Bowers & Wilkins ASWCM Electrical connections, Using more than one subwoofer, Fine-tuning

Electrical connections

Disconnect all sound system equipment from the power supply until the signal connections have been made and checked. This avoids the risk of damage whilst connections are made or broken.

The function of the subwoofer is to receive signals from the amplification chain and, where necessary for 2-channel audio, split the signal into low bass and higher frequencies and feed the latter back out to the satellite speakers. Left and right channel inputs may be combined into a single mono low bass feed to the subwoofer drive unit if required.

The subwoofer will input and output line-level signals via the RCA Phono sockets located on the back panel.

Use the following table to select the correct wiring method for your installation:

Application: Home Theatre

The subwoofer may be used with any decoder that has a line-level subwoofer output (normally from an RCA Phono socket). Most decoders with integral power amplifiers still output the subwoofer or Low-Frequency Effects (LFE) signal at line level.

•Decoder with one or more subwoofers – fig. 3

Application: 2-channel audio

Separate pre- & power amplifiers:

aOne or more subwoofers with output combined into a single mono signal – fig. 4

bTwo subwoofers with separate left and right signal – fig. 5

The subwoofer is not suitable for use with

2-channel integrated pre/power amplifiers.

Using more than one subwoofer

Using more than one unit in a single installation can improve performance in the following ways:

•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 2-channel audio, separation is improved if each channel has its own subwoofer, providing each one is placed close to the relevant satellite speaker.

Double-check the connections

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 to the satellite speakers. 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.

The MODE standby/auto/on switch (3) at the top left of the amplifier panel does not isolate the amplifier completely from the power supply. It maintains a low-power input to an auxiliary sensing circuit.

The switch (3) operates as follows:

On:

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

Auto:

On first switching the subwoofer to Auto, the amplifier becomes fully active and the light (10) above the on/auto/standby 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.

Standby:

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

If the subwoofer is to be out of use for an extended period of time, we recommend you isolate it from the power supply, either by using the POWER switch (10) or by removing the plug from the power socket.

•The LOW-PASS FILTER switch (5)

•The EQ (equalisation) switch (4)

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 ASW Active Subwoofer is not a THX® licensed component, but may be used with a THX® controller if desired.

•Set the 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 B.

•Set the PHASE switch initially to 0˚.

See also the section “Fine tuning”.

Only use the mono connection of figure 4 if you cannot place each subwoofer close to its satellite speaker.

Setting the controls

There are 5 controls to consider:	Fine-tuning
	There are two settings of the EQ switch. Position
• The VOLUME control (1)
	A is optimised to allow the subwoofer to provide
• The LOW-PASS FREQUENCY control (2)	the highest listening levels, while position B gives
• The PHASE switch (6)	greater bass extension coupled with a tighter
	sound.

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