My voice doesn't carry so I do use a bell. That being said, on the one MUP that is very congested I don't typically announce or all you would hear for that mile is a bunch of random bells and shouts of "On your Left". Most people in that section just pass when safe and go about their way, especially since it is a wider MUP. If I am on the more empty parts of that MUP then I ring depending on the situation but normally I can swing out wide and not come near the person I'm passing. There are some other not highly used trails that aren't quite as wide and on those I always announce since the passing zones aren't that wide so I'm closer to the walker/runner when I am passing.