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JPS5778100

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DESCRIPTION JPS5778100
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 3 are cross sectional views showing the
structure of the prior art, and FIG. 5 is a cross sectional view showing the structure of the main
parts for explaining the operation of the present invention. FIG. 9 is a simplified view of the
vibration system of the present invention, and FIG. 9 is a cross-sectional view of a structure
showing one embodiment of the present invention, FIG. 2, FIG. 4, FIG. FIG. 10 is a diagram
showing drive frequency characteristics. Reference Signs List 1 magnetic core with center pole 2
coil 3 magnet 4 support 5 diaphragm 5 6 yoke steel 7 acoustic case 8 ..., space ... 9 ... second
diaphragm, 10 ... space.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to broadening the
range of an electroacoustic transducer. The electro-acoustic transducer used as a sound source of
-J- type portable equipment such as a wristwatch or pocket pel utilizes co-operation from the
limitation of power consumption and the following are generally used, but the one utilizing
resonance is on the other hand, There is a drawback that the bandwidth can not be obtained
sufficiently. The present invention is intended to achieve a wide band while utilizing resonance.
In particular, the conventional 2- ^ S ") electroacoustic transducer has a mechanical tremorthoracic system with one degree of freedom, and thus a single mechanical resonant frequency, as
opposed to the conventional one. The acoustic transducer of the invention has a degree of
freedom f2 of the transverse vibration system, two mechanical resonance frequencies are
created, and the acoustic pressure between the two mechanical resonance frequencies makes the
sound pressure substantially equal, thereby broadening the bandwidth The Hereinafter, this will
be described according to the drawings. FIG. 1 is a cross-sectional view showing the structure of
the conventional example, 1 is a core with a center pole made of a soft magnetic material, 2 is a
coil, 6 is a magnet, 4 (1 support, 5 is a diaphragm, 6 is It is a yoke made of a soft magnetic
material fixed to a diaphragm SVC. In the acoustic transducer having such a configuration, a
suction force or a repulsive force acts on the yoke 6 by supplying an alternating current to the
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coil 2, and the diaphragm 5 is moved by this force to generate a sound. The vibration system is
basically one degree of freedom, and the sound pressure partial side frequency characteristic has
one resonance point as shown in FIG. 2, and the constant sound pressure P shown in FIG. The
resulting frequency band ?ft is usually quite narrow. Fig. 6 is a cross-sectional view showing
another conventional structure in which the narrow frequency band is improved. Those indicated
by numerals 1 to 6 are the same as in FIG. The new one is an acoustic case that is flooded with 7,
7a is a hole provided in the acoustic case 7, and a sound emission hole, and 8 is a space
configured by the acoustic case 7 and the diaphragm 5. In this configuration, a so-called
Helmholtz resonator is produced by the sound emission lower a and the space 8, so by
appropriately designing the diaphragm resonance frequency and the Helmholtz resonance
frequency closer to each other, as shown in FIG. The sound pressure-driving frequency
characteristic can be improved, and the sound pressure can be considerably improved over the
.DELTA.f1 obtained in the band .DELTA.f2vI-1 second vI structure of a constant sound pressure P
иии. In applications where one drive frequency is used, the electro-acoustic transducer of the
structure shown in FIG. 5 is sufficient, but when sounds of different frequencies are required, for
example, sounds different by ? or an octave. 4h can not meet the requirements with this
structure.
An object of the present invention is to provide a wide 4-J band electroacoustic transducer
capable of responding to such an iuw, which will be described below with reference to the
drawings. FIG. 5 is a view for explaining the present invention and is a cross-sectional view
showing a structure of a mechanical vibration system in which free honey of the mechanical
vibration system is 2. 1 and the figures 1 to 6 showing the prior art example are the same, but if
fundamentally different, they are opposed to the diaphragm 5 with the yoke 6 serving as a
permanent magnet. The important point is that the diaphragm 5 and the second diaphragm 9 are
air-spring-coupled with the air-tight space 9 and such a configuration 1 In the sound-to-acoustic
transducing word, an alternating current is flowed through the coil 2 to magnetically drive the
photographing unit 5 with the yoke 6, but no sound is generated from the diaphragm 5, and air
from the airtight space 10 is generated. Sound f is generated by the vibration of the second
diaphragm 9 coupled by a spring. The sound pressure-drive frequency characteristic of the
sound-acoustic transducer of the structure 1 is k having two resonance points as shown in FIG.
The sound pressure-drive frequency characteristics will be described below with reference to
FIGS. 7 and 8. 5->) If the vibration system in the structure of FIG. 5 is isometrically rewritten, it
can be written as shown in FIG. Here, M, XM are the equivalent mass 9 equivalent spring
coefficient of the imaging plate 5 with the longitudinal iron 6 in FIG. 5 respectively. The
amplitude is represented by m, and xm is represented by the equivalent mass 9 equivalent spring
modulus and amplitude of the displacement plate 11 of FIG. 5 at 2 in FIG. 5, respectively, and ka
is the air spring of the space 10 in FIG. It shows a constant 7. The above is the main = a-system
component, and in fact it is necessary to consider the resistance to decrease, the acoustic
impedance, etc., but this has been omitted for the sake of simplicity. The forced peristaltic
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solution when the alternating force Fm?t is added to the quality 11M of the vibration system is
expressed by the following equation. Fk-)-kaK + kak kazIl =-(--3) / (? 4- (-+-) is mmm mx k + x kaHcka 10 ?) III ka FK 10 ka k + ka,-=-/ 1 ? '-(-+-) M mmm mx k + x ka + cka + ?) As can be seen
from the set of Mm6, two resonance points appear, but the power-drive frequency characteristics
of this can be represented as shown in FIG. It will be clear from this FIG. 8 that the sound
pressure of FIG. 6 can be obtained in the amplitude xmlcml of the second vibration @ 9,
appropriately selecting the constant of the imaging system shown in FIG. By doing this, the finger
frequencies fl and f3 shown in FIG. 8 can be made quite close, but they can not be perfectly
matched at 1 unless m = 0, and there are always two collusion points Come out.
At the two resonance points of such a vibration system, the sound pressure becomes
considerably large, but in terms of the band, ?fi1 as shown in FIG. Mu fat is usually only usable
and there is nothing enough. It is the gist of the present invention to compensate for this by
sound effects and to make the band sufficiently wide, which will be described with reference to
the drawings. FIG. 9 is a cross-sectional view of the structure of the acoustic converter showing
one embodiment of the present invention. Basically, the acoustic case 7 is provided in FIG. 5, and
the holes shown by numerals in the figure are the same as those described above so far. is there.
In the acoustic transducer in such a structure, if the Helmholtz's resonance frequency is set
between 1 and f at the mechanical resonance frequency of the second diaphragm described in
FIG. 8, the sound-drive shown in FIG. It becomes a frequency characteristic, and it becomes a
wide band as shown by the band ?f4 in the figure above the foot sound pressure Po. Although
the e-to-machine conversion tW magnetic type has been described in the above description, the
same effect can be obtained even if another e-to-mechanical converter such as a piezoelectric
type or an electrodynamic type is used. It is obvious. Also, in the past, there has been a type in
which a thin plastic film or the like corresponding to the second scratch Wb plate 9 of the
present invention is stuck to the same place mainly for the purpose of moisture resistance and
dust resistance. 7 and the equivalent mass m of the second diaphragm in FIG. 7 corresponds to
almost zero as an effect on the vibration system, in order to broaden the bandwidth of the
present invention. The idea of is clearly different. In the present embodiment, the resonator is
described using a Helmhol * -11-T resonator as a resonator, and the hole is not limited to this,
and a resonance is formed by an air chamber and a sound emission port. If it is a vessel, it can be
changed. As described above, the electro-acoustic transducer according to the present invention
uses resonance actively and can obtain a wide band, so it can provide various tones with low
power consumption, and it can be used in wristwatches and pagers. Significantly contributing to
the multifunctionality of small portable devices such as
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