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JPH05176395

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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
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DESCRIPTION JPH05176395
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electromagnetic induction type speaker. 2. Description of the Related Art Conventionally, a
magnetic circuit unit for generating a direct current magnetic field, a diaphragm made of a
conductive material supported in a freely vibrating manner in the direct current magnetic field,
an electromagnetic induction coil disposed on the magnetic circuit unit side An electromagnetic
induction type speaker that vibrates the diaphragm to perform acoustic reproduction by
supplying a signal current to the electromagnetic induction coil to generate an AC magnetic field
and inducing an induction current to the diaphragm. Has been proposed. As this type of
electromagnetic induction type speaker, one configured as shown in FIG. 6 is known. The
electromagnetic induction type speaker shown in FIG. 6 includes a magnetic circuit unit 1 for
generating a direct current magnetic field, a diaphragm 2 made of a conductive material
supported in a freely vibrating manner in the direct current magnetic field, and the magnetic
circuit unit 1 side. And the electromagnetic induction coil 3 provided. The magnetic circuit unit 1
includes a yoke 4, a pole piece 5 disposed so as to be embedded in the center of the yoke 4, and
a ring-shaped magnet 6 disposed on the yoke 4 so as to surround the pole piece 5. It comprises a
ring-shaped top plate 7 disposed on the magnet 6. The magnetic circuit unit 1 has a ring-shaped
magnetic gap 8 for generating a DC magnetic field with air gaps facing each other between the
top plate 7 and the pole piece 5. The vibrating plate 2 is formed in a ring shape corresponding to
the magnetic gap 8, and is supported so as to be capable of vibrating so as to be located in the
magnetic gap 8. That is, the diaphragm 2 supports the outer peripheral side peripheral edge on
the inner peripheral surface of the top plate 7 via the visco-elastic support 9 and supports the
inner peripheral side peripheral edge on the outer peripheral surface of the pole piece 5 as
viscoelastic. By being supported via the body 9, it is vibratably supported in the magnetic gap 8.
Further, an electromagnetic induction coil 3 for inducing an induced current to the diaphragm 2
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is disposed on the back side of the diaphragm 2 and disposed to face the diaphragm 2. In the
electromagnetic induction type speaker thus configured, the ring-shaped diaphragm 2 formed of
a conductive material functions as a short circuit coil, and the electromagnetic induction coil 3
receives a signal current corresponding to a predetermined acoustic signal. When supplied, an
induced current is induced in the diaphragm 2. The induced current flows in the circumferential
direction of the diaphragm 2. Then, the induced current acts on the DC magnetic field in the
magnetic gap 8 to vibrate the diaphragm 2 and radiation of reproduction sound is performed.
SUMMARY OF THE INVENTION In the electromagnetic induction type speaker configured as
described above, it is necessary to prevent contact between the diaphragm 2 and the
electromagnetic induction coil 3 when the diaphragm 2 vibrates. Therefore, it is necessary to
provide a required distance between the diaphragm 2 and the electromagnetic induction coil 3.
Furthermore, since the electromagnetic induction coil 3 is disposed only on the back side of the
diaphragm 2, when the diaphragm 2 vibrates, the distance between the electromagnetic
induction coil 3 is changed, and the diaphragm 2 and the electromagnetic induction coil are
changed. The electromagnetic coupling between 3 is not constant, and the vibration of the
diaphragm 2 according to the signal current supplied to the electromagnetic induction coil 3 is
not performed. Further, since the electromagnetic induction type speaker has a configuration in
which the diaphragm 2 is disposed in the magnetic gap 8, when the area of the diaphragm 2 is
increased, the distance between the magnetic gaps 8 is increased. The magnetic flux density in
the magnetic gap 8 is reduced. Therefore, in the electromagnetic induction type speaker as
described above, sufficient sound pressure output characteristics can not be obtained, and good
sound reproduction can not be performed. Therefore, the present invention has been proposed
for the purpose of providing an electromagnetic induction type speaker which can obtain
sufficient sound pressure output characteristics with high efficiency and can achieve good sound
reproduction. SUMMARY OF THE INVENTION In order to achieve the above object, the present
invention is formed in a ring shape by a magnetic circuit portion generating a DC magnetic field
in a ring-shaped magnetic gap, and a conductive material. A diaphragm supported in a magnetic
gap in a vibrating manner, and first and second electromagnetic induction coils disposed close to
the front and back sides of the diaphragm with the diaphragm interposed therebetween. A signal
current is supplied to the first and second electromagnetic induction coils such that an
alternating magnetic field in phase is generated in the coils. In the electromagnetic induction
type loudspeaker according to the present invention, an alternating current magnetic field in
phase with the first and second electromagnetic induction coils disposed close to the front and
back sides of the diaphragm with the diaphragm interposed therebetween. By supplying the
signal current so as to generate the above, the diaphragm is driven to emit the reproduction
sound. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A specific embodiment of
the present invention will be described below with reference to the drawings. The
electromagnetic induction type loudspeaker according to the present invention comprises, as
shown in FIG. 1, a magnetic circuit unit 11 for generating a direct current magnetic field, a
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diaphragm 12 made of a conductive material vibratably supported in the direct current magnetic
field, and the vibration. It comprises a first electromagnetic induction coil 13 and a second
electromagnetic induction coil 14 which are disposed close to each other on the front side and
the rear side with the plate 12 interposed therebetween.
The magnetic circuit portion 11 includes a yoke 15 made of a magnetic material, a pole piece 16
made of a magnetic material disposed so as to be erected at the center of the yoke 15, and the
pole piece 15 It comprises a ring-shaped magnet 17 disposed on the yoke 15 and a top plate 18
formed of a ring-shaped magnetic material disposed on the magnet 17 so as to surround it. The
magnetic circuit portion 11 forms a ring-shaped magnetic gap 19 which generates a DC magnetic
field with air gaps facing each other between the top plate 18 and the pole piece 16. The
diaphragm 12 is formed in a ring shape corresponding to the magnetic gap 19 by a light-weight
well-conductive material such as aluminum foil, and a corrugation is concentrically formed on
the main surface portion. It is formed. The diaphragm 12 supports the outer peripheral side
peripheral edge on the top plate 18 via the support ring 20 and the inner peripheral side
peripheral edge on the pole piece 16 via the support ring 21 in the same manner as described
above. It is supported vibratably. By the way, in this electromagnetic induction type speaker, the
diaphragm 12 can be disposed in the magnetic gap 19 by placing it on the top plate 18 and the
pole piece 16. Is provided. That is, on the upper surface side of the top plate 18 and the pole
piece 16 and at the corner portion on the magnetic gap 19 side, the notch stepped portions 22
and 23 are formed. These notch steps 22 and 23 are formed to face the outer side of the upper
surface of the magnetic circuit portion 11 as shown in FIG. 1, so that the diaphragm 12 is formed
on the outer peripheral edge side from the upper surface side of the magnetic circuit portion 12
and The inner peripheral edge side is disposed in the magnetic gap 19 by being disposed so as to
be placed on the notch steps 22 and 23, respectively. Further, support rings 20 and 21 for
supporting the outer peripheral edge side and the inner peripheral edge side of the diaphragm
12, respectively, are also disposed in the notch stepped portions 22 and 23 by arranging them
from the upper surface side of the magnetic circuit portion 12. The notch stepped portions 22
and 23 are formed to such a depth that the diaphragm 12 supported thereon can be positioned
substantially at the center of the magnetic gap 19. Further, the support rings 20 and 21 are fixed
to the notch stepped portions 22 and 23 by an adhesive and support the diaphragm 12. Further,
the support rings 20 and 21 exposed to the magnetic gap 19 are formed of a ferromagnetic
material in order to make the transmission of the magnetic flux excellent.
The first electromagnetic induction coil 13 is supported on the upper end side of the coil holding
cylinder 24 disposed on the yoke 15 so as to be fitted on the outer peripheral side of the pole
piece 16, and the diaphragm It is arrange | positioned so that the back of 12 may be adjacent.
The coil holding cylinder 24 has its mounting position regulated in the horizontal direction by
fitting the base end portion to the mounting position regulating projection 15 a protruding from
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the yoke 15. Further, the second electromagnetic induction coil 14 is supported on the lower
surface side of the coil supporting projection 26 provided on the outer peripheral side of the
equalizer 25 disposed on the upper end surface side of the pole piece 16 and on the front surface
of the diaphragm 12. It is arranged to be close to each other. A plurality, for example, three, of
the coil support protrusions 26 are radially provided on the outer peripheral side of the equalizer
25 at equal intervals. The first and second electromagnetic induction coils 13 and 14 are
arranged to face each other, and can not contact the diaphragm 12 when the diaphragm 12 is
driven to vibrate. It is disposed close to the diaphragm 12 with a gap. Further, since the first and
second electromagnetic induction coils 13 and 14 are configured not to generate unnecessary
resonance when the diaphragm 12 is driven to vibrate and not to become an acoustic load, the
cross-sectional shape is substantially the same. It is wound to be round. Then, a signal current is
supplied to the first and second electromagnetic induction coils 13 and 14 so as to generate an
alternating magnetic field in phase to the coils 13 and 14 through a predetermined signal line. .
Further, a concave portion 27 is formed in the outer periphery of the pole piece 16 constituting
the magnetic circuit portion 11 and in the portion facing the first electromagnetic induction coil
13. The concave portion 27 widens the gap between the first electromagnetic induction coil 13
and the pole piece 16, and the magnetic circuit portion which is the back side of the diaphragm
12 when the diaphragm 12 is driven to vibrate. 11 to reduce the viscous drag of the air flow
generated in the air flow. In the magnetic circuit portion 11, a sound absorbing material 28 is
disposed which absorbs the reproduced sound radiated to the back side of the diaphragm 12. In
the electromagnetic induction type speaker configured as described above, when the first and
second electromagnetic induction coils 13 and 14 are supplied with a signal current that
generates an AC magnetic field in phase, the AC magnetic field causes a short circuit. An induced
current is induced in the diaphragm 12 which functions as a coil. The induced current flows in
the circumferential direction of the vibrating plate 12 and causes the vibrating plate 12 to
vibrate by the interaction with the DC magnetic field in the magnetic gap 19.
And since this speaker has the first and second electromagnetic induction coils 13 and 14
disposed so as to be closely opposed to the front and back sides of the diaphragm 12,
respectively, the diaphragm 12 vibrates and the magnetic gap is generated. Even when the
position in 19 is changed, the distance between the diaphragm 12 and the first electromagnetic
induction coil 13 and the distance between the diaphragm 12 and the second electromagnetic
induction coil 14 are always constant. As a result, the electromagnetic coupling state between the
diaphragm 12 and the first and second electromagnetic induction coils 13 and 14 also becomes
constant. Furthermore, since the first and second electromagnetic induction coils 13 and 14 are
supplied with a signal current that generates an in-phase alternating current magnetic field, the
diaphragm 12 is supplied with the signal current according to the supplied signal current. The
induction current is stabilized and induced, and the diaphragm 12 can be vibrated accurately
according to the signal current supplied. The sound pressure frequency characteristic of this
speaker exhibits the characteristic as shown in FIG. 3 and can be sufficiently put to practical use.
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By the way, since the second electromagnetic induction coil 14 disposed on the front side of the
diaphragm 12 functions as an equalizer, frequency characteristics can be obtained by
appropriately changing the shape and size of the coil 14. You can adjust the directional
characteristics. FIG. 5 shows another embodiment of the present invention, in which a horn is
provided and a second electromagnetic induction coil disposed on the front side of the
diaphragm 12 is divided. Are constructed. The speaker shown in FIG. 5 is provided with a horn
40 on the sound emitting surface side of the diaphragm 12, and in addition to the equalizer 25
disposed on the pole piece 16, two more equalizers 41 and 42 are provided around the equalizer
25. Is provided. Further, second electromagnetic induction coils 14a and 14b divided so as to be
integrated with the respective equalizers 41 and 42 are provided. That is, the divided second
electromagnetic induction coils 14 a and 14 b are disposed on the lower end surfaces of the
equalizers 41 and 42. In this speaker, the reproduction sound radiated from the front side of the
diaphragm 12 is radiated from the opening side of the horn 40 through between the horn 40 and
the equalizers 25, 41 and 42. Also in the configuration as shown in FIG. 5, the same sound
pressure frequency characteristic as that of the above-mentioned speaker can be obtained, which
can be practically used. As described above, according to the present invention, the alternating
current in phase with the first and second electromagnetic induction coils disposed close to the
front and back sides of the diaphragm with the diaphragm interposed therebetween. Since the
signal current is supplied so as to generate a magnetic field, the signal current supplied to the
diaphragm even if the distance between the diaphragm and the electromagnetic induction coil is
changed due to the vibration of the diaphragm. Thus, the induction current is stably induced, and
the diaphragm can be vibrated accurately according to the signal current supplied to the coils.
As a result, it is possible to provide an electromagnetic induction type speaker that can obtain
sufficient sound pressure frequency characteristics with high efficiency.
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