plenty a rave dj in the 90s also used their headphones as a mic, too
I did my first sound system install back in the mid 70s.
I needed a system to make announcements on to get people to "come to the Red Star shooting gallery-shoot out the star and win $500 in store merchandise".
The budge was $50. Yes Fifty dollars. For the WHOLE system
So I got 2 12" whizzer cone speakers from Radio Shack and a roll of wire.
I Used the boxes the speakers came in as cabinets (lots of duct tape to hold them together).
The boss had an old stereo that was probably 10 watts/channel.
I took a 3" speaker from an old TV set as used it as a mic. Back then most stereos had a mic input.
It seemed funny holding a speaker in front of my mouth-but hey-it worked.
It worked "just fine"-at least as I remember--------------------