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- GENERAL CRITERIA FOR INSTALLATION OF SOUND SYSTEMS
Introduction
This guide represents a quick introduction to the criteria for the installation of a sound system at constant
voltage or constant impedance.
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 connection for the
speakers and determine the section of the wiring.
Constant voltage systems
In terms of selection of speakers and their connection it's necessary to evaluate whether to use normal speak-
ers with 4/8/16Ohm impedance or speakers with transformer. The decision is usually influenced by the desti-
nation 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 classic 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.
Differences between 4/8/16 Ohms systems and constant voltage 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 indicated 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 in-
volves 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
MZX1002
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