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Definition of "m7":
M7 designates a type of condenser microphone capsule manufactured by Microtech Gefell in the former East Germany. This was the original capsule found on Neumann’s U-47 microphone.
The primary distinguishing characteristic of the M7 is that the diaphragm is made of PVC plastic rather than polyester (Mylar) film. The plastic is poured and cooled, forming a material ranging from 8-12 microns in thickness. This is thicker than typical Mylar diaphragms (of 3-9 microns).
As of 2003, Gefell published that its PVC diaphragms were 10 microns thick. In 2009, noted microphone technician Andreas Grosser claimed that the original M7 diaphragms varied from 10–12µm thick.
Each M7 capsule consists of two PVC membranes that are glued to a single, shared backplate. This assembly process is also somewhat unique to the M7, in that most other condenser microphone capsules use screwed-down tension rings to attach and tune their diaphragms.
The M7 backplate measures 32mm in diameter; the diameter of the suspended portion of the membrane is 25mm. The two diaphragms are center-terminated.
Neumann (Berlin) stopped producing the M7 in 1958. As of this writing, the only two sources for PVC capsules are Microtech Gefell and ex-MTG technician Sigfried Thiersch (whose STW7 is available with either diaphragms made of either Mylar or 6-micron PVC).
Read Klaus Heyne’s History of the M7 Capsule, and his 2009 - State of the M7 report.
Note that early Neumann microphones were equipped with M7 capsules as well, from 1949 until about 1960, when Neumann began using the K47 capsule in place of the M7. (The K47 retained the M7’s single-backplate architecture, but swapped Mylar for PVC as a membrane material, and attached the membranes via a screwed-down tensioning ring rather than with glue.)
The black ring around the circumference of the capsule in the photo above is a “protection cover [used] to [create] better isolation between electrode and membrane.”
Read Andreas Grosser’s M7 recollections.
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side-address large-diaphragm tube multipattern condenser transformer-coupled ef12 vf14 ef14 bv8 uf14 replica f7 center-terminated pvc lmg-95-es mullard ami multitrack thiersch ef86 cinemag continuously-variable pd86 dual-diaphragm k47 single-backplate 5840 ef732 telefunken bv8lp 6072 vf14k ec92 tripolar um351 ac701 msc2 mogami transformerless pressure-gradient hpf dl651 dl67 lundahl 6n1p b4 detachable-capsule b7 b6 b2 b3 b5 b0 b1
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side-address large-diaphragm tube multipattern condenser transformer-coupled ef12 vf14 ef14 bv8 uf14 replica f7 center-terminated pvc lmg-95-es mullard ami multitrack thiersch ef86 cinemag continuously-variable pd86 dual-diaphragm k47 single-backplate 5840 ef732 telefunken bv8lp 6072 vf14k ec92 tripolar um351 ac701 msc2 mogami transformerless pressure-gradient hpf dl651 dl67 lundahl 6n1p b4 detachable-capsule b7 b6 b2 b3 b5 b0 b1
