motional feedback (loud speaker) (MFB)

Motional Feedback (MFB) is a designation from Philips from the 70s for a current feedback in loudspeakers. With this method, the diaphragm movement of woofers can be linearized and the movement stroke can be controlled.

Since there is little space available for small loudspeakers in mobile devices, but the sound volume is still to be improved by bass reproduction, the technology of motional feedback is also used in mobile devices. With MBF technology, loudspeakers with small diaphragms can be controlled in the diaphragm stroke, whereby even very low frequencies can be reproduced without distortion.

In the MFB method, the current in the voice coil is compared with the input signal for this purpose. The resulting error signal is coupled in phase opposition to the amplifier input. This negative feedback ensures that the voice coil current is proportional to the input signal.