Curved Air were briefly a sensation in the world of British progressive-rock because of Sonja Kristina's sensual vocals and Darryl Way's romantic violin. Kristina was a veteran of the London musical Hair in the late 60s. This was the same combination tested in California by It's a Beautiful Day. Francis Monkman (the real genius behind their compositions) added a synthesiser. Air Conditioning (1970) contains "Vivaldi", their most celebrated piece. Second Album (1971) delivered their only hit, "Back Street Luv", and the twelve-minute "Piece of Mind".