May girls/women sing in private if their voices can be heard to the outside?
- At an event, such as a Farbrengen, is it permitted for women to sing even though their voices can be heard to the outside?
As stated above, it is forbidden for men to listen to a women’s voice of singing even if there are many women singing simultaneously, and even if he does not see the woman. It is therefore proper for women and girls to avoid singing in areas that men can hear their voices. This applies even towards girls in school and the like, when singing for spiritual purposes. However, some Poskim rule that one cannot protest those girls who gather in private to sing as part of their spiritual education, such as the singing of Niggunim or Davening. In such a case, the men are obligated to remove their minds from the women’s voices.
 Beir Sheva p. 119, brought in Kaf Hachaim 75/23; Elya Raba 75/5; Shaar Hatziyon 560/25; Shevet Halevi 5/197-4; Halichos Bas Yisrael 6/6; Piskeiy Teshuvos 75/12; see Beis Avi 3/32
 Shevet Halevi ibid
 Beis Avi 3/32; Ishei Yisrael 55/29 in name of Rav Elyashiv, brought in Piskeiy Teshuvos 75 footnote 125; Halichos Bas Yisarel ibid footnote 12 brings in name of Rav SZâ€A that girls may be lenient to sing on a bus with separate compartments if the male bus driver cannot see them.
 The reason: As perhaps singing out of service of G-d does not bring immoral thoughts, as was seen with Miriam and the women who sang Shiras Hayam. [Beis Avi ibid]
 Ishei Yisarel ibid