Crown Audio 133472-1A Distributed Speaker Systems, Sub-SonicCurrents, Crown Amplifiers In-Depth

Chapter 1: Crown Amplifiers In-Depth 17

Figure 1.25

Inductive Load (Trans- former) Network

4. Never connect the amplifi er’s input and output grounds together.

5. Never tie the outputs of multiple amplifi ers together.

6. Keep loudspeaker cables well separated from input cables.

7. Install a low-pass fi lter on each

input line (similar to the RF fi lters described in Section 1.2.2).

8.Install input wiring according to the instructions in your amplifi er’s Opera- tion Manual.

Figure 1.26

Typical Distributed Speaker System

Sub-Sonic Currents

Another problem to avoid is the presence of large sub-sonic currents when primarily inductive loads are used. Examples of inductive loads are 70-volt transformers and electro- static loudspeakers.

Inductive loads can appear as a short circuit at low frequencies. This can cause the amplifi er to pro- duce large low-frequency currents and activate its protection circuitry. Always take the precaution of install- ing a high-pass fi lter in series with the amplifi er’s input when inductive loads are used. A 3-pole, 18-dB- per-octave fi lter with a –3 dB fre- quency of 50 Hz is recommended (depending on the application, an even higher –3 dB frequency may be desirable).

Another way to prevent the amplifi er

from prematurely activating its protection systems and to protect inductive loads from large low-frequency currents is to connect a 590 to 708 µF nono- larized capacitor and 4-ohm, 20-watt resistor in series with the amplifi er’s output and the positive (+) lead of the transformer. The circuit shown in Figure 1.25 uses components that are available from most electronic supply stores.

1.3.6 Distributed Speaker Systems

Multiple-speaker systems for paging and background music systems are common in such facilities as schools, restaurants, industrial facilities offi ces and retail. In these systems, many speakers are distributed throughout the facility, often across long distances, making them diffi cult and expensive to implement with traditional, direct low-impedance amplifiers. A less expensive and more reliable method is the distributed speaker system.

A distributed speaker system consists of an amplifier or amplifi er channel driving one or more speakers with transformers connected to a pair of wires called a “home run.” The transformers step the line voltage down to a lower

Amplifier Application Guide