Design And Construction Of A 50W Public Address System

1.0 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, 50watts 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
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 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 50watts. 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 a 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 a 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.