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JPS5863296

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DESCRIPTION JPS5863296
[0001]
The present invention relates to a speaker, and more particularly to a speaker that
simultaneously satisfies an improvement in efficiency and an improvement in input-to-output
linearity. In the conventional speaker, a long voice coil or a short voice coil is used so that the
voice coil does not jump out of the magnetic gap even if the vibration amplitude of the voice coil
becomes large. Hereinafter, the long voice coil and the short voice coil will be described with
reference to FIGS. 1 and 2. In both figures, 1 is a top plate, 2 is a center pole, 5 is a permanent
magnet, 4 is a bottom plate, 5 is a bobbin 6 is a long voice coil, and 7 is a short voice coil. As
shown in FIG. 1, the long voice coil 6 has a winding width of the voice coil larger than the
thickness of the top plate 1. In this case, even if the amplitude increases, the long voice coil 6
does not pop out of the magnetic gap, so the driving force does not decrease and the input /
output relativeness is improved, but the voice coil in the part out of the magnetic gap Since the
current flows, the efficiency is reduced. In addition, as shown in FIG. 2, the short voice coil 7 has
a winding width of the voice coil smaller than the thickness of the top plate 1. In this case, even if
the amplitude increases, the topoise coil 7 does not jump out of the magnetic gap, so the driving
force does not decrease, and the linearity of the input-to-output is improved. Efficiency is
reduced. On the other hand, in order to improve the efficiency, it is necessary to use a voice coil
having a winding width substantially equal to the thickness of the top plate 1, but this would
lower the input-to-output linearity. As described above, in the conventional loudspeakers, the
efficiency and the input / output relativeness conflict with each other, and none of them have
been satisfied at the same time. It is an object of the present invention to provide a speaker
which has substantially improved the efficiency of the speaker and the linearity of input to
output simultaneously while eliminating the drawbacks of the prior art described above. The
speaker according to the present invention has n (n is an integer of 2 or more) voice coils having
a winding width substantially equal to the thickness of the top plate constituting the magnetic
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circuit in the axial direction of the bobbin. The voice coil is switched according to the output
voltage of the displacement detection device which detects the axial displacement of the bobbin,
and the input voltage is applied to only the voice coil facing the top plate constituting the
magnetic circuit among the n voice coils. Is applied.
Although the present invention will be described in detail with reference to the drawings below,
these are merely examples, and it goes without saying that various modifications and
improvements can be made without departing from the scope of the present invention. FIG. 3
shows an embodiment of the speaker according to the present invention, and in the axial
direction of the bobbin 5, five voices having a winding width substantially equal to the thickness
of the top plate 1 constituting the magnetic circuit. According to the output voltage of the
displacement detection device comprising the light emitting element 9, the light receiving
element 10 and the slit 14 provided on the bobbin 5 with the coils 8a, 8b 18C 18d, 8e
juxtaposed, the above five pieces by the switching circuit 1.1. The voice coil 8a18b18C18d18e is
switched to apply the input voltage only to the voice coil facing the top plate 1 constituting the
magnetic circuit among the five voice coils. As mentioned above, a great feature of the present
invention lies in that the displacement of the bobbin (ie, the displacement of the voice coil) is
directly detected by the displacement detection device to switch the plurality of voice coils, The
voice coil for applying the input voltage is always located at the maximum point of the magnetic
flux density, and the efficiency can be lowered to rapidly improve the input-to-output linearity.
Since the voice coil can be used as a voice coil having a winding width substantially equal to the
thickness of the top plate constituting the magnetic circuit, the efficiency is improved. Although
the number of voice coils is five in the embodiment shown in FIG. 3, it is of course possible to use
rj (n is an integer of 2 or more) in general. Here, when n is small, the input / output relativeness
should not be a broken line, and it is desirable that n be as large as possible. FIG. 4 is an enlarged
view showing the details of the displacement detecting device in FIG. 6, and the light emitting
element 9 and the light receiving element 10 are disposed at the same straight line on both sides
of the slit 14 provided in the bobbin 5 There is. A light emitting diode is suitable as the
fluorescent element 9, and a photodiode or phototransistor is suitable as the light receiving
element 10. In FIGS. 6 and 4, the light receiving element 10 is disposed inside the bobbin 5 and
the light emitting element 9 is disposed outside, but there is no difference in the operation
between the two even if the arrangement of the two is reversed. Of course. In FIG. 4, the bobbin 5
moves in the axial direction (at this time, the voice coil also moves in the axial direction). And the
slit 14 also moves up and down in the axial direction, and if the slit 14 has a structure in which
the horizontal width changes linearly, the cross-sectional area of the light path from the light
emitting element 9 to the light receiving element 10 As the movement of IJ 7) 14 changes, the
output voltage of the light receiving element 10 changes linearly.
FIG. 5 is a diagram for explaining the operation principle of this displacement detection device,
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but there is a relation of the following equation between the diameter De16 of the light emitting
element, the diameter Dr17 of the light receiving element, and the maximum lateral width T) 318
of the slit. Is desirable. When the relationship of the expression Dr DrDs and De ≧ Ds is satisfied,
the displacement detectable range becomes maximum. By the above configuration and operation,
the displacement of the bobbin 15 (that is, the displacement of the voice coil) can be detected.
FIG. 6 shows the case of the speaker of the long voice coil of the prior art 1 (code 19) and the
case of the speaker of the prior art 2 / iod voice coil (code 20) by combining the efficiency of the
input power versus the output sound pressure level of the speaker. It is the figure which
compared about the case of the speaker of this invention (code ¦ symbol 21), From this, it turns
out that the linearity of the speaker by this invention is far superior to a conventional product. As
described above, according to the present invention, in the speaker, the following effects can be
obtained. (A) Even-order harmonic distortion due to asymmetry of the magnetic flux density
distribution outside the magnetic gap is reduced because the magnetic flux outside the magnetic
gap is not used. (B) Since the driving force acting on the voice coil at the time of large input or
large amplitude is constant, the relative degree of input (input voltage) versus output (output
sound pressure level) can be improved. (C) The voice coil to which the input voltage is applied is
always located at the maximum point of the magnetic flux density, and the efficiency is improved
because there is no waste current and no wasted magnetic flux.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a schematic sectional view of a loudspeaker having a long voice coil according to the
prior art, FIG. 2 is a schematic sectional view of a loudspeaker having a short voice coil according
to the prior art, and FIG. 4 is an enlarged perspective view showing the details of the
displacement detecting device in FIG. 3, FIG. 5 is an explanatory diagram for explaining the
operation principle of the displacement detecting device, FIG. 6 is a prior art and according to the
present invention It is a figure which shows the input electric power versus output sound
pressure level of a speaker.
Description of symbols 1 · · · Top plate 2 · · · Center pole 6 · · · Permanent magnet 4 · · · Bottom
plate 5 · · · Bobbin 6 · · · Long voice coil · · · Short voice coil 3a, 8b, BCs 8d, Be-voice-y-il 9,..., Lightemitting element 10... Light receiving element 11... Switching circuit 1 4 .. Srinoto agent patent
attorney Junnosuke Nakamura 1-1 Figure-1 = Figure 1 -4 Figure 16 Input power
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