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I know with a ported box it is possible to tune to a certain sound. I was wondering how exactly this is done. Is it just a matter of the length of diameter of the port?

 
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you tune the frequency of the port. its dependant on box size vs port area vs port length. generally for spl purposes you tune the box to a high high frequency where you will have a peak in volume. only problem with this is that all teh other notes just sound shitty. for more of an sq setup you can tune much lower to get a flat response all the way down to your tuning frequency

 
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well, my box for the 13w7 is sealed right now, I might be moving into a truck with more space so i was thinking of making a new ported box for it. I would rather have the ported box in the civic but the JL specs make it to big to fit in there without some major work. IMO i like ported better than sealed, i want the SPL to blow everyone away while being able to understand the words of the song.

 
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so build one to jl spec size.

 
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I used this program. If you download the WinISD program from this site and input all of the specs it will help you in designing a tuned box. One trick with the site is that if you want to change a measurement type (for example meters to inches) just click on the measurement on the gray part...if that makes sense.

When the graphs first comes up it will give you the dimesions for a flat tuned box by defalt. If yoy want to tune it to a certain frequency, or you you want to have a bump in an area, it can graph it out for you.

I don't know how useful this program will be for you, but it worked for me once I got familiar with it...and it also helps that it can do isobaric graphs

edit: there are other programs that available if that one does not work for you...I am sure that some other members here can recommend some.