1 paging and distributed speaker systems basic telecommunications

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Paging and distributed speaker systems

BASIC TELECOMMUNICATIONS

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Paging systems are typically built into telephones connected to a PBX using only the speaker on the telephone set

In order to have an effective paging system the use of an amplifier and additional speakers throughout the building is necessary


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Distributed speaker systems refer to a network of horns and speakers which are connected to an audio amplifier using step-up and step-down transformers built into speakers to simplify impedance calculations and to minimize power loss over the long cable runs


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Most systems are either 25V, 70.7V and 100V

Wattage can range from 1/4W to 200W

The most commonly used system is a 70.7V system that is connected to a PBX


An amplifier that is designed to work in conjunction with a PBX

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Lets take a look at some of the components of a distributed speaker system

A desk top mic Tone generator AM/FM receiver


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PBX

interface module 2 different types of volume controls/attenuators


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Standard indoor ceiling speaker and T-bar to hold the speakers into a 2’ x 2’ drop ceiling grid

2’ x 2’ grid speaker


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A standard horn and Explosion proof outdoor horn


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In it’s most basic form a distributed speaker system consist of an input (microphone & music),

an amplifier, and speakers (indoor and outdoor)

IMPEDANCE MATCHING IS A KEY CONSIDERATION HERE

Remember impedance is a form of resistance and better matching of components allows for better power usage and sound clarity


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The power amplifier output must be matched to the effective impedance of the speaker system

Because it is often necessary to use more than one speaker system (per channel) to disperse sound to the entire area, two or more speaker systems must be wired together


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There is only three possible ways to connect speakers to a power amplifier, common ground and only one power amplifier terminal can be connected at one time

What are the three wiring configurations that speakers can be connected?

For best results, all speaker systems installed should have the same impedance


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Notice here that one lead connects to common and the other to the desired output impedance

LETS LOOK AT THE 3 CIRCUIT TYPES


8ΩSpeaker

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Here are the three different circuit types


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Since each speaker system has its own impedance, wiring them together changes the effective impedance presented to the power amplifier

Based on the type of speakers you have to work with you will need to determine how to wire them to match the impedance output of the paging amp

Series, parallel or series/parallel


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For speaker systems connected in series, simply add the impedances of all the speakers.

Example, if you connect two, 8-Ohm speakers in series, the effective impedance is 16-Ohms.

You then use the 16-Ohm output on the power amplifier for proper impedance matching.

Four, 4-Ohm speaker systems could be connected in series for the same 16-Ohm effective impedance


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There is a practical limit to the number of TIC speaker systems that can be effectively connected in series

Example, connecting four TIC 8-Ohm speaker systems in series presents an effective impedance of 32-Ohms to the amplifier

This is a decidedly bad idea


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An impedance mismatch at the power amplifier causes distorted sound because the amplifier is asked to operate at maximum voltage swing

If you connect speaker systems in parallel, and all have the same impedance, the effective impedance equals the impedance of one speaker system divided by the number of speaker systems


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Example, if two speaker systems rated at 8-Ohms each are connected in parallel, the effective impedance is 4-Ohms

8 divided by two=4

The 4-Ohm power amplifier output must be used


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Similarly, if four speaker systems rated at 16-Ohms each are connected in parallel, the effective impedance is 4-Ohms

The 4-Ohm power amplifier output must be used

Do not forget that the wiring pattern for speakers related to the output channels of the amplifier will determine how the system will be wired!


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Series connected


4 ohms each

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Parallel connected


16 ohms each

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Series/Parallel connected


2, 16 ohm speakers

2, 4 ohm speakers

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In the diagram below can you identify the 3 different circuits and determine the value of each speaker?


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For speaker systems connected in parallel that don’t have the same impedance, use the following equation to find effective impedance (Zt);

Z = Impedance


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From Valcom a sample speaker placement chart

For optimum audible intelligebality


1 paging and distributed speaker systems basic telecommunications

Documents

pbx basic telecommunications

ohm speaker systems

effective impedance

impedance output

power amplifier output

speakers indoor

impedance calculations

power amplifier terminal