First of all make sure you have the stage setup to make it as easy as possible to get every one hear what they need to.
1. It is often worth isolating each performer so the sounds from each do not excessively spill in to each other’s areas. For instance, if you have a loud lead guitarist, whos’ cabinets tend to be pretty directional, pointing his cabinet at his ear not at the lead vocalist can help a lot.
2. Try to avoid having the back line amps set to an expensive volume. Have the electric instrumentalists only set their amps up just loud enough to hear themselves, but not drown out the acoustic instruments.
3. As with the guitar amps make sure the monitor wedges are pointed at the ears of the performers they serve, so the level set in these can be kept to a minimum
Optimising gain before feedback using eq. and gain/master output controls
The set up of the graphic equaliser on the main and monitor systems is important. If there is a peak in the frequency response of the monitor, there will be a tendency for the monitor to feedback at this frequency, so flattening out their respond is important, if you want to use them over a natural band. The same is true of the main Pa’s frequency response.
When you come to channel eq set up; if there is a feed back problem on a group of channels, where you are having to apply the same corrective eq on lots of different channels, it tends to point toward a system frequency response problem, this is generally best corrected with the system eq controls. If however there is only a feed back problem on a single channel, it tends to point toward a source frequency response problem, which may either be related to its microphone or its source and is probably best resolved by the channel eq.
I will talk in more detail about the method of setting up the system and channel eq in a forthcoming post