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Old 27th October 2009, 08:57 AM   #1
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Default 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?
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Old 27th October 2009, 09:12 AM   #2
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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
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Old 27th October 2009, 09:21 AM   #3
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how simple! thanks!
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Old 27th October 2009, 11:32 AM   #4
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Quote:
Originally Posted by chris661 View Post
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

Based on your info., your port freq. is about 43 hz.
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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