Ew=36&Eh=15&Dia=4&Xmax=11.9&Vd=. 06&NumW=3&Vb=3&Fb=35&Qts=.432&Vas=2.3&Fs=23.1&CE=0 Plug in your numbers and pick a tuning freq, then just keep messing with them till you get your size and the tuning you want... But I don't understand that divider in the middle... ?