5
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.
For example, if using a 100-watt amplifier, the total load
from speakers should not exceed 80 watts.
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.
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
speaker set to a smaller value will be quieter than the others.
This allows you to compensate for the environment in which
the speaker is placed. For example, a speaker placed outside
would need to be louder than a speaker placed in a small
room.
SPEAKER WIRING
Most constant voltage speaker installations will consist of
multiple speakers per channel, with all speakers connected
in parallel, as shown in the diagrams below.
To wire speakers in parallel, connect the first speaker to the
amplifier as normal. Connect the positive terminal on the
first speaker to the positive terminal of the second speaker,
and the negative terminal on the first speaker to the