Transmission Distance And Efficiency - Yamaha XMV4280 Owner's Manual

High-impedance and Low-impedance Connections

Transmission Distance and Efficiency

The cables that transmit electric signals have resistance. The
resistance in short cables is small enough that it can be ignored,
but as transmission distance and cable length increase, resis-
tance can increase to the point that signal loss and degradation
occur. That can mean reduced output level and sound quality.
Below we examine the merits and demerits of low-impedance
and high-impedance connections in relation to transmission
over significant distances.

High Impedance
Even if the cable resistance reaches 8Ω due to an extended
transmission distance, this is an amount that can be ignored
relative to the impedance of the speaker system, meaning
that transmission loss due to the cable will be insignificant,
and thus will have little effect on the transmission efficiency
of the electrical signal.
Long distance
70V/100V
Cable resistance

Low Impedance
For short distances over which cable resistance is insignifi-
cant, low-impedance connection allows the power amp to be
directly connected to the speaker system without the need
for speaker transformers. That means that the full perfor-
mance potential of amp and speakers can be taken advantage
of for sound quality that is superior to high-impedance
installations. And since only one speaker system is usually
connected to each amplifier channel, different audio signals
can be sent to each speaker system, or "zone," as required.
But in a situation like the one shown in the diagram, where a
long cable with a resistance of 8Ω is required, transmission
loss will theoretically result in the output level being reduced
by half because the impedance of the speaker system itself is
only 8Ω. Half of the power gets absorbed by the cable, and
only the remaining half is available to drive the speaker. So
for low-impedance installations it is necessary to either keep
the cables short enough that cable resistance is not an issue,
or use thicker cables that have lower resistance for longer
runs, for example.
Long distance
8Ω
Cable resistance
26
XMV4280/XMV4140 Owner's Manual
Speaker
transformer (1kΩ)
Almost 100%
= 8Ω
50%
Speaker system
= 8Ω
inpedance = 8Ω