Not Enough Gain Before Feedback?

[Mike]

Try these solutions;

Move microphones closer to sources
Move loudspeakers farther from microphones
Move loudspeakers closer to listeners
Reduce the number of open microphones
Use directional microphones and loudspeakers
Eliminate acoustic reflections near microphones
Reduce room reverberation by acoustic treatment
Use equalizers to reduce system gain at feedback frequencies

Source: ProSoundweb.com

[Russell]

This one can be tough.

In my experience, it helps to know the mics you are using.
Then you need to get creative about mic placement.
Next you need to identify the problem frequency band.
Most importantly know were the feedback problem is being created; from the monitors or FOH.
FOH is usually mic placement too near the FOH speakers. In other words the mics polar pattern is reaching the FOH speakers causing feedback.
MONITORS are a result of monitor output level set too high or gain on mic too high bleeding over into monitors. This can be resolved by inserting a graph and lowering the troublesome frequency(or frequencies). If no graph available you will have to use the Mixing consoles mic-channel EQ; this is where you will need to be creative, especially if you have limited EQ, and you do not want to EQ so heavily that it changes the sound of that which is being EQ'd.

Last word, good luck & have fun!

[Claudius]

Good advice!