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A tweeter or treble speaker is a special type of
loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or " ...
(usually dome, inverse dome or horn-type) that is designed to produce high audio frequencies, typically deliver high frequencies up to 100 kHz. The name is derived from the high pitched sounds made by some
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s (tweets), especially in contrast to the low woofs made by many
dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s, after which low-frequency drivers are named (
woofer A woofer or bass speaker is a technical term for a loudspeaker driver designed to produce low frequency sounds, typically from 50 Hz up to 1000 Hz. The name is from the onomatopoeic English word for a dog's bark, " woof" (in contrast to th ...
s).


Operation

Nearly all tweeters are electrodynamic drivers using a
voice coil A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. The term ...
suspended within a fixed magnetic field. These designs operate by applying current from the output of an
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost the v ...
circuit to a coil of wire called a
voice coil A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. The term ...
. The
voice coil A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. The term ...
produces a varying magnetic field, which works against the fixed magnetic field of a permanent magnet around which the cylindrical voice coil is suspended, forcing the voice coil and the diaphragm attached to it to move. This mechanical movement resembles the waveform of the electronic signal supplied from the amplifier's output to the voice coil. Since the coil is attached to a diaphragm, the vibratory motion of the voice coil transmits to the diaphragm; the diaphragm in turn vibrates the air, thus creating air motions or audio waves, which is heard as high sounds. Modern tweeters are typically different from older tweeters, which were usually small versions of
woofer A woofer or bass speaker is a technical term for a loudspeaker driver designed to produce low frequency sounds, typically from 50 Hz up to 1000 Hz. The name is from the onomatopoeic English word for a dog's bark, " woof" (in contrast to th ...
s. As tweeter technology has advanced, different design applications have become popular. Many
soft dome tweeter The soft dome tweeter is a particular type of tweeter invented and patented in 1967 by Bill Hecht, a renowned pioneer in the early days of audio engineering and the founder of Phase Technology. Hecht states that he was confronted with what seeme ...
diaphragms are thermoformed from polyester film, or silk or polyester fabric that has been impregnated with a polymer resin. Hard dome tweeters are usually made of aluminium, aluminium-magnesium alloys, or titanium. Tweeters are intended to convert an electrical signal into mechanical air movement with nothing added or subtracted, but the process is imperfect, and real-world tweeters involve tradeoffs. Among the challenges in tweeter design and manufacture are: providing adequate damping, to stop the dome's motion rapidly when the signal ends; ensuring suspension linearity, allowing high output at the low end of its frequency range; ensuring freedom from contact with the magnet assembly, keeping the dome centered as it moves; and providing adequate power handling without adding excessive mass. Tweeters can also work in collaboration with the woofers that are responsible for generating the low frequencies or bass. Some tweeters sit outside the main enclosure in their own semi-independent unit. Examples include "
super tweeter A super tweeter is a speaker driver intended to produce ultra high frequencies in a multi-driver loudspeaker system. Its purpose is to recreate a more realistic sound field, often characterized as "airy-ness". Super tweeters are sometimes found in ...
s" and the novel "egg tweeter" by
Ohm Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm. Ohm or OHM may also refer to: People * Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm'' * Germán Ohm (born 1936), Mexican boxer * Jörg Ohm (b ...
. The latter plugs in and swivels to adjust the soundfield depending on listener position and user preference. The separation from the baffle is considered to be optimal under the theory that the smallest baffle possible is optimal for tweeters.


Range

Most tweeters are designed to reproduce frequencies up to the formally defined upper limit of the human
hearing range Hearing range describes the range of frequencies that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, although there is considerable variati ...
(typically listed as 20 kHz); some operate at frequencies up to approximately in between 5 kHz to 20 kHz. Tweeters with a greater upper range have been designed for psychoacoustic testing, for extended-range digital audio such as
Super Audio CD Super Audio CD (SACD) is an optical disc format for audio storage introduced in 1999. It was developed jointly by Sony and Philips Electronics and intended to be the successor to the Compact Disc (CD) format. The SACD format allows multiple aud ...
intended for
audiophile An audiophile is a person who is enthusiastic about high-fidelity sound reproduction. An audiophile seeks to reproduce the sound of a piece of recorded music or a live musical performance, typically inside closed headphones, In-ear monitors, open ...
s, for biologists performing research on animal response to sounds, and for ambient sound systems in zoos. Ribbon tweeters have been made that can reproduce 80 kHz and even 100 kHz.


Dome materials

All dome materials have advantages and disadvantages. Three properties designers look for in domes are low mass, high stiffness and good damping.
Celestion Celestion is a British designer and exporter of professional loudspeakers. History Origins What became Celestion was started in Hampton Wick (suburban London) in 1924. ''Cyril French'' and his three brothers had taken over a plating works ...
were the first manufacturers to fabricate dome tweeters out of a metal,
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
. Nowadays other metals such as
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
,
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, and
beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
, as well as various alloys thereof, are used, being both light and stiff but having low damping; their resonant modes occur above 20 kHz. More exotic materials, such as
synthetic diamond Lab-grown diamond (LGD; also called laboratory-grown, laboratory-created, man-made, artisan-created, artificial, synthetic, or cultured diamond) is diamond that is produced in a controlled technological process (in contrast to naturally formed ...
, are also being used for their extreme stiffness.
Polyethylene terephthalate Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods ...
film and woven
silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the coc ...
suffer less ringing, but are not nearly as stiff, which can limit their very high frequency output. In general, smaller dome tweeters provide wider dispersion of sound at the highest frequencies. However, smaller dome tweeters have less radiating area, which limits their output at the lower end of their range; and they have smaller voice coils, which limit their overall power output.


Ferrofluid

Ferrofluid Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid (usually an organic solvent or water). Each magnetic particle ...
is a suspension of very small (typically 10 nm) iron oxide magnetic particles in a very low volatility liquid, typically a synthetic oil. A wide range of
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
and magnetic density variants allow designers to add damping, cooling, or both. Ferrofluid also aids in centering the voice coil in the magnetic gap, reducing distortion. The fluid is typically injected into the magnetic gap and is held in place by the strong magnetic field. If a tweeter has been subjected to elevated power levels, some thickening of the ferrofluid occurs, as a portion of the carrier liquid evaporates. In extreme cases, this can degrade the sound quality and output level of a tweeter, and the fluid must be removed and new fluid installed.


Professional sound applications

Tweeters designed for sound reinforcement and musical instrument applications are broadly similar to high fidelity tweeters, though they're usually not referred to as tweeters, but as "high frequency drivers". Key design requirement differences are: mountings built for repeated shipping and handling, drivers often mounted to horn structures to provide for higher sound levels and greater control of sound dispersion, and more robust voice coils to withstand the higher power levels typically encountered. High frequency drivers in PA horns are often referred to as "
compression driver A compression driver is a small specialized diaphragm loudspeaker which generates the sound in a horn loudspeaker. It is attached to an acoustic horn, a widening duct which serves to radiate the sound efficiently into the air. It works in a "co ...
s" from the mode of acoustic coupling between the driver diaphragm and the horn throat. Various materials are used in the construction of compression driver diaphragms including titanium, aluminium, phenolic impregnated fabric,
polyimide Polyimide (sometimes abbreviated PI) is a polymer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, e.g ...
and PET film, each having its own characteristics. The diaphragm is glued to a voice coil former, typically made from a different material from the dome, since it must cope with heat without tearing or significant dimensional change. Polyimide film,
Nomex Nomex is a flame-resistant meta-aramid material developed in the early 1960s by DuPont and first marketed in 1967. Properties Nomex and related aramid polymers are related to nylon, but have aromatic backbones, and hence are more rigid and mo ...
, and glassfibre are popular for this application. The suspension may be a continuation of the diaphragm and is glued to a mounting ring, which may fit into a groove, over locating pins, or be fastened with machine screws. The diaphragm is generally shaped like an inverted dome and loads into a series of tapered channels in a central structure called a
phase plug In a loudspeaker, a phase plug, phasing plug or acoustical transformer is a mechanical interface between a speaker driver and the audience. The phase plug extends high frequency response because it guides waves outward toward the listener rather th ...
, which equalizes the path length between various areas of the diaphragm and the horn throat, preventing acoustic cancellations between different points on the diaphragm surface. The phase plug exits into a tapered tube, which forms the start of the horn itself. This slowly expanding throat within the driver is continued in the horn flare. The horn flare controls the coverage pattern, or directivity, and as an acoustic transformer, adds gain. A professional horn and compression driver combination has an output sensitivity of between 105 and 112 dB/watt/meter. This is substantially more efficient (and less thermally dangerous to a small voice coil and former) than other tweeter construction.


Types of tweeters


Cone tweeter

Cone tweeters have the same basic design and form as a woofer with optimizations to operate at higher frequencies. The optimizations usually are: * a very small and light cone so it can move rapidly; * cone materials chosen for stiffness (e.g., ceramic cones in one manufacturer's line), or good damping properties (e.g., paper, silk or coated fabric) or both; * a suspension (or spider) that is stiffer than for other drivers—less flexibility is needed for high frequency reproduction; * small voice coils (3/4 inch is typical) and light (thin) wire, which also helps the tweeter cone move rapidly. Cone tweeters were popular in older stereo hi-fi speakers designed and manufactured in the 1960s and 1970s as an alternative to the dome tweeter (which was developed in the late 1950s). Cone tweeters today are often relatively cheap, but many of those in the past were of high quality, such as those made by Audax/Polydax, Bozak, CTS, JBL, Tonegen and SEAS. These vintage cone tweeters exhibited very flat frequency response, low distortion, fast transient response, a low resonance frequency and a gentle low-end roll-off, easing crossover design. Typical of the 1960s/1970s-era was the CTS "phenolic ring" cone tweeters, exhibiting flat response from 2,000 to 15,000 Hz, low distortion and fast transient response. The CTS "phenolic ring" tweeter gets its name from the orange-colored edge suspension ring that it has which is made from phenolic. It was used in many makes and models of well-regarded vintage speakers, and was a mid-priced unit. Cone tweeters have a narrower dispersion characteristic that is the same as a cone woofer's. Many designers therefore believed this made them a good match to cone midranges and woofers, allowing for superb stereo imaging. However, the "sweet spot" created by the narrow dispersion of cone tweeters is small. Speakers with cone tweeters offered the best stereo imaging when positioned in the room's corners, a common practice in the 1950s, 1960s and early 1970s. During the 1970s and 1980s, the widespread introduction of higher quality audiophile discs and the advent of the CD caused the cone tweeter to fall out of popularity because cone tweeters seldom extend past 15 kHz. Audiophiles felt that cone tweeters lacked the "airiness" of dome tweeters or other types. Nevertheless, many high-end cone tweeters remained in limited production by Audax, JBL and SEAS until the mid-1980s. Cone tweeters are now rarely used in modern hi-fi usage and are routinely seen in low cost applications such as factory car speakers, compact stereo systems, and boom boxes. Some boutique speaker manufacturers recently have returned to high-end cone tweeters, especially recreations of CTS phenolic ring models, to create a vintage-sounding product.


Dome tweeter

A dome tweeter is constructed by attaching a voice coil to a dome (made of woven fabric, thin metal or other suitable material), which is attached to the magnet or the top plate via a low compliance suspension. These tweeters typically do not have a frame or basket, but a simple front plate attached to the magnet assembly. Dome tweeters are categorized by their voice coil diameter, and range from 19 mm (0.75 in), through 38 mm (1.5 in). The overwhelming majority of dome tweeters presently used in hi-fi speakers are 25 mm (1 in) in diameter. A variation is the ring radiator in which the 'suspension' of the cone or dome becomes the major radiating element. These tweeters have different directivity characteristics when compared to standard dome tweeters.


Piezo tweeter

A piezo (or piezo-electric) tweeter contains a piezoelectric crystal coupled to a mechanical diaphragm. An audio signal is applied to the crystal, which responds by flexing in proportion to the voltage applied across the crystal's surfaces, thus converting electrical energy into mechanical. The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing. The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa. The active element is basically a piece of polarized material (i.e. some parts of the molecule are positively charged, while other parts of the molecule are negatively charged) with electrodes attached to two of its opposite faces. When an electric field is applied across the material, the polarized molecules will align themselves with the electric field, resulting in induced dipoles within the molecular or crystal structure of the material. This alignment of molecules will cause the material to change dimensions. This phenomenon is known as
electrostriction Electrostriction (cf. magnetostriction) is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. Explanation Electrostriction is a property of all dielectr ...
. In addition, a permanently polarized material such as
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
(SiO2) or
barium titanate Barium titanate (BTO) is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a Ferroelectricity, ferroelectric, Pyroelectricity, pyroelectric, and ...
(BaTiO3) will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the
piezoelectric effect Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...
. Piezo tweeters rarely get used in high-end audio because of their low fidelity, although they did feature in some high-end designs of the late ‘70s, such as the Celef PE1 in which they were utilised as a super tweeter in combination with a conventional dome tweeter. They are often used in toys, buzzers, alarms, bass guitar speaker cabinets, cheap computer or stereo speakers and PA horns.


Ribbon tweeter

A ribbon tweeter uses a very thin diaphragm (often of aluminum, or perhaps metalized plastic film) that supports a planar coil frequently made by deposition of aluminium vapor, suspended in a powerful magnetic field (typically provided by
neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...
magnets) to reproduce high frequencies. The development of ribbon tweeters has more or less followed the development of
ribbon microphone A ribbon microphone, also known as a ribbon velocity microphone, is a type of microphone that uses a thin aluminum, duraluminum or nanofilm of electrically conductive ribbon placed between the poles of a magnet to produce a voltage by electromag ...
s. The ribbon is of very lightweight material and so capable of very high acceleration and extended high frequency response. Ribbons have traditionally been incapable of high output (large magnet gaps leading to poor magnetic coupling is the main reason). But higher power versions of ribbon tweeters are becoming common in large-scale sound reinforcement line array systems, which can serve audiences of thousands. They are attractive in these applications since nearly all ribbon tweeters inherently exhibit useful directional properties, with very wide horizontal dispersion (coverage) and very tight vertical dispersion. These drivers can easily be stacked vertically, building a high frequency line array that produces high sound pressure levels much farther away from the speaker locations than do conventional tweeters.


Planar-magnetic tweeter

Some loudspeaker designers use a planar-magnetic tweeter, sometimes called a quasi-ribbon. Planar magnetic tweeters are generally less expensive than true ribbon tweeters, but are not precisely equivalent as a metal foil ribbon is lighter than the diaphragm in a planar magnetic tweeter and the magnetic structures are different. Usually a thin piece of PET film or plastic with a voice coil wire running numerous times vertically on the material is used. The magnet structure is less expensive than for ribbon tweeters.


Electrostatic tweeter

An
electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber ...
tweeter operates on the same principles as a
full-range A full-range loudspeaker drive unit is defined as a driver which reproduces as much of the audible frequency range as possible, within the limitations imposed by the physical constraints of a specific design. The frequency range of these drive ...
electrostatic speaker An electrostatic loudspeaker (ESL) is a loudspeaker design in which sound is generated by the force exerted on a Acoustic membrane, membrane suspended in an electrostatic field. Design and functionality The speakers use a thin flat Diaphragm ( ...
or a pair of electrostatic headphones. This type of speaker employs a thin diaphragm (generally plastic and typically
PET A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence, ...
film), with a thin conductive coating, suspended between two screens or perforated metal sheets, referred to as stators. The output of the driving amplifier is applied to the primary of a step-up
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
with a center-tapped secondary, and a very high voltage—several hundred to several thousand volts—is applied between the center tap of the transformer and the diaphragm. Electrostatics of this type necessarily include a high voltage power supply to provide the high voltage used. The stators are connected to the remaining terminals of the transformer. When an audio signal is applied to the primary of the transformer, the stators are electrically driven 180 degrees out of phase, alternately attracting and repelling the diaphragm. An uncommon way of driving an electrostatic speaker without a transformer is to connect the plates of a push-pull vacuum tube amplifier directly to the stators, and the high voltage supply between the diaphragm and ground. Electrostatics have reduced even-order harmonic distortion because of their push-pull design. They also have minimal phase distortion. The design is quite old (the original patents date to the 1930s), but occupies a very small segment of the market because of high costs, low efficiency, large size for full range designs, and fragility.


AMT tweeter

The
Air Motion Transformer The Air Motion Transformer (AMT) is a type of electroacoustic transducer. Invented by noted physicist and scientist Dr. Oskar Heil (1908–1994), it operates on a different transduction principle from other loudspeaker designs, such as moving coil ...
tweeter works by pushing air out perpendicularly from the pleated diaphragm. Its diaphragm is the folded pleats of film (typically PET film) around aluminium struts held in a strong magnetic field. In past decades, ESS of California produced a series of hybrid loudspeakers using such tweeters, along with conventional woofers, referring to them as Heil transducers after their inventor,
Oskar Heil Oskar Heil (20 March 1908, in Langwieden – 15 May 1994, San Mateo, California) was a German electrical engineer and inventor. He studied physics, chemistry, mathematics, and music at the Georg-August University of Göttingen and was awarded h ...
. They are capable of considerable output levels and are rather more sturdy than electrostatics or ribbons, but have similar low-mass moving elements. Most of the current AMT drivers in use today are similar in efficiency and frequency response to the original Oskar Heil designs of the 1970s.


Horn tweeter

A horn tweeter is any of the above tweeters coupled to a flared or
horn Horn most often refers to: *Horn (acoustic), a conical or bell shaped aperture used to guide sound ** Horn (instrument), collective name for tube-shaped wind musical instruments *Horn (anatomy), a pointed, bony projection on the head of various ...
structure. Horns are used for two purposes — to control dispersion, and to couple the tweeter diaphragm to the air for higher efficiency. The tweeter in either case is usually termed a compression driver and is quite different from more common types of tweeters (see above). Properly used, a horn improves the off-axis response of the tweeter by controlling (i.e., reducing) the directivity of the tweeter. It can also improve the efficiency of the tweeter by coupling the relatively high acoustic impedance of the driver to the lower impedance of the air. The larger the horn, the lower the frequencies at which it can work, since large horns provide coupling to the air at lower frequencies. There are different types of horns, including
radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric) In mathematics, physics, and engineering, a Euclidean vector or simply a vector (sometimes called a geometric vector or spatial vector) ...
and constant directivity (CD). Horn tweeters may have a somewhat 'different' sonic signature than simple dome tweeters. Poorly designed horns, or improperly crossed-over horns, have predictable problems in the accuracy of their output, and the load that they present to the amplifier. Perhaps concerned about the image of poorly designed horns, some manufacturers use horn loaded tweeters, but avoid using the term. Their euphemisms include "elliptical aperture" "Semi-horn" and "Directivity controlled". These are, nonetheless, a form of horn loading.


Plasma or ion tweeter

Because ionized gas is electrically charged and so can be manipulated by a variable electrical field, it is possible to use a small sphere of
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
as a tweeter. Such tweeters are called a plasma tweeter or ion tweeter. They can be more complex than other tweeters (plasma generation is not required in other types), but offer the advantage that the moving mass is optimally low - if not relatively massless and so very responsive to the signal input. The early models of these tweeters were not capable of high output, nor of other than very high frequency reproduction, and so are usually used at the throat of a
horn Horn most often refers to: *Horn (acoustic), a conical or bell shaped aperture used to guide sound ** Horn (instrument), collective name for tube-shaped wind musical instruments *Horn (anatomy), a pointed, bony projection on the head of various ...
structure to manage usable output levels. One disadvantage is that the plasma arc can produce
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
and
NOx In atmospheric chemistry, is shorthand for nitric oxide () and nitrogen dioxide (), the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropos ...
,
poison Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...
gases, in small quantities as a by-product. Because of this, German-made Magnat "magnasphere" speakers were banned from import to the United States in the 1980s. Any modern design uses catalysts to reduce the gas output to negligible quantities. In the past, the dominant manufacturer in the US was DuKane near St Louis, who made the Ionovac; also sold in a UK variant as the Ionophone.
Electro-Voice Electro-Voice (EV) is an American manufacturer of audio equipment, including microphones, amplifiers, and loudspeakers, focused on pro audio applications such as sound reinforcement. As a subdivision of Bosch Communications Systems Inc. since 200 ...
made a model for a short time under license along with DuKane from the inventor Siegfried Klein. These early models were finicky and required regular replacement of the cell in which the plasma was generated (the DuKane unit used a precision machined quartz cell). As a result, they were expensive units in comparison to other designs. Those who have heard the Ionovacs report that, in a sensibly designed loudspeaker system, the highs were 'airy' and very detailed, though high output wasn't possible. In the 1980s, the
Plasmatronics Plasmatronics is a company, founded by former Air Force Weapons Laboratory (now Phillips Laboratory) scientist Dr. Alan E. Hill, which produced a plasma speaker design. This was first demonstrated at the 1978 Winter Consumer Electronics Show. The ...
speaker also used a plasma tweeter, though the manufacturer did not stay in business very long and very few of these complex units were sold.


See also

*
Loudspeaker enclosure A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often rectangular box-shaped) in which speaker drivers (e.g., loudspeakers and tweeters) and associated electronic hardware, such as crossover circuits and, in some cases, power ...
*
Audio crossover Audio crossovers are a type of electronic filter circuitry that splits an audio signal into two or more frequency ranges, so that the signals can be sent to loudspeaker drivers that are designed to operate within different frequency ranges. Th ...
*
Full-range speaker A full-range loudspeaker drive unit is defined as a driver which reproduces as much of the audible frequency range as possible, within the limitations imposed by the physical constraints of a specific design. The frequency range of these drive ...
*
Super tweeter A super tweeter is a speaker driver intended to produce ultra high frequencies in a multi-driver loudspeaker system. Its purpose is to recreate a more realistic sound field, often characterized as "airy-ness". Super tweeters are sometimes found in ...
*
Midrange speaker A mid-range speaker is a loudspeaker driver that reproduces sound in the frequency range from 250 to 2000 hertz, Hz. It is also known as a squawker. Mid-range drivers are usually cone types or, less commonly, dome types, or Compression_driver, co ...
*
Woofer A woofer or bass speaker is a technical term for a loudspeaker driver designed to produce low frequency sounds, typically from 50 Hz up to 1000 Hz. The name is from the onomatopoeic English word for a dog's bark, " woof" (in contrast to th ...
*
Subwoofer A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer is ...
*
Plasma speaker Plasma speakers or ionophones are a form of loudspeaker which varies air pressure via an electrical plasma instead of a solid diaphragm. The plasma arc heats the surrounding air causing it to expand. Varying the electrical signal that drives t ...


References

{{Reflist Loudspeakers