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JP2000341793

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DESCRIPTION JP2000341793
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sealed box type planar speaker in which a diaphragm is driven using a magnetostrictive speaker
driver to improve the sound pressure and to make the entire speaker thinner.
[0002]
2. Description of the Related Art FIG. 7 is a longitudinal sectional view showing an example of a
conventional closed box type planar speaker. The closed box type planar speaker 1 shown in the
same figure drives a flat diaphragm 2 from the back side by a voice coil type speaker driver 3.
The speaker driver 3 comprises a voice coil 5 one end of which is bonded to the center of the
back surface of the diaphragm 2 via the piston plate 4 and a columnar magnet 6 coaxially
disposed on the other end side of the voice coil 5. Be done. The columnar magnet 6 is
accommodated in a flanged bottomed cylindrical yoke 7, and a ring-shaped gasket is mounted on
the frame 9 assembled to the peripheral portion of the plate-like back plate 8 holding the
cylindrical portion of the yoke 7. The peripheral portion of the diaphragm 2 is fixed via 9a. The
voice coil 5 is connected to the ridge of the yoke 7 by a damper 10 whose one end is connected
to the side surface thereof. In the conventional speaker driver 3, when a voice current is supplied
to the voice coil 5 in the magnetic field formed by the columnar magnet 6 to excite the voice
current, the force of the framing generated in the voice coil 5 causes the piston plate 4 to move
forward and backward. In order to drive, the diaphragm 2 vibrates to generate a sound pressure.
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[0003]
However, since the diaphragm drive capability of the speaker driver 3 is proportional to the
number of turns of the voice coil 5, the sound pressure required for practical use is sufficient for
the above-mentioned conventional closed box type planar speaker 1 In order to ensure the
above, the voice coil 5 or the columnar magnet 6 also needs to have a shaft length of a certain
extent or more, and therefore, there is a problem that there is a certain limit to thinning in the
vibration direction. . In addition, when the sealed box type planar speaker 1 is miniaturized, the
air compliance between the back plate 8 and the diaphragm 2 is reduced as the internal volume
of the speaker is reduced. The reproduction frequency has risen, and the problem is that the
reproduction band can be narrowed and the sound reproduction with high quality can not be
expected.
[0004]
On the other hand, it has been a long time since the appearance of speakers of electrostatic type
or the like which drives the diaphragm without using the voice coil 5 or the like, and speaker
drivers using various materials have been put to practical use. For example, an electrostrictive
material that deforms upon application of a voltage such as barium titanate porcelain generally
functions as a "piezoelectric substance" because it apparently functions in the same way as a
piezoelectric substance (PZT) such as Rochelle salt. However, it is known that such a piezoelectric
substance changes its piezoelectric effect depending on the direction of the applied electric field.
In addition, while Rochelle salt exhibits the piezoelectric transverse effect that deforms most in
the direction perpendicular to the direction of the electric field, quartz and barium titanate
exhibit the piezoelectric longitudinal effect that deforms most in the same direction as the
direction of the electric field. . However, for example, an electrostrictive speaker driver using
barium titanate ceramic formed by sintering powdered barium titanate is used exclusively as a
high-pitched speaker (tweeter) because the resonance frequency of the vibrator is relatively high.
The current situation is that it can not be expected to be used as a low frequency transducer.
[0005]
On the other hand, some ferromagnetic materials such as single metals such as Ni and Co, Fe-Al
alloys or ferrites exhibit a magnetostriction phenomenon in which the dimensions of the element
change in response to an external magnetic field. It is known that the magnetic (magnetization)
characteristics of the element change due to twisting and torsional stress (torque) when the
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characteristics change or when orthogonal magnetic fields are simultaneously applied. Since a
magnetostrictive element obtained by processing this type of magnetostrictive material into a
specific shape can be used for a speaker driver, development of an element having a large stress
or stress distortion generated in response to an applied magnetic field is urgently required. In
fact, magnetic materials having a Laves-type crystal structure consisting of rare earth-transition
metals exhibit 50 to 100 times the displacement of conventional ferromagnetic materials, and
even 2 to 2 times the size of piezoelectric materials (PZT). It has been found that three times the
generated stress can be obtained. Among magnetostrictive devices represented by (Tb0.3Dy0.7)
Fe2 which is one of such magnetic materials, a device exhibiting a magnetostrictive deformation
whose displacement amount exceeds 1000 ppm has been discovered, and in order to distinguish
it from a normal magnetostrictive device, It may be called a magnetostrictive element or the like.
However, even with such a giant magnetostrictive element, there are hardly any ones that can
obtain practical sound pressure at present, and practical use of a speaker incorporating a
magnetostrictive speaker driver has been considered as a future issue.
[0006]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems,
and has an object to drive a diaphragm using a magnetostrictive speaker driver, to improve the
sound pressure and to make the entire speaker thinner.
[0007]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention
according to claim 1 is a square box-shaped speaker casing having a front opening, and a flat
plate slightly smaller than the front opening of the speaker casing. And a rectangular frameshaped damper which connects the peripheral portion of the diaphragm to the peripheral edge of
the opening of the speaker housing to seal the speaker housing, and receives an external
magnetic field in a direction substantially orthogonal to the magnetic field application direction.
An excitation coil is wound around an outer periphery of a thin-plate shaped magnetostrictive
element that undergoes magnetostrictive deformation to be disposed in the speaker housing, and
a magnetostrictive speaker driver is provided which vibrates and drives the diaphragm.
[0008]
The present invention according to claim 2 is a rectangular tubular speaker housing having an
open front and a back, a flat front diaphragm slightly smaller than a front opening of the speaker
housing, and a back of the speaker housing. A flat-plate back diaphragm slightly smaller than the
opening, and a square frame-shaped front damper connecting the peripheral edge of the front
diaphragm to the front opening periphery of the speaker housing to close the front opening of
the speaker housing And a rectangular frame-shaped rear damper connecting the peripheral
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edge of the rear diaphragm to the peripheral edge of the rear opening of the speaker enclosure
to close the rear opening of the speaker enclosure; An excitation coil is wound around the outer
periphery of a thin-plate shaped magnetostrictive element that undergoes magnetostrictive
deformation in the orthogonal direction to be disposed within the speaker housing, and a front
magnetostrictive speaker driver for vibrationally driving the front diaphragm, and an external
magnetic field An excitation coil is wound around the outer periphery of a thin plate
magnetostrictive element magnetostrictively deformed in a direction substantially orthogonal to
the magnetic field application direction and disposed in the speaker housing, and the back
magnetostrictive speaker driver It is characterized by having.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present
invention will be described with reference to FIGS.
FIG. 1 is an exploded perspective view showing an embodiment of the sealed box type flat
speaker of the present invention, and FIGS. 2 (A) and 2 (B) are partially cut front views of the
closed box type flat speaker shown in FIG. FIG. 3 is a front view and a longitudinal sectional view
of a part of the magnetostrictive speaker driver shown in FIG. 1, and FIG. 4 is a view showing the
magnetostrictive characteristics of the magnetostrictive element shown in FIG. FIG. 6 is an
exploded perspective view showing another embodiment of the sealed box type flat speaker of
the present invention, and FIGS. 6 (A) and 6 (B) are partially cut front views of the closed box
type flat speaker shown in FIG. And a longitudinal sectional view.
[0010]
The closed box type flat speaker 11 shown in FIG. 1 and FIGS. 2 (A) and 2 (B) is for generating
sound by pistoning two back faces of the rectangular thin plate-like diaphragm 12 and producing
a square box having an open front face. Inside the speaker housing 16, a pair of magnetostrictive
speaker drivers 13 for driving the four driving points of the diaphragm 12 at two positions are
arranged in two rows.
As shown in FIGS. 3A and 3B, the magnetostrictive speaker driver 13 forms a magnetostrictive
material exhibiting a magnetostrictive lateral effect that expands and contracts in a direction
substantially orthogonal to the application direction of the magnetic field into a rectangular thin
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plate shape. The magnetostrictive element 14 in which the two equidistant points are made to
correspond to the drive point of the diaphragm 12 by fixing the fixing portion 19 that holds the
part, and the magnetostrictive element 14 divided into three equally wound around the outer
circumference It comprises an exciting coil 15 in which wound coil pairs 15a, 15b, 15c are
connected in series.
The exciting coil 15 may be wound directly on the outer periphery of the magnetostrictive
element 14 or a spacer (not shown) such as butyl rubber or a vinyl sheet which allows relative
displacement of the exciting coil 15 in close contact with the magnetostrictive element 14. When
wound and using a spacer, the restriction of the exciting coil 15 on the magnetostrictive
deformation of the magnetostrictive element 14 is reduced.
[0011]
The diaphragm 12 has a flat plate shape slightly smaller than the front opening of the speaker
housing 16, and the peripheral portion thereof is connected to the periphery of the opening of
the speaker housing 16 via a damper 17 made of a square frame-shaped thin rubber or the like.
is there. Therefore, the gap between the speaker housing 15 and the diaphragm 12 is closed by
the damper 17 and the speaker housing 16 is sealed. Further, the diaphragm 12 couples two
drive points to two equidistant points of the magnetostrictive element 14 via the connection
piece 18. That is, the magnetostrictive speaker driver 13 winds the plurality of series-wound coil
pairs 15a, 15b and 15c at predetermined intervals on the outer periphery of the magnetostrictive
element 14, and the fixing portion 19 holding the both ends of the magnetostrictive element 14
The magnetostrictive elements 14 between the series wound coil pairs 15a and 15b and between
15b and 15c are connected to the casing 16 separately corresponding to two driving points
provided on the diaphragm 12.
[0012]
By the way, the magnetostrictive element 14 having the following characteristics is used for the
sample having 20 coils per 1 cm, and the magnetostrictive element 14 used in the present
embodiment shows (Tb0.3Dy0.7) Fe2 exhibiting magnetostrictive deformation exceeding 1000
ppm as described above. It can be said to be a super giant magnetostrictive element because it
exhibits a magnetostrictive deformation which is ten times greater than the giant
magnetostrictive element represented by. Electric resistance: (20 to 30) × 10 -8 Ω m Relative
permeability: 100 to 300 Holding power: 1 to 2 Oe Young's modulus: (15 to 20) × 10 10 n / m
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2 Tensile strength (10 to 40) x 107 Pa · thermal expansion coefficient; (10 to 12) ppm / ° C
[0013]
Note that, for example, a powder metallurgy method in which a plurality of raw material alloys
are crushed, formed in a magnetic field, processed and coated after sintering, or low pressure
casting of a raw material alloy is performed. It can be manufactured by the Bridgman method in
which crystal growth is followed by annealing treatment, processing and coating, or a method of
improving them or a method completely different from this. However, the magnetostriction
characteristics of such an ultra-magnetostrictive element 14 are easily influenced by the
component ratio of the raw material alloy and the way of blending, and it is necessary to repeat
various trial and error for manufacturing from the laboratory stage to the practical stage.
However, it is confirmed from, for example, the test results shown in FIG. 4 that the element has
a large generation stress with a magnetostrictive deformation capability which is more than ten
times that of a conventional element called a giant magnetostrictive element. The figure plots the
displacement of the other end with respect to the magnetic field when the magnetic field is
applied by fixing one end of the 28 cm-long magnetostrictive element 14. It is clear from this test
result that when the magnetic field of 40 oersteds (Oe) is applied to the magnetostrictive element
14, the magnetostrictive lateral effect close to 8 mm at maximum is exhibited, but both ends of
the magnetostrictive element 14 are fixed and the magnetic field is Even when applied, it has
been confirmed that the displacement of the two equidistant points of the magnetostrictive
element 14 is close to 6 mm when the magnetic field of 40 oersted (Oe) is applied.
[0014]
In the flat speaker 11 configured as described above, each drive point of the diaphragm 12 is
displaced in the front-rear direction when the three pairs of direct-wound coil pairs 15a, 15b,
15c disposed across the drive point are energized and excited. Since the exciting coil 15 is
excited by being supplied with a voice current, a magnetic field corresponding to the magnitude
of the voice current is generated. That is, since the series coil pairs 15a, 15b and 15c are
connected in series with each other, a magnetic field of the same polarity proportional to the
magnitude of the current and the number of coil turns is generated, and the magnetostrictive
element 14 is magnetostrictive according to the magnitude of the magnetic field. Deform. Since
the magnetostrictively deformed magnetostrictive element 14 is displaced in the back and forth
direction by the magnetostrictive lateral effect, the diaphragm 12 whose drive points are
respectively coupled to the magnetostrictive element 14 through the connection pieces 18 has a
total of two points 4 for each magnetostrictive speaker driver 13 The portions are driven in
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phase in the front-rear direction from the rear surface side, and piston vibration is generated in
the front-rear direction while bending and deforming the damper 17 to generate a sound
pressure. The stress generated by the magnetostrictive element 14 has a very large value
corresponding to that called a superparamagnetostrictive element, and therefore, even when the
sealed box type planar speaker 11 is miniaturized, the compliance with the decrease in the
volume inside the speaker, which has conventionally been a problem In spite of the decrease,
sufficient low-range regeneration ability can be exhibited.
[0015]
As described above, the closed box type flat speaker 11 is configured by combining the
magnetostrictive element 14 exhibiting the magnetostrictive lateral effect, which expands and
contracts in the direction substantially orthogonal to the application direction of the magnetic
field, and the diaphragm 12 at the driving point. The magnetostrictive element 14 can be
configured so as to face the back side of the back face 12, and the thickness of the speaker
measured in the vibration direction of the diaphragm 12 can be made sufficiently small, and the
structure can be made extremely thin. Moreover, since both ends of the magnetostrictive element
14 are fixed, the diaphragm 12 can be driven in the front-rear direction with strong driving force
from both sides sandwiching the driving point corresponding to two points dividing the
magnetostrictive element 14 into three. The vibration of the diaphragm 12 can be converted into
sound pressure without waste. Furthermore, by using, as the magnetostrictive element 14, an
extra-magnetostrictive element exhibiting magnetostrictive deformation that is several tens of
times greater than that of the extra-magnetostrictive element, a sufficient sound pressure not
comparable to existing magnetostrictive speaker drivers can be obtained. Thus, the diaphragm
can be piston-driven over a wide band from the low band to the high band, and good sound
reproduction is possible.
[0016]
In addition, since the exciting coil 15 is composed of a plurality of series wound coil pairs 15a,
15b, 15c wound around the magnetostrictive element 14 at a predetermined distance from each
other, the exciting coil 15 is subjected to magnetostrictive deformation of the magnetostrictive
element 14. Magnetostrictive speaker driver using a collectively wound excitation coil having the
entire length of the connection of the series-wound coil pairs 15a, 15b, 15c in which the seriespaired coil pairs 15a, 15b, 15c share the required deformation. As described above, excessive
stress is not generated over the entire length of the exciting coil, and it is possible to prevent
inconvenience such as plastic deformation of the exciting coil 15 or premature failure due to
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repeated magnetostrictive deformation. Further, since the plurality of series wound coil pairs
15a, 15b and 15c are connected in series with each other, the voltage applied to both ends of the
exciting coil 15 corresponds to the number of turns of each series wound coil pair 15a, 15b and
15c. A magnetic field can be generated.
[0017]
In the above embodiment, the front drive type closed box type flat speaker 11 which drives the
diaphragm 12 facing forward is taken as an example, but the closed box shown in FIG. 5 and
FIGS. 6A and 6B. As in the case of the planar speaker 21, it is also possible to adopt a doublesided drive type configuration. The sealed box type flat speaker 21 is configured by providing a
front diaphragm 12f, two rows of front magnetostrictive speaker drivers 13f and a rear
diaphragm 12r, and two rows of back magnetostrictive speaker drivers 13r on a speaker housing
26 having a front and a rear opening. It is In a word, the closed box type flat speaker 21 has a
structure in which the above-mentioned closed box type flat speakers 11 are closely connected to
each other on the back and the barrier of the connecting portion is removed. The space between
the front opening of the speaker housing 26 and the front diaphragm 12f is closed by the front
damper 17f, and the space between the rear opening of the speaker housing 26 and the rear
diaphragm 12r is closed by the rear damper 17f. is there.
[0018]
Since the closed box type planar speaker 21 drives the magnetostrictive speaker drivers 13f and
13r of the front and back two rows in phase, the sound pressure radiated forward and the sound
pressure radiated backward are in phase with each other. For this reason, the sound pressure of
the antiphase which went around from the back to the front of the speaker housing 26 does not
cancel the sound pressure emitted forward, and the sound pressure of the same phase goes
around from the rear to the front of the speaker housing 26 As a result of increasing the sound
pressure radiated forward, a very high sound pressure can be obtained.
[0019]
In each of the above-described embodiments, the magnetostrictive speaker drivers 13 or 13f and
13r may be arranged in one row or in three or more rows with respect to the diaphragms 12, 12f
and 12r. When three or more columns are provided, they are dispersed in a matrix of n × m
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based on the number n of driving points for each magnetostrictive speaker driver 13, 13f, 13r
and the number m of columns of each magnetostrictive speaker driver 13, 13f, 13r. The
diaphragms 12, 12f and 12r can be piston-driven with nm drive points.
[0020]
Furthermore, in the above embodiments, two points that divide the magnetostrictive element 14
into three equal parts correspond to the driving points of the diaphragms 12, 12f and 12r, but
for example, the middle of the magnetostrictive element 14 divided into three equal parts. It is
also possible to divide the magnetostrictive element 14 into two parts in such a manner that the
portions are cut off, and make the magnetostrictive speaker drivers correspond to the respective
driving points of the diaphragms 12, 12f and 12r one to one. In this case, the same number of
magnetostrictive speaker drivers having the other end of the magnetostrictive element fixed at
one end as the drive point is present, but unlike the closed box type planar speakers 11 and 21
described above, Since the magnetostrictive element is present only on one side, the back side of
the diaphragm can be made more compact, and a thin and small flat speaker can be provided.
Further, such a method in which one end of the magnetostrictive element is fixed and the other
end is used as a driving point can be applied regardless of the number of driving points.
[0021]
As described above, according to the present invention as set forth in claim 1, the square boxshaped speaker casing having an open front face and the flat diaphragm having a size slightly
smaller than the front opening thereof are formed into a square frame. The magnetostrictive
speaker driver has an exciting coil wound around an outer periphery of a thin plate
magnetostrictive element which is connected by a damper to seal the speaker housing and
receives an external magnetic field and magnetostrictively deforms in a direction substantially
orthogonal to the magnetic field application direction. The diaphragm is driven to vibrate by
driving the diaphragm. The diaphragm can be driven by a magnetostrictive element that exhibits
a magnetostrictive lateral effect that expands and contracts in a direction substantially
orthogonal to the application direction of the magnetic field. By constructing the speaker by
facing the magnetostrictive element in the near direction, the thickness of the speaker measured
in the vibration direction of the diaphragm can be made sufficiently small, and an extremely thin
structure can be obtained. By using a magnetostrictive speaker driver composed of a super
magnetostrictive element exhibiting magnetostrictive deformation, it is possible to obtain a
sufficient sound pressure which can not be compared with existing magnetostrictive speaker
drivers. Therefore, even when the speaker is miniaturized, Sufficient low frequency reproduction
capability can be exhibited regardless of the compliance decrease caused by the decrease in the
speaker internal volume, which causes the piston plate to drive the diaphragm over a wide band
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from low to high frequencies. Thus, excellent effects such as good sound reproduction can be
obtained.
[0022]
Further, according to the present invention according to claim 2, a square tubular speaker
housing having an open front and a rear surface, a flat front diaphragm and a rear diaphragm
slightly smaller than the respective openings, a square frame front A front surface
magnetostrictive speaker in which an excitation coil is wound around the thin-plate shaped
magnetostrictive element which is connected by a damper and a rear surface damper to seal the
speaker casing from the front and back and receives an external magnetic field and
magnetostrictively deforms in a direction substantially orthogonal to the magnetic field
application direction. The driver and the back surface magnetostrictive speaker driver are
disposed in the speaker housing, and the front diaphragm and the back surface diaphragm are
driven to vibrate respectively, so that the magnetostrictive lateral effect is expanded and
contracted in the direction substantially orthogonal to the application direction of the magnetic
field. The diaphragm can be driven by the magnetostrictive element, and the thickness of the
speaker measured in the vibration direction of the diaphragm is sufficiently small by configuring
the speaker by facing the magnetostrictive element close to the diaphragm. Using a
magnetostrictive speaker driver consisting of a super magnetostrictive element that can be made
extremely thin and exhibits a magnetostrictive deformation that is more than ten times as large
as that of the giant magnetostrictive element, making it incomparable to existing
magnetostrictive speaker drivers. The sound pressure radiated forward and the sound pressure
radiated backward are in phase with each other by driving the magnetostrictive speaker driver in
phase. The sound pressure of the reversed phase does not cancel the sound pressure emitted
forward, but the sound pressure of the same phase which got around from the rear to the front
of the speaker housing increases the sound pressure emitted forward It is possible to obtain a
very high sound pressure, and even when the speaker is miniaturized, the sound pressure is
sufficiently low regardless of the reduction in compliance caused by the decrease in the volume
of the speaker, which has been a problem in the past. It can exhibit the reproduction capability,
the diaphragm over a wide band up to the high-frequency low-pass and piston drive, an excellent
effect of equal are possible good sound reproduction.
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