Sound takes time to arrive
Sound travels through air at about 343 metres per second, almost a million times slower than light. A member of the audience 170 metres from the stage would hear the singer about half a second after seeing them on the screen. That's why big festivals build delay towers with extra speakers that play just late enough for the sound from the stage and from the tower to reach the audience at the same time.
Speakers in a row and headphones in the ear
Rigged line array systems stack dozens of speakers on top of each other to create a narrow beam of sound. That lets it carry a long way without deafening the front rows. Instead of floor monitors, musicians now wear in-ear monitors, small custom-fitted headphones that let them hear their own mix. Wireless microphones and headphones need assigned frequencies so they don't interfere with each other.
The audience as a screen
On Coldplay's 2012 tour, every member of the audience got a Xyloband wristband with LEDs that lit up in time with the music on a radio signal. Similar PixMob wristbands are now controlled by infrared light from the stage, letting an entire stadium display patterns. Drones, meanwhile, are replacing fireworks with light images in the sky.
The Sphere and digital ABBA
In Las Vegas in 2023, the spherical Sphere arena opened, with an indoor LED screen at 16K resolution and a sound system with more than 160,000 speakers. In London, since 2022, ABBA Voyage concerts have featured digital versions of the band's members, created by motion-capturing the real musicians and using computer graphics.