Answer: acapella

AnswerCrossword Clue
ACAPELLAWithout instrumental accompaniment (var.)
ACAPELLAWithout instrumentation
ACAPELLAWithout any musical accompaniment (var.)
ACAPELLALike many doo-wop sessions (var.)
ACAPELLALike some choirs: Var.
ACAPELLALike many doo-wop groups: Var.
ACAPELLALike many "Glee" numbers: Var.