Advantages of beryllium?

@mmeysarosh

The KEF R700 does measure well but the tweeter still has some hash and is not nearly as clean as the Seas Excel Millenium tweeter - see the outstanding lack of resonances (much better than any metal dome) in the waterfall plot for this speaker with the Seas Sonotex dome in their Excel Millenium tweeter (around 200 euros each!)

https://www.stereophile.com/content/joseph-audio-rm33si-signature-loudspeaker-measurements-part-2

@koost_amojan

You need to look for a clean waterfall with fast (damped) decay and no hashy stuff or resonances. The main resonant ringing is not normally in the audible band - my concerns are the additional resonances and lack of damping in rigid domes. The titanium dome on the JM Lab Utopia is up to 2 msec across the treble - this is a lot of vibration compared to something mostly clean or down 20 dB after 0.5 msec.

Here is a waterfall plot just for the Seas Excel Millenium fabric dome tweeter.

http://www.diyspeakers.net/snippets.org/ldsg.snippets.org/graphics/seas/e006w.gif

@shadorne 

Kinda like this?
https://www.stereophile.com/content/focal-aria-936-loudspeaker-measurements
That's what a pretty clean plot looks like with the exception of the excursion seen around 16kHz, which IS the resonance of the tweeter, which also reveals itself in the impedance/magnitude plot. That is NOT it's point of break up though. The internal damping of a Be tweeter is pretty much irrelevant because it's so easy to push it well beyond it's pass band. You seem to be confusing that with mechanical damping of the suspension. That's an entirely different matter. 
You seem to enjoy making broad, unequivocal statements about tweeter materials that don't reflect the reality.