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In addition to quad rebuilding, I also often have rebuilt pairs of speakers available for purchase. Information is available on the Quads For Sale page. As well as Quad loudspeaker work, I also provide circuits for a few vacuum tube based audio components. These boards rebuild aging parts and bring your component back to better than original performance.
In the footer of each page is a link to my old "classic site" that has a bunch of old, stale, but still useful information which was cluttering up the core information which I provide. They are widely admired for their clarity and precision, but known to be difficult speakers to run and maintain. As of , Quad maintains four electrostatic speakers in its range.
Acoustical Manufacturing Company had launched a ribbon-hybrid, horn-loaded "Corner Ribbon Loudspeaker" in ,  but this was not commercially successful. The electrostatics were designed by Theo Williamson , and the company's founder, Peter Walker, from a principle elaborated by Edward W. Kellogg for General Electric that was granted a patent in After more research, the large panel speaker with better response over the whole frequency range was demonstrated to the Physical Society in March Development of its successor began in , giving rise to the product name "ESL", launched in It attempted to address both the deficiency in bass response of the original ESL and its extreme directionality at high frequencies.
The latter goal is achieved by splitting the stators into eight concentric rings, each fed with a slight time delay compared to the ring immediately inwards, thereby attempting to emulate a point source. Stereophile described the speaker as having been designed for "serious-music call that 'classical' listeners who play records more for musical enjoyment than for the sound". Its descendants are still often simply referred to as Quad Electrostatic Loudspeaker as part of the legacy.
An electrostatic speaker has only a frame to support the charged diaphragm. There are two perforated plates with a potential difference of up to 10, volts, between which a very thin film, coated with a mildly electrically conductive substance, is sandwiched. The different charge between the two plates allows the diaphragm to be alternately attracted and repelled by each plate.
In the original QUAD, two bass panels flank one treble panel to provide full range sound. Its treble panel diaphragm is further subdivided into midrange and tweeter sections, achieved by clamping it on each side of its centre. Both midrange and tweeter sections are driven separately, and the entire treble unit operates at substantially lower voltages — operating voltages are specified as 6 KV for the bass and 1.
This is because the diaphragm operates in a "constant charge" mode, and it takes time for the charge to build up. In practice, the speaker is usable after charging for less than half a minute, but the sound gradually improves as the charge builds up. Best performance is achieved when the speaker has charged fully, which can take up to an hour.
The electricity is only to charge the diaphragm, so consumption is negligible. The electrostatic design does away with two major weaknesses of boxed speakers: enclosure colourations and signal degradation due to the crossover. The crossover in the ESL consists merely of resistors which work with the inherent capacitance of the speaker elements to obtain a first-order response.
Because it is bipolar, both sides of the elements are not enclosed, but radiate directly into the air. Thus, colourations due to crossover components minimized and box-induced reflections are eliminated. Fast transient response and low distortion are both characteristic of electrostatics.
The driver, being only 0. Kohli of TNT noted that upper register starts to taper above 10 kHz and then falls off severely beyond 13 kHz, and is dB down at 20 kHz. Although a slight deviation did not seem to make a difference, it is in practice not possible for more than one person to enjoy a reasonably balanced sound stage with the ESL. Contrary to the flat appearance of the loudspeaker, all three panels are slightly curved along the vertical axis to improve quality. The panels themselves are flat, but obtain their curvature by being slightly bent to a curved backing.
With the bipolar nature of the speaker emitting sound from both front and back surfaces as it does, the application of a felt sheet to the rear of the panels damps and absorbs high frequencies radiating from the back. A crossover network, set at Hz, remains necessary to adjust for back-to-front interference causing loss in output at low frequencies. The instructions book contains advice against placement of the speaker in corners or positions close to or parallel with walls, and further explains that a corner placement will adversely affect bass response and be detrimental to the midrange because of standing waves generated.
Its impedance is specified as ' ohm in range 40 Hz-8 kHz falling off above 8 kHz',  although another source states 'impedances are approximately 1. It does not consume large amounts of power so much as it feeds it back to the amplifier in opposition at some points during each cycle. This is very demanding on amplifiers' stability. Although it is designed to be used with the QUAD II, , or power amplifiers with limiters,  a power amplifier capable of delivering 15 watts per channel suffices — excessive voltage input is known to cause arcing within the speaker panels.
In the ESL's case, at the rated nominal impedance of 16 ohms, the limit of 33 peak volts would be reached when the amplifier's power output reaches 15 watts if it were driving a conventional load. The most common failure modes were loss of sensitivity caused by dust infiltrating the speaker panels, and internal arcing of the panels caused by excessive power to the step-up transformer;  use at high altitudes may also cause the same effect.
The ESL measures 31 by The earlier version has golden-bronze grilles and classic teak end caps. Later production versions have black grilles, and end caps have a rosewood finish; other minor variants exist. The original ESL suffered from reliability issues,  frequently caused by use of inappropriate amplification or being driven too hard.
The design's lack of structural integrity is seen as another significant weakness of the Quad ESL since its inception, and lived on in its various successors. Quad have now brought out five generations of the classic electrostatic design. Quad addressed the limitations of the original design to some degree with the ESL
The ESL was the world's first full range, ultra-low distortion electrostatic loudspeaker and set standards for accuracy and fidelity in loudspeakers that remain. The Quad Electrostatic Loudspeaker (ESL) is the world's first production full-range electrostatic loudspeaker, launched in by Quad Electroacoustics. A Quad ESL is made up of two bass panels and three centrally located "strips." The two outside or midrange strips operate in parallel and roll.