building ported boxes

I build alot of boxes and many times i have to build boxes without specs. I mostly build ported boxes. Does the size of a ported box matter? If i have to build a box without specs is there any general rule or advice that i could use to build a box which will give a good performance? I figured since in a ported box the volume is used to tune the box the size doesn't really matter. Am i wrong and why?

To properly build a vented (ported) box you need to take EVERYTHING into account)

Air space, port volume, and the parameters of the sub. (not to mention materials, sealing correctly etc.)

Most manufacturers these days will give you all that info for free, or it may be included with the sub.

If you wish to tune to a different fs for whatever reason you can experiment with port sizes by ear.

If you have access to an spl meter and a tone generator or good "system tuning cd" with accurate test tones, it can be pretty percise.

As far as the mathematics involved it is quite extensive so I won't leave it here. There are sources online but I would buy an enclosure design program for windows.

I don't want to list any specific as I personally know some of the people who designed and/or sell them but..

A good one will either have a database, or you can enter the specific t/s parameters of your sub, choose the enclosure type, see a graph that will predict performance, output and 3db downpoint.

I have one that in addition gives you a cut sheet (great if you don't have a good table saw, pay a few bucks for someone to cut the sheets saving you time) and a 3d view of the enclosure that you can "spin" Pretty cool.

Some are not cheap. some may be free if you surf around. depends on how many boxes you build and how extreme you get to warrant the costs.

Hope I helped.

^^Every sentence is a paragraph now, eh? 

prodigal, since you build a lot of these enclosures, your experience alone will account for a lot.  You just can't help but to make mental notes about how a box/sub combination comes out with your system of "winging it".  But it's really time now, since you asked, to take the next step in enclosure design.  Read my sticky on WinISD and use the links it provides to get yourself a copy of the program.  With your experience and the knowledge you've already accumulated, it wouldn't take long at all to get to the point where you can use the software successfully to build just the right box for the sub in question.

But to answer your questions more directly:  No, there is no one-size-fits-all standard.  And it really should be a rare case that specs, even just the basic Fs, Qts and Vas, couldn't be found somewhere.

Yeah Stevdart, I do seem to take things to "extremes" lol

I am not really doing it intentionally. Force of habit. I use MS word alot,  I am used to pressing return and it goes to the next line.

Here it skips automatically to paragraph spacing..I just can't win. But this has to be better then when I used no paragraphs at all.

And I agree with stevdarts reply 100%. As a matter of fact someone gave me a sub I never heard of yesterday. I entered the brand name and model number on google and found out more then I needed to know in seconds. However, I needed to do the same thing with a discontinued amp and had to pay 5 dollars on paypal to some manual finding service. Well worth it as there were over a million links with that model number and the first  dozen had no usable info. Major time saver and for all I know none of the links had the specs I needed posted for free.I was sent a link to all the info I needed via email in about an hour.

Before the internet you would of had to set up a mini lab to determine the ts parameters of an unknown sub and use equasions to determine enclosure size and type. I actually have a VHS tape somewhere buried in my closet that shows how to do just that. What a pain in the butt.

Take care.

In agreement with nouse all the way.

Use a program. I can post the formulas involved to calutate port volume, conversions to slot port, or any shape port for that matter.

But the math involved to do this is mind boggling to say the least. many decimal places and one little mistake and everything goes out the window. So basically you will find yourself double and triple checking to avoid the wrong specs., it's a nightmare.

I remember years ago when I was at RTTI they gave me a chart, I believe it was called a "nanogram" but don't hold me to that.

Basically, it gave you a rough idea on port size in relation to air space and the F3 you desired. However, it did not take t/s parameters into account. So what I would do is use a "telescoping" device I made and use a test tone and spl meter to determine the port length. You could also use a "flexport" if the physical size of the enclosure is too small to house the lenght of a round port.

As far as slot porting one of the other advantages is that you can effectivly "maze" it to achieve the desired length needed for your application.

Take care all.