Heron, Kenneth H;

Panel-form loudspeaker

To overcome acoustic distortion caused by local resonance in panel core cells, a resonant multi-mode radiator element is provided for a panel form loudspeaker with a functional upper frequency limit .function..sub.max. The element has skins and a cellular based core, the skins have a thickness h, a Young's modulus .EPSILON. a Poisson's ratio of .nu. and a material density .rho. and the core has a cell size lcell characterized in that the cell size lcell is less than equation (2).

What is claimed is:

1. A resonant multi-mode radiator element for a panel form loud speaker with a functional upper frequency limit .function..sub.max, the element having skins and a cellular based core, the skins having a thickness h, a Young's modulus .EPSILON. a Poisson's ratio of .nu. and a material density .rho., and the core having a cell size l.sub.cell characterised in that the cell size l.sub.cell is less than: ##EQU6##

2. A panel-form loudspeaker comprising a multi-mode radiator element; a mounting means which supports the element or attaches it to a supporting body in a free undamped manner, and an electro mechanical drive means coupled to the element which serves to excite a multi-modal resonance in the radiator panel in response to an electrical input within a functional frequency band for the loud speaker characterised in that the multi-mode radiator element is a multi-mode radiator element as claimed in claim 1.

3. A panel-form loudspeaker as claimed in claim 2 characterised in that no planform dimension is less than half the bending wavelength at the lower functional frequency limit of the loudspeaker.