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, the two legitimate companies that legitimately can claim having manufactured the original M7 PVC capsule, ever bothered to trademark "M7".
So now several manufacturers freely use the term without necessarily much regard for authenticity towards the original M7's features, dimensions or materials, let alone sound.
To distinguish:
1. The original (Neumann East/West/Gefell) M7 capsules were made with PVC diaphragms (ca. 8-10µ thick) - the only version that in my estimation can legitimately be called "authentic". With few exceptions (see below) it still has the dimensions, and material characteristics of the original invented in the 1930s by Georg Neumann with the help of Erich Kühnast. But through the years and location of manufacture versions of the brass back plate design vary slightly in build, and therefore, in tone and character.
For identification, there are slight design differences among and between Neumann Berlin and Gefell back plates. One is visible at the outer edge of the diaphragm: post-war Neumann/Berlin M7 feature three distinct ridges (bearing edges), 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. The easiest way to visually distinguish Gefell from Berlin M7 is the center lead-out screw, which is tiny in the Gefell version - .2mm smaller compared to the M7 made in Berlin
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 laborious PVC diaphragm which only a small handful of specialists know how to cast.
In the case of Gefell, at least the brass backplate of this polyester capsule is "100% original M7", whereas all other manufacturers copy, more or less successfully, that backplate design.
But there comes another problem for copycats: what was magic synergy between an 8-10µ PVC diaphragm with a peculiar resonance behavior and the original backplate construction sounds at best mediocre, often coarse and strident when combining that backplate design with a modern 6µ polyester diaphragm: the sound is off, decidedly not magic, and all those who copy that particular diaphragm/backplate combination end in a cul-de-sac with no way out.
If you want the sound of a true M7 today, there is only one way 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 used to cast their 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 different.
Oliver Archut added 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."
