Cabinet Tuning

[scary]

What is the procedure for calculating port dimensions to tune a cabinet for a certain frequency? I am building a pair of Cinema 893 towers that were designed for a sealed enclosure. I understand that a 70 liter box tuned to 35Hz works very well, so that got me interested in the process. Is there is a simple formula, or do I need cabinet design software?

Thanks
Scary

[DigitalMaven]

What is the procedure for calculating port dimensions to tune a cabinet for a certain frequency? I am building a pair of Cinema 893 towers that were designed for a sealed enclosure. I understand that a 70 liter box tuned to 35Hz works very well, so that got me interested in the process. Is there is a simple formula, or do I need cabinet design software?

Thanks
Scary

There are online port calculators...here's one of them

http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm

[---k---]

Here is the page for Unibox software. You use it with Excel. Works very well and straight forward to me.

http://audio.claub.net/software/kougaard/ubmodel.html

Jeff Bagby also has an excellent program that runs inside excel to model woofers. It will also do boundry loading and such:

http://audio.claub.net/software/jbabgy/jbagby.html

Finally, a LOT of people like to use WinISD. I don't get WinISD. You have to enter the driver parameters in a specific order and have accurate/correct driver parameters or it just doesn't work. Other things too. I like the other two programs better. But, a lot of people use WinISD. If you don't have Excel with the math solver add on, this might be the way to go.

http://www.linearteam.dk/?pageid=winisd

Give those a try. If you post screen shots of your input and such, we can help walk you through it.

[Audion]

Yes, I think that WinISD is very popular because the results that you get aren't overly complex and are rather easy to understand.
It doesn't require you to put in as many parameters as some other programs, so some people like that convenience.
However, the other commenter is right in that you have to get all of the parameters input properly, or you have to start over.
Also, you only get four graphs of results, and those don't tell you some of what you need to know.

One of the more important things that you'll need to know when designing an enclosure is cone excursion (how far the cone can move without distortion or even bottoming out).
Many small woofers and midbasses will play low frequencies according to the gain/SPL graph.
But, you may find that the speaker cannot play very loudly at all because you'll run out of cone excursion even at low SPL levels in some cases (because of the demands placed on it to play at very low frequencies).
So, it's nice to have a program that lets you input a power level, check the SPL level and also verify what the cone excursion is at those levels.

When using these programs, be sure to use the correct units when entering data, too.