View Full Version : Port question

07-13-2005, 04:11 PM
I have noticed that port theory dictates that as a port gets bigger in diam it's length must also get longer. And as it gets smaller, it gets shorter. :blink: No puns please ! ;)
Question: why does one need to use a port that is 4" in diameter when a 2" would work and be a lot shorter and hence easier to work with.

I know that the small port won't move as much air, but there has to be more to it ? :hmm:

07-13-2005, 04:17 PM
Has to do with the efficiency of the port itself...a smaller port creates more friction...and chuffing, or wind noise. The JBL Enclosure Design Reference Manual should have a better explanantion.


07-13-2005, 04:17 PM
It's the velocity if the air moving in and out of the port, which should be kept below 0.10 mach (speed of sound in air) at max SPL for the design. Below 0.05 mach is better, even.

If the port's too small, it will huff and whistle at high volumes. It it's too big (and thus, too long) it'll start resonating like an organ pipe.... :D