He CAN be pretty vocal. I don't know how to explain him. Because out in public, he's not. We can walk by tons of barking dogs, or a dog could be lunging/barking at him, and he will never bark back, etc.
But he is most definitely an alert barker. Oh myyy, when the doorbell rings or knocks, or someone walks in, he's got this high pitched super annoying charging type bark. It will only last for like 10 seconds until he realizes who the person is walking in the door. If it's a stranger, he will bark longer until I tell him to be quiet.
He also can be quite the excited barker. During rough play, he barks a lot. But he doesn't really play with dogs much anymore, as far as wrestling goes, but yeah when he does he can be very loud and obnoxious. Certain things trigger excitement in him - when anyone jumps on the diving board, it gets him amped up, and he barks until they're in the water. When the four wheelers drive by the fence, he barks as he runs and chases them.
But he's not a 'yapper'. My friends yorkies will just start freaking out over everything - a little sound outside, people walking by our car if we're parked, etc.