Panel-form loudspeakers

A loudspeaker system comprising:

• a member having selected values of certain physical parameters which enable the member to sustain and propagate input vibrational energy in a predetermined frequency range by a plurality of resonant bending wave modes in at least one operative area extending transversely of thickness such that the frequencies of the resonant bending wave modes along at least two conceptual axes of the operative area are interleaved and spread so that there are substantially minimal clusterings and disparities of spacings of said frequencies, the member when resonating having a plurality of sites at which the number of vibrationally active resonance anti-nodes is relatively high;
• an amplifier for amplifying a source signal;
• a first transducer coupled to the amplifier and mounted on the member at one of said sites on the member, the first transducer being capable of vibrating the member in the predetermined frequency range to couple to and excite the resonant bending wave modes in the member in response to the amplified source signal and cause the member to resonate and produce an acoustic output;
• a second transducer mounted on the member at one of said sites on the member for producing an output signal in response to resonance of the member due to incident acoustic energy, the second transducer adapted to couple to the resonant bending wave modes in the member and produce an output signal;
• and
• a signal receiver coupled to the second transducer for treating said output signal.