Loudspeaker having a voice coil and a piezoelectric feedback transducer

DETAILED DESCRIPTION What is claimed is: 1.
A loudspeaker comprising, a cone-shaped vibratory diaphragm having an inner portion secured to a coil form, a voice coil mounted on the coil form, means including the voice coil for vibrating the coil form and diaphragm, a piezoelectric transducer mounted on the coil form and comprising a thin plate of piezoelectric material having two opposed edges hingedly connected to the coil form and situated within the circumference of said voice coil and with its major surfaces lying in a plane substantially normal to the axis of the voice coil, and means for degeneratively coupling the output voltage of the piezoelectric transducer to an input of an amplifier adapted to drive the voice coil.
2.
A loudspeaker as claimed in claim 1 wherein the piezoelectric plate is rectangular and is clamped in rubber mounts along two opposed edges of the plate.
3.
A loudspeaker as claimed in claim 2, wherein the mounts are accommodated in a mounting board provided with printed wiring and on which electric components are inserted which together form an impedance transformer.
4.
A Loudspeaker as claimed in claim 2, further comprising a mounting board on which the rubber mounts are supported and wherein the mounting board is accommodated in a shallow cup which is coupled to the coil form and separates the piezoelectric transducer from the coil form in an airtight manner.
5.
A loudspeaker as claimed in claim 1 wherein the piezoelectric plate includes first and second electrodes and first and second electric connections connected to said first and second electrodes respectively, by means of solder drops of sufficient size to cause the natural frequency of the transducer and its suspension to exceed 3000 Hz.
6.
A loudspeaker comprising, a cone-shaped vibratory diaphragm having an inner portion secured to a coil form and an outer portion attached to a support member, a voice coil attached to the coil form for vibrating the coil form and the attached diaphragm, a transducer comprising a plate of piezoelectric material, means for mounting said piezoelectric plate on the coil form in non-cantilevered fashion within the circumference of said voice coil and with its major surfaces lying in a plane substantially normal to the axis of the voice coil so as to allow pivotal movement of the plate, and means for coupling the output voltage of the transducer to an input of an amplifier adapted to drive said coil