"Breakup distortion" is exactly the point here. Soft dome tweeters are great and forgiving, but they are not quite as clean and transparent as hard dome tweeters. The problem with hard dome / metal dome is the breakup distortion (the point where the material flexes and distorts from the movement). The breakup point of normal metal domes can range anywhere from 19 khz to 28 khz (on some of the best / treated / coated tweeters). However, they will still have a bit of a bright edge.
Alternative materials have shown a much higher breakup frequency because the material is stiffer. I think beryllium is somewhere around 45 khz or something. Diamond is upwards around 75-80 khz. I think ceramic is higher in these areas as well, but ceramic also presents a more controlled sound that is usually not as dynamic.
In a recent speaker project, I went from a Seas Excel softdome ($322) to a Seas Excel Berillyum ($770). The change was night and day. The Beryllium was much cleaner and much more realistic with a higher resolution. No harshness at all!
Alternative materials have shown a much higher breakup frequency because the material is stiffer. I think beryllium is somewhere around 45 khz or something. Diamond is upwards around 75-80 khz. I think ceramic is higher in these areas as well, but ceramic also presents a more controlled sound that is usually not as dynamic.
In a recent speaker project, I went from a Seas Excel softdome ($322) to a Seas Excel Berillyum ($770). The change was night and day. The Beryllium was much cleaner and much more realistic with a higher resolution. No harshness at all!