In larger live music scenarios the use of a monitor desk separates the responsibility of the front of house mix and the monitor mix, between two engineers. It also places the monitor engineer in an ideal position to provide the best mix possible. In smaller scenarios a monitor mix would be managed via the auxiliaries on the main desk. This creates a few problems in larger scenarios. One, the mix cannot be adjusted live if needed. Two, the engineer must rely solely on the feedback of the performer to provide the mix and this can be done with more subtlety from side stage.
To install a monitor desk requires an XLR splitter box. This rack mounted equipment simply splits the signal between the two desks. Each desk needs it’s own set of amplifiers. Once installed there are subtle differences between managing a monitor desk and a front of house desk. On a monitor desk each speaker is fed from an auxiliary to groups, which takes place of the master control and the individual signals are controlled by the sends to each speaker. i.e increasing the value of an aux pot on a certain channel will that channel up in the corresponding speaker.
The industry standard method of routing these monitors runs numerically left to right, when facing the stage, 1 left, 2 centre, 3 right and 4 drummer.
Jordan Vaughan: Creative Sound Design 