I use the bell mostly to warn pedestrians that I am coming up behind them on the MUP, not to warn drivers who are not paying attention. I yell or stop the bike until I make eye contact with the driver for that. It doesn't need to be super loud for my purpose. When I am running on the MUP and don't have a bell, I just cough and that is usually enough to let a walker know that I am behind them so I don't startle them. I can't remember an instance that I came across someone blocking the whole trail who couldn't hear my bell because they were listening to music. Usually, if they are blocking the trail it is because there is more than one person and they are talking to each other.