gratefulphish, let me try to explain the basics of microphone patterns. Microphone designers can't just make up any old pattern they want; directional patterns result from the basic physics of how sound pressure is used to move the membrane(s) in the microphone. Two basic arrangements exist. All directional patterns come from using one or the other or various combinations of those two, so it's worth knowing what they are and how they can be combined. Then this whole picture begins to make sense.
The first, simpler arrangement is when a membrane simply responds to the sound pressure that reaches its front. The other, more complex arrangement is, the membrane is exposed both in front and in back, and it responds to the difference in sound pressure between its front and back. The first, simpler arrangement ("pressure response") results in an omnidirectional pickup pattern, while the second, more complex arrangement ("pressure gradient response") results in a bidirectional pattern--a "figure 8" shape, with the two lobes having opposite signal polarity from each other.
A hypercardioid microphone is basically a bidirectional microphone with a small degree of pressure response added--a blend of maybe 1/4 omni plus 3/4 figure-8. Adding the omni component increases the microphone's front sensitivity (since signals in the same polarity add together) and decreases the sensitivity of its rear lobe (since signals in opposite polarity tend to cancel). But it still has a front and a rear lobe, even though they're unequal in sensitivity. A hypercardioid is really just a lop-sided ("lop-fronted"?) figure-8.
A cardioid, by comparison, is a 50/50 mix of the two methods. The strength of its omni component exactly cancels the rear lobe of its figure-8 component, while doubling the sensitivity in front. If you mainly want to minimize rear-incident sound, cardioid is the pattern that does this the best. If on the other hand you want the narrowest front pickup pattern, figure-8 has that. Unfortunately you can't optimize both at the same time; those two requirements physically contradict each other to some extent.
Now if you look at the pattern selector of your microphone, you'll see that its five possible settings (apart from the "R") are just points along a continuum from omni to figure-8. As you move the dial, you are selecting the polarization voltage (and thus the sensitivity) for the rear half of the twin-diaphragm capsule. Sensitivity is directly proportional to this voltage, and the polarization on the front half of the capsule remains constant. In the omni setting, the back half of the capsule is charged as strongly as the front half, and with the same polarity. It is charged more weakly, but still in the same polarity, for the "wide cardioid" setting. It isn't polarized at all for cardioid; the front half of the capsule is a cardioid by itself. The rear half is polarized weakly (in inverse polarity) for super- or hypercardioid response, and at full strength (but again, in inverse polarity) for the figure-8 setting.
Some variable-pattern microphones such as the Neumann M 269 used potentiometers for pattern selection rather than switches with definite "stops" to them; maybe now you can imagine how this is possible. For that matter, a few microphones have been designed with one pure pressure transducer and one pure pressure-gradient transducer in them, and the pattern control simply varies the mix between them, allowing any first-order pattern to be produced. In that type of design, the omni setting has full low-frequency response and freedom from proximity effect, wind and breath noise, etc., so it's a rather interesting approach.
--best regards
P.S.: Actually the so-called "hypercardioid" pattern of a TLM 170 is a bit closer to being supercardioid (it has a little more omni and a little less figure-8 than a classic hypercardioid), but that's equally true of most "hypercardioid" microphones, including the Schoeps MK 41 capsule and Neumann's own KM 185 or KM 150. Pragmatically, people mostly find that the rear lobe of a true hypercardioid is just too much, and for various reasons you can also get more extended response at both ends of the frequency spectrum if you move more toward a supercardioid pattern.
Topic: Technical Mic Questions (Read 8071 times)