Diffraction spheres and more
I may be interested in the spheres, it's good to see you making them.
For those interested, you might try the "pressure rings" that were furnished with the MKH20. The diameter of the mic is different (I think), but it can't be that difficult to find a soft washer (hardware) to place around the mic. These aren't the same as spheres at all, but they do provide a subtle increase of detail. They do this boosting the frequency response-but quite linearly (a shelf not a peak) over a mid range band of frequencies, perhaps 2-8 k or so. When combined with the diffuse EQ option offered on the MKH20s, they produce a result very different than you'd expect-in that case it is definitely a peak more along the lines of a sphere or peaky km130/183. You can probably find graphs somewhere on the Sennheiser site.