Bowers & Wilkins 800 Serie Mode D'emploi page 9

Use with home theatre decoders
The B&W ASW Active Subwoofer is not a THX®
licensed component, but may be used with a THX®
controller if desired.
• Set the decoder VOLUME control to the half way
(12 o'clock) position.
• The setting of the LOW-PASS FREQUENCY control
is irrelevant.
• Set the PHASE switch initially to 0˚.
• Set the LOW-PASS FILTER switch to OUT.
• Set the EQ switch initially to position A.
See also the section "Fine tuning".
If you have a THX® controller, ensure that the
subwoofer function is enabled. When so configured it
incorporates all the filtering and level setting required
for the subwoofer in all modes. For level calibration,
the internal test noise and channel level controls in the
THX® controller should be used. In all cases the levels
should be set to obtain 75dB SPL (C-weighted) at the
listening position from the controller's internal noise
test signal.
With other decoders, configure the front and surround
speakers to "large" or "small" as appropriate before
setting the levels. Use the internal noise test signal
and volume controls of the decoder to set the levels of
all the speakers. Only change the VOLUME control on
the subwoofer if there is not enough range in the
decoder to achieve the correct levels.
Inexpensive sound level meters are readily available
from electronics stores and should be used to
calibrate the levels. Refer to your decoder manual for
further details on how to set the levels.
Use for 2-channel audio
• Set the VOLUME control initially to the half way (12
o'clock) position.
• Set the LOW-PASS FREQUENCY initially to 80Hz.
• Set the LOW-PASS FILTER switch to IN.
• Set the EQ switch initially to position A.
• Set the PHASE switch initially to 0˚.
See also the section "Fine tuning".
Fine-tuning
There are two settings of the EQ switch. Position B is
optimised to allow the subwoofer to provide the
highest listening levels, while position A gives greater
bass extension coupled with a tighter sound.
2-channel audio
The optimum settings of the PHASE switch and the
LOW-PASS FREQUENCY control are inter-related and
also dependent on the low-frequency cut-off
characteristic of the satellite speakers and the relative
positions of all the speakers in the installation.
Set the system up in the preferred position and play
some programme with a steady bass content. The
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optimum setting for the LOW-PASS FREQUENCY
depends on several variables; the bass performance
and power handling of the satellite speakers, the
number of subwoofers used and their position relative
to the satellite speakers. The range 80 – 90Hz is a
good starting point for the LOW-PASS frequency.
Unless two subwoofers are used to preserve separate
right and left channel information and are sited close
to the relevant satellite speakers, using a higher cut-off
frequency may compromise the stereo image and
should only be considered if the bass performance of
the satellite speakers is particularly limited.
At each setting of the cut-off frequency, listen with the
phase switch in both positions. The correct one is that
which gives the fullest bass and that will depend on
the bass characteristics of your satellite speakers and
the relative distances of the subwoofer(s) and the
satellite speakers to the listeners. When using more
than one subwoofer, ensure that each one has its cut-
off frequency and phase switch set the same way.
Set the loudness of the subwoofer relative to the
satellite systems to your liking. Use a wide variety of
programme material to get an average setting. One
that sounds impressive on one piece may sound
overpowering on another. Listen at realistic levels as
the perception of balance varies with sound level.
Home theatre
The situation with home theatre is somewhat different
from 2-channel audio. The subwoofer (LFE) signal is a
separate channel rather than an extension of the
signal to the satellite speakers. The LOW-PASS filter is
switched out, because the decoder provides all the
filtering for any speakers set to "small". However, the
position of the phase switch must still be assessed.
Normally the phase will be set to 0˚, but if the
subwoofer is positioned at a distance significantly
different from the other speakers, or the power
amplifier driving the other speakers happens to invert
the signal, the 180˚ position may be preferable. Listen
with the switch in both positions and choose the one
that gives the fullest sound. If there is little difference,
leave the switch at 0˚.
Decoders normally have a calibrated noise signal that
can be used to set the relative levels of all the
speakers, making the task somewhat more
straightforward than for 2-channel audio. However, do
not be afraid to alter the settings to your personal
preference. It is all too easy to get carried away with
the capabilities of the subwoofer, especially with some
special low-frequency effects. Often a more realistic
portrayal, and one more satisfying in the long term, is
to be had by setting the subwoofer level lower that the
standard calibration level.
All applications
If you get problems with lumpy bass – if certain bass
notes are exaggerated more than others – then you
probably have a room interface problem and it is worth
experimenting with the placement of the subwoofer.
What may seem like small changes in position – 15cm
(6in) or so – can have a profound effect on the sound.