Advantages of beryllium?


Can someone please explain the advantages of beryllium drivers over titanium or aluminum?

Also, how concerning are health risks associated with beryllium?

many thanks for your input. 
defiantboomerang
@kosst_amojan

Obviously some implementations are better than other. My statement pertains to the problem of lack of internal damping in most metallic drivers (magnesium being perhaps a notable exception).

I count 5 resonances on the Focal Aria tweeter lasting up to 1.5 msec. These resonances are much much longer than the wavelength of the sounds that tweeter emits (an eternity in terms of PRAT) and will definitely color the sound in the way I described.

The resonances are multiple as a rigid disc has multiple resonant modes. I know this for sure as I have large collection of Sabian, Zildjian and Paiste cymbals and they shimmer with all kinds of non harmonic tones. A cymbal is an exaggerated example but the same principle stands.

If you want to hear musical timbre you need a driver that is critically damped - being inert it just gets out of the way once the desired movement is executed.

2 msec of waterfall hash on the first example I gave is really going to affect everything: the timbre of transients on percussive instruments (twang of guitar strings) to the articulation of sbilance on vocals.

The high but very narrow or sharp resonance peaks sometimes seen on JA plots is something to do with his measurement setup - you can ignore those - they look too narrow to be real effects.

FWIW the best waterfall plot I have seen, apart from the one on the Joseph Audio speaker linked above, is on a Quad electrostatic. So for those people who can hear what a difference a good electrostic speaker makes audibly in timbre then you can appreciate how a rigid tweeter can be coloring the sound in the way I describe.
@randy-11

Interesting link. I think they sum it up very well. Be is better in the very top octave than Aluminium or Titanium (10 to 20 KHz)

Note that on the plots Be is not necessarily the best from 3 to 10KHz (the really important range musically for the tweeter). This is the point I am trying to make about internally damped drivers - better performance over a narrower frequency range. If the sound from 10KHz to 20KHz is most important to you then Be is the way to go (at the expense of more resonance at 3KHz to 10KHz)

As as far as I am concerned there is not so much musically in the 10K to 20KHz range - so I prefer a tweeter that performs better from 3KHz to 10 KHz.
A - The 936 is not very clean
B - It has the Focal 100 Hz dip in impedance, which makes the speakers seem more "discerning" of various amplifiers. In some cases this is done artificially in the crossover.

Best,

E
shadorne, I dunno if what they say is accurate but it does seem to be a  pretty good summary - I'm not a dome kinda guy (Maggies) - tho if someone offered me a free pair of Sonus Faber Aida's I could be persuaded to switch.
@erik_squires 

Does the 936 have a Beryllium driver? Or is that reserved for higher up Focals?