Q: In live sound reinforcement, what are sidefill monitors used for?
A: This is an area that’s still widely debated by live sound engineers, but here’s our take: It is sometimes thought that sidefill monitors should be used to duplicate the FOH (Front of House) mix. This actually contributes to more bleed into open mics and results in the band playing even louder. Also, cranking the sidefills can ruin the FOH mix by virtue of phase cancellation and general muddiness created by too much sound pressure on stage. From our perspective, the proper usage of sidefills is to create what is called a cross-stage monitor system or X-stage mix.
True X-stage mixes separate the stage in half. Everything from the center of the stage to the right is mixed into the left X-stage system, and everything from center stage to the left is mixed into the right X-Stage system. This results in a more intimate sound field on the stage, similar to playing on much smaller stages. If a guitar player and bass player are standing next to each other, they can hear each other’s backline amplifier and don’t need more of these instruments blaring at them from a sidefill. However they may not hear the piano player on the opposite side of the stage. The piano player can hear his/her amp, but may need to hear the bass player and guitar. The cross-stage mix solves this problem. Usually some drums and lead vocals are mixed equally into both X-stage mixes.