[header] How to tune a pa system [title] Set up your pa system, and make sure it is working. [step] Including your graphic equalizer (s). Make sure that the inputs of your eq are connected to the left/right outputs of your mixing desk and the outputs of the equalizer are connected to your main left/right power amps. 
[title] Make sure that both the graphic eq and the eq on the mixing board are set' flat'. [step] That is neither boosting or attenuating any frequencies.