the closest approach to the original sound ELECTROSTATIC

ELECTROSTATIC LOUDSPEAKERS
...the closest approach to the original sound
The Quad
ESL
A legend in Electrostatic loudspeaker design
2
The Quad ESL is fundamentally different from
obvious that large cones and even larger electrostatic
conventional loudspeakers and even other electrostatic
diaphragms cannot be point sources, so how can they
designs. Whilst most conventional speakers use cone
be made to behave more like the perfect loudspeaker?
type drive units and a coil moving in a magnetic field,
Quad solved the problem with an elegant engineering
Quad uses the full-range electrostatic principle, first
solution that was subsequently awarded a patent.
introduced in 1956. The sound is not created by a
Instead of a large single electrode, Quad designed a
cone but by a very thin diaphragm, less than one tenth
number of electrodes arranged as a series of
the thickness of a human hair. This ultra-low mass
concentric rings. Each electrode is fed with a calibrated
diaphragm is coated with a conductive material and is
delay line so the sound first leaves the centre of the
stretched between two fixed electrode plates. The
speaker then, after a short delay, the sound leaves the
electrodes carry a positive charge and the diaphragm
next ring and so on. The delayed sounds build up into
carries a negative charge. The size of the charge on the
a spherical waveform identical to that produced by a
electrodes rises and falls to track the waveform of the
theoretical point source. This innovative step brought
musical signal; so attracting and repelling the
closer the achievement of the perfect loudspeaker.
diaphragm closer to and further from the electrode
The Quad ESL is a premiére music reproduction
plates. It is the movement of the almost mass-less
loudspeaker constructed from the finest materials with
diaphragm that creates the sound we hear.
meticulous attention to detail. It reaches the pinnacle
Quad’s unique ESL system takes the performance of
of high-fidelity performance with an unparalleled
electrostatic loudspeakers a step further. Acousticians
ability to sonically ‘disappear’, and create convincing
have long recognised that the ideal loudspeaker
three-dimensional sound stages. Instruments and
should be a point source from which the waves of
vocals occupy precise, accurately sized locations in
sound radiate in a fashion rather like the ripples
space, giving an uncanny realism to reproduced
resulting from a pebble dropped into a lake. It is
sound.
‘Even if price weren’t an issue I’d be hard pushed
to find speakers that better the 988s’ combination
of talents... I can’t recommend them too highly’
Gramophone (March 2001)
3
4
‘Quads can deliver a sublime
performance. They still take my breath
away with their profound revelation’
– Hi-Fi World , Noel Keywood
The closest approach...
There are few things in life as rewarding as a truly
It is often said of ‘box’ or cabinet mounted loudspeakers
invigorating live performance from our favourite artist
that you can hear more of the box than the driver. This
or orchestra.
is true, even with high-end ‘box’ loudspeakers. The box
Reproducing that experience accurately in the home
- no matter how inert - will always colour the sound.
requires loudspeakers that go beyond the conventional.
Electrostatic loudspeakers are therefore in a league of
To really understand the ESL, a listener needs to be
their own in terms of ‘transparency’.
familiar with the nature of a live performance. Whilst the
But to get really close to the original sound, a standard
performance may be impressive and communicate all
planar electrostatic speaker, needs more. At a live
kinds of emotions, it is never artificial. It sounds real
performance, each sound comes from an identifiable
and natural.
position on the stage. To reproduce this three-
At Quad, we believe this is the job of a loudspeaker.
dimensional sound ‘image’ accurately, we need to
To present the music in the raw, natural form -
produce an interference pattern upon the listener of
nothing added, nothing taken away. In this respect,
waves propagated from a pair of true point sources - in
the ESL is an acquired taste. It displays none of the
much the same way as a laser produces a hologram.
over-empasized bass boom or mid-range projection
The Quad ESL 988 and 989 speakers are the only
that plagues moving-coil, box-bound speakers - so in
electrostatic speakers in the world to effectively mimic a
comparison, the ESL can seem rather meek and polite.
point-source.
The characteristics, however, that can make these box
Five minutes spent listening to a well set-up pair of
speakers so impressive, are also those that cause
Quad ESLs will confirm their ability to project the
fatigue and wear down the listener. Spend some time
positions of each and every vocalist in a choir, and
with the ESL and you too will begin to realise that it’s
instrument in an orchestra - with a naturalness and level
not always the one that shouts the loudest that gets
of detail that makes the Quad ESL totally unique in
heard.
every respect.
5
‘Going back to conventional speakers
afterwards merely highlights how great
the 989 is’ – Hi-Fi News (July 2000)
The closest approach...
6
Ask many of the finest recording professionals in the
as an absolute reference? Next time you are visiting a hi-
world what their speaker of choice is as the answer is
fi show, look for the acoustic engineers - the amplifier
surprisingly common. The Quad ESL opens a window
designers - even the other loudspeaker designers. More
on a recording unlike any other speaker.
likely than not, they will have a pair of ESLs hidden
For professional musicians and studios, this is an
away in a corner.
invaluable asset, for no matter how good a moving coil
Lastly consider the magazine reviewers - the so-called
loudspeaker may seem - no matter how impressive its
critics with golden ears who listen daily to a multitude
dynamic ability, the laws of physics are such that it
of loudspeakers - assessing how they perform. What do
cannot be as fast and accurate as an electrostatic
they use to compare all other speakers?
transducer. An ESL is like a giant capacitor, tracking the
Once again, the results are clear. Although arguments
music signal with such precision and agility that using
rage between them - Ken Kessler, Senior Reviewer at Hi-
them is the only real way to know exactly what is on the
Fi News Magazine awarded the ESL-57 ‘Product of the
recording.
Millennium’ back in 2000 and in his mind it has never
The Quad ESL has been used by Tony Faulkner for many
been surpassed. Paul Seydor, Hollywood editor and the
years. He use the ESL 63, the ESL 63 Pro and now uses a
man in charge of the absolute sound waxes lyrical about
pair of ESL 989s for his critical monitoring.
the ESL 63 at every opportunity, whilst Stereophile
Tony has produced over a thousand classical music
magazine has awarded the ESL 989, not only Product of
recordings using the Quad ESL because he knows he
the Year in 2004, but Component of the Year as well -
can trust what he hears - that the very essence of the
the highest of all awards. The real answer is that Quad
performance is being transferred.
ESLs have always been in a class of their own, each
Likewise with acoustic engineers - what do they regard
generation winning new fans and enthusiasts.
‘When I return the 988s it will
be in a package much too small
for the speakers, but just large
enough to carry a check for
their remittance.’
– The Absolute Sound (July 2001)
‘The Best Late Night Speakers in
The World...ever!’
– Hi-Fi World (December 2000)
7
8
ESL 989 vintage
After a number of years producing just a
single colour version of the ESL 988 and
ESL 989speakers, we decided to offer our
customers a couple of new alternatives.
Picture here is the ‘vintage’ finish, with
wooden top and base caps and an
classical style cloth ‘sock’
9
ESL 988
‘Quad has done it again: the
988s are world class - the single
driver presents a fabulously
together sound that’s tough to
match at any price’
– What Hi-Fi? (December 2000)
The ESL-988 replaces the much-loved ESL-63 model.
Although of similar size and proportions, the
resemblance is only skin deep – for more than 90% of
the internal components have been re-designed,
upgraded, or modified. Twenty years of materials
science have led to improvements in virtually every
component and area of construction.
The new model has better audio transformers, a new
power supply, improved diaphragms, a strong
heavyweight moulded base and new grille assemblies.
Particular attention has been given to the structural
integrity of the loudspeakers, which has been improved
beyond all recognition.
The result of these changes is an electrostatic
loudspeaker that is as much a leader today as its
predecessor was 20 years ago. Larger dynamics and a
smoother response are two of the most noticeable
improvements in sound quality. A slight backward tilt
lifts the stereo image when these speakers are floor
standing.
ESL 989
The ESL-989 shares much of its technology with the ESL988, but it is a larger model with two extra bass panels
and a higher rated power supply. The extra panels
increase the bass output, but also contribute to an
enhanced performance in the mid-band, which was
already widely regarded as the cleanest in the world.
Although referred to as ‘bass panels’, the additional
electrostatic panels are, in fact, full range (as are all the
panels), but the increase in surface area allows a greater
volume of air to be moved, leading to an improvement
in the lower frequencies. This particular development
had been anticipated for many years, but was never
previously regarded as commercially and practically
viable.
The ESL-989 is Quad’s finest loudspeaker. It is a true full
range electrostatic loudspeaker reproducing music with
an ease and naturalness that is best described as
uncanny. It has a virtual absence of the familiar
loudspeaker problems of colouration, distortion, phase
and frequency response errors. All that remains is the
music and the original ambience. To the listener these
are the very ingredients needed to create a real
sensation of being there.
The Quad electrostatic loudspeakers are unique and
continue to be in a class of their own, but now have the
versatility and range to cope with a much wider
repertoire.
10
Specifications
Model
ESL 988
ESL 989
2N/m2 at 2m on axis
2N/m2 at 2m on axis
Sensitivity
1.5u bar per volt referred to 1m (86dB/2.83V RMS)
1.5u bar per volt referred to 1m (86dB/2.83V RMS)
Impedance
8 ohm nominal
8 ohm nominal
Maximum continuous input voltage
10V
10V
Programme peak ( 20 Hz to 20 kHz )
For undistorted output
Permitted peak input
40V
55V
40V
55V
Directivity index
125Hz . . . . . .5.0dB
500Hz . . . . . .6.4dB
1kHz . . . . . . . .7.2dB
8kHz . . . . . . .10.6dB
125Hz . . . . . .5.0dB
500Hz . . . . . .6.4dB
1kHz . . . . . . . .7.2dB
8kHz . . . . . . .10.6dB
Axis band limits
-6dB at 35Hz 3rd order
-6dB at 35Hz 3rd order
-6dB > 20kHz
-6dB > 20kHz
220-240V or 110-120V
220-240V or 110-120V
See rating details on base of unit
See rating details on base of unit
940mm x 670mm x 315mm
(including 185mm base)
1335mm x 670mm x 315mm
(including 185mm base)
20.5kg net
25.3kg net
Maximum Power Output
( low level )
AC Input
( double insulated )
Dimensions ( H x W x D )
(including 185mm base)
Weight
Vintage & Nouveau
Both our international award-winning ESL
loudspeakers are now available for the first time in a
choice of colours and finishes. Whilst for some
audiophiles such details are of trifling importance,
Quad recognise that for many, the ESL needs to vanish
into it's surroundings visually as well as audibly –
whether these surroundings be a stately home or
docklands apartment.
The original black-on-black finish is now
complemented with the ‘Vintage’ and the ‘Nouveau’
finishes. Sonically, these are identical to the standard
model, but aesthetically, they offer more variety. The
Vintage models include a wooden base-plate, as well as
the wooden top-cap, reminiscent of the older ESL-63
and a woven – yet acoustically transparent sock as an
alternative to black. The Nouveau model has a brushed
metal top-cap and co-ordinated base to complement
Vintage
Nouveau
the light blue colour of the cloth.
11
Quad Electroacoustics Ltd, IAG House, Sovereign Court, Ermine Business Park, Huntingdon, PE29 6XU
Tel :- 0845 4580011, Fax :- 01480 431767
www.quad-hifi.co.uk
Qu.ESL 25.10.2004
The information in this brochure is subject to change without notice.
All rights reserved © 2004 Quad
Quad is a member of the International Audio Group
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review
`static
After years of waiting, Quad has finally launched
its brand new 988 electrostatics. Here's what Hi-Fi
World made of Huntingdon's latest panel loudspeakers.
W
hen audiophiles heard
through the grapevine that
Quad was to release two
all-new electrostatic 'speakers, we held
our collective breath and waited for
almost three years. Now, at last, both
the 988 and larger 989 models are in
full production, and Hi-Fi World managed to procure an early pair of each,
plus the equally eagerly awaited new
QC-twenty-four preamp and II-forty
monobloc valve power amps, for
review. Here’s our view of the ESL988, plus a preview of the valve power
amp.
YOUNGER THAN YESTERDAY
Although work on the ESL-988 started
three years ago, this 'speaker shares
more than a passing visual and technical resemblance to its much- loved
ESL-63 predecessor - so much so that
it could almost be described as a `63
'Special Edition', as fundamentally the
two are the same. Circuit topology is
identical, and it uses the same principle
of a concentric ring of electrodes fed
through a calibrated delay line - sound
first leaves the centre and after a short
delay leaves the next ring, and so on.
This results in a spherical waveform
that resembles a theoretical point
source, traditionally thought to be
ideal.
PAGE 18
Despite the similarities, around
ninety percent of the internal
components have been re-designed,
upgraded or modified.Andy Grove,
who also designed the new Quad valve
amps reworked the 988's audio
transformers, power supply and delay
line. Mylar, a strong and non-stretchable substance (and apparently often
used for the sails of wind surfers), is
now used as the diaphragm, as well as
in the transformers.The 988s retain
the same loudspeaker protection and
clamping system of the 63s.
Electrostatics are easily damaged
through excessive input signals, so the
protection circuit uses a `multifuse'
device to prevent unwanted damage. If
the panel is over-driven for any length
of time, this circuit will effectively
reduce drive to the 'speaker. Quad
recommend caution if using power of
over 100W per channel into 8ohms the 988s should ideally be used with
amps of between 20v and 30v RMS
(50-100W into 8ohms).The protection
circuits limit maximum input voltage to
40v, so although an insensitive load,
there are no benefits from attempting
to drive the 988s with a kilowatt each
side!
One of the most common tweaks
on both the 57 and the 63 was to
wedge something under the frame to
angle the 'speaker upwards. Quad
claims to have eliminated this problem
by angling the diaphragm backwards
exactly five degrees.Also, a new lighter
grille has been employed, and heightadjustable floor spikes which screw
into the base plate are also available.
The benefits of spiking electrostatics
are less that those of spiking box
loudspeakers, however.
The biggest difference between the
988 and its predecessor is its superior
structural integrity - special attention
has been paid to the rigidity of the
DECEMBER 2000 HI-FI WORLD
988, whereas
the 63 was
flimsy. More
struts are now
present, as well as
a sturdy wood
frame, and a new
heavyweight moulded base
has been added - meaning it's
now more of a Rigid Rascal than
a Flexible Friend. One of the aims of
this structural improvement is to
create a more rhythmic and exciting
sound. I really get the feeling Quad
want to shake off the 57 and 63s' 'pipe
and slippers' image. Quite right too, as
the original Quad electrostatic design
was first demonstrated in 1956
PLACEMENT
Electrostatics are more sensitive to
placement than possibly any other
'speaker, despite having no 'hot spot'.
As such, trying them out in more
positions than you'll find in the Karma
Sutra pays dividends.There are many
schools of thought as to how and
where you should place them in your
listening room. Being a dipole design
that fires to the rear as well as the
front, many say you should put them
either two-thirds or three quarters of
the way down the listening room,
angled face-on flat, rather than angled.
Others say that two feet from the rear
wall and slightly toed in is the way. Like
most things in life, though, the best way
is to find your own. Often furnishings,
concrete floors and of course room
size make the biggest difference. One
thing's for sure though, you'll probably
have to play around with the 988s for
a while until you find a sound you're
comfortable with.We listened to them
in your average Victorian semi's front
room - smallish (13' x 13') with
suspended floorboards, a fairly high
ceiling and an average amount of soft
P 18-21
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review
electricity
furnishings. Placed about three feet in
from a bay window with heavy
curtains, face on (not toed in), we thus
found the right balance between
damping and reverberation.
SOUND
The first thing to say about the performance of the new ESL-988s is that
they need lots of warming up - they
didn't really come into their own until
a good three days of constant use.
Prior to this the sound was hollow and
sucked out with a fairly unpleasant,
shouty midrange. It's unwise to use
cold or hard sounding amps with the
988s, as they won't subjectively match
these ‘speakers, which possess stronger
treble than the ESL-63s.The rich sound
of Audio Analogue's 60W per channel
Puccini SE managed to get the 988s
sounding fluid during running in.An
ideal match for the 988s is powerful
valve amplification like Quad's own
new valve pre and power amps (see
next month's issue for a full review).
The new Quad II-fortys deliver 40W
RMS, and this blend of power and
vacuum tubes proved the ideal partner.
Source components included a Roksan
Caspian CD player, NAD's S500
Silverline CD player, and a Michell
GyroDec turntable with Musical
Fidelity X-LP2 phono stage (there's no
phono input on the Quad preamp as
yet). Speaker cables were van den
Hul's Royal Jade and Nordost's frighteningly expensive SPM, interconnects
were Chord Company's Anthem.
We started off with a finely honed
recording in the shape of Copland's
`Fanfare For The Common Man' by the
Minnesota Orchestra on Reference
Recordings. Its fine ambience and detail
shone out through the 988s.The
percussion and brass section under the
baton of Eije Oue seemed as though
they were transported from the
recording venue into my bay window,
such was the realism.The bass drum
solo that heralds the opening of the
piece put paid to one of the myths
surrounding electrostatic 'speakers -
that they have no bass.The 988s
delivered seismic low frequencies
coupled with that unmistakable
electrostatic transparency and lack of
coloration.The trumpets were smooth
and yet sunny, showing a clean and
detailed treble.
It's always been the mark of a
Quad electrostatic that they show up
fine low level detail, and the 988s
continue this tradition commendably.
Even at low volumes they picked up
the players' movements and the odd
elbow knocking the music stand. Eric
Bibb's bluesy acoustic strumming on
the fine Swedish Opus 3 label once
again confirmed that there's nothing
quite like a Quad ESL for sheer detail
and presence with acoustic music. His
fingers on both strings and guitar
bridge were frighteningly realistic and
his voice was pure and lucid beyond
the standard of most cabinet 'speakers
available at any price and anywhere.
His breathy, close microphoned vocals
drifted cleanly into the room. It's with
this type of music that the ESLs reign
supreme with a totally unaffected
performance - a light yet full wall of
sound with excellent imaging.
Something else new to these
Quads is the chance to enjoy rock,
pop and dance music.The previous
`statics were always far better suited
to string quartets than drum'n'bass,
and this is something Quad apparently
wished to put right. I tried them with
CDs and LPs ranging from Smashing
Pumpkins to LTJ Bukem, and
the good news is that they
rock.Admittedly maybe not as
much as some such as Ruark's
similarly priced Solstice or
KEF's Reference Model Four,
but they still have a real kick to
them. Odyssey's 'Submerge' had
the foundations shaking with
amazingly low and uncoloured
bass.This new-found rhythmic
injection gives an upfront sound to
rock and pop music that can
sometimes be a little grating,
especially with bad recordings.
According to our measurements
there's a slight upper mid peak present
in which guitars and vocals can sound
harsh, but this is the only gripe with an
otherwise - dare I say - surprisingly
funky sound!
The 988s are truly superb
performers which are well worthy of
the Quad badge.Their lifelike sound
and sheer presence is rarely bettered
in the audiophile universe and they
possess a clarity and intricacy at all
volume levels that makes them without
doubt `The Best Late Night 'Speakers
in The World. . .ever!'
Careful matching is needed.We
used Quad’s smooth valve amplifiers
but they work well with quality solidstate amps too.Their forward nature
and lucidity makes matching with solidstate amps a potentially painful
experience with the wrong choice.
Although the 988s play most music
with transparency and insight, they still
favour acoustic and classical music over
rock. If you've got lots of rock recordings ensure they're good ones, because
bad recordings sound really bad. By the
same token however, good recordings
sound superlative. ■
QUAD ELS-988
£3,500
Quad Electroacoustics IAG House
Sovereign Court,
Ermine Business House
Huntingdon, Cambs PE18 6WA
Tel: 01480 447700
The new Quad
ESL–989 and
below the ESL–988
Quad’s new II-forty
monobloc valve power
amp. The original Quad
II is in the background.
WORLD VERDICT
Partner with suitable
amplification and the
988s offer the
unmistakable
transparency of an
electrostatic coupled
with a firm hold on
rhythm and bass.
The bizzo!
Measured
Performance see
page 111
HI-FI WORLD DECEMBER 2000
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review
How an electrostatic works
n electrostatic loudspeaker
uses a thin lightweight Mylar
film to move air, instead of a
plastic or paper cone. Much like a
sheet of Clingfilm, it is feather light,
so problems associated with moving
mass, such as colouration and the
coarseness that comes from ‘breakup’
are eliminated.
The film is driven over its entire
surface by an electrostatic field.This
replaces the coil and magnet of a
cone loudspeaker and is a massless
drive system that distributes the
drive force evenly across the film.
Again, this is an ideal way of doing
things.
Our diagram shows in simple
outline how an electrostatic like the
988 is constructed. Fixed outer
electrodes carry the varying audio
signal, stepped up to thousands of
volts by a transformer fed from the
amplifier.The thin, vibrating diaphragm
lies between the electrodes,
stretched in a frame. Its tension is
critical. Sound generated by the
diaphragm passes out through the
perforations in the electrodes. An
A
electrostatic needs a mains supply
and carries on-board protection and
voltage supply circuits.
The original Quad ESL-57 used a
vertical-strip central treble panel,
flanked by bass panels.The ESL-63
used a series of annular ring
electrodes, connected by a delay line,
to simulate the radiation pattern of a
point-source.The new 988 retains
this system. Quad have revised and
improved the physical structure and
component quality of the ESL-63,
they say, to derive the 988, rather
than make fundamental changes.
In operating principle, electrostatic loudspeakers appear perfect. In
practice they are difficult to get right.
Although the diaphragm has little
mass, the perforated electrodes,
safety screens and dust screens
through which the sound must pass
can affect the sound. Electrostatics
work at thousands of volts, so need
internal power supplies.The
diaphragm has a constant, evenly
distributed charge maintained by a
5kV polarising supply. An audio input
transformer steps up the audio signal
to many thousands of volts on the
outer electrodes, as well as providing
isolation from the amplifier.
Maximum volume is less than
that developed by a cone
loudspeaker. Protection circuits
prevent overload, which would
otherwise lead to sparking. Most
parts must be specially sourced or
manufactured, unlike cone loudspeakers where parts are
produced worldwide. Even getting
the right film
tension is critical, a
black art
understood by few
except Quad.
In spite of the
difficulties and
limitations, a good
electrostatic
loudspeaker can
deliver a sound
unmatched by other
drive systems.The
988 further refines
Quad’s unique
position in this field.
Light, flexible
Mylar
diaphragm
-
P 18-21
+
Fixed, perforated
electrodes
5kV
Polarising
supply
Audio step-up
transformer
Audio in
The history of Quad’s electrostatic
Quad introduced their first electrostatic loudspeaker back in 1957. Called
“Walker’s little wonder”, after
company founder Peter Walker, it was
one of the earliest commercial designs
and became world famous. Gilbert
Briggs, founder of Wharfedale - not
then allied to Quad - said “I remember
meeting Stanley Kelly (a maker of
ribbon loudspeakers) at the first
demonstration of a full range ESL at
The ESL-57
the Waldorf in 1955, when we
solemnly agreed to change into black
and meet in due course in the
workhouse”. As good as it was, Quad’s
new electrostatic didn’t put conventional loudspeaker manufacturers out
of business, but it’s introduction caused
quite a stir in Britain and America.
Known at the time as the Quad
Electrostatic it was later dubbed the
ESL-57 to distinguish it from the ESL63.This is a little confusing because the
ESL-63 was introduced in 1981;
development was started in 1963.
Quad’s first electrostatic had a
vertical strip tweeter, flanked on either
side by bass panels.Technically, the
drawback of this arrangement is lateral
lobing, but in practice Quad owners
rarely complain about it because after
spending so much on such a special
loudspeaker they don’t listen off-axis.
All the same, Peter Walker decided he
could improve matters, moving to a
complex point-source radiator in the
ESL-63, a system retained in the 988.
Quad is now a part of
Wharfedale, itself owned
by International Audio
Group (IAG), based in
China.The company
started development of the
new 988 and 989 two
years ago at their
Huntingdon headquarters
and all manufacturing is
Peter Walker – founder of Quad
carried out there. ■
The ESL-63 with grille cover removed
HI-FI WORLD DECEMBER 2000
PAGE 21
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REVIEW • ESL 988
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DECEMBER 2000 –
REVIEW • ESL 988
QUAD BROCHURE (updated)
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