We only care about the signal when it’s traveling toward the speakers. Two wires are involved for a AC circuit. When the signal is going toward the speaker on one wire it’s going in the direction away from the speaker on the other wire. We can ignore the signal when it’s going away from the direction of the speakers, since that doesn’t affect the sound. The same logic applies to both + and - wires. That’s why wire and fuses are directional in AC circuits, I.e., they sound better in one direction than the other.

Eggs ackley! The electrons flowing (current) toward the voice coil in each wire + and - is what produces the sound. One wire + moves the diaphragm out and one - moves it back in. That’s why direction of the + and - wires is important. Wires are not symmetrical, so they favor one direction over the other sonically. The best direction of the speaker cables should be controlled from the very beginning of manufacture so that the best sounding direction of both + and - wires is pointed toward the voice coil. As I said we can ignore the current traveling away from the voice coil on both + and - wires.