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JP2000134696

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2000134696
[0001]
The present invention is a portable terminal device such as a mobile phone, PHS (registered
trademark) (Personal Handy Phone Set), pager (registered trademark), etc., and is mainly used to
reproduce a ringing tone for notifying an incoming call. The present invention relates to an
electromagnetic electroacoustic transducer.
[0002]
2. Description of the Related Art Conventionally, in a portable terminal device such as a portable
telephone, a personal handy phone set (PHS), a pager, etc., an electromagnetic type electricity
capable of reproducing high sound pressure using the resonance of a diaphragm in its main
body. An acoustic transducer has been attached and has been used to play a ring tone to indicate
an incoming call.
[0003]
A conventional electromagnetic electroacoustic transducer will be described with reference to
FIGS.
FIG. 9 is a cross-sectional view of a conventional electromagnetic electroacoustic transducer, in
which 1 is a center pole integrally formed at the center of the plate 2, 3 is an excitation coil
provided on the outer periphery of the center pole 2, 4 is The magnet 5 fixed to the upper
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surface of the plate 2 at the outer peripheral portion of the exciting coil 2 has a gap between the
upper surface of the center pole 1 and the upper surface of the magnet 4 and is made of
magnetic material placed on the upper surface of the projecting portion of the magnet outer
peripheral portion A first diaphragm 6, a second diaphragm 6 fixed to the center of the top
surface of the first diaphragm and made of a magnetic material, 7 covers the top surfaces of the
first and second diaphragms 5 and 6, and a magnet 4 And a case fixed to the outer periphery of
the plate 2, 8 an acoustic port provided on the wall of the case 7, and 9 an empty chamber
formed on the upper surface of the case 7 and the first and second diaphragms 5 and 6 . FIG. 10
shows a top view of the first diaphragm 5 and the second diaphragm 6, both of which are diskshaped, and generally the thickness of the diaphragm is, for example, 30 μm for the first
diaphragm 5, the second The second diaphragm is designed to be thicker than the first
diaphragm, assuming that the diaphragm 6 has a width of 150μ.
[0004]
The operation of the electromagnetic type electroacoustic transducer will be described. The first
diaphragm 5 and the second diaphragm 6 constituting the vibration system act between the
magnet 4 and the center pole 1 because they are magnetic materials. It is drawn by static suction
and it bends to the center pole side. When an electric signal is applied to the exciting coil 2, a
magnetic flux generated by the electric signal flows in the first diaphragm 5 and the second
diaphragm 6, and the first diaphragm 5 and the second diaphragm 6 are generated. The
magnetic attraction between the magnet 4 and the center pole 1 changes, and the first
diaphragm 5 and the second diaphragm 6 vibrate to generate sound. In this case, since the thin
first diaphragm causes magnetic saturation due to the magnetic flux generated by the magnet 4,
most of the attraction force generated by the electric signal applied to the exciting coil 3
corresponds to the center pole 1 and sufficient material It acts with the second diaphragm 6
having a thickness. The generated sound is transmitted to the space 9 covered by the case 7 on
the upper surface of the first diaphragm 5 and the second diaphragm 6, and emitted from the
acoustic port 8 provided on the wall surface of the case 7 .
[0005]
Curve A in FIG. 11 shows sound pressure frequency characteristics when a sine wave signal is
applied to the electromagnetic type electroacoustic transducer having the above-mentioned
configuration. The space 9 of the case 7 and the acoustic port 8 constitute a Helmholtz acoustic
resonator, and the acoustic resonance frequency f 3 is a resonance of a mechanical vibration
system constituted by the first diaphragm 5 and the second diaphragm 6. The frequency is set to
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be higher than the frequency f1, whereby the reproduction band can be expanded by the two
resonance peaks in the electromagnetic electroacoustic transducer.
[0006]
SUMMARY OF THE INVENTION In the above-mentioned conventional electromagnetic type
electroacoustic transducer, in order to apply a change to the ringing tone, the melody tone is
reproduced. The means reproduces the signal waveform applied to the exciting coil 2 as a
rectangular wave, and reproduces the harmonic components constituting the melody sound with
the frequency bandwidths f1 to f3 of the sound pressure frequency characteristic shown in FIG.
The C curve in FIG. 12 shows sound pressure characteristics including harmonic components
when a rectangular wave signal of duty = 50% is applied to the electromagnetic electroacoustic
transducer. Compared with the sound pressure frequency characteristics of FIG. 11 measured by
applying a sine wave signal, the characteristics of the bass range reproduced by the harmonic
component can be understood. However, in the conventional electromagnetic electroacoustic
transducer, the sound pressure level in the vicinity of the band f2 between the reproduction
bandwidths f1 and f3 of the sound pressure characteristic shown in FIG. 11 is low, and
harmonics of the melody sound reproduced in this band There is a problem that the sound
pressure level of the wave component is low, and the volume is reduced when the melody sound
is reproduced.
[0007]
Furthermore, a normal ringing tone that is not a melody tone uses a square wave of a single
period (1 point frequency of 2.5 k to 2.8 kHz). This band is realized by strictly managing the
resonance frequency f1 of the mechanical vibration system constituted by the first diaphragm 5
and the second diaphragm 6 of the electromagnetic electroacoustic transducer. On the other
hand, in order to obtain a high sound pressure level, it is necessary to reduce the mass of the
diaphragm, but the resonance frequency f1 is the vibration mass of the mechanical vibration
system composed of the first diaphragm 5 and the second diaphragm 6 Because it is determined
by the stiffness of the first diaphragm and the mass of the diaphragm, the resonant frequency f1
fluctuates and the sound pressure level of a normal ringing tone using a one-point frequency
decreases. The
[0008]
SUMMARY OF THE INVENTION In order to solve the above problems, an electromagnetic
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electroacoustic transducer according to the present invention comprises a plate having a center
pole at a central portion, and an exciting coil disposed on the outer peripheral portion of the
center pole. A ring-shaped magnet disposed on the plate at an outer peripheral portion of the
exciting coil, a first diaphragm supported by providing an air gap on the top surface of the center
pole and the magnet, and the first diaphragm Is fixed to the upper surface of the diaphragm, and
a notch is formed on the outer periphery or the material thickness of the outer periphery of the
diaphragm is made thinner than the center so that the magnetic flux density in the center and the
outer periphery is substantially uniform. By forming a second diaphragm having a shape and an
acoustic port covering the upper surfaces of the first and second diaphragms, the magnetic flux
flowing in the second diaphragm can be converted to the conventional one. Do not make major
changes , By weight of the mass of the vibration system constituted by the first and second
diaphragm, in which a high sound pressure level is obtained.
[0009]
In addition, a plate having a center pole at a central portion, an excitation coil disposed on an
outer peripheral portion of the center pole, a ring-shaped magnet disposed on the plate at an
outer peripheral portion of the excitation coil, the center pole A gap is provided on the upper
surface of the magnet, and the first diaphragm is supported on the outer peripheral portion, and
is fixed to the upper surface of the first diaphragm, and between the disc-shaped central portion
and the ring-shaped outer peripheral portion A second diaphragm having a substantially rod-like
connecting portion or a projecting portion provided on the outer peripheral portion, and
covering the upper surfaces of the first and second diaphragms By providing an acoustic port on
the wall surface, the stiffness value of the first diaphragm can be obtained without substantially
changing the mass of the vibration system constituted by the first diaphragm and the second
diaphragm. Change the said vibration The resonant frequency in which can be set to a
predetermined frequency.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings.
[0011]
(Embodiment 1) An electromagnetic electroacoustic transducer according to Embodiment 1 of
the present invention will be described with reference to FIGS.
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FIG. 1 is a plan view of the diaphragm of the electromagnetic electroacoustic transducer, and FIG.
2 is a structural cross sectional view of the electromagnetic electroacoustic transducer in which
the diaphragm of FIG. .
According to FIG. 1, 10 is a first diaphragm, 11 is a second diaphragm having a peripheral
portion cut away, and is joined onto the first diaphragm, and each material thickness is the same
as that of the conventional example. The second diaphragm is set to be thicker than the first
diaphragm.
Further, in FIG. 2, the same components as those in the prior art shown in FIG. 9 are denoted by
the same reference numerals, and duplicate descriptions will be omitted.
[0012]
The operation of the electromagnetic electroacoustic transducer configured as described above
will be described. When an electric signal is applied to the exciting coil 3, the combined magnetic
fluxes φ 1, φ 2 and φ 3 of the magnetic flux generated by the magnet 4 and the magnetic flux
generated by the exciting coil 3 form the first diaphragm 10 and the second diaphragm 11 from
the magnet 4. , Flows through the center pole 1 and the plate 2. Here, the magnetic flux φ1
indicates the magnetic flux flowing near the outer peripheral portion of the center pole 1, φ2
near the middle portion of the center pole 1, and φ3 near the central portion of the center pole
1. The magnetic fluxes φ1, φ2 and φ3 flow from the peripheral part of the diaphragm 11 to
the central part, and when there is no notch, the magnetic flux density B = φ / S (φ: magnetic
flux, S: area) which is the magnetic flux per unit area is the outer periphery As the cross sectional
area is larger, the magnetic flux density at the outer peripheral portion is smaller. Since the
diaphragm 11 is provided with a notch at its periphery, the cross-sectional area through which
the magnetic flux passes can be changed to make the magnetic flux density in the diaphragm 11
uniform. Further, on the opposing surface of the diaphragm 11 and the center pole 1, the
magnetic flux is divided into φ3, φ2, and φ1 from the outer peripheral portion of the center
pole 1, and the size thereof decreases toward the inside, so It is possible to have a uniform
magnetic flux density. Also, if a notch is provided to such an extent that magnetic saturation does
not occur, the magnetic flux flowing through the second diaphragm 11 does not differ much
from the conventional uniform disk diaphragm and acts on the second diaphragm 11 Vibration
forces can also be the same. As a result, between the magnetic flux density or the uniform second
diaphragm 11 and the center pole 1, the attractive force changes in accordance with the electric
signal applied to the exciting coil 3, and the second diaphragm 11 is integrally coupled. It
vibrates together with the first vibrating plate 10 being produced to produce a sound. Here, since
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the notch is provided in the peripheral portion of the second diaphragm 11 having a material
thickness larger than that of the first diaphragm 10, the notch is formed by the first diaphragm
10 and the second diaphragm 11. The weight of the vibration system is reduced.
[0013]
The B curve in FIG. 11 is the sound pressure frequency characteristic of the present embodiment
in which the mass of the vibration system is reduced. The sound pressure level in the vicinity of
the band f2 between the resonance frequency f1 of the vibration system and the acoustic
resonance frequency f3 is improved. The D curve in FIG. 12 shows sound pressure frequency
characteristics when a rectangular wave signal is applied to the electromagnetic electroacoustic
transducer of the present embodiment. The level in the low range is improved, and the sound
pressure level of the melody sound can be increased.
[0014]
The more specific shape of the notch of the second diaphragm is the notch that faces the top
surface of the center pole and extends to the outer peripheral portion based on the crosssectional area at a diameter equal to the outer diameter of the center pole. It is desirable that the
combined area on the circumference of the diaphragm excluding the portion be designed to be
substantially equal to the cross-sectional area at a diameter equal to the outer diameter of the
center pole.
[0015]
Second Embodiment A second embodiment of the present invention will be described with
reference to FIGS. 3 (a) and 3 (b).
FIG. 3 (a) is a cross-sectional view of the diaphragm as a main part, and FIG. 3 (b) is a plan view
thereof. The structure of the electromagnetic type electroacoustic transducer of the second
embodiment is the same as that of the first embodiment, and thus the description thereof is
omitted here.
[0016]
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According to FIG. 3, 12 is a first diaphragm and 13 is a second diaphragm. The main difference
between this embodiment and the first embodiment is the thickness of the outer peripheral
portion of the second diaphragm The material thickness is increased from the outer peripheral
portion to the central portion so that t1 and the thickness t2 of the central portion become t1
<t2. In this case, uniformization of the magnetic flux density due to the reduction of the
diaphragm cross-sectional area, which is realized by providing the cutaway portion in the first
embodiment, is achieved by reducing the material thickness of the outer peripheral portion of the
second diaphragm. It is a thing. As a result, the mass of the vibration system constituted by the
first diaphragm and the second diaphragm can be reduced in weight, and the sound pressure
level can be improved. The same effect as that of the first embodiment can be realized. .
[0017]
Third Embodiment The third embodiment of the present invention will be described with
reference to FIGS. 4 (a) and 4 (b). FIG. 4 (a) is a cross-sectional view of the diaphragm as a main
part, and FIG. 4 (b) is a plan view thereof. Also in the third embodiment, the structure of the
electromagnetic type electroacoustic transducer is the same as that of the first embodiment, and
thus the description thereof is omitted here.
[0018]
Referring to FIG. 4, 14 is a first diaphragm, and 15 is a second diaphragm. The main difference
between the present embodiment and the second embodiment is that the second diaphragm 15
is configured by laminating a plurality of diaphragms 15a, 15b and 15c having different
diameters. In this case, in the second embodiment, the material thickness of the second
diaphragm is continuously increased from the outer peripheral portion to the central portion,
and the magnetic flux density is made uniform by the change in the diaphragm cross-sectional
area. In the third embodiment, the diaphragms 15a, 15b and 15c having different diameters are
stacked to equivalently realize the change in thickness of the diaphragms, and the improvement
of the sound pressure level is the same as in the first and second embodiments. Positive effects
can be expected. In this case, since the second diaphragm may simply be combined with disks
having different diameters, it is relatively easy to realize as compared with the second
embodiment.
[0019]
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Fourth Embodiment The fourth embodiment of the present invention will be described with
reference to FIG. FIG. 5 is a plan view of the diaphragm which is the main part. Also in the fourth
embodiment, the structure of the electromagnetic type electroacoustic transducer is the same as
that of the first embodiment, and thus the description thereof is omitted here.
[0020]
Referring to FIG. 5, reference numeral 16 denotes a first diaphragm, and 17 denotes a second
diaphragm including a disk-shaped central portion 17a, an outer peripheral portion 17b in the
form of a ring, and connecting portions 17c, 17d, and 17e connecting between them. is there.
[0021]
The operation of the electromagnetic electroacoustic transducer composed of the above
diaphragm will be described.
It is well known that the resonance frequency f1 of the vibration system is strictly determined by
the vibration effective mass of the diaphragm and its stiffness and the negative stiffness caused
by the magnetic attraction force. Also, although the diaphragm is composed of the first
diaphragm and the second diaphragm, the second diaphragm is thicker than the first diaphragm
to provide rigidity, The stiffness of the vibration system is substantially the stiffness exhibited by
the first diaphragm, that is, the flat portion from the outer peripheral support of the first
diaphragm (protrusion of the outer periphery of the magnet) to the junction with the second
diaphragm It is determined by the stiffness of the
[0022]
Therefore, even if the weight is reduced by reducing the diameter of the second diaphragm, the
flat surface between the bonding portion between the outer peripheral support portion of the
first diaphragm and the second diaphragm is expanded and the stiffness is reduced. The smaller
the resonance frequency, the smaller the resonance frequency. Strictly, since the negative
stiffness also changes, the fluctuation of the resonance frequency may be more difficult to
predict. FIG. 6 shows the measurement results of the vibration system resonance frequency when
the diameter of the second diaphragm with a material thickness of 150 μ is changed using the
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first diaphragm with a diameter of 9.4 mm and a material thickness of 30 μ. When the diameter
of the second diaphragm is reduced, the diaphragm mass is reduced and the resonance
frequency is increased, but the stiffness of the first diaphragm is reduced and the resonance
frequency is reduced. FIG. 6 shows that as a result, as the diameter of the second diaphragm
decreases, the resonance frequency decreases.
[0023]
In the present embodiment, the central portion 17a of the second diaphragm has a role as an
original diaphragm to obtain a vibration force with the center pole. The ring-shaped outer
peripheral portion 17b connected by the connecting portions 17c, 17d, and 17e is joined to the
first diaphragm 16 to narrow the width of the flat portion of the first diaphragm. As a result, the
stiffness of the first diaphragm is increased, and the diameter of the central portion 17a can be
reduced to raise the lowered resonance frequency to a predetermined frequency. As described
above, by setting the diameter of the ring-shaped outer peripheral portion 17b of the second
diaphragm to a predetermined size, one point in a narrow band of 2.5 k to 2.8 kHz used in a
normal ringing sound Since the resonance frequency of the vibration system can be matched to
the frequency, a high sound pressure level can be secured.
[0024]
Furthermore, if the diameter of the central portion 17a of the second diaphragm is reduced, the
mass of the vibration system can be reduced, and the sound pressure level near the band f2
between the resonance frequency f1 of the vibration system and the acoustic resonance
frequency f3 is also large. It is also possible to increase the sound pressure level of the melody
sound. For this purpose, it is desirable to make the ring-shaped peripheral portion and the
connecting portion of the second diaphragm thin so as not to increase the mass. Furthermore, as
in the second embodiment, a notch may be provided in the central portion of the second
diaphragm. Also, as in the third embodiment, the material thickness of the central portion of the
second diaphragm may be changed.
[0025]
Further, as shown by 20 in FIG. 8, the mass can be further reduced by partially cutting out the
ring-shaped outer peripheral portion of the second diaphragm.
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[0026]
Fifth Embodiment The fifth embodiment of the present invention will be described with reference
to FIG.
FIG. 7 is a plan view of a diaphragm which is an essential part. Referring to FIG. 7, reference
numeral 18 denotes a first diaphragm, and 19 denotes a second diaphragm including a central
portion 19f and projections 19a, 19b, 19c, 19d, 19e, 19f and 19g. The main difference between
the present embodiment and the second embodiment is that the protrusions 19a, 19b, 19c, 19d,
19e, 19f, 19g are extended in the outer peripheral direction on the first diaphragm. In this case,
assuming that a virtual circle connecting the apexes of the protrusions 19a, 19b, 19c, 19d, 19e,
19f, and 19g is E, a junction between the first diaphragm and the second diaphragm is a virtual
circle. E is expanded to the vicinity of E, the first diaphragm stiffness is increased, and the
resonance frequency of the oscillation system can be raised to a predetermined frequency as in
the fourth embodiment. In this case, as compared to the fifth embodiment, there is an advantage
that the shape of the second diaphragm is simplified.
[0027]
As described above, when the electromagnetic type electroacoustic transducer according to the
present invention is configured, the central portion and the outer peripheral portion of the
second diaphragm in the vibration system constituted by the first and second diaphragms. It is
possible to reduce the weight of the vibration system by forming a notch on the outer periphery
or making the material thickness of the outer periphery thinner than that of the central portion
so that the magnetic flux density of the magnetic flux becomes substantially uniform. It is.
Furthermore, if magnetic saturation does not occur in each part of the second diaphragm, the
attraction force does not greatly change from the conventional one, so the sound in the vicinity
of f2 which is a band between the resonance frequency f1 of the vibration system and the
acoustic resonance frequency f3 The pressure level is improved, and the level of the harmonic
component in the bass region is improved, so that an electromagnetic electroacoustic transducer
capable of highly efficient melody sound reproduction can be realized.
[0028]
Furthermore, the vibration system is configured by connecting the disk-shaped central portion of
the second diaphragm and the ring-shaped outer peripheral portion by a bar-like connecting
portion, or by providing a projection at the outer peripheral portion. The stiffness of the first
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diaphragm can be set to an arbitrary value by substantially enlarging the outer shape with almost
no change in the mass of It is possible to realize an electromagnetic electroacoustic transducer
that reproduces a bell sound at a high sound pressure level by matching the resonance frequency
of the diaphragm to a narrow band of one point frequency.
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