Slotted vent calculation?

[G]

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

[mikee12345]

www.diysubwoofers.org >ported box xls file

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

www.jlaudio.com >tutorials

[OMNIFEX]

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,

[G]

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.

G

[KevinLee]

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.

Thanks

KevinLee

[G]

Thank you Kevin. That helps a lot.

G

[bostarob]

download winisd, it helps alot, and you can see graphically what changes in port size make.
-andy

[Pete Mazz]

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

[KevinLee]

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

[mikee12345]

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