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CONSTANT VOLTAGE VS LOW IMPEDANCE SPEAKER
SYSTEMS
A constant voltage speaker system differs from a traditional low impedance (e.g., 8-ohm)
speaker system in that it uses a step-up transformer at the audio source to raise the
voltage and lower the current on the transmission line. At the speaker end, a step-down
transformer converts the signal back to a normal speaker level voltage. This reduces power
loss during transmission, which allows for the use of longer speaker wire runs using smaller
gauge wire.
Additionally, a constant voltage speaker system allows for the use of multiple speakers on
each channel, without the need for complicated impedance calculations and
configurations. In a constant voltage system, all speakers on a given channel are connected
in parallel and the complicated impedance calculations are replaced by simple wattage
calculations.
For example, if you want to connect two speakers per channel in a traditional 8-ohm
speaker system, you must either connect them in series, which results in an overall 16-ohm
impedance, or in parallel, which results in an overall 4-ohm impedance. In the first case, the
16-ohms impedance effectively halves the output power of your amplifier, resulting in
lower overall volume levels. In the latter case, the 4-ohms impedance means that your
amplifier will have to work harder and must be rated as stable at 4 ohms. Adding a third
speaker to the mix would complicate it further, producing either a 24-ohm or 2.67-ohm
overall impedance. Note that very few amplifiers are stable under 2-ohm loads, so that is
usually not an option.
On the other hand, with a constant voltage system, you consider first the RMS output
wattage of the amplifier. This should be reduced by 20% to compensate for insertion loss.
Each individual speaker on a given channel is set to a value such that the total does not
exceed the rated power, less 20%. You do not need to worry about making the total as
close as possible to the limit; just ensure that the total does not exceed the limit. For
example, with this 30-watt amplifier, the total load from speakers should not exceed 24
watts.
If all speakers are set to the same wattage value, they will all have the same volume level.
If one speaker is set to a higher wattage value, it will be louder than the others, while a
