other than the JL Audio website formula, here is a modified formula that OLD_SCHOOL gave to me that i wrote in lamens math with a more detailed description so that it was possible to understand without using all the Lv\Av\Fb\Vb terms that arent described very well.
say the box is 1 cubic foot
the port is 4x12
and its tuned to 36hz
this is where to get the informtion to put into the formula;
the cross section would be (4*12) 48in^2.
the net volume would be (12*12*12) 1728in^3.
and the square root of 36 would be 6.
this IS the formula;
and remember...Code:x = cross sectional area of port (inches^2) y = net volume of box after displacements (inches^3) z = tuning frequency of port (hz) PL= Port length (inches) x[1.84 * 10^8] ____ _______________ - .823 * \/ x PL = y[z\.159^2]
do all math on TOP
do all math on BOTTOM
SUBTRACT .823*square root of X from the quotient of the numerator and denomenator (use dictionary.com if you dont know those words)
the awnser is the port length.
***THANKS TO OLD_SCHOOL FOR HELPING WITH THIS****
this way was eaiser for me.