120 Years of Electronic Music is a very good history of electronic music and sonic art for the past two centuries. That’s Karlheinz Stockhausen at the WDR studios in the 1970s (wearing a robe?).
It’s also worth noting that the site was started in 1996; thus showing the perils of using relative timespans when naming things. The authors admit those 120 years are now closer to 140, plus another century of electronic music pre-history. Yes, the Web is now old enough for such embarrasments.