d&b 10AL - Manual (Page 8)

2.3.1. Controller settings
For acoustic adjustment the functions CUT, HFC and CPL can be
selected.
CUT circuit
Set to CUT, the cabinet low frequency level is reduced. The
cabinets are now configured for use with d&b active subwoofers.
HFC circuit
Selecting the HFC (High Frequency Compensation) circuit
compensates for loss of high frequency energy due to absorption
in air when loudspeakers are used to cover far field listening
positions.
The HFC circuit has two settings (HFC1, HFC2) for different
distance ranges the cabinets have to cover. The settings should be
used selectively, only for those cabinets covering the respective
distances, HFC1 for distances larger than 25 m (80 ft) and HFC2
for distances larger than 50 m (160 ft).
The compensation is adjusted for a typical relative humidity of
40 %. With lower humidity the absorption by air increases
therefore the distances where the respective HFC setting provides a
correct equalization are shorter than indicated above.
Using the HFC function provides the correct sound balance
between close and remote audience areas, whilst all amplifiers
driving the array can be fed with the same signal.
CPL circuit
The CPL (Coupling) circuit compensates for coupling effects
between the cabinets of an array. CPL begins gradually around
1 kHz, with the maximum attenuation below 200 Hz. As coupling
effects increase with the length of the line array, the CPL circuit can
be set to dB attenuation values between 0 and –9. With higher
attenuation values the corner frequency of the filter shifts towards
lower values.
Positive CPL values create an adjustable low frequency boost (0 to
+5 dB) and can be set when the system is used in full range mode
without subwoofers.
Note: Make sure that all cabinets within the line array are
operated with the same CPL setting.
Fig. 6: Frequency response correction of HFC circuit
Fig. 7: Frequency response correction of CPL circuit
d&b 10AL/10AL-D Manual (1.2 EN) 8