I'm looking to learn about Air Motion Transformer technology

Any way you look at it, the transducer on amt is a ribbon that is folded. 

Most on here will most likely disagree with me about amt vs ribbon tweeters.  They do have separate patents, but that doesn't dismiss the FACT that they are different applications on a similar design.  
An AMT is a ribbon that has been folded.  This can change frequency, dispersion patterns etc,  but none the less dissect them both and you will find that a Air Motion Transformer is in fact a folded ribbon.
 Like a horn or dome or any design,  there are many variations and most sound different from one another.  To directly answer your question,  they are fast, typically fairly smooth, often, but not always have a rise on the top end.  Used properly,  AMT's are normally a very satisfying driver to listen to.  Like Ribbons,  you will find some excellent examples and some that can make your ears bleed.  So Not all are created equal,  good luck, Tim    

Ok the shape of material? AMT is folded. Impedance on  both are quite flat. Flow of current varies by the source of opposing force on both, we call these magnets. Radiation patterns are effected on both by mouth shape, horn load felting etc.  Don't let some cute answer fool you. Heil himself on occasion called his original AMT a ribbon dirivative. I own heil, and mundorf amts as well as fountek ribbons right now. 

Yes, regardless of the smart aleck,  it is a ribbon. 

No, I don't need to clutch at the shape of an impedance curve. I clutch at the fact to make an amt, you take ribbon basic design and fold it. I've not argued differences. And once again you turn smart aleck.