Bowers & Wilkins DS8 - Manual (Page 5)

2
help the perception of the central image
for any listeners sitting away from the
centre line of the installation. (figure 3)
If you are also using the speakers for
movies, you should try to match the
audio image to the size of the screen.
That generally means that the speakers
should be closer together. A good
starting point is to put the speakers
about 0.5m (20-in) from the edges of the
screen. (figure 4)
Bookshelf or on-wall speakers should be
placed at a height that brings the
tweeters approximately to ear level. In
the vertical plane, the dispersion narrows
in the crossover region between the
midrange and tweeter drive units, when
both units are working together. To
preserve the optimum sound balance, try
to keep within ±5º of this.
Floor-standing speakers have the angle
of their optimum listening window
adjusted for the height of the speakers
and the typical range of ear height of
seated listeners.
f Go to section 3.
2.2 FRONT CENTRE
If you have an acoustically transparent
screen, place the speaker behind the
centre of the screen. Angle it towards the
listeners if the tweeter is more than 5º
from ear height. (figure 5)
If you have a normal screen, place the
speaker immediately above or below the
screen, whichever is nearest ear height.
Angle it towards the listeners if the
tweeter is more than 5º from ear height.
A stand with tilt adjustment is available
for the HTM2D, HTM2S and HTM4S.
Consult your dealer for details. (figure 6)
If you are just listening to audio, place
the speakers centrally and mount
bookshelf or wall mount speakers with
the tweeters at ear height. (figure 7)
f Go to section 3.
2.3 SURROUND
Surround speakers generally fall into two
main types – those that one might
describe as 'normal' speakers – so-
called monopoles, where the sound
comes from a set of drive units mounted
on the front of the enclosure – and those
that give a more diffuse sound field, such
as dipoles. Each type has its
advantages.
Most multi-channel music is recorded
with home entertainment in mind and is
monitored using monopole surround
speakers, whatever the multi-channel
recording format. This enables better
location of side and rear images,
although the formation of such images is
never quite as precise as it is between
the front speakers.
Most films are originally balanced for
cinemas, where a large number of
speakers spread around the auditorium
are used to create the surround sound
field. In that case there are more
surround speakers than there are
discrete channels of information and a
less precise image is created that gives
an all-enveloping effect. Dipoles and
similar diffuse speakers are better at
recreating this type of sound field in the
home, but using fewer speakers to do it.
Image positioning with these types of
speaker is never as precise as it can be
with monopoles. However, they do have
the advantage of making it easier to
balance the system for a larger listening
area.
You may well receive conflicting advice
from different sources on the best type of
surround speaker to use. The truth is
that there is no one perfect solution for
all situations and the final choice for any
given application will be influenced by
several criteria, some of which may have
a degree of conflict.
DS8S only
Within the 800 series, the DS8S is the
only speaker to offer dipole operation.
In fact, this specialist surround speaker
has the advantage of offering a choice
of both monopole and dipole
operation, either via a switch located
on the front baffle, behind the
removable grille, or remotely, using a
12V trigger from the surround
processor. You may therefore choose
whichever type of operation best suits
the conditions of the listening room, the
size of audience and the type of
programme being played. Indeed, you
may even change the characteristic for
different types of programme and, as
the total energy into the room is the
same in both modes, no recalibration
of the installation is necessary when
switching between them.
In monopole mode, only the two drive
units on the front face operate. In
dipole mode, the front tweeter is
disconnected; the side firing drivers are
brought into operation and the
crossover frequency to the bass unit is
lowered. The drive units on opposing
sides are connected out of phase with
one another, which creates a wedge-
shaped null zone, approximately 60º
wide, at right angles to the wall. If the
listeners sit within this zone, they
become less aware of the location of
the speakers and hear more reflected
sound; hence the diffuse nature of the
sound field.
Contact your dealer if there are any
missing items.
2 POSITIONING
Stray magnetic fields
If you are using speakers in a home
theatre set-up and you are using a CRT
screen (a traditional tube television or
back projector), make sure the picture is
not going to be distorted by stray
magnetic fields from the drive unit motor
systems. The following dedicated centre
speakers are magnetically shielded
because their application requires them
to be placed right next to the screen:
HTM1D
HTM2D
HTM3S
HTM4S
All other speakers in the Series should
be placed at least 0.5m (20-in) from such
screens. Some television brands are
particularly sensitive to magnetic fields
and may require extra spacing. Plasma
and LCD screens are not affected and
front projectors are usually well away
from the speakers anyway.
Application f Go to
Front left and right 2.1
Front centre 2.2
Surround 2.3
2.1 FRONT LEFT AND RIGHT
If you're only interested in audio and not
movies, space the speakers apart
approximately the same distance as you
sit from them. This means that the
included angle is about 60º. This applies
whether or not you are using a centre
speaker.
Apart from the dedicated on-wall model
SCMS, the balance of the speaker is
more natural if the speakers are at least
0.5, (20-in) from the rear wall. This also
helps to improve the impression of
perspective. (figure 2)
If you are only concerned with 2-channel
audio, having the speakers further apart
can lead to what is known as the hole-in-
the-middle effect, where it's difficult to
generate a stable phantom central
image. If you have a centre speaker, you
can space the left and right speakers
further apart. All that happens is that the
image widens. It's just like being closer
to the performance.
If you have to space the speakers further
apart because of domestic constraints,
the central image can often be improved
if you toe the speakers in towards the
centre of the listening area. This can also