Take a look at the Scanspeak silk Illuminator tweeter and the Beryllium tweeter. On paper and using most common measuring techniques, they are 99% identical. But to an ear, the difference is night and day.
They are hardly identical.
One is ±1db from 1,000hz on with a pretty smooth response. The other is ±2db with a fairly peaky response and a peak a pretty large peak at 15khz. The price of that Beryllium tweeter is outlandish. One second you hear 10khz which is nice and flat, than
BAM 2db peak at 15khz or the very slightly worse peak at 5khz. Fatiguing? Probably not. Noticeable on some material? Definitely. I'd rather own the Silk version myself. Usually, in theory, I like metal domes because they do not decouple as early, but I'd rather have the Silk dome vs the Beryllium dome. Silk has a controlled breakup, but intuitively I think it's bad for detail. Peaks/dips in a response are never a good thing. I can hear increase in volume in 1db increments.
Audible Difference in Sound Level Blind Listening Test
