This is an original Fillmore East program from 1971, from my personal collection.
There's a reason this is special to me...
...it was the first time I'd seen Frank Zappa. Portions of that June 5, 1971 concert appeared on the Mothers of Invention's Fillmore East – June 1971 album. I attended the show with my friend and former Stereophile writer Bob Reina. We completely flipped out.
One of the best explanations of stereophonic sound I've ever seen, courtesy of this circa late-1950s/early-1960s Audio Fidelity brochure. Scanned at high-res to make it as readable as possible.
Here's a thank you note that Harry Pearson, founder of The Absolute Sound, sent to attendees after his fifth Friendship Party, which was in 1984 or maybe 1985. I didn't remember I'd saved this until I found a box of stuff in my attic a couple of weeks ago.
And we thought wireless mics were a new idea! Electronics Illustrated, March 1961. Courtesy of Wikimedia Commons/public domain.