Sure, it's approx. 0.002Ohms per meter (3ft) on a 2x2.5mm2 diameter good quality speaker cable. Compared to the speaker load and the output impedance of a solid state power amp, there is not much influence by the cable. The bigger influence goes by the fact when speakers in a 4x12 cabinet are wired in series instead of parallel. This changes the impedance curve dramatically and influences the saturation behavior of a tube amp - and you'll notice a slight difference when checking the impedance curve on a solid state power amp (with high damping factor). I guess this is the main reason for the difference of your Wizard vs. D120 plots.
Which brings me to another point: Cliff, please check out ARTA LABs signal analysis software.....
ARTA Software - gives you much better frequency plots you can share with all the tech geeks out there. It's highly recommended - and not expensive.....
