Port Length Trade Offs - diyAudio
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Old 29th July 2003, 07:06 PM   #1
jbandpc is offline jbandpc  United States
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Default Port Length Trade Offs

I learn well using extremes, so let me pose this question:

In a given subwoofer with a given tuning, (According to WinISD) I could put the typical port configuration and use 2 ports that are 3 inches in diameter and 10.25" inches long and end up with a vent mach of 0.15. I can also have 189 ports 2 millimeters in diameter and 3/4" long, which would be vary handy when using 3/4" material. That would have a vent mach of 0.02.

You could tune by drilling holes with your 2 millimeter drill bit, and plugging holes with gum.

What's the disadvantage to this?
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Old 29th July 2003, 07:19 PM   #2
Eul is offline Eul  Netherlands
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What will be the difference in air speed between the two possibility’s? Can you see that?
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Old 29th July 2003, 08:08 PM   #3
Wizard of Kelts
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Many small holes instead of one or two large ports was covered by A.N. Thiele, (of Thiele-Small parameters), and was labelled the "distributed vent" back in 1971 when he wrote his famous paper about vented boxes.

Thiele showed that it was a way of adding resistance to the port, something like stuffing the port with fiberglass.

If you go the Adire site and download LspCAD, you will see that making 9 holes instead of one actually changes the impedance curve considerably.

It is an interesting way to make an "aperiodic" enclousure, but not a good idea if you want full port action.
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