CHAPTER ONE
INTRODUCTION
1.1 PREAMBLES
Wireless speakers are very similar to traditional loudspeakers that are wired, but they transmit audio signals using radio frequency (RF) waves rather than over audio cables. As things stands today, the term 'wireless' in the audio and video world does not mean 'wireless' - rather all it means is less wires. And this applies to any wireless speaker system presently. Still, this in itself can turn out to be a great advantage. Home audio systems can be enhanced and made more versatile by incorporating the ability to listen to music from a single source in multiple locations. However, distributing music throughout the homes, theaters, churches, stadiums, arenas, and broadcast facilities has proved to be logistically difficult (Syafiqah, 2010). Home owners could extend the listening range of an audio source by purchasing a multi-room amplifier and having additional wiring installed through-out the house by a professional electrician. However, for many consumers who do not own their homes or who cannot afford such an upgrade, this solution would be impractical. The alternative of having interconnecting wires laid out visibly throughout the home has also been unappealing to most consumers for reasons of safety and aesthetics. Therefore, the lack of an available, affordable technology that would overcome the need for wired audio device interconnection greatly restricted the home audio possibilities for most people. Recently, wireless systems have become available that offer home wide music distribution that is in many cases more practical and more elegant than the wired methods previously mentioned Using wireless communication technology for home entertainment becomes popular.
Wireless speaker system is not a new invention for this century; however, the goal of this project is to improve the size, quality and range of the communication system. Here, wireless speakers are composed of two units: a main speaker unit combining the loudspeaker itself with an RF receiver, and an RF transmitter unit (Syafiqah, 2010). There is normally an amplifier integrated in the speaker's cabinet because the RF waves alone are not enough to drive the speaker. This integration of amplifier and loudspeaker is known as an active loudspeaker. Manufacturers of these loudspeakers design them to be as lightweight as possible while producing the maximum amount of audio output efficiency. Wireless speakers still need power, so require a nearby AC power outlet, or possibly batteries (DC). Only the wire to the amplifier is eliminated.
The transmitter connects to the audio output of audio devices like speakers. Wireless technology is relatively new for home surround sound systems as well as other systems. There are two types of transmission media for wireless speakers. RF signal based systems, and infrared signal based systems. RF, or radio frequency based systems use radio signals to transmit data, and in this case music, to the remote receiver. RF systems commonly use radio frequencies between 300 MHz and 1000 MHz, with 900 MHz being the most common frequency. Transaction rates range up to 40,000 bits per second (Binti, 2011).
This technology does well for speaker systems that will not have direct LOS (line of sight) from the receiver to the transmitter. Some barriers, such as cement, metal, electronic devices, some plastics, and other materials interrupt or absorb RF signals. The speaker placement can be test by moving speakers around slightly to see where the best reception and audio quality is. This solution is common for outdoor speaker systems, systems that are located in a different room that the audio source, or home wide audio systems. In the location where it would like to place, the speakers is limited to areas of bad coverage, RF repeaters can be purchased to assist transmissions around barriers that are causing transmission problems (Syafiqah, 2010).
These systems are susceptible to radio interference from electronic devices, although new technologies in shielding and spread spectrum solutions are making this less of an issue. RF systems tend to transmit more data, communicate further, are more reliable and are more expensive than the infrared alternative. A transmitter in a wireless network is responsible for generating a high power output signal with adequate signal strength to deliver a sender's message. Wireless transmitters provide modulated radio waves to carry (transmit) data signals from one place to another that may include a radio frequency (RF) filter system which is used to ensure that the integrity of a sender's message is not threatened by the many compromising system components that the signal encounters as it progresses through the transmitter.
1.2 System Block Diagram
The system is made up of the transmitter which is incorporated with the microphone; and the receiver unit, the tone control and mixer unit, the audio amplifier unit and the loudspeaker. The block diagram of the system is drawn below
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MICROPHONE |
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ANTENNA |
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POWER SUPPLY UNIT |
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SIGNAL |
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RECIEVER UNIT |
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PRE- AMPLIFIER |
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TONE CONTROL AND MIXER |
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AUDIO AMPLIFIER |
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LOUDSPEAKER |
Figure 1; Block Diagram of a Public Address Loudspeaker System
Source: Franco, (1988)
1.3 Background Study
A wireless loudspeaker system allows you to broadcast information to a large group of people, whether you are giving a speech or playing live or recorded music. The sound system typically consists 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.
Microphone is a device that converts sound waves into electrical waves. Sometimes 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 to be used in this project; a wireless microphone is one in which communication is not limited by a cable.
Figure 2: A Transmitter Circuit
Source: Kouwenhoven, (2003).
Culprit’s oscillator that the frequency is determined by L1, C4, C6, and the transistor’s internal base-emitter capacitance as shown in figure 2 above. The antenna use 1/16 wave length to compromise between the first transistor (Q1) is the pre-amplifier for the microphone, and you can omit this circuit if you don’t want to transmit the sound picked up by the microphone, for example you can connect your mp3 player directly to C1. The core of this FM transmitter circuit is Q2, a modified efficiency and the size. If you want the microphone to be less sensitive, we can replace the R1 by a higher resistor, such as 10k or 22k , and this might overcome the feedback problem if you use this wireless microphone FM transmitter for a public address system.
The receiver captures the radio waves sent out by the transmitter, demodulates the signal, amplifies it to an appropriate level, and sends it out to the audio mixer. A receiver is an electronic circuit that receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts through demodulation and decoding the signal into a form usable for the consumer, such as sound, and digital data, etc.
Amplifier or simply amp is any device that changes, usually increases, the amplitude of a signal. The “signal” is usually voltage or current. Amplifier is a device for increasing the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with larger amplitude. Routing the low-frequency parts of the signal to an amplifier can substantially improve the clarity of the overall sound reproduction.
Power amplifiers have also become lighter, smaller, more powerful and more efficient due to increasing use of Class A amplifiers, which offer significant weight and space savings as well as increased efficiency. Power amplifier circuits (output stages) are classified as A, B, AB and C for analog designs, and class D and E for switching designs, based upon the conduction angle or angle of flow, , of the input signal through the output amplifying device, that is, the portion of the input signal cycle during which the amplifying device conducts. The image of the conduction angle is derived from amplifying a sinusoidal signal. (If the device is always on, = 360°.) In this project a class A amplifier is used because it offers low signal distortion.
Loudspeaker is an electro-acoustical transducer that converts an electrical signal to sound. A transducer that turns an electrical signal into sound waves is the functional opposite of a microphone. Since a conventional speaker is constructed much like a dynamic microphone, (with a diaphragm, coil and magnet), speakers can actually work “in reverse” as microphones. The speaker pushes a medium in accord with the pulsations of an electrical signal, thus causing sound waves to propagate to where they can then be received by the ear. The loudspeaker to be used in this project is a load of 8 Ohms (8 .
1.4 Aim and Objectives
The aim of this project is to design and construct a wireless loudspeaker.
The objectives of this project are:
- i. to study how wireless system were applied in speaker and how radio frequency is used as transmitter medium is used in transmitting signals.
- ii. to design the receiver and the transmitter circuits and
- iii. to construct a wireless loudspeaker.
1.5 Problem Statement
A common complaint against home audio systems has been the cables that interconnect the speakers to the audio receiver, tuner, CD player, or stereo units. As more and more channels are added to modern home audio equipment the problem of connecting the speakers to the audio sources has getting worst. Running cables through the house walls or church walls is messy and time consuming. Cables running over the carpet are a tripping hazard. Running cables along the ceiling or walls are just an eyesore. Some homes have a nice deck, patio or gazebo in the yard that is a common relaxation area for meeting and entertaining guests. Playing soft or popular music has a tendency to relax people, and help with awkward gaps in communications, as well as provide a topic of discussion when one isn't forthcoming.
1.6 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, basic electronics and lab practice. I chose to combine all these ideas in embarking on this project to develop a special system that utilizes all the above stated knowledge in one system; “THE WIRELESS LOUDSPEAKER SYSTEM”.
This system makes use of radio communication system, it utilizes radio frequency to achieve all its set objectives, like data communication in the operation of wireless communication between the transmitter and the receiver. This system is intended to provide a fast and reliable means of communication in small venues such as school auditoriums, churches, and small bars.
The expected outcome of this project is that this wireless speaker should be able to function in home (or any other place) in a maximum distance between each other by transmitting the signal between receiver and transmitter in a house with little interference signal from each other. The signal sent between the transmitter and receiver should be received in a long distance with help by amplifier that will be used where the area to be covered and capacity requirements do not justify the installation of a full base station system with managed frequency-channel allocation. With this wireless speaker, problems comes out from application using cable speaker can be solved easily. The application of interfacing software will help this signal to be controlled on.
1.7 Scope of Study
This project will focus on using transmitter and receiver circuit in implementing the wireless signal between speakers by doing research on reference circuit. Thus, the function and operation of transmitter and receiver circuit would be studied to accomplish this project. In this project, RF signal would be used as transmitting medium in wireless home application. The transmitter and receiver circuits would be used in implementing the wireless signals between speakers by carrying out a research on the reference circuit.
