In article , Rob
wrote:


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 two speakers will normally be placed well apart, so if using just one
'ground' lead you'd have to run it to one of them, and then to the other.
This would mean that the lengths of ground cables for each differ.

A) The main result would be a difference in cable resistance for the two
speakers, possibly causing an imbalanced change in frequency response.

B) Unless you ran both 'live' cables along the same path, one speaker
connection would have a very wide spacing between its live and ground. The
result would be very high inductance. Again possibly producing a
significant difference in frequency response for the two channels. Might
also make RF pickup a problem.

C) If you *did* run the 'live' wires together then this would mean the
'live' to one speaker would be longer than the other - making effect (A)
worse.

D) Even if you used a symmetric 'Y' shape of cable for the ground to try
and avoid some of the above, using a common ground connection increases the
level of crosstalk as the common resistance will cross-connect the signals
to some extent. Aso, (C) would increase EM crosstalk.

Should I go on?... :-)

Basically, it isn't a good idea to try and skimp by using one ground cable
for the two speakers. Probably saves almost no money, and can cause all
sorts of problems. Although the problems may be small enough that it can be
done if there is no easy alternative.

Best to use distinct cables for the two speakers, have them of similar
lengths, and run them well clear of each other.

Slainte,

Jim

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