Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-06-18
2001-08-21
Woo, Stella (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S190000, C381S431000, C310S324000
Reexamination Certificate
active
06278790
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electro-acoustic transducers for generating acoustic waves. An audio loudspeaker is an example of such a transducer. More particularly, the invention relates to transducers which include a panel, such as a flat panel, which can be vibrated to generate sound and one or more actuators for receiving a driving signal and vibrating in response thereto, the actuator(s) being coupled to the panel at one or more locations remote from the edges of the panel so that the panel vibrates, in response to the vibration of the actuators(s), in a multi-modal, non-pistonic, bending manner without any significant bodily translational movement of the panel.
DESCRIPTION OF RELATED ART
Such transducers are known in which the panel is made to vibrate in a multi-modal, non-pistonic manner, ie with bending vibrations in the panel rather than any significant bodily translational movement of the panel. In order to prevent any significant bodily translational movement, the panel is either rigidly clamped in a rigid frame, or is supported in a frame by a soft elastic suspension at its corners. A problem with such transducers, and with which a first aspect of the present invention is concerned, is that sound is generated from both sides of the panel and is allowed to interfere. Thus, if the panel is placed near an acoustically reflective surface, for example a wall, considerable interference can take place between the sound generated from the front of the panel and the sound generated from the back of the panel.
BRIEF SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, a frame is provided for mounting the panel, and a seal is arranged between the frame and the edges of the panel for holding the panel in the frame, substantially isolating the frame acoustically from the edges of the panel, and substantially sealing the frame to the edges of the panel. Thus, acoustic vibrations in the air generated by the front and rear faces of the panel can be acoustically isolated and prevented from interfering, whilst acoustic reflections at the edges of the panel can be reduced. In other words, the seal can act as a barrier to acoustic vibrations passing around the panel member, and also act to damp out acoustic reflections at the interface between the panel and the frame, thus acting as a semi-anechoic termination.
(It should be noted that patent document JP-A-58-007999 shows a flat-plate transducer, the plate being arranged to vibrate in a single-mode, pistonic, bending manner with significant bodily translational movement of the plate, and the plate being mounted to a frame by peripheral rubber ring.)
Preferably, the seal comprises a strip of flexible resilient material, which may be arranged to wrap around the edges of the panel. (It should be noted that patent document JP-A-56-056095 discloses a different type of transducer, but with a vibratable plate mounted edge-to-edge inside a frame with an H-section element between the edges.) The strip may be received in a channel in the frame, and the strip may provide a channel which receives the edges of the panel. Conveniently, the strip may be formed from a length of resilient tubing, for example of silicone rubber, cut lengthwise and opened to clamp over the edges of the panel.
In some embodiments, the frame forms part of an enclosure disposed generally to one side of the panel. Thus, the enclosure can be arranged to absorb and damp out vibrations produced from one side of the panel, and sound can be radiated from the other side of the panel, with the seal substantially preventing sound from escaping from the enclosure to the outside.
The transducer may further include: a second panel which can be vibrated to generate sound and which is mounted to the frame; second coupling means for mechanically and acoustically coupling the second panel to the first panel and/or the actuator means at one or more locations remote from the edges of the second panel so that the second panel also vibrates, in response to vibration of the actuator means, in a multi-modal, non-pistonic, bending manner without any significant bodily translational movement of the second panel; and a second seal arranged between the frame and the edges of the second panel for holding the second panel in the frame, substantially isolating the frame acoustically from the edges of the second panel, and substantially sealing the frame to the edges of the second panel. If the first and second panels are parallel to each other, then the first and second seals can prevent sound generated in the space between the panels from escaping to interfere with sound generated from the other sides of the panels. If the first and second panels are side-by-side, then the seals have the same effect as if there were only one panel. (It should be noted that patent document WO-A-96-35313 shows a transducer having a pair of parallel panels rigidly fixed to a frame and bridged by an actuator which causes each panel to vibrate in a single mode, pistonic, bending manner with significant bodily translational movement of the panels.)
The first and second seals may have different acoustic isolation properties to assist in providing a flatter frequency response for the transducer as a whole, so that, for example, a trough in the frequency response of one of the panels coincides with a peak in the frequency response of the other panel.
A second aspect of the present invention is concerned with making other improvements to known electro-acoustic transducers of the type described in the opening paragraph. In accordance with the second aspect of the present invention, there is provided an electro-acoustic transducer, comprising: first and second panels each of which can be vibrated to generate sound; actuator means for receiving a driving signal and vibrating in response thereto; first coupling means for mechanically and acoustically coupling the first panel to the actuator means at one or more locations remote from the edges of the first panel so that the first panel vibrates, in response to vibration of the actuator means, in a multi-modal, non-pistonic, bending manner without any significant bodily translational movement of the panel; and second coupling means for mechanically and acoustically coupling the second panel to the first panel and/or the actuator means at one or more locations remote from the edges of the second panel so that the second panel also vibrates, in response to vibration of the actuator means, in a multi-modal, non-pistonic, bending manner without any significant bodily translational movement of the second panel. The first and second panels may therefore have different acoustic properties and/or the first and second coupling means may have different acoustic coupling properties to assist in providing a flatter frequency response for the transducer, again, for example, by arranging that a trough in the frequency response of one of the panels coincides with a peak in the frequency response of the other panel.
It should be noted that features of the first and second aspects of the invention described above may be combined in a single transducer.
In some embodiments of either aspect of the invention, the first and second panels are arranged face-to-face. In this case, the second coupling means may be arranged to couple the second panel mechanically and acoustically to the first panel. In one embodiment, the second panel has at least one aperture therein which receives the actuator means. Alternatively, the second coupling means may be arranged to couple the second panel mechanically and acoustically to the actuator means. In this case, the actuator means may be common to the first and second panels and may comprise at least one piezo-electric actuator bridging between the first and second coupling means. In this case, the, or at least one of the, piezo-electric actuators may comprise a stack formed of layers of piezoelectric material.
In other embodiments, the first and second panels are arranged side-by-side, and the second coupling means is
Davis Gillian Margaret
Lundie Thomas
McDonald Anthony Malcolm
Larson R. Michelle
NCT Group, Inc.
Ni Suhan
Woo Stella
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