Air traffic controllers wear a small in the ear style headphone, and only in one ear. It was far easier to wear ATC headset than headphones all day. Plus I usually took a 30 min break every two hours so I didn't need to wear it all day.
The guys in the tower are ATC, they do ground control (still ATC) and local control, surface to 2500' with a 5-mile radius. The dark room guys (TRACON) do surface to the top of their airspace (depends, 18k, 23k) with a 60-mile radius (roughly). Then there is center/en route, which does air traffic above the TRACON when you are level flying at 30k+.
Simplified version.
Source: Was an air traffic controller.