It has a 12", treated paper driver. I shellacked the inside surface of the driver and filled the box loosely with polyfill taking care not to stuff around the port. These changes were actually sanctioned by the designer of the sub who was contracting to Sony. He claimed that by doing this, the sub would sound tighter and it sure did! I got a lot of musical subbage for $160 from London Drugs \:\) .

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated