The 1960’s and the 1970’s saw the birth of the large concerts (stadiums and outdoor venues). Prior to this the largest shows were at theaters and honky tonks, and the sound was basic consisting of just microphones and amplifiers (mono tube amps).
When the Beatles and other popular bands started to play in large venues (ticket sales) it was found that the normal sound systems as we knew them were not good enough. When the Beatles played at New York the only people that could hear them were in the front rows (the Beatles couldn’t even hear themselves play).
Phil Spector hit the scene and became the top dog with his “wall of sound”. Then many others followed copying his massive use of multiple stacked speaker cabinets and amps.
Music was being controlled and polarized by the record labels and producers who had the equipment to do the large shows. By the end of the 1960’s an underground movement had been started by musicians wanting to have their own large sound systems. But this was a major financial burden to bands. So a new phenomenon emerged in places like San Francisco. Bands started to find people with skills in carpentry, electronics and sound to help them build equipment. As the new equipment was made bands started to set up their own large shows. The best example of this was the Grateful Dead.