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Discussion Starter · #1 ·
Hello,

Ok here is what I have ended up with an intenal size cabinet without bracing.

Hight 30.5"
Wide 25"
Deep 26.26"

Going with a Tempest X ported for dedicated HT what size and length port do I need to have? Also can the port be out of PVC pipe?

Thanks Rick
 

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Your internal size is 11.6 cubic feet. Deductions for the volume of the sub, bracing and port must be made. It should wind up being close to the recommended 10.6 cubic feet tuned to 17Hz with 100% poly-fill. The Tempest-X application notes can be found here.

http://www.diycable.com/main/pdf/tempest.pdf

Tuning to 17hz would require a 6 inch port being 21 inches long if the ends are not flared and 19.5inches long if the ends are flared. PVC pipe can be used for the port. A cheaper solution is to use a concrete forming tube in 6 inch diameter.
 

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The manufacturer recommends 10.6 cubic feet tuned to 17Hz. If you want to tune to 15hz, then the unflared port would be 28 inches long and a flared port would be 26.75 inches long. All lengths are figured out using WinISD. All measurments assume the net volume of the box is 10.6 cubic feet.
 

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Discussion Starter · #7 ·
Mike,

Let say I am going with the 21" long port. Can part of the port stick out of the box? I have my sub box built into a false wall and need to make sure that the port exits the wall. Does it matter if the port is totally in the box or can 17" be in the box and 4" outside of the box to give me one continues port length of the 21"?

Thanks Rick
 

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Mike, do you have your straight/flared port lengths reversed or are you not including the actual flare in the length? You consistently list the straight port as being longer than the flared port. However, everything I've read, and PSP's own calculator says the flared port, when including the flares, will be longer since some of the air in the flare mouth doesn't contribute to the port air mass.

-Brent
 

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Good eye Brent! I use WinISD for port calculations. I assumed the flared port length included the flares. I'll be using the PSP calculator from now on since it includes the flares in the length. According to the PSP calculator 10.6 cubic feet tuned to 15hz with a six inch port:
Straight Length Port required 27.56 inches
Flared Length Port required 28.56 inches
 

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Good eye Brent! I use WinISD for port calculations.
WinISD does "flanged" port length corrections for straight ports, not flared. A flange just being a fancy word for panel/wall/baffle, hence the default being "one flanged end" with the other end of the port assumed to be in free space...typical speaker/subwoofer with a straight port opening in an exterior cabinet panel. Some of Collo's PVC art would almost qualify as "no flanged ends" with both port ends free of a mounting baffle. Place the internal port opening in flush in a panel brace and you're "double flanged". Overall the effects are relatively minor and probalby not worth losing sleep over.

PSP's calculator is really only 100% reliable for the flare radius they use on their products as opposed to a DIY flare or another brand of commercial flare. Again, that's probably getting overly analytical and splitting hairs since the difference is probably in the tenths of Hertz and could easily be swamped by driver manufacturing tolerances. Collo's got some tables showing effective vs. physical length based on flare radius here.

-Brent
 
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