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, characterised in that the vibration exciting system is adapted to apply a bending couple to the panel-form member.
1 . A loudspeaker comprising a resonant panel-form member and a vibration exciting system on the panel-form member and adapted to apply bending wave energy to the panel-form member by applying torsion thereto to cause the panel-form member to produce an acoustic output.
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 or claim 2 , wherein the vibration exciting system is coupled to the panel-form member to span a plurality of nodal lines in the panel-form member.
4 . A loudspeaker according to claim 1 , wherein the vibration exciting system comprises a suspension on which the panel-form member is mounted, the suspension acting as a pivot about which at least a portion of an edge of the panel-form member local to the vibration exciting system can hinge.
5 . A loudspeaker according to claim 4 , wherein the suspension is of a plastics foam of high shear stiffness.
6 . 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.
7 . A loudspeaker according to claim 6 , wherein the piezoelectric device is attached to a face of the panel-form member.
8 . A loudspeaker according to claim 7 , comprising mirror-image piezoelectric devices attached to opposite faces of the panel-form member.
9 . A loudspeaker according to claim 6 , wherein the piezoelectric device has a portion disposed adjacent to the suspension, and a portion disposed remotely from the suspension.
10 . A loudspeaker according to claim 6 , wherein the piezoelectric device is a thin strip-like device fixed to the panel-form member by adhesive.
11 . A loudspeaker according to claim 6 , wherein the piezoelectric device is a unimorph device.
12 . A loudspeaker according to claim 11 , wherein the unimorph device comprises opposed parts arranged such that one part increases in length while the other part contracts.
13 . A loudspeaker according to claim 1 , claim 4 or claim 6 , wherein the panel-form member is transparent.
14 . A loudspeaker according to claim 13 , wherein the piezoelectric device is transparent.
15 . A loudspeaker according to claim 6 , wherein the piezoelectric device is of PZT.
16 . A loudspeaker according to claim 1 or claim 4 , wherein the vibration exciting system comprises an inertial device.
17 . A loudspeaker according to claim 16 , wherein the inertial device comprises an inertial mass rigidly fixed to the panel-form member to form a suspension pivot.
18 . A loudspeaker according to claim 16 , wherein the inertial device is an inertial vibration exciter.
19 . A loudspeaker according to claim 18 , comprising opposed inertial vibration exciters on opposite sides of the panel-form member.
20 . A loudspeaker according to claim 18 , 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.
21 . A loudspeaker according to claim 1 or claim 4 , wherein the vibration exciting system comprises an electrodynamic motor having a rotor with a current-carrying conductor array fixed to the panel-form member with its axis parallel to the plane of the member to apply torsion thereto, and a magnet forming a magnetic field in which the rotor is positioned.
22 . A loudspeaker according to claim 1 or claim 4 , wherein the vibration exciting system comprises a bimorph piezoelectric device which is generally rectangular and orientated diagonally to act as a twister.
23 . A loudspeaker according to claim 1 or claim 4 , wherein the vibration exciting system comprises an element rigidly coupled to and projecting away from the panel-form member, and an exciter which induces bending moments in the element.
24 . A loudspeaker according to claim 23 , wherein the element is generally perpendicular to the panel-form member, bending moments are produced by displacement in a part of the element spaced from the panel-form member, and the displacement is generally perpendicular to the element.
25 . A loudspeaker according to claim 24 , wherein the displacement is effected using a piezoelectric device.
26 . A loudspeaker according to claim 24 , wherein the displacement is effected by an inertial device.
27 . A method of making a loudspeaker having a resonant panel-form member adapted to be excited to produce an acoustic output by the application of bending wave energy, comprising defining the panel-form member, mapping the panel-form member to determine the location of nodal lines, arranging a vibration exciting system on the panel-form member to apply bending wave energy thereto, with the exciting system spanning a plurality of the nodal lines and mounting the vibration system exciting to the panel-form member to apply a couple thereto.
28 . A method according to claim 27 , wherein the panel-form member is defined in terms of geometry, size and/or mechanical impedance.
29 . A method according to claim 27 or claim 28 , wherein the panel-form member is mapped using finite element analysis.
30 . A method according to claim 27 , comprising mounting the panel-form member on a suspension such that the suspension acts as a pivot about which an adjacent portion of the panel-form member can hinge, and arranging and mounting a vibration exciter on the adjacent portion of the panel-form member to bend the panel-form member.
31 . A vibration exciter for applying bending wave energy to a stiff resonant loudspeaker panel-form member and adapted to apply a bending couple to the member.