The Klangfilm GmbH was founded in 1928 by AEG and Siemens & Halske AG, they pooled their expertise in sound-on-film technology and supplied Europe and the rest of the world (aside the US) with talking sounds equipment.
The focus was on the development, production and sale of cinema and sound film equipment. In 1941, as part of the agreements known as the "Telefunken settlement," Siemens & Halske AG took over the shares previously owned by AEG and in return AEG gain 100% control over Telefunken.
After WWII the name was changed to Siemens-Klangfilm and in the mid 70s the Klangfilm name disappeared, up to the mid 80s the production continued under Siemens but eventualy the company was dissolved end of the 80s.
From 1928 on Klangfilm developed and build all needed equipment in their own manufacturing plant, with minor help form both of the main owner corporation. Everything from tubes, x-former, projector, microphones (they made a killer version of their own M7 type capsule).
After the war everything changed and Klangfilm became just a trade name and sold relabeled products, made by Siemens, Telefunken, Bauer and Neumann/Schoeps. (There are a few U47 labeled as Siemens with a Klangfilm logo on the back)
The pre war equipment sells for insane amount of money these days; a portable (wartime) movie theater sold for up to $10K on eBay not to long ago.... I remember scapping similar ones in the 80s...
The post war equipment is either the Siemens/Telefunken/TAB U/V series , or WSW made items (Wiener Schwachstrom Werke = Vieana low current Manufacturing Plant) relabeled to Klangfilm.
There is a very good Klangfilm web-page
http://klangfilm.free.fr/ by a French gentleman, with lots of good infos and even more pics...
Best regards,