How does the Bard’s Arcane Art work in your world?
I had a situation where an unconscious constable was bleeding out on the street and the bard wanted to heal him. We had a bit of a discussion about whether or not it would work because the constable could not experience the performance.
We ended up deciding that the performance was just a medium for the magic, and allowed it.
How does it work in your fiction?
The performance is the medium by which the Bard imposes his will on reality. Whether or not that means people must hear it depends on what it is he wants to affect;
To change the hearts and minds of others, they must be swayed by his performance. To evoke effects such as healing, whether or not they can hear it is irrelevant; the universe hears the bard.
In our game we treat it as if it could be heard, rather than if it is heard. So, if there is a magical effect (think “silence” type spell) or a strong roar of a storm from a storm dragon, then it doesn’t function at hearing range.
Otherwise the bard could simply heal someone for whom they are singing about (a king, who is an ally, in a far away land for example) and it could happen at an infinite range.
I once wanted to heal one of my allies by singing in front of Death at the Black Gates to heal my ally back at where they were still fighting the big scary monster. As it says “choose an ally” so we had to make a ruling on the range of it. Since later in the description it says, “reverberates” we went with sound as the medium for if it could reach a target.