i think this will depend on the location* and amount of people you want to address, and on what will be run through the PA. just your voice, or a whole band, maybe including drums?
* a backyard will need less wattage than a wide open field, for example.
I only use active speakers. This question needs more information. People power Passive PA speakers with amplifiers, but those amps need to provide the correct output to not destroy the speakers. I don't know enough about this nor think this forum would have the best answers. I recommend facebook or reddit groups. List out your equipment.
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* a backyard will need less wattage than a wide open field, for example.