Hi. As the subject line says, Schoeps has decided to rename its venerable MK 3 omni capsule to "MK 2 XS" so that all Schoeps omni capsules will have an "MK 2" designation of some kind from now on.
The MK 2 XS is the one with flat response in a "diffuse" sound field, i.e. at a distance (and in an environment) where the predominant sound energy is reflected rather than direct--farther from the sound sources than most of us would probably prefer to place our mikes most of the time. It isn't sold in very large quantities, but it has a definite value and purpose.
When you graph a microphone of this type on axis in an anechoic chamber (as microphone frequency response curves nearly always are done), its response curve will show a ~6 dB elevation at high frequencies. But at the prescribed distance in a normally reverberant environment, the high-frequency elevation isn't heard as brightness or hardness, which it would be if the mike were placed more closely. The overall, integrated response (considering all angles of incidence equally) is flat--and in a diffuse sound field, that's what matters; only a small amount of sound energy arrives directly in front of the capsule, and even that sound isn't mostly direct sound.
This type of omni was used more commonly back in the mono era for single-mike pickup of large orchestras, orchestras with chorus and/or soloists, etc., while in the stereo era it is less often used; many people, I think, shy away from using a spaced-omni pickup at that kind of distance. But this is precisely the type of omni that can compensate well for losses due to the high-frequency absorption characteristics of the various surfaces that the sound bounces off of. And especially when add-on spheres are used (such as the Schoeps KA 40), this type of microphone can make recordings with good focus even at surprisingly great distances from the sound sources.
--best regards
P.S.: The other three "MK 2" capsule types are the MK 2 itself--which is flat on axis and therefore suitable mainly for close miking--and the MK 2 H and MK 2 S, the two models that should be the main interest for people here, I think, since they give essentially flat response when the arriving sound has a fairly even mix of direct and reflected energy.
P.P.S.: Schoeps also renamed two of its speech capsules, withdrew one model of speech capsule, and introduced two new types of speech capsules. I can give the specifics if anyone's interested; I use speech capsules often for spot miking, but I don't know how many other people here are concerned about them. On the other hand, a lot of people here use speech capsules without seeming to realize it (many miniature cardioid capsules from Far Eastern manufacturers are in fact speech capsules).