Loudspeakers
A loudspeaker comprising a resonant panel-form member adapted to produce an acoustic output and a vibration exciting system on the panel-form member and adapted to apply bending wave energy thereto, characterized in that the vibration exciting system is adapted to apply a bending couple to the panel-form member.
1. A loudspeaker comprising:
a panel-form member mounted on a suspension; and
a vibration exciting system mounted on the panel-form member;
the vibration exciting system being adapted to apply bending wave energy to the panel-form member and cause resonance, thereby producing an acoustic output;
wherein the suspension acts as a pivot, thereby supporting the panel-form member in a simple fashion and causing nodal lines corresponding to the resonance of the panel-form member to move towards an edge of the member as compared to a generally corresponding but resiliently or freely edge-suspended panel-form member;
the vibration exciting system being positioned so as to bridge across several of said nodal lines.
2. A loudspeaker according to claim 1 , wherein the vibration exciting system is adapted to apply shear to the panel-form member.
3. A loudspeaker according to claim 1 , wherein the vibration exciting system comprises a piezoelectric device attached to the panel-form member to apply a bending couple thereto by introducing alternating tension and compression to the panel-form member in the plane thereof.
4. A loudspeaker according to claim 3 , wherein the piezoelectric device is attached to a face of the panel-form member.
5. A loudspeaker according to claim 4 , comprising mirror-image piezoelectric devices attached to opposite faces of the panel-form member.
6. A loudspeaker according to claim 3 , wherein the piezoelectric device has a portion disposed adjacent to the suspension, and a portion disposed remotely from the suspension.
7. A loudspeaker according to claim 3 , wherein the piezoelectric device is a thin strip-like device fixed to the panel-form member by adhesive.
8. A loudspeaker according to claim 3 , wherein the piezoelectric device is a unimorph device.
9. A loudspeaker according to claim 8 , wherein the unimorph device comprises opposed parts arranged such that one part increases in length while the other part contracts.
10. A loudspeaker according to claim 1 or claim 3 , wherein the panel-form member is transparent.
11. A loudspeaker according to claim 10 , wherein the piezoelectric device is transparent.
12. A loudspeaker according to claim 3 , wherein the piezoelectric device is of PZT.
13. A loudspeaker according to claim 1 , wherein the vibration exciting system comprises an inertial device.
14. A loudspeaker according to claim 13 , wherein the inertial device comprises an inertial mass rigidly fixed to the panel-form member to form a suspension pivot.
15. A loudspeaker according to claim 13 , wherein the inertial device is an inertial vibration exciter.
16. A loudspeaker according to claim 15 , comprising opposed inertial vibration exciters on opposite sides of the panel-form member.
17. A loudspeaker according to claim 15 , comprising an additional inertial vibration exciter on the panel-form member and coupled to the first said inertial vibration exciter in anti-phase to damp unwanted whole body movement of the panel-form member.
18. A loudspeaker according to claim 1 , wherein said suspension comprises a high shear stiffness material.
19. A loudspeaker according to claim 18 , wherein said suspension comprises high shear stiffness foam plastics material.
20. A loudspeaker according to claim 1 , claim 18 or claim 19 , wherein the suspension acts as a pivot only in the region local to the vibration exciting system.
21. A loudspeaker according to claim 20 , wherein the suspension in regions other than the region local to the vibration exciting system is resilient.
22. A loudspeaker according to claim 21 , wherein the suspension in regions other than the region local to the vibration exciting system is soft foam material.