Calibration; General Recommendations To Prevent Feedback - Bosch LBB 1968 Installation And Operating Manual

Plena Feedback Suppressor | Installation and Operating Manual |
4.2

Calibration

The Plena Feedback Suppressor requires a source signal in order to measure the acoustic environment and to set the
adaptive filter. When no such signal is present (e.g. before the event or the conference):
• Press the calibrate button (9). Random noise at -6 dBr will be generated for a few seconds to allow the feedback
suppression algorithm to calibrate quickly. During this time, the calibrate indicator (8) will light up.
or
• Make sure there is a source signal, e.g. by playing some background music.
When the unit perceives a too high input signal, the input signal overload indicator (2) lights up. In this case, adjust
the input signal level using the signal level switches on the rear of the unit.
When howling noises are heard, the Feedback Suppressor is operating at its feedback suppression limit. In this case,
decrease the overall signal gain (e.g. by decreasing the microphone gain on the mixing panel or by decreasing the
master volume on the power amplifier).
4.3

General recommendations to prevent feedback

• Ensure correct arrangement of microphones and loudspeakers. Pay special attention to the directivity of the
microphones and loudspeakers and to the proper distance between microphones and loudspeakers. This applies
especially to buildings with long reverberation times, such as houses of worship.
• Always use the microphones and loudspeakers according to the manufacturer's specifications.
• Improve poor and reverberating room acoustics, e.g. by covering highly reflective (tiled) walls and floors with
curtains or carpets.
• Never use loudspeakers above their rated power. Due to power compression of the loudspeakers, the feedback
margin is reduced. Try to ensure enough headroom.
Bosch Security Systems | 2003-11 | 9922 141 81681en
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