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JPS56116400

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complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPS56116400
Description 1, title of the invention
Flat speaker
3. Detailed Description of the Invention The present invention relates to a flat loudspeaker having
a flat diaphragm, and in particular, to provide a flat loudspeaker capable of obtaining a flat sound
pressure characteristic in a wide band. Conventionally, as shown in FIG. 1, a flat loudspeaker
having a flat diaphragm is provided with a ring-shaped magnet 3 and a ring-shaped top plate 4
on a plate 2 with a hollow center pole 1 to form a magnetic circuit 6. The frame 6 is disposed on
the magnetic circuit 5, the peripheral portion of the damper 7 is fixed to the lower portion of the
frame 6, and the voice coil 8 is fitted to the central portion of the damper 7. The lower end is
held in the magnetic gap S, and the flat plate end page 1 moving plate 11 whose peripheral edge
is fixed to the upper surface of the frame 6 via a free engine 1 ░ is disposed at the upper end of
the voice coil and the thread 8 . In the flat plate speaker of the above configuration, the voice coil
8 is disposed in contact with the position of the node of the primary resonance mode of the flat
plate diaphragm 11 in order to obtain the reproduction sound pressure characteristic flatly to the
high frequency. That is, at the first resonance frequency f1 ░, the flat diaphragm 11 causes
divided vibration as shown by the first resonance mode 12 of FIG. Therefore, by causing the
voice coil 8 for driving the flat plate diaphragm 11 to abut on the position of the node of the first
resonance mode 12 of the flat plate diaphragm 11, the divided vibration shown by the broken
line 12 is prevented from occurring. The next resonance is prevented (this is called node drive).
The reproduction sound pressure characteristics (characteristic curve 14) of the flat-plate
speaker thus driven in node drive are shown in FIG. 2 in comparison with the case where the
center is driven by the small diameter voice coil (sound pressure characteristic curve 15). In this
figure, the sound pressure characteristic curve 15 in the case of central drive has a bulge at
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around the first resonance frequency f1o of the flat diaphragm. On the other hand, the sound
pressure characteristic curve 14 in the case of the node drive has a flat reproduction region in
the high region as compared to the case of the center drive in which the audio signal is
reproduced evenly at the first co-frequency f1 ░. It can be seen that it can be greatly expanded.
However, even when the voice coil is brought into contact with the position of the node of the
first resonance mode and the node drive is performed as described above, the divided vibration
(dot and dash line 13) generated near the second resonance frequency f2o (f2o> flo) The position
of the clause changes and second collusion is inevitable. Therefore, as shown in FIG. 2, the sound
pressure characteristic curve 16 has a sound pressure peak near the second resonance frequency
f2 ░. In order to cope with this, in the band above the second resonance frequency f2o, a high
sound speaker separately provided is driven using a branching circuit, but the peak near the
second resonance frequency f20 is large. If a branching circuit with a steep characteristic is not
used, sharing of the frequency band between the speakers can not be smoothly performed in the
vicinity of the second resonance frequency of 12 ░.
Therefore, also when another high-tone speaker is used, the sound pressure peak near the
second resonance frequency f20 may be reduced, or the sound pressure peak may be removed to
expand the reproduction band to a higher frequency. Was desired. The present invention has
been made in consideration of the above-mentioned matters, and is a flat plate speaker provided
with a voice coil for driving a central portion of a flat plate diaphragm and a voice coil for driving
a position of a node of a first resonance mode. To eliminate the sound pressure peak at the
second resonance frequency f2oK and to extend the reproduction band to a higher frequency.
Hereinafter, embodiments of the present invention will be described in detail based on the
drawings. FIG. 3 is a front cross-sectional view of a flat loudspeaker according to an embodiment
of the present invention, in which a ring-shaped magnet 18 and a ring-shaped top plate 19 are
disposed on a plate 17 having a hollow center pole 16. The magnetic circuit 2o is configured, the
frame 21 is disposed on the magnetic circuit 20, the peripheral portion of the damper 22 is fixed
to the lower portion of the frame 21, and the voice coil 23 with a large diameter is Are arranged
such that the upper end portion thereof abuts on the node portion of the first resonant mode of
the flat plate moving plate 24, and at the same time, the lower portion is held in the magnetic
gap 25. Further, the small diameter voice coil 26 is disposed such that the upper end thereof
abuts against the central portion of the flat plate diaphragm 24 so as to be coaxial with the large
diameter voice coil 23. The lower portion of the magnetic disk is held by the damper 29 in the
magnetic gap 28 of the small magnetic circuit 27. Further, the peripheral edge portion of the flat
diaphragm 24 is fixed to the upper surface portion of the frame 21 via the free edge 30. The
feature of this embodiment is that, as already described, the flat plate speaker has the large
aperture voice coil 23 and the small aperture nowice coil 26, and the large aperture voice coil 23
is used as a node of the first resonance mode of the flat diaphragm 24. The small diameter voice
coil 26 is mounted at the same position and coaxially with the large diameter voice coil 23 at the
center of the diaphragm. Next, FIG. 4 will be described together with an embodiment of a
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diplexer circuit used for the flat panel loudspeaker of the above-mentioned construction. The
input terminal EndPage: 2a-a 'is connected to the amplifier, and the output terminals b-b' and 7CC 'are connected to the large diameter voice coil 23 and the small diameter voice coil 26,
respectively. Here, the inductance L and the capacitance C connected in series to the output
terminal Cc / on the small diameter voice coil 26 side are set to have the following relationship
with the second resonance frequency f2 ░ of the flat diaphragm 24 ).
By satisfying the above equation, the branching circuit of FIG. 4 has the function of a band pass
filter, and only when an audio electric signal of a frequency near the second resonance frequency
f2 ░ is input to the input terminal aa / The output terminal C-c'l / 'C audio signal is output, and
this audio signal is input to the small diameter voice coil 26. On the other hand, at the output
terminal b-b' on the large diameter j coil 23 side An audio signal is output regardless of the
frequency of the audio signal from the input terminal a-a ', and this audio signal is always input
to the voice coil 23 with a large aperture. Next, the operation when such a branching circuit is
provided in the flat panel speaker of FIG. 3 will be described in the following cases (1) and (2),
and the audio signal is output from the output terminal b-b '. It is input to the large diameter
voice coil 23 and simultaneously input to the small diameter voice coil 26 from the output
terminal C-C ', and the large diameter voice coil 23 and the small diameter voice coil 26
simultaneously operate the flat diaphragm 24. There is no sound pressure peak due to driving. If
the flat diaphragm 24 is simultaneously driven by the large diameter voice coil 23 and the small
diameter voice coil 26 as described above, the reason why the sound pressure peak does not
occur in the vicinity of the second resonance frequency f20 is explained by the following
principle. it can. First, considering the case where only the large-diameter voice coil 23 drives the
flat diaphragm 24 with the force FL, the moment when the voice coil 23 pushes the flat
diaphragm 24 by the upward force FL, as shown in FIG. A second resonance mode 31 as shown
is generated. Next, considering the case where only the small-diameter voice coil 26 drives the
flat diaphragm 24 in phase with the large-diameter voice coil 23, the voice coil 26 is driven to
the flat diaphragm 24 at the same moment as FIG. The second resonance mode 32 shown in FIG.
5B is substantially opposite in phase to the second resonance mode 31 shown in FIG. 5A due to
the difference in the position to be driven. When the large diameter voice coil 23 and the small
diameter voice coil 26 simultaneously drive the flat plate diaphragm, the second resonance mode
31 of FIG. 5 a and the second resonance mode 32 of FIG. The vibration mode 33 shown in FIG.
This vibration mode 33 is displaced upward in parallel with the flat diaphragm 24 at rest, and
performs piston vibration which is an ideal vibration as the vibration of the flat diaphragm. When
the forces FL and FS are directed downward, the same action causes the force to change
downward parallel to the stationary flat diaphragm 24, that is, on the large diameter voice coil
23 and the small diameter voice coil 26. Assuming that the amplitude of the flat diaphragm 24 is
? L and ?S, respectively, and the forces of the large diameter voice coil 23 and the small
diameter voice coil 26 on the flat diaphragm are FL and FB, respectively, the second resonance
frequency f20 in ?LFL + ?5Fs-? ............ (1) so as to satisfy the second be selected arrangement
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of the force FL and the Fs and small diameter of the voice coil 26 large diameter of the voice coil
29 The second resonance mode can be extinguished.
That is, as shown in FIGS. 5a and 5b, make the respective amplitudes ? L and ? S in opposite
phase, and satisfy equation (1) so that the zero force FLgFS from each boy 7: I ? ? becomes in
phase. Can eliminate the second resonance mode. (2) Voice input to the input terminal a-a 'of the
branching circuit. When the frequency of the signal is other than the second resonance
frequency f2o: In this case, the impedance of the inductance L capacitance C connected in series
on the output terminal C-C 'side becomes large, and the voice coil EndPage: 326 of the small end
face No voice signal is input, and the voice signal is manually input only to the large-diameter
voice coil 23. Since the frequency of the audio signal is other than the secondary resonance
frequency f20, the flat plate diaphragm 24 is driven by the large diameter voice coil 23, and
generates normal voice by vibrating the piston. Next, FIG. 6 shows the reproduction sound
pressure characteristics of the flat plate speaker having the above-described configuration. As
shown in the figure, the characteristic curve 14 (identical to that shown in FIG. 2) in a flat plate
speaker only driven by a large diameter voice coil has a sharp sound pressure beak near the
resonance frequency f2 ░. On the other hand, the characteristic curve 34 in the flat panel
speaker according to the embodiment of the present invention is such that the sound pressure
beak near the resonance frequency f2 (about 3, 15 KHz) is removed and the band up to the third
resonance frequency f3 (about 5 KHz) It is expanded. As described above, the loudspeaker
according to the present embodiment has an effect that flat sound pressure characteristics can be
obtained in a much wider band as compared with the conventional flat loudspeaker. 7a and 7b
show another embodiment of the flat loudspeaker according to the present invention. In this
embodiment, the voice coils 3.9, 40 and 41.42 each having a small magnetic circuit 35.degree.
36.37. 38 are circular so as to contact the node of the first resonance mode of the circular flat
diaphragm 43. The voice coil 45 provided with a magnetic circuit 44 is abutted at the center of
the circular plate diaphragm 43, and these magnetic circuits 35.36 ░ 37.38.44 are arranged in a
frame 46. The rim of the frame 46 is coupled to the rim of the circular flat diaphragm 430 via
the free edge 47. In the operation of the flat plate speaker of this embodiment, when an audio
signal having a frequency near the second resonance frequency f20 is output from the amplifier,
the voice arranged at the node of the first resonance mode of the circular flat plate diaphragm 43
Coils 39.40, 41.42 and centrally located. The voice coil 45 is input to simultaneously drive the
circular flat diaphragm 43 in phase with these voice coils simultaneously, and when an audio
signal having a frequency other than that is input from the amplifier, the third flat circular
diaphragm 43 The flat diaphragm 43 is driven only by the voice coils 39, 40, 41. 42 disposed at
the node positions of the primary resonance mode.
If the flat plate spill force is configured as in this embodiment, the freedom of the arrangement
place of the voice coil becomes large along with the effect of the flat speaker of the embodiment
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shown above, and a voice coil with a large diameter with high accuracy is formed. There is an
effect that manufacturing problems can be eliminated. In addition, in the flat plate spill force of
the above Example, although the circular flat diaphragm was used, it is a rectangle and a square.
Flat-plate diaphragms of other shapes, such as oval, may also be used. As described above, in the
flat panel speaker of the present invention, the sound pressure beak of the second resonance in
the high region is removed, and an effect of obtaining flat sound pressure characteristics in a
wider band compared to the conventional flat panel speaker is obtained. It is something that has
a practical value as a dog.
4. Brief description of the drawings FIG. 1 is a front sectional view of a conventional flat panel
speaker, FIG. 2 is a graph showing sound pressure characteristics of the conventional flat panel
speaker, and FIG. 3 is a flat panel speaker according to one embodiment of the present invention.
FIG. 4 is a circuit diagram showing an embodiment of a diplexer circuit used for the flat plate
speaker, FIG. 5 a, b. C is a diagram for explaining the operation of the flat panel speaker
according to the present invention, FIG. 6 is a sound pressure characteristic diagram of the flat
panel speaker of FIG. 3 provided with the branching circuit of FIG. FIG. 16 is a plan view and a
front cross-sectional view of a flat panel speaker in an embodiment of the present invention. 20
иииии Magnetic circuit, 23 иииииии Voice coil, 24 ииииии Flat plate, 26 иии Voice coil, 27 и и и Magnetic circuit,
35, 36.37, 38 ░ 44 ииииии Magnetic circuit, 39, 40, 41.4, 2 ░ 46 и и и и Voice coil, 43 и и и и и и Circular
plate diaphragm. Name of agent Attorney Nakao et al. 1 person EndPage: 4 Fig. 1 Fig. 2 = 7 units
1 I I 1 [1]; Fig. 3 Fig. 6 Fig. 7; 7q44??EndPage: ?
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