QSC CX4T User Manual download pdf (Page 20)

Part 2—CX Series Application Guide

ith the helpful advice and input from contractors and consultants around the world, engineers at

QSC designed the CX Series amplifiers to be a versatile and reliable foundation for

high-quality installed sound systems.

This applications guide will help you design your sound system properly and utilize your CX amplifier(s) effectively.

VIII. Distributed lines

The best way to distribute audio power from a common amplifier among numerous relatively low-powered

loudspeakers is to use a distributed line, whether all the loudspeakers are meant to receive the same or different

power levels.

A distributed line is usually referred to by its maximum voltage-

25-, 70-, 100-, or 140-volt lines are most common. An amplifier’s

power rating is determined by how much current it can put out

at a standard voltage level; a low-power 70-volt amp has less

current capability than a high-powered 70-volt amp, even though

they can both put out the same voltage. The high-powered amp

can drive more speakers and at higher power levels than the

lower-powered one can. This is somewhat analogous to AC

electrical distribution, where you might have circuits rated for

15A, 20A, 30A, etc., at 120 or 240 VAC, and you can connect any

number of appliances to them as long as you don’t exceed the circuit’s current capacity.

Loudspeakers on a distributed line use tapped

transformers to match their power requirements

to the line. A loudspeaker with a 70-volt trans-

former tapped at 2 watts, for example, will

receive that amount of power when the amplifier

puts out 70 volts on the distributed line. Trans-

former taps are usually set at 3 dB intervals, i.e.,

each successive tap is twice the power level of its

predecessor. An example would be a transformer

tapped at 0.5, 1, 2, and 4 watts. This allows you

to select a power level that is most appropriate

for the situation while still retaining the versatil-

ity of configuring other loudspeakers on the same

line for different power levels.

COM

10W

2.5W

1.2W

70V

4.5V

Amplifier

70V

COM

SPKR

0.5W

COM

10W

2.5W

1.2W

COM

10W

2.5W

1.2W

Example of a 70 volt

distributed line

Example of a loadspeaker connected to a

distributed line through a transformer

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QSC CX4T User Manual Page 20

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