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Appendix
High-impedance and Low-impedance
Connections
For a high-impedance connection a speaker transformer that
raises the impedance to several hundred or thousand ohms is
added to the speaker system. This allows the speaker system to
be effectively driven with much lower current than is required
for a low-impedance system. That, in turn, makes it possible to
connect a larger number of speaker systems to each power
amplifier output. High-impedance speaker connections work at
a specific maximum voltage—usually 70 or 100 volts—and are
therefore also referred to as "constant voltage" speaker systems
(the label "constant voltage" is somewhat misleading: the actual
output voltage fluctuates according to the input signal).
For a low-impedance speaker connection, the power amplifier is
directly connected to a speaker system that has an inherent
impedance of 4–16Ω.
The difference between these types of connection are outlined
below.
Multiple Speaker System Drive Capability
High impedance
As long as the total nominal power input rating for all
speakers is within the power output capability of the
amplifier, any number of speaker systems can be con-
nected in parallel. In a high-impedance installation, the
power input rating is determined by the speaker trans-
formers used.
If the 280W output XMV4280 is used with a speaker sys-
tem having speaker transformers that make the rated
input 10W, you can connect a speaker system with a max-
imum of 24 speakers per channel based on the calculation
(*), giving you a total of up to 96 speakers for the four
channels. In a high-impedance installation it is also possi-
ble to simultaneously drive speaker systems that have dif-
ferent input power ratings.
(*) Yamaha recommends that you allow a 20% margin to
this number, considering variations in the trans-
former's primary impedance, possible tap changes in
the future, and the addition of speakers.
70V/100V
10W
30
XMV4280/XMV4140/XMV4280-D/XMV4140-D Owner's Manual
Speaker transformer
10W
10W
10W
10W
Low impedance
Normally only one speaker system is connected to each
amplifier channel, as shown in the diagram.
This means that the number of speaker system that can be
connected to an XMV is limited to four.
However, even with low impedance connections, there is
a way by which multiple speaker systems can be con-
nected to one channel.
When multiple speakers systems having the same imped-
ance are connected in parallel, the total impedance
becomes the individual speaker system impedance
divided by the number of systems connected. This means
that if the XMV is set to 4Ω, up to two 8Ω speaker sys-
tems can be connected to one channel.
4Ω
8Ω
8Ω
Total impedance = 4Ω
The second method is series connection. In this case the
total impedance is simply the sum of the impedances of
the speaker systems connected. But as you can see in the
series connection wiring diagram, if one speaker system
fails the second speaker system will be affected as well.
4Ω
Failure
No sound
4Ω
Interruption
Cannot be
connected
8Ω
Total impedance
= 8Ω