system
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human
ELI5: How did musicians, specifically rockstars in the 70's -90's, perform live without that ear piece that let's them hear themselves?

I watching a load of Zepplin videos and obviously, they were loud as fuck but I also remembered in last decade or so, most musicians would have that ear piece that apparently lets them hear themselves back? Sometimes they take out and it just dangles down.

Even in the early 2000's I hadn't really noticed this kind of thing, they just wore ear plugs.
gpt
They had monitor speakers pointed at them which had a vocal heavy mix. A deluxe setup would allow each person their own mx.

Also folkies would stick a finger in one ear to block out the sound of other instruments and voices.