So what is special about Beryllium? After Takajo San, a hifi and music critic joined Goto in the 60s, he led the R&D at Goto to record acoustic instruments live and to try and reproduce them through Goto drivers. Listening, rather than measurements, was his style. Goto’s R&D went down this road, and ended up changing their aluminum diaphragms (then the most widely used in Altec, JBL, Goto etc) to titanium. After that, Takajo San started recording sounds of chirping insects and other sounds from nature to test his drivers. This effort to reproduce sounds of nature led Goto to develop Beryllium diaphragms.
The Be diaphragms changed to duralumin in 2005 only because of the cost, as Be became very expensive due to countries using it for defense/atomic purposes. But their upper models continue to be Beryllium
TAD horns/Cessaro are Be, as as are horns Universum. Does it have brightness downside if not managed correctly? Yes