TOA a-503a Supplementary Manual
11
TOA Electronics Amplifier Guide
Chapter 3: Amplifier/Speaker Matching
Interfacing between the amplifier and speakers is commonly done in one of two ways. Small systems
with one or two speakers will typically use a direct connection between the speakers and the amp.
This is sometimes called low impedance operation, because the load impedance ranges from 4 to 16
ohms nominal. Systems with more than 2 speakers usually use transformers at the amp and at each
speaker to simplify impedance matching and reduce line loss. These systems are commonly called
distributed line systems, 70.7 volt (or 25 volt) systems, or constant voltage systems. In both cases, speakers
should be wired in parallel (plus to plus and minus to minus).
with one or two speakers will typically use a direct connection between the speakers and the amp.
This is sometimes called low impedance operation, because the load impedance ranges from 4 to 16
ohms nominal. Systems with more than 2 speakers usually use transformers at the amp and at each
speaker to simplify impedance matching and reduce line loss. These systems are commonly called
distributed line systems, 70.7 volt (or 25 volt) systems, or constant voltage systems. In both cases, speakers
should be wired in parallel (plus to plus and minus to minus).
Low Impedance Systems
When matching amplifiers with speakers, there are a couple of important rules to remember. First, low
impedance amplifier outputs are described in terms of the recommended load impedance, i.e.“4 ohm
output” or “8 ohm output” (the actual source impedance of a power amplifier output is seldom spec-
ified but is typically less than one ohm). Second: With rare exceptions, when using more than one
speaker, the speakers should be wired in parallel.
impedance amplifier outputs are described in terms of the recommended load impedance, i.e.“4 ohm
output” or “8 ohm output” (the actual source impedance of a power amplifier output is seldom spec-
ified but is typically less than one ohm). Second: With rare exceptions, when using more than one
speaker, the speakers should be wired in parallel.
Parallel wiring always results in a lower load impedance than the individual rating of each speaker. For
example, two 8 ohm speakers in parallel results in a 4 ohm load. Two 16 ohm speakers in parallel
results in an 8 ohm load. The general-purpose equation for calculating the load of multiple speakers
in parallel is shown in Figure 7. But as the above two examples illustrate, you will find that when all
the speakers have the same impedance, the total load will be equal to the rated impedance divided by
the number of speakers.
example, two 8 ohm speakers in parallel results in a 4 ohm load. Two 16 ohm speakers in parallel
results in an 8 ohm load. The general-purpose equation for calculating the load of multiple speakers
in parallel is shown in Figure 7. But as the above two examples illustrate, you will find that when all
the speakers have the same impedance, the total load will be equal to the rated impedance divided by
the number of speakers.
A commercial-grade speaker without any transformer may have a rated nominal impedance any-
where from 4 ohms to 16 ohms. The most common ratings are 4 ohms, 8 ohms or 16 ohms. The most
common recommended load ratings for low impedance amplifier outputs are 4 ohms and 8 ohms.
This means that in most cases, you will be limited to one or two speakers per amp channel when con-
necting low impedance speakers in parallel.
where from 4 ohms to 16 ohms. The most common ratings are 4 ohms, 8 ohms or 16 ohms. The most
common recommended load ratings for low impedance amplifier outputs are 4 ohms and 8 ohms.
This means that in most cases, you will be limited to one or two speakers per amp channel when con-
necting low impedance speakers in parallel.
Calculating Speaker Impedance
Total Impedance =
1
1
R
1
+
1
R
2
+
1
R
3
+
. . .
+
-
+
-
+
-
+
-
Total Load
Speaker 1
Speaker 2
Speaker 3
Figure 7