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Multi-Way Conventional loudspeakers with crossovers

Port Length Trade Offs
Port Length Trade Offs
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Old 29th July 2003, 06:06 PM   #1
jbandpc is offline jbandpc  United States
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Join Date: Mar 2003
Location: Franklin, TN
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, 06:19 PM   #2
Eul is offline Eul  Netherlands
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Join Date: Jul 2003
Location: Netherlands
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, 07:08 PM   #3
kelticwizard is offline kelticwizard  United States
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Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Port Length Trade Offs
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.
"A friend will help you move. A really good friend will help you move a body."
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