May a man listen to the recording of a woman singing, such as on an MP3 or radio?
Some Poskim rule it is permitted to hear a woman sing through a radio or recording if he does not know what she looks like. Other Poskim rule it is permitted even if he knows what she looks like. Other Poskim rule it is forbidden to do so. Practically, so is the final ruling. According to all, listening to a woman sing will not bring one towards fear of Heaven, and there is hence no place in the life of a Chassid to ask a Rav for a Heter in this matter. Accordingly, listening to a woman sing even through a tape or radio is to be completely negated irrelevant of the technical Halachic discussion.
Must a man leave or not enter an area in which a woman is singing?
One is not required to leave, or not enter an area that contains a woman singing. One may thus enter a bus or taxi or store even though the radio is on with a woman singing. He is however required to remove his mind from the voice and pay no attention to it. If one sees that despite his efforts it is leading him to immoral thoughts, he is to leave the area.
 See Sichas Parshas Balak 7th Tamuz 1984; Ohel Yaakov p. 205; Nitei Gavriel Yichud 54/11
 Beis Shearim 33; One way of learning Maharam Shick E.H. 53
 The reason: As one is allowed to hear a woman’s voice if he does not know her identity, as the Yetzer Hara only has a lust towards that which he sees. [Beis Shearim 33; One way of learning Maharam Shick E.H. 53]
 Tzitz Eliezer 5/2; Yabia Omer 1/6; Rav Elyashiv, brought in Ohel Yaakov ibid
 The reason: As a radio sound and recording is not her real voice but a mechanical voice. [Poskim ibid]
 Peri Hasadeh 3/32; Ohel Moshe 1/32; Birchas Chaim 21; Birchas Shamayim 30; Poskim in Otzer Haposkim 21; Yaskil Avdi 5/12; Chelkas Yaakov 1/30 and 163; Minchas Yitzchak 7/70; Shevet Halevi 3/181; 5/197-3; Az Nidbaru 9/59; Rav SZ”A in Halichos Shlomo 20/12
 The reason: As one is not allowed to hear a woman’s voice even if he does not know her identity, as the rule that the Yetzer Hara only has a lust towards that which he sees was said only regarding future erotic thoughts, however at the time of the hearing of the sound, it certainly has erotic thoughts. Likewise, although the recorded sound is not the true voice, since it is similar and can bring to erotic thoughts there is therefore no reason to differentiate. [Poskim ibid]
 Nitei Gavriel Yichud 54/11 in name of Poskim ibid
 Rebbe ibid
 See Sdei Chemed Kelalim Mareches Kuf 42; Ohel Yaakov 76 [p. 203] in name of Poskim; See Admur 75/6 based on previous Poskim “Even by the singing voice of a woman, if one is able to concentrate on his prayer to the point that he does not even consciously hear or pay attention to her voice, then it is permitted [to learn and Daven while hearing it].” And certainly it is permitted tp be in the area.