This was removed from a Sony SS-U211 3-Way speaker. It fits other models but I am unsure of which. Some people list this is a tweeter.  I am assuming on some models this driver is used as a tweeter but in the SS-U211 it was used as a mid-range. The diameter is 4" across (end to end).  Tested inside of the speaker and tested with a meter outside. Measure at or above 9 ohms.