Motional Feedback
Motional Feedback (MFB) is the name of an active high fidelity loudspeaker system which was developed by the Dutch Philips brand in the early 1970s. The loudspeakers had built-in amplifiers and featured a revolutionary feedback sensor on the woofer. The sensor measured the output signal of the woofer and compared it to the amplifier input signal. This resulted in a very low distortion and furthermore a more extended low frequency response in a relatively small enclosure. Any distortion induced by the enclosure or the woofer itself is immediately corrected by the feedback loop.
Although the Motional Feedback technology had been experimented with for several years, Philips was the first company to successfully create a working prototype and create a commercial product line of loudspeakers and equipment. Product Manager of the Philips High Fidelity group, Piet Gouw, was responsible for the launch of most of the Motional Feedback loudspeakers and other High Fidelity equipment. Even today, at the age of 86, Piet is an active member of MFBfreaks.com, the home of Motional Feedback collectors. He shares historical stories and answers questions on the MFBfreaks.com forum.
Even today, Motional Feedback is used by High End audio designers. It is said that Tentlabs owner Guido Tent has recently designed an active subwoofer which uses Motional Feedback technology.