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[aremos]

Is there (should there be) a sonic difference in Cardioid between 2 "identical" models where one mic has only one capsule & the other has dual capsules?

[klaus]

Could you be more specific, please: what microphone model has two versions, one with one capsule, the other with two?

[David Satz]

aremos, are you asking about cardioid microphones whose capsules have two membranes (diaphragms) versus cardioid microphones with single-diaphragm capsules? I think that is more likely to be the question you intended to ask.

If so, then yes, there is a very important difference: Unlike a single-diaphragm cardioid capsule, a dual-diaphragm capsule when used as a cardioid (e.g. when only the front diaphragm is polarized and/or connected to the amplifier) doesn't maintain its cardioid directivity at low frequencies; its pickup pattern spreads out and becomes more of a "wide cardioid" which takes in more room sound. Thus if the room is not extremely dry, such microphones may well pick up more bass than they would do if their pattern remained a true cardioid to the bottom of the range.

(Just as a note, this is sometimes mistaken as an effect of large diaphragms--a somewhat understandable misperception, given that nearly all large-diaphragm condenser microphones use dual-diaphragm capsules. But small dual-diaphragm capsules also have this characteristic while large, single-diaphragm capsules do not, so it actually has nothing to do with large vs. small.)

The loss of low-frequency directivity in dual-diaphragm cardioids is also a good reason to prefer single-diaphragm microphones for recording in stereo with a coincident or closely-spaced pair of cardioids. Any loss of directivity at low frequencies will mean reduced separation between channels at those frequencies, which in turn leads to a loss of spaciousness in the recording.

--best regards

P.S. (added later): Dual-diaphragm microphones are generally side-addressed, while single-diaphragm microphones can be either side-addressed or whatever you call it when they aren't ("end-addressed" maybe?). This also affects the cardioid pickup pattern, mainly at high frequencies where a side-addressed microphone can again maintain something closer to a true cardioid pattern; when that occurs, the result is less off-axis brightness as compared with the microphone's on-axis brightness. Whether that characteristic is desirable or not depends on many things (I generally prefer it for the kinds of recording that I mostly do), but either way, my point is that the difference can be quite audible.

[aremos]

Thanks David. For both the answer to my question (which incorrectly used the word "capsule" instead of "diaphragm") and the information on the dual capsules from Schoeps, Neumann & Josephson.

The question was geared towards dual diaphragm multi-pattern mics & their single cardioid-only equivalent.
[In the Neumann Camp an example would be TLM170 & TLM 193. Set to Cardioid, do they both sound "identical"?
Other examples could be between the Bock 251 & the 241, Brauner VM1 & VM1 Lite (or as I believe it's now called VM1 Cardioid only), etc.

[David Satz]

aremos, you replied to an earlier version of my message, which I later trimmed down by taking out the information about dual-capsule microphones from Schoeps, Neumann and Josephson. I'll put that information back as a P.S. to this message.

OK, I think I understand your question now, especially because you gave the TLM 170 vs. the TLM 193 as an example. Those two microphones use the same capsule (K 89), and in terms of acoustical factors, it makes no difference whatsoever that the TLM 193 is single-pattern while the TLM 170 is multi-pattern. However, the rear diaphragm of the TLM 193 isn't connected at all to its amplifier circuitry, while in the TLM 170's cardioid setting, the diaphragm is connected but no polarization voltage is applied to it. As a result the TLM 193 is several dB quieter than the cardioid setting of the TLM 170 (21 vs. 26 dB CCIR equivalent noise).

A similar situation exists with the Neumann M 269, which has a cardioid-only setting that is ~3 dB quieter than the cardioid setting of the same microphone in its "F" (remote-controlled) setting, for the same reason. Although I'm certainly no expert on the U 67, it looks to me as if its cardioid setting does something similar; its equivalent noise in the cardioid setting is also ~3 dB below what it is in the omni and figure-8 settings. This does not appear to have carried over to the U 87 or U 87A.

Note that the TLM 170's capsule head is slightly larger than the TLM 193's, which has some small effect, but not enough that either microphone's response will go beyond the other one's tolerance limits. Thus Neumann prints the identical response graphs for both models.

--best regards

P.S. (what I trimmed from my earlier reply):  Apart from stereo microphones which naturally require two capsules, I can think of only three dual-capsule microphone designs in the history of studio condenser microphones. The first was a pair of Schoeps models from the early-to-mid 1950s that combined a pressure (omnidirectional) capsule with a pure pressure-gradient (figure-8) capsule inside a single capsule head. This allowed the microphone to be switched between omni and cardioid patterns by including or excluding the signal from the figure-8 capsule. (Theoretically a figure-8 pattern could also have been produced, but that option wasn't offered.)

About a decade later Neumann introduced the KM 66, which was followed later by the KM 76 and 86; it had a capsule head in which two separate, single-membrane cardioid capsules were placed back to back, a slight distance apart. The microphones had three patterns but when they were set as cardioids, only the front-facing capsule was used while the rear-facing capsule had little if any acoustical influence.

Finally, the Josephson C700A microphone (a current model) takes the principle introduced by Schoeps and uses it to produce a continuously variable pattern microphone. It has separate outputs for the two capsules, so the user has to mix those signals externally to obtain the desired pattern.

(and a P.S. to the P.S.) One advantage of the Schoeps and Josephson approach, as compared with conventional dual-diaphragm capsules, is that the omni setting uses a pure pressure transducer which has flat response down to the lowest audio frequencies, no proximity effect, and greatly reduced sensitivity to wind and breath noise as well as to solid-borne sound. An omni pattern synthesized by summing the outputs of two cardioids back-to-back doesn't have these advantages.

[aremos]

David,
Great info!
Thanks,
Ariel

[Kai]

...dual-capsule microphone designs...a pair of Schoeps models from the early-to-mid 1950s that combined a pressure (omnidirectional) capsule with a pure pressure-gradient (figure-8) capsule inside a single capsule head. ...
About a decade later Neumann introduced the KM 66, which was followed later by the KM 76 and 86;

Do you know the model no. of this Schoeps? I never heard of it!

There was the famous Neumann KM56 too (the Motown mic!), the AC701 tube version predecessor of the mentioned KM66 ...

Regards
Kai

[David Satz]

Kai, the KM 66 was also based on the AC 701k and the KM 56 didn't have two separate capsules; it had one dual-membrane capsule. That's why I didn't mention it. The only unusual thing about its construction was that it was a small-diaphragm capsule (also used in the SM 2, SM 23 and KM 88), while most dual-membrane capsules are large-diaphragm.

The Schoeps models that I had in mind were the CM 51 (the 1951-53 series) with the capsule head which I believe was called CM 51/7, and the M 201 during the years 1952-54 (a later version used a different two-pattern capsule design). There's a good close-up photo of this type of capsule head on www.schoepsclassics.de/1952.htm on the left side of the page.

--best regards

P.S.: A photo of an M 201 using this type of capsule head is attached, from a 1954 Telefunken sales brochure.

[panman]

David, Thanks for the great info!
I saw, that David was faster, so my posting was not necessary anymore. Just like to add some thouhgts. I believe the confusion is mainly caused by some old Neumann publications saying the capsule is two kk54:s put together, but that would mean two true cardioids and that is not the case as David pointed out. Furthermore the 56 membranes have a smaller diameter than the 54:s, but apart from that they are very similar.
Esa

[klaus]

Kai, the KM 56 didn't have two separate capsules; it had one dual-membrane capsule.

That is erroneous. The KM56 consists of 2 KK54 capsules tied together with three copper clasps fed through holes in the frames of the capsules. Each capsule has its own backplate, just as in a KM54.

I speak from experience, having had to match or replace clients' KM56 capsule halves, which is royal pain.

[David Satz]

Very interesting, Klaus. Thanks for that information. Dual-diaphragm capsules can have two separate backplates or one shared backplate, but from what you say, the KK 56 could legitimately be called a dual capsule so Kai, my apologies--you were right!

Neumann's history page for the KM 56 has a picture of a disassembled K 56 and says, "For the microphone capsule itself, substantial parts of two cardioid KM 54 capsule [sic] are used. The photograph shows the individual components. Each half of the capsule consists of a membrane, back electrode and delay plate. The two capsule halves are mounted together back-to-back with a distance foil, thus forming a dual membrane capsule, similar to the proven M 7 capsule from U 47, U 48 and M 49 fame, but considerably smaller. ... Of course, contacting the capsule needs to be executed differently from that of the M 7, where the connections to the membranes are achieved via a screw contact in the capsule center. Contacts for the nickel diaphragm of the miniature capsules use the rim. The connections to the back plate electrodes are made via insulated holes through contact springs forming a ring inside, at the perimeter of the electrodes. The double membrane capsule is then installed in a plastic mounting support with three contacts."

--best regards

[panman]

So, where is the borderline between the dual-membrane capsule and dual capsule? I always thought that kk56 at least functionally is more like a dual-membrane capsule, but the contact needles speak for the dual capsule definition.

"The only difference between a K54 and the 2 K54 mounted in KM56 is the shortened contact needles."

I already pointed out, that the capsules in the kk56, though very similar as k54, are not the same size. To me that is a difference enough not to call them k54. I know that as a fact, because I have taken these capsules apart a couple of times too and measured the capsules. No way a k54 could fit inside a kk56 capsule assembly. 
Regards,
Esa

[klaus]

Sorry to disagree. K54 and 1/2 of a K56 are identical in overall construction: membrane, backplate, size and shape. I have transplanted portions from each type to the other in the past.

Please cite where you think the two types diverge in size.

[panman]

Sorry to disagree. K54 and 1/2 of a K56 are identical in overall construction: membrane, backplate, size and shape. I have transplanted portions from each type to the other in the past.

Please cite where you think the two types diverge in size.

The capsule diameter is bigger in k54. I happen to be in Finland right now and do not have access to kk54 at the moment, but I happen to have a kk56 with me, because I want to send it back cheaper to a friend who lives here. I just measured 15mm diameter from the front of the capsule-rim outer dimension. anything bigger than that will not fit into the plastic mounting-frame. You or anybody else possessing a kk54 is hopefully able to measure it and further post it here. Or I can do it next week, when I am back in Cheeseland. Wanted to post pics, but the batteries in my camera are flat.

Your mentioning of the shortened contact needles is confusing. The capsules in Kk56 do not have needles like k54, but as in David`s previous quote:" The connections to the back plate electrodes are made via insulated holes through contact springs forming a ring inside, at the perimeter of the electrodes."That to me is a big difference between those capsules. By the way the page quoted can be found here:

http://www.neumann.com/?lang=en&id=hist_microphones&cid=km56_publications

Look "General information about the KM 56" and you can see the springs and all the other components too.

Klaus, that you have been able to transplant portions from each type to the other does not mean I am wrong, but rather suggests, that there are two versions of kk56. Changes were done later too, like the membrane tensioning got tighter. Possibly the publication is not wrong either, but there were early models fitting to that: "For the microphone capsule itself, substantial parts of two cardioid KM 54 capsule [sic] are used". "Substantial parts" does not allow too wide an interpretation. Just like the Neumann papers do mention, that the nickel membrane of k54 is made through galvanizing. True, but only in the beginning and was later rolled nickel. No mention of that though. Sometimes these descriptions are just too "general".
Regards,
Esa

[Dominick Costanzo]

Kai, For the record the KM86 is the "Motown mic".