Is Berylium hazardous? More so than stuff in other headphones?
If I was going to spend a lot of time listening only to headphones I would consider spending 4K if seems worth it.
My audition was short but listening to some well recorded familiar tracks not sure I heard the value proposition with these. They cost almost 20x more than my most expensive current phones.
I have worked extensively with using beryllium-copper alloy in various components and don't recall any special handling procedures in the factory for such materials. We used them in designing the casings for components that were exposed directly to salt water in under-sea telecom cable applications. I don't think anyone uses pure beryllium in any consumer product applications. I have little doubt Focal has done enough research to make sure it is harmless. This is of course all moot (for me) since I would never ever pay that much for headphones unless that was the only method I could listen to music for the rest of my life....
I personally wouldn't get too paranoid about it, The women I referred to worked in an electro-plating plant handling and wiring components all day long. There are many potentially toxic materials in all our lives that are potentially worse. The beryllium domes used in transducers are always covered often due to their fragility as seen on Yamaha NS1000 monitors. Beryllium may be toxic if handled directly over extended periods but it's not exactly radioactive. Some people swear by beryllium drivers and some swear at them , at the end in this hobby it's all about subjective implementation and I'm certain Focal have done their homework and sound wonderful as they should for the money..
Don't know if they are worth a try at $4000 but I have a pair of Shure SE846 IEM for $1500 and I have never heard anything even remotely as good in an IEM. These IEM sound very close to the very best open back cans I have heard and have incredible noise reduction because of the great seal with memory foam.
Lots of paranoia around here. The effect of any poison is dependent on the specific compound involved and dose along with the frequency and duration of exposure. For example, many old houses contain asbestos, but there is no particular risk if the material is stable and not disturbed. It is when the material is removed that things become hazardous unless special precautions are taken.
Here's a link to the CDC web site on beryllium: https://www.atsdr.cdc.gov/csem/csem.asp?csem=5&po=15
And, just to make everyone extra paranoid, don't forget that apple seeds contain cyanide and solanine can be found in potato skins.