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Loudspeaker
Luminescence
Light that is produced when
a special material is struck by ultraviolet light. That happens in a fluorescent tube, for example. In the tube a flow of electricity through a gas causes ultraviolet
light to be produced. This light strikes special sensitive material on the inside of the tube, and the ultraviolet light is converted into visible light. The important thing about this process is that very
little heat is given off, so that
the light is produced much more efficiently than through an ordinary light bulb (see: Electric light). (See also: Phosphorescence.)
Luminous
Glowing in the dark. Paint that glows in the dark is called luminous paint. It contains material that sends out light for a period of time after it has been illuminated.
Cone made of paper or fabric
Loudspeaker
A device for converting electrical energy into sound energy within the range of hearing (20 to 20,000 hertz).
Traditionally, a loudspeaker consists of a cone that is made to vibrate by a special coil called a driver. This coil sits in a strong magnetic field. When an electrical signal passes through the coil, the coil makes its own magnetic field. The two magnetic fields interact and the coil is forced to move.
The moving coil is attached to
the cone of the loudspeaker. The cone amplifies the movement of the coil, making it loud enough for us to hear.
Modern loudspeakers use other ways of making the cone vibrate. For example, a crystal can be made to vibrate by passing an electrical signal through it. Each method of vibration produces its own sound quality.
A single loudspeaker cannot cover the whole range of hearing,
Coil made up as a tube with a loose fit over the magnet.
Magnet
Metal frame to hold cone
Connections from amplifier
 Loudspeaker – The central part of the speaker is called the driver. The driver makes the cone vibrate.
and for this reason a number
of different kinds of speakers
are used, each corresponding to
a particular range of vibrations. The deepest notes are reproduced by a large loudspeaker called a woofer. The high-pitched notes are reproduced by a loudspeaker called a tweeter. The rest of the notes are reproduced by a mid- range loudspeaker.
(See also: Amplifier; Distortion of sound; Dynamic range.)
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