MFB LOUD SPEAKER

摘要

PURPOSE:To reduce the distortion of the sound which is given through a loud speaker without increasing the weight of a vibrating system, by detecting the vibrating displacement of a diaphragm optically and indirectly to convert it into an electric signal and applying this electric signal as a negative feedback signal of a driving amplifier of the diaphragm. CONSTITUTION:A light emitting element 1 and a photodetector 2 are provided on the upper edge planes of a yoke and a center pole 13 to face oppositely the surface 3 of a light reflecting plate of a diaphragm 4 which is parallel to the upper edge plane of the pole 13. The light irradiated from the element 1 is reflected by the surface 3 and made incident to the detector 2. The quantity of the light to be made incident to the element 2 varies by the position of the surface 3 which responses to the vubrating displacement of the disphragm 4 and the output current of the element 2 increases/decreases accordingly. Thus the signal are obtained in response to the vibrating displacement of the disphragm 4. Then the electric signal given from the detector 2 is applied to an adverse phase input terminal of a driving amplifier 18 as a negative feedback signal through an amplifier 6 and a differentiater 17. In such a way, the distortion is reduced for the sound radiated through a loud speaker without increasing the weight of a vibrating system.