Motional Feedback

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Motional Feedback (MFB) is an active high fidelity loudspeaker system[1] which was developed by the Dutch Philips brand in the early 1970s. The loudspeakers have built-in amplifiers and feature a feedback sensor on the woofer. The sensor measures the output signal of the woofer and compares it to the amplifier input signal.[2] This results in very low distortion, as any distortion induced by the enclosure or the woofer itself is immediately corrected by the feedback loop.[3] This low distortion also allows for extended low frequency response in a relatively small enclosure. To a degree, the sensor-feedback system also compensates for non-optimal room acoustics.[citation needed]

Although the Motional Feedback technology had been experimented with for several years, such as G.H. Brodie's 1958 patent on a feedback system using capacitive sensors,[4] Philips was the first company to successfully create a working prototype and create a commercial product line of loudspeakers and equipment,[4] starting with the RH541. The 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.[citation needed] Today[when?], at the age of 86, Gouw is an active member of MFBfreaks.com, the home of Motional Feedback collectors.[citation needed] He shares historical stories and answers questions on the forum.[citation needed]

Today,[when?] Motional Feedback is used by high-end[clarification needed] audio designers. Grimm Audio / Tentlabs have developed the Pro-ls1s-dmf, a digital motional feedback subwoofer which, according to the company, lowers low frequency distortion by 30dB.

A commercial product aimed at the end-consumer market is developed and build by Dutch Archidio, and uses the same technology as the original Philips implementation.

## References

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1. ^ Stereo Review. CBS Magazines. 1977.
2. ^ Hi-fi News & Record Review. Link House Publications. 1981.
3. ^ John Borwick (10 September 2012). Loudspeaker and Headphone Handbook. CRC Press. pp. 278–. ISBN 978-1-136-12086-2.
4. ^ a b "Philips RH 545 Studio". Inner Magazines. 2021-09-08. Retrieved 2025-02-13. "Philips did not invent motion(al) feedback. As early as 1958, G.H. Brodie left a patent on a plate capacitor structure that controls the movement of the cone. … starting with the small RH541"

## External links

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* MFBfreaks.com - Official Philips Motional Feedback (MFB) collectors' website with Piet Gouw stories (in Dutch)
* Another Philips MFB website (in Dutch)
* MFB Patente, Funktion (in German)
* Panasonic MF-800 Motional Feedback power amplifier and speakers from the 1960s using Luxman technology
* Panasonic Motional Feedback Article from the Miami News, October 19, 1964.