LV-1 Course: Public Broadcasting (Address) System

Introduction: 

Public address system is used in hotels, commercial buildings, ports, airports, subways, schools to provide background music and radio programs. In recent years, public broadcasting system also caters to emergency broadcasts, can be linked with the fire alarm system.

PA systems are for reproduction of speech and recorded music in buildings and institutions and it can’t be used as Sound reinforcement systems for live music.

Comparison between PA system & Sound reinforcement systems:

s/n	PA system	Sound reinforcement systems
1	Contain ceiling speakers and/or box speakers usually is 3 watt each	contain bigger speaker and powerful amplifier
2	Used mainly for reproduction of speech and recorded music and announcement	Used mainly for Live music

The public address system components: 

1- Input stage: 

It includes Microphones and/or tape recorders and/or CD/DVD players (see fig.1 ).

fig (1): input stage components

For more information about input stage components and how to select the right types among them, please review the following previous topics:

•  Microphones
• Sound recorder

2- Intermediate stage: 

It includes a lot of components (see fig. 2)that can be used as intermediate devices to control input sound and reproduce enhanced ones. 

fig (2): Intermediate stage components

For more information about intermediate stage components and how to select the right types among them, please review the following previous topics:

•   Audio mixer
•  Equalizers
•  Mixer amplifier
• Pre-amplifier
• Audio amplifier (boosters)
• Monitor unit
• Speaker selector
• Power supply
• Terminal Boards
• Crossover

3- Output stage: 

This stage contains only speakers (see fig.3 ) and of course speakers have types differed in sizes, power ratings, characteristics and applications. But mainly PA system contains ceiling speakers or/and box speakers distributed to cover the intended area and it will be divided into different zones, the ceiling speakers are usually 3 watts and have high impedance transformer for link many ceiling speaker for one zone. So a 240 watts amplifier can power to about 70 nos. of 3 watts ceiling speaker covering the building area.

fig (3): different types of speakers

For more information about output stage speakers and how to select the right types among them, please review the following previous topic:

• Speakers

4- Sound Rack
It contains a lot of sound system devices For Protection and Easy Use, there are many types of racks according to size and method of installation/usage (see fig.4).

fig (4): different types of Racks

For more information about Sound Racks and how to select the right types among them, please review the following previous topic:

• Sound rack 

Public address systems types:

1. Simple public address system.
2. Large public address system.

1- Simple public address system: see fig.5 &6

The simplest PA systems consist of a microphone, a modestly powered mixer amplifier and one or more loudspeakers. Simple PA systems of this type, often providing 50 to 200 watts of power, are often used in small venues such as school auditoriums, churches, and small bars.

                                                     fig (5)                                                      fig (6)

2- Large public address system: see fig.7&8

Some PA systems have speakers that cover an entire campus of a college or industrial site, or an entire outdoor complex (e.g., an athletic stadium). More than often this PA system will be used as voice alarm system that make announcement during emergency to evacuate the occupants in a building.

                                              fig (7)                                                               fig (8)

Public address system design:
To design the public address system in a building we need to do the following:

• determine the number of ceiling speakers needed to cover the area. Most of the buildings will either have high level ceiling like the lobby area at the entrance or lower level ceiling commonly seen in the office block. By indicating the correct number of the speakers needed for each this area will ensure coverage. As a rule of thumb the more ceiling speaker the better is the sound distribution.
• calculate the number of amplifier needed to power the speaker.
• Finally we divide the speakers into different zones for easy identification like different zone for each office block in each floor and zone for lobby area and another zone for car park area. 

Please note that, we will explain the detailed design process of sound systems later in this course, so please keep following.



In the next topic, I will introduce other types of sound systems like Indoor radio system.