After Wayne posted the Hemlholtz formula and the recent questions
I've seen go by about ports for this box or that, I wrote a perl
script that will calculate (if I didn't screw it up) a port for
a given box volume and desired resonant frequency. Its non-GIU
and runs on *nix systems and probably Windows if you have a perl
for that. Example output:

./portcalc.pl 32 3.5
Freq of port: 32.952 Hz
Port diameter: 4.000 in
Port length: 5.125 in

I suppose it could be attached to a web page form also...