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how to calculate a rectangle port

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=22029
Printed Date: July 19, 2025 at 4:15 AM


Topic: how to calculate a rectangle port

Posted By: tumbrick
Subject: how to calculate a rectangle port
Date Posted: November 27, 2003 at 7:53 AM

i would like to build boxes with rectangle ports and not round ports because of the lenght



Replies:

Posted By: DYohn
Date Posted: November 27, 2003 at 9:52 AM

Here you go:

Round to Square Port Conversions:

Converting round ports into square/rectangular ports in speaker enclosures is just a matter of math. For example: If a subwoofer calls for a 6" port that is 13" long, take ˝ of the port size, in this case it would be 3. Multiple this number by itself, so 3x3=9. Now multiply the 9 x PI (3.14) and this is the total area of the square port opening or 28.26 square inches of opening. (If you notice you have just use the area of a circle formula (Pi x r (squared).)   This size opening can be built using any geometry, such as 14.13 X 2 inches, 9.42 x 3 inches, etc.

If you speaker calls for more than one port, multiply the number of ports by the number you calculated to get the combined calculated port area needed.  As for how long the square port should be, the length stays the same as the round port. The reason is because the length of the port determines the tuning of the port and the length is not effected by the conversion from round to square ports.




Posted By: pureRF
Date Posted: November 29, 2003 at 10:07 AM
you would still make it 13 inches deep correct?

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dream it, build it, fiberglass it



Posted By: DYohn
Date Posted: November 29, 2003 at 10:33 AM
Yea, in the example it would still be 13" long.  The length is not affected by the port size or shape.


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