Beryllium Tweets

one of those people. Most ( say 90%+) of the Beryllium drivers I have heard can get bright and unpleasant to my ears

Thats what i am guessing will be my response after a  seassion with the Be midtweet.
Metal has that fault at  the highest fq;s. 
Whereas the Millennium has some special fabric, can't recall the name, which avoids these high fq's voicing with a  ~~tinnness~. And my guess is the Be will havea  bit of ~~Bark~~ in certain fq's when they peak high. 
The Millennijm has no such faults. 
There is no such ~~perfect midtweeter~~ But all in all the Millennium meets certain criterion that i wish to hear  in a  midtweet. 
With every mod in my system,,the Millennium continues to shine its true inner virtues of purity and clarity. 

Wow!  Let's all listen to the sound quality of YouTube to evaluate our components.  Besides, beryllium can and does work well with electronics that do not need the high end rolled off.  I have some, and they are great at making mediocre amps sound as horrible as the really are.  On the same system, my woven soft domes alleviate this flaw from crappy electronics.

I have some, and they are great at making mediocre amps sound as horrible as the really are. On the same system, my woven soft domes alleviate this flaw from crappy electronics.

As I said above, soft domes are more forgiving on bad electronics  /components, but not as revealing.  Beryllium/Diamond are very revealing, but you need top shelf electronics to make them sing.

Not sure if anyone on this thread invest in high end car audio along with high end home audio. If I didn’t see you at an IASCA Car Audio Sound Quality Championship (top 20 individuals), I’m sure you didn’t invest that much in that field. I won’t have the time to educate you on how some home audio products come from car audio. Example, JL Audio, Straightwire, and Focal Utopia BE to name a few. Pure Beryllium Inverted Dome Tweeter was Designed to be used in Car Audio to drown out engine noise in most Italian and German vehicles. They created massive feedback due to how the ground wire was routed and various ECU/ Computers in these vehicles. American vehicles don’t suffer the same consequences back in the day. I have been involved in high end audio for home as well as high end car audio since 1988. I’ve had the pleasure of experimenting with quite a few tweeter and crossover application. I was very fortunate to experience this. With tweeters of this magnitude, it really depends on your complete setup (amps, CD Players, preamps, speaker wires, etc). For car audio and even some home audio application, it was a bit bright for me but I did have the pleasure of utilizing the Pure Beryllium Inverted Dome Tweeter in several applications. 
https://www.focal.com/en/car-audio/car-audio-kits-solutions/elite/utopia-be/tweeters/tweeter-tbe
 https://www.focal.com/en/car-audio/car-audio-kits-solutions/elite/utopia-be

https://www.jlaudio.com/

Regarding the Yamaha NS-5000, here are some "specs" for zylon vs. beryllium.  Yamaha says the "sound velocity" is comparable to beryllium.  Keep in mind the same material is used for all 3 drivers and Yamaha uses a big dome midrange, not a cone.  Go looking for another loudspeaker with those two parameters.  I couldn't find one. 

A good test for this speaker, or any speker, is the opening of the movie Bladerunner 2049, which is on the soundtrack.  The bass is visceral.  The 12" woofers really move with no distortion I could discern.  They go really low.

From AV Hub Australia June 30, 2016

"As you’ll read in our interview with Koji Okazaki, Yamaha’s audio division has long harboured a desire to revisit the elements that made the NS-1000 and its pro version such a success. But not, we should note immediately, the element of beryllium. Instead Yamaha claims to have matched and possibly gone beyond this awkward substance in “adopting a new development diaphragm with a speed of sound comparable to beryllium in all units” — quite the claim, given that beryllium already has twice the sound propagation velocity of titanium or magnesium. The mystery material is a synthetic polymer called ‘Zylon’, which is manufactured in two varieties, Zylon-AS and Zylon-HM. It is used by NASA and in Formula One cars, and according to manufacturer Toyobo’s spec sheet for Zylon, it is indeed lighter and stronger than beryllium, its density 1.55g/cm3 compared with 1.8g/cm3 for beryllium, and its tensile strength 5.8 gigapascals compared with only 0.24 gigapascals for beryllium, and surpassing even carbon fibre at 3.5GPa. Zylon is also amazingly flame resistant, according to Toyobo, hopefully something prospective NS-5000 owners will never need to discover."

"The zylon fibers are coated with Monel using vapor deposition.   The reason we chose the new material is that it helps to express the small nuances of wind instruments such as a flute and clarinet that fibre materials can’t do. In addition, it prevents Zylon from degrading by ultraviolet rays."

When the speakers are reviewed in the USA, as I expect they will be, I'm not sure how much of all the detail behind the technology such as this will make it into any story, because there's a lot.  Yamaha's R&D on zylon diaphragms and the speaker's development began 8 years before the speakers made their debut in late 2015 or early 2016.