100V

A standard for fixed audio installations

100V systems are referred to as “constant-voltage” distributed audio systems. The constant voltage system is the most economical way to install a multi-speaker sound reinforcement system.

The term “100V system” relates to the maximum output voltage of the amplifier. 100V is the usual voltage in Europe, 70V in the United States. A higher voltage up to 200V can also be used for very long cable runs and higher power requirements.

To generate this high voltage, the amplifier is equipped with a step-up transformer, which transforms the regular output voltage, in the 15 to 30 Volts range, up to the necessary 100V (or 70V respectively).

A 100V-loudspeaker is equipped with a step-down transformer with a relatively high input impedance. The transformer’s output impedance matches the included chassis’ impedance (usually 8 Ohms). The ratio between the low output impedance of the amplifier and the transformer input impedance of the individual speaker is usually between 1:100 and 1:1000.

Directly proportional to the maximum output power of the amplifier, each 100V amplifier matches a certain minimum impedance than can be connected to this output. It does not matter how the connected impedance is achieved. A large number of smaller speakers (with high input impedance at their step-down transformers) or a small number of larger speakers (with lower impedance) can be connected to the 100V line. Any combination of different 100V-loudspeakers is possible, as long as the total impedance of the 100V line doesn’t fall below the minimum impedance of the amplifier’s output.

The real output voltage of the amplifier during the transmission of music or speech is mostly far less that the maximum 100V, proportionally representing the input signal. The term “100V” defines the maximum voltage in the system in the same way as the term +6 dB defines the maximum level for a line signal.

• Infobox
  • Bittner Audio
    September 2011