Port length and tuning frequency

[neonblack 10+ year member]

I know that port size/length and tuning frequency are dependent on each other but what is physically taking place inside an enclosure when you use a port? The port effects the pressure (and behavior of the subwoofer) inside the enclosure? Doesn't port shape (round, rectangular, etc.) and location also have an effect on tuning frequency and performance of the subwoofer? I would think that enclosure shape also has an effect on sub performance. I've taken plenty of math and physics but I don't know much about acoustics.

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[StickyFingaz 10+ year member]

The air inside the port acts as a piston being driven by the subwoofer, in effect acting as additional cone area. If the port is too big the subwoofer will perform like it is a sealed box with a big hole, most likely causing over excursion and eventual failure of the driver. Location shouldn't change the tuning frequency, but it would have an effect on the ports performance. Ideally air should be able to enter and exit the port with the least amount of turbulence.

 

[neonblack 10+ year member]

Thanks for the explanation. I understand it better. A lot of ports are located in turbulent locations (ie. home stereo speakers like tower speakers). The only location which has the least turbulence is directly behind the driver where the wave has not been disturbed, correct?