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Setting the controls
There are 4 controls to consider:
• The volume control (v) (6)
• The low-pass frequency control (Hz) (7)
• The PHASE switch (8)
• The EQ (equalisation) switch (9)
The optimum settings depend on the other
equipment used with the subwoofer. If
using more than one subwoofer, ensure the
controls on each one are set the same.
Use with home theatre decoders
The B&W Active Subwoofer is not a THX®
licensed component, but may be used with
a THX® controller if desired.
• Set the volume control initially to the
12 o’clock (detent) position.
• Set the EQ switch initially to position i.
• Set the PHASE switch initially to +.
• The setting of the low-pass frequency
control is irrelevant.
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. The detent
position of the volume control on the
subwoofer corresponds to the THX®
standard of 88dB spl at 1m for an input at
the LINE IN socket of 100mV.
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. If there is not enough range in the
processor to achieve the correct levels,
adjust the volume control on the subwoofer.
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.
2-channel audio
• Set the volume control initially to the
12 o’clock (detent) position.
• Set the EQ switch initially to position i.
• Set the PHASE switch initially to –.
• Set the low-pass frequency to the
-6dB cut-off frequency of your satellite
speakers.
Both -3dB and -6dB figures are to be
found in the specification of each B&W
speaker model. However, if the
manufacturer of the satellite speakers does
not quote a -6dB frequency, but only a
-3dB frequency, the optimum setting for the
low-pass filter frequency control will be
between 0.6 and 0.9 times the -3dB
frequency, depending on the roll-off
alignment. The more gradual the roll-off
rate of the satellite speakers, the lower the
frequency should be set.
See also the section "Fine tuning".
Fine-tuning
Home theatre
With home theatre the subwoofer (LFE)
signal is a separate channel rather than an
extension of the signal to the satellite
speakers. The low-pass filter does not
operate in the line level input circuit,
because the processor 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 +, 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 – 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 +.
Surround sound processors 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.
2-channel audio
The optimum settings of the PHASE switch
and the low-pass filter frequency control are
inter-related and also dependent on the
low-frequency cut-off characteristic of the
satellite speaker. However, the settings
recommended above for the low-pass filter
frequency and PHASE have been chosen to
add well to most bass alignments, whether
closed-box or vented-box (reflex), with
-6dB frequencies within the adjustment
range of the subwoofer.
Set the system up in the preferred position
and play some programme with a steady
bass content.
Using the initial settings guide, first check
the setting of the PHASE switch. Choose
the position that gives the fullest sound.
Normally the recommended position will be
optimum, but may not be in certain
circumstances, such as if the power
amplifiers feeding the satellite speakers
invert the signal, or if the subwoofers are
not placed close to the satellite speakers.
Next, 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.
Finally, adjust the low-pass filter frequency
to give the smoothest transition between
the subwoofer and satellite speakers. This is
probably the most difficult to optimise.
All applications
The EQ switch alters the bass extension of
the subwoofer. The lower the frequency, the
more the driver diaphragm must move to
achieve a given loudness level. You can
therefore trade off bass extension for a
higher average output level. Position i gives
the greatest bass extension and position iii
the least. We recommend you use position i
unless the subwoofer shows signs of
distress at the required replay level.
If you get problems with uneven 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.
The use of multiple subwoofers can smooth
the effects of room resonances, as each
subwoofer will tend to excite resonances at
different frequencies. If you alter the relative
distances from the subwoofer(s) and
satellite speakers to the listeners
appreciably, reassess the phase switch
setting. You should also check the level
setting of the subwoofer (using either the
processor output levels or the volume
control on the subwoofer amplifier as
appropriate), but only after setting the
phase correctly.
When using more than one subwoofer,
ensure that each one has its low-pass filter
frequency and PHASE set the same way.
Taking care of the subwoofer
The cabinet of the subwoofer may be
cleaned by dusting with a dry cloth. If you
wish to use an aerosol cleaning spray, do
not spray directly on the cabinet; spray
onto the cloth.
If the system is taken out of use for a long
period, disconnect the subwoofer from the
power supply.
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