Wayne Parham Messages: 18754 Registered: January 2001
Illuminati (33rd Degree)
Check out the Helmholtz formula below. You can tune to the same frequency using different port sizes. As port area is increased, port length also has to be increased to tune to the same frequency. When in doubt, measure impedance and look for the minimum between the peaks.
Here's a little BASIC program that will calculate the formulas for you: