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View Full Version : How do corners affect the tuning frequency (& required length/volume) of a slot-port?



emilimo701
05-18-2010, 06:34 PM
I am new to this forum, and car audio in general. So I think I put my previous post in the wrong discussion forum...

http://www.caraudio.com/forum/subwoofers/475445-advanced-question-box-build-rf-t115d4.html

Basically, this is the question I still have: how does a corner -- whether 90 degrees or 180 degrees -- affect the tuning frequency of an enclosure?

Intuition tells me that it is simply about the port volume, and that adding the length of one side of the corner (which would be equal to the port width) to the total port length would yield the proper length to put into a tuning frequency calculator.

However, Rockford Fosgate seems to ignore the corner altogether when they describe the port length (see thread link above). I was also advised to "round off" the corner by one member, and I have actually seen box diagrams where this is done. So this makes me believe that the effective tuning frequency isn't JUST influenced by the volume of the port, but that the shape of the port matters. (As an aside... I have compared port calculators and noticed that for square vs circle isolated ports with EQUAL port AREA, they both required DIFFERENT port VOLUMES.)

Any answers/help/advice would be appreciated!

EDIT: What I'm looking for is equations, or explanations of the physics behind effects of a port. But any type of inspiration/casual observations would be appreciated as well. Thanks all

PrestigeSounds
05-19-2010, 11:50 PM
first of all it wouldnt be a corner if it was 180 degrees, right?....of course a round port will differ from a slot port. two different shapes, two different formulas. length width and height affect the tuning frequency in slotted....for round: diameter and length....realistically you want the ports diameter to be the woofers radius, theres a formula to figure it out but its basically the same thing....slot ports should be atleast 2 inches in width, and the rounding off of edges inside the port will allow the air to escape the enclosure more smoothly as it flows smoother over a clean rounded corner then it would a sharp edge, resulting in cleaner output, so you heard correct...and for figuring out the tuning freq.....calculators

wenn_du_weinst
05-19-2010, 11:54 PM
no a corner is 90 degrees 180 is complete u turn