I have put on sale too a set of Goertz Python cables, 2.6 meters in length. These have a very peculiar geometry: there are 4 flat copper strips, intimately put one on top of the other, with a very thin coat of high grade (teflon) dielectric between, twisted along its length at a rate of aproximately 1,5 turns per feet, and then covered by other dielectric to make it cylindric. It has the same electrical properties of the fleet Goetz MI2.
What is this geometry for?. Typically, you are feeding a loudspeaker from an amplifier that has an output impedance below 1 ohm, and in many cases much lower than that. It is then used to feed a loudspeaker that has an average impedance between 4 and 8 ohms.
Now, the typical speaker cable characteristic impedance is between 50 and 200 ohm. This implies huge mismatches, which in turn cause signal reflections at the cable ends, which imply rounding of waveforms and worse treble performance. On the other hand a low characteristic impedance is better to maximize the power transfer - something that is required with high power amplifiers and demanding speakers.
The geometry dictates the characteristic impedance, through the relation between inductance and capacitance, which in turn gives the characteristic impedance: Z_0 = sqrt(L/C). As this cable has very low inductance (both cables are very much together, with very small area between them) and high capacitance (it looks like an unrolled capacitor). As a consequence, it is the best cable I have used so far. I am using it with a Devialet D200 amplifier, driving a couple of Gallo Stradas loudspeaker.
I have not posted pictures yet, since I still have them connected to my amp and speakers.
Why am I selling it? Because I have a roll of Goertz MI2 flat cable, which I have used to produce a shorter run of speaker cable that I have subsequently sent to deep cryogenic treatment, in a company specialized in doing so for razing car applications, but that is also used by a couple of audio companies to treat their cables. Stay tuned to hear about its performance when they come back!