The bow was the first lyre, no?
So when you brace a bow, you can hear the tune of the string before drawing the bow.
Typically, after a few shots or draws, you hear the tune has dropped a bit, representing a reduction in tension on the string because the wood is not pushing back as much anymore. In other words, set. Even bows which hardly show set get tuned down a bit, typically a half to a full note.
Just out of curiosity, does anyone listen to the bow to measure set?