XMV4280/XMV4140 Owner’s Manual 25
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 more orthodox 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.
High Impedance
As long as the total nominal power input rating for all speak-
ers is within the power output capability of the amplifier, any
number of speaker systems can be connected in parallel. In a
high-impedance installation, the power input rating is deter-
mined by the speaker transformers used.
If the 280W output XMV4280 is used with a speaker system
having speaker transformers that make the rated input 10W,
you can connect a speaker system with a maximum 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 possible to simultaneously
drive speaker systems that have different input power rat-
ings.
(*) Yamaha recommends that you allow a 20% margin to
this number, considering variations in the transformer’s
primary impedance, possible tap changes in the future,
and the addition of speakers.
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 connected to
one channel.
When multiple speakers systems having the same impedance
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 systems can be connected to one
channel.
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.
Multiple Speaker System Drive Capa-
bility
10W10W10W10W10W
70V/100V
Speaker transformer
4Ω
8Ω8Ω8Ω
Total impedance = 4Ω
Cannot be
connected
4Ω
4Ω
Interruption
Total impedance
= 8Ω
Failure
No sound