The general consensus of most contemporary Halachic authorities is that like live music, listening to recorded music is prohibited during the Three Weeks mourning period. (Click here for more mourning practices observed during this time.)

Recorded a cappella music is the subject of debate between Halachic authorities. Rabbi Moshe Feinstein (1895-1986, foremost Halachic authority of the last generation), rules that it is permissible to listen to such music during the Three Weeks, while others disagree. You would be well-advised to consult with your local rabbi regarding this matter.

Best wishes,

Rabbi Baruch S. Davidson