Is a woman's voice part of her Awrah?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The voice of the woman is not an ‘Awrah. The evidence for this is the following verse. Allah Says (what means): {… And when you ask (his wives) for anything you want, ask them from behind a screen, ….} [Quran 33:53]

So, it is not forbidden for the woman to speak to men, but it is forbidden for her to be soft and lenient in speech.
Allah Says (what means): {… then be not soft in speech, lest he in whose heart is a disease (of hypocrisy, or evil desire for adultery, etc.) should be moved with desire, but speak in an honorable manner.} [Quran 33:32]

But if the listener finds some pleasure in listening to a woman's voice, then he should avoid listening to her; otherwise it is not forbidden.

For more benefit that a woman's voice is not an 'Awrah, please refer to Fataawa 263791 and 83899.

Allah knows best.