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Old 30th December 2001, 01:07 PM   #1
diyAudio Member
Join Date: Oct 2001
Location: UW Stevens Point Campus
Question Bass reflex enclosure

Hello all,
I am building a subwoofer and I am trying to figure out what port diameter to use. The factory specs for the sub say that I should use a 2.5 inch diameter port tube, but this is only for one port. My question is wheather I can use 2 ports of 2 inch diameter? Will I have problem with port turbulence because of the smaller size?

I don't know what I would do if I didn't have this forum to answer my questions.

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Old 30th December 2001, 07:13 PM   #2
Super is offline Super  United States
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I would say yes. Theres a good chance that you'll get huffing noises coming from ports that small in diameter. Your better off going with the larger port.
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Old 30th December 2001, 10:51 PM   #3
Wizard of Kelts
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Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
The (2) 2" tubes will have to be longer than the one 2.5" port.

Just for the heck of it, what size enclosure are you planning, what tuning frequency, and which driver? I wouldn't use (2) 2" ports for anything over a 10 inch driver.
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Old 4th January 2002, 09:58 PM   #4
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I plan to use a 10" sub tuned to 32 hz in 1.2cu ft enclosure. The port length will be 12in using two ports.

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Old 4th January 2002, 10:59 PM   #5
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Join Date: Feb 2001
Location: Columbia, SC
Bear in mind that the longer the port is, the more it tends to achieve a life of its own. The air acquires enough momentum that it becomes difficult to stop once it begins moving. As such, you get a lag between the port response and the driver; a distortion mechanism, in other words.
Better to use a short port...but then you end up with it being narrow in cross section, hence more likely to make noise.
Your choice--just be aware of the tradeoffs.

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Old 5th January 2002, 01:36 AM   #6
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Join Date: Dec 2001
If you REALLY want to know about the port size, you could download WinISD and enter in your speaker parameters if you know them. It has a utility that determines the mach number (air speed velocity) in the port for a given size. It can give you and idea if your port is too small or not.

Just a suggestion. Good luck!
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