View Full Version : ported box question

09-03-2006, 08:56 PM
I notice when I see alot of box designs(on paper)for vented ported boxes, they have a whole bunch of zig zags for the port. Now I was wondering, could you just make the port wider and have it only going straight back with no turns and yield the same results? Like instead of it being 2 inches wide and like 30 inches long you can make it 3 inches wide and 20 inches long and get the same results? or 4 inches wide and 15 inches long? Because don't you just need a certain amount of Sq ft of port to achieve the desired hz?

Thanks a bunch

09-03-2006, 09:08 PM
It's actually reverse of that. It would go from 2" wide, 30" long to 1" wide, 20" long.... The lower the tuneing freq. the longer the port will need to be. The width of the port is important because the air comming out tends to be turbulent and noisy if you make the opening too small.

09-03-2006, 10:02 PM
i don't get it from what your saying.
If you calculate the port measuring 2" x 30" it comes out WAY bigger than 1" x 20"
how does that work? I don't get it.

If the box is 15" high internally then 2x30x15 is alot bigger than 1x20x15.

I want to go from a really long port that zig zags to a very short but fat port that is a straigh line, keeping them same Hz. Just wanting to know if I can do it.

09-04-2006, 01:06 AM
The Hz, or tuneing frequency of a box is determined by length and width.

Try going here: http://www.diysubwoofers.org/misc/portcal.htm

"Port Length
The port length required to tune a volume of air to a specific frequency can be calculated by using the following equation:
Lv = (23562.5*Dv²*Np/(Fb²*Vb))-(k*Dv)


Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction (normally 0.732)"

The way that equation ends up working, you need the port to be narrower in order to have a shorter length and the same tune.

09-04-2006, 05:24 PM
the larger the port opening, the longer it needs to be to maintain the same tuning. the tuning is adjusted by the length, not the opening (area). the port area can be too small and cause turbulance, or port noise, or too large to cause the sub to act if it were in a free air environment...need to find a happy medium.