Design And Construction Of A Public Address System

Project and Seminar Material For Electrical Electronics Engineering EEE

Abstract

It has become inevitable that there would be communication and due to the inherent limitation of the human voice, the public address system came to being. A public address 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.

The voice signal is passed through a 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 output 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 of electrical power into an 8 ohm load (loudspeaker).

Table of Content

Chapter One

Introduction

1.1 Background of the Project
1.2 Problem Statement
1.3 Aim / Objective of the Project
1.4 Significance of the Project
1.5 Application of the Project
1.6 Limitation of the Project
1.7 Scope of the Project
1.8 Project Justification
1.9 Project Organisation

Chapter Two

Literature Review

2.0 Literature Review
2.1 Review of Public Addressing System
2.2 Historical Background of Public Addressing System
2.4 Different Types Pubic Addressing System

Chapter Three

3.0 Construction Methodology

3.1 Block Diagram of the System
3.2 Circuit Diagram
3.3 Circuit Description
3.4 System Operation
3.5 Description of Major Components Used

Chapter Four

Result

4.1 Result Analysis
4.1 Construction Procedure And Testing
4.2 Casing And Packaging
4.3 Assembling Of Sections
4.4 Testing Of System Operation
4.5 Cost Of Production

Chapter Five

Conclusions and Recommendation

5.1 Conclusions
5.2 Recommendation
References

Chapter One

Introduction

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, 40 watts distributed among a number of receiver-projectors arranged in a circle is ample to reach an audience of 700,000 persons.

1.2 Problem Statement

This project is to overcome communication problems that usually occur in areas where it is hard to find a device for making important announcements or speeches so that everyone can listen precisely to what the speaker is talking about. This simple project may also be used by lecturers in lecture halls to bridge communication gap between the lecturers and student in a lecture, as shouting during lectures may be very exhausting.

1.3 Objective of the Project

The objective of this work is to construct 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 and rail terminals with ac and battery power source.

1.4 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

1.6 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.

1.7 Scope of the Project

This system is for public address; it has an estimated power rating of 20watts. For power supplies, it uses a 220/12Vac transformer for the amplifier and loudspeaker units. It has a power On/Off button with volume control.

1.8 Limitation of the Project

Interference:

Interference can be a problem. There are lots of devices that emit radio waves. If those radio waves are on the same frequency as with the transmitter and receiver, you could get some garbled signals as you listen to the output. Dropped signals can also be an issue — if a transmitter or receiver stops working or drops out, it will affect your listening experience.

Bandwidth:

Another problem is bandwidth. Wired PA can carry a lot of information in the form of electrical signals. Wireless signals can’t really compete. Audio may seem less full or rich. It’s a subjective element that can be difficult to put into words. If you’re an audiophile, you may find wireless PA lacking from a performance standpoint.

1.9 Project Work Organisation

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to public addressing system. In this chapter, the background, significance, objective limitation and problem of solar power inverter were discussed.
Chapter two is on literature review of public addressing system. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.

Chapter Five

Conclusion and Recommendation

5.1 Conclusion

Public address systems are an essential tool in communication throughout a premises or campus. Clear View has nearly 20 years experience of manufacturing, installing and servicing a wide range of audio and public address equipment.

Public address systems can broadcast information from single or multiple sources to large groups of people in:

Specific areas of a building – “zones”
All areas of a building – “all call”

Messages are sent from an operator via a microphone console or telephone handset and are routed through amplifiers before being distributed from speakers in the designated areas. PA Systems can distribute music into work places from digital media or radio.

It has been proven to be the fastest and safest method of evacuation because it delivers an emergency attention drawing signal followed by a recorded message, whilst also delivering live emergency announcements from the fire officer.

Standard facilities available on PA systems include:

Routine paging announcements
Background music,
Interfaces to other devices
Spot announcements

If a new public address system is required, our implementation process includes:

Examining your public address specification requirements, including minimum sound pressure levels and post installation speech intelligibility testing eg. STI or RASTI testing
Providing a detailed evaluation of the space that the PA system will serve
Seeking compliance with any performance specification and / or relevant standards.

If a public address system has already been installed, we will undertake commissioning exercises to determine the electro-acoustic performance of the system. This is likely to include measurements of speech intelligibility and audibility testing.

5.2 Recommendation

This project is designed to be used in homes and industries and wherever the need for Public addressing. And should be used and maintain by a qualified personnel.

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