We were discussing gong type telephone bells on FB group Bell Telephone…
Back maybe ten years ago I snagged an AT&T bell out of a bldg before the bldg was remodeled. It was a bell without an enclosure, the two bells were exposed, with the clapper between them. It connected directly to the incoming line from the CO, no power was needed. It hadn’t been in use for more than a decade, since when we converted to the digital PBXes.
These were a bigger version of the same ringers that were used in a regular AT&T phone, except the two bells were larger. Maybe louder, too. They worked great for larger open spaces inside bldgs.