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Old 18th November 2005, 12:10 PM   #1
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Default speaker box design physics question

Hey all,
i was just building my speaker box, (See attached image) i stumbled a across a problem, see the ports where the wrong diameter. so heres the question
If the port was meant to be 7.5cm diameter and 27.5cm long, and i have 8.5cm diameter pipe, how long should the pipe be to be equivalent?
as in the relationshipt between diameter, wavelength and length of the pipe.
i thought i should make it shorter, so i tried that, works OK. But id like it to be better.
thanks all again
daniel
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Old 18th November 2005, 01:11 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

as the port is bigger in crossectional area it needs to be longer.

Its a square relationship, doubling the diameter of a port means
its length needs to be four times as long for the same frequency.

Which gives an answer of 35cm long.

/Sreten.
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Old 18th November 2005, 02:36 PM   #3
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thanks man , cheers, now i have to put a right angle in the pipe so it'll fit!
daniel
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Old 18th November 2005, 05:02 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

don't go the right angle route - it won't work well.

Line the current shortened port with say a stiffish foam to reduce
the effective diameter to nearer say 6.5cm, length then = 21cm.

/sreten.
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Old 19th November 2005, 12:07 AM   #5
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yeah i was originally goin to use smaller pipe, 6.5cm, dam it lol. But yeah i think ill have to go the right angle way cause i can use foam without it looking shocking
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