View Full Version : Formula Question

05-09-2007, 10:39 PM
ive used the

dV = is the required diameter of port in inches.
Fb = is the tunning frequency of the enclosure in hertz.
Vd = is the volume displaced by the driver (woofer)
Lv = is the LENGHT of port in inches.
R = is the internal radius of vent tube
Vb = is the internal volume of the enclosure cubic inches.

Lv = [(1.463*10^7R^2)/(Fb^2*Vb)] - 1.463
ive plugged everything in

my question is when u plug the Vb in do you plug the total w/ driver displacement and port displacement in or does the formula account for that.

Heres a pic of my design and my calculations. If anyone wants to take a shot at calculating my Fb.( i have it at 36hz).and net volume. Also, my driver displacement is .055*2 = .11

05-09-2007, 11:10 PM
i believe your vB is what you want your internal volume to be after all displacements

05-10-2007, 01:22 PM
if your box is already built, then you need to find the total displacement of the port and sub(s) and subtract this from the internal total volume.

you port displacement should be 153.66cu"

(you don't count the front baffle, which will make the lenght 6.66 - .75 = 5.91. the height is 13. the width needs to include the inner port wall, so 1.25 + .75 = 2. that concludes: 5.91 x 13 x 2 = 153.66)

when using the formula, use the cu" the driver requires. find the port length. find it's displacement, like i showed, and add driver displacement to it. add this displacement to you driver's required volume. this will be you total internal volume.

16.25sq" of port is awefully small for two subs and a box that size. i do like 30-40 minimum.

05-12-2007, 10:17 AM
Vb is net. The formula can't account for driver displacment because it's different for every driver. Same with port displacement, different for every box.