Topic: Schoeps microphone answers

[DSatz]

Gutbucket, you've got it right as far as the material goes (though there is a soft inner lining to be kind to the capsule), and also the very important point that this technique is usable only with sealed = pressure transducer = omnidirectional capsules.

The main effect of the sphere is to create a presence boost in front of the capsule and to narrow (but not by a lot) its polar pattern at mid-high frequencies. This allows you to back away from the sound sources somewhat, and to pick up a (possibly) improved blend as a result, plus more reverberation at low and mid-low frequencies without losing "focus."

The original application for which this type of microphone was designed (by Dr. Herbert Grosskopf at the NWDR in Germany in the late 1940s) was single-mike pickup of an entire orchestra in a concert hall. This was, of course, in the mono-and-vacuum-tube era. If you're picking up an entire orchestra with a single mike, that mike has to be quite some distance away from the orchestra or else the balance will favor the instruments in the front and center too much. But Grosskopf wanted the full low-frequency response that can only be obtained from a pressure capsule, so he came up with this approach which allows the microphone to be placed farther back.

This, by the way, also explains why microphones such as the Neumann KM 183 have such a pronounced elevation at high frequencies--they're successors to the "diffuse-field equalized" microphones that were used for single-microphone pickup in reverberant spaces in the mono era. Nowadays we mike in stereo and somewhat more closely, so omni microphones with less high-frequency emphasis are generally favored.

--best regards

[digifish_music]

For omni mics only, they'd block the rear ports of a directional.

Yes ... actually I was wondering if that would convert a card into an omni?

digifish

[DSatz]

It would convert a cardioid into an omni with terrible frequency response and an inordinate sensitivity to wind and breath and handling noise. The diaphragm tension and the air volume of the internal acoustical chambers behind the backplate of a cardioid are totally inappropriate for an omnidirectional microphone.

If all it took to make a usable two-pattern capsule was putting an acoustically opaque collar around a the rear sound inlets of a cardioid, that's how everyone would do it.

[digifish_music]

If all it took to make a usable two-pattern capsule was putting an acoustically opaque collar around a the rear sound inlets of a cardioid, that's how everyone would do it.

Mom! DSatz is being mean to me again!!!

[DSatz]

> Mom! DSatz is being mean to me again!!!

Sorry--that probably was a little blunt. But I wanted to drive home the point that these sphere attachments--or putting duct tape over the rear sound inlets for that matter--aren't the easy way to a two-pattern capsule.

Schoeps as a company turned 60 years old this year, and one of my projects has been to help them prepare for a historical retrospective. In the process I researched the company's inventions, and read as many of their patent applications as I could track down. Their 1950s patent application for a two-pattern capsule using a single membrane features a cross-sectional drawing which I've attached below. It's not nearly as tricky as their three-pattern capsule, but its internal features do need to be designed specifically for two-pattern operation.

It's interesting to note that in the years since this patent expired, only one other manufacturer (Shure) has successfully implemented this approach. It's the only known way to make a switchable-pattern capsule with (a) an omni setting that has full low-frequency response and no proximity effect or sensitivity to wind, breath and handling noise, plus (b) a cardioid setting that remains a true cardioid even at the lowest frequencies.

--best regards

[Gutbucket]

Does that approach use some sort of mechanism to adjust diaphragm tension as well as opening an acoustic labyrinth to the back side of the diaphragm for the cardioid mode, or is there some other clever scheme that gets around the fundamental diaphragm tension difference issue?

Having sifted through the bizarre lexicon of patent speak searching for the real workings of things rarely described elsewhere in conceptual detail, reviewing all those Schoeps patents sounds both intriguing and utterly exhausting. You'll surely end up one of the more knowledgeable native English speaking experts on that rich history of innovation. I envy the conceptual insights while I'm overwhelmed just imagining the sheer quantity of effort required to sift the details. I really look forward to seeing that 60 year historical retrospective.

It may seem i constantly post accolades for your clear, informative posts, but thanks again for lending a unique perspective and your outstanding contribution to educating us amateur recordistapers.

~Lee

[DSatz]

Gutbucket, thanks for the kind words, but my only formal education is in classical music; I don't know enough physics to understand everything that is said in these patent applications. The distinction between electrostatic charge and voltage, for example, has me stumped these days; in a condenser microphone capsule, as the membrane vibrates, the charge remains constant while the voltage varies, and that varying voltage is where the signal comes from. At the same time the membrane is being charged from a constant voltage source--though there's a very large resistance in between which prevents that voltage from canceling out those variations in the short term (and thus smoothing the audio signal into nonexistence). I can say the words and work some of the formulas, but what do they really say and how would you build on that understanding?

What has helped me the most has been finding the occasional journal article in which someone who does understand the physics has broken it down for normal people. Also I have some friends I can call and ask, and fortunately, one of them is Jörg Wuttke--the guy in the video that started this whole thread. I've translated his work for many years now, and each time I work on a major project with him (as I'm doing now--a paper that he'll be delivering in English at the Munich AES), as part of my "payment" I throw a few questions at him.

Jörg is officially retired now, though he still consults for Schoeps and still does his educational speaking and writing (in three languages). The two guys who now have the top positions at Schoeps are also very friendly humans, and have been quite helpful to my continuing education. They're Dr. Helmut Wittek--who, by the way, does a lot of live recording himself, and would be very much at home in some of the discussions on this forum--and Christian Langen, their director of new product development. You can see both of them in other videos that are on YouTube.

Anyway, no--the pattern-change mechanism in the Schoeps MK 5 and MK 6 doesn't adjust the membrane tension; I doubt that such a mechanism could ever be precise and robust enough to do so reliably, especially over a span of decades. The first product built according to the design shown in this patent was the M 934 two-pattern capsule of the M 221 series (later renamed the MK 5 when it reached the "C" revision level, with a Mylar membrane and a new, recessed actuator lever design that is the familiar one nowadays). Quite a few of those capsules have been in use for 40 to 50 years now without an overhaul, though I bet some of them could use a good cleaning by now.

--best regards