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In Reply to: RE: 5 ports??? What is the tuning frequency? posted by Bill Fitzmaurice on August 19, 2022 at 10:45:47
I think I understand what you meant, but if one created a box and wanted to use 2 ports, wouldn't the port need to be twice as long as a single port of same diameter and each port area would be twice the area of a single port?
Edits: 08/19/22Follow Ups:
For instance, 5 ports times 2" ID area would be equal (approx.) to a 5" dia, x 6 in. long port. Could be front baffle space limitations using a 5" dia. port (6" long).
As an example five 4 square inch ports is the same as one 20 square inch port or twenty 1 inch square ports. Judging by the OP's picture it appears that they used five smaller area ports rather than one or two larger area ports as that's what fit best on the baffle.
Edits: 08/19/22
Equal Area was said.
My brain heard equal volume.
Multiples are also selected for lower mach value.
The mach value is determined by area...repeat, area...so it doesn't matter if it's one port or a dozen, port speed will be relatively constant with constant total area. Relatively, because there's a region of high friction close to the port walls, which reduces the effective port area. That increases port velocity and lowers box tuning. Using multiple smaller ports or narrow slot ports increases the percentage of the total port area that's high friction region. When multiples are used to reduce port velocity it's via increasing area with more than one port, as opposed to one larger area port, which also requires increasing length.
Let me ask a question to help clarify your info
If I have a 2 inch square port with a port speed of X, but if use 4 ports of 1 inch square ( same area I believe ) will each of the 4 ports have a speed of X or multiple of X or a fraction of X?
The nominal velocity of a 2x2 inch versus four 1x1 inch square ports will be the same.
What I was hinting at was the combined area of the ports. It seems like the tuning frequency would be rather high.
It may look that way, but the size of the box is rather large, which impacts the tuning frequency to the same degree that the total port area does. Judging by the age of the design I doubt Fs is lower than 40Hz in any event.
Nothing is EVER what it "seems" only what is MEASURED (after simulation of course).
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