# HT DIY sub- port question



## bumpnzx3 (Apr 6, 2007)

I am going to build a pair of 12" Fi X series for my HT.

I spent some time modeling them and talking with Scott of Fi. I came up with each sub having 4.4cu tuned to 20hz having 2- 4" ports and a port length of about 35.5". Now here comes the question of all questions......keep in mind this is my first venture into any kind of ported setup- car audio or HT- until now, all I ever cared to have was sealed, so I never read up on ported setups.....does that port length of 35.5" mean each port will need to be that long, or I will have 35.5" of total port length- meaning I would have a pair of 17.75" ports?


Also- when designing my enclosure- I know I have to account for the airspace the ports will take up. When I am calc'ing it- can I just calc 4" ports or should I measure the O.D. of the PVC pipe? I know sealed boxes aren't real picky- I just didn't know how picky ported enclosures were.


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## Oliver (Jun 25, 2007)

See what these guys have to say  

http://mobile.jlaudio.com/support_pages.php?page_id=165

http://mobile.jlaudio.com/support_pages.php?page_id=164


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## ClinesSelect (Apr 16, 2006)

Two 4" ports each 35.5" in length in a 4.43 CF (net) enclosure would tune the enclosure to 20hz. Gross would be 5.34 CF and the displacement of the ports would be 0.65 CF assuming my math is correct.


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## bumpnzx3 (Apr 6, 2007)

Good deal- I was thinking 2x 35.5" long- but I thought I would check first.

Assuming 4" OD (I know- I will have to measure the real OD and re-calc), I came up with .51cu port displacement plus another .10cu from the sub.


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## ClinesSelect (Apr 16, 2006)

The section of 4" PVC I have sitting here measured out at 4.75" OD but the wall thickness is far more thick than what is necessary. If you used something along the lines of a Precision Port, the displacement would be closer to the number you obtained as the walls are quite a bit thinner thus reducing the displacement.


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