hey,
just a quick question on port lengths.
I built a ported box for my freinds 12in rockford punch sub. I followed the specs fro m rockford which call for 2.0 cu feet with a 4" port 10.75 long. So i sent my freind to get the port but all they had was 2" ones. I typed in the new info in the calc on this website but there saying the port should only be 2 inches.
Is this right??? seems kind of small for a port.
thanks guys
That would be correct for tuning 2 cuft to approx. 35Hz. I suggest if you must use 2" ports, to install 2 of tham, each about 5.5" long.
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Support the12volt.comhow did you get that number. did you just take the long one and divide by 2???
Actually the tuning frequency has nothing to do with the amount of air that is moved through the port. It is a Helmholtz resonator and the sound produced by the port is caused by air flow across it, the same way a flute makes music. The reason to use two smaller ports instead of one smaller port is that the smaller the port diameter, the more likely it will make air noises.
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Support the12volt.comYou will need to use four 2" ports to equal the opening area of one 4" port. You should consider getting acquainted with the relatively easy-to-use WinISD Pro when designing enclosures. See the sticky on this forum.
Here's how you calculate square inch opening area of a circle: pi R squared.
pi is always 3.14 (accepted figure, although the numbers after the decimel point go on forever...)
R is radius of the circle, or half the diameter.
A 4" port is a diameter of 4", or a radius of 2".
- Square the radius, meaning multiply it times itself
- Multiply the result by 3.14
- The result for a 4" port is 12.56"
- The result for a 2" port is 3.14".
- 12.56 / 3.14 = 4.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.