Acoustic actuators
An acoustic transducer comprises an active element which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass and a foot which in use engages a surface whereby audiofrequency vibrations produced by the active element are transmitted to the surface, characterised in that the foot is hingedly connected to the inertial mass and the active element is located between the foot and the mass such that the angle between the first axis and the surface is less than 90°, in use.
1. An acoustic transducer adapted to co-operate with a surface to induce into the surface audiofrequency vibrations whereby the surface radiates sound therefrom, the transducer comprising an active element which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass and a foot which engages a surface whereby audiofrequency vibrations produced by the active element are acoustically coupled into the surface, wherein the foot is hingedly connected to the inertial mass and the active element is located between the foot and the mass such that the angle between the first axis and the surface is less than 90°, and the connection between the inertial mass and the foot comprises a resiliently flexible material.
2. An acoustic transducer according to claim 1 , wherein the said angle is 45° or less.
3. An acoustic transducer according to claim 1 , wherein the first axis extends substantially parallel to the surface.
4. An acoustic transducer according to claim 1 , wherein the connection between the inertial mass and the foot comprises a resiliently flexible material.
5. An acoustic transducer according to claim 1 , wherein the resiliently flexible material is a low compliance material.
6. An acoustic transducer according to claim 1 , wherein said material is spring steel.
7. An acoustic transducer according to claim 1 , wherein the centre of the foot is directly below the centre of gravity of the transducer.
8. An acoustic transducer according to claim 1 , wherein the inertial mass includes one or more of batteries, electrical circuitry, and a housing for the transducer.
9. An acoustic transducer according to claim 1 , wherein the active element comprises a magnetostrictive material.
10. An acoustic transducer according to claim 1 , wherein the active element comprises a piezoelectric material.
11. An acoustic transducer adapted to co-operate with a surface to induce into the surface audiofrequency vibrations whereby the surface radiates sound therefrom, the transducer comprising an active element which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass and a foot which engages a surface whereby audiofrequency vibrations produced by the active element are acoustically coupled into the surface, wherein the foot is hingedly connected to the inertial mass and the active element is located between the foot and the mass such that the angle between the first axis and the surface is less than 90°, wherein the centre of the foot is directly below the centre of gravity of the transducer.
12. An acoustic transducer according to claim 11 , wherein the said angle is 45° or less.
13. An acoustic transducer according to claim 11 , wherein the first axis extends substantially parallel to the surface.
14. An acoustic transducer according to claim 11 , wherein the active element comprises a magnetostrictive material.
15. An acoustic transducer according to claim 11 , wherein the active element comprises a piezoelectric material.
16. An acoustic transducer adapted to co-operate with a surface to induce into the surface audiofrequency vibrations whereby the surface radiates sound therefrom, the transducer comprising an active element which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass and a foot which in use engages a surface whereby audiofrequency vibrations produced by the active element are acoustically coupled into the surface, wherein the foot is hingedly connected to the inertial mass and the active element is located between the foot and the mass such that the angle between the first axis and the surface is less than 90°, wherein the inertial mass includes one or more of batteries, electrical circuitry, and a housing for the transducer.
17. An acoustic transducer according to claim 16 , wherein the said angle is 45° or less.
18. An acoustic transducer according to claim 17 , wherein the first axis extends substantially parallel to the surface.
19. An acoustic transducer according to claim 16 , wherein the active element comprises a magnetostrictive material.
20. An acoustic transducer according to claim 16 , wherein the active element comprises a piezoelectric material.
21. An acoustic transducer adapted to be located against a surface to induce audiofrequency vibrations into said surface whereby said surface radiates sound therefrom, the transducer comprising an active element which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass and a foot which engages a surface whereby audiofrequency vibrations produced by the active element are acoustically coupled into the surface, wherein the foot is hingedly connected to the inertial mass and the active element is located between the foot and the mass such that the angle between the first axis and the surface is less than 90°.
22. An acoustic transducer according to claim 21 , wherein the said angle is 45° or less.
23. An acoustic transducer according to claim 22 , wherein the first axis extends substantially parallel to the surface.
24. An acoustic transducer according to claim 21 , wherein the active element comprises a magnetostrictive material.
25. An acoustic transducer according to claim 21 , wherein the active element comprises a piezoelectric material.