San Francisco-based a cappella group The Clef Divers performed at the library on September 21, 2011. Â They treated over 75 people to 30 minutes of music, then taught an "A Cappella 101" class where we learned and practiced how to breathe, the basics of vocal percussion, and how a song on the radio can be arranged for voices only. Â Thanks to the Friends of the Sunnyvale Library for generously sponsoring this event. More information on the Clef Divers website.