12.23 Why are speakers labeled + and - or Red and Black?
Description
This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
12.23 Why are speakers labeled + and - or Red and Black?
Speakers make sound my pushing and pulling at the air with the
motion of their cones or diaphrams. When a positive voltage is
applied to the red or "+" terminal on a standard speaker, it
causes the cone to move outwards and push air.
If you have two speakers side by side and one cone moves out
while the other moves in, air will move between the two
speakers but not much sound will escape. The two cone motions
will cancel eachother. So when you have two speakers close
together, it is vital that they be wired "in phase", with
positive voltage going to the "+" terminal of both speakers at
once. You can do this by wiring the speakers in parallel or
series. In almost all cases, parallel is preferred. If wiring
speakers in parallel, the "+" output should go to both "+"
terminals and the "-" output should go to both "-" terminals.
If wiring speakers in series, the "+" output should go to one
"+" terminal. The other terminal ("-") should go to the second
speaker "+" terminal. The other terminal ("-") of the second
speaker should go to the "-" output. See the FAQ section on
amplifiers for more on series and parallel connections.
Even if speakers are not side by side, it is good to wire them
in phase. For very low frequencies, speakers 15 feet apart
are effectively close together and the same cancellation
effects mentioned above apply. For higher frequencies, the
effects are more subtle but still important. One symptom of
wiring speakers wrong is that the stereo effect is imperfect.
Instead of a main sound seeming to come from the center, the
sound of the lead vocalist, for example, may seem to come from
outside the room. Other odd effects are also possible.
So when in doubt, always wire "+" to "+".
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