Acoustic feedback will
occur when the microphone picks up audio from
the loudspeaker and transmits it back into the amplifier.
A "loop" of sound occurs which builds in intensity to a piercing
scream.
This is usually due to the volume being too high or the microphone
too near to the equipment - and the scream won't stop until
you physically break the loop of sound!
You could benefit from a Feedback
eliminator
CC-FE2 COMPACT FEEDBACK ELIMINATOR
An ultra-compact feedback eliminator unit for use with
line level signals or vocals. 12 extremely versatile filters
per channel sweep through the spectrum, detecting the
audio signature of feedback. As soon as this is detected,
the particular filter notches out that frequency until
the risk of feedback has subsided. Various setting options
are available to suit the particular implementation and
environment.
2 x 12 sweeping notch filters
Stereo in / stereo out
Variable feedback sensitivity
Power supply 9Vac
PSU (included)
Controls Process, Input,
Output, Mono/stereo, Hold filters, Auto/fixed attenuation,
Sensitivity
Connections L + R in, L
+ R out (unbal. 6.3mm jack)
Frequency response 20Hz
- 20kHz
Sample rate 20-bit AD/DA
Dimensions 140 x 125 x
40mm
Weight 0.48kg
OUR
PRICE
£82
inc VAT
How to avoid feedback
Turn it down!
Every venue has a point where feedback can not be avoided.
Is the singer using the mike correctly?
If the singer is holding the mike too far away from his mouth
then you may have to turn the
PA system up louder
to compensate and then you will get more feedback. Also, the
singer should not be touching the wire at the top of the mic
otherwise the vents that create the cardioid pickup pattern
get covered and this causes foldback.
Are you
using cheap microphones?
Cheap microphones are more prone to feedback.
Are your
speakers in the right position?
Are your speakers positioned far enough in front of the line
of your mikes? Try moving them forward a little at a time.
If the singer says he can't hear, consider getting stage monitors.
Try angling
the PA speakers differently
Even slightly changing the angle of the speakers can affect
feedback enormously.
Isolate
which mike is causing the problems and change the EQ settings
Feedback occurs at varying frequencies. You may be able to
adjust the EQ on the mixer to cut down the feedback.
Are you
using the right type of microphones?
Omni-directional microphones pick up as much sound from behind
(unwanted sound) as they do from the front. Cardioid, Super
Cardioid, Rifle and especially Microline pickup patterns are
much better for stage use though you should be aware of the
drawbacks with each type. For example, Super Cardioid pickup
patterns might reject sound from the back very effectively
but they are also very susceptible to handling noise and tend
to emphasise "P" and "B" consonants explosively through the
sound system, especially when used close to the mouth.
What are
the natural room acoustics like?
Establish what the natural room acoustics are like - try shouting
loudly or clapping. If there is a basic echo in the room then
you may be fighting a losing battle. If there are curtains
or drapes, try closing them to reduce the amount of natural
reflections you get.
Feedback
at sound check time
When you do your sound check, the room will be empty and cooler
than when you actually play. Bodies absorb sound and cold
rooms make feedback worse. You may therefore be able to cope
without the feedback when you are actually on stage.
Using
wireless microphones
These are more prone to feedback as the singer is free to
move around the stage more and can move in front of the speakers.
Use the sound check to establish their 'working area'.
Click here for an excellent Sound On Sound article "Getting
Your Studio Sound Live" which goes into more detail about
positioning your equipment on stage and the causes of feedback.
Send us your comments
If you have any comments on this section or would like to
add something to it, please email us!
