K87

Wait, what's the difference between "In-Spec" and "Run Out" anyway?

Awesome question, theoretical customer! Over the course of production, the original capsule varied a lot. In the 60s, it the backplates were produced quite close to their specification (or, perhaps, In-Spec...), with careful drilling of tightly-toleranced holes:

However, as they moved into the 70s and 80s, things started to lax a bit. Drills ran out, bits bent, detachments happened. Some of the plates in shipped 70s capsules are pretty chewed up:

I mean, look at the first hole on the left from the center! Rough!

These chewed up capsules each have a distinct sound, though, due to the differently-distributed air beneath the diaphragm. Many people ask "Why are there so many magical-sounding "golden units" from the 70s?" The answer is, to put it bluntly, bad manufacturing. These issues allowed for a larger breadth of sounds to be represented in the final product, and the ones that were worse off were quickly replaced and lost in the annals of history, leaving only ones that were "improved" by the poor manufacturing behind to create a mythology. So during the 20 months that it ended up taking to find a backplate manufacturer that was up to my standards, I became curious... and I set a goal for myself: Find the best-sounding wrong K67 and copy it. Thus was born tuning #2: Run Out.

For the nerds, here are the FRs of both. This is only pseudo-anechoic, and it is fairly close, so the shape of these curves are not representative of the absolute sound of each capsule. The relative difference between the two types, however, is accurate:

This was really, really hard. It's hard enough to manufacture something with holes to micron tolerances when the holes are "round" sizes. It is infinitely more difficult to manufacture something with holes to micron tolerances if the holes are fractional sizes. I had to process design a way to control hole features that I'm not sure has ever been done before, but thankfully, since changing machine shops was taking so long, I had time to get it done.