Hybrid sound radiation device for vibrating a heavy-weight rigid plate at audio frequencies

A hybrid sound radiation device (100) for vibrating a heavy-weight rigid plate at audio frequencies, the device comprising:

• a fixed support member (120);
• a permanent magnet (210), one end of which is fixed to the support member (120);
• a fixed first coil (220) arranged around the permanent magnet (210), the central axis of which defines a primary axial direction (110);
• a second coil (240) disposed around the first coil (220) and movable along the primary axial direction (110),
• an intermediate member (140) to a first side of which an end of the second coil (240) remote from the support member (120) is attached and said intermediate member (140) is guided along guide support members (130) attached to the support member (120) and extends in the primary axial direction (110);
• a fluid reservoir attached to the second side of the intermediate member (140) opposite the first side, having a side wall of variable length along the first axial direction (110), and
• wherein the fluid reservoir contains a medium (310) comprising at least one thixotropic fluid and a predetermined mixture of a rheopectic fluid and a magnetorheological fluid, wherein the three-fluid medium (310) has a substantially constant viscosity as a function of frequency, and
• wherein a third coil (330) is arranged around the side wall (320) of the fluid reservoir, the central axis of which is parallel to the primary axial direction (110), and
• wherein a first electrode (340) and a second electrode (350) of opposite polarity are provided in the fluid reservoir at its side connected to the intermediate member (140), the electrodes (340, 350) providing a substantially constant electric field inside the fluid reservoir;
• a vibrating element (160) in the form of a heavy-weight, rigid, planar plate rigidly connected to the side of the fluid reservoir opposite the intermediate member (140);
• and
• control circuits (270, 370) connected to the first, second and third coils (220, 240, 330) and the electrodes (340, 350).