Behringer FEEDBACK DESTROYER PRO DSP1100P User Manual download pdf (Page 9)

The filter bandwidth can also be expressed in

octaves

(as on the FEEDBACK DESTROYER). The following

table shows a list of decimal Q values vs. octaves:

Octave Quality factor (Q)

1/6 8.65

1/4 5.76

1/3 4.32

1/2 2.87

3/4 1.90

11.41

3/2 0.92

20.67

30.40

Fig. 1.1: Octaves vs. Q factors

Now the following relationship becomes clear: the higher the Q factor, the narrower the frequency band that

can be cut or boosted. On the Behringer FEEDBACK DESTROYER you can adjust the relative bandwidth

conveniently with the infinitely variable jog wheel. The filter bandwidth can be tuned from 2 octaves (120/60

octaves) down to 1/60 octave (for fine adjustments).

1.1.1 Feedback as a physical phenomenon

Almost every concert goer may have experienced with their own ears the howling and squealing of an

improperly set sound reinforcement system. Feedback is one of the main problems encountered during live

events. A feedback loop is produced when a microphone signal is reproduced by an amplifier system, to be

picked up again (with the same phase position) by the microphone. Thus, feedback is built up at all frequencies

where the distance between microphone and speaker corresponds to a multiple of the signal’s wavelength.

Microphone

Mixing Console

Power Amp

Speaker Box

Fig. 1.3: Typical feedback loop

Basically, any microphone signal passing through an amplifier is liable to generate feedback. Unfortunately,

the feedback frequencies of P.A. systems differ, and even one single system can have varying feedback

frequencies, as these depend largely on the room acoustics. Feedback can be caused by the following

conditions:

s The microphones are too close to the speaker boxes or the speakers are badly positioned (monitor

system).

s The microphone channels on the mixing console are not set up correctly.

1. INTRODUCTION

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Behringer FEEDBACK DESTROYER PRO DSP1100P User Manual Page 9