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Old 8th April 2003, 11:59 PM   #1
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Question Slotted vent calculation?

Hi all,

I am building a pair of bass reflex speakers and I need a little help. The design in the pdf below( the bass reflex enclosure at the bottom right) uses a round port. I would like to use a slotted port. Can anyone be so kind as to give me the formula for calculating the port dimensions for a slotted port? Any help is appreciated. Thanks.

G

http://www.fostex.co.jp/int/pages/pr.../206e_encl.pdf
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Old 9th April 2003, 03:10 AM   #2
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www.diysubwoofers.org >ported box xls file

www.linearteam.dk >winisd,and port calculator.

www.jlaudio.com >tutorials
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Old 9th April 2003, 06:16 PM   #3
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Please keep in mind Slotted, Shelfed, ducted, vents
take up more of the internal chamber, than a circular
vent.


Pending on how over, or, under you're scaling the
optimum enclousure, this may play a factor.


Best Regards,
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Old 9th April 2003, 06:38 PM   #4
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I had planned on using this duct:

http://www.psp-inc.com/images/4%20x%...0seperated.jpg

In the instructions on how to calculate the length they say that it should be positioned at least one port diameter away from any adjacent walls of the enclosure. Why? The duct is from Precision Sound Products. Using this would certainly make things easier and look better but my enclosure is only about 11" wide which rules out using the 4" duct.

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Old 9th April 2003, 08:02 PM   #5
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Hello,

You can use a slot port in the place of a round port. The length will remain the same.

To calculate the port size in square inches you need to take the round port radius and multiply it by 2, then multiply by 3.14, this will give you the square inches of the port.

For example a 6inch round port has a radius of 3". Multiply 3 x 3 to get 9 and then by 3.14 for approx 28" square.

To calculate your slot port of same size simply use length x width until you come up with the shape you want. A 4" x 7" would work for the 6" round port above.

As a rule your inner port end should be no closer to a wall than 1/3rd the port diameter.

That's all I know.

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KevinLee
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Old 9th April 2003, 09:22 PM   #6
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Thank you Kevin. That helps a lot.

G
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Old 9th April 2003, 11:38 PM   #7
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download winisd, it helps alot, and you can see graphically what changes in port size make.
-andy
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Old 10th April 2003, 01:00 AM   #8
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According to this site slot ports are much shorter than rectangular ports to achieve a desired tuning freq. Seems that because you're using a wall of the enclosure as part of the port, the slot port gets shorter. Hard to believe it's this much, tho I've never tested them.

Pete
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Old 10th April 2003, 01:51 AM   #9
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Pete,

you are correct! Slot ports are different than square or rectangle ports.

In my post above when I said slot port, I should have said rectangle port.

Thanks

KevinLee
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Old 10th April 2003, 01:59 AM   #10
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yep having the duct against the wall of the box causes it to be 1/2 the distance across the duct,shorter


www.jlaudio.com >tutorials >>ports an ducts
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