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Author Topic: What is an "M7" Capsule?  (Read 1000 times)

klaus

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What is an "M7" Capsule?
« on: March 21, 2024, 11:58:39 AM »

It may be a good idea to define "M7 capsule", considering that more than one manufacturer currently uses the term which originated as a Neumann product almost 100 years ago.

The original M7 capsule design was first developed in the early 1930s by Georg Neumann with the help of Erich Kühnast (his son later took the helm of Neumann/Gefell/Microtech Gefell, now retired), though the term was not used at the time. Please read below David Satz's corrections to the date of introduction [date of "first confirmed mention of an M7 in a Telefunken catalogue" is 1939, according to David's research] and who he believes to be its true inventors.

It was a dual-diaphragm, single backplate  construction capable of three patterns (cardioid, omni, figure-eight) when correctly polarized. Its first verifiable commercial application was in the U47 (1949), U48 (1957) and M49 (1951). M7 had cast PVC diaphragms and a characteristic hole pattern to the backplate which to a large degree is still present in the polyester-skinned K47 which succeeded the M7 in the late 1950s and which is still being produced by Neumann today.

After Neumann/Berlin switched to Mylar K47, Neumann/Gefell, later renamed to Microtech Gefell, continued producing its version of the PVC M7, to install it in all of its large Diaphragm mics. Around 2000, the German government clamped down on environmental toxins, including the PVC solvent Microtech Gefell used to make these capsules, forcing MG to reformulate the PVC mix.

MG also added a PE- (polyester) skinned version of the M7 to its lineup, using it in some of its LD mics.
AFAIK, only the flagship model, 92.1S, still uses the PVC version M7.

Gefell's PVC M7 made prior to approximately the year 2000 were every bit as sexy and emotionally attractive-sounding as the original Neumann/Berlin version, yet with a slightly different timbre, which changed (at least to my ears) dramatically when MG was forced to reformulate the PVC mix and their PVC capsules never sounded the same again. If you are ever in doubt which version you have before you: the Gefell version used and still use an M1.2 center lead-out screw, while Neumann always has used M1.4.

PVC M7 diaphragms were recreated by Siegfried Thiersch in Möschitz, East Germany, in the 1990s (Thiersch had resigned from MG, where he was in charged of nickel diaphragms). He first offered reskinning of original Berlin and Gefell M7 capsules, later he also started offering complete M7 capsules with PVC ("Blue Line" and PE ("Red Line") skins. STM (Thiersch's monogram) no longer offers the PVC version. As Thiersch also could no longer use the original toxic PVC material after 2000, its capsules too have the mid-forward emphasis of the post-2000 MG M7 capsules.)

All current copy versions of the "M7" (which Neumann neglected to trademark) currently manufactured use polyester/Mylar® material for its membranes.

Aside of one manufacturer who will remain nameless, to my knowledge, the original M7 PVC backplate dimensions and acoustic network were never modified by any of the copy companies to accommodate a polyester skin of roughly half the thickness of the originally 10µ PVC membranes.

In sum, there are many versions of "M7" in circulation today, and to my ears they all sound different from each other, with none sounding identical to the original M7 PVC Berlin or Gefell version.

Please add any corrections or other relevant M7 facts.
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Klaus Heyne
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consicerecording

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Re: What is an "M7" Capsule?
« Reply #1 on: April 07, 2024, 09:19:45 AM »

I've been pondering about the 'nameless' M7 capsule maker mentioned in this post. Is it possible that Dany Bouchard/Poctop, known for his D7 capsule and his contributions to the DIY microphone community, could be the one? Could you share if there's any collaboration between you and this capsule maker for another KLAUS HEYNE EDITION tube microphone, perhaps similar to your past project with Dirk Brauner (VM1 KHE) &  Cathedral Guitar/Oliver Archut (OA-1)?  Additionally, I'm curious if there's any possibility of another classic KHE Tube Mic in the pipeline.

Thank you for taking the time to address my inquiries.
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klaus

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Re: What is an "M7" Capsule?
« Reply #2 on: April 07, 2024, 12:30:49 PM »

Hello Mark Anthony,
I currently have no contract with any manufacturer for issuing another mic or mic components under my name. If and when that changes, I will post it here.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

David Satz

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Re: What is an "M7" Capsule?
« Reply #3 on: June 24, 2024, 09:59:47 PM »

just for the record, I know of no particular evidence that the so-called "M 7" capsule was designed by Neumann and/or Kühnast, nor do I know of any evidence that would support the 1932 date even though Neumann still gives it in their chart. I say "so-called" because names of the type "M 7" and "M 8" were the Reichsrundfunkgesellschaft's way of referring to complete microphones, not capsules, to which they had granted type acceptance for purchase by broadcasting organizations within the Reich. Neumann's own names for these capsule types were CM 8 and CM 7 respectively. (Yes, the figure-8 came first.)

No microphones with these capsule types appear in any catalogs or price lists that I've seen or heard of prior to 1936. Until then, all Neumann condenser microphone capsules were single-diaphragm, diffuse-field-equalized pressure transducers. We might call them "omnidirectional" except that they were so large, their pickup pattern started to become narrow already in the upper range of voice frequencies. This general type of capsule (based on the classic Western Electric designs) dominated the condenser microphone market for its first 20+ years, but has faded into obscurity in the stereophonic era.

The actual inventors of the two capsule types were almost certainly Dr. Hans Joachim von Braunmühl and Walter Weber, working at the RRG. They patented both designs in 1935 (the first page of the German patent is attached)--or actually, there seems to have been a March, 1935 filing for just the figure-8 capsule design, which was then superseded in September by the filing for both designs. The next month the same two researchers explained the workings of the capsules at length in an article published in the journal Hochfrequenztechnik und Elektroakustik. (I wanted to attach several scans from this article, but the board's maximum file size for the sum of all attachments to any one message has somehow gotten set to only 512 KB, so there's only room for the first few paragraphs.)

These same two men also wrote a textbook, Einführung in die Angewandte Akustik (Introduction to Applied Acoustics), the manuscript of which was handed in to the publisher S. Hirzel in Leipzig right around when the above article was published. It's a snapshot of a particular moment in condenser microphone history: Its section on condenser microphones mentions only pressure transducers, and features a photo of a Neumann bottle microphone with a pressure capsule--but then at the end of the subchapter on microphones, a section seems to have been added in at the last minute describing pressure-gradient condenser microphones and saying that they'd been developed only quite recently ("in neuester Zeit"). No photos of any such capsules, or microphones using them, are shown in the book, however, while the Hochfrequenztechnik und Elektroakustik article shows prototype capsules that don't look like they're from Neumann.

None of that is consistent with their already having been introduced commercially some years before. Maybe most people don't care very much about history, but that's no excuse for perpetuating false history.

P.S.: I've seen many dozens of photos of Neumann bottle mikes being used before the end of World War II, but all the photos clear enough to allow the capsules to be identified show pressure capsules (CM 5 or CM 9). Does anyone know of any clear photos showing an M 7 (or for that matter an M 8) being used on a CMV 3a prior to 1945, other than catalog photos? It seems as if the M 7 may have achieved substantial use only once it was incorporated into the U 47 microphone of the postwar era, but I don't know whether that conclusion is supportable or not; it's just an "I wonder" kind of thing.
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afterlifestudios

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Re: What is an "M7" Capsule?
« Reply #4 on: June 25, 2024, 09:31:26 AM »

Very interesting, David. When you mention “the 1932 date” are you referencing this spreadsheet, allegedly from Neumann in 1999? 

https://funkwerkes.com/web/wp-content/techdocs/MixedProAudio/Neumann-Microphone-Capsules.pdf
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gtoledo3

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Re: What is an "M7" Capsule?
« Reply #5 on: June 25, 2024, 10:59:31 AM »

David, is the Hochfrequenztechnik und Elektroakustik article the one that shows the way different shapes apart from a plastic ball will affect the frequency response of an omni? Trying to jog my
memory on materials that I have read which were prior to Neumann’s claims. There was definitely some such research article made prior to Neumann’s omni.

Also. My understanding is that M7, M8, etc, originally refer to the entire modular capsule assembly; capsule plus housing.

My understanding is that initially Neumann was working for AEG (or their predecessor, can’t recall this timeline aspect) when his earliest work on condensers was being done, and that they had also directly licensed the WE condenser tech. I recall hearing this from Oliver Archut at first, but then being able to confirm it through info from contemporaneous publications.
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David Satz

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Re: What is an "M7" Capsule?
« Reply #6 on: June 25, 2024, 04:49:57 PM »

John, yes, that series of tables anyway; it's been updated periodically and re-issued, and the later versions sometimes have important corrections as well as new information added. The latest version that I know of is dated October, 2019. It's available for download on www.neumann.com. I do wish that people wouldn't repost older versions of it since they may contain outdated information.

George, no, this is not that article; it's from the October, 1935 issue, pages 187-192. Since this reply gives me another lavish quota of 512 KB to fill, I'm taking the opportunity to post the next page of the article here. The New York Public Library has the original journal and although it's fragile, this past March they let me scan it on the wonderful scanner that they have in their art and architecture department, which is well equipped to scan bound volumes. The files here are at only half the resolution which that scanner actually delivers.

--As far as I'm aware, at this time the RRG type-approved only complete microphones under "M" designations; capsules (or capsule assemblies as you call them) were regarded as accessories. Telefunken followed a similar scheme--thus the "MZ" rather than "M" names for capsules in their catalogs and price lists; the "Z" stands for the German word Zubehör ("accessory").

--I'm keenly aware of Oliver's narrative, and wish that I could follow it up, but I have yet to come across any particular documentary support for it. I think he had an accurate notion of the cartel-like arrangement that existed among the producers of equipment for German broadcasting during the Weimar era, and even more so under the "command economy" of the Nazi era, with the RRG having been subsumed almost immediately under Goebbels' "Ministry for Propaganda and Public Enlightenment" in 1933. According to Oliver, AEG had (this must have been in the mid-1920s) licensed Western Electric's patents on the condenser microphone and was producing condenser microphones which naturally would have been pressure transducers. I've seen one photo that was allegedly of one such microphone, but no published listings that refer to it or any other AEG-produced types.

I would certainly like to know about the "contemporaneous publications" through which you say you confirmed whatever they may have confirmed for you. It's potentially tricky because AEG and Siemens each had their own, ostensibly competing Ela departments which were then moved into their daughter company Telefunken in 1931--and since each distributor back then insisted on the products being labeled as their own, and laboratory designs were often licensed for manufacture to one company or another, the fact that something is listed under one name or the other proves nothing about the actual origin of the equipment.

At any rate Mr. Neumann is said (not only by Oliver) to have been a kind of trainee at AEG, perhaps like an intern, working under the supervision of Eugen Reisz, who subsequently broke away and took Neumann with him. Neumann then developed the high-quality carbon microphone with marble base that was so widely used in German broadcasting, recording and public address applications for years afterward (sold as the "Reisz" microphone). And Mr. Neumann was (according to Oliver) also tasked at some point with working around the Western Electric patents on the condenser microphone--although there is an even more widespread story that Neumann left Reisz specifically because Reisz didn't want to develop condenser microphones. I suppose both stories could be true--but responsible history requires that some evidence be available.

The time relationship is furthermore unclear, such that one doesn't know whether it was AEG or Reisz who supposedly wanted Neumann to work around those patents. It sounds plausible enough to me--I really see very little (OK, actually nothing at all) new in Neumann's 1929 patent (DE 574 428) other than his choice of membrane material. Oliver's story may have come from the old Telefunken engineers whom he knew and had interviewed. But if so, all the parties to those conversations have died in the meantime. It's frustrating for anyone who wants to follow up and can't.
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