Sound of metal-on-metal scratching and significant resistance when I push on it.
Voice coil?
Yes, you have burnt out the voice coil most likely. However they have a pretty soft suspension, so you might have caused the VC to leave the gap and then become deformed on return by catching on the pole piece.
That was a pretty low powered driver and would be easy to blow with most modern equipment
The thing that was unusual about it, was the lack of a hard break up and then a smooth roll off at about 6 KHz.
Now those speakers claimed to be phase coherent. If that is correct, then they would have first order crossovers. With those drivers you could just about get away with it.
They have a petty high F3 as you would expect form a fairly high efficiency driver. Qts was on the high side, so I suppose the high F3 was made up for with a little excess warmth.
Really that driver would have been much better employed as a dedicated mid range driver. I'm not surprised you have burnt one out.
Sorry, but those speakers have got to the end of the road.