It was not controlling sound source that was OP. It was controlling what you hear that is OP. You can naturally focus on a certain set of sounds, but that happens between ears and consciousness (i.e. in brain). The ears still take in the other sounds. Only by covering them up with something can you prevent them from taking in sound. As such, noises of high volume close by will be dangerous to anyone, especially someone who relies upon hearing to "see". 

You can't exactly focus on whispers at the other side of the room if someone is banging on a gong right beside you. Just as most can't focus well if someone keeps screaming in their ears.

if noises go above a certain intensity, it will be harmful to anyone nearby. Thankfully, that intensity isn't easy to reach. Especially not in medieval times.