Now that I think of it wouldn’t it have made more sense for the sirens to feed off of love since their songs are suppose to be alluring and they’re constantly talking about how they want people to love them and to be adored. Feasting off of hatred seems counterproductive.
So they never needed to sing to charge up their gems. All they had to do was find the busiest spots, plant their gems nearby and let rush hour do its work.
Edited
“No, Aria, I didn’t mean—”
“I’ve wanted to do this for centuries.”