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JPH05137194

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JPH05137194
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
improvement of the frequency characteristics of a loudspeaker, and more particularly to a domeshaped loudspeaker with reduced first order high-frequency resonance.
[0002]
2. Description of the Related Art A dome type speaker has a sound pressure frequency
characteristic extending to a high frequency range compared to a cone type speaker, while the
voice coil portion has no damper used for a cone type diaphragm, so the first height is high. It
has a high sound pressure peak called area resonance. Therefore, it is desirable to obtain a flat
sound pressure frequency characteristic by reducing the peak of sound pressure of a specific
frequency.
[0003]
Here, the configuration of a conventional dome-shaped speaker will be described with reference
to FIG. FIG. 6 is a cross-sectional view along the central axis showing an example of a
conventional dome-shaped speaker. In the drawing, the frame 1 is a mounting portion having an
opening fixed to the housing of the speaker body. A top plate 2 formed of an annular magnetic
body is attached to the back of the frame 1. Further, a cylindrical magnet 3 is coaxially fixed to
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the rear surface of the top plate 2, and a yoke 4 is attached to the other surface of the magnet 3.
The yoke 4 is a member having an inverted T-shaped cross section including its central axis, and
is a magnetic body in which a cylindrical center pole and a disk-shaped plate for holding the
center pole are integrally formed at its center. The upper side surface of the center pole of the
yoke 4 forms a uniform gap with the cylindrical inner peripheral surface of the top plate 2, and
this gap is called an air gap 5.
[0004]
As described above, the magnetic circuit including the top plate 2, the magnet 3, the yoke 4 and
the air gap 5 constitutes a field section of a voice coil to be described later. In the air gap 5, the
magnetic flux generated from the magnet 3 penetrates through the top plate 2 to the center pole
of the yoke 4 to form a uniform magnetic field. Next, an annular edge 6 is bonded to the inner
peripheral portion of the frame 1. A bent portion having an arc-shaped cross section is formed on
the inner periphery of the edge 6, and the bent portion holds the outer peripheral portion of the
dome-shaped diaphragm 7 in a vibrating manner.
[0005]
The dome-shaped diaphragm 7 is a hemispherical diaphragm, and is formed of, for example,
paper, light metal, plastic or the like. In addition, the dome-shaped diaphragm 7 includes an
elastic portion 7a around the hemispherical portion and the periphery thereof, and is held by the
edge 6 via the elastic portion 7a. Furthermore, the dome-shaped diaphragm 7 is connected to the
upper end of the cylindrical portion 8. The cylindrical portion 8 is a coil bobbin inserted into the
air gap 5 and the voice coil 9 is wound around the outer peripheral side surface thereof. When
an excitation current is applied to the voice coil 9, the dome-shaped diaphragm 7 performs a
piston motion integrally with the cylindrical portion 8 by receiving an electromagnetic force by
the magnetic field of the air gap 5.
[0006]
FIG. 7 (a) is an equivalent circuit showing the vibration characteristic of the above-mentioned
conventional dome-shaped speaker. The driving force F is an electromagnetic force that the voice
coil 9 receives from the magnetic field of the air gap 5, and is equivalently a power supply. The
current I flowing through this circuit represents the vibration velocity of the dome-shaped
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diaphragm 7, and the value of the current is determined by the load connected to the driving
force F. Among the loads, the compliance C1 is equivalent to the elastic coefficient of the elastic
portion 7a on the outer periphery of the dome-shaped diaphragm 7, and the inductance M1 is
equivalent to the mass of the dome-shaped diaphragm 7. The resonant circuit formed by the
compliance C1 and the inductance M1 determines the first higher-order resonant frequency. The
second, third and higher order resonant circuits are formed by compliances C2, C3... And
inductances M2, M3.
[0007]
The frequency characteristic of the sound pressure in the dome-shaped speaker having such a
configuration is, for example, as shown in FIG. That is, in the sound frequency band from 20 Hz
to 20 KHz, a characteristic having a gentle peak centered on the middle sound band is obtained,
but a large sound pressure peak occurs in the narrow band portion of 4 to 5 KHz. This resonance
frequency is due to the mass of the dome-shaped diaphragm 7 and the resonance of its elastic
portion 7a etc. The frequency is the elasticity of the edge 6 and the speed of sound of the
material constituting the dome-shaped diaphragm 7, height and diameter of the diaphragm It is
known to depend on
[0008]
Therefore, in order to reduce this resonance, for example, as shown in FIG. 6, a dome-shaped
speaker in which an annular braking piece 10 is attached to the center of the inner surface of the
dome-shaped diaphragm 7 has been proposed. The braking piece 10 is, for example, an annular
butyl rubber braking piece with a diameter of 20 mm and a thickness of 1 mm for a domeshaped speaker with a diameter of 12 cm. The measured sound pressure frequency
characteristics of the speaker when this braking is attached is shown in FIG. In this case, the
resonance of the central portion of the dome-shaped diaphragm 7 is suppressed by the damping
effect of the braking piece 10, and the peak of the first high-order resonance of the sound
pressure frequency characteristic is slightly reduced.
[0009]
FIG. 7B is an equivalent circuit showing the vibration characteristic of the dome-shaped speaker
to which the braking piece 10 is attached. A portion different from FIG. 7A is that an inductance
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Md equivalent to the mass of the braking piece 10 is connected in series with the inductance M1
indicating the mass of the dome-shaped diaphragm 7. Essentially, although the braking piece 10
has both mass and viscous resistance, it exhibits a damping effect only when an external force is
applied such that the braking piece itself is deformed. However, since the damping piece 10
vibrates integrally with this in the present embodiment because it is affixed to the top of the
dome-shaped diaphragm 7, it is presumed that the damping effect is small and only the mass
effect is exhibited.
[0010]
As described above, in the above-described conventional dome-shaped speaker, in the first-order
high-resonance mode, the most greatly deformed outer peripheral portion of the dome-shaped
diaphragm 7 is not damped. The next high frequency resonance mode can not be suppressed
sufficiently, and the resonance peak of the sound pressure frequency characteristic can not be
eliminated.
[0011]
The present invention has been made in view of such conventional problems, and it is an object
of the present invention to provide a dome-shaped speaker in which the first high-order
resonance of the sound pressure frequency characteristic is suppressed.
[0012]
The invention according to claim 1 of the present application is a frame for fixing a speaker main
body, a frame having an opening, an annular top plate, a cylindrical magnet fixed to the rear
surface of the top plate, and magnets. A field portion including a yoke having a cylindrical
surface opposed to an inner circumferential side surface of the top plate via an air gap and fixed
to the back surface of the frame to generate magnetic flux in the air gap, and an air gap of the
field portion A dome-shaped speaker having a voice coil to be inserted, a dome-shaped
diaphragm attached to the voice coil to vibrate, and an edge attached to the opening of the frame
to vibratably hold the outer periphery of the dome-shaped diaphragm. And a braking piece
concentrically attached in the vicinity of the connection portion of the voice coil of the domeshaped diaphragm.
[0013]
The invention according to claim 2 of the present application fixes the speaker body, a frame
having an opening, an annular top plate, a cylindrical magnet fixed to the rear surface of the top
plate, and a magnet holding the inner periphery of the top plate A field section including a yoke
having cylindrical surfaces facing each other through an air gap, fixed to the back of the frame to
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generate magnetic flux in the air gap, a voice coil inserted into the air gap of the field section,
and a voice coil A dome-shaped speaker having a dome-shaped diaphragm that is attached to and
vibrated, and an edge that is attached to the opening of the frame and holds the outer periphery
of the dome-shaped diaphragm in a freely vibrating manner, A braking piece is provided
concentrically mounted in the vicinity of the connection portion on the back surface of the domeshaped diaphragm.
[0014]
According to the present invention having such characteristics, the dome-shaped diaphragm is
attached to the voice coil inserted into the air gap of the field section, and the braking piece is
attached in the vicinity of the connection section of the voice coil. This braking piece acts on the
diaphragm with viscosity.
As a result, the outer peripheral portion of the dome-shaped diaphragm, which is the largest in
deformation, is damped, so that a speaker with sound pressure frequency characteristics is
obtained by suppressing the first high-frequency resonance mode.
[0015]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dome-shaped speaker according
to a first embodiment of the present invention will be described below with reference to the
sectional view of FIG.
Since the configuration other than the braking pieces is the same as that of the conventional
example shown in FIG. 6, the same parts will be denoted by the same reference numerals and the
detailed description will be omitted.
[0016]
The dome-shaped diaphragm 7 is fixed to the cylindrical portion 8 and supported by the frame 1
of the speaker via the elastic edge 6.
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The field section is composed of the top plate 2, the magnet 3, the center pole of the yoke 4, and
the air gap 5. This field section gives the voice coil 9 a uniform magnetic field, as in the prior art.
.
[0017]
Now, in the present embodiment, the braking piece 11 is attached in the vicinity of the
cylindrical portion 8 connected to the voice coil 9 on the back surface of the dome-shaped
diaphragm 7.
The braking piece 11 is a ring-shaped braking member having elasticity.
[0018]
In such a dome-shaped speaker, when a voice current is applied to the voice coil 9, an
electromagnetic force is received by the magnetic flux of the air gap 5, and the cylindrical
portion 8 holding the voice coil 9 performs a piston motion according to the voice current. . This
vibration is transmitted to the dome-shaped diaphragm 7, and a sound is generated by the
vibration of the air in contact with this. When the frequency rises, the entire inner peripheral
portion of the dome-shaped diaphragm 7 becomes mass as a driving load, and the outer
peripheral portion of the diaphragm including the edge 6 elastically operates, as shown in FIG. As
shown by the broken line, the portion of the dome-shaped diaphragm 7 in proximity to the edge
6 is deformed and vibrates. Due to this deformation vibration, a first high-order resonance mode
is generated in the sound pressure frequency characteristic. However, here, since the braking
piece 11 is attached in the vicinity of the connection portion of the back surface of the domeshaped diaphragm 7 with the cylindrical portion 8, a viscous element is connected to the
elastically operating portion. The entire outer periphery of the dome-shaped diaphragm 7 that
vibrates with great deformation is damped.
[0019]
FIG. 2 (b) is an equivalent circuit showing the vibration characteristics of the dome-shaped
speaker of this embodiment. Unlike FIG. 7 of the conventional example, the viscous resistance R1
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of the vibrating reed 11 is added in series with the equivalent compliance C1 of the elastic
portion 7a of the dome-shaped diaphragm 7. Therefore, a damping element is added to the
resonance circuit formed by the equivalent mass M1 of the dome-shaped diaphragm 7 and the
equivalent compliance C1 of the elastic portion 7a, and the first high-order resonance mode up to
this point determined by this resonance circuit is suppressed. Ru. Therefore, the sound pressure
peak due to the resonance of the conventional sound pressure frequency characteristics can be
sufficiently reduced.
[0020]
FIG. 3 shows sound pressure frequency characteristics of the dome-shaped speaker in the
present embodiment. Here, for example, in a dome-shaped speaker with a diameter of 12 cm,
butyl rubber having a width of 6 mm and a thickness of 0.5 mm is attached to the inside of the
dome-shaped diaphragm 7 via an adhesive. It can be seen that the sound pressure peak at a
frequency of about 4.5 kHz is sufficiently reduced in the dome-shaped speaker of the present
embodiment, and a flatter sound pressure frequency characteristic can be obtained.
[0021]
Next, a second embodiment of the present invention will be described with reference to FIG. This
embodiment is the same as the first embodiment except for the attachment position of the
braking piece, so only the braking piece will be described. The braking piece 12 is attached in a
band shape over the vicinity of the connection with the voice coil 9 on the back surface of the
dome-shaped diaphragm 7 and the inner surface of the end of the cylindrical portion 8. The
braking piece 12 is a ring-shaped braking member made of the same material as that of the first
embodiment.
[0022]
The sound pressure generation operation of the dome-shaped speaker with such a configuration
is the same as that of the first embodiment, but the upper end portion of the inner periphery of
the voice coil 9 is also damped by the braking piece 12, so When the outer periphery of the
dome-shaped diaphragm 7 is deformed, the deformation of the upper end of the cylindrical
portion 8 is suppressed. Therefore, the peak of the first order high frequency resonance mode
can be sufficiently reduced.
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[0023]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 5
is a cross-sectional view of the dome-shaped speaker in the third example, cut at the top of the
frame. Also in this embodiment, the configuration is the same as that of the first embodiment
except that the shape and mounting position of the braking piece are different, so only the
braking piece will be described. For example, four braking pieces 13 are attached on the back
surface of the dome-shaped diaphragm 7 in the vicinity of the connection with the voice coil 9.
The braking piece 13 is, for example, a band-shaped braking member made of the same material
as that of the first embodiment.
[0024]
In the dome-shaped speaker configured in this way, piston vibration generated by the voice coil 9
is transmitted to the dome-shaped diaphragm 7 to generate a sound, but since the braking piece
13 is divided into small pieces and attached, The portions to which these braking pieces are
attached become locally large in mass and viscosity. Therefore, the vibration mode of the outer
peripheral portion of the dome-shaped diaphragm which operates elastically in the first
resonance mode and in which the deformation is the largest is made nonuniform. For this reason,
the sound pressure frequency characteristic in which the first order high frequency resonance
mode is suppressed can be obtained. Further, since the braking piece 13 is divided into small
pieces, it is easy to attach to the diaphragm, and it has an advantage of being excellent in mass
productivity of the speaker.
[0025]
In the present embodiment, a part of the braking piece 13 is attached in the vicinity of the voice
coil joint on the back surface of the dome-shaped diaphragm 7, and the others are from the inner
peripheral upper end of the cylindrical portion 8 to the dome-shaped diaphragm The same effect
can be obtained by pasting over the back of 7. Further, although four braking pieces 13 are
provided in the present embodiment, the same effect can be obtained by using other numbers.
Further, even in the case of the dome-shaped speaker in which the dome-shaped diaphragm 7
and the cylindrical portion 8 of the voice coil are integrally formed, it is apparent that the effect
can be obtained even when pasting as in the first to third embodiments. It is.
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[0026]
As described above, according to the present invention, the braking action is divided into a ring
or a small piece in the vicinity of the connection portion of the voice coil of the dome-shaped
diaphragm, and the viscous action of the diaphragm is obtained. In operation, the first high-order
resonance mode of the sound pressure frequency characteristic is suppressed. For this reason, it
is possible to obtain an effect that a dome-shaped speaker having excellent frequency
characteristics can be realized without changing the configuration of the field portion of the
speaker and the diaphragm itself.
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