Vifa Peerless XT19NC30-04 Compact 19mm Ring Radiator Tweeter.
Horn loaded compact ring radiator diaphragm with central waveguide / phase plug. No ferrofluid - dynamic extended response to 30Khz with good linearity. This tweeter also features a high power NdFeB magnet and specially profiled 66mm diameter faceplate with recessed mounting holes for minimal reflection.
A full datasheet can be downloaded from the bottom of this page.