BSS Audio FDS-388 OMNIDRIVE Owner's Manual - Manual (Page 49)

49
Absorption at 25m (dB)
0
1
2
3
4
5
6
100 1000 10000 Frequency (kHz)
Absorption at 25m (dB)
0
1
2
3
4
5
6
100 1000 10000
10%
30%
50%
70%
100%
Frequency (kHz)
Relative Humidity
20.0 Meteorology
Meteorology
Humidity Effects
Fig 20.2 Correction
Curves at 0
°
C and 25m
Fig 20.1 Correction
Curves at 20
°
C and 25m
Temperature and humidity cause dramatic changes in the absorption of sound
in air over a broad frequency range, which can cause inconsistent sound
quality during the course of a performance. The FDS-388, equipped with the
optional meteorology probe, can compensate for these effects. Figures 20.1
and 20.2 show the absorption curves under various humidity and temperature
conditions at a distance of 25m.
The FDS-388 provides absolute compensation. It compensates for conditions as
they differ from lossless air, therefore under all atmospheric conditions some
form of correction will be applied. It is most important, therefore, when
initially setting up the system that correction is set to ON when adjusting the
house EQ. The compensation is always in the form of a 6dB/Oct high shelf
providing various amounts of boost. The actual boost value set is not only
determined by temperature and humidity but is also directly proportional to the
user set distance. The correction distance should be set to the distance of the
average listening position from the speakers. At this position the atmospheric
effects and shelving EQ will cancel each other. The presence of the
meteorology filter in the system will result in different settings for the house
EQ. Once the system is set up, however, as the conditions change the filter
parameters will be adjusted and sound quality will remain constant.
The FDS-388 will also adjust the user set delay times to ensure that the delay
distance is kept constant with temperature changes. As the ambient
temperature changes, the speed of sound in air changes and the delay heard at
a constant distance will change accordingly. With Delay Corrn in the Delay
Utility Screen set to Auto, the FDS-388 will adjust delay times to keep delay
distances constant. Delay Corrn will have to be set to Auto or Manual before
setting the delay times or distances.