That's one nasty phase discontinuity due to steep shelf eq or crossover. And despite that, they still ring at (0.5), (1), (2), 4, 6, 8, 16kHz.
Alternative pattern is 3.5, (7), 14kHz - Etymotic style, less annoying.
Numbers in parentheses denote ringing that is on some models.
Why would anyone buy that?
Funny thing, almost all BA have multiple ringing with nasty consequences - sounds worse than single ringing frequency to me. (YMMV)
PP6 high frequency ringing pattern is typical of FK/WFK Knowles armature, even dampened versions.
Sonion ones don't ring nearly as much, but are more bandlimited. (what I heard in Sleek Audio SA6)
Star Micronics I haven't heard.