Help w/Precision ports

[sak384]

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.

.................2

Lv=8466.4R

....._______.......-1.463R

..................2

...... (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

Click to read more...

 

[JG903 10+ year member]

how many ports are you using?

 

[Mattd0344 10+ year member]

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

 

[cycloneman 10+ year member]

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.

 

[sak384]

using 2 ports and ii was not aware they had help on theiir site. both subs have independent chambers

 

[JG903 10+ year member]

You should use about 4 of them in a 4.5 cu. ft. box

 

[sak384]

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?

 

[sak384]

is thiis correct to cut 5"shorter they websiite calc does not meention thiis

 

[sak384]

ii am confused the iinstructiions do state to trim tube 5" shorter than Lv

 

[Mattd0344 10+ year member]

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