Tzniut is a term used within Judaism and it plays a role in Orthodox Judaism. It is used to describe both the character trait of modesty and humility, as well as a group of Jewish religious laws pertaining to conduct in general and especially between the sexes.
The singing voice of a woman is referred to as "ervah" in the Talmud, which literally means "naked," but is best understood as that which is not meant for public consumption.
The legend of the sirens in Greek mythology is possibly an example of the seductive nature with which a woman's voice.
But we live in a modern world and so these ideas of Orthodox behaviour that was fine in the ancient time is passé in today's context.