I have some cheap DAB radios with shitty amplifiers, which have clipping. Not sure if that’s the right term, but on volumes above the 4th level the quality goes to shit (depending on the accoustic frequency). At the same time, I need more volume because I’m running a fan as summer heats up.
So I put two shitty DAB radios in the same room on the same channel at levels just below the clipping. I knew this would happen: they decode at different speeds so the speakers are out of sync. The device that has an auxillary input is the one with the crappiest speaker.
FM does not have this issue. So if you go to a Critical Mass demonstration where hundreds of cyclists converge and ride together, sometimes they are organised enough that one person broadcasts tracks on an unused FM channel and everyone else with speakers can tune in to that station. That would not work well after DAB replaces FM, and FM radios become obsoleted.
Bluetooth is not exactly up to the task. The consumer grade BT gear is very short ranged. And I think most consumer grade BT devices are 1-to-1 pairing. Not sure if the 1-to-many long-range bluetooth transmitters are affordable.
You can get local FM transmitters. USB ones are quite common (i.e. for turning computer audio output into FM), and there are ones that can take input through a 3.5mm jack too.
So in theory you could take any cheap DAB radio, plug in an FM transmitter, and then have all your FM radios tuned into that.
Indeed I had some back in the pre-bluetooth days as a way to play MP3s to a car’s ill-equipped sound system. That would be a useful way around devices that have no AUX input. Good idea!
Though it wouldn’t solve the problem of a cycling party like that of Critical Mass.