YORKVILLE M8 Manuel De L'utilisateur page 10

Keep the Main Speakers
between mics and audience
to minimize feedback
DO NOT place Main
Speakers in back of
the stage!!
8
Level controls until the performers can hear themselves on the stage at adequate volume
levels without feedback.
9. Feedback during a performance is usually caused by one of the stage monitors. The main
PA is less likely to feed back because the microphones are so far away from the main PA
speakers. Therefore, if one of the monitors and a microphone are feeding back, try the
following procedures
a) Turn the AUX Send channel level controls to 0.
b) Turn each AUX Send channel level control up one at a time until you find which
channel is causing the feedback at a low level.
c) Reposition the microphone for the channel causing the feedback further away from
the stage monitor closest to the microphone.
d) Now turn the rest of the AUX Channel controls and the AUX Send master control back
up. If the feedback recurs, repeat the procedure b) and c) until you have gained enough
headroom below the feedback threshold.
e) In the rare case of main system feedback, follow the above type of procedure, but
using the Main Level, and Channel Level controls.
Note: To increase your sound system's immunity towards feedback a graphic equalizer could
be inserted between the Main Output jacks and the Amplifier Input jacks. Then the audio sig-
nal passing from the mixer to the amplifiers will flow through the off board equalizer. Then
as the Main Level control is turned up to the point where feedback occurs, pull down each
band control (which reduces the gain of the sound system at the frequency marked on that
band of the equalizer) on the off board equalizer one at a time until the feedback disap-
pears. It is best if the least amount of adjustment is made on the off board equalizer as too
much gain reduction will greatly change the tonal quality of your music.
Tips on Getting a Good Mix
If you've never mixed at high power levels before, the following suggestions may help you
to get a consistently good sound.
Feedback
When you have live microphones, don't run the volume level right up to the point of feed-
back! This is the most common mistake made by people mixing live events. We've all heard
systems on the verge of feedback and they sounded terrible, even when no feedback was
actually occurring! This happens because working at the feedback point warps the frequency
response of the system.
To understand how volume level can affect frequency response, lets look at what happens as
you increase it to the point of feedback. Notice that feedback wants to occur at a certain
frequency? This is because the entire system - the room, the microphones, the speakers, the
people, everything - is showing a tendency to Resonate at a particular frequency. You can
see the effect of resonance when you talk into an empty tin can. You hear a hollow droning
sound. The technical term for a system that shows a tendency to resonate is a High Q Filter.
So by turning up to the feedback point, you are making the whole system behave like a
high Q filter. This gives you the same sound as if you turned everything down a lot and then
boosted, say, the 1KHz graphic equalizer to +12dB!
This is why cutting certain frequencies with the graphic equalizer can control stage feedback.
However, using the graphic to control feedback means that, as the room changes, (more people
come in, it gets hotter, the dance floor empties or fills up, etc.), the system's equalization will
change as the rooms resonance changes. You'll be fighting the room all night.
Having things loud doesn't make up for the poor sound produced by spurious response
peaks. Fortunately, the Q of a system decreases rapidly as gain drops. The professional way
to avoid resonance effects is to keep about 3dB (30% lower) from the first sign of feedback.
The system will still be very loud, but it will sound a whole lot better. Ideally, the graphic
equalizer should be used to flatten the overall response, not to fix feedback.
Reverb
If you are using reverb, use short reverb sounds and modest amounts of reverb. Long rever-
beration effects cause the music to smear and can make things sound out of tune, especially
as the music goes through harmonic changes. Shorter reverb decay will enhance the sound
without spoiling definition. Don't forget that the room you are in may have lots of its own
reverberation, and that you can't hear that in the headphones.