Adrian C wrote:
Woody wrote:

Maplin JK30H @ £3 each. You only need to switch the live side of the
speaker feed - the ground sides can stay connected in parallel
throughout.


Though the OP should check (with a DVM) before doing this, that that
negative speaker outlets of *both* amplifiers concerned are actually
internally connected to ground. Ye don't want to upset a
bridge-tied-load amp, if ye have one of those in your setup ...

http://en.wikipedia.org/wiki/Bridge-tied_load


Thanks both, and Woody in particular for those links.

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)?