Speaker ports and impedance

there is generally a saddle shape in the impedance curve where the low point between peaks is usually the port frequency.

I'm not a speaker designer but I *think* I understood this correctly:

As Thinkat mentioned there are 2 peaks for speakers with reflex ports. One peak is the resonance of the port, the other peak is the resonance of the woofer. The minima in between is the tuned freq. of the port.

the impedance has NO relationship to cabinet design. It is a function of driver impedance and wether those drivers are wired in series or parallel

Yes, if you mean a speaker driver. A driver's impedance, by definition, is a change in resistance at different frequencies at constant voltage. While impedance depends on electrical factors, the driver's surrounding also affects the impedance.

A driver in free air will be at its highest impedance at its resonance frequency. When it is in an enclosure, the resonance frequency shifts to a different value, which depends on the enclosure size. The new rf will have a different impedance, which is much lower than in free air.

A ported type enclosure will cause the driver to have its lowest impedance at resonance - whereas in a sealed box the same driver will have its highest impedance.