Kirk McElhearn’s piece on the origins of noise canceling headphones would be worth the read just for that background, but my favorite part is this bit:

A great example of effective noise cancellation is the Grateful Dead’s Wall of Sound. Back in 1974, sound man and chemist extraordinaire Owsley Stanley came up with a setup for the band that was distortion-free, and also served as monitors, so the band could hear themselves play without having blowback monitors on the stage in front of them.

If you are interested in some music history, take a few minutes to read about Owsley Stanley, the Grateful Dead’s Wall of Sound and, on a related topic, the origins of a more well known Wall of Sound. Owsley was a chemist, in the drug sense of the word, cooking LSD for the Dead and others. But he was truly a gifted sound engineer and is famous for the high quality of his live recordings (no pun intended).

The original Wall of Sound was an important recording technique developed by the infamous Phil Spector that influenced a generation of sound engineers and an incredible number of famous recordings.