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Electrodynamic speaker driver
An electrodynamic speaker driver, often called simply a speaker driver when the type is implicit, is an individual transducer that converts an electrical audio signal to sound waves. While the term is sometimes used interchangeably with the term speaker (loudspeaker), it is usually applied to specialized transducers that reproduce only a portion of the audible frequency range, or to the one or more drivers within a loudspeaker cabinet (or simply "speaker".). For high fidelity reproduction of sound, multiple loudspeakers are often mounted in the same enclosure, each reproducing a different part of the audible frequency range. In this case the individual speakers are referred to as drivers and the entire unit is called a loudspeaker. Drivers made for reproducing high audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers (much less commonly called squawkers), and those for low frequencies are called woofers, while those for very low bass range are subwoofers. Less common types of drivers are supertweeters and rotary woofers.
The electroacoustic mechanism most widely used in speakers to convert the electric current to sound waves is the dynamic or electrodynamic driver, invented in 1925 by Edward W. Kellogg and Chester W. Rice, which creates sound with a coil of wire called a voice coil suspended between the poles of a magnet. There are others that are far less widely used: electrostatic drivers, piezoelectric drivers, planar magnetic drivers, Heil air motion drivers, and ionic drivers, among other speaker designs.
The most common type of driver, commonly called a dynamic loudspeaker, uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension, commonly called a spider, that constrains a voice coil to move axially through a cylindrical magnetic gap. A protective dust cap glued in the cone's center prevents dust, most importantly ferromagnetic debris, from entering the gap.
When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact in a manner similar to a solenoid, generating a mechanical force that moves the coil (and thus, the attached cone). Application of alternating current moves the cone back and forth, accelerating and reproducing sound under the control of the applied electrical signal coming from the amplifier.
The following is a description of the individual components of this type of loudspeaker.
The diaphragm is usually manufactured with a cone- or dome-shaped profile. A variety of different materials may be used, but the most common are paper, plastic, and metal. The ideal material is rigid, to prevent uncontrolled cone motions, has low mass to minimize starting force requirements and energy storage issues and is well damped to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonance frequency as determined by its usage. In practice, all three of these criteria cannot be met simultaneously using existing materials; thus, driver design involves trade-offs. For example, paper is light and typically well-damped, but is not stiff; metal may be stiff and light, but it usually has poor damping; plastic can be light, but typically, the stiffer it is made, the poorer the damping. As a result, many cones are made of some sort of composite material. For example, a cone might be made of cellulose paper, into which some carbon fiber, Kevlar, glass, hemp or bamboo fibers have been added; or it might use a honeycomb sandwich construction; or a coating might be applied to it so as to provide additional stiffening or damping.
The chassis, frame, or basket, is designed to be rigid, preventing deformation that could change critical alignments with the magnet gap, perhaps allowing the voice coil to rub against the magnet around the gap. Chassis are typically cast from aluminum alloy, in heavier magnet-structure speakers; or stamped from thin sheet steel in lighter-structure drivers. Other materials such as molded plastic and damped plastic compound baskets are becoming common, especially for inexpensive, low-mass drivers. A metallic chassis can play an important role in conducting heat away from the voice coil; heating during operation changes resistance, causes physical dimensional changes, and if extreme, broils the varnish on the voice coil; it may even demagnetize permanent magnets.
The suspension system keeps the coil centered in the gap and provides a restoring (centering) force that returns the cone to a neutral position after moving. A typical suspension system consists of two parts: the spider, which connects the diaphragm or voice coil to the lower frame and provides the majority of the restoring force, and the surround, which helps center the coil/cone assembly and allows free pistonic motion aligned with the magnetic gap. The spider is usually made of a corrugated fabric disk, impregnated with a stiffening resin. The name comes from the shape of early suspensions, which were two concentric rings of Bakelite material, joined by six or eight curved legs. Variations of this topology included the addition of a felt disc to provide a barrier to particles that might otherwise cause the voice coil to rub.
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Electrodynamic speaker driver
An electrodynamic speaker driver, often called simply a speaker driver when the type is implicit, is an individual transducer that converts an electrical audio signal to sound waves. While the term is sometimes used interchangeably with the term speaker (loudspeaker), it is usually applied to specialized transducers that reproduce only a portion of the audible frequency range, or to the one or more drivers within a loudspeaker cabinet (or simply "speaker".). For high fidelity reproduction of sound, multiple loudspeakers are often mounted in the same enclosure, each reproducing a different part of the audible frequency range. In this case the individual speakers are referred to as drivers and the entire unit is called a loudspeaker. Drivers made for reproducing high audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers (much less commonly called squawkers), and those for low frequencies are called woofers, while those for very low bass range are subwoofers. Less common types of drivers are supertweeters and rotary woofers.
The electroacoustic mechanism most widely used in speakers to convert the electric current to sound waves is the dynamic or electrodynamic driver, invented in 1925 by Edward W. Kellogg and Chester W. Rice, which creates sound with a coil of wire called a voice coil suspended between the poles of a magnet. There are others that are far less widely used: electrostatic drivers, piezoelectric drivers, planar magnetic drivers, Heil air motion drivers, and ionic drivers, among other speaker designs.
The most common type of driver, commonly called a dynamic loudspeaker, uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension, commonly called a spider, that constrains a voice coil to move axially through a cylindrical magnetic gap. A protective dust cap glued in the cone's center prevents dust, most importantly ferromagnetic debris, from entering the gap.
When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact in a manner similar to a solenoid, generating a mechanical force that moves the coil (and thus, the attached cone). Application of alternating current moves the cone back and forth, accelerating and reproducing sound under the control of the applied electrical signal coming from the amplifier.
The following is a description of the individual components of this type of loudspeaker.
The diaphragm is usually manufactured with a cone- or dome-shaped profile. A variety of different materials may be used, but the most common are paper, plastic, and metal. The ideal material is rigid, to prevent uncontrolled cone motions, has low mass to minimize starting force requirements and energy storage issues and is well damped to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonance frequency as determined by its usage. In practice, all three of these criteria cannot be met simultaneously using existing materials; thus, driver design involves trade-offs. For example, paper is light and typically well-damped, but is not stiff; metal may be stiff and light, but it usually has poor damping; plastic can be light, but typically, the stiffer it is made, the poorer the damping. As a result, many cones are made of some sort of composite material. For example, a cone might be made of cellulose paper, into which some carbon fiber, Kevlar, glass, hemp or bamboo fibers have been added; or it might use a honeycomb sandwich construction; or a coating might be applied to it so as to provide additional stiffening or damping.
The chassis, frame, or basket, is designed to be rigid, preventing deformation that could change critical alignments with the magnet gap, perhaps allowing the voice coil to rub against the magnet around the gap. Chassis are typically cast from aluminum alloy, in heavier magnet-structure speakers; or stamped from thin sheet steel in lighter-structure drivers. Other materials such as molded plastic and damped plastic compound baskets are becoming common, especially for inexpensive, low-mass drivers. A metallic chassis can play an important role in conducting heat away from the voice coil; heating during operation changes resistance, causes physical dimensional changes, and if extreme, broils the varnish on the voice coil; it may even demagnetize permanent magnets.
The suspension system keeps the coil centered in the gap and provides a restoring (centering) force that returns the cone to a neutral position after moving. A typical suspension system consists of two parts: the spider, which connects the diaphragm or voice coil to the lower frame and provides the majority of the restoring force, and the surround, which helps center the coil/cone assembly and allows free pistonic motion aligned with the magnetic gap. The spider is usually made of a corrugated fabric disk, impregnated with a stiffening resin. The name comes from the shape of early suspensions, which were two concentric rings of Bakelite material, joined by six or eight curved legs. Variations of this topology included the addition of a felt disc to provide a barrier to particles that might otherwise cause the voice coil to rub.