Among a few others, i had a some stock single-sided K67-type large diaphragm condenser capsules out of the several AKG Perception 200's i've collected these last few years. Fortunately, they're actually assembled out of two nearly-identical halves. The front has the gold-sputtered Mylar / PET diaphragm, and the rear one (since they're cardioid-only capsules) is skinned with a plain, non-metallized diaphragm.
Out of the 16 screws visible on each side, 14 of them are for tensioning the diaphragm, while the remaining two are longer, reaching all the way into the brass backplate of the other side (or half, if you will). These longer mounting screws, two from each side, are 90 degrees offset between the two sides. That is to say, if the longer screws are at the top and bottom of the front side, they're on the left and right on the rear side.
Between the two backplates there's also a thin conductive shim. This follows from the U87A version of the Neumann K67 capsule, which these emulate. In the earlier U87 (non-A), the shim between the backplates was made from an insulator, which allowed the obtaining of the usual three polar patterns most often used (cardioid, omnidirectional and figure-of-8) without a negative capsule bias voltage. Following the inclusion of a DC-DC converter in the U87A, the isolation between the two capsule halves was no longer necessary.
Either way, back to the task at hand, as it were. Just for kicks, i had the idea of assembling together two metalized-diaphragm capsule halves, to create a double-sided capsule. Because why not? These were only just gathering dust in a box, and non-cardioid-only capsules afford greater flexibility in the resulting microphone.
Yeah, i'm fully aware this won't necessarily have the <ahem> "mojo" perhaps, of a factory capsule, and that the two halves may well not be as closely matched as they might be from a ready-made double-sided capsule, but i'm thinking more from a feature standpoint, rather than sonic qualities or whatnot. And hey, it's DIY and it's a one-off, so here's to throwing caution to the wind!..
On the bright side, at least in the case of these particular capsules (34mm diameter, by the way), i was fortunate to notice that the mounting screws (as opposed to the more numerous diaphragm-tensioning ones) had an ever so slightly different head - a tiny bit smaller in diameter, and a smidge taller and more rounded. As can be seen, the tensioning screws have the larger and flatter-faced heads.
The "transplant" went through with no real drama. The brass shim got a bit stuck to the "active" half of one capsule (and subsequently deformed - the shim, that is), but the other one was intact. So yeah, at least until i get around to connecting this up to a mic circuit, i'm calling this a success.
Ah, screw it, i'm on a roll! I'll do another "conjoining", this time on a 32mm version of the K67 design. These capsules are out of some sE Electronics sE2200A microphones. I have five of them, so that'll make two double-sided capsules with one cardioid-only to spare. Oh wait, i also have that other sE mic, an X1 (with a noisy circuit, which i'll have to replace / rebuild someday).
Unfortunately, this time, identifying the relevant mounting screws was impossible, so i was forced to resort to "brute force". Don't panic, i only meant i needed to try "all" the screws in sequence. Fortunately though, i had the rear halves of the capsules to use as guinea-pigs, so the process was quite risk-free.
Oddly enough though, these sE capsules only have an 80% shim, as in, an incomplete "washer" (as opposed to the AKG ones). That being said, it IS also a slightly smaller-diameter design, so the resonances would likely need to be tuned differently.
Final score: one 34mm and three 32mm K67-type capsules. I can live with that. I have four cheapo BM800 mics that i've bought basically simply as body-"donors", and several (self-designed) circuit boards for multipattern mics, so that should keep me busy for a while.
awesome man! Helped me a lot!
ReplyDeleteVery glad to hear that!
Delete