View Full Version : Help w/Precision ports

08-09-2008, 01:24 AM
I am in the process of building a ported box for (2) 12" JBLGTIMKII's using precision ports. Included with the ports is a formula to calculate the length needed.

...... (Vb)Fb

Lv=port length in inches
Vb=volume of box in cubic feet
Fb=tuning frequency
R= radius of port (1/2 of port diameter)

My subs call for 2.25 cubic feet,tuned to 39hz, with 4" port length of 13.31"
Before i cut these ports ii would like to double check and this does not work for me. Anyone understand this...
please ignore the dots used as spacing cause the editor adjusts them all the way over

08-09-2008, 01:31 AM
how many ports are you using?

08-09-2008, 01:32 AM
use the port calculator on their site and see if they match, if they do, you did it correctly. remember that both port flares add up to 5 inches of useable port so substract 5 inches from your total number and thats how much tubing you should cut out

08-09-2008, 01:34 AM
Just use their online calculator - http://www.psp-inc.com/

Remember, with the aeroports......cut the middle section 5" shorter than the length that the calculator tells you.

08-09-2008, 01:36 AM
using 2 ports and ii was not aware they had help on theiir site. both subs have independent chambers

08-09-2008, 01:39 AM
You should use about 4 of them in a 4.5 cu. ft. box

08-09-2008, 01:49 AM
THANKS for the website siite link and guys for all your help. Using 2 independent chambers @ 2.25 cu ft each. Jbl says 13.31 , 4" port
website says straight length port req'd =13.80
Flare length port req'd = 14.80
they suggest addiing 1". what do you guys think?

08-09-2008, 01:51 AM
is thiis correct to cut 5"shorter they websiite calc does not meention thiis

08-09-2008, 01:53 AM
ii am confused the iinstructiions do state to trim tube 5" shorter than Lv

08-09-2008, 02:49 AM
the number you get from your calculations or the calculator is the total amount of port length you should have. the flares have 5 inches of useable port so you subtract 5 inches of the total length..giving you how long your tube should be