Cross-section of a full-range loudspeaker driver using a whizzer cone design.
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Fostex FE206e (modified) full range drive unit using a whizzer cone.
Goodmans Axiette, one of the first single-cone full-range drivers.

A full-range loudspeaker drive unit is defined as a driver which reproduces as much of the audible frequency range as possible, within the limitations imposed by the physical constraints of a specific design. The frequency range of these drivers is maximized through the use of a whizzer cone and other means. Most single driver systems, such as those in radios, or small computer speaker designs, cannot reproduce the entire audio range.

Typical designs[edit]

Typically, a full-range drive unit consists of a single driver element, or voice coil, used to move and control a diaphragm. Often the cone structure includes optimizations to enhance high-frequency performance. For example, a small low-mass horn or whizzer cone can be mounted where the voice coil and diaphragm meet, thereby increasing the output at high frequencies. The shape and materials used in the cone and whizzer are highly optimized.

Another arrangement uses a radiating dome in place of the usual dust-cap; it is acoustically active. In most speaker drivers such dust-caps are constructed so as to be relatively acoustically inert. Sometimes the dust-cap takes the form of a small conical shape, claimed to improve dispersion at higher frequencies. Yet other designs simply modify the diaphragm and dome/whizzer materials instead of compliantly coupling the diaphragm to achieve full-range operation.[citation needed]

In some designs, the main diaphragm may be coupled to the voice coil using a compliant bond such that high frequency vibrations are not transmitted into it, but instead move the whizzer cone. The technique of using a compliantly coupled (or modified) diaphragm for the low frequencies and auxiliary whizzer or modified dust-cap (dome) for the high frequency response of a speaker is a mechanical implementation of an audio crossover.

Since the requirements of a full-range driver include both good low and high frequency response (which are contradictory in terms of physical construction), a full-range driver is usually limited to covering the audio spectrum above perhaps 100 Hz—leaving lower frequencies to be handled / augmented by a separate sub woofer or by a special cabinet design for low frequency reinforcement. These requirements usually mean that the full-range must have good sensitivity (for lower frequencies) with a light voice coil (for high frequencies) – these speakers commonly use a larger or more powerful magnet than usual, which improves sensitivity and thus lowers the power requirement at low frequencies as well as allowing a lighter voice coil. In addition, many have limited maximum excursions, requiring special enclosures which do not require large excursions at low frequencies for reasonable low end output.

There are rare exceptions that use multiple elements to drive a common diaphragm, but these should not be confused with coaxial speakers that use separate and concentrically aligned elements to achieve the desired range of reproduction, and are not, strictly, classified as full-range drivers.

Full-range drivers are seen in applications ranging from televisions and computer speakers, to hi-fi speaker systems. The performance of the driver is substantially affected by their enclosure, and enclosures vary from mundane beige plastic boxes, at the low end of the scale, to large horn loadedenclosures with spectacular audio performance.

Atypical designs[edit]

A German company, Manger, produces an unusual full-range driver in the form of a differentially flexing flat diaphragm driver, about eight inches in diameter. Manger claims performance, both maximum level and extended low frequency response, which is rather better than traditional full-range drivers.

Another unusual full-range driver design is the Walsh driver, popularized in Ohm hi-fi speaker systems, where they reproduced almost the entire audible range of frequencies. Early Walsh units were large and expensive. These drivers used a single cone made with paper at the base, reproducing low frequencies, aluminium in the middle area, and titanium at the neck zone, to produce high frequencies. Slits in the paper area of the cone, covered with silicone damping, together with internal foam pads provided mechanisms for tailoring the frequency response to be as flat as possible. Loudspeakers using the Walsh driver are still in production, though they have adopted a tweeter so no longer qualify as full-range drivers. A variation on the Walsh driver, from a German firm, is available in two forms (a titanium cone and a carbon fibre cone) and incorporated into commercial loudspeaker systems.

Large electrostatic loudspeakers may be considered as full-range speakers in the sense that they are capable of reproducing most of the audio frequency band.

Applications[edit]

Full-range drive units may be found in applications ranging from inexpensive multimedia loudspeakers to more costly esoteric systems, the latter often using large transmission line or horn loadedenclosures to increase low frequency output. There is an active hobbyist speaker construction group on the Web focusing on full-range drivers and enclosures for them.

Since every electronic, mechanical or acoustical component in reproduction chain will, regardless of purpose, degrade fine detail, the fewer components between the amplifier terminals and the listening room, the better. This includes conventional 'mid-kilohertz' crossovers, which, in addition, destroy the natural integrity of the harmonic structure by the abrupt severance of the harmonics from the fundamental frequencies. These problems are avoided with the single cone moving coil driver which is to loudspeakers as the wheel is to the car.

Edward James Jordan, interviewed by TNT-Audio[1]

Commercial applications[edit]

Spherical Speaker with single driver

A large number of full-range drive units are used in commercial sound systems, which may employ a number of 200 mm (8') full-range drivers, mounted into suspended ceilings or small 'back-box' enclosures. These convey background music and announcements to workers and visitors in retail stores, and public spaces. While these drivers are classed as 'full-range', it may be more accurate to term them 'wide-range' drivers, since their output abilities rarely extend to the extremes of the frequency range. Several manufacturers build small (typically 115 mm (4.5')) diameter full-range drivers into miniature enclosures, and many of these include 25 or 70-volt line transformers, for use on commercial sound systems employing long speaker cables. Some full-range speaker systems are designed with limited-range drivers, and must be used with equalizers to flatten and extend their frequency response, while others achieve acceptable response without electronic assistance. There are full-range speaker systems using up to 15' single drivers.[2]

Critical reaction[edit]

Critics of full range drivers cite their inability to reproduce the full range of audio frequencies at similar amplitudes, leading to inaccurate reproduction of the audio signal sent to it. Reproducing multiple frequencies with the same diaphragm causes intermodulation distortion, a non-linear effect that occurs when one surface attempts to reproduce both frequencies simultaneously. The audible severity of modest intermodulation distortion is not well established. The result is a degree of 'frequency mixing', albeit at a relatively low level. A full range driver may have reduced output at both ends of its frequency range, or a more severely limited frequency response, resulting in a more compromised sound. Partisans of full-range loudspeakers claim superior phase coherence, while some critics describe them as midrange speakers working at or beyond their limits. Some full range drivers have been developed using 12' and 15' drivers, e.g. Audio Nirvana, and have overcome the bass limitations of smaller drivers using bass reflex cabinets. Also, as most adults cannot hear above 15 kHz the lack of high end frequency is generally not an issue with modern well designed full range drivers.

See also[edit]

References[edit]

  1. ^'Interview with Ted Jordan, of E.J.Jordan Designs'. TNT-Audio. 2000. Archived from the original on 2008-02-05. Retrieved 2009-01-23.
  2. ^'About Our Product'. R2R Audio. Retrieved 2014-12-27. After many years of research and development R2R Audio introduced in 2010 the flagship product – 15 inch Full Range loudspeaker active system.
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Woofer speaker drivers

A speaker driver is an individual loudspeaker transducer that converts an electrical audio signal to sound waves. While the term is sometimes used interchangeably with the term loudspeaker (speaker), it is usually applied to specialized transducers which reproduce only a portion of the audible frequency range. 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, 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 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 which are far less widely used: electrostatic drivers, piezoelectric drivers, planar magnetic drivers, Heil air motion drivers, and ionic drivers, among others.

Components[edit]

Cut-away view of a dynamic loudspeaker

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 for low and mid frequencies or a dome for higher frequencies, or less commonly, a ribbon, 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, pure cross carbon 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, aluminum, fiberglass or plastic. This cone, dome or other radiator is mounted at its outer edge by a flexible surround to a rigid frame 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.

Enclosures and acoustic isolation[edit]

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 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.

Operation[edit]

In operation, a signal is delivered to the voice coil by means of electrical wires, from the amplifier through speaker cable, then through flexible tinsel wire to the moving coil. The current creates a magnetic field that causes the diaphragm to be alternately forced one way or the other, by the magnetic field produced by current flowing in the voice coil, against the field established in the magnetic gap by the fixed magnet structure 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.

The spider and surround act as a spring restoring mechanism for motion away from the balanced position established when the driver was assembled at the factory. In addition, each contributes to centering the voice coil and cone, both concentrically within the magnet assembly, and front-to-back, restoring the voice coil to a critical position within the magnetic gap, neither toward one end nor the other.

The voice coil and magnet essentially form a linear motor working against the centering 'spring tension' of the spider and surround. If there were no restriction on travel distance imposed by the spider and surround, the voice coil could be ejected from the magnet assembly at high power levels, or travel inward deep enough to collide with the back of the magnet assembly. The majority of speaker drivers work only against the centering forces of the spider and surround, and do not actively monitor the position of the driver element or attempt to precisely position it. Some speaker driver designs have provisions to do so (typically termed servomechanisms); these are generally used only in woofers and especially subwoofers, due to the greatly increased cone excursions required at those frequencies in a driver whose cone size is well under the wavelength of the some of the sounds it is made to reproduce (ie, bass frequencies below perhaps 100 Hz or so).

Performance characteristics[edit]

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, super tweeters, mid-range drivers, woofers, and subwoofers.

Applications[edit]

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.

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See also[edit]

References[edit]

High Efficiency Single Driver Stereo Speakers

  1. ^ ab'Understanding how speaker drivers work'. Yahoo!.

Full Range Speaker Enclosure

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