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Figure 6-2.—Two speakers connected in series. | Up
Construction Electrician Basic - Electricity handbook for electricians | Next
Interoffice Communication Systems |
Figure 6-4.—Matching four speakers connected in series
parallel.
When you use more than one speaker in a sound
system installation, phase the speakers to reduce the
cancellation effect, as shown in figure 6-5. Speakers out
of phase will lose up to one half of their normal volume
and operate with degraded tone quality.
For speakers facing in the same general direction,
they are in phase when their respective diaphragms
move in the same direction. This is achieved by
connecting the speakers + to + and - to -. For speakers
facing each other, they are in phase when their
respective diaphragms move in opposite Directions.
This is achieved by connecting the speakers + to - and -
to +.
Efficient transfer of power from the amplifier to the
speakers is the prime consideration in sound system
connections.
Basically, there are two methods of
connection. One connection runs from the amplifier
directly to the speaker voice coils and the other
connection runs from the amplifier to the speaker voice
coils through a transformer. You should use the first
method with short runs (not over 200 feet) of wire and a
simple speaker arrangement with low impedances. Use
the second method whenever a 15-percent power loss in
the transmission lines is noted or when wire runs are
more than 200 feet, or there is a complex speaker
arrangement. Constant voltage transformers are most
commonly used for this purpose although impedance-
matching transformers may be used. For an in-depth
look, refer to NEETS, Module 8, Introduction to
Amplifiers.
Cable
Cable installations are just as important as the other
component installations.
The cable used should be
recommended by the manufacturer and in compliance
with the NEC©. For the best results in sound, a two-
conductor shielded cable should be used.
In complex systems where the input lines are run in
close proximity to the speaker lines for long distances,
currents in the speaker lines may be picked up by the
input lines. When these stray currents are fed back to
the amplifier, cross talk and hum can be heard, or the
amplifier may oscillate. Because of this, balanced line
connections are recommended when long input and
speaker lines are run close together. A balanced line is
achieved by ungrounding the common terminal,
leaving the outputs floating. Any current that develops
on one side of the line and is offset by an equal and
opposite current on the other side is called a
BALANCED LINE. This reduces the possibility of
creating stray currents in nearby input tines.
If hum is encountered with a balanced line, it may
be necessary to run a shielded two-conductor cable to
the speakers and ground the cable at the amplifier.
Figure 6-5.—Phasing speakers facing in the same and opposite direction.
6-3
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