Originally Posted: Sun, 03 July 2005
This is only a short history of the M7. (For additional info, check some of the Microtech Gefell sites.)
The M7's history, design and description is a bit confusing, because neither Neumann/Berlin nor Neumann/Gefell ever bothered to trademark the capsule. So now several manufacturers freely use the term "M7" without necessarily much regard for authenticity towards the original M7's features, dimensions or materials.
Today, Microtech Gefell (one of the original M7 manufacturers-the other being the old Neumann company which had relations during WWII and after with today's Gefell company and location) and various international capsule manufacturers make capsules that look but don;t necessarily perform, like an original M7 capsule.
1. The original (Neumann East/West/Gefell) M7 capsule made with PVC diaphragms (ca. 8-10µ thick) is the only one that can in my estimation be legitimately called "authentic". With few exceptions (see below) it has the dimensions, and material characteristics of the original- because it IS the original. But even here, you have versions and generations of the brass back plate design which vary slightly in build, and therefore, tone and character.
(For identification, there are slight design difference among and between Neumann and Gefell back plates. One is visible at the outer edge of the diaphragm: Post-war Neumann/Berlin M7 feature three distinct ridges, where the Gefell M7 to this day have two, just as those found in pre-WWII M7. Then there are different gaps between the ridges and widths of the grooves in between, as well. Another difference is how the sack-holes are arranged.)
2. Various manufacturers (including Gefell) make an M7- looking capsule, using an M7- inspired or copied brass backplate, but using the much easier to manufacture Mylar/Polyester/"PE"- diaphragm (mostly 6µ thin) instead of the very laborious PVC diaphragm.
In the case of Gefell, at least the brass backplate of this polyester capsule is "original M7", whereas all other manufacturers copy, more or less successfully, that backplate design.
If you want the sound of a true M7, there is only one way today to get it: Buy one of the very few, still intact, old stock Neumann/Berlin PVC M7 (made up until 1959), or a Gefell PVC M7 made until about 2005. (Current M7 PVC capsules by Microtech Gefell exhibit noticeable low-end loss, and other timbre changes, due to new PVC material they are using, and the retirement of the long-serving specialist who cast the membranes.)
Everything else, including Gefell's valiant effort of marrying the M7 backplate and diaphragm dimensions with modern diaphragm material using pre-manufactured polyester films, will most definitely sound differently., though not necessarily worse.
Oliver Archut adds this bit of history:
"I would include as "original M7" those made by MWL (Mechanische Werkstätten Lensaal) from 1945 to 1947 for the NWDR. (North West German Radio.) Because after the war the Neumann company was now located in Soviet-occupied Germany, with no access to their West German customers, MWL made these M7s for the (West German) broadcasters to the original Neumann blueprints. After Georg Neumann moved from temporary headquarters in Gefell back to (West) Berlin, MWL stopped production. Aside of the markings on the MWL capsules, these M7s are absolute identical to the Berlin-made M7 capsules before 1942."