Music is considered a universal language. It can invoke many emotions in people. It can inspire, it can move one to tears, and it can bring one to an ecstatic joy. In Jewish law, however, vocal music can have another result, and that is sexual arousal, at least, that is if you are a man listening to a woman sing. This concept is known as kol isha (קול אישה), literally meaning "[a] woman's voice." The premise behind קול אישה is that the woman's voice is an intimate part of herself, and extension, her sexuality. The view that a woman's voice is nakedness (קול אישה ערבה) is classified in the Talmud, which, if you haven't already guessed, is forbidden in traditional circles. What makes this prohibition intriguing is that it is not biblical in nature. In fact, we see enough instances in the Tanach in which women sing in front of men without divine admonition (Exodus 15:20-21, 1 Samuel, 18:6, 2 Samuel 19:36, Ezra 2:65). The blanket prohibition is based on later rulings that are based on a couple of discussions in the Talmud. We first see this view in tractate Berachot 24a where the sages (חז׳׳לֹ) are trying to discern what ערבה (nakedness) is.
In Berachot, R. Yitzchak starts off by saying that ערבה is an exposed handbreadth (טפח), which, as you can imagine, is not particularly that much. I am glad that חז׳׳לֹ rejected R. Yitzchak outright by saying this only refers to when one's wife says Shema (also see Raaviyah, Masechet Berachot, vo. 1, on. 77; Ritva in his Hidushim on Masechet Berachot). Some of the sages try to go further than that limited context. Shmuel says that a woman's singing voice is ערבה, and cites a verse from the Song of Songs (2:14) as a supposed prooftext. If you look at Rashi's commentary, the voice is the Jewish people crying out to G-d. Why? Because in Rashi's interpretation of the entirety of Song of Songs, it is an allegory of the love between G-d (the man) and the people Israel (the woman). Look at the Artscroll edition of Song of Songs, and I will tell you right now there is no recognition that the book can be translated literally, most likely because of the Orthodox taboo about sex in general. But if we're going to interpret the verse literally, even though the tradition has been to interpret it allegorically, we might as well throw in some context because what's the point of interpreting anything if we're going to strip the context from a verse and attempt to make blanket prohibitions? This is a poetic passage (emphasis on "poetic") of two individuals who deeply love one another. This is not an ephemeral fling, but rather a profound connection based on true love. This could explain why חז׳׳לֹ tries to limit the prohibition to something like one's wife (אישתו) saying Shema.
Even when looking at the other mentioning of in Kiddushin 70b, it is Shmuel (again!) who points out that this in the context of a married woman exchanging greetings with another man (commentary of R. Yitzhak Alfasi). Looking at the passage in its context, it is the adulterous intent of the relationship that is the issue, not the voice of the woman itself. Interestingly enough, HaMeiri's commentary (R. Saul Berman, p. 53), as well as Rav Hai Gaon, shows that if a man can "control himself," he is permitted to greet the woman. It could very well explain why a handshake in business transactions, which could be considered a violation of shomer negiah, is actually permissible. Also, since neither Berachot 24a nor Kiddushin 70b explicitly state that "it is forbidden," it is reasonable to assume, much like R. Yitzhak Alfasi did, that these passages were not to make halachic rulings, but were aggadic in nature (also see here).
For me, reality dictates how we view halacha, not vice versa. Taking a look at the first two tractates of the Talmud, this is indeed the case. In tractate Berachot, the blessings we make are based on the reality of the object or event being blessed, not our perceptions thereof. When looking at the nuanced rulings in tractate Shabbat, the permissible or prohibitive nature of a certain act changes when the reality of a given situation is altered ever so slightly. The same goes here when we ask ourselves "is the voice of a woman prima facie a form a sexual arousal?"
If a woman's voice were inherently arousing, women would have to be prohibited from speaking, which is ridiculous. It's probably why later rabbis confine the prohibition to singing only (Rama, commentary on Shulchan Aruch, O.C. 75:3; Beit Shmuel's commentary on S.A., O.C. 21:4). Even if there is something about women singing that is sexually arousing, why do we find exceptions in modern-day halacha? For one, if you're listening to the radio and a female vocalist comes on the air, most rabbis permit one to listen to the vocalist (Maharam Schick, Even Ha-Ezer, no. 53) because there are no visual stimuli (which is problematic for those who argue that the female voice is inherently arousing). There is also the question of whether women can sing זמירות (songs sung at the table during Shabbat and Yom Tov). The answer for this question is based on the Talmud (Megillah 21b), which states that "two voices cannot be heard simultaneously (also see R. Yeheil Weinberg, Seridei Eish, 1:121)." In Divrei Cheifitz, it is also explained that it is permissible in this case because women are not sexually appealing in this context.
The inconsistent application of preventing a woman's voice is all the more reason to question the prohibition. Let's ask a few more questions regarding the nature of the prohibition. Even if you want to argue that men tend to have a stronger sex drive as a basis for prohibiting a woman's voice only, women also have a sex drive and can also be attracted by a man's voice, so why is it that men aren't prohibited from singing? Even if we forget for a moment that not everyone is heterosexual, why can't we recognize that not everyone is sexually aroused by the same thing? Furthermore, why do we prohibit women from singing when there are situations in which women singing are not sexually arousing, but situations in which women talking can be sexually arousing? After all, flirtation is typically spoken, not sung. If we're that worried about women tempting men to commit sexual licentiousness, why not prohibit women from speaking? Much like with speaking, there are contexts in which singing is arousing and situations in which they are not.
The intention behind the prohibition of קול אישה was to prevent singing in a licentious and flirtatious context, which is a far cry from a blanket prohibition on women singing. Furthermore, the slippery slope argument that is used, i.e., singing will automatically lead to licentious sex, is tenuous, especially since a woman's singing voice is more commonly heard than it used to be. The problem with traditional, Jewish sexual mores is that they assume that all women are temptresses and all men have zero impulse control. All this premise does is gives us the false impression that we are merely sexual creatures, and that it is impossible to transcend sexual desires to have meaningful, spiritual relations with other human beings.
I am not stating that we should not have sexual mores or that the sexual mores of Western society are perfect (because they really aren't). What I am saying is that what should be done is apply the mores on a case-by-case basis, as well as a person-by-person basis, because different people will react differently in certain cases. Intent matters greatly. To quote Maimonides (Hilchot Issurei Biah 21:2), "and for one who looks at even the little finger of a woman to take pleasure in it is one who looks at her genitalia, and even to hear a voice of an ערבה or to see her hair is forbidden." Maimonides' prohibition is conditional upon sexual arousal, i.e., the prohibition only applies if it is for the intent of sexual stimulation or arousal (also see R. Saul Berman's teshuvah on the topic).
This leniency is not absolute because if the potential for licentiousness is present, the prohibition still applies. For example, if there is a concert with a blatantly lewd singer, that would be a clear case of "don't go to the concert." Since there is an applicability to both women and men, individuals should view it as a personal chumra based on what they know about their sexuality and sexual attractions (even the Ritv'a [p. 4], a 13th century rabbi, agreed on this matter) since no one knows that facet of their lives better than the given individual. Conversely, if the singing is innocent in nature, then there is no halachic issue because there is no worry of sexual sensuousness (e.g., women singing sacred songs; R. Weinberg, Sereidei Eish II, no. 8; S'dei Chemed, Klalim, Ma'arechet Ha-Kuf no. 42). Not only do I think this more nuanced, case-by-case take on modesty (צניעות) lines up better with the reality of the human condition, but I think it also creates a better sense of spirituality, particularly for women who would like to sing as an expression of spirituality. Rather than stifle women, I hope that those in the Orthodox community realize there is halachic basis to allow for a leniency, thereby giving Jewish women another avenue to better connect to G-d.