What is complimentary EQ?
Complimentary EQ can be viewed as “corrective” eq. A complimentary EQ curve is one that is the inverse of what you measure (usually based on averages taken from multiple locations in a venue).
If your complimentary EQ is successful, you will end up with a PA system that is relatively flat in frequency response.
Unlike “channel EQ” where you might be making artistic decisions about how an instrument or voice might sound, complimentary EQ serves the purpose of solving an inherent unevenness in either a sub system of a PA system or the entire PA.
Complimentary EQ is not optional. It’s not something you leave at the shop because you may not need it. Instead it’s an inherent part of preparing a PA system installed in a specific space a specific way. If you need to change the direction of the PA, you should plan on revisiting your EQ settings and making whatever adjustments might be necessary.
Complimentary EQ might be achieve at the output of a digital console or via an external DSP device but one way or another you need parametric EQ to make the adjustments and a way to measure and reference your measurements as you make EQ decisions.