QUAD ESL 2905, ESL 2805 User Manual
the closest approach to the original sound.
ESL 2805 & ESL 2905
Reference
s e r i e s
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The
Quad ESL
Contemporary Electrostatic Loudspeaker Design
The new ESL-2805 and ESL-2905
Electrostatics are Quad’s latest reference
loudspeakers and like their predecessors
should be regarded amongst the finest
loudspeakers in the world today. In
areas such as transparency, and lack of
colouration, they are without peer.
It should be noted that whilst movingcoil loudspeakers are the norm, the
physical principles upon which they
work are fatally flawed - and not even
the latest advances in materials science
can address their shortcomings.
Quad alone has sought a different path
- to push the boundaries of electrostatic
technology to the point where our ESLs
are closer to the ideal loudspeaker than
any other.
Quad’s patented panel technology
results in a combination of the speed
and accuracy only possible from an
electrostatic loudspeaker; together
with the imaging and soundstaging
only possible from a theoretically ideal
point source; and the coherence and
continuity of a single drive unit.
With possibly the lowest distortion
of any loudspeaker, the ESL can be
enjoyed for hours on end without
fatigue; never adding or subtracting
from the original recording. Even at low
volume levels, they retain the full detail
and drama of the music.
In short, the Quad ESL technology is
unique in its clarity of sound, lack
of distortion, lack of interference and
continuity of response.
The ESL-2805 and ESL-2905
loudspeakers are the absolute pinnacle
of that technology. Engineered without
compromise, they are destined to
become modern classics.
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Quad products stand alone in the hi-fi
world - renowned for their longevity;
quality of build; and consistently high
standard of performance. Our awardwinning service department regularly
maintains products over 50 years in
age. Products which still bring their
owners immeasurable pleasure.
Quad products are designed with the
single aim of reproducing recorded
music as accurately as possible.
Simplicity of use and elegance of
design are purely consequential to
the application of sensible engineering
principles.
We have never sought to design
statement pieces or style icons, yet
almost every Quad product has
become regarded as such.
The case for a
closer
approach...
The moving-coil conundrum
A moving-coil speaker consists of a
wire coil suspended inside a magnet.
When an audio signal passes through
the coil a varying magnetic field is set
up which interacts with the magnet and
causes the coil to move back and forth.
A cone (or in the case of high frequency
speakers, a dome) is attached to the
coil, which compresses and rarifies the
air generating sound waves.
Flexible
Surround
Back Plate
Voice Coil
Pole Piece
Coil Former
Rear Suspension
Front Plate
Air Vent
Dust Cap
Speaker Cone
Chassis (or Basket)
Because large speaker drive-units
cannot reproduce high frequencies
well, and small ones cannot reproduce
low frequencies at all, practical hi-fi
loudspeakers use two or more driveunits connected via a ‘crossover
network’ which divides the frequencies
between the bass and the treble units.
Additionally, because even a large
bass- unit is very small compared to the
length of a low-frequency sound wave,
some form of box is needed to prevent
the waves from the back of the cone
cancelling the sound from the front.
Moving-coil speakers have undeniable
advantages of cost and ease of
manufacture, and the cabinets can be
designed in many different shapes, sizes
and finish. However, the cabinet is also
a prime source of colouration in the
bass region. Additionally, because the
cone of a bass-unit is large and heavy,
it cannot start and stop instantaneously.
Some of the energy is stored and
releases over time, causing smearing
and ‘boom’ in the bass. In the crossover region, where not only are the
masses between the drive units hugely
dissimilar but so are their dispersion
patterns, this shows up as unevenness
of response and a confused image,
precisely in the critical area where the
ear is at its most sensitive.
The
Electrostatic
alternative
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.
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