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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
flat panel speaker used for various acoustic devices. (Prior Art) A conventional flat loudspeaker
will be described with reference to FIGS. FIG. 2 is a cross-sectional view showing the
configuration of a conventional flat plate speaker, wherein the flat plate speaker is formed by an
annular magnetic gap formed by a bottom plate 3 having a top plate 11 ring magnet 2 and a
center ball 3a. The voice coil 6 supported by the damper 5 is inserted into the frame 4 fixed to
the flat plate, and the upper end of the drive cone 7 connected to the voice coil 6 is supported by
the frame 4 via the edge 8 A gasket 10 is mounted on the upper surface of an edge 8 which is
fixed to the lower surface 9 and fixed to the outer peripheral flat edge 4a of the frame 4
described above. The joining position of the flat diaphragm 9 and the drive cone 7 shown by the
dimension line 2r in the figure is matched with the node circle of the first mode of the primary
resonance frequency of the flat diaphragm 9, The frequency band of the flat loudspeaker is
extended to the second resonance frequency band. FIG. 4 is a frequency characteristic diagram of
a flat panel speaker, in which the vertical axis represents sound pressure indicated by unit dB,
and the horizontal axis represents frequency. The frequency characteristic of the conventional
flat loudspeaker having the above-mentioned configuration generates a sharp peak a near the
second resonance frequency as shown by the solid line, and is incorporated in the loudspeaker
system or used alone as a full range loudspeaker system In the case where it is extremely difficult
to handle, the following measures are taken. That is, peak down is achieved by utilizing a reverse
resonance circuit in which a coil and a capacitor element are incorporated on the drive circuit
side, or as shown in FIG. 3 (a) and FIG. 4b, a flat diaphragm A countermeasure is taken to squeeze
the material 11 having compliance between 9 and the drive cone 7 or hate the material 12
having compliance between the voice coil 6 and the drive cone 7 to achieve peak down.
(Problems to be Solved by the Invention) However, in the above configuration, incorporating the
reverse resonance circuit in the drive circuit causes the problem that the coil and the capacitor
element are required, which results in an increase in cost. In addition to the narrowing of the
frequency band as shown by the broken line in FIG. 4 when taking measures against the problem,
there is a problem that the characteristics vary and the reliability decreases due to the variation
in the degree of flexibility of the materials used. . SUMMARY OF THE INVENTION The present
invention solves the above-mentioned problems, and provides a flat-plate speaker which achieves
peak-down while having the same price and frequency band as the conventional flat-plate
(Means for Solving the Problems) In order to solve the above-mentioned problems, the present
invention uses a flat diaphragm having a sand-inch structure in which the upper and lower
portions of the core material are covered with a skin material. The core material is provided with
at least one slit of an appropriate length which intersects the node circle of the first mode at two
places. (Operation) As mentioned above, the volume velocity of vibration is changed and the peak
is lowered by providing the slit intersecting the two points at the node circle of the first mode in
the core material constituting the flat diaphragm. Do. (Embodiment) An embodiment of the
present invention will be described with reference to FIGS. 1 and 4. FIG. FIG. 1 is a plan view of
the flat diaphragm 13 of the flat speaker according to the present invention, wherein the flat
diaphragm 13 is a flat diaphragm indicated by a dimension line 2r on a core member having
skins fixed on both front and back surfaces. The slit 15 shown by the dimension line Q which
intersects with the nodal circle 14 of the 13th first mode and two places is provided. In this
example, a flat diaphragm 13 with a diameter of 72 mn + using an isotropic paper honeycomb as
a core material was provided with a slit 40 having a length of 40 mm in contact with a circle with
a radius of 17.5 mm. The peak value when the level is O dB is reduced to +4 dB in the present
embodiment, compared to +10 dB in the conventional example shown in FIG. 2 (FIG. 4 C). (Effects
of the Invention) As described above, according to the present invention, the core material of the
flat diaphragm is provided with slits intersecting at two points in the node circle of its first mode,
and the volume of the flat diaphragm By changing the speed, it is possible to reduce the sharp
peak of the second resonance frequency, and to obtain a wide band flat speaker having no peak
of the second resonance frequency at the same price as a conventional flat speaker.
Brief description of the drawings
1 is a plan view of a flat diaphragm of a flat loudspeaker according to the present invention, FIG.
2 is a cross sectional view of a conventional flat loudspeaker, and FIGS. 3 (a) and 3 (b) are flat
loudspeakers subjected to peak reduction measures. FIG. 4 shows sound pressure frequency
characteristics of the conventional example and the embodiment of the present invention.
1 top plate 2 ring magnet 3 bottom plate 4 frame. 5 · · · · · · · · · · · · · · · voice coil, 7 · · · drive cone,
8 · · · 9, 13 · · · plate-like diaphragm, 10 · · · gasket, 11 ° 12 · · · compliance Material with, 14 ...
Nodal circle of first mode, 15 ... Slit. Patent Applicant Matsushita Electric Industrial Co., Ltd. Fig. 1
Fig. 2 Fig. 7 · Doc 4 Gecone
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