Porting 101

ok ok I know the title may be a little misleading, I am not offering any advice on porting boxes, I am actually asking for advice.

With all of the new stickies going up lately I think it would be pretty cool to have one all about porting, its something I have no grip on, and even when I ask or read other's questions on this site there is very little response.  Its something that can greatly limit ones ability to build a quality box, Im tired of relying on re-measuring the same old ports every time I build a box in order to get the same frequency, I want to know exactly what to do in order to adjust the frequency of ports that I make.  Hopefully someone on here knows all about this and can fill me in on what is involved with ports and tuning.

Thanks,

Jeff

Stickies suck then they die and go away.  The truth about porting is:  it takes a lot of research and time to understand the principles of tuning an enclosure.  I try, but ask me to explain it?  Uhhmmm....  One thing I know I've been looking for an answer to is this:  do you tune the enclosure to the woofer resonant frequency, or above it?  Can you tune below it?

But to your point...as soon as the box size differs, or a bigger or smaller woofer is installed, everything changes.   The port has to be adjusted to the enclosure size and the parameters of the woofer.  And, the primary type of music source that's going to be played.  Look at it cross-eyed...it changes.

I think the best thing to do is download a tuning calculator and get to know it.  Try out a lot of different box sizes, port lengths and such, and see what the output on the graph looks like.  I highly recommend WinISD.  It's free and simple enough for me to understand, but it takes some time and effort to get it down.

But sometimes when I'm doing this experimenting with the program, I get a tuning frequency below the woofer Fs and I think it must be wrong.  Or I get port lengths into the stratosphere.  So I listen a lot to some of the experts here on the forum when they say what tuning frequency they try to shoot for.  That's tried and true stuff there, so I pay attention to it.

I'm glad this topic has been brought up because i plan on building my first box very soon and i need some info on porting. I downloaded WinISD a week ago and it seems fairly simple if you can find all the speaker parameters..which i cant..i'm plannin on runnin a single sx15 in a slot ported box. It was suggested that i go with 3 cubic feet tuned to 26-28 hz. Does anyone know the parameters on that sub? RE doesn't have them on their site and i tried emailing them...they probably wont reply anytime soon...So if anyone has everything i would need for that sub to use WinISD then it would be appreciated. Also, does the size of the box have anything to do with the size of the slot port? For example if i was tuning a 2.0 cubic feet slot ported box to 28 hz..would the size of that port be the exact same as a 3.0 cubic feet slot ported box tuned to 28 hz? It would be helpful if someone could explain this and/or give me a link to a site that can explain this.

Thanks

I can give you some of the info, but not all.  First, for inputting parameters into the program, just make sure you have Qes, Qem, Vas, Fs, Xmax....I think those are the necessary ones.  The program will want to automatically figure what it can, and Qts is one of those it wants to figure.  Sometimes if you input both Qes and Qem, and also input Qts, the program will pop up a computerspeak error box....so just leave the Qts out if you have the other two.

Put what tuning frequency you want to get, and when you change box size the port size will change with it to keep the same tuning.  Any change at all in box size will change the port.  The bigger you can make the box, the more manageable it is to get a workable port size (in most cases)....but watch the graph output....you don't want a big bump in it.