al. Lautsprecher (m), Fr. Hautparleur (m), Eng. loudspeaker. An instrument that converts electrical current changes into sound vibrations.
In the 1920s, inventions emerged that allowed the recording and broadcasting of electrical sound waves. As a result of these inventions, the first loudspeaker was made in 1924-1925. Work by C.W.Rice and E.W.Kellegg developed the loudspeaker. The system revealed by these two scientists has not undergone any significant changes today.
There are four types of loudspeakers, namely electrodynamic, magnetostatic, electrostatic and electromagnetic loudspeakers, according to their working patterns. Moving coil loudspeakers consist of a circular or elliptical diaphragm. The diaphragm is suspended on a metal frame with springs along its middle and sides. In the middle of the diaphragm is a tightly attached cylindrical core and a voice coil wound on top of it. The coil and core are placed between the poles of a magnet. Previously, electromagnets operating with direct current from an amplifier were used, today permanent magnets of soft iron or ceramic materials are used.
The coil is a current-carrying conductor in a magnetic field. When the signal arrives, it moves under the influence of an electromagnetic force. Since the coil is firmly attached to the diaphragm, it also moves the diaphragm. The movement of the diaphragm adapts to changes in the electrical signal and emits sound waves into the air. When a louder sound is desired, it is sufficient to increase the intensity of the signal. A good speaker should not distort the sounds. Today, loudspeakers are usually housed in boxes covered with soundproof materials to prevent sound propagation from the back of the diaphragm.
Electrostatic loudspeaker is also very useful. In electrostatic loudspeakers, the diaphragm consists of a light, stretched metal or a metal-clad plastic sheet. The diaphragm is attached to a motionless plate. Very high DC (direct current) voltage passes between the motionless plates, which are drilled for sound transmission. A mechanical force is created. The signal from the amplifier passes through an isolating transformer. When the signal arrives, the force generated by the electricity between the plates is shaped, allowing the diaphragm to move, thus producing sound. The sound waves emitted into the air as a result of the vibration of the vocal cords in the throat strike the diaphragm in the microphone, making it vibrate. The pressure change that occurs as a result of the vibration transmitted to the coal particles behind the diaphragm changes the electrical resistance of the particles. This results in an alternating current. This, in turn, passes to the speaker, creating sound waves and radiating them into the air, in a reverse process to that of the microphone. Moving coil, banded electrostatic and crystalline microphones work on similar principles.
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