What is the status of a-capella music during the three weeks?
I've heard (but don't remember where) that the music that is prohibited during the three weeks is one or both of: music with instruments, recorded music. I've heard conflicting things about a capella music.
What is the status of a capella music? Does it matter if it is live or recorded? Does it matter if it is one singer or a group? Does the nature of the music itself matter (maybe it's ok to sing mournful songs but not joyous ones?)? Does it matter how many people are listening (maybe singing for a few friends, or a group practicing for a later performance, is different from giving a public concert)?