Dell 2135CN, Service Manual

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Chapter 6 Principle of Operation (Fax)
Version 1 2008.02.01
1. Telephone System
1.1 Converting and Sending Voice in the Form of Electrical Signals
The human voice is a sound wave; in other words, air vibrations. Conversation between two people
results when such vibrations travel through the air and reach each other's ears. A string telephone
transmits the air vibrations generated between two people along a string stretched tight, thus allowing
conversation over a distance. In this system, a paper cup at one end of the string receives the air
vibrations, which are then transmitted along the string. A paper cup at the other end of the string
transmits them back to the air, so that they again become again audible sound waves.
A telephone is a device that replaces the vibrations transmitted by string with electrical signals. The two
paper cups correspond to microphone and speaker and the string to the telephone line. Because
electrical signals travel over the telephone line at a high speed with minimal attenuation, the telephone
enables conversation over great distances.
Voice is changed into electrical signals using electromagnetic induction, a process by which electrical
signals are generated by vibrating a coil in a magnetic field. Both the microphone and speaker exploit
this process. The microphone transduces sound into electrical signals using electromagnetic induction
that occurs at a moving coil coupled to a diaphragm picking up air vibrations.
On the other hand, the speaker functions in the reverse manner, transducing electrical signals back to
air vibrations. Therefore, its construction is basically the same as that of a microphone. Electrical
signals passing through a coil in the magnetic field vibrate the coil, which in turn vibrate the air to
reproduce the voice.