Stereo equipment is DC, which is a directional current
Of all the stuff written here, this I follow the least, but there are plenty of other contenders!
DC refers to Direct Current, that is to say it only flows in one direction. Sure, our equipment runs internally on rectified and smoothed DC derived from external AC, but our equipment is fed and delivers AC signals.
AC or Alternating Current flows for a short period in one direction, then reverses direction repeatedly. Analog audio signals are AC, and current flows as a result, in speaker and interconnect cables alike. Current is the net movement of electrons in a direction.
In a metal conductor, a cloud of free electrons exists, with each electron randomly whizzing about. When we measure a current, it is because there is slightly more movement of electrons in the other direction - and it is called electron drift and is very slow. Often you could run faster.
That does not mean the signal is slow! Newton's balls illustrate this, because a ball impacting on end of a line of balls causes the ball on the far end to fly off, even though the net movement (flow) of the row of balls in the middle is almost imperceptible.
Solid metals form crystal lattices, where all the atoms line up in rows. The atoms vibrate with thermal energy. Sometimes an atom is missing (called a vacancy) and sometimes a part row is missing, forming a slip line. Big bits of metal are formed from many crystals, known as grains, and where these grains join, there is a disorganised mess. Impurities tend to migrate to these grain boundaries. Current flow is impeded by such messes.
When a metal is plastically deformed (permanent shape change) bigger crystals break up into smaller ones. This happens when a wire is drawn, a sheet is rolled, or a shape is forged. The grains tend to become orientated. The grain structure along a wire will show elongated crystals, compared with the structure across the wire. It will have lower resistance along the wire than across it.
If the metal is heated sufficiently, grains tend to coalesce again to form bigger structures in a process known as annealing but this rarely happens at normal temperatures (lead does creep very, very slowly because its vacancies can move at room temperature).
Given that speaker and interconnect wires generally carry currents that alternate in direction, I would expect any effect along the length of the wire in one direction to be exactly the same in the other direction along the wire. The only directional effect is from shielding.
