The female voice, according to Islam, is also included in the category of Satar, i.e. it has to be ‘concealed’ and NOT ‘revealed’. Since the female voice is an entity NOT to be displayed or advertised, it is NOT permissible for males to listen to women singing or even reciting the Quran …

When necessity demands that they have to speak to males then their speech should not be attractive, gently and alluring like the deliberate ‘lure’ put in speech by ‘trained’ women of the disbelievers. Recognizing the danger of allurement in the female voice, the Quran commands women thus:

"…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." (Al-Ahzab 33:32)

Islam has, hence, FORBIDDEN its women to speak in a soft or "sexually" sweet tone. Islam COMMANDS the concealment of the female voice and prohibits its display in public.  If anyone is aware of the springs of sex-psychology he will clearly see the justification for Islam’s restriction in this matter.

Women's Voice -

"O wives of the Prophet! You are not like any other women. If you keep your duty (to Allaah), 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 honourable manner." (Al-Ahzab 33:32)

What is forbidden is being too soft in speech. It is obligatory for women to speak in an honourable manner, which means, as the mufassireen (scholars of interpreting the Holy Quran) explained, that they should not make their voices soft when addressing men.