Bowers & Wilkins 808 User manual

Instruction Manual

Introducing
Model 808
Model 808 is B&W's response
to the demand for a system
capable of safely delivering
sound pressure levels up to
120dB. The same basic
sophistication of BO1F/S —
now regarded as the
professional standard monitoring
loudspeaker worldwide — but
incorporating a whole range
of new design concepts
and techniques.
808 is a five-driver, three-way
system with sensitivity double
that of 801F/S, and overall
frequency linearity free from
colouration and distortion,
providing both the professional
recording engineer and the
dedicated home user with the
particular requirements for
producing realistic sound
levels in a large environment.
WARNING
Because Model 808 is capable of
such high sound pressure levels,
permanent hearing damage can
result from a daily exposure
duration longer than these
examples:
120dB 30 seconds. 110dB 4 minutes.
100dB 30 minutes. 9098 8 hours,

Unpacking
To avoid damaging the
loudspeaker when removing from
the outer case, itis important
to follow these instructions
carefully.
1. Stand the case on its bearers. Remove
the strapping, unscrew the lid and lift off.
2. Remove the three foam packing pieces from
loudspeaker sides and bottom, but leave the
packing at the top.
4. Gently ease the loudspeaker from the case
and remove plastic cover.
Electrical Connection
Connect the loudspeaker to
your amplifier by means of
either the screw terminals or
4mm plugs. The red terminal
on the loudspeaker should be
connected to the red terminal
on the amplifier, or the
connection marked positive.
Correct phasing of stereo loud-
speakers is extremely important
and incorrect connection will
produce a loss of bass and a
poor stereo image. This will be
rectified by reversing the
connections to one of the
loudspeakers.
itis good practice to keep the
connecting leads between the
power amplifier and speakers
as short as possible, and to use
a heavy gauge wire to keep the
DC resistance to a minimum.
It will be appreciated that the
input to the laudspeaker is of
complex impedance, and when
your system is operating at
high levels very high currents
will be carried by the inter-
connecting cables.
Considerable work has been
carried out in recent years on
the effect of different cables,
and there is fairly conclusive
evidence to show that, although
subtle, these differences are
apparent. We would recom-
mend, therefore, that if cable
lengths exceed 2 metres care
should be taken over their
choice, and in any event it is
good engineering practice to
employ really heavy gauge
cables of the highest quality.
Bi- and tri-amplification
In order to facilitate bi- or tri-
amplification, the inputs to each
individual filter section (low-
frequency, midrange, high-
frequency) have been brought
out to three separate terminals.
No electronic crossover is
required.
With normal operation using a
single amplifier, shorting links
are provided which parallel the
input terminals, and the ampli-
fier may therefore be
connected to any of these
terminals.
Obviously with tri-amplification
separate amplihers will be used
for each section, but the more
usual and recommended sys-
tem would be bi-amplification
where the larger of the two
amplifiers is used for the bass
section, and the smaller ampli-
fier for the midrange and treble
sections which are then con-
nected in parallel with one pair
of the shorting links provided.

The Listening Room and Positioning Your Loudspeakers
Environmental Controls
In professional applications the
acoustics will be well
controlled. Domestic listening
rooms however da vary widely
both in their acoustics and in
the positioning preferred to
operate the loudspeakers.
For this reason, control has
been provided for both the
midrange and high-frequency
sections with precision-switched
attenuators. The resulting
characteristics are shown in
the plots below (fig. 1).
In terms of professional
application, Model 808 provides
linear extension of free-field
response to 30Hz, as this
characteristic is ideal for a
controlled environment with
particular reference to digitally
recorded material. In less well
controlled domestic environ-
ments, however, some
attenuation of the bass
extension may be desirable,
and an electronic bass contour
control unit is in the process of
development,
The driver configuration in
Model 808 has been deliber-
ately conceived as a mirror-
image pair, with the midrange/
high-frequency assernblies
offset from the vertical centre
line of the cabinet. This con-
figuration gives an asymmetrical
polar characteristic relative to
the centre axis of the loud-
speaker and can help in
improving stereo imagery.
It is perfectly acceptable to
position the loudspeakers so
that these assemblies are more
closely or more widely spaced.
As а general rule, if the loud-
speaker placing is relatively
wide then the pairing should be
such that the assemblies are
adjacent (fig. 2). Conversely,
i closely spaced, they can be
further apart (fig. 3).
Both the listening room and
positioning your loudspeakers
within the room will widely
influence the tonal balance and
stereo information you receive.
Choice of a listening room is
often restricted but if you are
able to choose, the following
points may be helpful.
All enclosed volumes exhibit
resonances which, in the case
of the listening room, will be
essentially determined by the
distance between parallel
surfaces. The strongest res-
onances will lie between 30Hz
and 180Hz in average domestic
room sizes.
The most unsuitable listening
room would be one where all
dimensions (wall spacing and
ceiling height) are similar, since
all resonances occur over a
narrow band of frequencies
Rooms where all dimensions
are different give the most
even and natural bass
response.
Protuberances and larger
items of furniture tend to break
up these resonances and,
where practical, varying the
position of such items can
often favourably influence
sound reproduction.
Soft furnishings, wall coverings
and even pictures influence
middle and high frequencies.
ideally you should aim to avoid
discrete resonances or ring-
ing’, and an easy test for this
problem is a simple hand-clap.
if resonances exist there will be
a distinct 'overhang' or sustain-
ing of the response which could
last between 0.5 and 1 second.
A bookcase, placed on a wall
opposite a reflective surface
such as a window, will often
help to alleviate the problem
outlined above. Alternatively,
a panel of acoustic tiles placed
on a wall can produce a
remarkable improvement.
In all B&W designs the config-
uration of the drive units and
the characteristic of the
crossover network are So
designed that the horizontal
dispersion of the sound is
broader than the vertical
dispersion, thus ensuring
wider freedom of seating
with accurate stereo
information. Figs. 4 & 5.
The actual position of your
loudspeakers within the listen-
ing room can widely influence
sound reproduction. Two typical
positions are shown in figs.
647.
The environmental measure-
ments, fig. 8, show the wide
variation which can be achieved
by loudspeaker positioning.
We cannot emphasise too
strongly that time spent in
experimenting with the
position of your loudspeakers
is invariably worthwhile.
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- Overload
. Protection
B&W were the first major loud-
speaker manufacturer in the
word to introduce full electronic
protection against damage and
overload to their loudspeakers.
APOC (audio powered over-
load circuit).
In Model 808, this protection is
fitted individually to the
midrange and high-frequency
drivers. Should a thermal or
transient overload condition
occur, drive will be automatically
removed from the appropriate
unit and the LED will show until
the fault condition is removed.
The loudspeaker will then
automatically retum to normal
operation.
The voice coils in 808 have
been designed to withstand
temperatures in excess of
250°С. Mechanical clearances
also ensure that peak
excursions cannot damage
the bass driver voice coils.
Therefore, to reduce insertion
loss APOC is omitted from the
bass section. However, some
caution should be observed
with amplifiers of over 600
watts per channel.
Ancillary
Equipment
As a discriminating listener,
you will not have chosen your
808 loudspeakers without
thorough preliminary listening
tests. You will have discovered
that far from being the weakest
link in the chain — as loud-
speakers are so often described
— the performance of the 808
warrants the best ancillary
equipment available in order to
realise its full potential.
While we cannot of course
recommend specific equipment
manufacturers, there is a wide
range of top-quality components
available. Since you have
already invested in one of the
world's finest speakers, you
should therefore pay equal
attention to your choice of
pickup arm, cartridge, amplifier,
tuner, tape recorder or CD
player. Differences between
them may be subtle but they do
exist, and your own listening
experience is an invaluable
quide.
Because of its high power
handling capability and
protection circuits, no damage
can result to your 808 system
by using an adequately
high-powered amplifier. This is
preferred as it allows sufficient
headroom for the high level of
transient information available,
and our minimum amplifier
power recommendation is 200
rms per channel into 8 ohms.
Reliable advice is always avail-
able irom a reputable hi-fi
specialist, and our own
specially-appointed B&W
dealer will be pleased to give
you expert assistance. Natu-
rally, if itis possible to carry out
a listening test in your home,
using familiar recordings, this is
the best way to ensure lasting
satisfaction.
Free-field Frequency Response
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Fault Finding Service
Model 808 has been specifi- Throughout the world BAW
cally designed to withstand Loudspeakers have appointed
high power levels. With the distributors who are respon-
combination of APOC, ferro- sible for service. Should you
fluid tweeter, high temperature experience any difficulty,
Kapton coils and polyester please contact the dealer from
capacitors it is perhaps the whom you purchased the loud-
world's most reliable loud- speakers.
speaker and should give years
of trouble-free service.
Polar Response : wt
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Specification
Frequency Response
30Hz 1o 20kHz + 2d8
Low Frequency
Bass rellex employing Two 300mm drive units
Helmholtz box resonance 22H».
Midrange System |
Acoustic line taading employing two 100mm units
Bass Drivers: BT300
Ckaphragm 270mm thermoplastic cone wih PVA compound
coating
Ultra long throw suspension voice cod Sor dia. high temperature
Kapton magnet system 4.5kg ceramic.
Thus unl i-a high power handling development of the bass unit
used in 801
Midrange Drivers: MT100
Diaphragm 100mm aromatic polyamide Fibre matre cone, cntically
lormed and PVA impregnated following a laser interleromeiny
computer-iinked pattem
Voice cod 26mm high temperature Kapton
This unit es a high power handling version ol the midrange unit
used in ВОЯ
Harmonic Distortion
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High Frequency Driver: TX32 |
Diaphragm 32mm polyamide formed to а critical contour determined
by computer-linked laser inlerlerometny
Coil, aluminium former with high power Ipead-out terninahons and
immersed in ferra fluid or state-otHne-artr performance
Magnet system, lernte employing reversed held technology for
increased flux
on
Vertical +0, =1.5 dB over 10* arc,
Hornzantak +0, -2dB over AC" arc ZO0Hz — 15847
Distortion: 20Hz to 100Hz 100Hz to 20kHz
: 2nd Harmon 1.00% 140%
10008 а! Vm Sr Harmonic 1.00% 0.79%
Е ¿nd Harmonie 0.50% 0,64%
9600 а Im | 3rd Harmonic 0.70% 050%
"Maxımum % figuras at each teve!
Impedance
Bohms nominal, not ess than 4ohme al amy (гедиегиу
Sensitivity | ;
1 Wall into &ohms load lora sp. or tdg. al Tm. Sinewave input
at 1kHz
Power Handling
No upper limit on midrange and tweeter due lo automalic protection
cifctats
Bass FW continuous sinewave polw 400Hz
Crossover
ath-order Bulterworth squared cantiguratian with crossover
hequéncos of 400Hz and ЗЕН. with line delay correción between
midrange and tweeter by means огап all-pass network
Bi and tri ampinc 5 made easy hy separate terminals for each unit
No electrolytic capacilors are used
Dimensions
Height: 1050mm (АЛ Van]; 113mm (43un) with ninth
11 22mm (44 Vain) with wheels and pnt
Width: samm (25%.
Depth 510mm (20m) without gre;
542mm [21 in) with grille.
Weight! 7Bkg (1801b)
MSN o |
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