Port Length Trade Offs

[jbandpc]

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?

[Eul]

What will be the difference in air speed between the two possibility’s? Can you see that?

[kelticwizard]

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.