Electrostatic loudspeaker
[citation needed] 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.
In one recent design, the diaphragm is driven with the audio signal, with the static charge located on the grids (Transparent Sound Solutions).
The electrostatic construction is in effect a capacitor, and current is only needed to charge the capacitance created by the diaphragm and the stator plates (previous paragraphs referred to as grids or electrodes).
Advantages of electrostatic loudspeakers include: Musical transparency can be better than in electrodynamic speakers because the radiating surface has much less mass than most other drivers and is therefore far less capable of storing energy to be released later.
Electrostatics can also be executed as full-range designs, lacking the usual crossover filters and enclosures that could color or distort the sound.
Planar (flat) drivers tend to be very directional giving them good imaging qualities, on the condition that they have been carefully placed relative to the listener and the sound-reflecting surfaces in the room.
[citation needed] Curved panels have been built, making the placement requirements a bit less stringent, but sacrificing imaging precision somewhat.
[citation needed] Recent, technically more advanced solutions for perceived lack of bass include the use of large, curved panels (Sound-Lab, MartinLogan CLS), electrostatic subwoofer panels (Audiostatic, Quad), and long-throw electrostatic elements allowing large diaphragm excursions (Audiostatic).
A cone speaker's sound pressure level, on the other hand, decreases by 6 dB for each doubling of distance because it behaves as a point source.
This can be overcome by the theoretically more elegant solution of using conventional cone woofers in an open baffle, or a push-pull arrangement, which produces a bipolar radiation pattern similar to that of the electrostatic membrane.
[citation needed] This is still subject to phase cancellation, but cone woofers can be driven to far higher levels due to their longer excursion, thus making equalization to a flat response easier, and they add distortion thereby increasing the area (and therefore the power) under the frequency response graph, making the total low frequency energy higher but the fidelity to the signal lower.
This avoids the many disadvantages of dipole operation, most importantly a great reduction in room reflections and thus also in adulteration of the recorded ambiance.
Since there's no attempt at making the speaker visually see-through, it also allows the application of materials to the rear of the panel to impart full damping of the membrane resonance, which improves transient response.
Lastly, most of the remaining 3 dB roll-up can be counteracted by filtering the high frequencies from the signal to half or more of the width, which coincidentally widens the dispersion and thus the sweet spot.
They also use acoustic suspension woofers (sealed enclosures), which have the lowest group delay of all configurations and thus the best chance of seamlessly integrating with the electrostatics.
The directionality of electrostatics can also be a disadvantage in that it means the 'sweet spot' where proper stereo imaging can be heard is relatively small, limiting the number of people who can fully enjoy the advantages of the speakers simultaneously.
Critical Mass engineer and CEO Wayde Alfarone's design capitalized on the directional nature of electrostatics by creating separate sound fields for different seating locations in the vehicle.
They are one of the few types of speakers in which the transducers themselves can be built from scratch by an amateur as basic hardware for complete ESL DIY projects can be found available online.
Such supplies include resistors and capacitors for RC circuit frequency equalization, if necessary; step-up transformers; perforated metal sheets or grids and insulating plastics for the stators; polymer film and conductive paint (e.g. a liquid graphite suspension) for the membrane; simple tensioning equipment for proper membrane tuning; and a frame, usually of wood, to hold everything together.
Manufacturers who only make electrostatic-type speakers include SoundLab, Audiostatic, JansZen and Sanders Sound Systems (previously Innersound).
MartinLogan, JansZen, Metrum Acoustics,[13] Sanders Sound Systems,[14] and Sound-Lab,[15] and others build hybrid designs with conventional woofers or subwoofers.
