Port calculation

[dbrown23 1]

I build ported boxes on a pretty regular basis using the re enclosure calculator and they are always slot ports but i want to build a different box that uses a square port that isnt a slot port but I dont know the formulat to calulate the port area or convert the round port to a square port can anyone please give me some insite on how to do this please thanks alot .

[B-Rich 0]

I use this calculator.

http://www.carstereo.com/help/Articles.cfm?id=31

[NB50 206]

http://mobile.jlaudio.com/support_pages.php?page_id=165