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Capacitive motional feedback for loudspeakers

Welcome to the site. Here you can find information about the capacitive motional feedback method for loudspeakers. This system comprises of cylindrical capacitor placed inside the voice coil former of the loudspeaker driver. Please read Tech -section or more comprehensive "white paper" with measurements for more information. Picture on the left also shows the measurement capacitor as red / green.

Using this feedback method, THD (Total Harmonic Distortion) of a typical loudspeaker driver at lowest frequencies is reduced significantly. In some measurements THD drops below one fourth (12dB) of the THD of the same speaker driver without motional feedback. Typical drop in THD is about 50% (6dB) at 20 Hz. This method can also be used to modify the frequency response of the speaker.

What does motional feedback mean?

Motional feedback in loudspeaker means using some method for measuring the motion of loudspeaker diaphragm (usually cone) and using this measurement to alter the speaker's driving voltage and/or current so that the diaphragm moves the way it is wanted to.


Forum was removed because most of the traffic was caused by spambots (and because the forum was broken during the change of web-hotel (my bad)).


This method was presented on the may issue of the Hi-Fi World magazine (on sale 31st March 2008). The article "Historically speaking" states: "Servo Speaker's drive unit design - Motional Feedback lives on!". Although the company called "Servo Speaker" does not exist (at least not currently), the article is very interesting read with many technical innovations mostly from the past (as can be assumed from the title).

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