@MicUlli: Those plots look weird. If measurement conditions for both were identical, I'm pretty sure the mic with the red plot is out of spec and should be serviced (i.e. needs a new capsule). Even for non-matched KM 184 the difference is way too big, and there seems to be quite some bass loss.
Here's a plot of my own pair of KM 184. I bought them as the standard matched pair set.
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Regarding the difference between the KM 184 and the KM 84, I have a feeling people are exaggerating. I often read that the KM 184 is a bright mic. As the plot shows, that's not the case. I worked as a reviewer for close to 20 years and during that time I measured quite a number of small diaphragm mics, and just about all of them had a (much) bigger treble boost.
I don't own a KM 84, but I have a vintage KM 86. Here's a comparison plot of the KM 184 vs KM 86 in cardioid mode (please excuse the slightly different scaling; those plots were not done a the same time):
View attachment 109631