A collection of articles on motional feedback
Motional feedback was invented decades ago, but the information is generally a bit hard to get online. Here is a collection of links to this technology.
Some commercial products
links are randomly arranged, it does not represent any forms of ranking
https://www.soundonsound.com/music-business/story-philips-rh544
https://www.hifinews.com/content/philips-ah585-loudspeaker
https://piratelogic.nl/
https://velodyneacoustics.com/en/products/digital-drive-plus/
https://www.rythmikaudio.com/
https://gr-research.com/product-category/subwoofers/
https://rmsacoustics.nl/activecontrol.html
https://www.grimmaudio.com/pro-products/pro-loudspeakers/pro-sb1/
And Some Hobbyist Attempts
https://www.by-rutgers.nl/PDFiles/Motional%20Feedback.pdf
https://circuitstoday.com/motional-feed-back-amplifier
https://www.mfbfreaks.nl/motional-feedback-mfb/
https://www.vintage-radio.net/forum/showthread.php?t=147781
https://www.hifisystemcomponents.com/forum/philips-mfb-speakers_topic4557.html
There are also a few articles on the related non-linearities motional feedback trying to solve