Patents and Trademarks
Most of the patents covering Ambisonic developments have now expired (including those covering the Soundfield microphone) and, as a result, the basic technology is available for anyone to implement. Exceptions to this include Dr Geoffrey Barton's Trifield technology, which is a three-speaker stereo rendering system based on Ambisonic theory (US 5594800 ), and so-called "Vienna" decoders, based on Gerzon and Barton's Vienna 1992 AES paper, which are intended for decoding to irregular speaker arrays (US 5757927 ).
The "pool" of patents comprising Ambisonics technology was originally assembled by the UK Government's National Research & Development Corporation (NRDC), which existed until the late 1970s to develop and promote British inventions and license them to commercial manufacturers – ideally to a single licensee. The system was ultimately licensed to Nimbus Records (now owned by Wyastone Estate Ltd) who hold the rights to the "interlocking circles" Ambisonic logo (UK trademarks 1113276 and 1113277), and the text marks "AMBISONIC" and "A M B I S O N" (UK trademarks 1500177 and 1112259).
Note that applications to register the word marks (trademarks) "AMBISONICS" and "AMBISONIC" in the USA were abandoned in 1992 and 2009 (US trademark serial numbers 74118119 and 77695983).
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