Motional Feedback
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Motional Feedback (MFB) was a speaker system developed in the early 1970s by Philips. It introduced a feedback system to the woofers of HiFi loudspeakers, enabling them to achieve a more extended low frequency response in a relatively small enclosure.
The key benefits are a very controlled bass response. Any distortion induced by the enclosure or the woofer itself is immediately corrected by the feedback.
These hand-built speakers (primarily Dutch) had a very high production cost, while in the 1980s the market turned towards cheaper consumer electronics.