"Rob" wrote in message
...

Just out of curiosity, why has it always been the case that four wires run
to speakers, when three would do (link the ground on a stereo pair)?

The alternative would be a 3-wire system. The common wire would have to have
twice the copper per unit length. In general, the savings in terms of copper
and wire would be negligible.

If you had a typical bookshelf system with the amp or receiver in the
middle, and a speaker on each side, I can see where a 3-wire system would
make the wires longer, than separate grounds for each channel.