Our co-pending earlier patent application Ser. No. 08/707,012 includes general teaching as to nature, structure and configuration of acoustic panel members having capability to sustain and propagate input vibrational energy through bending waves in acoustically operative area(s) extending transversely of thickness usually (if not necessarily) to edges of the member(s). Specific teaching includes analyses of various specific panel configurations with or without directional anisotropy of bending stiffness through/across said area(s) so as to have resonant mode vibration components distributed over said area(s) beneficially for acoustic coupling with ambient air; and as to having determinable preferential location(s) within said area(s) for acoustic transducer means, particularly operationally active or moving part(s) thereof effective in relation to acoustic vibrational activity in said area(s) and related signals, usually electrical, corresponding to acoustic content of such vibrational activity. Uses are also envisaged in that earlier patent application for such members as or in "passive" acoustic devices, i.e. without transducer means, such as for reverberation or for acoustic filtering or for acoustically "voicing" a space or room; and as or in "active" acoustic devices with bending wave transducer means, including in a remarkably wide range of loudspeakers as sources of sound when supplied with input signals to be converted to said sound, and also in such as microphones when exposed to sound to be converted into other signals.
Our co-pending U.S. patent application Ser. No. 09/246,967, filed Feb. 9, 1999 concerns using features of mechanical impedance in achieving refinements to geometry and/or location(s) of bending wave transducer means for such panel members as or in acoustic devices. The contents of application Ser. No. 08/707,012 and 09/246,967 are hereby incorporated herein to any extent that may be useful in or to explaining, understanding or defining the present invention. These applications are collectively referred to herein as the "two prior patent applications."
This invention arises particularly in relation to active acoustic devices in the form of loudspeakers using panel members to perform generally as above (and as may be called distributed mode acoustic radiators/resonant panels later herein), but further particularly achieve satisfactory combination of pistonic action with bending wave action. However, more general or wider aspects of invention arise, as will become apparent.