QUAD ESL 2805 - Manual (Page 6)

6
Although deeply flawed, their cost and
convenience advantages are such that the
overwhelming majority of loudspeakers
in today’s marketplace are moving-coil,
and at Quad we manufacture some of
the finest examples of this genre. But,
as a counsel of perfection, we have to
look elsewhere.
Electrostatic speakers have long been
renowned for their superlative accuracy
and clarity in mid-range and upper
frequencies but deficiencies in the bass
response and indifferent dispersion
characteristics
have presented
difficulties which few manufacturers
have satisfactorily overcome. Many
hybrids have been attempted over the
years which combine moving-coil
speakers in the bass with electrostatics
handling the upper registers, but these
designs have not been successful.
An electrostatic speaker is a plastic
membrane which is coated with a
resistive material and suspended
between two perforated metal plates. A
polarising voltage of several thousand
volts is connected to the membrane
which at rest is suspended at an equal
distance between the two plates. When
an audio signal (also stepped up to
a few thousand volts by a matching
transformer) is applied to the metal
plates, the varying signal across the
plates attracts or repels the membrane,
and sound is reproduced. Because
the membrane is extremely light, and
driven across its entire surface, transient
response and freedom from overhang is
exemplary – quite unlike moving-coil
loudspeakers.
Of course, if it were as simple as this,
there would be many more electrostatic
loudspeakers. The challenge has been
to produce an electrostatic loudspeaker
with extended bass response and a
satisfactory dispersion. Virtually none
have succeeded. A combination
of acoustic problems and extreme
difficulties of manufacture has resulted
in a bare handful of true full-range
electrostatic loudspeakers being
available to the audiophile and in this
field Quad are pre-eminent.
Electrostatic
The
alternative