Running though the Helmholtz equations to design a ported speaker enclosure gives me a whole range of port options from 9mm diameter x 25mm length through to 20mm ID and 140mm length. Is the functional effect the same in all cases?

[Edited on 31-7-2009 by smart51]

Smaller ports can cause 'whooshing' noises as the air rushes in and out of the port. Generally, use the largest diameter port that is practical.

I find that this site is quite helpful for most speaker designs.
linky

Ed.
http://www.madinventions.co.uk