General Criteria For Installation Of Sound System; Introduction; Constant Voltage System; 4/8/16 Ohms Systems And Dc Systems - Pro Audio AM412R User Manual

- 6 - GENERAL CRITERIA FOR INSTALLATION OF SOUND SYSTEMS

6.1 INTRODUCTION

This guide represents a quick introduction to the criteria for the installation of a sound system at constant
voltage or constant impedence.
A sound system must be made by qualified personnel only, who must evaluate the needs of the user and
the environmental characteristics of the spaces to be covered, select the speakers according to the spaces
and the type of message to be broadcasted (ie: speech / music ), identify the suitable amplifier model to
drive the complex of all the speakers and having an adequate number of inputs, evaluate the proper con-
nection for the speakers and determine the section of the wiring.
6.2 CONSTANT VOLTAGE SYSTEMS
In terms of selection of speakers and their connection it's necessary to evaluate whether to use normal
speakers with 4/8/16Ohm impedance or speakers with transformer. The decision is usually influenced
by the destination of the system (supermarket, disco , pub, house, ...) and by the number of speakers to
employ. Constant voltage speakers are normally used into situations where it is necessary to install several
speakers with low power to get a homogeneous distribution of audio and overall low volume. The clas-
sic example is the sound installation in airports or supermarkets. In these situations several speakers are
usually placed within a short distance between them, normally a volume low enough to not disturb and a
frequency covering the entire area with same sound pressure.

6.3 4/8/16 OHMS SYSTEMS AND DC SYSTEMS

The 4/8/16Ohm systems are affected by problems of impedances:
• speakers connected in "series" mode add their impedance (example: 4Ohm + 4Ohm = 8Ohm)
• speakers connected in "parallel" mode divide their impedance (example: 8Ohm / / = 8Ohm 4Ohm)
In the following pictures find a few examples of connections: series, parallel, series + parallel. Also the
applicable power is reported according to type and impedance of each speaker. Please note polarity indi-
cated for each speaker.
Constant voltage systems use speakers equipped with transformer. Normally they can be con-
figured on 2 or more different maximum power levels. In this type of system only 2 conduc-
tors are employed: the black one is connected to the negative terminal (usually marked by "0" or
"COM"), the red one is connected to one of the contacts (50V, 70V, 100V). The amplifier driving all
speakers will be connected to such 2 wires paying attention that right polarities are respected.
Please note that:
• Voltage selected on speaker transformer must match the voltage selected on the amplifier.
• Total sum of speakers power must not exceed power of the amplifier.
• To ensure a correct reproduction of the audio signal it is important to setup the connection with no
phase shifts: the connection between positive and negative poles of the amplifier must match the
polarity on speaker transformer.
• It is important that cables have an adequate section: increasing total length of the sound installation
involves increasing of cable section to avoid distortion or signal loss.
• Cables for connection of the speakers should be passed separately from other electrical or microphone
cables, to avoid ground loops or triggers of any kind.
• It 's always important to use cables with twisted wires.
AM412R/AM430R
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