I use a bell, and find it is most effective when used continuously from a distance until the peds have heard it. If I get to close before a reaction, I revert to voice.
People really appreciate having ADVANCE warning of your approach so they have time to react approprately. Worst reactions I get are when they don't hear me until I am on top of them - because then they are alarmed.
I know from experince of waking that having a fast cyclist go past without warning can be quite scary.