> In super busy old European capitals I find that people increasingly just ride around with speakers playing a constant tune at a reasonable volume, a massive improvement on dense streets full of varyingly sober people.

I sometimes do that. It helps not having music that could be described as aggressive. I often use reggae.

However it means you need a speaker charged so it is not something I have ready everytime I use my bicycle, nor do I want to carry it everyday when leaving the bike attached somewhere so it can't be the goto solution.