soft dome versus hard dome tweeters

A lot of what passes for common wisdom for hard vs. soft domes is like 20-40 years old. 

It's important to consider placement as well.  Speakers with hard domes that demonstrate on-axis ringing sound very good off, and are often recommended for minimum toe-in. 

I think rather than debate this endlessly audiophiles should consider a variety of examples, like for Be listen to Magico and Focal.  To my ears the tweeters sound very different and demonstrate how much the motor as well as the overall integration with the other components matter. 

Lastly, I've said this before, audiophiles are obsessed with tweeters.  I too have spent TOO much money on tweeters, when the reality is that so often we'd barely noticed if they just stopped working.  Point is, they just don't generate that much of the music we hear.  Better debates IMHO are what kind of mids you like, and how off-axis power response matters. 

My experience is that it has less to do with the tweeter material and more to do with the crossover.  Many say Be tweeters are harsh but my Rockports and anything but harsh.

For more than 33 years, I lived with a wonderful pair of Thiel 2.2 speakers with a metal-dome tweeter. The high end was revealing and detailed, with exceptional imaging due to careful crossover design and time/phase coherence. As long as I was careful with choice of amps and cables, I could keep my Thiels from wandering off into the world of hardness/harshness that seems to affect some metal-dome tweeters. From time to time, I'd listen to speakers with soft domes (e.g., Sonus Faber) to see if they might be an upgrade for my Thiels. Although some of these speakers sounded quite pleasant, they never seemed to sound good enough to be worth the expense compared to my Thiels.

Earlier this year, though, I decided to do a home trial of the Aspen FR10, a PS Audio product about the same size as my Thiels, to see if speakers with a planar-magnetic tweeter and midrange could sound better than the Thiels. In 2022, the legendary audio reviewer Anthony Cordesman (no longer with us, sadly) had reviewed the FR30 speaker, the larger sibling of the FR10 and stated that "the FR30’s midrange and high-frequency sound quality was the best I’ve heard from any speaker.” Since the smaller FR10 uses the same planar tweeter as the FR30 and a slightly smaller planar midrange of similar design, I thought that a planar tweeter (and midrange) might finally be able to dethrone my Thiels.  

Compared to the Thiels, the Aspen FR10 sounds clearer, faster, more open, and more transparent. The soundstage is also wider, deeper, and more realistic. What is most amazing is that these advances in sound quality are present along with increased smoothness and without any listening fatigue.

Based on my own listening experience (and apparently on the extensive experience of Tony Cordesman as well), neither soft-dome nor hard-dome tweeters can match the sound quality of planar-magnetic tweeters.  

I think at 1 point I had the persona 7f, revel salon 2, dsp8000se, Usherbe20dmd and kanta 3 on loan in my listening room at the same time and. I also had a couple other more affordable speakers in the house, I'm not a dealer but I was trying out speakers as fast as I could resell them and these all overlapped. I got the impression the days of harsh metal domes are behind us and a speakers personality was most identified by the mids and rise in the midbass as Eric already suggested,   

There are also solid diamond tweeters like from Acuton.