Some "cardioid" condensers are really speech cardioids

Summary: A fair number of the "cardioid" microphones sold on okay are actually "speech cardioids." This article is meant both as a warning and a guide. Speech cardioids have their uses, but they aren't generally good substitutes for regular cardioids, so it's important to know which ones are which. Unfortunately, some sellers either don't know the difference or don't wish to point it out in their ads.
Background: As most sound engineers know, if you place a directional microphone close to a sound source, its low frequency pickup will increase considerably. This is known as "proximity effect." Sometimes it can be put to good use--it can make a singer sound "bigger"--but oftenthe exaggerated bass has to be filtered or EQed out. This is particularly true when the application involves close pickup of a speaking voice. In addition to their tiring, "boomy" sound, ordinary directional microphones tend to exaggerate "popping" and other breath noises unless a good pop screen is used.
Since the 1950s the main German manufacturers of studio condenser microphones (e.g. Neumann and Schoeps) have offered special "speech cardioid" microphones for close pickup of a speaking voice. The membranes in the capsules of these microphones have higher than normal tension, which reduces their low frequency response and increases their resistance to "popping," breath noise and handling noise.
For announcers and panelists in broadcasting, as well as users of public address systems, this type of microphone was very convenient. "Speech cardioid" microphones have been used by many radio and TV studios, governmental and academic institutions, public meeting places and large churches. Such microphones aren't good general-purpose microphones for recording music, though, since the reduction in their low-frequency response is so great. Typically the benchmark for such microphones is 12 dB reduction in sensitivity at 50 Hz. A speech cardioid may have certain uses in music recording--it may be good for very close pickup of an acoustic guitar, for example. But in general, a microphone of this type would be considered quite "thin" sounding by most people, when it is used at ordinary miking distances.
Unfortunately, many people seem to be unaware that this type of microphone exists at all. And I've noticed that often, okay ads for speech cardioid microphones fail to mention that the capsule has this severe low-frequency rolloff as part of its inherent design. Often the microphonesare described simply as "cardioid." They are, of course, but that's only part of the story. So I'd like to point out some ways to tell what is what.
Indentification: Speech cardioid microphones are generally small-diaphragm types, and most often are part of a manufacturer's series that has interchangeable capsules. If you have a microphone of this type, you could convert it to a normal cardioid by obtaining a normal cardioid capsule and attaching it in place of the speech cardioid capsule. However, replacement capsules can be quite expensive (e.g. $600 nowadays), so buying a speech cardioid isn't usually a good way to get a bargain indirectly on a general-purpose cardioid.
Neumann speech cardioids: One speech cardioid often seen on okay is the Neumann KM 85, which was the speech cardioid counterpart of the widely-sold KM 84. That microphone series included the KM 83 (omni), KM 84 (cardioid) and KM 85 (speech cardioid) microphones; spare, interchangeable capsules of all three types were also sold separately. If you put the capsule from a KM 83 or KM 85 onto the body (amplifier) of a KM 84, that microphone became a KM 83 or KM 85 in every respect except for the marking on the body. As a result, some microphones which are marked "KM 84" on the body of the microphone are actually speech cardioids (KM 85) or omnis (KM 83) because someone changed the capsule. Similarly, a microphone marked "KM 83" or "KM 85" could have any of the three capsule types on it.
Because of this confusion, Neumann eventually gave up marking the bodies specifically, and just printed "KM" or "KMi" on them all, since internally they were all the same anyway. Unfortunately, I have seen microphones with KM 84 markings on the body but with speech cardioid capsules, sold on okay as "KM 84" when they should have been listed as "KM 85". It's the capsule that makes the difference.
If you're buying a "KM 84" (for example) you really need to see pictures of the capsule to make sure that it has the capsule you expect, and not one of the other two possible types. The markings vary with the age of the capsule. With older capsules, the KM 85 had a black dot (2 or 3 mm across) printed on the rim of the capsule. Later capsules had the number "85" and/or a cardioid symbol with a broken horizontal line inside it engraved in gold (the left part of the line angles downward to indicate the low-frequency rolloff). A capsule with no markings may be from a KM 83 or a KM 84; in that case you'd need to see the backplate (where the long gold pin goes into the back of the capsule). The backplates of directional microphones have a pattern of small air holes, while the backplates of omni capsules are sealed.
In Neumann's current product line, the only speech cardioid is the model KM 145 (= KM 100 amplifier body AK 45 speech cardioid capsule).
Schoeps speech cardioids/supercardioids: With Schoeps the situation is similar except that speech cardioid capsules have been available in five or six different series of their microphones. Capsules whose model number ends in a "0" are always speech cardioid capsules, e.g. MK 40 or MK 240. However, some Schoeps speech capsules of the present-day CMC and CCM series don't follow this numbering pattern, e.g. the MK 4A, MK 4S, MK 41S or MK 4VXS of the Colette series, or the corresponding CCMs (CCM 4A, CCM 4S, etc.).
Nearly all Schoeps or "Strsser" microphones from the old CM 60 series were speech cardioids, e.g. the CM 640; unfortunately, these often show up on okay simply as "cardioid" with no further indication, particularly from European sellers. As with the Neumann KM 83/84/85, sometimes a Schoeps microphone's body will have a model number that doesn't match its capsule type because of the interchangeability of capsules. Always be sure that you know the exact capsule type.