I don't have any modeling software and need to now how long to make the ports on these speakers. I'm hoping someone here will find this task easy.

Cabinet internal volume: 5.75 cu ft
Driver is an Altec 416-8C. The specs I found here: http://www.lansingheritage.org/image...6-8c/page1.jpg
Re:6.5 ohms
Fs:24.1 Hz
Qts:0.26
Qm:6.73
Qes:0.28
Vas:22.9 ft3
Vd:0.20 ft3

So with two 4" ports, how long should they be?
Thanks