[inigyou]

Sometimes, but not too often, in Berlin of all places you encounter someone biking around with a massive speaker attached to their bike blaring (obviously) techno

Not always a bike. Sometimes just a trolley or a handcart or a custom jerry-rigged contraption.

[bluGill]

In the US "boom boxes" went out with the 1970s. They need to get with the times.

Okay, in all seriousness: boom boxes were a thing in the 1970s and early 1980s. There are still people who use the latest generation of them, but thankfully not nearly as many. These days people cranking music in a public place are generally doing it as part of a group that all want to hear the same thing. (and in back then the group wanting to hear the same music was the common case)

[maxerickson]

Here, in a small US town, the most frequent public music is one or two people ~destroying the speaker on their phone.

Second is probably motorcycles blasting it over the engine noise.

[inigyou]

Oh I've never seen a boom box around. It's always, like, a box of car batteries and a speaker on top. Clearly DIY.

[setsewerd]

You see this type of thing daily in Brooklyn NY still, but instead of techno it's any genre, primarily hip hop, reggaeton, or afrobeats.