Vifa / Peerless BC25SC08-04 4Ω soft dome tweeter, high output.
This high efficiency tweeter features a 4 ohm 25 mm voice coil, high energy NdFeB Neodymium magnet assembly, a damped textile dome and ferrofluid in the magnetic gap for enhanced cooling of the voice coil - further cooling is achieved via a heatsink bonded to the magnet. The BC25SC08-04 has a compact horn loaded faceplate (70mm diameter) with recessed mounting holes, and comes complete with a foam sealing gasket to reduce vibration. The upper frequency range extension is very good with a commendable off-axis response.
A full datasheet can be downloaded from the bottom of this page.