Bowers & Wilkins Complete Guide to AS2 Subwoofer and B&W AS2 Setup

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. 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.

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