PA-CP
User Guide
31
AB SPEAKER OUTPUTS
The power amplifier
outputs are available on Speakon® connectors. These are
robust locking connectors designed to handle high power
loudspeaker signals. The popular 4-pin NL4 version is used.
Two pins carry the speaker signal. Wire the speaker positive
(+) cable to pin 1+ and speaker negative (-) to pin 1- as
shown. Use heavy duty 2-core speaker cable of at least 16swg
(1.5mm
2
) rating. For long cable runs 14swg (2.5mm
2
) or
heavier is recommended. Make sure that the connections are
reliable and observe the correct polarity (s to amp +,
and speaker – to amp-). To connect the Speakon® , first align
the locating tag and press the plug in. Next, rotate the plug
clockwise until it locks in place. Audio signal will only be
present once the plug has been locked in this way.
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How to check speaker polarity
If the s and –
connections are crossed over they are referred to as wired ‘out
of phase’, or more correctly, reversed polarity. This means that
the speaker cone will be working backwards. The effect
becomes obvious when you have more than one speaker in
the system. You can carry out a simple listening test to check if
two speakers are wired with the same polarity. Route the same
mono signal to both speakers at a similar level. Pink noise is
the ideal test source as it contains all audio frequencies at
equal energy per octave. However, a music source will do.
Stand half way between the speakers. Correctly wired, they
will have a solid centre image with the sounds adding.
Reversed wired, they produce a weak centre image with
strange phasing effects due to frequency cancellation. If you
hear this then check the wiring of the amps, cables and
speaker connections.
Speaker Impedance
Live sound speakers are
typically 4 ohm or 8 ohm, although some are available at 16
ohms. Check the manufacturers specification. Usual
application is one speaker per amplifier channel. However,
there may be times when you want to wire them in series or
parallel, for example when using one amplifier channel to feed
two linked foldback wedges. Calculate the combined
impedance to check that it is no less than the amplifiers rated 4
ohm minimum. Divide the impedances when connecting in
parallel, add them when connecting in series.
Do not connect a speaker impedance less than 4
ohms. Failure to observe this may result in damage to the
amplifier.
Do not use bridged connection. Do not common or
link the speaker pins in any way.
CONSTANT POWER SWITCH
Set the rear panel
slide switch to match the impedance of the speakers used.
Use the combined impedance value if you are connecting
speakers in series or parallel. Choose the nearest match if the
value is not exactly 4 or 8 ohms. Note that no damage will be
done if the switch is left in the wrong position. However, you
may not benefit from the full capability of the amplifier.
Constant power explained
The typical amplifier is
optimised to produce full power into 4 ohms and therefore
considerably less into 8 ohms. The
PA Series
features a
unique facility that ensures you get full power output into either
4 or 8 ohm speakers. It does this by reconfiguring the power
supply for optimum current (4 ohms), or voltage (8 ohms).
8 OHMS
4 OHMS
CONSTANT POWER SWITCH
☺
No amplifier output?
Check that
the Speakon® plugs have been rotated
and locked into position.
