I found this equation....is it the right one to use???
Fb - is the tuning frequency of your enclosure in Hertz.
Lv - is the length of your port in inches.
R - is the inside radius of your vent tube.
Vb - is the internal volume of your enclosure in cubic inches. To convert cubic feet to cubic inches, multiply by 1728.
If you want to use multiple ports, divide your enclosure volume by the number of ports you want to use, then use the result of this calculation as your Vb in the formula below to find out how long each port should be (a tip from JL Audio™).
If you want to calculate square vents, the formula below will give you the value of R to use in the formula above.
In the formula above, a is the area of your square vent (height x width), and (Pi) is approximately 3.141592
and if it is right, and i want to use multiple ports, does each port have to be the specified length? for example...if i want 2 4" aero ports and the equation said i needed a length of 20 inches for correct tuning...would that be per port? or 2 ports cut to 10 inches???