Electrostatic speakers use a thin flat diaphragm usually consisting of a plastic sheet impregnated with a conductive material such as graphite sandwiched between two electrically conductive grids, with a small air gap between the diaphragm and grids. Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ...

The diaphragm is usually made from a polyester film (thickness 2-20 µm) with exceptional mechanical properties, such as Mylar. By means of the conductive coating and an external high voltage supply the diaphragm is held at a DC potential of several kilovolts with respect to the grids. The grids are driven by the audio signal; front and rear grid are driven in counterphase. As a result a uniform electrostatic field proportional to the audio signal is produced between both grids. This causes a force to be exerted on the charged diaphragm, in turn driving the air surrounding it. Mylar is a trade name of DuPont Teijin Films of Hopewell, VA, United States, for biaxially-oriented polyethylene terephthalate (BOPET) polyester film used for its high tensile strength, chemical and dimensional stability, transparency, and electrical insulation. ... In physics, a potential is a scalar quantity that can be used to analyze the effects of complicated vectorial forces and similar quantities by means of simple conservation laws. ... In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ...

In all but a few modern electrostatic loudspeakers the diaphragm is driven by two grids, one on either side, because the force exerted on the diaphragm by a single grid is non-linear, thus causing harmonic distortion. Using grids on both sides cancels out non-linearity. The result is near complete absence of harmonic distortion. The total harmonic distortion, or THD, of a signal is a measurement of the harmonic distortion present, that is, any departure of the output signal waveform from that which should result from the input signal waveforms being operated on by the systems specified or ideal transfer function. ...

The grids must be able to generate as uniform an electric field as possible, while still allowing for sound to pass through, and should be perfectly flat. Suitable grid constructions are therefore perforated metal sheets, a frame with tensioned wire, or wire rods.

To generate a sufficient field strength, the audio signal on the grids must be of high voltage. Current is only needed to charge the capacitance between both grids. This makes this type of speaker a high-impedance device. In contrast, a modern electrodynamic cone loudspeaker is a low impedance device driven by current. As a result, impedance matching is necessary in order to use a normal amplifier. Most often a transformer is used to this end. Construction of this transformer is critical as it must provide a constant (often high) transformation ratio over the entire audible frequency range. In the physical sciences, potential difference is the difference in potential between two points in a conservative vector field. ... In electrical engineering, impedance is a measure for the manner and degree a component resists the flow of electrical current if a given voltage is applied. ... Closeup of a loudspeaker driver A loudspeaker is a device which converts an electrical signal into sound. ... An electronic amplifier is a device for increasing the power of a signal. ... Transformers - Typical electrical configurations. ...

Advantages of electrostatic loudpseakers include very fast transient response due to the extreme light weight of the diaphragm, and exemplary frequency response (both in amplitude and phase). Transparency is usually better than in electrodynamic speakers because of the large radiating surface. Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation. ... Waves with the same phase Waves with different phases The phase of a wave relates the position of a feature, typically a peak or a trough of the waveform, to that same feature in another part of the waveform (or, which amounts to the same, on a second waveform). ...

Since most electrostatic speakers are tall and slim designs without enclosure they act as a vertical dipole line source. This makes for totally different acoustic behaviour inside rooms. Planar (flat) types tend to be very directional which gives them superb imaging qualities, on the condition that they have been carefully placed inside the room. Curved panels have been built, making the placement requirements a bit less stringent but sacrificing stereo imaging somewhat. A dipole (Greek: dyo = two and polos = pivot) is a pair of electric charges or magnetic poles of equal magnitude but opposite polarity (opposite electronic charges), separated by some (usually small) distance. ...

Disadvantages include a lack of bass response due to phase cancellation from a lack of enclosure, and a sensitivity to ambient humidity levels. While bass is lacking quantitatively it is often of much better quality than that of electrodynamic (cone) systems. Phase cancellation can be remedied by electronic equalization (a so-called shelving circuit boosts the region inside the audio band where the generated sound pressure drops because of phase cancellation). When two or more waves (vibrations) in a medium pass through a specific point at a specific time, they will all simultaneously try to move the medium there in the directions of their current vibration displacements (phases) and to distances from the mediums steady state position equal to their... In audio processing, equalization (EQ) is the process of modifying the frequency envelope of a sound. ...

The lack of bass is often remedied with a hybrid design utilizing a dynamic loudspeaker handling lower frequencies with the electrostatic diaphram handling middle and high frequencies. However some purists feel that this detracts from the purity of the "electrostatic sound" and insist on a pure electrostatic design. Many feel that the best low frequency unit for hybrids are transmission line woofers or horns, since they possess roughly the same qualities (at least in the bass) as electrostatic speakers, i.e. good transient response, almost no box colouration, and flat frequency response. Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves. ... At the most fundamental level, a horn speaker uses a horn to get more sound (volume) from the driving loudspeaker. ... Transient means passing with time. ...

The directionality of electrostatics is also a disadvantage in that it means the 'sweet spot' where proper stereo imaging can be heard is relatively small, restricting the number of people who can fully enjoy the advantages of the speakers simultaneously. Some designs are more suited to a personal, as opposed to shared, listening environment.

Commercial speakers

The first commercial design was the Quad ESL-57 designed in England by Peter Walker, founder of Quad Electro-Acoustics of Huntingdon, in 1955 and put into commercial production in 1957. This highly-regarded loudspeaker remained in production until 1985 and 54.000 units were sold. In 1981 Quad introduced the ESL-63 the successor of the ESL-57. This model remained in production until 1999 and sold 35.000 units. The ESL-63 attempted to address amongst other things the deficiency in bass reproduction of the 1957 design and its extreme directionality. In 1999 Quad introduced the ESL-988 and the ESL-989, currently in production. Current manufacturers other than Quad are Martin-Logan and Sound Lab in the United States. Final and Audiostatic are two less well-known Dutch manufacturers. Royal motto: Dieu et mon droit (French: God and my right) Englands location within the UK Official language English de facto Capital London de facto Largest city London Area  - Total Ranked 1st UK 130,395 km² Population  - Total (2001)  - Density Ranked 1st UK 49,138,831 377/km² Ethnicity... Martin-Logan is a North American company producing floor-standing hybrid electrostatic speakers. ...