What happens to port dia/length when an enclosure is doubled?
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 27th October 2009, 09:57 AM #1 gripracer   Banned   Join Date: Mar 2009 Location: Atlanta, GA What happens to port dia/length when an enclosure is doubled? The (single woofer) cabinet spec for the woofer I'm implementing is: .60 cubic feet w/ 2" dia x 6.25" length port. I want to use two of the woofers, and I have a 1.2 cubic foot box ready to go. So, does the port spec double as well? ie 4" D x 12.5" L?
 27th October 2009, 10:12 AM #2 chris661   diyAudio Member     Join Date: Feb 2008 Location: Sheffield No, it stays as it is. Changing the port diameter and length changes the tuning, but with twice the box size and twice the woofers, the tuning will stay the same. Try it on something like winISD. Chris __________________ My work: www.grimshawaudio.com
 27th October 2009, 10:21 AM #3 gripracer   Banned   Join Date: Mar 2009 Location: Atlanta, GA how simple! thanks!
skeptic43
diyAudio Member

Join Date: Oct 2009
Location: new england
Quote:
 Originally Posted by chris661 No, it stays as it is. Changing the port diameter and length changes the tuning, but with twice the box size and twice the woofers, the tuning will stay the same. Try it on something like winISD. Chris
I disagree. Doubling the number of woofers has no direct impact on the vent calculation. It is strictly a function of the port size, tuning freq. and box volume as dictated by the helmholtz formula.

Port Length = 14630000*R^2/fb^2*Vb - 1.463*R

where R is the port radius in inches
where fb is the tuning freq.
where Vb is the box volume cu. inches

Doubling the vol. will reduce the port length to 2.4 inches with a 2 inch dia port.
If you increase the port dia. to 3 inches, then the port length can stay about the same (actually 6.4"). This is advisable to minimize chuffing (high air volicity noises in the port tube)

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