12-680/62Hex-KEG (because the speaker dosn't have any marking we gave it a name by himself) it is a Kevlar Hexacone woofer, which was made by Eton (Germany) company by a special order for the loudspeaker manufacturer Kharma (Netherland) to be used in their top line loudspeakers at that time (around 2008 year) - Kharma Exquisite Grand (The Absolute Sound's review), those retail price tag was near $300000.
Eton had a woofer model 12-680/62Hex in serial production which Kharma woofer version was based on and had very close parameters, so in the "Technical data" section we indicated data from stock 12-680/62Hex model.
Today (2019) Kharma company is continuing produce that loudspeaker model, but now with upgraded low frequency speaker drivers - Omega with Carbon-Rohacell-Carbon cones.
It's always interesting to see what speakers are used in the world's top loudspeakers!
The THD measurements at distance of 315 mm and voltage levels from 2.83 Volt to 16 Volt were carried out with High Pass Filter "on" (2nd order Butterworth type, 50 Hz cutoff, HPF2-50).