ESL

Electrostatic Loudspeaker (ESL, often called ESL-57). Loudspeaker, Quad, 1957

The first production full-range electrostatic loudspeaker, launched commercially in 1957 and adopted by the BBC for monitoring.

A-08, isometric, same camera for both

Drawing: A-08
Introduced: 1957
Produced: 1957 to 1985
Made in: United Kingdom
Designed by: Peter Walker, Theo Williamson
Launch price: GBP 52 (1957)
Size: 867 x 787 x 266 mm
Weight: 17.7 kg

Quad demonstrated its electrostatic loudspeaker in 1956 and put it on sale in 1957, building on a principle from a 1934 patent by Edward W. Kellogg of General Electric. Peter Walker and Theo Williamson are named as designers. A thin diaphragm about 0.00137 inch thick and weighing 3 milligrams is driven at 6 kV for the bass section and 1.5 kV for the treble section, with a crossover at 500 Hz. About 54,000 pairs of the original model were sold.

In the collections of Science Museum Group (a 1969 Quad electrostatic loudspeaker made by Thorens, Switzerland, object 1969-13/4).

See it in listening room no. 01, at the Farnsworth House

Front elevation of the Quad Electrostatic Loudspeaker (ESL, often called ESL-57), 867 mm wide and 787 mm high — Front elevation, dimensions in millimetres. Drawn from published dimensions and descriptions; detail is simplified.

Specification

Item	As published
Design bandwidth	40 Hz to 10 kHz; usable response claimed from 40 Hz to well past 20 kHz
Impedance	30 to 15 ohms from 40 Hz to 8 kHz, falling off above 8 kHz
Operating voltage	6 kV for bass, 1.5 kV for treble
Crossover	500 Hz
Diaphragm	About 0.00137 in thick, weighing 3 mg
Maximum SPL	98 dB at 1 m on axis
Amplifier limit	No more than 33 V peak into any load (instruction book)

Its successor

Quad ESL 2912X

Quad sells its direct descendant today. Pricing is through dealers.

See it at quad-hifi.co.uk

The house

Founded: 1936
Founder: Peter Walker
Origin: London, United Kingdom (moved to Huntingdon in 1941)
Today: Quad HiFi has belonged to the IAG Group of brands since 1997 and is based in Huntingdon, England.

Further sheets

Sources

Notes for the record: Dimensions and weight are Radiomuseum's 867 x 787 x 266 mm, listed as width, height, depth, and 17.7 kg. Wikipedia gives 31 x 34.5 x 10.5 in (79 x 88 x 27 cm) and 35 lb (16 kg) without naming axes, consistent with a speaker wider than it is tall. Radiomuseum's build years (1956 to 1981) and DM price refer to a 1967 to 1968 price and are not used. Wikipedia says ESL-57 manufacture continued in the UK until 1995. The Science Museum Group unit is a 1969 Thorens-built example, with overall size 800 x 940 x 250 mm and no axes given. The ESL 2912X is a later design in the ESL lineage that Quad dates from the ESL-63, which differs from the 1957 design.