A Matter of Materials
There is much hay made by marketing people about Teflon being the best insulator because it makes the cable “faster” due to the low dielectric constant. However, in terms of transmission speed of the signal from one end of the wire to the other, it doesn’t make much sense.
Nevertheless, the dielectric constant is an essential factor in the design of a capacitor. A higher dielectric constant would be used to increase the capacitance of a particular design. Hence, when we design a cable to minimize inductance and capacitance, using an insulator of lower dielectric constant decreases the capacitance of a particular design. All things being equal, with the same distance between the two wires to keep inductance constant, going from a PVC insulator to a Teflon insulator would halve the capacitance of the cable.
A second reason to use Teflon is that it has the lowest dielectric soakage. This is the capacitor’s propensity to regain charge after a short circuit. Intuitively, the dielectric soakage is also a form of storage of energy, hence, looking for a material that would not do this would result in a cable that would have better micro-dynamic detail.
Which Solder or No Solder?
Much has been said about the “sound” of solder. Indeed, every solder we have used has sounded subtly different. There are arguments that the interface between wire and the solder and the connector can act as a diode junction.
To completely eliminate any possible effect of “diode rectification” caused by solder, the connectors are cold-welded to the wire.
In the picture below, copper wire and an imperfect joint is used to illustrate the effect of cold-welding. The silver banana plug and copper cable has been flowed together under intense pressure to form one piece that cannot be separated.
In the Absolute Fidelity Loudspeaker Interface Cable, silver-plated wire is welded to a silver-plated banana plug resulting in an even better joint (if it can even be called a joint at all!!!) The interface is almost non-existent.
Silver, Copper, or Both?
When we took apart an old speaker cable, the strands under the insulation was practically green with corrosion. This copper oxide is an insulator, and this corrosion is likely to make the cable sound worse over time. It has been blamed for diodic rectification within the cable.
For this reason, silver-plated pure copper is used. Silver oxide is a conductor, whereas copper oxide is an insulator. Hence, even if silver oxide does form, it will not insulate the individual strands. Nevertheless, the Teflon insulator used is also much more impervious to oxygen than the commonly used PVC, and makes the cable even more resistant to corrosion.
With silver-plated copper wire and an extruded PTFE insulation, the cable is likely to last you for the rest of your life.