Acoustic device

DETAILED DESCRIPTION What is claimed is: 1.
An acoustic device adapted for operation over an operative frequency range of interest, comprising: a substantially rectangular member extending transversely of its thickness and capable of sustaining bending waves at least over an intendedly active area of the transverse extent of the member, the member having certain physical parameters the values of which affect the distribution of resonant modes of bending wave vibration over the active area of the member, said parameters having selected values such that the resonant bending wave modes are beneficially distributed in frequency over the active area of the member so that the member is a well-behaved acoustic element when vibrating in the frequency range of interest, wherein the member has a cellular core having a shear modulus of at least about 10 megapascals, and a skin having a Young's modulus of at least about 1 gigapascal, and a transducer coupled to the member in a region of the active area of the member where a plurality of lower frequency resonant bending wave modes in the operative frequency range of interest have vibrationally active anti-nodes so that the transducer will couple with the resonant bending wave modes.
2.
An acoustic device according to claim 1, adapted for use as either of a loudspeaker and a microphone.
3.
An acoustic device according to claim 1, wherein said parameters are associated with at least two different directions across the active area of the member.
4.
An acoustic device according to claim 3, wherein said parameters comprise geometrical shape and bending stiffness.
5.
An acoustic device according to claim 3, wherein said parameters comprise the lengths of the major and minor axes of the member.
6.
An acoustic device according to claim 5, wherein the lengths of the major and minor axes of the member are selected such that the frequencies of the resonant bending wave modes along one of said axes substantially do not overlap with the frequencies of the resonant bending wave modes along the other of said axes