Click image to view full size image
The C31 is a surface mount ceiling speaker designed to deliver high-quality sound in a variety of commercial and public spaces. With a 6-inch driver unit and an integrated 70V/100V transformer.The 70V/100V transmission operates in a high-voltage, low-current mode, enabling longer-distance transmission and the parallel connection of multiple loudspeakers.
link:https://www.loudspeakerchina.com/ceiling-speakers/surface-mount-ceiling-speakers.html
Surface Mount Ceiling Speakers