Behringer Feedback Destroyer Pro DSP1100P - Manual (Page 21)

21
E
0 dB
-2 dB
-4 dB
-6 dB
-8 dB
-10 dB
-12 dB
1 kHz 5 kHz 200 Hz
Bandwidth = 600 Hz
Filter attenuated by 8 dB at 1kHz
Center frequency
= 1 kHz
-3 dB
Fig. 4.2: Typical equalizer filter curve
The filter bandwidth can also be expressed in octaves (as on the FEEDBACK DESTROYER PRO). 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
1 1.41
3/2 0.92
2 0.67
3 0.40
Tab. 4.1: 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 PRO 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).
4.1 Feedback
Almost every concert goer may have experienced 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) 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.
4. TECHNICAL BACKGROUND