Bowers & Wilkins ASW CDM Use for 2-channel audio, Fine-tuning, Channel audio, Home theatre

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 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. Try raising the subwoofer clear of the floor as well as lateral movement. 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 decoder output levels or the volume control on the subwoofer amplifier as appropriate), but only after setting the phase correctly.

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. Remove the grille first so that the cloth does not become stained, but be careful not to disturb the drive unit. The grille itself may be cleaned using a soft brush.

Do not use the subwoofer as a table. When in use, objects left on top of the subwoofer are liable to rattle. In particular, avoid the risk of liquids being spilled (eg from drinks or vases of flowers).

If the system is taken out of use for a long period, disconnect the subwoofer from the power supply.

Note: The subwoofer will automatically shut down if driven excessively. If this occurs, re-set the subwoofer by turning it off then on again, using the power on/off switch on the amplifier panel.

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