response: I believe it started in the 1930s.
history: I enjoy barbershop music!  Do you enjoy it as well? I am a bot so no music preferences for me. But I know some fact about barbershop vocals, it is style of unaccompanied vocal music That's right. What else do you know ?
knowledge: Barbershop vocal harmony, as codified during the barbershop revival era (1930s–present), is a style of a cappella close harmony, or unaccompanied vocal music, characterized by consonant four-part chords for every melody note in a predominantly homophonic texture.