| 摘要 |
The invention relates to a flat loudspeaker (10) comprised of a flexible panel (11) serving as a sound transmitter. The rear side of the panel is acoustically separated by a box (14). By virtue of the system and thanks to the comparatively large panel surface, the box depth is extremely small compared to that of a conventional piston-type loudspeaker, hence the name flat loudspeaker. Flexural waves are induced inside the panel by an electrodynamic oscillator (12) analogous to that in a piston-type loudspeaker and, together with the reflections on the panel edge, form a standing wave field. The interaction with the surrounding air causes sound to be radiated. This simplicity is obtained at the cost of a series of drawbacks. The density of the flexural wave modes is relatively wide-meshed thus resulting in a poor oscillatory and acoustic frequency response. The reverberation is disruptive. Directivity and radiation efficiency also pose a problem. The maxima and minima of the flexural wave modes destructively interfere and only the oscillation differential thereof provides useful sound. These drawbacks are avoided by effecting a termination by using impedance transmitters (14). In particular, the wave components traveling outward with the flexural wave velocity are eliminated. The positioning and the spectral frequency response of the impedance transmitters (14) enable the simultaneous fixing of evanescent, i.e. non-traveling modes, and likewise enable the spectral adjustment of a priori fixed near-fields in the area of the oscillators. Evanescent modes and the near-fields are resonance-free, oscillate in a conphasal manner, and are optimized here as a sound transmitter. By eliminating the sound radiation of the traveling waves, the coincidence condition does not apply, the panel (10) decreases in size, disruptive sound extinctions no longer occur thus obtaining an improved directivity. |
