View Full Version : length of ports (35hz)

07-02-2003, 03:39 AM
I need help I dont know how long the walls have to be to tune it to 35hz I have a pic of the box measurements its (36" wide, 14" high, and 12" deep, i will be putting two 12" woofers in it) and I am trying for a port between the two subs. thank you for any help i need all the feedback i can get, peace

07-02-2003, 02:21 PM
If the dimensions you listed are external and you are using 3/4" material for the box.
The total volume of the box is around 2.6 cu ft.
Then subtract the sub displacement for two 12" subs. That's around .15 cu ft.
So you're left with about 2.45 cu ft. internal volume.

Your port opening is 12" x 3"

With that size port, tuning to 35Hz would require a port length around 27.4"

You might want to move your port from the center. Also you might try a slot port instead of a square port. Slot ports are slightly shorter than square ports and they are simple to build.

A 12" x 3" slot port would be about 25.9" long.

07-02-2003, 08:01 PM
what program did u use to draw that?
and where can i figure out how long to make my port to tune my box
any formulas? thanks

07-02-2003, 08:30 PM
You can get calculations done eay with winISD pro. Might not be 100% accurate, but it's supposed to be accurate enough. :)

As for the drawing, either he's downloaded it off somehwere, or it can be done in MS paint.

07-02-2003, 10:23 PM
Originally posted by Matt0528
what program did u use to draw that?
and where can i figure out how long to make my port to tune my box
any formulas? thanks
I used good ol' Paint to draw that.

winISD is a good program to figure out port sizes and other goodies.

carstereo.com has a port calculator on its site somewhere that is fairly accurate.

07-02-2003, 11:38 PM
I did it in adobe photo shop, on my computer if you want me to do one for you give me a discription of the box and its dementions.

07-03-2003, 09:59 AM
If your like me and sometimes don't trust calculators, here is the formula to figure out port lenght:

Lv = 1.463 x 10^7 x R^2 / Fb^2 x Vb - 1.463R

Lv = length in inches.
Fb = tuning freq.
Vb = internal volume of enclosure in cubic inches.
R = inside radius of port.

Note: If if multipule vents are used, divide the enclosure volume by the number of vents to be used. Use the result in the formula as "Vb" to find out how long each one should be.

Note: If using a square port, use this formula to get the value of "R":

sq.rt.of a / 3.14

a = area of vent opening. (h x w)

Hope this helps.