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M7 / K47 remarks
Author: Posted by Klaus Heyne
Date: 02/26/2004
After a recent (criticaI) comment regarding the successor to the M7, I checked the Archives for info- it's rather thin.
The recent craze and myths building around the M7 capsule justifies an update on it and its successor, the K47/49.
1. The introduction of the K47/49, according to Neumann, was 1960. I would like to disagree- politely and with all deference to the Grand Poopas in Berlin. I have had in my hands plenty of K47 that came out of never-opened U47, U48 and M49 with capacitor-and other component date codes from 1958, and, in the case of M49, with design elements that were introduced in 1958 and 1959. Unless all these mics were retrofitted in Berlin after the fact, my belief is that the K47 was installed as early as Fall 1958 in most large diaphragm products.
2. Original M7s -well justified myth not withstanding- are not an option for serious recordists today: with few exceptions, the original ones are all deteriorated beyond fidelity and beyond any reasonable S/N (even new, the output/S/N was ca. 4dB lower than that of a K47.) This of course is due to the PVC materials that were used. The audible changes and drying-up tendencies of the M7 pretty much started as soon as it was poured, and never stopped until it was deteriorated beyond usability.
3. Aftermarket suppliers do not use PVC diaphragms on M7 backplates (whether original- or copy-backplates). Most likely, because no one knows how to pour PVC anymore. Exception: Microtech Gefell (stellar capsules with consistently tight tolerances, but not for sale) and one independent German diaphragm refurbisher (fairly good, but he no longer does it anymore either) Aftermarket suppliers instead use PET/PE/Mylar/Polyester diaphragms which are significantly thinner (typically 5 micron) and have different mechanical properties with audibly different results.
4.The K47 which, except for some minor changes, is still identical to that made in the late Nineteen-Fifties, is a time-stable, well-balanced product with audible properties that often equal (a few even surpass) good, original M7 in their sensual beauty.
No question- a few K47 of current production are barely tolerable in their mediocrity, but, like all capsules made by any manufacturer, so were some of the M7 in their time. The difference here is that Neumann stands behind the current product: on the rare occasions where I had to send a K47 back because of questionable sound, Neumann replaced it without a fuss. I find the K47 to have one of the tightest manufacturing tolerances ever achieved by any capsule manufacturer. With other words, when retrofitting it into an old U47 or M49, I am often astonished at the level of life and personality it consistently pumps again into these mics.
In summary, I reject the claim, often advanced by those who know the least, that today the M7 is a superior alternative to the K47, or that the K47 is sonically inferior to the M7.
Both Neumann products have a secure spot in the Hall of Fame of microphone capsules- one in the historical wing, the other as one of the finest capsules made by anyone today.
Kind regards, Klaus Heyne  
Posted by Klaus Heyne
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