Bowers & Wilkins CCM818 Manuel D'utilisation page 6

6.1 channel
Position two speakers to the sides in line with the
centre of the listening area and one centrally behind
the listeners, with the frames rotated so that the
bass/midrange drive units are directed towards the
centre of the listening area. (figure 5)
7.1 channel
Position two speakers to the sides in line with the
centre of the listening area and two behind the
listeners, subtending an angle of approximately 40º.
(figure 6)
PREPARING THE LOCATION
Choosing cable
Excessive resistance in the speaker cable wastes
power and alters the frequency response of the
speaker. Always try to keep the resistance as low as
possible with the loop resistance preferably below
0.5 ohms for non-critical applications and below
0.2 ohms for best results. Use the table of figure 10 to
calculate the minimum gauge of cable required.
Existing drywall construction (retrofit)
Mark the centre position of the speaker and position
the template so the mark shows through the hole in
the middle.
Trace round the outer edge of the template and cut
neatly just inside the line.
To improve the mechanical integrity of the ceiling or
wall and reduce the likelihood of rattles, we
recommend you apply a bead of wood glue or mastic
along the joints between the back of the plasterboard
and the studs in the vicinity of the speaker.
Run the cable to the aperture, allowing enough length
to comfortably connect the speaker, but not too much,
as the excess may rattle against the structure.
New drywall construction
The speaker can be installed once the ceiling or wall is
completed in the same manner as retrofitting, but it is
easier to position and cut the hole if the optional pre-
mount kit is used before the plasterboard (sheetrock)
is fitted.
Staple or nail the PMK to the studs as described in
the instructions with the kit. Run the cable and secure
it to the fixing point on the PMK. Allow enough length
to comfortably connect the speaker, but not too much,
as the excess may rattle against the structure.
Results are affected by how well the plasterboard is
attached to the studs and we recommend gluing as
well as screwing or nailing the panels to the studs in
the vicinity of the speaker.
Once the board is fitted, the inner flange of the PMK
serves as a guide for a hole router or saw.
Solid wall construction
In order for the bass performance not to be
compromised, the speaker requires a cavity volume of
at least 20 litres (0.7 cu ft). This means that, in a
standard 10cm (4 in) thick wall, the cavity will extend
beyond the boundaries of the speaker frame. It is
possible to provide this cavity simply by using a lintel,
covering the hole with plasterboard and fitting the
speaker as described above for retrofitting into a
drywall. (figure 7)
Damping the cavity
Fill the wall cavity, allowing room for the speaker itself,
with unlined fibreglass or mineral wool matting. The
packing density should be just enough to comfortably
prevent the material from dropping or sagging over
time. In an open wall cavity, fill to a distance of at least
30cm (1 ft) above and below the speaker. (figure 8)
In the ceiling, drape the matting at the back of the
ceiling board, covering the aperture and extending at
least 30cm (1 ft) around the speaker into open void.
(figure 9)
IMPORTANT: Ensure that the materials you use meet
local fire and safety regulations.
Fitting the speaker
All connections should be made with the equipment
switched off.
Connect the cable, observing the correct polarity.
With the grille removed, position the speaker in the
aperture and screw in the 4 screws visible from the
front (see the note above in the contents section).
These screws automatically swing out clamping dogs
that locate behind the mounting surface. Ensure that
they have located properly before fully tightening the
screws. A certain amount of flexing of the frame is
allowed to take up unevenness in the mounting
surface, but do not over-tighten the screws as
excessive distortion of the speaker frame may result.
Adjusting the speaker
The speaker is designed to point towards the listening
area and for most instances this gives best results.
However, for some surround speaker applications,
better overall results may be obtained if the sound is
directed away from the listening area.
Typically this may apply if:
a. The room is particularly live and the sound
becomes harsh.
b. The listening area is a large proportion of the room.
Increasing the amount of reflected sound and
reducing the amount of direct sound may give a
better average balance between the speakers for
all listeners.
Customising
The frame and grille have a paintable white semi-matte
finish, ready if necessary to be re-finished to match
your own decor.
Before painting the grille, remove it from the frame.
Do not re-finish the drive units or baffle area behind
the grille. Use the paint mask provided. Avoid touching
the drive units, as damage may result.
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