Output Signal Level Indicators; Cd Horn Equalisation Selector; Mono Lo Selector - BSS Audio FDS-318 User Manual

Using the FDS-318
11.6 Output signal
level indicators
11.7 CD Horn
equalisation switch
Fig 11.2 CD Horn EQ
response
11.8 MONO LO
switch
26
Each output has two LED indicators showing the level of signal within each
band at the output connector. The lower SIG LED operates to show that a
signal is being received . Steady illumination means high drive levels and
periodic flashing indicates a moderate drive level. The LED will not light if the
peak signal level at the output connector stays below -20dBu.
The PEAK LED lights if the output signal of the crossover approaches a level
likely to overload the subsequent sound system, which is set to be in excess of
+10dBu. The signal level appearing at the output connectors depends on the
position of the LEVEL control. Most power amplifiers, however, will be driven
hard into clip at levels approaching +10dBu, so under normal operating
conditions this LED will NEVER flash. Should they do so, we recommend that
you investigate the sound system gain structure, the interconnecting cabling
and the power amplifiers' gain structure. For amplifiers which do have an input
sensitivity of +10dBu, the PK LED will indicate when the system is driving at its
hardest, and its likely to flash during times of high peak power.
Selecting the rear panel switch CD EQ will insert a correcting equalisation to
all relevant MID and HIGH outputs. This is confirmed on the front panel by the
appropriate LED. The amplifier response of the equalisation is shown if figure
11.2.
Modern constant directivity horns are often used in sound system as they have
good control of dispersion, and are often used in 2-way systems at low
crossover frequencies. However, their output falls off progressively above
4kHz, and to compensate for this extra boosting EQ is used. The correcting EQ
in the FDS-318 is designed to accurately match horn manufacturers
specifications, and restores the high frequency output.
Care should be exercised in the use of this function, as it can be potentially
dangerous if used on systems not utilising Constant Directivity components.
The table in figure 11.1 shows which outputs have the option, dependent on
the mode selected.
Because human hearing is insensitive to the location of low frequency sound
sources below 100Hz, stereo operation is normally dispensed with for sub-
woofer systems. Selecting the MONO LO switch on the rear panel of the FDS-
318 automatically sums the left and right hand inputs signals for the low
frequencies. The table in figure XX indicates which outputs are affected for
each mode , and a front panel LED lights to confirm the function is selected.
This function does not operate in the 2-way modes.