Specifically a beryllium tweeter, with the failure being that it fails in a way that it can no longer reproduce its entire operating range of frequencies. Let’s say in a particular speaker design the tweeter covers from 3,000-20,000 Hz. Is a failure mode possible such that it works fine up till, say, 10KHz but after that it’s output fails - either outright or in some degraded fashion? Could a failure in the crossover cause this to happen? This is all theoretical - not having any issues with my stuff. Just curious. And in case anyone is thinking it - yes my hearing is quite good well past 10KHz! 
