Live Sound Engineering
It was the Grateful Dead who introduced the positioning of the live sound engineering mixing desk in the audience in around 1966. Beforehand the desk was meant to be out of sight. No one had considered that the engineer needed to hear the music from the front of the stage in order to get a good balance.
In case you haven’t heard the Grateful Dead here’s a video of them doing a live performance instrumental called Dark Star from their ‘Sunshine Daydream’ unreleased video way back in 1972. It’s a great ‘chill out’ track for the time.