What amplifier should you use?
There are several things you should keep in mind when selecting
an amplifier.
First, you need an amplifier with enough output power. Even if
you are not planning to run your system very loud, an amplifier
needs to have enough power so that the dynamics of speech and
music will not cause “clipping.” A solid-state amplifier that is
pushed beyond its output power capability will distort badly
(clip signals). Not only does this sound bad, but the effect on a
low frequency speaker or mid- or high-frequency driver is
similar to hitting the cone or diaphragm with a hammer. Because
of this, too small an amplifier can be more damaging to speakers
than one that seemingly has too much power. Peaks in speech
or music signals can easily exceed the average power levels by
a factor of ten. If your amplifier is not big enough, these peaks
become clipped and distorted.
The impedance or speaker load the amplifier "sees" is very
important. If the amplifier is not rated for the impedance load,
the internal protection circuitry of the amplifier may prevent
full-power output. Additionally, if the amplifier is not of high-
quality or does not have good internal protection against over-
load, the amplifier may be damaged - or the speakers connected
to the amplifier may be damaged.
When you connect two speakers together so that both speakers
work off one amplifier channel, you are connecting them in
parallel. Two speakers connected in parallel do not have the
same impedance as one speaker. Knowing the combined imped-
ance is very important when selecting an amplifier. You need to
select an amplifier that will operate at the combined impedance
and produce enough power for both speakers. Check to make
sure the amplifier you wish to use will match this requirement.
To figure out how much power you need, just add the program
power of the two speakers. The drawing below shows the
combined impedance for two 4 ohm and two 8 ohm speakers
connected in parallel and their combined power requirements.
4
