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?
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.
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.
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.
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