Most manufacturers don't care much about drivers FR matching, they check for impedance matching and call it a day. If you want a higher grade, DT48 and T1 might be your golden ticket.
on my DT770/600, when I slowly went through a sinewave sweep in SineGen some frequencies would either whine or be completely silent on one driver or the other.
dumb question, but you did the same test by wearing the headphones the other way around?


















