Ports: Big and long vs. small and short

[Shelbyturbo1989 10+ year member]

I am going to build a ported box using a JL 12w3v2. I was using a program that calculates port lengths and I got an interesting result. As the port gets larger in diameter, the port gets longer to maintain the same tuning, and vice versa as the port gets smaller in diameter, the port gets shorter. Knowing this, how do you choose a port diameter since you can get the same tuning frequency by using different sizes?

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[JimJ 5,000+ posts]

You choose the diameter that allows you to get the tuning you want without excessive air velocity in the port, which leads to port noise and chuffing...

 

[Shelbyturbo1989 10+ year member]

Holy crap that was fast. Is there anywhere you could direct me to help me learn more about port velocity, like what is too high to low etc, and how to calculate it?

 

[swimfreak26 10+ year member]

By no means comprehensive, and the size should change as the driver changes, but as a rule of thumb, and somewhere to start.... 12-15sq inches of port per cubic foot.

 

[tRiGgEr 5,000+ posts]

http://www.carstereo.com/help2/Articles.cfm?id=31

Very crude, general velocity calculator.