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Old 19th August 2010, 05:42 AM   #1
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Default Port paranoia

i've just about completed a 3.5 cu ft cab utilizing a 12" driver. plugged in some numbers for the port and got one port at 6.5 inches diameter x 8 inches long. is it just me or does that seem too big? this is my first speakerbox, so i dunno. would it be better to do two ports? if so, how?
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Old 23rd August 2010, 12:15 AM   #2
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Without the tech parameters of the speaker you will not get much of a response (no punn!) E
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Old 23rd August 2010, 12:24 AM   #3
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6.5" will handle one mean 12. If you're still working with the mid-grade PA speakers you could easily use half that diameter without having any trouble.
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Old 25th August 2010, 10:09 PM   #4
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Quote:
Originally Posted by Andrew Eckhardt View Post
6.5" will handle one mean 12. If you're still working with the mid-grade PA speakers you could easily use half that diameter without having any trouble.
Maybe, I guess, if the speakers don't have much throw and there's not much power going in.

From a car audio point of view, we like a 5" diameter port for a 12 to avoid any problems. This often means the port won't really fit and you have to build a shelf port of equivalent area. After all, if the port is too small, it means the enclosure is acting like a ported box during quieter/less bass passages, and when the boom hits the enclosures "chokes off" to a sealed box-not good for the sound, plus you lose the benefit of having the port at all!

By the way, all that port flaring and stuff was found by Harman/JBL to help the sound at lower volumes. At continous high SPL, it didn't matter-the air in the port just jetted in and out without spreading.
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Old 25th August 2010, 11:07 PM   #5
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I think we're talking about woofers with around 4mm coil overhang.

Most car audio 12's would qualify as pretty mean in comparison, capable of many times that excursion, and a 6.5" port has half again more area than a 5, and then some.

Last edited by Andrew Eckhardt; 25th August 2010 at 11:15 PM.
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