Tannoy CMS50, User Manual

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4. Polarity Checking
It is most important to check the polarity of the wiring. A simple method of doing this
without a pulse based polarity checker is as follows: Connect two wires to the +
ve
and
-
ve
terminals of a PP3 battery. Apply the wire which is connected to the +
ve
terminal of
the battery to the speaker cable leg which you believe to be connected to the red
speaker terminal, and likewise the -
ve
leg of the battery to the black speaker terminal.
If you have wired it correctly the LF drive unit will move forward, indicating the wiring is
correct. All that remains now is to connect the +
ve
speaker lead to the +
ve
terminal on
the amplifier and the -
ve
lead to the -
ve
terminal on the amplifier. If, however, the LF
driver moves backwards, the input connections need to be inverted.
If problems are encountered, inspect the cable wiring in the first instance. It should
also be noted that different amplifier manufacturers utilise different pin configurations
and polarity conventions. If you are using amplifiers from more than one
manufacturer, check the polarity at the amplifiers as well as the loudspeakers.
5. Amplification & Power Selection
As with all professional loudspeaker systems, the power handling is a function of
voice coil thermal capacity. Care should be taken to avoid running the amplifier into
clip (clipping is the end result of overdriving any amplifier). Damage to the
loudspeaker will be sustained if the amplifier is driven into clip for any extended period
of time. Headroom of at least 3 dB should be allowed. When evaluating an amplifier, it
is important to take into account its behaviour under low impedance load conditions. A
loudspeaker system is highly reactive and with transient signals it can require more
current than the nominal impedance would indicate.
Generally higher power amplifier running free of distortion will do less damage to the
loudspeaker than a lower power amplifier continually clipping. It is also worth
remembering that a high powered amplifier running at less than 90% of output power
generally sounds a lot better than a lower power amplifier running at 100%. An
amplifier with insufficient drive capability will not allow the full performance of the
loudspeaker to be realised.
It is important when using different manufacturers amplifiers in a single installation
that they have very closely matched gains, the variation should be less than +/-0.5dB.
This precaution is important to the overall system balance when only a single
compressor/limiter or active crossover is being used with multiple cabinets; it is
therefore recommended that the same amplifiers be used throughout.
6. Voltage & Power Selection (CMS50T ICT)
When using 70.7V or 100V distributed-line systems, the transformer can be tapped at
30W, 15W and 7.5W, with an extra 3.75W tapping for 70.7V line systems. The taps
are selected via a rotary switch, as shown in Figure 4a, and is located on the front of
the unit, behind the grille, Figure 4b.
When the relevant voltage tappings have been selected add the individual power in
Watts at all speakers and select and amplifier with a rating equal to or exceeding the
total power in Watts. All of the transformer primaries should be connected in parallel
to the output of this amplifier. If for example, you select the 7.5-watt transformer tap, it
means that at full rated amplifier output the speaker will receive the full 7.5 watts. If
the amplifier gain is reduced each speaker will receive a proportional amount of
power, maintaining the overall system balance.
It is recommended that a generous power safety margin (3dB of headroom) be left so
that the system does not have to operate continuously at its full rated output power.