Yamaha XMV8140-D Owner's Manual download pdf (Page 31)

Appendix

XMV8280/XMV8140/XMV8280-D/XMV8140-D Owner’s Manual

 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.

 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.

70V/100V

Long distance

Cable resistance

= 8Ω

Speaker

transformer (1kΩ)

Almost 100%

8Ω

Long distance

Cable resistance

= 8Ω

Speaker system

inpedance = 8Ω

50%

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