JPH08140185

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DESCRIPTION JPH08140185
[0001]
The present invention relates to an electroacoustic system in which an alternating current as an
electrical signal is supplied to a drive coil to generate a driving force, and a diaphragm is vibrated
by the driving force to convert an electrical signal to sound. The present invention relates to a
conversion device, and more particularly to an electroacoustic conversion device having a
structure effective for thinning.
[0002]
2. Description of the Related Art As electro-acoustic transducers, dynamic loudspeakers utilizing
electromagnetic force according to Fleming's left hand law and magnetic loudspeakers utilizing
attraction and repulsion resulting from magnetic induction are known. There is. First, a dynamic
speaker will be described, and then a magnetic speaker will be described.
[0003]
FIG. 12 shows the structure of a dynamic speaker. A flat casing is configured by joining a
cylindrical cover (14) with one end opened and a cylindrical frame (23) with an equal outer
diameter and one end opened with the cover (14). In the cover (14), a plurality of small holes
(15) for sound emission are opened in a circle. A disc-shaped diaphragm (42) is disposed at the
central portion of the casing, and the diaphragm (42) is fixed by sandwiching the outer
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peripheral portion between the cover (14) and the frame (23). A cylindrical drive coil (52) having
a winding axis perpendicular to the diaphragm (42) is fixed to the lower surface of the
diaphragm (42). Further, a recess is formed in the center of the frame (23) toward the inside, and
a disk-like yoke (9) is attached to the recess. A disk-shaped DC magnetic field generating magnet
(31) is fixed to the center of the yoke (9). A pole piece (91) is attached to the upper surface of the
DC magnetic field generation magnet (31), and a ring-shaped air gap G 'is formed between the
pole piece (91) and the yoke (9). The drive coil (52) is accommodated in the air gap G 'with a
margin. Further, an electrode (61) is attached to the casing for supplying a cross current to the
drive coil (52).
[0004]
In the dynamic speaker, the magnetic flux generated from the DC magnetic field generating
magnet (31) is guided to the yoke (9) and the pole piece (91), and is focused to the air gap G 'as
shown by the broken line in the figure. A magnetic field is generated in the air gap G '. Therefore,
by passing an electric signal (cross current) to the drive coil (52) through the electrode (61), the
drive coil (52) generates an electromagnetic force according to Fleming's left-hand rule. As a
result, the diaphragm (42) vibrates integrally with the drive coil (52), and the electrical signal is
converted to sound.
[0005]
Next, the magnetic type speaker will be described. FIG. 13 shows the structure of a magnetic
speaker. A flat casing is configured by joining a cylindrical cover (16) whose one end is open and
a cylindrical frame (24) whose outer diameter is equal and whose one end is open, and the cover
(16). A round shaft shaped pole piece (92) protrudes downward at the center of the inner surface
of the cover (16), and a plurality of small holes (17) for sound emission are provided around the
pole piece (92). It has been set up in yen. Also, a drive coil (53) is disposed surrounding the pole
piece (92) and fixed to the inner surface of the cover (16). Furthermore, a DC magnetic field
generating magnet (32) is disposed surrounding the drive coil (53) and fixed to the inner surface
of the cover (16). On the other hand, on the frame (24), a diaphragm (43) is disposed with a
predetermined gap G ′ ′ between it and the pole piece (92), and its outer peripheral portion is
fixed to the inner peripheral wall of the frame (24). ing.
[0006]
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In the magnetic type speaker, the magnetic flux generated from the DC magnetic field generating
magnet (32) is guided by the cover (16) and the pole piece (92), and is focused to the air gap G
′ ′ as shown by the broken line in the figure. Pass G ′ ′ to the diaphragm (43). As a result, a
magnetic field is generated in the air gap G ′ ′ and the diaphragm (43) is magnetized by
magnetic induction. As a result, the diaphragm (43) is elastically deformed by the suction force
from the pole piece (92), and stands still at the mechanical midpoint where the suction force and
the elastic return force are balanced. Here, when an electric signal (cross current) is supplied to
the drive coil (53) through the electrode (62), the drive coil (53) generates a magnetic field
according to the right-handed screw law. In order to change the magnetic field generated in the
air gap G ′ ′ by the magnetic field, the attraction force received by the diaphragm (43)
changes, and the diaphragm (43) vibrates about the dynamic midpoint.
[0007]
However, in the dynamic type speaker of FIG. 12, a large amount of leakage flux does not
contribute to the drive of the diaphragm (42), and this is a loss, so that sufficient efficiency can
not be obtained. Also, from the viewpoint of power consumption, it is advantageous for the
impedance to be high, and in order to realize the high impedance, it is necessary to increase the
number of turns of the drive coil (52). As the method, a method of increasing the number of
turns in the radial direction of the drive coil (52) and a method of increasing the number of turns
in the axial direction can be considered. In the former method, since the width of the air gap G 'is
expanded, the leakage flux which is a loss is increased. In the latter method, the speaker is
increased as the axial length of the drive coil (52) is increased. There is a problem that the overall
thickness increases.
[0008]
On the other hand, in the magnetic type speaker of FIG. 13, since the pole piece (92) is formed to
protrude long from the drive coil (53), there is a problem that the overall thickness of the
speaker becomes large. In addition, although narrowing the gap G ′ ′ between the pole piece
(92) and the diaphragm (43) is effective for reducing the leakage flux and thus improving the
efficiency, if the gap G ′ ′ is set too small, the diaphragm There is a problem that (43) contacts
the pole piece (92) to generate an abnormal sound. In order to prevent this, it is necessary to use
a diaphragm (43) having a large rigidity, but in this case, it is difficult to emit low tones, and the
range is narrowed. As a result, the gap G ′ ′ has a large value to some extent, and the
efficiency is low.
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[0009]
Furthermore, in both dynamic and magnetic speakers, the number of parts is large because a
yoke and a pole piece are required, and this is a limitation on the design of the drive coil and
causes low impedance. It has become. An object of the present invention is to provide an electroacoustic transducer which consumes less power and which is thin and highly efficient.
[0010]
SUMMARY OF THE INVENTION An electroacoustic transducer according to the present invention
comprises a diaphragm having a peripheral portion as a fixed end, and is fixed to a central
portion of one surface of the diaphragm and to the diaphragm. A disk-shaped direct current
magnetic field which is fixed at a fixed position by providing a predetermined gap between a
cylindrical drive coil having a vertical winding axis, a diaphragm and the drive coil, and coaxially
with the drive coil. And a generating magnet. Then, most of the magnetic flux radiated from the
entire surface of the DC magnetic field generating magnet on the drive coil side passes through
the air gap and reaches the drive coil.
[0011]
In the above-described electro-acoustic transducer of the present invention, when a cross current
is supplied to the drive coil, a magnetic flux in accordance with the right-hand screw law is
generated in the drive coil. On the other hand, a magnetic flux is emitted from the DC magnetic
field generating magnet toward the drive coil. Here, since the drive coil can be considered as a
magnet having cross-distributed magnetic poles, attraction or repulsion acts on the drive coil in
relation to the DC magnetic field generation magnet, and the diaphragm is integrated with the
drive coil. It will vibrate. As a result, the electrical signal is converted to sound.
[0012]
As described above, since the magnetic flux radiated from the DC magnetic field generation
magnet is radiated to the air gap without focusing, the yoke and the pole piece are unnecessary,
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thereby reducing the number of parts and making it possible to reduce the thickness. Also, since
there is no design restriction due to the yoke or the pole piece, not only can the device be made
thinner by free design, but it is also possible to increase the number of turns of the drive coil,
thereby increasing the impedance. Be
[0013]
Specifically, the outer diameter of the drive coil is set to 80% or more and 116% or less,
preferably 88% or more and 107% or less of the outer diameter of the DC magnetic field
generation magnet.
[0014]
In the specific configuration, since the drive coil is formed to have an outer diameter in the above
range, the magnetic flux emitted from the DC magnetic field generating magnet is radiated
substantially perpendicularly from the magnet surface at the central portion of the magnet,
While the drive coil is vertically penetrated, the peripheral portion of the magnet radially extends
from the magnet surface and obliquely penetrates the drive coil.
Therefore, an attraction or repulsion force is exerted on the drive coil by the magnetic flux
penetrating substantially perpendicularly as described above. At the same time, the magnetic flux
penetrating obliquely as described above causes the same attraction force or repulsive force due
to the component perpendicular to the diaphragm, and the horizontal component causes the
electromagnetic force according to Fleming's left hand rule. As a result, the driving force based
on the above-mentioned two principles is simultaneously applied to the drive coil, and the
diaphragm is efficiently driven.
[0015]
Further, specifically, the inner diameter of the drive coil is 66% to 94%, preferably 77% to 89%,
of the outer diameter of the DC magnetic field generation magnet.
[0016]
By the way, it is experimentally demonstrated that the driving force based on the magnetic flux
penetrating the driving coil obliquely as described above largely contributes to the driving of the
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diaphragm similarly to the driving force based on the magnetic flux penetrating the driving coil
substantially perpendicularly as described above. It has been confirmed.
Therefore, the inner diameter of the drive coil is set to the above specific range, and the
diaphragm is driven mainly based on the driving force based on the magnetic flux penetrating
the drive coil obliquely. Then, by reducing the weight of the drive coil, the mass of the vibration
system including the diaphragm is reduced, the response of the vibration system is improved,
and the efficiency is improved.
[0017]
More specifically, the drive coil is fixed to the surface of the diaphragm on the side of the DC
magnetic field generating magnet or the surface on the opposite side, and in either case, the
diaphragm is driven according to the above principle.
[0018]
According to the electro-acoustic transducer of the present invention, the yoke and the pole piece
can be omitted, so that the device can be made thinner.
Also, due to the free design free from yoke and pole piece constraints, the number of turns of the
drive coil can be increased to increase the impedance, thereby reducing power consumption.
However, since the magnetic flux generated from the DC magnetic field generation magnet is
effectively used for driving the diaphragm, the efficiency of electroacoustic conversion can be
improved.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention
applied to a small speaker mounted on a portable telephone or the like will be described in detail
with reference to the drawings based on two embodiments. FIG. 1 is a cross-sectional view
showing the structure of the loudspeaker of the first embodiment, and FIG. 2 is an exploded
perspective view of the loudspeaker. A flat casing (20) is configured by joining a cylindrical cover
(1) having an open end and the cylindrical frame (2) having an equal outer diameter and an open
end, and the cover (1) . The cover (1) and the frame (2) are formed of, for example, a resin such
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as polybutylene terephthalate PBT or polyacetal POM.
[0020]
In the cover (1), a plurality of small holes (11) for sound emission are opened in a circle. On the
inner surface of the cover (1), a disc-shaped magnet for direct current magnetic field generation
with an outer diameter of 9.0 mm and a thickness of 1.0 mm mainly composed of neodymium,
samarium cobalt or the like on the central axis of the cover (1) 3) is fixed by a thermosetting
adhesive such as an acrylic adhesive or an epoxy adhesive.
[0021]
In the inside of the casing (20), a gap G of 0.6 mm is provided from the lower surface of the DC
magnetic field generation magnet (3), a disc-shaped diaphragm (4) is disposed, and the outer
periphery of the diaphragm (4) The part is adhesively fixed by being sandwiched between the
cover (1) and the frame (2). The diaphragm (4) is formed of a resin sheet having a thickness of
50 to 75 μm, for example, polyimide PI, polyetherimide PEI, polyethylene terephthalate PET or
the like. A drive coil (5) having a winding axis perpendicular to the diaphragm (4) coaxially with
the DC magnetic field generation magnet (3) is fixed to the lower surface of the diaphragm (4) by
a rubber adhesive. It is done. The drive coil (5) is formed in a cylindrical shape having an inner
diameter of 1.0 mm, an outer diameter of 9.5 mm, and a thickness of 0.25 mm by winding a
copper wire having a wire diameter of 0.04 mm.
[0022]
In addition, an electrode (6) made of brass or phosphor bronze or the like for supplying a crossspreading current to the drive coil (5) is heat-fused and fixed to the bottom surface of the frame
(2) along the inner peripheral wall. At the end of the electrode (6), a lead wire (not shown)
extending from the drive coil (5) is twisted and connected by soldering.
[0023]
As indicated by a broken line in the figure, the magnetic flux radiated from the DC magnetic field
generating magnet (3) is radiated substantially perpendicularly from the magnet surface at the
center of the magnet and penetrates the drive coil (5) substantially perpendicularly. On the other
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hand, at the periphery of the magnet, it radially extends from the magnet surface and obliquely
penetrates the drive coil (5).
[0024]
FIG. 3 shows the direction of the driving force generated when a current is supplied to the
driving coil (5) clockwise.
Here, FIG. 3 (a) shows a magnetic flux radiated substantially perpendicularly from the central
portion of the DC magnetic field generating magnet (3) and penetrating the driving coil (5)
substantially vertically and the driving coil (5) generated by the magnetic flux Shows the
direction of the driving force acting on the When a current is supplied clockwise to the drive coil
(5), a downward magnetic flux is generated in the drive coil (5) as shown by a broken line
according to the right-handed screw law. On the other hand, the DC magnetic field generating
magnet (3) has an N pole on the drive coil (5) side and an S pole on the opposite side, and a
magnetic flux is radiated downward toward the drive coil (5) as shown by the broken line. As a
result, in the drive coil (5), an S pole appears on the DC magnetic field generating magnet (3)
side, and an N pole appears on the opposite side, and an upward attractive force F with the DC
magnetic field generating magnet (3) Will occur.
[0025]
FIG. 3 (b) shows the magnetic flux penetrating radially from the periphery of the DC magnetic
field generation magnet (3) toward the drive coil (5) and obliquely passing through the drive coil
(5) and the drive coil generated by the magnetic flux The direction of the driving force acting on
(5) is shown. On the right side of the figure, the magnetic flux Br emitted from the direct current
magnetic field generation magnet (3) and obliquely reaching the drive coil (5) is a component Bry
perpendicular to the component Brx horizontal to the diaphragm (4) as shown. The vertical
component Bry causes the drive coil (5) to generate an upward suction force as in FIG. 3 (a). On
the other hand, for the horizontal component Brx, a direction according to Fleming's left-hand
rule, that is, an upward electromagnetic force Fr in the figure, is generated in relation to the
current flowing through the drive coil (5). Further, on the left side in the figure, the magnetic flux
Bl radiated from the DC magnetic field generation magnet (3) and obliquely reaching the drive
coil (5) is perpendicular to the component Blx horizontal to the diaphragm (4) as shown. The
component Bly is decomposed, and the vertical component Bly causes the drive coil (5) to
generate an upward suction force as in FIG. 3A. On the other hand, for the horizontal component
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Blx, a direction according to Fleming's left-hand rule, that is, an upward electromagnetic force Fl
in the figure, is generated in relation to the current flowing through the drive coil (5).
[0026]
Accordingly, the drive coil (5) receives an overall upward driving force by the upward suction
force shown in FIG. 3 (a) and the upward suction force and electromagnetic force shown in FIG. 3
(b).
[0027]
FIG. 4 shows the direction of the driving force generated when a current is supplied to the
driving coil (5) counterclockwise.
Here, FIG. 4 (a) shows a magnetic flux radiated substantially perpendicularly from the central
portion of the DC magnetic field generation magnet (3) and penetrating the drive coil (5)
substantially vertically and the drive coil (5) generated by the magnetic flux Shows the direction
of the driving force acting on the When a current is supplied to the drive coil (5) in a
counterclockwise direction, an upward magnetic flux is generated in the drive coil (5) as shown
by a broken line according to the right-handed screw law. As a result, in the drive coil (5), the N
pole appears on the DC magnetic field generating magnet (3) side, and the S pole appears on the
opposite side, and the downward repulsive force F with the DC magnetic field generating magnet
(3) Will occur.
[0028]
FIG. 4 (b) shows a magnetic flux penetrating radially from the periphery of the DC magnetic field
generation magnet (3) toward the drive coil (5) and obliquely passing through the drive coil (5)
and the drive coil generated by the magnetic flux The direction of the driving force acting on (5)
is shown. On the right side of the figure, the magnetic flux Br emitted from the direct current
magnetic field generation magnet (3) and obliquely reaching the drive coil (5) is a component Bry
perpendicular to the component Brx horizontal to the diaphragm (4) as shown. The vertical
component Bry causes the drive coil (5) to produce a downward repulsive force as in FIG. 4 (a).
On the other hand, for the horizontal component Brx, a downward electromagnetic force Fr
occurs in the direction according to Fleming's left hand law in the relationship with the current
flowing through the drive coil (5) in the figure. Further, on the left side in the figure, the
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magnetic flux Bl radiated from the DC magnetic field generation magnet (3) and obliquely
reaching the drive coil (5) is perpendicular to the component Blx horizontal to the diaphragm (4)
as shown. The component Bly is decomposed, and the vertical component Bly generates a
downward repulsive force on the drive coil (5) as in FIG. 4A. On the other hand, for the horizontal
component Blx, a direction according to Fleming's left-hand rule, that is, a downward
electromagnetic force Fl in the drawing, is generated in relation to the current flowing through
the drive coil (5).
[0029]
Therefore, the drive coil (5) receives a downward driving force as a whole by the downward
repulsive force shown in FIG. 4 (a) and the downward repulsive force and electromagnetic force
shown in FIG. 4 (b).
[0030]
Here, the current flowing as an electrical signal to the drive coil (5) is a cross current, and the
direction of the current flowing to the drive coil (5) temporally changes, so the drive coil (5) 4
and the downward driving force of FIG. 4 are alternately received.
As a result, the diaphragm (4) vibrates integrally with the drive coil (5), and the electrical signal
is converted into sound.
[0031]
FIG. 5 shows the sound pressure level-frequency characteristics of the loudspeaker according to
the first embodiment in solid lines and the sound pressure level-frequency characteristics of the
conventional dynamic loudspeaker and magnetic loudspeaker in broken lines and a two-dot
chain line, respectively. It is a thing. In general, as the characteristics of the speaker, the sound
pressure level is required to be high and flat from the low frequency range to the high frequency
range of the frequency, and the sound pressure level is regarded as an index of the efficiency. As
shown, in the loudspeaker of the first embodiment, a high sound pressure level is obtained in a
wide frequency range as compared with the conventional magnetic loudspeaker. In addition, flat
frequency characteristics are obtained as compared with the conventional dynamic type speaker.
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[0032]
Second Embodiment FIG. 6 is a cross-sectional view showing the structure of a loudspeaker
according to a second embodiment, and FIG. 7 is an exploded perspective view of the
loudspeaker. A flat casing (25) is configured by fitting a cylindrical cover (12) open at one end
and a cylindrical frame (21) open at one end. The cover (12) is formed of a metal such as
stainless steel SUS304, and the frame (21) is formed of a resin such as a liquid crystal polymer.
[0033]
In the cover (12), eight holes (13) with a diameter of 1.0 mm for sound emission are opened at
intervals of 45 °. Also, eight holes (22) with a diameter of 0.4 mm are opened at an interval of
45 ° in the frame (21). On the inner surface of the cover (12), a disc-shaped DC magnetic field
generating magnet (3) having an outer diameter of 9.0 mm and a thickness of 1.0 mm mainly
composed of neodymium is provided on the central axis of the cover (12). It is fixed by an acrylic
thermosetting adhesive.
[0034]
Inside the casing (25), a disc-shaped diaphragm (41) made of polyethylene terephthalate PET and
having a thickness of 75 μm is disposed. The outer peripheral portion of the diaphragm (41) is a
cover (12) and a frame (21). Bonded and fixed between). An air gap G of 0.6 mm is provided
between the upper surface of the diaphragm (41) and the DC magnetic field generating magnet
(3), and the drive coil (51) is coaxial with the DC magnetic field generating magnet (3). Is
installed and fixed by a rubber adhesive. The drive coil (51) is formed to have an inner diameter
of 7.0 mm, an outer diameter of 9.5 mm, and a thickness of 0.25 mm by winding a polyurethane
copper wire having a wire diameter of 0.03 mm. Therefore, although the drive coil (51) has the
same outer diameter and thickness as the drive coil (5) of the first embodiment, the inner
diameter is increased, so that weight reduction is achieved.
[0035]
Also, an electrode (6) formed by applying solder plating to brass is attached to the bottom of the
frame (21), and an end of the electrode (6) is a lead extending from the drive coil (51) Wires (not
shown) are twisted and connected by soldering.
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[0036]
A ring-shaped thin sound absorbing material (7) made of polyurethane and nylon is adhesively
fixed on the inner surface of the cover (12) at a position covering the hole (13).
Further, the same sound absorbing material (8) is adhered and fixed to the bottom of the frame
(21) at a position covering the hole (22).
[0037]
In the speaker of the second embodiment, the drive coil (51) is formed to have a larger inner
diameter than the drive coil (5) of the first embodiment, so as shown in FIGS. 3 (a) and 4 (a). The
driving force based on the magnetic flux penetrating the driving coil (51) substantially vertically
is not generated, and the driving based on the magnetic flux penetrating the driving coil (51)
obliquely shown in FIGS. 3 (b) and 4 (b) The force is the main factor and the diaphragm (41) is
driven.
[0038]
FIG. 8 shows the sound pressure level-frequency characteristics in the mounted state of the
sound absorbing material in the solid line and the sound pressure level-frequency characteristics
in the non-mounted state of the sound absorbing material in the speaker of the second
embodiment. It is
The loudspeaker according to the second embodiment can obtain a high sound pressure level as
compared with the conventional magnetic loudspeaker shown in FIG. 5 in the non-mounted state
of the sound absorbing material, and has a flat characteristic compared to the conventional
dynamic loudspeaker. Is obtained. Although the sound pressure level of the sound absorbing
material is lower than that of the non-mounted state due to the sound absorbing effect of the
sound absorbing material, a sufficient value can be obtained as the sound pressure level of a
small speaker. Flatter characteristics are realized over the high region.
[0039]
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FIG. 9 is a chart showing characteristics of the above-described loudspeaker of the present
invention and the conventional dynamic loudspeaker and magnetic loudspeaker. The apertures of
the loudspeakers are substantially the same, but the overall height is lower in the first
embodiment and the second embodiment as compared with the prior art. This is because the
yoke and the pole piece are omitted in the present invention.
[0040]
The impedance is higher in both the first embodiment and the second embodiment than in the
dynamic type. This is because, in the present invention, the omission of the yoke and the pole
piece enables a free design, and the number of turns of the drive coil can be increased.
Incidentally, although the outer diameter and height of the drive coil of the second embodiment
are the same as those of the first embodiment, and the inner diameter is larger than that of the
first embodiment, the same impedance is obtained. This is because the wire diameter of the
copper wire of the drive coil in the second embodiment is thinner than that in the first
embodiment.
[0041]
The sound pressure level is higher than that of the magnetic type in the first embodiment and the
second embodiment without the sound absorbing material. This is because, in the present
invention, the magnetic flux radiated from the DC magnetic field generating magnet is effectively
used.
[0042]
Here, effective utilization of the magnetic flux in the present invention will be discussed based on
FIGS. 10 and 11. FIG. In FIG. 10, the horizontal axis is the distance in the x-axis direction from the
origin O provided on the central axis of the DC magnetic field generation magnet, and the vertical
axis is the magnetic flux density component Bx parallel to the DC magnetic field generation
magnet. It is a graph which shows magnetic flux density distribution in the case of 0.3, 0.4, and
0.5 mm of air gaps Gap. As shown in the figure, regardless of the value of the gap Gap, a high
magnetic flux density component Bx exceeding 800 G is obtained when the distance in the x-axis
direction is in the range of 3.6 to 5.2 mm, and the distance in the x-axis direction is 4.0 A higher
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magnetic flux density component is obtained in the range of -4.8 mm, and a peak appears at
about 4.4 mm. As the magnetic flux density component Bx in the x-axis direction increases, the
electromagnetic force according to Fleming's left-hand rule in the drive coil increases. Therefore,
by setting the outer diameter of the drive coil to 7.2 to 10.4 mm, preferably 8.0 to 9.6 mm, the
drive coil can be efficiently driven by an electromagnetic force based on Fleming's left-hand rule.
. Therefore, in the first and second embodiments, the outer diameter of the drive coil is set to 9.5
mm close to the optimum point. As a result, as described above, the sound pressure levels of the
first and second embodiments are higher than those of the magnetic type.
[0043]
Also, as shown in FIG. 9, in the sound absorbing material non-wearing state of the second
embodiment, the sound pressure level is higher than that of the first embodiment. The reasons
for this will be discussed below. In FIG. 11, the abscissa represents the distance in the x-axis
direction from the origin O provided on the central axis of the DC magnetic field generation
magnet, and the ordinate represents the magnetic flux density component By perpendicular to
the DC magnetic field generation magnet. It is a graph which shows magnetic flux density
distribution in the case of 0.3, 0.4, and 0.5 mm of air gaps Gap. As shown, regardless of the value
of the gap Gap, a high magnetic flux density component By exceeding 1000 G is obtained in the
range of 0 to 4.2 mm in the distance in the x axis direction, and the distance in the x axis
direction is 3.5 to 4 An even higher flux density component is obtained in the range of .0 mm,
and a peak appears at about 3.8 mm. As the magnetic flux density component By in the y-axis
direction increases, the attractive force and repulsive force of the magnet in the drive coil
increase. However, when the distance in the x-axis direction exceeds 4.7 mm, the magnetic flux
density component By has a negative value.
[0044]
Here, if FIG. 10 is added to FIG. 11, since the electromagnetic force based on Fleming's left-hand
rule shown in FIG. 10 is small if the distance in the x-axis direction is less than 3.0 mm, the inner
diameter of the drive coil is 6.0 mm or more If the relative magnetic flux density component By is
obtained at 8.4 mm or less, preferably 7.0 to 8.0 mm, in addition to the electromagnetic force
based on Fleming's left-hand rule, the attractive force and repulsion of the magnet The driving
coil can be efficiently driven by using the force as an auxiliary force. Therefore, in the second
embodiment, by setting the inner diameter of the drive coil to 7.0 mm with respect to 1.0 mm in
the first embodiment, efficient drive of the drive coil and weight reduction of the drive coil are
achieved. By reducing the weight of the drive coil, the mass of the vibration system including the
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diaphragm is reduced, and the response of the vibration system is improved. As a result, the
sound pressure level of the second embodiment is higher than that of the first embodiment.
However, in the second embodiment, the sound pressure level-frequency characteristic is
improved to be flatter as shown in FIG. 8 by mounting the sound absorbing material.
[0045]
Further, as shown in FIG. 9, the number of parts is reduced in both the first embodiment and the
second embodiment as compared with the prior art. This is because the yoke and the pole piece
are omitted in the first embodiment and the second embodiment. However, in the second
embodiment, since the sound absorbing material is used, the number of parts is increased as
compared with the first embodiment.
[0046]
As described above, in the present invention, since the magnetic flux radiated from the DC
magnetic field generation magnet is radiated to the air gap without focusing, the yoke and the
pole piece are unnecessary, thereby reducing the number of parts and reducing the thickness. It
becomes possible. In addition, since there is no design restriction due to the yoke or the pole
piece, not only it is possible to achieve thinning by free design, but it is also possible to increase
the number of turns of the drive coil, thereby realizing high impedance. Power consumption is
reduced.
[0047]
Further, by setting the outer diameter of the drive coil to a value that can effectively utilize the
electromagnetic force based on the left side of Fleming, the drive coil is efficiently driven to
improve the efficiency.
[0048]
Furthermore, in the second embodiment, the inner diameter of the drive coil is set to a value that
combines the effective use of the magnetic flux emitted from the DC magnetic field generation
magnet and the weight reduction of the drive coil. It drives efficiently and aims at the further
improvement of efficiency.
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[0049]
The above description of the embodiments is for the purpose of describing the present invention,
and should not be construed as limiting the scope of the invention as set forth in the claims.
Further, the configuration of each part of the present invention is not limited to the above
embodiment, and it goes without saying that various modifications are possible within the
technical scope described in the claims.
[0050]
Brief description of the drawings
[0051]
1 is a cross-sectional view showing the structure of the speaker in the first embodiment.
[0052]
2 is an exploded perspective view of the embodiment of the same.
[0053]
3 is a view showing the direction of the driving force generated when a current is supplied to the
driving coil clockwise in the embodiment of the present invention.
[0054]
4 is a diagram showing the direction of the driving force generated when a current is supplied to
the driving coil counterclockwise in the embodiment of the same.
[0055]
5 is a graph showing sound pressure level-frequency characteristics in the embodiment of the
above and the conventional speaker.
[0056]
<Figure 6> It is the cross section diagram which shows the structure of the speaker in 2nd
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execution example.
[0057]
7 is an exploded perspective view of the embodiment of the same.
[0058]
FIG. 8 is a graph showing sound pressure level-frequency characteristics in the mounted state
and in the non-mounted state of the sound absorbing material in the embodiment of the present
invention.
[0059]
9 is a table showing various characteristics of the first embodiment and the second embodiment
and the prior art.
[0060]
10 is a graph showing the distribution of the magnetic flux density component parallel to the DC
magnetic field generating magnet.
[0061]
11 is a graph showing the distribution of the magnetic flux density component perpendicular to
the DC magnetic field generation magnet.
[0062]
12 is a cross-sectional view showing the structure of a conventional dynamic speaker.
[0063]
13 is a cross-sectional view showing the structure of a conventional magnetic type speaker.
[0064]
Explanation of sign
[0065]
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(3) Magnet for direct current magnetic field generation (4) Diaphragm (5) Drive coil (6) Electrode
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