A speaker driver is an individual transducer that converts electrical energy to sound waves, typically as part of a loudspeaker, television, or other electronics device. Sometimes the transducer is itself referred to as a speaker, particularly when a single one is mounted in an enclosure or as surface-mounted device (as in a wall-mounted speaker, car audio speaker, and so on). There are many different types of speaker drivers. The most common ones are the woofer, mid-range and tweeter, as well as subwoofers which are becoming very common. Less common types of speaker drivers are supertweeters and rotary woofers, a new technology that is still proprietary of Eminent Technology.
Description and operation
Speaker drivers include a diaphragm that moves back and forth to create pressure waves in the air column in front, and depending on the application, at some angle to the sides. The diaphragm is typically in the shape of a cone or, less commonly, a ribbon or a dome, and is usually made of coated or uncoated paper or polypropylene plastic.[1] More exotic materials are used on some drivers, such as woven fiberglass, carbon fiber, aluminum, titanium, and a very few use PEI, polyimide, PET film plastic film as the cone, dome or radiator.
All speaker drivers have a means of electrically inducing back-and-forth motion. Typically there is a tightly wound coil of insulated wire (known as a voice coil) attached to the neck of the driver's cone. In a ribbon speaker the voice coil may be printed or bonded onto a sheet of very thin paper, aluminium, fiberglass or plastic. This cone, dome or other radiator is mounted to a rigid chassis which supports a permanent magnet in close proximity to the voice coil. For the sake of efficiency the relatively lightweight voice coil and cone are the moving parts of the driver, whereas the much heavier magnet remains stationary. Other typical components are a spider or damper, used as the rear suspension element, simple terminals or binding posts to connect the audio signal, and possibly a compliant gasket to seal the joint between the chassis and enclosure.
Drivers are almost universally mounted into a rigid enclosure of wood, plastic, or occasionally metal. This loudspeaker enclosure or speaker box isolates the acoustic energy from the front of the cone from that of the the back of the cone. A horn may be employed to increase efficiency and directionality. A grille, fabric mesh, or other acoustically neutral screen is generally provided to cosmetically conceal the drivers and hardware, and to protect the driver from physical damage.
In operation, a signal is delivered to the voice coil by means of electrical wires. The current creates a magnetic field that causes the diaphragm to be alternately attracted to, and repelled by, the fixed magnet as the electrical signal varies. The resulting back-and-forth motion drives the air in front of the diaphragm, resulting in pressure differentials that travel away as sound waves.
Speaker drivers may be designed to operate within a broad or narrow frequency range. Small diaphragms are not well suited to moving the large volume of air that is required for satisfying low frequency response. Conversely, large drivers may have heavy voice coils and cones that limit their ability to move at very high frequencies. Drivers pressed beyond their design limits may have high distortion. In a multi-way loudspeaker system, specialized drivers are provided to produce specific frequency ranges, and the incoming signal is split by a crossover.[1] Drivers can be sub-categorized into several types: full-range, tweeters, mid-range drivers, woofers, and subwoofers.
Applications
Speaker drivers are the primary means for sound reproduction. They are used among other places in audio applications such as loudspeakers, headphones, telephones, megaphones, instrument amplifiers, television and monitor speakers, public address systems, portable radios, toys, and in many electronics devices that are designed to emit sound.
References
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