how long should this port be?

HI,

I'm almost done building my speakers and I think my boxes might be tuned wrong. I used WinISD to design rectangular ports for some speakers that I'm building. The wider I make my ports using the program (keeping the same cross section area; 14.25 sq. in.) the shorter the port becomes. My questions is why does it do this? It seems to conflict with the tuturial on rectangular ports at this link http://www.jlaudio.com/tutorials/ports/index.html The webpage states that the rectangular port is the same length as the round port if you keep the cross sectionarea the same. I'm not sure what to believe. Anyone know who's right?

Also this link suggests that when using ports near a wall you should subtract a correction factor from your calculations that you make if the port wasn't part of a wall. Does WinISD already take into consideration that a rectangular port is against a wall? Any suggestions?

I already built a port 1.5 x 9.5 x 6.15" (6.9 - .75" suggested correction factor), but I haven't closed the boxes yet. It's in a 44.4 lter box tuned to 46.87 Hz. Is this right?
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
The jlaudio site is right about the cross sectional area.

WinISD has a lot of errors, some of which I have reported to the author. He doesn't seem to care enough to change or remove bad functionality. The new version, pro alpha, is better but still has calculation errors. Due to the author's attitude to my previous error report, I have no desire to help him out by telling him what they are.

If you want a decent program, use Unibox or Isaac's (f4ier) subsim. The only problem with those is that you need to know something to use them, and many people get incorrect results because of the increased functionality ;)

The correct port length to tune your 44.4 Liter box to 46.9 Hz with a 1.5x9.5" port would be 8 inches.