Yamaha XMV4280 Manuale d'uso - Pagina 31
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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, resistance 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 demer-
its 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 sys-
tem, 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
= 8Ω
Low impedance
For short distances over which cable resistance is insig-
nificant, low-impedance connection allows the power
amp to be directly connected to the speaker system with-
out the need for speaker transformers. That means that
the full performance 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 sys-
tem, 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
= 8Ω
Speaker
transformer (1kΩ)
Almost 100%
50%
Speaker system
inpedance = 8Ω
XMV4280/XMV4140/XMV4280-D/XMV4140-D Owner's Manual
Appendix
31