Bowers & Wilkins 4000 Double check the connections, Switching on and off, Setting the controls

•Maintain stereo separation to the lowest frequencies.

•Cope with larger listening rooms.

•Enable greater maximum sound output – often useful for effectively reproducing special effects in Home Theatre applications.

•Smooth out the effects of low-frequency room resonances.

If you are using two subwoofers for stereo audio, stereo separation is improved if each channel has its own subwoofer, providing each one is sited close to the relevant satellite speaker.

If using a decoder, use the phono ‘T’-piece provided, and make connections to the decoder input on each subwoofer. For two channel audio, use both line input channels.

Double check the connections

ENSURE THAT THE VOLTAGE INDICATED ON THE AMPLIFIER PANEL MATCHES THAT OF THE POWER SUPPLY.

Before auditioning the sound quality of your new installation and fine tuning it, double check the connections. All too often, users complain that they cannot get a decent sound however they set the controls, only to discover something has been wrongly connected. Make sure that:

•The phasing is correct – there should be no positive to negative connections (this applies only to speaker level interconnects). If something is out of phase you may get a fuzzy sound with an imprecise and floating image, a lack of bass or a combination of the two.

•There are no left to right mix-ups – this can result, for example, in the orchestra being the wrong way round or, more disastrously, sounds on your Home Theatre going in the opposite direction to the action on the screen.

Switching on and off

We recommend that you switch the subwoofer on before any power amplifiers receiving signals from the subwoofer. Similarly, when switching off, switch the subwoofer off last.

Auto:

On first switching the subwoofer to Auto, the amplifier becomes fully active and the light above the on/auto/off switch glows green. After a period of about 5 minutes without an input signal, the amplifier automatically reverts to standby mode, and the light glows red. When an input signal is detected, the amplifier automatically becomes fully active and the light glows green.

On:

With the switch in this position, the amplifier remains permanently on, and the light glows green.

Off:

In this position, the amplifier is in standby, and the light glows red.

Setting the controls

Line and speaker level inputs

There are three controls to consider:

•The LOW-PASS filter frequency

•The VOLUME control

•The PHASE switch

Decoder input

There are three controls to consider:

•The DECODER VOLUME control

•The PHASE switch

•The EQUALISATION switch

The optimum settings depend on the other equipment used with the subwoofer. If using more than one subwoofer, make sure the controls on each one are set the same.

Use with THX® controllers (including THX controllers set in non-THX mode)

The ASW™4000 is not a THX® licensed component, but may be used with a THX® controller if desired.

•Set the decoder volume control to the detent at the half-way (12 o’clock) position (this is a standard THX® pre-set level of 88dB SPL @ 1m for 100mV input signal).

•Set the EQUALISATION switch initially to position A, then see the section below on fine tuning.

•Set the PHASE switch initially to 0°, then see the section below on fine tuning.

Ensure that the subwoofer function on the THX® controller 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 so as to obtain 75dB spl (C-weighted) at the listening position from the controller’s internal noise test signal. Refer to your controller manual for further details as to how to set the levels. Inexpensive sound level meters are readily available from electronics stores and should be used to calibrate the levels.

Use with other Home Theatre decoders

•If the decoder has a dedicated subwoofer output and an internal LOW-PASS filter for the subwoofer having a slope of 2nd-order (12db/octave) or greater, set the LOW-PASS filter frequency to maximum, otherwise set it initially to 80 Hz.

•Set the VOLUME control initially to the half-way (12 o’clock) position, then see the section below on fine tuning.

•Set the PHASE switch initially to 0°, then see the section below on fine tuning.

Use for stereo audio

•Set the LOW-PASS filter initially to 80 Hz then

see the section below on fine tuning.

•Set the volume control initially to the half way (12 o’clock) position, then see the section below on fine tuning.

•Set the PHASE switch initially to 0°, then see the section below on fine tuning.

Fine tuning

The setting of the EQUALISATION switch affects only the signal via the decoder input. Position A is optimised to allow the subwoofer to provide the highest listening levels, while position B gives greater bass extension.

The optimum settings of the PHASE switch and the LOW-PASS filter frequency 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 optimum setting for the LOW-PASS cut-off 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 80-90 Hz 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.

If at any time you make changes to the amplification of the system such that you change from speaker to line level connections to the subwoofer, it is worth checking the phase setting again, as the speaker level and line level high-pass filter phase characteristics of the subwoofer are different.

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.

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.

7