The D27TG-05-06 is a conventional 1″ fabric dome tweeter with ferro fluid (pictured below on the left). Resonance is a respectable 1 kHz with a Qts of 0.77, sensitivity is advertised at 92 dB. Testing is done at -5 dBW (should have done at -2 or -3 dBW).
The frequency response is quite smooth, with a few dB of gradual roll-off on the top end.
What is even more impressive is the distortion performance – this unit is 6 years old, been sitting around in a box! Distortion is at -50 dB from the fundamental through most of the band above 2 kHz. The third harmonic only rears its head at 4-5 kHz. This tweeter could easily cross over at 2 kHz at 2nd order, and maybe 1.8 kHz at 4th order if you wanted to push it. That explains why this tweeter has had such a long life and is still available.