Need help with making a port for a custom enclosure.

[the cobbler]

Hi all, I'm new to this forum and relatively new to making my own subwoofer enclosures. I'm working on one now and I'm trying to make a ported enclosure. My question is, when using an online port volume calculator, if I calculate a port width, length, height etc. for a rectangluar port opening, as long as the volume of the port remains the same can I change the shape of the port? Or does it absolutely have to be a rectangular prism?

[Andersonix]

Short answer: No, you can't change the shape (in the way you describe) without changing the tuning.

Best to ask in the 'subwoofers' area, as there's much more traffic there.

[Arty]

It is not the volume that counts.
You need a surface area to avoid port velocity noise.(a minimum area, larger is never a problem noise wise)
The lenght of the port vs the crossectional area -for a given cavity) defines the tuning freqvency.

The short answer:
if the crosscetional area remains as the original, then You can change the shape, but the lenght must allso remain the same. Still, the port tuning will be altered a bit, it may or may not be a problem in Your case.

Solution is to give it 5% longer port, mesure the tuning freqvency, and cut the port a bit, mesure again, then cut and.. you know the deal, repeat till You get the tuning You need.

If it is Your first build, try to stick with circular ports, with no corners in them.
Allso, to maintain a transfer function closer to simulated one, place the port somewhere where it is approx. 1 diameter away from the driver, and the edges of the box. Make sure the inside end of the port is not obstructed in the box, 1 diameter distance "rule" applys there too.

Not "scientific" advice, but it will save You from a large heap of intresting problems.