Design & Construction Of A 500W Wireless Public Address System (Pa System)

ABSTRACT

This work is titled design and construction of a public address system with ac and battery power source. A public address system (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air and rail terminals.

Public addressing system is often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations. Intercom systems, installed in many buildings, have microphones in many rooms allowing the occupants to respond to announcements.

This Public Addressing Systems have a potential for audio feedback, which occurs when sound from the speakers is picked up by the microphone, which converts the sound energy to electrical energy, the energy electrical signal being transmitted is been received and amplified by the amplifier circuit. The amplifier’s output is fed into the loudspeaker which converts the electrical energy back to the original form but amplified sound energy. This project is made up of the power supply unit, the pre-amplifier and power amplifier units, and the tone control unit. This system is capable of delivering 20W of electrical power into a 8 ohm load(loudspeaker).

CHAPTER ONE

• INTRODUCTION

A public address system allows you to broadcast information to a large group of people, whether you are giving a speech or playing live or recorded music.

Public address systems typically consist of input sources, preamplifiers, control and monitoring equipment, and loudspeakers. Input sources refer to the microphones that provide a sound input for the system. These input sources are fed into the preamplifiers. The pre amplified signals are then passed into the audio power amplifiers.

These amplifiers will amplify the audio signals to an adequate speaker line level. In view of the above, one can now say that the public address system is an electronic amplification system used for communication in public areas.

Microphone is a device that converts sound waves into electrical waves. Sometimes colloquially called a micro mike is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, and for non-acoustic purposes such as ultrasonic checking. The sensitive transducer element of a microphone is called its element. Since a wireless microphone is used in this project; a wireless microphone is one in which communication is not limited by a cable.

1.1                                         BACKGROUND OF THE PROJECT

A public address system comprises electrical equipment to greatly amplify a speaker’s voice so it will reach a much larger assemblage than he could speak to unaided. Beginning with the presidential conventions of the two major parties in 1920 and the inaugural address of President Harding in March 1921, when a special address system installed by the telephone engineers enabled him to address an audience estimated at 125,-000, there followed in rapid succession, many public events demonstrating the value of such systems. One of the most notable of these occurred on Armistice Day 1921, when the speeches, prayers and music at Arlington, Virginia, were heard, not only by 100,000 persons gathered there at the National Cemetery, but by some 35,000 in New York City and 20,000 in San Francisco. On this occasion the three public address systems, one for each of these cities, were joined by long distance telephone circuits.

The fundamental requirements of a satisfactory public address system are naturalness of reproduction and wide range of output volume. The meeting of these two requirements for music proves more difficult than for speech.

The public address system here described is most readily considered in three sections—“pick-up” apparatus which is placed in the neighborhood of the speaker and converts his words into undulatory electric currents; a vacuum tube amplifier for amplifying these currents; and a “receiver-projector” for reconverting the current into sound waves and distributing the sound over all of the audience. In the present system each of these three parts of the equipment has been designed with the intention of making it as nearly distortionless as possible, so that the various parts might be adaptable for audiences ranging in size from possibly one thousand to several hundred thousand, and might also be used in connection with the long distance telephone lines and with either radio broadcasting or receiving stations. One of the larger public address systems is easily capable of magnifying a speaker’s voice as many as 10,000 times.

The pick-up device whether of the carbon microphone variety or a condenser transmitter need not be placed close to the speaker’s lips but will operate satisfactorily when four or five feet away. The loud-speaking receiver mechanism is so designed that it will carry a power of several watts with small distortion. Under normal conditions, 500 watts distributed among a number of receiver-projectors arranged in a circle is ample to reach an audience of 700,000 persons.

1.2                                             OBJECTIVE OF THE PROJECT

This work focuses on  construction of an electronic sound amplification and distribution device with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air.

The major objective of this project is to design and construct a public address system with relatively unique operational characteristics that is capable of delivering 500 watts of electrical power into an 8 Ohms load (loudspeaker). This will be achieved with adequate tone controls and mixer stages so as to enable communication or reproduction of speech and recorded music in buildings and institutions.

1.3                                           SIGNIFICANCE OF THE STUDY

Public addressing system is often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations. Public addressing system is naturalness of reproduction and wide range of output volume. The meeting of these two requirements for music proves more difficult than for speech.

1.5                                          APPLICATION OF THE PROJECT

Public addressing system is often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations.

1.6                                  SCOPE OF THE PROJECT

This system is for public address; it has an estimated power rating of 500watts. For power supplies, it uses a power supply, receiver, and amplifier and loudspeaker units. It has a power On/Off button with volume control.

1.7                                 PROJECT JUSTIFICATION

Over the ages, science and technology has been developing with new inventions in various fields; including the increase in modifications on existing technology all gearing towards improving effectiveness and reliability of equipment and achieving to a great degree miniaturization and optimal cost.

This project is backed by my interest in the area of electronics and communication, and having been groomed to a great extent with introductions into the various fields of electrical and electronics engineering, with the knowledge in principles of telecommunications, telecommunication engineering.