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Feedback is the ringing noise that you hear
from the speakers which tends to occur where sound system levels
are pushed too high.
It occurs because an input device (almost always a microphone
or group of microphones), picks up a sound that is coming from
the speakers hat the input device is feeding. This sound is then
amplified again and comes out of the speakers at an increased
level, and so is picked up again and so on until a ringing is
heard. This tends to happen at a specific frequency, hence the
ringing, pure tone type of noise, but can occur at several frequencies
all at once. You tend to find that for a given situation (room
type, speaker system, number of mics, amount of EQ, temperature)
the initial feedback frequency is reproducable; however, the
number of factors that can change the situation is so varied
that is very difficult to predict with certainty in advance where
the feedback frequency will come and at what level.
The possibility of feedback is always there. To avoid it, you
must be aware of the limitations of your system and the space,
and design and use it so that feedback only occurs beyond the
sound levels that you need.
General avoidance measures are:-
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1 |
Have as few microphones 'live' at any one
time as possible |
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2 |
Have the speakers as far away from the microphones
as possible. This is obviously difficult when you are using monitor
speakers. |
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3 |
Use directional microphones and speakers where
possible; keep the mics as close to the sound source as possible
and aim speakers with care. |
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4 |
If you are using EQ on the system, use as
little boost as you can. Boosting a specific frequency always
affects the frequencies around it, and if these are problem feedback
frequencies, you are more likely to get feedback. |
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5 |
Find at what level feedback occurs and don't
go above this. If you find the position with your master faders
where feedback happens, back them off from this by approximately
6dB. |
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6 |
If an individual mic is causing a problem,
try pressing the phase reverse switch on its input. |
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