QSC Audio CX Series VIII. Distributed lines, Part 2-CXSeries Application Guide, 70V 10W, 4.5V

Example of a loadspeaker connected to a distributed line through a transformer

Part 2—CX Series Application Guide

With 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	1.2W
	2.5W
power rating is determined by how much current it can put out
	5W
at a standard voltage level; a low-power 70-volt amp has less

current capability than a high-powered 70-volt amp, even though	70V 10W
they can both put out the same voltage. The high-powered amp	COM
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.

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8

4

COM

4.5V

8

	1.2W
	2.5W
	5W
70V	10W
Amplifier
0	COM

0.5W

1W

2W

16
8
4
COM	8

1.2W

2.5W

5W

10W

COM

A

16	8
8
4
COM
	8

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.,

B 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

	SPKR
Example of a 70 volt	COM
distributed line

C

for the situation while still retaining the versatil-

ity of configuring other loudspeakers on the same

line for different power levels.

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