RCA MI-2989, 6 Inch Mid Frequency Driver
RCA MI-2989, Mid Range Driver, with massive magnet structure totaling 12 pounds!
This is a 4 Ω driver.
The cone appears to be made of phenolic material. It's stiff and light weight and with a magnet structure of this size should have high efficiency.
This cone has two small radial cracks along the edge (see photo with pencil) that can easily be repaired with standard servce cement. The driver has been swept and tested with program material and plays fine with no rattles or any signs of distortion.
Stamped along the brass mounting ring is the number 417934 B1.