Place all of the sliders on the graphic equalizer at the 0.0 mark. The location of this mark may vary based on your graphic equalizer model. The 0.0 mark is usually found at the middle of the slider range. Any slider at 0.0 indicates that the signal is not being boosted or cut.
Slide the frequency band slider up to boost the signal of the associated frequency band. Boosting a signal increases the proportion of any sound in that frequency range in relation to the rest of the mix. For example, boosting the lower frequency sliders would increase the volume of a bass in relation to higher pitched instruments, like a violin or flute.
Slide the frequency band slider down to cut the signal of the associated frequencies. Cutting a signal decreases the proportions of sound in the frequency range compared to the rest of the mix. Cutting the lower frequency sliders, for example, would decrease the volume of a bass in relation to a violin in the same mix.
Turn up the volume of the pro audio system until you hear feedback through the speakers. Feedback is usually heard as higher pitched squealing noises.
Adjust each individual slider until you find one that alters the tone of the feedback.
Slide the frequency slider that affects the feedback down until the feedback noise disappears.
Repeat Steps 1 to 3 until the graphic equalizer is at performance volume with no feedback.