What is Sound Art? And why?

Tom Service considers the rise of Sound Art, commonly found in art galleries today, and wonders whether it is a new genre or simply music in an art space? He consults musician and sound artist Mark Fell, finds precedents in Wagner's operas, considers how a 16th-century choral work became a contemporary art installation, and celebrates the American performance artist Laurie Anderson who accidentally had a pop hit with her piece O Superman.