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Appendix B: Technical Info
Do The Math: Ohms, Loads, and
Such
An ohm is a unit of resistance — the more ohms,
the more resistance (or, more accurately in this case,
impedance). The more the resistance, the less the
power.
If you’re dealing with just one speaker (or cabinet)
per output, the load in ohms is usually printed on it
somewhere. That’s your load, usually 8 ohms or 4
ohms.
If you’re driving an assortment of speakers,
things can get complicated. There are two basic
ways of linking multiple loads (or speakers in this
case): series and parallel.
Since series connections are not normally used
in PA applications, we’ll concentrate on the parallel
connection. Parallel means that the positive amp
output connects to the positive terminals of all the
speakers, and the negative amp output connects
to the negative terminals of all the speakers. If one
speaker fails in a parallel configuration, the others
will still work.
Calculating parallel loads is easy, as long as
each speaker has the same value — just divide the
value by the number of speakers. For instance, four
8-ohm speakers, connected in parallel, will equal 2
ohms (8/4 = 2). If the loads are not all the same, the
formula gets a little more complicated, but nothing
that you can’t do with a simple calculator.
Z
T
=
1
1
Z
1
+
1
Z
2
+
1
Z
3
+
. . .
Using this formula, an 8-ohm speaker and a 4-
ohm speaker, connected in parallel, will equal 2.7
ohms. Remember that the Juice amplifiers require
2 ohms or greater per channel in Stereo or Mono
mode, and 4 ohms or greater in Bridge mode.