If you don't mind an old man with lots of time fleshing out the story of why I liked ribbon and air motion transformer speakers, here goes..
So there I was, 16 years old and in addition to listening to music on the radio, as well as from jukeboxes at the off-campus school supply and lunch stores, I had stumbled upon the world of excellent acoustic music in the form of classical and jazz. And that first HiFi system I owned with its big three-way bass reflex speaker design and Jensen drivers played the music on my LP's with a sense of "ease" that I have always loved, and tried to reproduce over the years. However, it had a horn midrange, the "honkiness" of midrange horns eventually came to bother me as not natural, especially for acoustic and solo vocal music.
In the mid 1970's I bought a pair of big custom JBL speakers with the S8 3-way drivers (LE-15A woofer, 375 horn midrange, 075 ring-radiator tweeter) driven by a McIntosh 1900 receiver (55 "real" WPC). The system fantastic for rock, but the midrange "honkiness" again came to bother me with classical, jazz and folk/vocal music. Financial failure in my first attempt to become a salesman (solar heating) led me to downsize, sell the speakers to a friend. I bought a much smaller pair of Design Acoustics D6 speakers when I moved from San Francisco to the Los Angeles area for my first real sales job in aerospace.
The third attempt with horn midrange (and this time, horn tweeters) - came over 20 years later when I bought a used pair of 99dB sensitive Klipsch Forte II's. I used a Mick Maloney (Australia) custom Supratek 6SN7 preamp and an Attilio Caccamo (Italy) Tektron 2A3 single-ended amp. I really liked that system, but in 2005, I lost my retirement investments in the stock market, also the shared rental of the house with the big living room, so I sold everything when I moved to a smallish apartment in town.
About those Heil AMT's and Apogee ribbons...I was taken in by the magazine hype and an audition at a local Bay Area dealer in the early 1970's, and bought a pair of the original ESS Heil AMT1's. They were good, with the "ease" and clear treble without exaggerated sibilance that I liked great for jazz, folk and classical in the sweet spot. But the AMT1's had two weaknesses - HF beaming and poor bass for loud rock. I "upgraded" to the bigger ESS AMT1-T towers with the transmission line cabinet, and liked them much better. After a divorce, my ex-wife kept them and enjoyed them for many more years. But they did have a limited sweet spot for the treble.
I bought the Apogee Centaurus ribbon monitors used in about 1997 or 98, and didn't sell them until I moved to Panama in 2012. I used them in my office system for the 1+ years when I had the Forte II's in the living room. I used a Bryston B60 to drive them, and my sources were a Yamaha TX-950 tuner and a Denon DVD-1800BD for playing CD's player. That was one of my favorite systems of all, and the limited vertical dispersion of the 4" ribbons no longer bothered me.
The last of the original five patents on the "air motion transformers" expired 9 years ago, and a number of companies around the world have developed their own variants of the technology. According to Wikipedia:
