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York University
Natural Science
NATS 1720
Carl Wolfe

Introduction In this essay I am going to write about different sound systems, for instance: Monophonic system, Stereophonic system, Surround sound and THX. I would like to focus on the special features of each one and to describe in detail how does it work. My aims by doing so are: [1] To expand horizons about the field of Physics of sound. [2] To provide a comprehensive analysis concerning prominent functions of each sound system. Accompanied with highly schematic fashion illustrations, the most crucial similarities as well as differences between those sound systems are emphasized and well-explained. For clarification, a channel is an individual discrete audio track. When referring to more than two channels it is called multichannel. Monophonic Sound System Monophonic, or monaural, sound reproduction (often shortened to mono) is a single- channel of audio for sound output . In this sound system, the original sound is picked up by one (or more) microphone(s). Regardless of the number of microphones, however the significant fact is that only one signal is recorded and only one signal is involved in the playback stage. In other words, the signal sent to the sound system encodes one signal stream of sound and it usually uses just one speaker. The monophonic system is illustrated in the following figure : 2 Sound systems for home use can take many forms. The program sources available are record albums, tapes, and AM/FM signals. These program sources which are audio sources require a turntable, a tape deck, and a tuner for their implementation. A preamplifier (control unit) and a power amplifier prepare the signal for delivery to the loudspeaker. A monophonic sound reproduction system is shown in the block diagram below : 2 The boxes represent the components and the lines represent the interconnections between components. Since there is only one signal involved in a monophonic system, a single cable-two conducting paths- between each component is sufficient. The main components are shortly explained in the following passage:  Audio source – The recorded audio information, which is recorded from a digital or analog recording, is being read by the audio source. Then the information is 3 sent in an electrical signal via audio cable .  Turntable (or phonograph) – is a device which is used in order to record and 4 reproduce sound recordings .  Tape deck (or tape recorder) - is an audio storage device that his main feature is to 5 record and play back sounds by using magnetic tape for storage .  Tuner – a subsystem that receives radio frequency transmissions and converts the selected carrier frequency and its associated bandwidth (the difference between 6 the upper and lower frequencies in a continuous set of frequencies )into a fixed frequency that is suitable for further processing usually because a lower frequency 7 is used on the output .  Preamplifier - serves as control unit in 4 steps: reading the signal, breaking it down into appropriate channels, increasing the voltage of the signal slightly from 3 a source and finally sending it to the amplifier .  Amplifier – The signal sent from preamplifier is too weak to effectively drive the speakers and vibrate the coil so that one can hear sound. Thus, the amplifier is needed in order to add significant power to that signal .3  Speakers - a conventional speaker uses several drivers, each od them contains (1)a stationary magnet, (2) an electromagnetic coil and (3) a cone. The electric signal sent from the amplifier is an AC or alternating current signal -this means that the current switches directions on a regular basis. Running through a wire coil, the alternating current creates a magnetic field that is persistently reversing polarity. The reversion of the polarity of coil causes a constant shift between attraction and repulsion with the stationary magnet. The electric voice coil is continually oscillating because of this magnetic force and in turn vibrates the cone. This vibration cause to a motion of air molecules, which become the vessel by which sound is delivered to the ears . The tuner, preamplifier, and power amplifier cab be separate components or they can be combined into a signal chassis called a receiver. Monaural sound, commonly called non-stereo sound, has been replaced by stereo sound in most entertainment applications. Nonetheless, it remains the standard for radiotelephone communications, telephone networks, and audio induction loops for use with hearing aids. Thanks to the fact that a monaural signal has a slight advantage in signal strength over a stereophonic signal of the same power, few FM radio stations choose to broadcast in monaural. Stereophonic Sound System Stereophonic sound is a method of sound reproduction that creates an illusion of sound heard from various directions, as in natural hearing, which is usually achieved by using two or more independent audio channels through a configuration of two or more . 8 A stereophonic sound system employs two or more microphones to pick up the original sound. The spacing between these microphones is large enough so that the acoustic signals reaching them are distinctly different. Two different signals are recorded and the individual integrity of 2 these signals is maintained in the playback stage . As the monophonic sound system, a stereo system must contain an audio source which requires a turntable, a tape deck and a tuner for its implementation. The next component in the stereo is a preamplifier which reads and decodes audio information sent from the source to the amplifier. The amplifier increases the power of the signal to properly drive the speakers. Finally, the speakers convert the electrical audio signal to sound. The interconnections are not simply wires; rather, they are shielded audio cables designed to reduce unwanted harm and noise. A 2 diagram of a stereophonic sound system is given below : Although the layouts of the stereo and mono systems are very similar, the fundamental differences are obvious. A stereo system is equipped to handle two independent signals. There are in essence two preamplifiers, two power amplifiers, and there are two loudspeakers. Stereo sound is now common in entertainment systems such as: broadcast radio, recorded 9 music, TV and the cinema . Surround Sound Surround Sound is a system in which the sound output appears to surround the listener by 360 degrees — in other words, this technology gives the impression that sounds are coming from all possible directions. The surround sound works because multiple audio channels are received through speakers that are positioned at various locations in the room. This is programmed into the source and the sound tracks are decoded when the source is played. Moreover, it is important to remember that sound systems started out with monophonic sound, a single channel system. Advancements led to stereophonic sound (stereo) where the sound was split between two channel
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