I experimented a little more. About 6 am several weeks back there were 3 women jogging ahead of me, otherwise the mup was deserted. Rang the bell several times and no sign that they hear me approaching. Called out "passing on your left" and they gave me some clearance to ride past. This time I stopped and asked them if they heard the bell, or if they reacted to my voice. They told me they didn't even notice the bell, but that I didn't call out my passing to them early enough.

A few days later, I was on some rails to trails (Mineral Wells, for those familiar with the area) and tried the bell a few times there, since Doohickie suggested that the busy location where I was using it was the issue. I think I had one time when the bell got the pedestrian's attention, the rest of the time it was ignored or not heard.

I'll keep a bell on my utility bike, but I'm going to count on my voice to notify pedestrians that I am passing.