BSS Audio FDS-318, User Manual

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11.2 Crossover
frequency
adjustment
The large control knobs on the left hand side of the front panel adjust the
frequency of the fourth order Linkwitz-Riley crossover filters. They are
arranged in stereo pairs to aid the setting up of like values on each channel. In
the 2- and 3-way modes, the last two control knobs remain non functional. The
frequency range that is adjustable with each control is also modified according
to whether the 2 WAY HI, 2 WAY MID or 2 WAY LO mode is selected. This
range scaling of x10 or /10 is indicated on the front panel by the relevant
adjacent LED.
The table in figure 11.1 indicated the respective function of each control,
dependant on the MODE selected. They must be adjusted to suit the
loudspeaker system being used, as incorrect settings can cause poor sound and
will ultimately damage the loudspeakers. Refer to the loudspeaker data sheet if
the correct frequency is not known.
11.3 Output level
alignment
The eight smaller control knobs provide a range of adjustment of output level
for each of the possible eight outputs, and are arranged in stereo pairs to aid
the setting up of like values .on each channel. They are designed to give an
accurate and controlled range of +/-6dB about 0dB, the unity gain position.
When turned fully anticlockwise, they continue to attenuate the output down
to an infinity cut-off (The separate MUTE selector should be used when
individual bands require muting). It is recommended that the controls are first
positioned at their 0dB mark, and small adjustments are then made to balance
the system. If attenuation greater than -dB is required on any individual output,
you should suspect an imbalance somewhere else in the system and rectify the
fault there rather than continue with the crossover controls excessively set.
11.4 Output MUTE
switch
Each output can be individually silenced by pressing the MUTE switch. Press
again to restore the output signal. The number on the switch cap corresponds
to the numbered output connectors on the rear panel. Push button muting is an
invaluable facility when setting up a sound system, and avoids the necessity of
using the output level controls which would upset previously made settings.
11.5 Output
polarity reverse
switch
Each band of the FDS-318 includes a polarity switch. Depressing it reverses
(REV) the polarity (or 'phasing') of the signal coming from the related output.
Should the sound system exhibit a cancellation or dip in its frequency response
at or around the crossover frequency, this could be due to a reverse wired
loudspeaker driver, a reverse wired connecting lead, or a power amplifier
wired to a different input balanced connection. This is easily corrected by
pushing the REV switch for the particular output. A similar situation could arise
when a loudspeaker system is designed to receive a reverse polarity signal for
one of its component parts. In either case, the REV function can be readily
selected and the decision to which position is required can be judged either by
careful listening to program music, or by using a Pink noise source and real
time analyser (RTA). If switching does not improve the sound, and the drop is
appreciable, the cause is undoubtedly acoustic and linked to the drive unit
spacing and cabinet design.
Using the FDS-318