adding up the ports

[xploder]

I am building a ported box for 2-JL12W0-8's. I am making them in a common chamber box with no seperation. In the specs it says to double the ports or add them up if making a single port. Here comes the question which may not make sense. When using a speaker box program. Lets say one of the speakers require a 2.5 cubic foot of space. You double it to 5.0 cubes. The port for a single woofer in a 2.5 cubic foot box is 4" by 12" which came to a tuning of 31 hertz. Now if you double the ports up, it comes to a single port measuring 8" x 12'', you will no longer have the box, which is 5 cubic foot, tuned to 31 hertz. When using the speaker box program and you tune a 5 cubic foot box with the 8" x 12" port it comes to around 39 hertz. Does this make any sense to anyon? So would you tune the box as if it was a single 5.0 cubic foot box which, when using the program, would come out to a 6" x 11.5" port at 31 hertz. I am using the WinISD program. I also tried other programs and came to the same conclusion.

[havoc06]

just use two ports...looks better when you have 2 subs anways.....

[Trixter]

To find the length of multi-port set ups, divide the size of the box (in cu') by the number of ports to be used.

You have to count in port displacement. The larger the port is going to be, the larger the box is going to have to be. Also, the bigger around the port is, the longer it has to be. If you port was 6" x 12" you would be at 31Hz in a 5cu' box. Personally I put a slot port in between the subs.

[xploder]

Ok..I understand now. I ended up making a rectangular port equivalent to a 5.65 round port. Finished making a box for 2- 12W0's in a 4.4 cubic foot box (2.2 per driver) in a common chamber. Ported to 31 hertz with a single rectangular port. The box sounds good. Thanks for all your help.