The Grand Ayatollah Sistani answered a question about the level a non-Mahram man can hear a woman’s voice.
Question: To what level a non-Maharam man is allowed to hear a woman’s voice?
The Grand Ayatollah Sistani: There is no problem in hearing a non-Mahram woman’s voice if it is not out of enjoyment or fear of falling into Haram.
source : Shafaqna