speaker connection

Speaker specifications generally include:

• Speaker or driver type (individual units only) – Full-range, woofer, tweeter, or mid-range.
• Size of individual drivers. For cone drivers, the quoted size is generally the outside diameter of the basket.^[21] 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. Voice-coil diameter may also be specified. If the loudspeaker has a compression horn driver, the diameter of the horn throat 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). A driver may be damaged at much less than its rated power if driven past its mechanical limits at lower frequencies.^[22] Tweeters can also be damaged by amplifier clipping (lots of high frequency energy in such cases) or by music or sine wave input at high frequencies. Each of these situations passes more energy to a tweeter than it can survive without damage.^[23]
• Impedance – typically 4 Ω (ohms), 8 Ω, etc.^[24]
• Baffle or enclosure type (enclosed systems only) – Sealed, bass reflex, etc.
• Number of drivers (complete speaker systems only) – two-way, three-way, etc.

and optionally:

• Crossover frequency(ies) (multi-driver systems only) – The nominal frequency boundaries of the signal 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 often includes a variance limit, such as within "± 2.5 dB".
• Thiele/Small parameters (individual drivers only) – these include the driver's F_s (resonance frequency), Q_ts (a driver's Q [more or less, its damping factor] at resonant frequency), V_as (the equivalent air compliance volume of the driver), etc.
• Sensitivity – The sound pressure level produced by a loudspeaker in a non-reverberant environment, usually specified in dB and measured at 1 meter with an input of 1 watt or 2.83 volts, typically at one or more specified frequencies. This rating is often inflated by manufacturers.
• Maximum SPL – The highest output the loudspeaker can manage, short of damage or not exceeding a particular distortion level. This rating is often inflated by manufacturers and is commonly given without reference to frequency range or distortion level.

Crossover

A passive crossover.

Bi-amped.

Used in multi-driver speaker systems, the crossover is a device that separates the input signal into different frequency ranges suited to each driver. 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-polar capacitors. 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.^{[citation needed]} 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.^[13] 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 bandpass.^[13] Passive filtering may also be used in this way before power amplification, but it is an uncommon solution, due to its 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.^[14] 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.^[15][16]

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 small, separate box, necessary to accommodate the size of the components used. 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 reduce undesirable characteristics of driver, horn, or enclosure resonances,^[17] and can be tricky to implement, due to component interaction. Passive crossovers, like the driver units that they feed, have power handling limits, and have about a 10% insertion loss, which is converted into heat.^[17] When high output levels are required, active crossovers may be preferable. Active crossovers may be simple circuits that emulate the response of a passive network, or may be more complex, allowing extensive audio adjustments. Active crossovers, called digital loudspeaker management systems, may include facilities for precise alignment of phase and time between frequency bands, equalization, and dynamics (compression and limiting) control.^[13]

Some hi-fi and professional loudspeaker systems now include an active crossover circuit as part of an onboard amplifier system. These designs are identifiable by their need for AC power in addition to a signal cable. This active topology may include driver protection circuits and other features of a digital loudspeaker management system. 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.^[18]

[edit]Enclosures

An unusual three-way speaker system. The cabinet is narrow in order to reduce a diffraction effect called the "baffle step".

Most loudspeaker systems consist of drivers mounted in an enclosure, or cabinet. The role of the enclosure is to provide a place to mount the drivers 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.^{[citation needed]}

The simplest driver mount is a flat panel (i.e., baffle) with the drivers mounted in holes in it. However, in this approach, 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. With an infinitely large panel, this interference could be entirely prevented. A sufficiently large sealed box can approach this behavior.^[19][20]

Since panels of infinite dimensions are impractical, most enclosures function by containing the rear radiation from the cone. 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, 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.^{[citation needed]}

However, a rigid enclosure reflects sound internally, which can then be transmitted back through the loudspeaker cone—again resulting in degradation of sound quality. 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.^{[citation needed]}

Other enclosure types alter the rear 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.

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 drivers forward or back so that the acoustic center of each driver is in the same vertical plane. 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.

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. 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, or using absorptive material around a driver.

[edit]Wiring connections

Two-way binding posts on a loudspeaker, connected usingbanana plugs.

A 4-ohm loudspeaker with two pairs of binding posts capable of accepting bi-wiring after the removal of two metal straps.

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 using binding posts or spring clips on the back of the enclosure. 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. 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. This type of wiring error doesn't damage speakers, but isn't optimal.

An audio engineering rule of thumb is that individual electrodynamic drivers provide quality performance over at most about three octaves. Multiple drivers (e.g., subwoofers, woofers, mid-range drivers, and tweeters) are generally used in a complete loudspeaker system to provide performance beyond three octaves.

[edit]Full-range drivers

A full-range driver is designed to have the widest frequency response possible, despite the rule of thumb cited above. 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 and in televisions, although some models are suitable for hi-fi listening. In hi-fi speaker systems, the use of wide-range drive units can avoid undesirable interaction between multiple drivers caused by non-coincident driver location or crossover network issues. 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, together with their requirement for large, elaborate, expensive enclosures—such as transmission lines, or horns—to approach optimum performance.^{[citation needed]}

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. 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. 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. Since the whizzer cone is smaller than the main diaphragm, output dispersion at high frequencies is improved relative to an equivalent single larger diaphragm.^{[citation needed]}

Limited-range drivers are typically used in computers, toys, and clock radios. 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.^{[citation needed]}

[edit]Subwoofer

A subwoofer is a woofer driver used only for the lowest part of the audio spectrum: typically below 120 Hz. Because the intended range of frequencies in these is limited, subwoofer system design is usually simpler in many respects than for conventional loudspeakers, often consisting of a single speaker enclosed in a suitable box or enclosure.^{[citation needed]}

To accurately reproduce very low bass notes without unwanted resonances (typically from cabinet panels), subwoofer systems must be solidly constructed and properly braced; good ones are typically extraordinarily heavy. Many subwoofer systems include power amplifiers and electronic sub-filters, with additional controls relevant to low-frequency reproduction. These variants are known as "active subwoofers".^{[citation needed]} "Passive" subwoofers require external amplification.

[edit]Woofer

A woofer is a driver that reproduces low frequencies. Some loudspeaker systems use a woofer for the lowest frequencies, making it possible to avoid using a subwoofer. Additionally, some loudspeakers use the woofer to handle middle frequencies, eliminating the mid-range driver. This can be accomplished with the selection of a tweeter that responds low enough combined with a woofer that responds high enough that the two drivers add coherently in the middle frequencies.^{[citation needed]}

[edit]Mid-range driver

A mid-range speaker is a loudspeaker driver that reproduces middle frequencies. Mid-range drivers can be made of paper or composite materials, or they can be compression drivers. If the mid-range driver is cone-shaped, it can be mounted on the front baffle of a loudspeaker enclosure, or it can be mounted at the throat of a horn for added output level and control of radiation pattern. If it is a compression driver, it is invariably mated to a horn.^{[citation needed]}

[edit]Tweeter

A tweeter is a high-frequency driver that typically reproduces the highest frequency band of a loudspeaker. 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. Ribbon tweeters have gained popularity in recent years, as their output power has been increased to levels useful for professional sound reinforcement, and their pattern control is conveniently shaped for concert sound.^{[citation needed]}

[edit]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 as Altec, Tannoy, Pioneer, KEF, BMS, Cabasse and Genelec.^[12]

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. 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 an 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, thereby 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.^{[citation needed]}

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 would be stiff, to prevent uncontrolled cone motions; light, to minimize starting force requirements; and well-damped, to reduce vibrations from continuing after the signal has stopped. 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 not stiff; metal can be made stiff and light, but it is not usually well-damped; plastic can be light, but typically, the stiffer it is made, the less well-damped it is. As a result, many cones are made of some sort of composite material. This can be a matrix of fibers, including Kevlar or fiberglass; a layered or bonded sandwich construction; or simply a coating applied to stiffen or damp a cone.^{[citation needed]}

The basket, or frame, must be designed for rigidity to avoid deformation, which would change the magnetic conditions in the magnet gap and could even cause the voice coil to rub against the walls of the gap. Baskets are typically cast or stamped metal, although molded plastic baskets are becoming common, especially for inexpensive drivers. The frame also plays a considerable role in conducting heat away from the coil.^{[citation needed]}

The suspension system keeps the coil centered in the gap and provides a restoring force that causes the speaker cone to return 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, and the "surround", which helps center the coil/cone assembly and allows free piston-like motion aligned with the magnetic gap. The spider is usually made of a corrugated fabric disk, generally with a coating of a material intended to improve mechanical properties. 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 adding a felt disc to provide a barrier to particles that might otherwise cause the voice coil to rub. A German company, Rulik, still offers a spider made of wood. The surround can be a roll of rubber or foam, or a ring of corrugated fabric (often coated), attached to the outer circumference of the cone and to the frame. The choice of suspension materials affects driver life, especially in the case of foam surrounds, which are susceptible to aging and environmental damage.^{[citation needed]}

The wire in a voice coil is usually made of copper, though aluminium—and, rarely, silver—may be used. 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. 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.^{[citation needed]}

Modern driver magnets are almost always permanent and made of ceramic, ferrite, Alnico, or, more recently, neodymium magnet. 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 neodymium magnets instead of ferrite types. Very few manufacturers use electrically powered field coils, as was common in the earliest designs. The size and type of magnet and details of the magnetic circuit differ, depending on design goals. 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. The benefits of this are 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. On the other hand, the copper cap requires a wider voice-coil gap, with increased magnetic reluctance; this reduces available flux, requiring a slightly larger magnet for equivalent performance.^{[citation needed]}

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. Adjusting a design to improve performance is done using magnetic, acoustic, mechanical, electrical, and material science theory; high precision measurements; and the observations of experienced listeners. Designers can use an anechoic chamber to 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. A few of the issues speaker and driver designers must confront are distortion, lobing, phase effects, off-axis response, and crossover complications.^{[citation needed]}

The fabrication of finished loudspeaker systems has become segmented, depending largely on price, shipping costs, and weight limitations. High-end speaker systems, which are heavier (and often larger) than economic shipping allows outside local regions, are usually made in their target market area and can cost $140,000 or more per pair.^[11] The lowest-priced speaker systems and most drivers are manufactured in China or other low-cost manufacturing locations.^{[citation needed]}

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. Nikola Tesla reportedly made a similar device in 1881, but he was not issued a patent.^[1] 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. 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. 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.

The modern design of moving-coil drivers was established by Oliver Lodge in (1898).^[2] The first practical application of moving-coil loudspeakers was established by Peter L. Jensen andEdwin Pridham, at Napa, California. Jensen was denied patents. Being unsuccessful in selling their product to the phone 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.^[3]

The moving-coil principle as commonly used today in direct radiators was patented in 1924 by Chester W. 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.^{[citation needed]}

About this same period, Walter H. Schottky invented the first ribbon loudspeaker.^[4]

These first loudspeakers used electromagnets, because large, powerful permanent magnets were generally not available at a reasonable price. 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 theamplifier to which the loudspeaker was connected. 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.^{[citation needed]}

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.^[5] In 1937, the first film industry-standard loudspeaker system, "The Shearer Horn System for Theatres"^[6] (a two-way system), was introduced by Metro-Goldwyn-Mayer. It used four 15″ low-frequency drivers, a crossover network set for 375 Hz, and a single sectoral horn with two compression drivers providing the high frequencies. John Kenneth Hilliard, James Bullough Lansing, andDouglas Shearer all played roles in creating the system. 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.^[7]

Altec introduced their coaxial Duplex driver in 1943, incorporating a high-frequency horn sending sound through the middle of a 12-inch woofer for near-point-source performance.^[8] Altec's "Voice of the Theatre" loudspeaker system arrived in the marketplace in 1945, offering better coherence and clarity at the high power levels necessary in movie theaters.^[9] The Academy of Motion Picture Arts and Sciences immediately began testing its sonic characteristics; they made it the film house industry standard in 1955.^[10] Subsequently, continuous developments in enclosure design and materials led to significant audible improvements.^{[citation needed]} 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 analysis

A loudspeaker (or "speaker") is an electroacoustic transducer that converts an electrical signal into sound. The speaker pulses in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.

Loudspeakers (and other electroacoustic transducers) are the most variable elements in a modern audio system and are usually responsible for most distortion and audible differences when comparing sound systems