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Advanced Topics
Advanced Discussions
Speaker & Wiring Impedance
Speaker impedance often is and should be straight for
-
ward. Speakers, like other resistors, wired in parallel “show”
lower values than the individual components. In case you
have forgotten, there is an example here for calculating
speakers wired in parallel.
Often the real world is more complicated than the theory
and for speakers this is the case. An eight ohm speaker is not
eight ohms at all frequencies. Plus passive crossover networks
add their own changing conditions. What you should be
aware of and sensitive to are speakers that have significant
dips from “nominal” values in portions of their frequency
range and speakers that are rated at unusual impedances, for
example 3.5 ohms. The Director is tolerant of lower imped
-
ance loads, however, all good designs use some margin of
error.
Your choice of speaker wire gauge and the length of the
runs also affects the speaker impedance load presented to
the amplifiers. As you can see in this table below, even fairly
short speaker runs can have significant resistance if you use a
smaller wire gauge. This can be a benefit if you are parallel
-
ing lots of speakers. The wire itself acts as an impedance lim
-
iter, since the amplifier cannot see a speaker load lower than
the resistance of the wire. The downside of this resistance in
the wire is that you waste some part of the total power avail
-
able to the speakers.
25’
50’
100’
250’
500’
24 GA
1.3
Ω
2.6
Ω
5.1
Ω
12.8
Ω
25.7
Ω
22 GA
0.8
Ω
1.6
Ω
3.24
Ω
8.1
Ω
16.0
Ω
20 GA
0.5
Ω
1.0
Ω
2.0
Ω
5.0
Ω
10.1
Ω
18 GA
0.3
Ω
0.6
Ω
1.28
Ω
3.2
Ω
6.4
Ω
16 GA
0.2
Ω
.4
Ω
0.8
Ω
2.0
Ω
4.0
Ω
14 GA
0.1
Ω
.25
Ω
0.5
Ω
1.26
Ω
2.5
Ω
12 GA
0.08
Ω
.16
Ω
0.32
Ω
0.8
Ω
1.6
Ω
Speaker Wire Resistance
Wire Gauge versus Run Length
Speaker connection wiring
Calculating Impedance
For three 8 ohm speakers wired in
parallel (pluses connected to pluses)
the impedance is
1/8 + 1/8 + 1/8 = 3/8
Then take the inverse or
8/3 = 2.66 ohms
