A cable is a mechanical system that needs burn-in. Every material subject to an electrical field creates a dipole. For non conducting material this dipole is at the atom level so that electrons are more to the side of nucleus that randomly around.
^that^ almost sounds like magnetism?
The overall charge of the material remains neutral. The electrons having a mass (very very light), moving them around amounts to a mechanical action.
A charge moving around a coil also produces a magnetic field.
The atoms in the cable insulation get organized in a dipole one way or the other, when ever there is signal traveling in the wires. As the burn in progress the atoms dipoles get organized from a random state, so that less energy is extracted from the signal and more of it reaches the next component in the chain.
What happens in an AC signal, the the polarity flips 180?
Or if I wire the speakers in reverse polarity, then do they need a long time to reform?