Installation manual

Community WET II - Operation and Installation Manual - Page 18
70.7V and 100V Systems
Several voltage standards have been put in place regarding so called ‘constant voltage systems.’ In the
United States, 25V, 70.7V and 100V are common. Occasionally 140V systems can be found, usually in very
large venues such as racetracks, where the need to overcome cable resistance by scaling the voltage
upwards becomes extremely important, due to the very long cable lengths from the amplifiers to the
loudspeakers. In Europe and Asia, most constant voltage systems use the 100V standard.
A WET II loudspeaker equipped with an optional autoformer supports both the 70.7V and 100V standards.
The same physical conductors are used for both voltage standards, but the power level of each tap is
different, depending on whether the voltage is 70.7V or 100V.
A 100V system will produce twice the power at a given tap, as that of a system that is operated at 70.7 volts.
This can be verified by the simple Ohm’s Law calculation E
2
/Z = W, where E is the voltage applied, Z is the
load impedance, and W is the power expressed in Watts. Assuming a load impedance of 50 ohms, we can
see that 70.7 x 70.7 / 50 = 99.97 and that 100 x 100 / 50 = 200. Therefore, when scaling up from 70.7V to
100V the power will double; when scaling down, the power will halve.
CAUTION: Be sure to carefully observe polarity when wiring your loudspeakers. If one loudspeaker is
wired with the opposite polarity from another loudspeaker, acoustic cancellation will occur. The result
will be less power output than if only one loudspeaker were used by itself.