The QUAD ESL63 Loudspeaker

Description

The Quad ESL63 is a full range electrostatic doublet (FRED) loudspeaker. It consists of a very light electrically polarized diaphragm suspended between two sets of concentric annular electrodes. Signal is fed to the electrodes via sequential delay lines and the motion of the diaphragm produces a sound pressure pattern which is an exact replica of that from an idea source placed some 30 cm behind the plane of the diaphragm.

Amplifier requirements and loudspeaker protection

The Quad Electrostatic Loudspeaker ESL63 should be used with an amplifier of output capability between 20 and 30V rms (50 – 100 watts into 8 ohms). The impedance characteristic of the loudspeaker is essentially resistive and presents no problem to the amplifier. The protection circuit in the loudspeaker limits the maximum input voltage to 40V and there is no benefit to be gained from using an amplifier with an output capability greater than 30V rms (approximately 100 watts into 8 ohms)

Amplifiers with an output capability in excess of 35V rms (approximately 150 watts into 8 ohms) may be used, but care should be taken to ensure that the protection circuit is not required to operate continuously as this will cause overheating and damage the protection circuit.

Steady state signals in excess of 10V rms should not be fed to the loudspeaker.

The loudspeaker elements are completely protected from excessive input signal by circuit which shorts the signal from the amplifier if arcing is about to occur. Signal input automatically restored once the speaker elements are safe.

When the AC input is switched off or disconnected the signal protection circuits operate to prevent excessive being fed to the loudspeaker elements and care should be taken to ensure that the loudspeakers are not driven for long periods (minutes) with no AC applied.

Amplifiers which are not short circuit protected may be damaged and should not be used.

The listening room and loudspeaker placement

The Quad ESL63 being a dipole source has considerable advantages over conventional loudspeakers in terms of room placement. No energy is radiated in the plane of the diaphragm and as a consequence the respective axial room modes are discriminated against. Normally the loudspeaker is placed at an angle to both horizontal room axes and will excite both sets of horizontal axial modes 3db less than with a conventional source and discriminate entirely against the vertical axial modes.

The loudspeaker should placed at least 60 cm (2 ft) from the rear wall of the listening room and angled towards the listener and never in corners or alcoves or behind furniture. Because the loudspeaker is a totally homogeneous sound source it will be found that the loudspeakers can be placed considerably further apart than normal, broadening the stereo sound stage. Close proximity to the side walls is not detrimental to performance. Simple geometry will show that if the loudspeaker is placed at an angle to the wall, there will be no audile reflection at the listening position.

If there is a tendency for the loudspeaker to lean forward when standing on a deep carpet, we recommend removing the plastic plus from the two rear feet.

Specification

Height 92.5cm
Width 66 cm
Depth 27 cm including 15 cm base
Weight Net 18.7 kgs
Gross 23 kgs
A.C Supply 240/200V 120/100V 50 – 60Hz 5 VA
Impedance 8 ohms nominal
Sensitivity 1.5 ubars per volt referred to 1m. (i.e. 86dB/2.83V rms)
Maximum Input Continuous input voltage 10V rms
Programme peak for undistorted output 40V
Maximum Output 2 N/m 2 at 2m on Axis
Directivity Index
125Hz 5.0dB
500Hz 6.4dB
2kHz 7.2dB
8kHz 10.6dB
Axis Band limits -6dB at 3Hz 3 rd order
(Low Level) -6dB > 20kHz