I'm looking to learn about Air Motion Transformer technology

I have a DIY pair of 2-ways and used the "Great" Heil AMT (the big AMTs, almost certainly from an old pair of ESS speakers) along with Altec 416s. After a couple of years I switched to the Beyma TPL150 AMTs. The Heils are bipoles with an open back, and sound a bit more airy than the Beymas. The Beymas are closed back and have a bit more meat, more bite on sax and horns and such. I prefer the Beymas but could easily live with the Heils which I keep for backup.

I think AMTs sound great, but of course I’ve heard many other tweeters that sound fantastic as well. The advantage for me is that the AMTs can go down to where the Altecs drop off (1K-ish), so a pretty good combination in a 2-way.

As many are aware, ELAC purchased Oscar Heils' AMT tweeter patent
in 1993, and took it much further with design upgrades that has resulted
IMO the finest tweeter on the planet. Their current jet 5 tweeter is killer.
During the past six months, while recovering from a massive heart attack,
I spent well over a hundred hours listening to HD videos on Youtube of 
the best high end speakers using my Koss Pro headphones on my HP computer with the Altec Lansing processor. I came to the conclusion
after listening to the ELAC FS series with the jet 5 tweeter, that it is the smoothest, richest tweeter I have ever heard during the past thirty years.
I test a tweeter with three musical instruments only, the violin, the piano, and the trumpet. Especially the violin where the jet 5 really shines resulting in the richest, smoothest and most natural tonal character I have ever heard to date through a tweeter and true music lover's of Classical and Jazz who own ELAC's with the AMT jet 5 know exactly what I'm talking about and would agree with my conclusion.

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    

An AMT is not a ribbon.

In a ribbon the moving part is entirely conductive, and very low impedance so much that they usually require a matching transformer.

In an AMT the conductor is longer, much thinner and attached to a moving membrane which provides the actual moving surface area.  As a result the impedance is much more reasonable.

Further, AMT's have amazing power handling and linearity and lower distortion than most ribbons which tend to be delicate diva's by comparison.

Buy what you'd like!! :)

Best,

Erik