Vifa / Peerless XT25SC90-04, Compact 25mm Ring Radiator Tweeter, 4Ω.
Patented ring radiator diaphragm and central waveguide / phase plug give a dynamic extended response to 30Khz with good dispersion. This tweeter also features a tuned rear chamber giving a low Fs. Very compact body with a profiled 65mm diameter faceplate. Recessed mounting holes for minimal reflection.
A full datasheet can be downloaded from the bottom of this page.