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10 février 2011 4 10 /02 /février /2011 08:26

A loudspeaker (or "speaker") is an electroacoustic transducer that produces sound in response to an electrical audio signal input.

Terminology

The term "loudspeaker" may refer to individual transducers (known as "drivers") or to complete speaker systems consisting of an enclosure including one or more drivers  (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk .

To adequately reproduce a wide range of frequencies, most loudspeaker systems employ more than one driver, particularly for higher sound pressure level or maximum accuracy. Individual drivers are used to reproduce different frequency ranges. The drivers are named subwoofers (for very low frequencies)      Dell Studio XPS 1640 Battery ;

woofers (low frequencies); mid-range speakers (middle frequencies); tweeters (high frequencies); and sometimessupertweeters, optimized for the highest audible frequencies. The terms for different speaker drivers differ, depending on the application. In two-way systems there is no mid-range driver, so the task of reproducing the mid-range sounds falls upon the woofer and tweeter Dell Vostro 1710 Battery .

Home stereos use the designation "tweeter" for the high frequency driver, while professional concert systems may designate them as "HF" or "highs". When multiple drivers are used in a system, a "filter network", called a crossover, separates the incoming signal into different frequency ranges and routes them to the appropriate driver   Dell KM958 battery .

A loudspeaker system with n separate frequency bands is described as "n-way speakers": a two-way system will have a woofer and a tweeter; a three-way system employs a woofer, a mid-range, and a tweeter  Dell Studio 1555 battery .

History

Johann Philipp Reis installed an electric loudspeaker in his telephone in 1861; it was capable of reproducing pure tones, but also could reproduce speech. Alexander Graham Bell patented his first electric loudspeaker (capable of reproducing intelligible speech) as part of his telephone in 1876, which was followed in 1877 by an improved version from Ernst Siemens  Sony VGP-BPS13 battery .

Nikola Tesla reportedly made a similar device in 1881, but he was not issued a patent. During this time, Thomas Edison was issued a British patent for a system using compressed air as an amplifying mechanism for his early cylinder phonographs, but he ultimately settled for the familiar metal horn driven by a membrane attached to the stylus      Sony VGP-BPS13/B battery .

In 1898, Horace Short patented a design for a loudspeaker driven by compressed air; he then sold the rights to Charles Parsons, who was issued several additional British patents before 1910. A few companies, including the Victor Talking Machine Company and Pathé, produced record players using compressed-air loudspeakers       Sony VGP-BPS13/S battery .

However, these designs were significantly limited by their poor sound quality and their inability to reproduce sound at low volume. Variants of the system were used for public address applications, and more recently, other variations have been used to test space-equipment resistance to the very loud sound and vibration levels that the launching of rockets produces   Sony VGP-BPS13A/B battery .

The modern design of moving-coil (also called dynamic) drivers was established by Oliver Lodge in 1898.The first practical application of moving-coil loudspeakers was established by Peter L. Jensenand Edwin Pridham, in Napa, California. Jensen was denied patents   Sony VGP-BPS13B/B battery .

Being unsuccessful in selling their product to telephone companies, in 1915 they changed strategy to public address, and named their product Magnavox. Jensen was, for years after the invention of the loudspeaker, a part owner of The Magnavox Company.

The moving-coil principle as commonly used today in direct radiators was patented in 1924 by Chester W  Sony VGP-BPL9 battery .

Rice and Edward W. Kellogg. The key difference between previous attempts and the patent by Rice and Kellogg was the adjustment of mechanical parameters so that the fundamental resonance of the moving system took place at a lower frequency than that at which the cone's radiation impedance had become uniform. See the original patent for details  Sony VGP-BPS13B/B battery .

About this same period, Walter H. Schottky invented the first ribbon loudspeaker.

These first loudspeakers used electromagnets, because large, powerful permanent magnets were generally not available at a reasonable price     Sony VGP-BPL15 battery .

The coil of an electromagnet, called a field coil, was energized by current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a choke coil, filtering the power supply of the amplifier to which the loudspeaker was connected      Dell Inspiron E1505 battery .

AC ripple in the current was attenuated by the action of passing through the choke coil; however, AC line frequencies tended to modulate the audio signal being sent to the voice coil and added to the audible hum of a powered-up sound reproduction device Dell Latitude E6400 battery .

In the 1930s, loudspeaker manufacturers began to combine two and three bandpasses' worth of drivers in order to increase frequency response and sound pressure level. In 1937, the first film industry-standard loudspeaker system, "The Shearer Horn System for Theatres" (a two-way system), was introduced by Metro-Goldwyn-Mayer  HP Pavilion dv6000 Battery .

It used four 15? low-frequency drivers, a crossover network set for 375 Hz, and a single multi-cellular horn with two compression drivers providing the high frequencies. John Kenneth Hilliard, James Bullough Lansing, and Douglas Shearer all played roles in creating the system      SONY VAIO VGN-FZ Battery .

At the 1939 New York World's Fair, a very large two-way public address system was mounted on a tower at Flushing Meadows. The eight 27? low-frequency drivers were designed by Rudy Bozak in his role as chief engineer for Cinaudagraph. High-frequency drivers were likely made by Western Electric      SONY VAIO VGN-FZ18 Battery .

Altec Lansing introduced the '604', which was to become their most famous coaxial Duplex driver, in 1943, incorporating a high-frequency horn sending sound through the middle of a 15-inch woofer for near-point-source performance     SONY VAIO VGN-FZ21E Battery .

Altec's "Voice of the Theatre" loudspeaker system arrived in the marketplace in 1945, offering better coherence and clarity at the high output levels necessary in movie theaters. The Academy of Motion Picture Arts and Sciences immediately began testing its sonic characteristics; they made it the film house industry standard in 1955  SONY VAIO VGN-FW21E Battery .

Subsequently, continuous developments in enclosure design and materials led to significant audible improvements. The most notable improvements in modern speakers are improvements in cone materials, the introduction of higher-temperature adhesives, improved permanent magnet materials, improved measurement techniques, computer-aided design, and finite element analysisSONY VAIO VGN-NR11S/S Battery .

Driver design

The most common type of driver uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension that constrains a coil of fine wire to move axially through a cylindrical magnetic gap  SONY VAIO VGN-NR11M/S Battery .

When an electrical signal is applied to the voice coil, a magnetic field is created by the electriccurrent in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth     SONY VAIO VGN-NR11Z/S Battery ,

thereby reproducing sound under the control of the applied electrical signal coming from theamplifier. 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  SONY VAIO VGN-NR11Z/T Battery .

A variety of different materials may be used, but the most common are paper, plastic, and metal. The ideal material would be 1) rigid, to prevent uncontrolled cone motions; 2) have low mass, to minimize starting force requirements and energy storage issues  Sony VAIO VGN-FZ21E Battery ;

3) be well damped, to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonancefrequency 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     Sony VAIO VGN-FW21E Battery .

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       Sony VAIO VGN-NR11S/S Battery .

For example, a cone might be made of cellulose paper, into which some carbon fiber, Kevlar, fiberglass, 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       Sony VAIO VGN-NR11Z/S Battery .

The chassis, frame, or basket, is designed to be rigid, avoiding deformation which would change critical alignments with the magnet gap, perhaps causing the voice coil to rub against the sides of the gap. Chassis are typically cast from aluminum alloy, or stamped from thin steel sheet        Sony VAIO VGN-NR11M/S Battery ,

although molded plastic and damped plastic compound baskets are becoming common, especially for inexpensive, low-mass drivers. Metallic chassis can play an important role in conducting heat away from the voice coil; heating during operation changes resistance, causing physical dimensional changes, and if extreme, may even demagnetize permanent magnets      Sony VAIO VGN-NR11Z/T Battery .

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 frame and provides the majority of the restoring force   SONY VAIO VGN-FZ180E Battery ,

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"  SONY VAIO VGN-FZ220E Battery .

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. The German firm Rulik still offers drivers with uncommon spiders made of wood.

The cone surround can be rubber or polyester foam, or a ring of corrugated, resin coated fabric  SONY VAIO VGN-FZ340E Battery ;

it is attached to both the outer diaphragm circumference and to the frame. These different surround materials, their shape and treatment can dramatically affect the acoustic output of a driver; each class and implementation having advantages and disadvantages      SONY VAIO VGN-FZ430E Battery .

Polyester foam, for example, is lightweight and economical, but is degraded by exposure to ozone, UV light, humidity and elevated temperatures, limiting its useful life to about 15 years.

The wire in a voice coil is usually made of copper, though aluminum—and, rarely, silver—may be used     SONY VAIO VGN-FZ460E Battery .

The advantage of aluminum is its light weight, which raises the resonant frequency of the voice coil and allows it to respond more easily to higher frequencies. A disadvantage of aluminum is that it is not easily soldered, and so connections are instead often crimped together and sealed     SONY VAIO VGN-FZ480E Battery .

These connections can corrode and fail in time. Voice-coil wire cross sections can be circular, rectangular, or hexagonal, giving varying amounts of wire volume coverage in the magnetic gap space. The coil is oriented co-axially inside the gap; it moves back and forth within a small circular volume (a hole, slot, or groove) in the magnetic structure  SONY VAIO VGN-FZ4000 Battery .

The gap establishes a concentrated magnetic field between the two poles of a permanent magnet; the outside of the gap being one pole, and the center post (called the pole piece) being the other. The pole piece and backplate are often a single piece, called the poleplate or yoke   SONY VAIO VGN-FZ31E Battery .

Modern driver magnets are almost always permanent and made of ceramic, ferrite, Alnico, or, more recently, rare earth such as neodymium and Samarium cobalt. A trend in design—due to increases in transportation costs and a desire for smaller, lighter devices (as in many home theater multi-speaker installations)—is the use of the last instead of heavier ferrite types  SONY VAIO VGN-FZ31B Battery .

Very few manufacturers still use electrically powered field coils, as was common in the earliest designs (one such is French). When high field-strength permanent magnets became available, Alnico, an alloy of aluminum, nickel, and cobalt became popular, since it dispensed with the power supply issues of field-coil drivers   SONY VAIO VGN-FZ31J Battery .

Alnico was used for almost exclusively until about 1980. Alnico magnets can be partially degaussed (i.e., demagnetized) by accidental 'pops' or 'clicks' caused by loose connections, especially if used with a high power amplifier. This damage can be reversed by "recharging" the magnet  SONY VAIO VGN-FZ31M Battery .

After 1980, most (but not quite all) driver manufacturers switched from Alnico to ferrite magnets, which are made from a mix of ceramic clay and fine particles of barium or strontium ferrite. Although the energy per kilogram of these ceramic magnets is lower than Alnico     SONY VAIO VGN-FZ31Z Battery ,

it is substantially less expensive, allowing designers to use larger yet more economical magnets to achieve a given performance.

The size and type of magnet and details of the magnetic circuit differ, depending on design goals    SONY VAIO VGN-FZ38M Battery .

For instance, the shape of the pole piece affects the magnetic interaction between the voice coil and the magnetic field, and is sometimes used to modify a driver's behavior. A "shorting ring", or Faraday loop, may be included as a thin copper cap fitted over the pole tip or as a heavy ring situated within the magnet-pole cavity   SONY VGP-BPS8 Battery .

The benefits of this complication is reduced impedance at high frequencies, providing extended treble output, reduced harmonic distortion, and a reduction in the inductance modulation that typically accompanies large voice coil excursions   SONY VGP-BPS13/S Battery .

On the other hand, the copper cap requires a wider voice-coil gap, with increased magnetic reluctance; this reduces available flux, requiring a larger magnet for equivalent performance.

Driver design—including the particular way two or more drivers are combined in an enclosure to make a speaker system—is both an art and science   SONY VGP-BPS13A/B Battery .

Adjusting a design to improve performance is done using some combination of magnetic, acoustic, mechanical, electrical, and material science theory; high precision measurements, generally with the observations of experienced listeners. A few of the issues speaker and driver designers must confront are distortion, lobing, phase effects, off-axis response, and crossover complications  SONY VGP-BPS13B/B Battery .

Designers can use an anechoic chamberto ensure the speaker can be measured independently of room effects, or any of several electronic techniques which can, to some extent, replace such chambers. Some developers eschew anechoic chambers in favor of specific standardized room setups intended to simulate real-life listening conditions   SONY VGP-BPS13A/S Battery .

The fabrication of finished loudspeaker systems has become segmented, depending largely on price, shipping costs, and weight limitations. High-end speaker systems, which are typically heavier (and often larger) than economic shipping allows outside local regions, are usually made in their target market region and can cost $140,000 or more per pair  SONY VGP-BPS13AS Battery .

The lowest-priced speaker systems and most drivers are manufactured in China or other low-cost manufacturing locations.

Driver types

Individual electrodynamic drivers provide optimal performance within a limited pitch range   Dell Inspiron 1320n Battery .

Multiple drivers (e.g., subwoofers, woofers, mid-range drivers, and tweeters) are generally combined into a complete loudspeaker system to provide performance beyond that constraint.

Full-range drivers

A full-range driver is designed to have the widest frequency response possible   Dell Inspiron 1464 Battery .

These drivers are small, typically 3 to 8 inches (7.6 to 20 cm) in diameter to permit reasonable high frequency response, and carefully designed to give low-distortion output at low frequencies, though with reduced maximum output level. Full-range (or more accurately, wide-range) drivers are most commonly heard in public address systems   Dell Inspiron 1564 Battery ,

in televisions (although some models are suitable for hi-fi listening), small radios, intercoms, some computer speakers, etc. In hi-fi speaker systems, the use of wide-range drive units can avoid undesirable interactions between multiple drivers caused by non-coincident driver location or crossover network issues   Dell Inspiron 1764 Battery .

Fans of wide-range driver hi-fi speaker systems claim a coherence of sound, said to be due to the single source and a resulting lack of interference, and likely also to the lack of crossover components. Detractors typically cite wide-range drivers' limited frequency response and modest output abilities (most especially at low frequencies)   Dell Studio 1450 Battery ,

together with their requirement for large, elaborate, expensive enclosures—such as transmission lines, or horns—to approach optimum performance.

Full-range drivers often employ an additional cone called a whizzer: a small, light cone attached to the joint between the voice coil and the primary cone   Dell Studio 1457 Battery .

The whizzer cone extends the high-frequency response of the driver and broadens its high frequency directivity, which would otherwise be greatly narrowed due to the outer diameter cone material failing to keep up with the central voice coil at higher frequencies     Dell Latitude D610 Battery .

The main cone in a whizzer design is manufactured so as to flex more in the outer diameter than in the center. The result is that the main cone delivers low frequencies and the whizzer cone contributes most of the higher frequencies      Toshiba NB100 Battery .

Since the whizzer cone is smaller than the main diaphragm, output dispersion at high frequencies is improved relative to an equivalent single larger diaphragm.

Limited-range drivers, also used alone, are typically found in computers, toys, and clock radios   Toshiba Satellite M65 battery .

These drivers are less elaborate and less expensive than wide-range drivers, and they may be severely compromised to fit into very small mounting locations. In these applications, sound quality is a low priority. The human ear is remarkably tolerant of poor sound quality, and the distortion inherent in limited-range drivers may enhance their output at high frequencies, increasing clarity when listening to spoken word material  Toshiba Satellite M60 battery .

Subwoofer

A subwoofer is a woofer driver used only for the lowest part of the audio spectrum: typically below 200 Hz for consumer systems,below 100 Hz for professional live sound, and below 80 Hz inTHX-approved systems  Dell Latitude D830 Battery .

Because the intended range of frequencies is limited, subwoofer system design is usually simpler in many respects than for conventional loudspeakers, often consisting of a single driver enclosed in a suitable box or enclosure       Dell Latitude D620 Battery .

To accurately reproduce very low bass notes without unwanted resonances (typically from cabinet panels), subwoofer systems must be solidly constructed and properly braced; good speakers are typically quite heavy. Many subwoofer systems include power amplifiers and electronic sub-filters, with additional controls relevant to low-frequency reproduction  Dell Inspiron Mini 10 Battery .

These variants are known as "active subwoofers". In contrast, "passive" subwoofers require external amplification.

Woofer

A woofer is a driver that reproduces low frequencies  Sony VGN-FW11S Battery .

The driver combines with the enclosure design to produce suitable low frequencies (see speaker enclosure for the design choices available). Some loudspeaker systems use a woofer for the lowest frequencies, sometimes well enough that a subwoofer is not needed. Additionally, some loudspeakers use the woofer to handle middle frequencies, eliminating the mid-range driver  Sony VGN-FW11M Battery .

This can be accomplished with the selection of a tweeter that can work low enough that, combined with a woofer that responds high enough, the two drivers add coherently in the middle frequencies.

Mid-range driver

A mid-range speaker is a loudspeaker driver that reproduces middle frequencies   Sony VGN-FW139E/H battery .

Mid-range driver diaphragms can be made of paper or composite materials, and can be direct radiation drivers (rather like smaller woofers) or they can be compression drivers (rather like some tweeter designs). If the mid-range driver is a direct radiator, it can be mounted on the front baffle of a loudspeaker enclosure       Dell Latitude E5400 Battery ,

or, if a compression driver, mounted at the throat of a horn for added output level and control of radiation pattern.

Tweeter

A tweeter is a high-frequency driver that reproduces the highest frequencies in a speaker system      Dell Latitude E4200 Battery .

Many varieties of tweeter design exist, each with differing abilities with regard to frequency response, output fidelity, power handling, maximum output level, etc. Soft-dome tweeters are widely found in home stereo systems, and horn-loaded compression drivers are common in professional sound reinforcement       Dell Inspiron 300M Battery .

Ribbon tweeters have gained popularity in recent years, as their output power has been increased to levels useful for professional sound reinforcement, and their output pattern is wide in the horizontal plane, a pattern that has convenient applications in concert sound        Dell Vostro A840 Battery .

Coaxial drivers

A coaxial driver is a loudspeaker driver with two or several combined concentric drivers. Coaxial drivers have been produced by many companies, such asAltec, Tannoy, Pioneer, KEF, BMS, Cabasse and Genelec   Dell Studio 1737 battery .

Loudspeaker system design

Crossover

Used in multi-driver speaker systems, the crossover is a subsystem that separates the input signal into different frequency ranges suited to each driver       Dell Inspiron E1505 battery .

The drivers receive only the power in their usable frequency range (the range they were designed for), thereby reducing distortion in the drivers and interference between them   .

Crossovers can be passive or active. A passive crossover is an electronic circuit that uses a combination of one or more resistors, inductors, or non-polarcapacitors   Dell RM791 battery .

These parts are formed into carefully designed networks and are most often placed between the power amplifier and the loudspeaker drivers to divide the amplifier's signal into the necessary frequency bands before being delivered to the individual drivers   Dell XPS M1530 battery .

Passive crossover circuits need no external power beyond the audio signal itself, but do cause overall signal loss and a significant reduction in damping factor between the voice coil and the crossover.An active crossover is an electronic filter circuit that divides the signal into individual frequency bands before power amplification, thus requiring at least one power amplifier for each bandpassDell XPS M2010 battery .

Passive filtering may also be used in this way before power amplification, but it is an uncommon solution, due to inflexibility compared to active filtering. Any technique that uses crossover filtering followed by amplification is commonly known as bi-amping, tri-amping, quad-amping, and so on, depending on the minimum number of amplifier channels  Acer Aspire One battery .

Some loudspeaker designs use a combination of passive and active crossover filtering, such as a passive crossover between the mid- and high-frequency drivers and an active crossover between the low-frequency driver and the combined mid- and high frequencies  Toshiba Satellite P10 Battery .

Passive crossovers are commonly installed inside speaker boxes and are by far the most usual type of crossover for home and low-power use. In car audio systems, passive crossovers may be in a separate box, necessary to accommodate the size of the components used   SONY VGN-FZ210CE Battery .

Passive crossovers may be simple for low-order filtering, or complex to allow steep slopes such as 18 or 24 dB per octave. Passive crossovers can also be designed to compensate for undesired characteristics of driver, horn, or enclosure resonances, and can be tricky to implement, due to component interaction     Dell Precision M70 Battery .

Passive crossovers, like the driver units that they feed, have power handling limits, have insertion losses (10% is often claimed), and change the load seen by the amplifier. The changes are matters of concern for many in the hi-fi world.[26] When high output levels are required, active crossovers may be preferable     Toshiba Satellite L305 Battery .

Active crossovers may be simple circuits that emulate the response of a passive network, or may be more complex, allowing extensive audio adjustments. Some active crossovers, usually digital loudspeaker management systems, may include facilities for precise alignment of phase and time between frequency bands, equalization, and dynamics (compression and limiting) control  Toshiba Satellite T4900 Battery .

Some hi-fi and professional loudspeaker systems now include an active crossover circuit as part of an onboard amplifier system. These speaker designs are identifiable by their need for AC power in addition to a signal cable from a pre-amplifier. This active topology may include driver protection circuits and other features of a digital loudspeaker management system  Toshiba PA3399U-2BRS battery .

Powered speaker systems are common in computer sound (for a single listener) and, at the other end of the size spectrum, in modern concert sound systems, where their presence is significant and steadily increasing.

Enclosures

An unusual three-way speaker system      Toshiba Satellite A200 Battery .

The cabinet is narrow in order to raise the frequency at which a diffraction effect called the "baffle step" occurs.

Most loudspeaker systems consist of drivers mounted in an enclosure, or cabinet. The role of the enclosure is to provide a place to physically mount the drivers      Toshiba Satellite 1200 Battery ,

and to prevent sound waves emanating from the back of a driver from interfering destructively with those from the front; these typically cause cancellations (e.g., comb filtering) and significantly alter the level and quality of sound at low frequencies   Toshiba Satellite M300 Battery .

The simplest driver mount is a flat panel (i.e., baffle) with the drivers mounted in holes in it. However, in this approach, sound frequencies with a wavelength longer than the baffle dimensions are canceled out, because the antiphase radiation from the rear of the cone interferes with the radiation from the front   SONY VGP-BPS13A/Q Battery .

With an infinitely large panel, this interference could be entirely prevented. A sufficiently large sealed box can approach this behavior.

Since panels of infinite dimensions are impractical, most enclosures function by containing the rear radiation from the moving diaphragm     SONY VGP-BPS13A/Q Battery .

A sealed enclosure prevents transmission of the sound emitted from the rear of the loudspeaker by confining the sound in a rigid and airtight box. Techniques used to reduce transmission of sound through the walls of the cabinet include thicker cabinet walls, lossy wall material  SONY VGP-BPS13B/Q Battery ,

internal bracing, curved cabinet walls—or more rarely,visco-elastic materials (e.g., mineral-loaded bitumen) or thin lead sheeting applied to the interior enclosure walls.

However, a rigid enclosure reflects sound internally, which can then be transmitted back through the loudspeaker diaphraghm—again resulting in degradation of sound quality  SONY VGP-BPS13B/Q Battery .

This can be reduced by internal absorption using absorptive materials (often called "damping"), such as fiberglass, wool, or synthetic fiber batting, within the enclosure. The internal shape of the enclosure can also be designed to reduce this by reflecting sounds away from the loudspeaker diaphragm, where they may then be absorbed  SONY VGP-BPS13/Q Battery .

Other enclosure types alter the rear sound radiation so it can add constructively to the output from the front of the cone. Designs that do this (including bass reflex, passive radiator, transmission line, etc.) are often used to extend the effective low-frequency response and increase low-frequency output of the driver   SONY VGP-BPS13/Q Battery .

To make the transition between drivers as seamless as possible, system designers have attempted to time-align (or phase adjust) the drivers by moving one or more driver mounting locations forward or back so that the acoustic center of each driver is in the same vertical plane   SONY VGP-BPS21A/B Battery .

This may also involve tilting the face speaker back, providing a separate enclosure mounting for each driver, or (less commonly) using electronic techniques to achieve the same effect. These attempts have resulted in some unusual cabinet designs   SONY VGP-BPS21/S Battery .

The speaker mounting scheme (including cabinets) can also cause diffraction, resulting in peaks and dips in the frequency response. The problem is usually greatest at higher frequencies, where wavelengths are similar to, or smaller than, cabinet dimensions  SONY VGP-BPS21B Battery .

The effect can be minimized by rounding the front edges of the cabinet, curving the cabinet itself, using a smaller or narrower enclosure, choosing a strategic driver arrangement, using absorptive material around a driver, or some combination of these and other schemes  SONY VGP-BPS21A Battery .

Wiring connections

Most loudspeakers use two wiring points to connect to the source of the signal (for example, to the audio amplifier or receiver). This is usually done usingbinding posts or spring clips on the back of the enclosure   SONY VGP-BPS21 Battery .

If the wires for the left and right speakers (in a stereo setup) are not connected "in phase" with each other (the + and ? connections on the speaker and amplifier should be connected + to + and ? to ?), the loudspeakers will be out of polarity. Given identical signals, motion in one cone will be in the opposite direction of the other   Sony VGP-BPS21A/B Battery .

This will typically cause monophonic material within a stereo recording to be canceled out, reduced in level, and made more difficult to localize, all due to destructive interference of the sound waves. The cancellation effect is most noticeable at frequencies where the speakers are separated by a quarter wavelength or less; low frequencies are affected the most  Sony VGP-BPS21/S Battery .

This type of wiring error doesn't damage speakers, but isn't optimal.

Specifications

Speaker specifications generally include:

  • Speaker or driver type (individual units only) – Full-range, woofer, tweeter, or mid-range  Sony VGP-BPS21A Battery .
  • Size of individual drivers. For cone drivers, the quoted size is generally the outside diameter of the basket. However, it may less commonly also be the diameter of the cone surround, measured apex to apex, or the distance from the center of one mounting hole to its opposite   Sony VGP-BPS21 Battery .
  • Voice-coil diameter may also be specified. If the loudspeaker has a compression horn driver, the diameter of the horn thro at may be given.
  • Rated Power – Nominal (or even continuous) power, and peak (or maximum short-term) power a loudspeaker can handle (i.e., maximum input power before destroying the loudspeaker; it is never the sound output the loudspeaker produces)  Sony Vaio PCG-5G2L Battery .
  • A driver may be damaged at much less than its rated power if driven past its mechanical limits at lower frequencies. Tweeters can also be damaged by amplifier clipping (amplifier circuits produce large amounts of energy at high frequencies in such cases) or by music or sine wave input at high frequencies   Sony Vaio PCG-5G3L Battery .
  • Each of these situations passes more energy to a tweeter than it can survive without damage. In some jurisdictions, power handling has a legal meaning allowing comparisons between loudspeakers under consideration. Elsewhere, the variety of meanings for power handling capacity can be quite confusing     Sony Vaio PCG-5J1L Battery .
  • Impedance – typically 4 ? (ohms), 8 ?, etc.
  • Baffle or enclosure type (enclosed systems only) – Sealed, bass reflex, etc.
  • Number of drivers (complete speaker systems only) – two-way, three-way, etc  Sony Vaio PCG-5K2L Battery .

and optionally:

  • Crossover frequency(ies) (multi-driver systems only) – The nominal frequency boundaries of the division between drivers.
  • Frequency response – The measured, or specified, output over a specified range of frequencies for a constant input level varied across those frequencies. It sometimes includes a variance limit, such as within "± 2.5 dB"  Sony Vaio PCG-5J2L Battery.
  • Thiele/Small parameters (individual drivers only) – these include the driver's Fs (resonance frequency), Qts (a driver's Q; more or less, its damping factorat resonant frequency), Vas (the equivalent air compliance volume of the driver), etc  Sony Vaio PCG-5K1L Battery .
  • Sensitivity – The sound pressure level produced by a loudspeaker in a non-reverberant environment, often specified in dB and measured at 1 meter with an input of 1 watt (2.83 rms volts into 8 ?), typically at one or more specified frequencies. This rating is often specified by manufacturers to be impressive    Sony Vaio PCG-5L1L Battery .
  • Maximum SPL – The highest output the loudspeaker can manage, short of damage or not exceeding a particular distortion level. This rating is often specified by manufacturers to be impressive, and is commonly given without reference to frequency range or distortion level     Sony Vaio PCG-6S2L Battery .

Electrical characteristics of a dynamic loudspeaker

The load that a driver presents to an amplifier consists of a complex electrical impedance—a combination of resistance and both capacitive and inductivereactance, which combines properties of the driver, its mechanical motion  Sony Vaio PCG-6S3L Battery ,

the effects of crossover components (if any are in the signal path between amplifier and driver), and the effects of air loading on the driver as modified by the enclosure and its environment. Most amplifiers' output specifications are given at a specific power into an ideal resistive load     Sony Vaio PCG-6V1L Battery ;

however, a loudspeaker does not have a constant resistance across its frequency range. Instead, the voice coil is inductive, the driver has mechanical resonances, the enclosure changes the driver's electrical and mechanical characteristics, and a passive crossover between the drivers and the amplifier contributes its own variations     Sony Vaio PCG-6W1L Battery .

The result is a load resistance that varies fairly widely with frequency, and usually a varying phase relationship between voltage and current as well, also changing with frequency. Some amplifiers can cope with the variation better than others can  Sony Vaio PCG-6W2L Battery .

To make sound, a loudspeaker is driven by modulated electrical current (produced by an amplifier) that pass through a "speaker coil" (a coil of copper wire), which then (through resistance and other forces) magnetizes the coil, creating a magnetic field  Sony Vaio PCG-6W3L Battery .

The electrical current variations that pass through the speaker are thus converted to varying magnetic forces, which move the speaker diaphraghm, which thus forces the driver to produce air motion that is similar to the original signal from the amplifier  Sony Vaio PCG-7111L Battery .

Electromechanical measurements

Fully characterizing the sound output quality of a loudspeaker driver or system in words is essentially impossible. Objective measurements provide information about several aspects of performance so that informed comparisons and improvements can be made Sony Vaio PCG-7112L Battery ,

but no combination of measurements summarizes the performance of a loudspeaker system in use, if only because the test signals used are neither music nor speech. Examples of typical measurements are: amplitude and phase characteristics vs. frequency; impulse response under one or more conditions (e.g., square waves, sine wave bursts, etc.)  Sony Vaio PCG-7113L Battery ;

directivity vs. frequency (e.g., horizontally, vertically, spherically, etc.); harmonic and intermodulation distortion vs. SPL output, using any of several test signals; stored energy (i.e., ringing) at various frequencies; impedance vs. frequency; and small-signal vs. large-signal performance   Sony Vaio PCG-7133L Battery .

Most of these measurements require sophisticated and often expensive equipment to perform, and also good judgment by the operator, but the raw sound pressure level output is rather easier to report and so is often the only specified value—sometimes in misleadingly exact terms  Sony Vaio PCG-7Z2L Battery .

The sound pressure level (SPL) a loudspeaker produces is measured in decibels (dBspl)  .

Efficiency vs. sensitivity

Loudspeaker efficiency is defined as the sound power output divided by the electrical power input   Sony Vaio PCG-8Y1L Battery .

Most loudspeakers are actually very inefficient transducers; only about 1% of the electrical energy sent by an amplifier to a typical home loudspeaker is converted to acoustic energy. The remainder is converted to heat, mostly in the voice coil and magnet assembly      Sony Vaio PCG-8Y2L Battery .

The main reason for this is the difficulty of achieving proper impedance matching between the acoustic impedance of the drive unit and that of the air into which it is radiating (at low frequencies improving this match is the main purpose of speaker enclosure designs)     Sony Vaio PCG-8Z1L Battery .

The efficiency of loudspeaker drivers varies with frequency as well. For instance, the output of a woofer driver decreases as the input frequency decreases because of the increasingly poor match between air and the driver.

Driver ratings based on the SPL for a given input are called sensitivity ratings and are notionally similar to efficiency Sony Vaio PCG-8Z2L Battery .

Sensitivity is usually defined as so many decibels at 1 W electrical input, measured at 1 meter (except for headphones), often at a single frequency. The voltage used is often 2.83 VRMS, which is 1 watt into an 8 ? (nominal) speaker impedance (approximately true for many speaker systems)      Sony VAIO PCG-5G2L Battery .

Measurements taken with this reference are quoted as dB with 2.83 V @ 1 m.

The sound pressure output is measured at (or mathematically scaled to be equivalent to a measurement taken at) one meter from the loudspeaker and on-axis (directly in front of it), under the condition that the loudspeaker is radiating into an infinitely large space and mounted on an infinite baffle   Sony VAIO PCG-5G3L Battery .

Clearly then, sensitivity does not correlate precisely with efficiency, as it also depends on the directivity of the driver being tested and the acoustic environment in front of the actual loudspeaker. For example, a cheerleader's horn produces more sound output in the direction it is pointed by concentrating sound waves from the cheerleader in one direction, thus "focusing" them  Sony VAIO PCG-5J1L Battery .

The horn also improves impedance matching between the voice and the air, which produces more acoustic power for a given speaker power. In some cases, improved impedance matching (via careful enclosure design) will allow the speaker to produce more acoustic power     Sony VAIO PCG-5K2L Battery .

  • Typical home loudspeakers have sensitivities of about 85 to 95 dB for 1 W @ 1 m—an efficiency of 0.5–4%.
  • Sound reinforcement and public address loudspeakers have sensitivities of perhaps 95 to 102 dB for 1 W @ 1 m—an efficiency of 4–10%      Sony VAIO PCG-5J2L Battery .
  • Rock concert, stadium PA, marine hailing, etc. speakers generally have higher sensitivities of 103 to 110 dB for 1 W @ 1 m—an efficiency of 10–20%     Sony VAIO PCG-5K1L Battery .

A driver with a higher maximum power rating cannot necessarily be driven to louder levels than a lower-rated one, since sensitivity and power handling are largely independent properties. In the examples that follow, assume (for simplicity) that the drivers being compared have the same electrical impedance        Sony VAIO PCG-5L1L Battery ;

are operated at the same frequency within both driver's respective pass bands; and that power compression and distortion are low. For the first example, a speaker 3 dB more sensitive than another will produce double the sound power (or be 3 dB louder) for the same power input      Sony VAIO PCG-6S2L Battery ;

thus, a 100 W driver ("A") rated at 92 dB for 1 W @ 1 m sensitivity will put out twice as much acoustic power as a 200 W driver ("B") rated at 89 dB for 1 W @ 1 m when both are driven with 100 W of input power. In this particular example, when driven at 100 W, speaker A will produce the same SPL, or loudness, as speaker B would produce with 200 W input  Sony VAIO PCG-6S3L Battery .

Thus, a 3 dB increase in sensitivity of the speaker means that it will need half the amplifier power to achieve a given SPL. This translates into a smaller, less complex power amplifier—and often, to reduced overall system cost         Sony VAIO PCG-6V1L Battery .

It is not possible to combine high efficiency (especially at low frequencies) with compact enclosure size and adequate low frequency response. One can, more or less, choose only two of the three parameters when designing a speaker system. So, for example, if extended low-frequency performance and small box size are important, one must accept low efficiency  Sony VAIO PCG-6W1L Battery .

This rule of thumb is sometimes called Hoffman's Iron Law (after J.A. Hoffman, the "H" in KLH).

Listening environment

The interaction of a loudspeaker system with its environment is complex and is largely out of the loudspeaker designer's control  Sony VAIO PCG-6W2L Battery .

Most listening rooms present a more or less reflective environment, depending on size, shape, volume, and furnishings. This means the sound reaching a listener's ears consists not only of sound directly from the speaker system, but also the same sound delayed by traveling to and from (and being modified by) one or more surfaces   Sony VAIO PCG-6W3L Battery .

These reflected sound waves, when added to the direct sound, cause cancellation and addition at assorted frequencies (e.g., from resonant room modes), thus changing the timbre and character of the sound at the listener's ears     Sony VAIO PCG-7111L Battery .

The human brain is very sensitive to small variations, including some of these, and this is part of the reason why a loudspeaker system sounds different at different listening positions or in different rooms.

A significant factor in the sound of a loudspeaker system is the amount of absorption and diffusion present in the environment  Sony VAIO PCG-7112L Battery .

Clapping one's hands in a typical empty room, without draperies or carpet, will produce a zippy, fluttery echo which is due both to a lack of absorption and to reverberation (that is, repeated echoes) from flat reflective walls, floor, and ceiling     Sony VAIO PCG-7113L Battery .

The addition of hard surfaced furniture, wall hangings, shelving and even baroque plaster ceiling decoration, will change the echoes, due primarily to the diffusion caused by somewhat reflective objects with shapes and surfaces having sizes on the order of the sound wavelengths being diffused    Sony VAIO PCG-7Z1L Battery .

This somewhat breaks up the simple reflections otherwise caused by bare flat surfaces, and spreads the reflected energy of an incident wave over a larger angle on reflection.

Placement

In a typical rectangular listening room, the hard, parallel surfaces of the walls, floor and ceiling cause primary acoustic resonance nodes in each of the three dimensions: left-right, up-down and forward-backward      Sony VAIO PCG-7Z2L Battery .

Furthermore, there are more complex resonance modes involving three, four, five and even all six boundary surfaces combining to create standing waves. Low frequencies excite these modes the most, since long wavelengths are not much affected by furniture compositions or placement      Sony VAIO PCG-8Y1L Battery .

The mode spacing is critical, especially in small and medium size rooms lik

e recording studios, home theaters and broadcast studios. The proximity of the loudspeakers to room boundaries affects how strongly the resonances are excited as well as affecting the relative strength at each frequency       WD passport essential (500GB/640GB) .

The location of the listener is critical, too, as a position near a boundary can have a great effect on the perceived balance of frequencies. This is because standing wave patterns are most easily heard in these locations and at lower frequencies, below the Schroeder frequency – typically around 200–300 Hz, depending on room size      WD passport essential (250GB/320GB) .

Directivity

Acousticians, in studying the radiation of sound sources have developed some concepts important to understanding how loudspeakers are perceived. The simplest possible radiating source is a point source, sometimes called a simple source   WD  passport essential SE (750GB/1TB .

An ideal point source is an infinitesimally small point radiating sound. It may be easier to imagine a tiny pulsating sphere, uniformly increasing and decreasing in diameter, sending out sound waves in all directions equally, independent of frequency   WD  passport elite(250GB/320GB) .

Any object radiating sound, including a loudspeaker system, can be thought of as being composed of combinations of such simple point sources. The radiation pattern of a combination of point sources will not be the same as for a single source, but rather will depend on the distance and orientation between the sources        WD passport elite(500GB/640GB) ,

the position relative to them from which the listener hears the combination, and the frequency of the sound involved. Using geometry and calculus, some simple combinations of sources are easily solved; others are not      WD  passport studio for Mac(320GB/500GB) .

One simple combination is two simple sources separated by a distance and vibrating out of phase, one miniature sphere expanding while the other is contracting. The pair is known as a doublet, or dipole, and the radiation of this combination is similar to that of a very small dynamic loudspeaker operating without a baffle       WD  passport studio for Mac(500GB/640GB) .

The directivity of a dipole is a figure 8 shape with maximum output along a vector which connects the two sources and minimums to the sides when the observing point is equidistant from the two sources, where the sum of the positive and negative waves cancel each other       WD  Elements series(250GB/320GB) .

While most drivers are dipoles, depending on the enclosure to which they are attached, they may radiate as monopoles, dipoles (or bipoles). If mounted on a finite baffle, and these out of phase waves allowed to interact, dipole peaks and nulls in the frequency response result        WD  Elements SE(500GB/640GB) .

When the rear radiation is absorbed or trapped in a box, the diaphragm becomes a monopole radiator. Bipolar speakers, made by mounting in-phase monopoles (both moving out of or into the box in unison) on opposite sides of a box, are a method of approaching omnidirectional radiation patterns      WD Elements SE(750GB/1TB) .

Polar plots of a four-driver industrial columnar public address loudspeaker taken at six frequencies. Note how the pattern is nearly omnidirectional at low frequencies, converging to a wide fan-shaped pattern at 1 kHz, then separating into lobes and getting weaker at higher frequencies      WD  Elements desktop(500GB/640GB) .

In real life, individual drivers are actually complex 3D shapes such as cones and domes, and they are placed on a baffle for various reasons. A mathematical expression for the directivity of a complex shape, based on modeling combinations of point sources, is usually not possible, but in the farfield  WD  Elements desktop(750GB/1TB) ,

the directivity of a loudspeaker with a circular diaphragm will be close to that of a flat circular piston, so it can be used as an illustrative simplification for discussion. As a simple example of the mathematical physics involved, consider the following: the formula for farfield directivity of a flat circular piston in an infinite baffle radius, ? is the wavelength the first kind WD  Elements desktop(1.5 TB/2TB) .

A planar source will radiate sound uniformly for low frequencies whose wavelength is longer than the dimensions of the planar source, and as frequency increases, the sound from such a source will be focused into an increasingly narrower angle. The smaller the driver, the higher the frequency where this narrowing of directivity occurs  WD  passport essential SE (750GB/1TB)--USB 3.0)  .

Even if the diaphragm is not perfectly circular, this effect occurs such that larger sources are more directive. Several loudspeaker designs have been built which have approximately this behavior. Most are electrostatic or planar magnetic designs   WD  passport essential (500GB/640GB) .

Various manufacturers use different driver mounting arrangements to create a specific type of sound field in the space for which they are designed. The resulting radiation patterns may be intended to more closely simulate the way sound is produced by real instruments     WD  passport for Mac(320GB/500GB) ,

or simply create a controlled energy distribution from the input signal (some using this approach are called monitors, as they are useful in checking the signal just recorded in a studio). An example of the first is a room corner system with many small drivers on the surface of a 1/8 sphere     WD  passport for Mac(640GB/1TB) .

A system design of this type was patented by, and actually produced commercially, by Professor Amar Bose—the 2201. Later Bose models have deliberately emphasized production of both direct and reflected sound by the loudspeaker itself, regardless of its environment      My book essential 4 generation  (640GB/1TB) .

The designs are controversial in high fidelity circles, but have proven commercially successful. Several other manufacturers' designs follow similar principles.

Directivity is an important issue because it affects the frequency balance of sound a listener hears, and also the interaction of the speaker system with the room and its contents  WD  My book essential 4 generation( 1.5TB/2TB) .

A speaker which is very directive (i.e., on an axis perpendicular to the speaker face) may result in a reverberant field lacking in high frequencies, giving the impression the speaker is deficient in treble even though it measures well on axis (e.g., "flat" across the entire frequency range)       WD  My book elite( 1TB/1.5TB) .

Speakers with very wide, or rapidly increasing directivity at high frequencies, can give the impression that there is too much treble (if the listener is on axis) or too little (if the listener is off axis). This is part of the reason why on-axis frequency response measurement is not a complete characterization of the sound of a given loudspeaker   WD  My book studio(1TB/2TB) .

Other driver designs

Other types of drivers which depart from the most commonly used direct radiating electro-dynamic driver mounted in an enclosure include          WD  My book essential 4 generation( 1.5TB/2TB) :

Horn loudspeakers

Horn loudspeakers are the oldest form of loudspeaker system. The use of horns as voice-amplifying megaphones dates at least to the 17th century, and horns were used in mechanical gramophones as early as 1857        WD  My book elite(640GB/2TB) .

Horn loudspeakers use a shaped waveguide in front of or behind the driver to increase the directivity of the loudspeaker and to transform a small diameter, high pressure condition at the driver cone surface to a large diameter, low pressure condition at the mouth of the horn Seagate  expansion portable (320GB/500GB) .

This increases the sensitivity of the loudspeaker and focuses the sound over a narrower area. The size of the throat, mouth, the length of the horn, as well as the area expansion rate along it must be carefully chosen to match the drive to properly provide this transforming function over a range of frequencies  Seagate  expansion (1.5TB/2TB)

(every horn performs poorly outside its acoustic limits, at both high and low frequencies). The length and cross-sectional mouth area required to create a bass or sub-bass horn require a horn many feet long. 'Folded' horns can reduce the total size, but compel designers to make compromises and accept increased complication such as cost and construction  Seagate  Freeagent Desktop (500GB/1TB) .

Some horn designs not only fold the low frequency horn, but use the walls in a room corner as an extension of the horn mouth. In the late 1940s, horns whose mouths took up much of a room wall were not unknown amongst hi-fi fans. Room sized installations became much less acceptable when two or more were required       Seagate  Freeagent Go(250GB/320GB) .

A horn loaded speaker can have a sensitivity as high as 110 dB at 2.83 volts (1 watt at 8 ohms) at 1 meter. This is a hundredfold increase in output compared to a speaker rated at 90 dB sensitivity, and is invaluable in applications where high sound levels are required or amplifier power is limited        Seagate  Freeagent Go(500GB/640GB) .

Piezoelectric speakers

Piezoelectric speakers are frequently used as beepers in watches and other electronic devices, and are sometimes used as tweeters in less-expensive speaker systems, such as computer speakers and portable radios      Seagate  Freeagent Go(750GB/1TB) .

Piezoelectric speakers have several advantages over conventional loudspeakers: they are resistant to overloads which would normally destroy most high frequency drivers, and they can be used without a crossover due to their electrical properties  Seagate  Freeagent Goflex(250GB/320GB) .

There are also disadvantages: some amplifiers can oscillate when driving capacitive loads like most piezoelectrics, which results in distortion or damage to the amplifier. Additionally, their frequency response, in most cases, is inferior to that of other technologies. This is why they are generally used in single frequency (beeper) or non-critical applications  Seagate Freeagent Goflex(500GB/640GB) .

Piezoelectric speakers can have extended high frequency output, and this is useful in some specialized circumstances; for instance, sonar applications in which piezoelectric variants are used as both output devices (generating underwater sound) and as input devices (acting as the sensing components of underwater microphones)  Seagate  Freeagent Goflex(750GB/1TB) .

They have advantages in these applications, not the least of which is simple and solid state construction which resists the effects of seawater better than, say, a ribbon based device would.

Magnetostrictive speakers

Magnetostrictive transducers, based on magnetostriction, have been predominantly used as sonar ultrasonic sound wave radiators, but their usage has spread also to audio speaker systems    Seagate  Freeagent Goflex Pro(500GB/750GB) .

Magnetostrictive speaker drivers have some special advantages: they can provide greater force (with smaller excursions) than other technologies; low excursion can avoid distortions from large excursion as in other designs; the magnetizing coil is stationary and therefore more easily cooled       Seagate  Freeagent Goflex desktop(1TB/2TB) ;

they are robust because delicate suspensions and voice coils are not required. Magnetostrictive speaker modules have been produced by Fostex  and FeONIC  and subwoofer drivers have also been produced.

Electrostatic loudspeakers

Electrostatic loudspeakers use a high voltage electric field (rather than a magnetic field) to drive a thin statically charged membrane  Seagate  Freeagent go for Mac(320GB/640GB) .

Because they are driven over the entire membrane surface rather than from a small voice coil, they ordinarily provide a more linear and lower distortion motion than dynamic drivers. They have the disadvantage that the diaphragm excursion is severely limited because of practical construction limitations        Samsung  G2 protable (250gb/320GB) ;

the further apart the stators are positioned, the higher the voltage must be to achieve acceptable efficiency, which increases the tendency for electrical arcs as well as the increasing the speaker's attraction of dust particles. For many years electrostatic loudspeakers had a reputation as a generally unreliable and occasionally dangerous product  Samsung  G2 protable (500GB/640GB) .

Arcing remains a potential problem with current technologies, especially when the panels are allowed to collect dust or dirt, or when driven with high signal levels.

Electrostatics are inherently dipole radiators and due to the thin flexible membrane are less suited for use in enclosures to reduce low frequency cancellation as with common cone drivers     Samsung  S2 protable (320GB/500GB) .

Due to this and the low excursion capability, full range electrostatic loudspeakers are large by nature, and the bass will roll off at a frequency corresponding to a quarter wavelength of the narrowest panel dimension. To reduce the size of commercial products, they are sometimes used as a high frequency driver in combination with a conventional dynamic driver which handles the bass frequencies      Samsung S1 Mini (120GB/160GB) .

Ribbon and planar magnetic loudspeakers

A ribbon speaker consists of a thin metal-film ribbon suspended in a magnetic field. The electrical signal is applied to the ribbon which moves with it, thus creating the sound        Samsung  S1 Mini (250GB/320GB) .

The advantage of a ribbon driver is that the ribbon has very little mass; thus, it can accelerate very quickly, yielding very good high-frequency response. Ribbon loudspeakers are often very fragile—some can be torn by a strong gust of air. Most ribbon tweeters emit sound in a dipole pattern; a very few have backings which limit the dipole radiation pattern       Samsung story station (1TB/1.5TB) .

Above and below the ends of the more or less rectangular ribbon, there is less audible output due to phase cancellation, but the precise amount of directivity depends on ribbon length. Ribbon designs generally require exceptionally powerful magnets which make them costly to manufacture        Samsung Story station (1.5TB/2TB) .

Ribbons have a very low resistance that most amplifiers cannot drive directly. As a result, a step down transformer is typically used to increase the current through the ribbon. The amplifier "sees" a load that is the ribbon's resistance times the transformer turns ratio squared       Samsung story station Esata(1TB/1.5TB) .

The transformer must be carefully designed so that its frequency response and parasitic losses do not degrade the sound, further increasing cost and complication relative to conventional designs.

Planar magnetic speakers (having printed or embedded conductors on a flat diaphragm) are sometimes described as "ribbons", but are not truly ribbon speakers        Samsung  G3 station (1TB/1.5TB) .

The term planar is generally reserved for speakers which have roughly rectangular shaped flat surfaces that radiate in a bipolar (i.e., front and back) manner. Planar magnetic speakers consist of a flexible membrane with a voice coil printed or mounted on it        Maxtor  one touch 4 plus (500GB/750GB) .

The current flowing through the coil interacts with the magnetic field of carefully placed magnets on either side of the diaphragm, causing the membrane to vibrate more or less uniformly and without much bending or wrinkling. The driving force covers a large percentage of the membrane surface and reduces resonance problems inherent in coil-driven flat diaphragms  Maxtor one touch 4 plus (1TB/1.5TB) .

Bending wave loudspeakers

Bending wave transducers use a diaphragm that is intentionally flexible. The rigidity of the material increases from the center to the outside        Maxtor cool black(640GB/1TB) .

Short wavelengths radiate primarily from the inner area, while longer waves reach the edge of the speaker. To prevent reflections from the outside back into the center, long waves are absorbed by a surrounding damper. Such transducers can cover a wide frequency range (80 Hz to 35,000 Hz) and have been promoted as being close to an ideal point sound source  Maxtor Black diamond (320GB/500GB) .

This uncommon approach is being taken by only a very few manufacturers, in very different arrangements. The line of Ohm Walsh speakers use a unique driver designed by Lincoln Walsh. Lincoln Walsh was a brilliant engineer who was part of the engineering team that developed radar during World War II       Hitachi  simple touch (250GB/320GB) .

He later designed audio amplifiers, and his final project was a unique, one-way speaker with one driver. It was a large cone that faced down into a sealed, airtight enclosure. Rather than move back-and-forth as conventional speakers do, the cone rippled and created sound using a principle known as “transmission line”       Hitachi simple touch (320GB/500GB) .

The new speaker created a single, perfectly rendered sound wave of remarkable clarity. A new company, Ohm Acoustics, was formed to develop and market Walsh’s new speaker design. Lincoln Walsh died before his speaker was released to the public. After developing the Ohm A prototype, in 1973 Ohm introduced the Ohm F speaker to critical acclaim   Hitachi  life studio (320GB/500GB).

Flat panel loudspeakers

There have been many attempts to reduce the size of speaker systems, or alternatively to make them less obvious. One such attempt was the development of voice coils mounted to flat panels to act as sound sources     Hitachi life studio (250GB/320GB) .

These can then be made in a neutral color and hung on walls where they will be less noticeable than many speakers, or can be deliberately painted with patterns in which case they can function decoratively. There are two related problems with flat panel techniques      Hitachi  life studio platinum (250GB/320GB) :

first, a flat panel is necessarily more flexible than a cone shape in the same material, and therefore will move as a single unit even less, and second, resonances in the panel are difficult to control, leading to considerable distortions. Some progress has been made using such lightweight, rigid, materials such asStyrofoam       Hitachi life studio platinum (320GB/500GB) ,

and there have been several flat panel systems commercially produced in recent years.

Distributed mode loudspeakers

A newer implementation of the flat panel speaker system involves an intentionally flexible panel and an "exciter", mounted off-center and located so as to excite the panel to vibrate with minimal resonances        Hitachi life studio desk (500GB/1TB) .

Speakers using such techniques can reproduce sound with a wide directivity pattern (paradoxically somewhat like a point source) and have been used in some computer speaker designs and bookshelf loudspeakers.

Heil air motion transducers

Oskar Heil invented the air motion transducer in the 1960s       Hitachi life studio plus (320GB/500GB) .

In this approach, a pleated diaphragm is mounted in a magnetic field and forced to close and open under control of a music signal. Air is forced from between the pleats in accordance with the imposed signal, generating sound     Hitachi life studio plus (320GB/500GB) .

The drivers are less fragile than ribbons and considerably more efficient (and able to produce higher absolute output levels) than ribbon, electrostatic, or planar magnetic tweeter designs.

ESS, a California manufacturer, licensed the design, employed Heil, and produced a range of speaker systems using his tweeters during the 1970s and 1980s       Hitachi X mobile (250GB/320GB) .

Radio Shack, a large US retail store chain, also sold speaker systems using such tweeters for a time. At present, there are two manufacturers of these drivers in Germany, one of which produces a range of high end professional speakers using tweeters and mid-range drivers based on the technology       Hitachi X mobile(320GB/500GB) .

Martin Logan produces several AMT speakers in the US.

Plasma arc speakers

Plasma arc loudspeakers use electrical plasma as a radiating element. Since plasma has minimal mass, but is charged and therefore can be manipulated by an electric field, the result is a very linear output at frequencies far higher than the audible range  Hitachi  XL (1TB/2TB) .

Problems of maintenance and reliability for this approach tend to make it unsuitable for mass market use. In 1978 Alan E. Hill of the Air Force Weapons Laboratory in Albuquerque, NM, designed the Plasmatronics Hill Type I, a tweeter whose plasma was generated from helium gas       Toshiba canvio portable(320GB/500GB) .

This avoided the ozone and nitrous oxide  produced byRF decomposition of air in an earlier generation of plasma tweeters made by the pioneering DuKane Corporation, who produced the Ionovac (marketed as the Ionofane in the UK) during the 1950s  Toshiba  canvio portable(750GB/1TB) .

Currently, there remain a few manufacturers in Germany who use this design, and a do-it-yourself design has been published and has been available on the Internet.

A less expensive variation on this theme is the use of a flame for the driver, as flames contain ionized (electrically charged) gasesToshiba  anvio for Mac(500GB/750GB) .

Digital speakers

Digital speakers have been the subject of experiments performed by Bell Labs as far back as the 1920s. The design is simple; each bit controls a driver, which is either fully 'on' or 'off'.

There are problems with this design which have led to it being abandoned as impractical for the present  Toshiba  canvio for Mac(750GB/1TB) .

First, for a reasonable number of bits (required for adequate sound reproduction quality), the physical size of a speaker system becomes very large. Secondly, due to inherent analog digital conversion problems, the effect of aliasing is unavoidable, so that the audio output is "reflected" at equal amplitude in the frequency domain  Sony Vaio VGN-NR11Z/T battery ,

on the other side of the sampling frequency, causing an unacceptably high level of ultrasonics to accompany the desired output. No workable scheme has been found to adequately deal with this        Sony Vaio VGN-NR11Z/T Battery .

The term "digital" or "digital-ready" is often used for marketing purposes on speakers or headphones, but these systems are not digital in the sense described above. Rather, they are conventional speakers which can be used with digital sound sources (e.g., optical media, MP3 players, etc.), as can any conventional speaker       Sony Vaio VGN-NR11M/S Battery .

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