Loudspeaker

A loudspeaker, or simply speaker, is an electromechanical device which converts an electrical signal into sound. The term is used to refer to both the transducer, or driver itself, and a complete system consisting of one or more transducers in an enclosure. The loudspeaker is the most variable element in an audio system. The audible differences between speaker systems are considerable.

Dynamic loudspeakers

Cross Section of a Dynamic Cone Loudspeaker

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The traditional design is in two parts, a fibrous semi-rigid cone and, attached to the apex of the cone, a coil of fine wire (usually copper), called the voice coil or moving coil. The coil is oriented coaxially with a permanent magnet where one pole is outside the coil, whilst the other is within the axis of the coil. (During the early days of loudspeaker-equipped radios, permanent magnets with sufficient strength were a rarity, and an electromagnet was often used to provide the stationary magnetic field. This winding often did double duty by serving as a choke coil in the power supply).

Related Topics:
Copper - Voice coil - Permanent magnet - Electromagnet - Choke coil - Power supply

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When an electrical signal is applied, a magnetic field is induced by the electric current in the coil which becomes an electromagnet. The coil and the permanent magnet interact with magnetic force which causes the coil and whole semi-rigid cone (diaphragm) to oscillate and reproduce sound at the frequency of the applied electrical signal. When a multi-frequency signal is applied, the complex vibration results in reproduction of the applied signal as an audio signal.

Related Topics:
Magnetic field - Current - Electromagnet - Magnetic force - Diaphragm - Oscillate - Frequency

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As well as the magnet, the voice coil and the cone, dynamic cone speakers also include a suspension system to provide lateral stability and make the speaker components return to a neutral point after moving. A typical suspension system includes the 'spider', which is at the apex of the cone, often of 'concertina' form; and the 'surround', which is at the base of the cone. The parts are held together by a chassis or basket.

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Driver cones may be constructed of a variety of materials, including paper, metal, various polypropylenes, and kevlar. Baskets must be designed in order to preserve rigidity and are typically cast or stamped metal. The size and type of magnets can also differ. Generally, larger and more powerful magnets are associated with higher quality speakers. Tweeters are subject to a unique set of variables and parameters; their design and construction is extremely variable.

Related Topics:
Polypropylene - Kevlar - Cast - Stamped

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The moving coil principle was patented in 1924 by two Americans, Chester W. Rice and Edward W. Kellogg. There is some controversy in that an application was made earlier by the Briton Paul Voigt but not granted until later. Voigt produced the first effective full range unit in 1928, although using electromagnets rather than permanent magnets, and he also developed what may have been the first system designed for the home.

Related Topics:
1924 - Chester W. Rice - Edward W. Kellogg - Paul Voigt - 1928

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Despite marketing claims, lighter and more rigid cones do not always sound better. The weight and damping of the cone in a dynamic speaker should be appropriate for the characteristics of the rest of the driver and enclosure in order to produce accurate sound.

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Dynamic loudspeakers can be used as passive loudspeakers as well, without the need of using a power supply.

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