Moving coil loudspeaker with feedback arrangement - has parabolic reflector with optical sensor in circuit with output amplifier

摘要

The membrane (17) of a moving coil loudspeaker has a mirror-like surface (18) on its concave surface which acts as parabolic reflector. A source of light (21) mounted in a cylindrical opening of the axial core of the loudspeaker magnet system (12, 13, 14) casts a beam of light onto the mirrored face of the membrane in such a manner that the reflected light converges on a light sensitive cell (20) positioned close to the focal point of said mirror. Axial movements of the membrane would be accompanied by a shift in the focal point and therefore by corresp. increases and decreases of the light density received by the photocell (20). From this, derive signals that may be fed back to the input of the output amplifier. The concept can be realised also in modified forms. Common to the different versions is the fact that the membrane of the moving coil and its excursions from a quiescent condition determine the amount and phase of the negative feedback.