ESL
Electro Static Loudspeakers
QUAD’s founder, Peter Walker, was a true visionary who revolutionised the world of hi-fi loudspeakers in the 1950s with the original Electrostatic Loudspeaker. The world’s first production full-range electrostatic loudspeaker — the ESL-57 — was a radical departure from conventional cone-driver designs. Entering the home audio market in 1957, this pioneering system used a thin, electrically charged diaphragm suspended between stators to achieve extremely low distortion and remarkable transparency. The ESL-57 shattered preconceptions of what hi-fi loudspeakers could sound like. QUAD has since continued to refine Walker’s design, earning a reputation as one of the finest audio brands in the world and as the home of one of the greatest hi-fi innovations of all time.
Such is the technology employed in the QUAD Electrostatic Loudspeaker that it has been scarcely updated. From 1957 until 2025, QUAD issued just five major design iterations of the ESL model: the ESL-57, ESL-63, ESL-988/989, ESL-2805/2905, and ESL-2812/2912 — the latter introduced in 2012. Each model represented QUAD’s finest electrostatic loudspeaker of its time. The refinements employed in the ESL-2812 and ESL-2912 consistently impressed both seasoned ESL fans and newcomers alike. QUAD’s reputation as a leader in the world of audio is well earned, and the ESL remains a testament to the company’s unwavering commitment to quality and innovation.
QUAD ESL – the original electrostatic speaker
Electrostatic “panel” loudspeakers differ from the more common dynamic driver type in that they use an ultra-thin, electrically charged diaphragm suspended in an electrostatic field to create sound waves, instead of woofer cones and tweeter domes driven by a voice coil in a magnetic field. The diaphragm in QUAD’s ESL speakers is made from stretched Mylar, which is approximately ten times thinner than a human hair and so light that it closely approaches the mass of the air to which it is coupled. As a result, there is virtually no inertia inherent in the moving parts, allowing the diaphragm to respond with exceptional accuracy to musical detail and transients. The precision of an ESL is unmatched.
There are few loudspeakers that can play a 1kHz QUAD ESL square wave clearly and precisely!
The QUAD ESL loudspeaker features highly charged stator elements positioned on both sides of the diaphragm. These stators are connected to a power supply that provides a 5kV EHT (Extra High Tension) charge. This charge controls the movement of the diaphragm and maintains a stable voltage at the diaphragm-to-stator interface, resulting in exceptionally low distortion in the reproduced sound.
A key evolutionary step came in 1981 with the introduction of the ESL-63, which employed a novel delay-line approach to simulate a point source. This innovation significantly improved coherence and spatial accuracy, enhancing the immersive quality of the electrostatic listening experience and broadening its appeal among serious listeners.
The 1990s and 2000s saw further refinement through models such as the ESL-988, ESL-989, and later the ESL-2805 and ESL-2905. Each built upon the strengths of its predecessors with incremental improvements in panel performance, protection circuitry, and structural rigidity.
The Evolution
In 2012, QUAD unveiled the ESL-2812 and ESL-2912, fifth-generation models that integrated advanced panel construction and updated electronics. These speakers delivered a beautifully transparent and refined sound, with improved control and dynamic expression, earning enduring respect from enthusiasts worldwide.
The ESL-2812 featured a four-panel configuration that balanced elegant form with full-range electrostatic performance, while the larger ESL-2912 expanded the radiating area to offer greater scale and authority in larger listening spaces. These models exemplified QUAD’s ability to combine tradition with modern expectations. Each panel was carefully crafted by specially trained operatives, led by a team of British engineers with over 100 years of combined experience under the QUAD umbrella.
QUAD ESL speakers use two inner panels with concentric rings of electrodes, enabling pinpoint imaging from a true point source and delivering accurate stereo imagery across the listening area. The panels are mounted within a high-mass structure of tensioned aluminium extrusions connected to stainless-steel supports, ensuring optimal transmission of sound energy and supremely accurate transient performance.
In developing the ESL-2812 and ESL-2912, QUAD engineers focused on improving the EHT power supply. The objective was to minimise electrical “creepage” between components on the circuit boards. This was achieved through the introduction of a new two-layer PCB using 2oz copper, alongside improved insulation, optimised component spacing, and symmetrical layout. Cable dressing was also refined, further reducing the effects of creepage, particularly in high-humidity environments.
As with all high-performance audio systems, the power supply and transformers play a critical role. In the ESL-2812 and ESL-2912, new components were introduced, including Vishay metal-film resistors and Murata audio-grade capacitors. While not directly in the signal path, these components significantly improved theconsistency of the EHT supply and, in turn, signal purity during music reproduction.
Considerable attention was also given to the stators. Each stator consists of a copper layer bonded to a thin insulating substrate, perforated to ensure acoustic transparency. The copper is precisely etched to form a conductive pattern that accurately supports the point-source behaviour of the ESL design. Following etching, the copper layer is carefully insulated from the diaphragm, which operates in close proximity.
A proprietary insulation material — applied in three coats using a specialised spraying technique perfected over hundreds of hours of training — forms a crucial part of the panel construction process. Only a small number of highly trained technicians are entrusted with this work within the ESL laboratories. This technique prevents degradation of the EHT charge under high dynamic conditions, allowing the ESL-2812 and ESL-2912 to play louder and handle more power than earlier models.
Despite their enhanced power handling, ESL loudspeakers remain susceptible to overdrive, like any loudspeaker. By design, distortion in the ESL-2812 and ESL-2912 is so low that listeners may be unaware of the very high sound pressure levels being produced. Based on nearly 70 years of user application data, QUAD recognised the need for protection. As a safeguard, power protection circuitry is incorporated. If overdrive is detected — through EHT collapse or arcdetection— the speaker is temporarily muted. The discreet QUAD logo on the front panel flashes to indicate protect mode, preserving performance and preventing damage.
Further refinements were made to the physical design of the 2012 ESL models. The speakers were slightly taller than previous generations, yet narrower and less deep. A newly developed grille cloth provided improved acoustic transparency, while reinforced grille supports reduced resonance and ensured consistent tension over time.
Matching wood-veneered panels adorned the tops of the speakers and the sides of their substantial bases. The bases, constructed from high-density plywood, were designed to damp frame resonances and finished with hand-polished layers of piano lacquer. The shielding cover featured an embossed QUAD logo, with gold-lacquer typography, gold-plated terminals, and comprehensive wiring improvements throughout.
The X Generation
Despite the continued success and acclaim of the ESL-2812 and ESL-2912, QUAD engineers identified further opportunities for refinement. In 2019, an intensive review of electrostatic manufacturing processes began. The aim was not to alter the fundamental ESL principle, but to elevate every critical element of the platform for the next era. This review focused on electrostatic panels, operational electronics, and audio transformers. Electronics were reconfigured into three independent modules rather than a single PCB, improving signal integrity, stability, and noise performance.
Continuing this legacy, QUAD introduced the ESL X Series in 2025 — only the sixth generation of its iconic full-range electrostatic loudspeakers.
Alongside years of design review and component development, the electrostatic panels themselves were refined using updated production techniques. While retaining the core ESL architecture, these refinements improved panelconsistency, performance potential, and long-term reliability, albeit requiring more meticulous assembly.
Another major advancement was the introduction of custom-designed, UK-built audio transformers. These transformers enhance signal dynamics and resolution across the frequency range, reinforcing midrange clarity and upper-frequency linearity — attributes central to the electrostatic listening experience.
The result is the sixthgenerationof QUAD electrostatic loudspeakers: the ESL-2812X and ESL-2912X. Representing the pinnacle of more than six decades of development, these models preserve the classic electrostatic character while delivering enhanced control, scale, and musical engagement.
In keeping with modern expectations, the ESL X Series adopts the most contemporary visual design ever applied to a QUAD ESL. A refined matte-black “stealth” finish, redesigned grille cloths, and optional low-profile illumination allow the speakers to integrate seamlessly into modern interiors without detracting from their technological pedigree.
