Description
Speaker Magnetic Circuit, Speaker Device, and Method of
Manufacturing speaker Magnetic Circuit
Field of the Invention
[ 0001]
The present invention relates particularly to a speaker
magnetic circuit suitable for use in a thin-type speaker
device mounted in a portable electronic device such as a
cellular phone, a portable radio set or a PDA (Personal Digital
Assistants) . This invention also relates to a speaker device
including the speaker magnetic circuit, and a method of
manufacturing the speaker magnetic circuit.
Technical Background
[ 0002]
A portable electronic device such as a cellular phone, a
portable radio set, or a PDA is required to be compact in size
and small in thickness in order to be portable. Therefore,
a speaker device used in such a portable electronic device
is also needed to have a compact size and a small thickness.
To meet the requirement of having a compact size and a small
thickness for the above-mentioned speaker device, it is
usually considered necessary to reduce the thickness of a
speaker magnetic circuit containing magnet and yoke. In order
to reduce the thickness of a speaker magnetic circuit, what
is required is for example to utilize a radially magnetized
magnet.
[ 0003]
A conventional speaker magnetic circuit of the
above-mentioned type can have for example the following
structure. Namely, as shown in Fig.l, the conventional
speaker magnetic circuit contains a yoke 1 having a generally
tabular cross-sectional shape. A cylindrical magnet 2 is
arranged at the central portion of the yoke 1, and an annular
magnet 3 is arranged around the cylindrical magnet 2. In
addition, a top plate 4 is fixed on the cylindrical magnet
2, and an top plate 5 is fixed on the annular magnet 3. A
magnetic gap 6 is formed between the top plate 4 and the top

plate 5 (e.g., patent document 1).
[ 0004]
Patent document 1: Japanese Utility Model Publication
No.1983-599 (utility model, claim 1, Fig.2, etc.)
Problem(s) to be Solved by the Invention
[ 0005]
In the conventional speaker magnetic circuit described
above, the cylindrical magnet 2 and the annular magnet 3 are
magnetized in the vertical direction shown in Fig. 1, i.e.,
in a direction perpendicular to the yoke 1. In other words,
these magnets are magnetized in a direction parallel to the
oscillation direction of a voice coil (not shown) inserted
into the magnetic gap 6. In such a conventional speaker
magnetic circuit, if it is required to increase the magnetic
flux density in the magnetic gap 6, the top plate 5 can be
removed and the thickness of the cylindrical magnet 2 can be
increased by an extent substantially equal to the thickness
of the top plate 5. This, however, will cause the magnetic
flux to flow from the top plate 4 to the yoke 1 (i.e. causing
a leakage of magnetic flux), resulting in a decrease of the
magnetic flux density in the magnetic gap 6 formed between
the cylindrical magnet 2 and the annular magnet 3, rendering
it impossible to ensure a sufficient magnetic flux density
in the magnetic gap 6.
[ 0006]
Besides, in the speaker magnetic circuit described above,
since the peak of the magnetic flux density is in the side
of the yoke 1, it is difficult to ensure a sufficient magnetic
flux density at a position where the voice coil is mounted.
On the other hand, if the voice coil is arranged at a position
where the magnetic flux density is maximum, it will be
difficult to ensure a sufficient vibration amplitude of the
voice coil , As a result, when a speaker device is fabricated
by reducing the thickness of a conventional speaker magnetic
circuit, it is difficult to ensure a high sensitivity for the
speaker device.
[ 0007]
In view of the problems discussed above, it is an object of

generally conical (cone-shaped) and Fig. 3(b) shows an example
in which the diaphragm is generally tabular.
Fig. 4 is a graph showing a magnetic flux density
distribution with respect to distances from the upper surface
of a bottom portion of a yoke contained in the speaker device
of Fig. 3.
Fig. 5 is a schematic sectional view showing a first example
of the structure of a speaker magnetic circuit according to
embodiment 2 of the present invention.
Fig. 6 is a schematic sectional view showing a second example
of the structure of the speaker magnetic circuit according
to embodiment 2 of the present invention.
Fig. 7 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 3 of
the present invention.
Fig. 8 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 4 of
the present invention.
Fig. 9 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 5 of
the present invention.
Fig.10 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 6 of
the present invention.
Fig.11 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 7 of
the present invention, wherein Fig. 11(a) is a plane view and
Fig. 11(b) is a sectional view taken along a line A-A in Fig.
11(a).
Fig.12 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 8 of
the present invention.
Fig.13 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 9 of
the present invention.
Fig.14 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 10 of
the present invention.

Fig. 15 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 11 of
the present invention.
Fig.16 provides schematic views showing the structure of
a speaker magnetic circuit according to embodiment 12 of the
present invention, wherein Fig. 16 (a) is a plane view and Fig.
16 (b) is a sectional view taken along a line A-A in Fig. 16 (a) .
Fig.17 provides conceptual views showing a method of
manufacturing of the speaker magnetic circuit of embodiment
13 of the present invention.
Fig.18 is a schematic view showing the structure of a
magnetizing device used in the method of manufacturing the
speaker magnetic circuit of embodiment 13 of the present
invention.
Fig.19 is a schematic sectional view showing the structure
of a speaker magnetic circuit according to embodiment 14 of
the present invention.
Best Mode for Carrying out the Invention
[ 0012]
Embodiment 1
Fig. 2 is a schematic view showing the structure of a speaker
magnetic circuit 11 according to embodiment 1 of the present
invention, wherein Fig. 2(a) is a plan view and Fig. 2(b) is
a sectional view taken along a line A-A in Fig. 2(a). In
embodiment 1 of the present invention, the speaker magnetic
circuit 11 comprises a yoke 12 and a magnet group 13. The
speaker magnetic circuit 11 is about 15mm inlongitudinal
length, about 10mm intransverse length, and about 1.5mm in
thickness.
[ 0013]
The yoke 12 is made of a pure iron, an oxygen-free steel,
a silicon steel or the like. The whole shape of the yoke 12
is substantially rectangular in a plan view. A through-hole
12a having a substantially rectangular shape is formed at a
substantially central portion of the yoke 12. The yoke 12 is
formed by integrally including a bottom portion 12b, an outer
circumferential side portion 12c, and an inner
circumferential side portion 12d. The bottom potion 12b has

a substantially square ring-shaped structure. The outer
circumferential side portion 12c is set substantially upright
on the outer edge of the bottom portion 12b, while the inner
circumferential portion 12d is set substantially upright on
the inner edge of the bottom portion 12b.
[ 0014]
The magnet group 13 comprises outer magnets 21-24 and inner
magnets 25-28. The outer magnets 21-24 and the inner magnets
25-28 are made of a permanent magnet material such as Nd magnet,
Sm-Co magnet, Al-Ni-Co magnet, ferrite magnet or the like.
The outer magnets 21-24 and the inner magnets 26, 28 are each
in a substantially prism shape. On the other hand, when the
magnets 25, 27 are fixed to the upper surface 12ba of the bottom
portion 12b of the yoke 12, among eight corners of the inner
magnets 25 and 27, four corners opposing the outer
circumferential side portion 12c of the yoke 12 are rounded.
The outer magnets 21-24 and the inner magnets 25-28 are each
in a thickness substantially equal to a distance from the upper
surface 12ba of the bottom portion 12b of the yoke 12 to the
upper end of the outer circumferential side portion 12c.
[ 0015]
The outer magnets 21-24 are in contact not only with the
upper surface 12ba of the bottom portion 12b and the inner
surface 12ca of the outer circumferential side portion 12c
of the yoke 12, but also with other adjacent outer magnets,
and are fixed to the yoke 12 with an adhesive agent. On the
other hand, the inner magnets 25-28 are in contact not only
with the upper surface 12ba of the bottom portion 12b and the
outer circumferential surface 12da of the inner
circumferential side portion 12d of the yoke 12, but also with
other adjacent inner magnets, and are fixed to the yoke 12
with an adhesive agent.
[ 0016]
A magnetic interval (magnetic gap) 14 is formed between
the outer magnets 21-24 and the inner magnets 25-28 . The outer
magnets 21-24 and the inner magnets 25-28 are magnetized in
an oblique direction with respect to their thickness direction.
Specifically, the outer magnets 21-24, as shown in Fig. 2 (b) ,
have S pole on the front side (in sound emission direction)
of the speaker device (see Fig.3) including the speaker
magnetic circuit 11 and N pole on the rear side of the speaker

device (opposite to sound emission direction), and are
magnetized in a direction at an angle of about 10°-70° with
respect to the horizontal direction facing outwardly from the
center of the yoke 12 . In this way, if the outer magnets 21-24
are magnetized at an angle of about 10°- 70° as described above,
a peak of the magnetic flux density can be disposed near a
position where a voice coil described below is supported.
Further, if the outer magnets 21-24 have S pole on the front
side of the speaker device (in sound emission direction) and
N pole on the rear side of the speaker device (opposite to
sound emission direction), and are magnetized in a direction
at an angle of about 30° - 45° with respect to the horizontal
direction facing outwardly from the center of the yoke 12,
it is possible to increase a magnetic flux density in the
magnetic gap 14.
[ 0017]
On the other hand, the inner magnets 25-28, as shown in
Fig.2 (b) , have S pole on the rear side of the speaker device
(opposite to sound emission direction) and N pole on the front
side of the speaker device (in sound emission direction) and
are magnetized at an angle of about 10°-70° with respect to
the horizontal direction facing outwardly from the center of
the yoke 12. In this way, if the inner magnets 25-28 are
magnetized at an angle of about 10°-70° as described above,
the peak of magnetic flux density can be disposed near the
position where the voice coil described below is supported.
Moreover, if the inner magnets 25-28 have S pole on the rear
side of the speaker device (opposite to sound emission
direction) and N pole on the front side of the speaker device
(in sound emission direction) and are magnetized at an angle
of about 30°- 45° with respect to the horizontal direction
facing outwardly from the center of the yoke 12, it is possible
to increase the magnetic flux density in the magnetic gap 14.
[ 0018]
Fig. 3 provides schematic sectional views showing the
structure of a speaker device containing the speaker magnetic
circuit shown in Fig.2, wherein Fig. 3(a) shows an example
in which the longitudinal cross-sectional shape of a diaphragm
is generally conical (cone-shaped) and Fig. 3(b) shows an
example in which the diaphragm is generally tabular. The
speaker device has the speaker magnetic circuit 11 described
above and a diaphragm assembly 31. The diaphragm assembly 31

comprises a diaphragm 32, a voice coil bobbin 33, a voice coil
34, and a frame (not shown) . The diaphragm 32 has a generally
rectangular shape in a plan view, its longitudinal cross
sectional shape is generally conical (cone-shaped) (see Fig.
3(a)) or generally tabular (see Fig.3 (b)).
[ 0019]
A material forming the diaphragm 32 can be a paper, a cloth
formed of a fiber, a woven fabric formed of a fiber, a
non-woven fabric formed of a fiber, or a woven fabric
impregnated with a phenol resin, a silicone resin or a solution
containing such a resin and an organic solvent. The diaphragm
32 can also be formed of a metal material, a synthetic resin,
or an acryl foamed material. The metal material can be
aluminum, titanium, duralumin, beryllium, magnesium, or an
alloy thereof. The synthetic resin can be a polypropylene,
a polyethylene, a polystyrene, a polyethylene terephthalate,
a polyethylene naphthalene, a polymethyl methacrylate, a
polycarbonate, a polyarylate, an epoxy resin or the like. In
addition, an acryl foamed material can be made by using a methyl
methacrylate, a methacrylate, a styrene, an anhydrous maleic
acid, and a methacrylamide as raw materials.
[ 0020]
A through-hole 32aa having a generally rectangular shape
in a plan view is formed on the inner circumference 32a of
the diaphragm 32 shown in Fig. 3 (a) . The outer peripheral
surface of the voice coil bobbin 33 having a generally square
and tubular shape is fixed near its upper end to the
through-hole 32aa with an adhesive agent. A voice coil 34 is
wound around the outer peripheral surface of the voice coil
bobbin 33 near the lower end thereof. On the other hand, a
voice coil housing part 35 having a generally rectangular
shape in a plan view is formed integrally with the diaphragm
32, in proximity of the inner circumference 32a of the
diaphragm 32 shown in Fig. 3(b). A voice coil 36 having a
generally cylindrical shape is housed in the voice coil
housing part 35, and is fixed therein with an adhesive agent.
In addition, in proximity of the outer circumference 35a of
the voice coil housing part 35, an edge portion 37 having a
generally square and annular shape in a plan view is formed
integrally with the voice coil housing part 35 and the
diaphragm 32.
[ 0021]

Both ends of each of the voice coils 34 and 36 are led out
respectively along the voice coil bobbin 33 or the diaphragm
32, and electrically connected to a pair of lead wires (not
shown) near the inner circumference of the diaphragm 32. The
pair of lead wires (not shown) are made of bending-resistant
wires having a plurality of thin electric wires twisted.
[ 0022]
When audio signals (sound current) are supplied to the
speaker device having the above-described structure, the
audio current is supplied to the voice coil 34 or the voice
coil 36 through the pair of lead wires (not shown) . The outer
magnets 21-24 and the inner magnets 25-28 are magnetized in
an oblique direction with respect to their thickness direction.
Therefore, the magnetic flux developed from the inner magnets
25-28 flows towards the outer magnets 21-24. Consequently,
the magnetic fluxes can be efficiently collected at a position
of the voice coil (described below) capable of ensuring the
enough vibration amplitude for the voice coil 34 or the voice
coil 36.
[ 0023]
In this way, under an electromagnetic force (Lorentz force)
produced by an interaction between the magnetic flux developed
from the magnet group 13 constituting the speaker magnetic
circuit 11 and the audio current flowing to the voice coil
34 or 36, a driving force in the axial direction of the speaker
device is induced on the voice coil 34 or 36. This driving
force is transferred through the voice coil 34 or 36 to the
diaphragm 32. The diaphragm 32 oscillates under the driving
force, thus emitting a sound wave corresponding to the audio
current towards a space on the front side (in sound emission
direction).
[ 0024]
As described above, in embodiment 1 of the present invention,
since the magnetization direction of the outer magnets 21-24
and the inner magnets 25-28 is oblique with respect to the
thickness direction of the magnets and since the magnetic flux
developed from the inner magnets 25-28 flows toward the outer
magnets 21-24, it is possible to reduce an occurrence of a
magnetic flux leakage flowing towards the bottom portion 12b
of the yoke 12. Consequently, it becomes possible to increase
the magnetic flux density in the magnetic gap 14 formed between

as those shown in Fig.2 (b), with the explanations thereof
omitted.
[ 0029]
In this way, since the speaker device including the speaker
magnetic circuit 41 or 43 can prevent a decrease of magnetic
flux density in the magnetic gap 42 or 44, it is possible to
ensure a great magnetic flux density in the magnetic gap 42
or 44. Furthermore, it is also possible to reduce the number
of parts involved.
[ 0030]
Embodiment 3
In embodiment 1 described above, there is shown an example
in which the bottom surfaces and side faces of the outer magnets
21-24 and the inner magnets 25-28 are in contact with the upper
surface 12ba of the bottom portion 12b of the yoke 12, the
inner surface 12ca of the outer circumferential side portion
12c, or the outer surface 12da of the inner circumferential
side portion 12d. The above-discussed embodiment 1 also shows
an example in which the outer magnets 21-24 and the inner
magnets 25-28 are in a thickness substantially equal to a
distance from the upper surface 12ba of the bottom portion
12b of the yoke 12 to the upper end of outer circumferential
side portion 12c. However, the present invention is not
limited to these examples. For example, in place of the outer
magnets 21-24 and the inner magnets 25-28, as in the speaker
magnetic circuit 45 shown in Fig.7, intervals are provided
between the upper surface 12ba of the bottom portion 12b of
the yoke 12 and the outer magnets 21-24 as well as the inner
magnets 25-28, while the side faces of the outer magnets 21-24
and the inner magnets 25-28 are attached to the outer
circumferential side portion 12c and the inner
circumferential side portion 12d of the yoke 12. In Fig. 7,
the parts corresponding to those shown in Fig.2 are labeled
with the same reference numerals as those shown in Fig.2, with
the descriptions thereof omitted.
[ 0031]
In the example shown in Fig.7, there are outer magnets 46
and 47 corresponding to the outer magnets 22 and 24 shown in
Fig. 2(a) and Fig. 2(b) but thinner than the outer magnets
22 and 24, such as having a thickness which is substantially
half of the thickness of the outer magnets 22 and 24. In the

same example, there are inner magnets 48 and 49 corresponding
to the inner magnets 26 and 28 shown in Fig. 2(a) and Fig.
2(b) but thinner than the inner magnets 26 and 28, such as
having a thickness which is substantially half of the
thickness of the inner magnets 26 and 28. On the other hand,
Fig. 7 does not show two other outer magnets corresponding to
the outer magnets 21 and 23 shown in Fig. 2(a) but thinner
than the outer magnets 21 and 23, such as having a thickness
which is substantially half of the thickness of the outer
magnets 21 and 23. Fig. 7 does not show two other inner
magnets corresponding to the inner magnets 25 and 27 shown
in Fig. 2(a) but thinner than the inner magnets 25 and 27,
such as having a thickness which is substantially half of the
thickness of the inner magnets 25 and 27.
[ 0032]
The above-described outer magnets 46, 47 and the two other
outer magnets (not shown) are in contact with the inner
surface 12ca of the outer circumferential side portion 12c
of the yoke 12, as well as with other adjacent outer magnets,
and are fixed to the yoke 12 with an adhesive agent. On the
other hand, the above-described inner magnets 48, 49 and the
two other inner magnets (not shown) are in contact with the
outer surfacel2da of the inner circumferential side portion
12d of the yoke 12, as well as with other adjacent inner magnets,
and are fixed to the yoke 12 with an adhesive agent. In the
example shown in Fig.7, a magnetic interval (magnetic gap)
50 is formed between the outer surfaces of the inner magnets
48, 49 as well as the two other inner magnets (not shown) and
the inner surfaces of the outer magnets 46, 47 as well as the
two other outer magnets (not shown).
[ 0033]
Moreover, the outer magnets 46, 47 and the two other outer
magnets (not shown) have S pole on the front side of the speaker
device including the speaker magnetic circuit 45 (in sound
emission direction) and N pole on the rear side of the speaker
device (opposite to sound emission direction), and are
magnetized in a direction at an angle of about 10°-70° with
respect to the horizontal direction to facing outwardly
from the center of the yoke 12. In this way, if the outer
magnets 46, 47 and the two other outer magnets (not shown)
are magnetized at an angle of about 10°- 70° as described above,
a peak of the magnetic flux density can be ensured near a

position where a voice coil is supported. Further, if the
outer magnets 46, 47 and the two other outer magnets (not shown)
have S pole on the front side of the speaker device (in sound
emission direction) and N pole on the rear side of the speaker
device (opposite to sound emission direction), and are
magnetized in a direction at an angle of about 30° - 45° with
respect to the horizontal direction e facing outwardly from
the center of the yoke 12, it is possible to increase a magnetic
flux density in the magnetic gap 50.
[ 0034]
On the other hand, the inner magnets 48, 49 and the two
other inner magnets (not shown) have S pole on the rear side
of the speaker device (opposite to sound emission direction)
and N pole on the front side of the speaker device (in sound
emission direction) and are magnetized at an angle of about
10°-70° with respect to the horizontal direction facing
outwardly from the center of the yoke 12. In this way, if the
inner magnets 48, 49 and the two other inner magnets (not shown)
are magnetized at an angle of about 10°-70° as described above,
the peak of magnetic flux density can be ensured near the
position where the voice coil described below is supported.
Moreover, if the inner magnets 48, 49 and the two other inner
magnets (not shown) have S pole on the rear side of the speaker
device (opposite to sound emission direction) and N pole on
the front side of the speaker device (in sound emission
direction) and are magnetized at an angle of about 30°- 45°
with respect to the horizontal direction facing outwardly
from the center of the yoke 12, it is possible to increase
the magnetic flux density in the magnetic gap 14.
[ 0035]
In addition, it is also possible to provide a spacer between
the upper surface of the bottom portion 12a of the yoke 12
on one hand and each of the bottom surfaces of the outer magnets
46, 47, the two other outer magnets (not shown), the inner
magnets 48, 49, and the two other inner magnets (not shown)
on the other.
[ 0036]
In this way, as the speaker device concluding the speaker
magnetic circuit 45 can prevent a decrease of the magnetic
flux density in the magnetic gap 50, it is possible to ensure
a great magnetic flux density in the magnetic gap 50.

[ 0037]
Embodiment 4
In embodiments 1-3 described above, there is shown an
example in which the yoke 12 is obtained by integrally forming
the bottom portion 12b, the outer circumferential side portion
12c, and the inner circumferential side portion 12d. However,
the present invention should not be limited to this example.
For example, it is possible to replace the yoke 12 with a yoke
52 having a generally rectangular tabular shape in a plan view,
as shown in Fig. 8 which illustrates a speaker magnetic circuit
51. In Fig.8, parts corresponding to those shown in Fig.2 are
labeled with the same reference numerals as those shown in
Fig.2, with the description thereof omitted. Further, in
Fig. 8, the outer magnets 22, 24 and the inner magnets 26, 28
are shown, but the outer magnets 21, 23 in Fig. 2 (a) and the
inner magnets 25, 27 in Fig.2(a) are not shown. The yoke 52
can be made of a pure iron, an oxygen-free steel, a silicon
steel or the like.
[ 0038]
The above-described outer magnets 22, 24 and the two outer
magnets 21, 23 (not shown) are in contact with the upper surface
of the outer circumference of the yoke 52, and are fixed to
the yoke 52 with an adhesive agent. The inner magnets 26, 28
are provided at a certain interval in a generally central
position of the upper surface of the yoke 52. Meanwhile, the
two inner magnets 25, 27 (not shown) are arranged such that
their upper and lower ends of the same side surfaces are in
contact with the end faces of the inner magnets 26, 28, and
are fixed to the yoke 52 by applying an adhesive agent to the
contacting portions. In the example shown in Fig.8, a
magnetic gap 14 is formed between the outer circumferential
surfaces of the inner magnets 26, 28 as well as the two other
inner magnets 25, 27 (not shown) and the inner circumferential
surfaces of the outer magnets 22, 24 as well as the two other
outer magnets 21, 23 (not shown). Using the speaker device
including the speaker magnetic circuit 51 can prevent a
decrease of the magnetic flux density in the magnetic gap 14,
thereby ensuring a high magnetic flux density in the magnetic
gap 14.
[ 0039]
Embodiment 5

Fig.9 is a schematic sectional view showing the structure
of a speaker magnetic circuit 53 according to embodiment 5
of the present invention. In Fig.9, parts corresponding to
those shown in Fig. 8 are labeled with the same reference
numerals as those shown in Fig. 8, with the description thereof
omitted. As shown in Fig.9, the outer magnets 22, 24 shown
in Fig. 8 and two other outer magnets 21, 23 (not shown) have
been replaced with outer magnets 54, 55 and two other outer
magnets (not shown) . Though the outer magnets 54, 55 and the
two other outer magnets (not shown) are made of a material
similar to the outer magnets 21-24, they are thinner than the
inner magnets 26 and 28, having a thickness which is
substantially a half of the thickness of the inner magnets
2 6 and 28 . Moreover, though Fig. 9 shows the outer magnets 54,
55 and the inner magnets 26, 28, the figure does not show the
two other outer magnets corresponding to the outer magnets
21, 23 in Fig.2(a) and having a smaller thickness than the
outer magnets 21, 23 (for example, half the thickness of the
outer magnets 21, 23) . Besides, Fig. 9 does not show the inner
magnets 25 and 27 shown in Fig. 2 (a), either.
[ 004 0]
The outer magnets 54 and 55 described above and two other
outer magnets (not shown) are in contact with the upper surface
of the outer circumference of the yoke 52, as well as with
other adjacent outer magnets, and are fixed to the yoke 52
with an adhesive agent. On the other hand, the inner magnets
26 and 28 are provided at a certain interval from each other
in a generally central portion of the yoke 52, while two other
inner magnets (not shown) are arranged in such a condition
that the upper and lower ends on the same side surface are
in contact with the end surfaces of the inner magnets 26 and
28, and are fixed to the yoke 52 by applying an adhesive agent
to the contacting portions. In the example shown in Fig.9,
a magnetic gap 56 is formed between the outer circumferential
surfaces of the inner magnets 26, 28 and the two other inner
magnets (not shown) on one hand and the inner circumferential
surfaces of the outer magnets 54, 55 and two other outer magnets
(not shown) on the other.
[ 0041]
Moreover, the outer magnets 54, 55 and the two other outer
magnets (not shown) have S pole on the front side of the speaker
device including the speaker magnetic circuit 53 (in sound

which is approximately half of the thickness of the magnets
22 and 24 . Fig. 10 shows the inner magnets 58, 59 and the outer
magnets 22, 24, but does not show the two inner magnets
corresponding to the inner magnets 25, 27 shown in Fig. 2 (a)
and thinner than the inner magnets 25 and 27 (having a thickness
which is half of the thickness of the inner magnets 25 and
27) . Besides, Fig. 10 does not show the outer magnets 21, 23
shown in Fig. 2(a).
[ 0044]
The inner magnets 58, 59 and the two other inner magnets
are provided in a generally central position of the upper
surface of the yoke 52, with the inner magnets 58, 59 separated
at a predetermined interval. Meanwhile, the two inner magnets
(not shown) are arranged in a condition such that the upper
and lower ends on the same side surface are in contact with
the end faces of the inner magnets 58 and 59, and are fixed
to the yoke 52 by applying an adhesive agent to the contacting
portions. On the other hand, the outer magnets 22, 24 and the
two other outer magnets 21 and 23 (not shown) are in contact
with the upper surface of the outer circumference of the yoke
52, as well as with other adjacent inner magnets, and are fixed
to the yoke 52 with an adhesive agent. In the example shown
in Fig. 10, a magnetic gap 60 is formed between the outer
circumferential surfaces of the inner magnets 58, 59 and the
two other inner magnets (not shown) on one hand and the inner
circumferential surfaces of the outer magnets 22, 24 and the
two other outer magnets 21, 23(not shown) on the other.
[ 0045]
Moreover, the inner magnets 58, 59 and the two other inner
magnets (not shown) have S pole on the rear side of the speaker
device including the speaker magnetic circuit 57 (opposite
to sound emission direction) and N pole on the front side of
the speaker device (in sound emission direction), and are
magnetized in a direction at an angle of about 10°-70° with
respect to the horizontal direction facing outwardly from the
center of the yoke 52. In this way, if the inner magnets 58,
59 and the two other inner magnets (not shown) are magnetized
at an angle of about 10°- 70° as described above, a peak of
the magnetic flux density can be ensured near a position where
a voice coil is supported. Further, if the inner magnets 58,
59 and the two other inner magnets (not shown) have S pole
on the rear side of the speaker device (opposite to sound

emission direction) and N pole on the front side of the speaker
device (in sound emission direction), and are magnetized in
a direction at an angle of about 30° - 45° with respect to
the horizontal direction facing outwardly from the center of
the yoke 52, it is possible to increase a magnetic flux density
in the magnetic gap 60. In addition, if the magnetization
direction of the outer magnets 21-24 is different from the
magnetization direction of the inner magnets 58, 59 and two
other inner magnets (not shown) , it is possible to ensure the
peak of the magnetic flux density near the position where the
voice coil is supported.
[ 0046]
According to the above-described structure, the speaker
device including the speaker magnetic circuit 57 can prevent
a decrease of magnetic flux density in the magnetic gap 60,
thereby ensuring a great magnetic flux density in the
magnetic gap 60.
[ 0047]
Embodiment 7
Fig.11 is a schematic view showing the structure of a
speaker magnetic circuit 61 according to embodiment 7 of the
present invention, wherein Fig. 11(a) is a plan view and Fig.
11(b) is a sectional view taken along A-A line of Fig.11(a) .
The speaker magnetic circuit 61 of embodiment 7 has a yoke
62, a magnet group 63, and a plate 64. The yoke 62 can be made
of, for example, a pure iron, an oxygen-free steel, a silicon
steel or the like. The whole shape of the yoke 62 is generally
rectangular and tabular in a plan view. The yoke 62 can be
structured such that the bottom portion 62a and the outer
circumferential edge portion 62b are formed separately or
integrally. In the example shown in Fig.11, the bottom
portion 62a and the outer circumferential edge portion 62b
are formed separately. The shape of the bottom portion 62a
is generally rectangular and tabular in a plan view. The
outer circumferential edge portion 62b has a generally square
and ring-shape in a plan view. The outer circumferential edge
portion 62b is in contact with the outer circumference of the
bottom portion 62a and is fixed to the bottom portion 62a with
an adhesive agent.
[ 0048]
The magnet group 63 comprises outer magnets 71-74 and inner

magnet 75. The outer magnets 71-74 and the inner magnet 75
can be made of a permanent magnet material such as Nd magnet,
Sm-Co magnet, Al-Ni-Co magnet, ferrite magnet or the like.
The outer magnets 71-74 are in a generally prism shape. On
the other hand, the shape of the inner magnet 75 is generally
rectangular and planar in a plan view. In the example shown
in Fig.11, the outer magnets 71-74 are in a thickness
substantially equal to a distance from the upper surface 62aa
of the bottom portion 62a of the yoke 62 to the upper end of
the outer circumferential edge portion 62b. Nevertheless, in
the example shown in Fig.11, the inner magnet 75 is in a
thickness smaller than the thickness of the outer magnets
71-74, such as a half of a distance from the upper surface
62aa of the bottom portion 62a of the yoke 62 to the upper
end of the outer circumferential edge portion 62b.
[ 0049]
The outer magnets 71-74 are in contact not only with the
upper surface 62aa of the bottom portion 62a and the inner
circumferential surface 62ba of the outer circumferential
edge portion 62c of the yoke 62, but also with other adjacent
outer magnets, and are fixed to the yoke 62 with an adhesive
agent. On the other hand, the inner magnet 75 is fixed to a
generally central position of the upper surface 62aa of the
bottom portion 62a of the yoke 62 with an adhesive agent. The
plate 64 is fixed on upper surface of the inner magnet 75 with
an adhesive agent. The shape of the plate 64 is generally
rectangular and tabular in a plan view, having a size
substantially the same as the inner magnet 74 . Here, the plate
64 can be made of, for example, a soft magnetic material (e.g.,
a low carbon steel).
[ 0050]
A magnetic interval (magnetic gap) 65 is formed between
the outer magnets 71-74 and the inner magnet 75. The outer
magnets 71-74 are magnetized in an oblique direction with
respect to their thickness direction. Specifically, the
outer magnets 71-74, as shown in Fig. 11(b), have S pole on
the front side of the speaker device including the speaker
magnetic circuit 61 (in sound emission direction) and N pole
on the rear side of the speaker device (opposite to sound
emission direction), and are magnetized in a direction at an
angle of about 10°-7 0° with respect to the horizontal
direction facing outwardly from the center of the yoke 62.

In this way, if the outer magnets 71-74 are magnetized at an
angle of about 10°- 70° as described above, a peak of the
magnetic flux density can be ensured near a position where
a voice coil described below is supported. Further, if the
outer magnets 71-74 have S pole on the front side of the speaker
device (in sound emission direction) and N pole on the rear
side of the speaker device (opposite to sound emission
direction) , and are magnetized in a direction at an angle of
about 30° - 45° with respect to the horizontal direction facing
outwardly from the center of the yoke 62, it is possible to
increase a magnetic flux density in the magnetic gap 65.
[ 0051]
On the other hand, the inner magnet 75, as shown in Fig.2
(b) , has S pole on the rear side of the speaker device (opposite
to sound emission direction) and N pole on the front side of
the speaker device (in sound emission direction) and is
magnetized in a direction generally parallel to the vertical
direction (thickness direction of the inner magnet 75).
[ 0052]
In this way, with the speaker device containing the speaker
magnetic circuit 61, it is possible to prevent a decrease of
the magnetic flux density within the magnetic gap 65, making
it possible to ensure a great magnetic flux density in the
magnetic gap 65. Further, if the magnetization direction of
the outer magnets 71-74 is different from the magnetization
direction of the inner magnet 75, it is possible to ensure
a peak of the magnetic flux density near the position where
the voice coil is supported.
[ 0053]
Embodiment 8
Fig.12 is a schematic sectional view showing the structure
of a speaker magnetic circuit 81 according to embodiment 8
of the present invention. In Fig. 12, the parts corresponding
to those shown in Fig.11 are labeled with the same reference
numerals as those shown in Fig.11, with the description
thereof omitted. As shown in Fig.12, the outer
circumferential side portion 62b and the outer magnets 71-74
shown in Fig. 11 have been replaced with outer circumferential
side portion 62c, outer magnets 82, 83, and two other outer
magnets (not shown) . The outer circumferential side portion
62c is made of a material similar to the outer circumferential

side portion 62b, having a thickness substantially equal to
the thickness of the inner magnet 75. Fig.12 shows the inner
magnet 75 and the outer magnets 82, 83, but does not show two
other outer magnets corresponding to the outer magnets 71,
74 in Fig.11 and having a thickness substantially equal to
the thickness of the inner magnet 75.
[ 0054]
The outer circumferential side portion 62c has a generally
square and ring-shape in a plan view. The outer
circumferential side portion 62c is in contact with the outer
circumference of the bottom portion 62a, and is fixed to the
bottom portion 62a with an adhesive agent. The outer magnets
82, 83 and the two other outer magnets (not shown) are in
contact with the upper surface 62aa of the bottom portion 62a
and the inner circumferential surface 62ca of the outer
circumferential side portion 62c, as well as with adjacent
other outer magnets, and are fixed to the bottom portion 62a
and the outer circumferential side portion 62c with an
adhesive agent.
[ 0055]
A magnetic interval (magnetic gap) 84 is formed between
the outer magnets 82, 83 and the two other outer magnets (not
shown) on one hand and the inner magnet 75 on the other. The
outer magnets 82, 83 and two other outer magnets (not shown)
are magnetized in an oblique direction with respect to their
thickness direction. Specifically, the outer magnets 82, 83
and two other outer magnets (not shown), as shown in Fig.12
for example, have S pole on the front side of the speaker device
including the speaker magnetic circuit 81 (in sound emission
direction) and N pole on the rear side of the speaker device
(opposite to sound emission direction), and are magnetized
at an angle of about 10°- 70° with respect to the horizontal
direction e facing outwardly from the center of the bottom
portion 62a. Thus, if the outer magnets 82, 83 and the two
other outer magnets (not shown) are magnetized at an angle
of about 10°-70° as described above, the peak of the magnetic
flux density can be ensured near the position where the voice
coil is supported. Moreover, for example, if the outer
magnets 82, 83 and two other outer magnets (not shown) have
S pole on the front side of the speaker device (in sound
emission direction) and N pole on the rear side of the speaker
device (opposite to sound emission direction) and are

magnetized at an angle of about 30°- 45° with respect to the
horizontal direction facing outwardly from the center of the
bottom portion 62a, it is possible to increase the magnetic
flux density in the magnetic gap 84.
[ 0056]
In this way, with the speaker device including the speaker
magnetic circuit 81, it is possible to prevent a decrease of
the magnetic flux density within the magnetic gap 84, making
it possible to ensure a e great magnetic flux density in the
magnetic gap 84. Further, if the magnetization direction of
the outer magnets 82, 83 and the two other outer magnets (not
shown) is different from the magnetization direction of the
inner magnet 75, it is possible to ensure a peak of the magnetic
flux density near the position where the voice coil is
supported.
[ 0057]
Embodiment 9
Fig.13 is a schematic sectional view showing the structure
of the speaker magnetic circuit 85 according to embodiment
9 of the present invention. In Fig.13, the parts
corresponding to those shown in Fig.11 are labeled with the
same reference numerals as those shown in Fig.11, with the
description thereof omitted. As shown in Fig.13, the yoke 62
shown in Fig. 11 has been replaced with a yoke 86. The yoke
86 is made of a material similar to the bottom portion 62a,
and has a generally rectangular tabular shape in a plan view,
like the bottom 62a. The area of the yoke 86 is smaller than
that of the bottom portion 62a by an area substantially equal
to the bottom area of the outer circumferential side portion
62b {here, it has been removed) . Here, Fig. 13 shows the inner
magnet 75, the outer magnets 82, 83 and the plate 64, but does
not show the outer magnets corresponding to the outer magnets
71, 74 in Fig. 11 and having a thickness substantially equal
to the thickness of the inner magnet 75.
[ 0058]
The outer magnets 82, 83 described above and the two other
outer magnets (not shown) are in contact with the upper surface
62aa of the bottom portion 62a, as well as with adjacent other
outer magnets, and are fixed to the yoke 86 with an adhesive
agent. On the other hand, the inner magnet 75 is fixed to
a substantially central position of the upper surface of the

yoke 86. Here, a magnetic interval (magnetic gap) 87 is formed
between the outer magnets 82, 83 and the two other outer magnets
(not shown) on one hand and the inner magnet 75 on the other.
[ 0059]
In this way, with the speaker device including the
speaker magnetic circuit 85, it is possible to prevent a
decrease of the magnetic flux density within the magnetic gap
87, making it possible to ensure a great magnetic flux density
in the magnetic gap 87. Further, if the magnetization
direction of the outer magnets 72, 14 and the two other outer
magnets (not shown) is different from the magnetization
direction of the inner magnet 75, it is possible to ensure
a peak of the magnetic flux density near the position where
the voice coil is supported.
[ 0060]
Embodiment 10
Fig.14 is a schematic sectional view showing the structure
of the speaker magnetic circuit 8 8 according to embodiment
10 of the present invention. In Fig.14, parts corresponding
to those shown in Fig.11 are labeled with the same reference
numerals as those shown in Fig.11, with the description
thereof omitted. As shown in Fig.14, the yoke 62 shown in
Fig.11 is replaced with the yoke 86 shown in Fig.13. That
is, the structure of the speaker magnetic circuit 88 according
to embodiment 10 is similar to the speaker magnetic circuit
61 according to embodiment 7, except the outer circumferential
side portion 62b removed. Here, a magnetic interval (magnetic
gap) 65 is formed between the outer magnets 72, 74 and two
other outer magnets71, 73 (not shown) on one hand and the inner
magnet 75 on the other.
[ 0061]
In this way, with the speaker device including the
speaker magnetic circuit 88, it is possible to prevent a
decrease of the magnetic flux density within the magnetic gap
65, making it possible to ensure a e great magnetic flux density
in the magnetic gap 65. Further, if the magnetization
direction of the outer magnets 72, 74 and the two other outer
magnets (not shown) is different from the magnetization
direction of the inner magnet 75, it is possible to ensure
a peak of the magnetic flux density near the position where
the voice coil is supported.

[ 0062]
Embodiment 11
Fig. 15 is a schematic sectional view showing the structure
of the speaker magnetic circuit 91 according to embodiment
11 of the present invention. In Fig.15, parts corresponding
to those shown in Fig.9 are labeled with the same reference
numerals as those shown in Fig. 9, with the description thereof
omitted. As shown in Fig. 15, the outer magnets 54, 55 shown
in Fig.9 and two other outer magnets (not shown) isreplaced
with outer magnets 92, 93 and two other outer magnets (not
shown) . In addition, plates 94, 95 and two plates (not shown)
are fixed respectively on the upper surfaces of the outer
magnets 92, 93 and the two other outer magnets (not shown)
with an adhesive agent. In the example shown in Fig.15, the
plates 94, 95 and the two plates (not shown) are wider than
the corresponding outer magnets 92, 93 and the two outer
magnets.
[ 0063]
In addition, the outer magnets 92, 93 and the two outer
magnets (not shown), as shown in Fig.15 for example, have S
pole on the front side of the speaker device including the
speaker magnetic circuit 91 (in sound emission direction) and
N pole on the rear side of the speaker device (opposite to
sound emission direction), and are magnetized in a direction
generally parallel to the vertical direction. Here, a
magnetic interval (magnetic gap) 96 is formed between the
outer magnets 92, 93 and the two outer magnets (not shown)
on one hand and the inner magnets 26, 28 on the other.
[ 0064]
In this way, with the speaker device including the speaker
magnetic circuit 91, it is possible to prevent a decrease of
the magnetic flux density within the magnetic gap 96, making
it possible to ensure a great magnetic flux density in the
magnetic gap 96. Further, if the magnetization direction of
the outer magnets 92, 93 and the two other outer magnets (not
shown) is different from the magnetization direction of the
inner magnets 26, 28 and the two other inner magnets (not shown) ,
it is possible to ensure a peak of the magnetic flux density
near the position where the voice coil is supported. In this
way, even if a speaker device including a speaker magnetic
circuit 91 is thin and compact in size, it is possible to ensure

a great magnetic flux density.
[ 0065]
Embodiment 12
In the embodiments described above, the whole shape of the
speaker magnetic circuit is generally rectangular in a plan
view. However, the present invention should not be limited
by this. In fact, it is also possible for the whole shape of
the speaker magnetic circuit to be generally circular,
elliptical, or polygonal in a plan view. Further, in the
embodiments described above, the outer magnets and the inner
magnets provided on upper surface of the yoke are each composed
of a plurality of magnets. Similarly, the present invention
should not be limited by this. Actually, it is also possible
for each or both of the outer magnets and the inner magnets
to be formed of single one annular magnet. Hereinafter,
description is given to explain an example in which an whole
shape of the speaker magnetic circuit is generally circular
in a plan view and the outer magnet and the inner magnet
arranged on upper surface of the yoke are each formed of one
annular magnet.
[ 0066]
Fig.16 is a schematic view showing the structure of a
speaker magnetic circuit 15 according to embodiment 12 of the
present invention, wherein Fig. 16 (a) is a plan view and Fig. 16
(b) is a sectional view taken along A-A line in Fig.16 (a).
The speaker magnetic circuit 15 according to embodiment 12
comprises a yoke 16, an outer magnet 17, and an inner magnet
18 . The speaker magnetic circuit 15 has, for example, an outer
diameter of about 10mm and a thickness of about 1.5mm.
[ 0067]
The yoke 16 is made of, for example, a pure iron, an
oxygen-free steel, a silicon steel or the like. The whole shape
of the yoke 16 is generally circular in a plan view. At a
generally central position of the yoke 16 there is formed a
through-hole 16a having a generally circular shape . Yoke 16
includes a bottom portion 16b, an outer circumferential side
portion 16c, and an inner circumferential side portion 16d,
which are formed integrally to form the yoke. The bottom
portion 16b is generally annular in shape. The outer
circumferential side portion 16c is arranged generally
upright on the outer circumference of the bottom portion 16b.

On the other hand, the inner circumferential side portion 16d
is arranged generally upright on the inner circumference of
the bottom portion 16b.
[ 0068]
The outer magnet 17 and the inner magnet 18 are made of a
permanent magnet material such as Nd magnet, Sm-Co magnet,
Al-Ni-Co magnet, ferrite magnet or the like. The outer magnet
17 and the inner magnet 18 are each in a generally annular
shape. The outer magnet 17 and the inner magnet 18 are each
in a thickness substantially equal to a distance from the upper
surface 16ba of the bottom portion 16b of the yoke 16 to the
upper end of the outer circumferential side portion 16c.
[ 0069]
The outer magnet 17 is in contact with the upper surface
16ba of the bottom portion 16b and the inner circumferential
surface 16ca of the outer circumferential side portion 16c
of the yoke 16, and is fixed to the yoke 16 with an adhesive
agent. On the other hand, the inner magnet 18 is in contact
with the upper surface 16ba of the bottom portion 16b and the
outer circumferential surface 16da of the inner
circumferential side portion 16d of the yoke 16, and is fixed
to the yoke 16 with an adhesive agent.
[ 0070]
A magnetic interval (magnetic gap) 19 is formed between
the outer magnet 17 and the inner magnet 18. The outer magnet
17 and the inner magnet 18 are magnetized in an oblique
direction with respect to their thickness direction.
Specifically, the outer magnet 17, as shown in Fig.16 (b),
has S pole on the front side of the speaker device (not shown)
including the speaker magnetic circuit 15 (in sound emission
direction) and N pole on the rear side of the speaker device
(opposite to sound emission direction), and is magnetized at
an angle of about 10°-70° with respect to the horizontal
direction facing outwardly from the center of the yoke 16.
Thus, if the outer magnet 17 is magnetized at an angle of about
10°-70° as described above, the peak of magnetic flux density
can be ensured near the position where the voice coil is
supported. Moreover, for example, if the outer magnet 17 has
S pole on the front side of the speaker device (in sound
emission direction) and N pole on the rear side of the speaker
device (opposite to sound emission direction), and is

magnetized at an angle of about 30°- 45° with respect to the
horizontal direction facing outwardly from the center of the
yoke 16, it is possible to increase the magnetic flux density
in the magnetic gap 19.
[ 0071]
On the other hand, the inner magnet 18, as shown in Fig.2
(b) for example, has S pole on the rear side of the speaker
device (opposite to sound emission direction) and N pole on
the front side of the speaker device (in sound emission
direction) and is magnetized at an angle of about 10°-70° with
respect to the horizontal direction facing outwardly from the
center of the yoke 16. Thus, if the inner magnet 18 is
magnetized at an angle of about 10°-70° as described above,
the peak of the magnetic flux density can be ensured near the
position where the voice coil is supported. Moreover, for
example, if the inner magnet 18 has S pole on the rear side
of the speaker device (opposite to sound emission direction)
and N pole on the front side of the speaker device (in sound
emission direction) and is magnetized at an angle of about
30°- 45° with respect to the horizontal direction facing
outwardly from the center of the yoke 16, it is possible to
increase the magnetic flux density within the magnetic gap
19.
[ 0072]
In this way, with the speaker device including the speaker
magnetic circuit 15, it is possible to prevent a decrease of
the magnetic flux density within the magnetic gap 19, making
it possible to ensure a e great magnetic flux density in the
magnetic gap 19.
[ 0073]
Embodiment 13
Next, description will be given to explain a method of
manufacturing the speaker magnetic circuit 88 according to
embodiment 10 of the present invention shown in Fig.14, with
reference to Fig.17 and Fig.18.
(i) Step 1 (magnet formation step)
First, a container 101 as shown in Fig.17 is fully filled
with an amount of magnetic powder (magnetic fluid) 102. At
this time, a magnetic field is applied in an oblique and upward
direction with respect to the vertical direction (oblique with

respect to the thickness direction of a magnet 103 described
below) from the bottom 101a of the container 101, as
represented by an arrow in Fig.17. Next, as shown in Fig.17,
a pressure is applied to the magnetic powder (magnetic fluid)
to form a magnet (solid) 103. At this moment, it is preferred
that the pressure should be applied in a direction generally
perpendicular to the magnetic field direction, so as to
maximize the magnetic performance of the magnet 103. In this
way, the orientation of the magnetic powder (magnetic material)
102 can be determined through the magnet formation step
described above.
[ 0074]
(ii) Step 2
The magnet 103 obtained in the above Step 1 is fixed along
the outer circumference of the upper surface of the yoke 86
using an adhesive agent, thereby producing a yoke assembly.
(iii) Step 3 (magnet magnetizing step)
Next, description will be given to explain a magnet
magnetizing step using a magnetizing apparatus 111 shown in
Fig.17. As shown, the magnetizing apparatus 111 comprises a
magnetizing yoke 112 and a magnetizing coil 113. At first,
the yoke assembly obtained in the above Step 2 is set in the
magnetizing apparatus 111. Then, as shown in Fig. 17, a
magnetic field is applied in a direction substantially
parallel to a direction of a magnetic orientation of the magnet
103, so as to magnetize the magnet 103, thereby obtaining the
outer magnets 71-74. At this point, it will be difficult to
successfully magnetize the magnet 103 even if the magnet 103
is to be magnetized by applying a magnetic field in a direction
different from the direction of the magnetic orientation of
the magnet 103.
[ 0075]
(iv) Step 4
Then, using an adhesive agent, a plate 64 is fixed on a
magnet being as an inner magnet 75, thereby producing a plate
assembly.
(v) Step 5
Next, the plate assembly obtained in the above Step 4 is
set in the magnetizing apparatus. Then, as shown in Fig.14,

a magnetic field is applied in a direction substantially
parallel to the thickness direction of the above plate
assembly, thereby magnetizing the magnet of the plate assembly,
thus obtaining the inner magnet 75.
(vi) Step 6
Next, the assembly obtained in the above Step 5 is fixed
with an adhesive agent or a jig to a generally central position
of the yoke 86 in the assembly obtained in the above Step 3,
thereby obtaining the speaker magnetic circuit 88 shown in
Fig.14.
[ 0076]
In this way, according to the embodiment 13 of the present
invention, it is possible to manufacture the speaker magnetic
circuit 88 using a simple apparatus through simple steps.
[ 0077]
Embodiment 14
Fig.19 is a schematic sectional view showing the structure
of the speaker device according to embodiment 14 of the
present invention. In Fig.19, parts corresponding to those
shown in Fig. 14 are labeled with the same reference numerals
as those shown in Fig. 14, with the description thereof omitted.
As shown, the speaker device comprises a speaker magnetic
circuit 88 according to embodiment 10 of the present invention
as shown in Fig. 14, a frame 121, a diaphragm 122, and a voice
coil 123.
[ 0078]
The frame 121 can be made of a ferrous metal, a non-ferrous
metal or their alloy, or a synthetic resin. A ferrous metal
can be a pure iron, an oxygen-free steel, a silicon steel or
the like. A non-ferrous metal can be aluminum, magnesium,
zinc or the like. A synthetic resin can be produced by adding
a glass-fiber or a fibrillated thermotropic liquid crystal
polyester resin as a reinforcing filler in a thermoplastic
resin such as an olefin resin including a polypropylene or
the like, an ABS (acrylonitrile butadiene styrene), or a
polyethylene terephthalate. Here, the frame 121 can be
produced, for example, by squeezing and forming a ferrous
metal, or molding and forming non-ferrous metals or their
alloy, or injection molding a synthetic resin.

[ 0079]
An whole shape of the frame 121 is generally rectangular
in a plan view. Specifically, the frame 121 has a stepped
engaging portion 121a formed at the upper end on the side
of an inner circumference for engaging with an end of the yoke
86, and a stepped engaging portion 121b formed at the upper
end on the side of an outer circumference for engaging with
an end of the diaphragm 122.
[ 0080]
The diaphragm 122 comprises a dome-shaped vibrating part
131, a voice coil bobbin 132, a conical vibrating part 133,
and an edge 134 . The dome-shaped vibrating part 131, the voice
coil bobbin 132, the conical vibrating part 133, and the edge
134 are formed integrally together. The diaphragm 122 can be
made of, for example, a paper, a cloth formed of a fiber, a
woven fabric, a non-woven fabric, , all impregnated with a
phenol resin, a silicone resin or a solution containing the
resins and an organic solvent. The diaphragm 122 can also be
made of a metal material, a synthetic resin, a propylene foamed
material or the like. The metal material can be, for example,
aluminum, titanium, duralumin, beryllium, magnesium, or their
alloy. The synthetic resin can be, for example, a
polypropylene, a polyethylene, a polystyrene, a polyethylene
terephthalate, a polyethylene naphthalate, a polymethyl
methacrylate, a polycarbonate, a polyarylate, an epoxy resin
or the like. In addition, the acrylic foamed material can be
made from, as a raw material, a methylmethacrylate, a
methacrylate, a styrene, an anhydrous maleic acid, or an
methacrylamide.
[ 0081]
The dome-shaped vibrating part 131 has a shape protruding
in the center of the diaphragm 122 on the front side of the
speaker device (in sound emission direction). The
dome-shaped vibrating part 131 has a longitudinal section
formed in a radially curved shape, a semispherical domed shape,
a conical shape, a multi-stepped curved shape or the like.
In the example shown in Fig. 18, the dome-shaped vibrating part
131 is so formed that its longitudinal section is in a radially
curved shape and its central top is higher than the edge 134.
With such configuration, it is possible to obtain a
broad-angled directional characteristic. The dome-shaped
vibrating part 131 can be supported in a predetermined

position on the plate 64 with the voice coil bobbin 132, the
conical vibrating part 133 and the edge 134, vibratably in
the driving direction.
[ 0082]
The voice coil bobbin 132 is formed between the dome-shaped
vibrating part 131 and the edge 134, and has a generally
L-shaped cross-section in the example shown in Fig.18. Onthe
voice coil bobbin 132, a voice coil 123 formed into an
substantially square and tubular shape, falls into a concave
part formed between the voice coil bobbin 132 and the conical
vibrating part 133, and is fixed with an adhesive agent such
as an epoxy resin or the like.
[ 0083]
As shown in Fig. 18, the conical vibrating part 133 is formed
from the lower end of the voice coil bobbin 132 to the edge
134 of the diaphragm 122. Further, the conical vibrating part
133 has a cross section whose generatrix is generally conical.
In addition, the conical vibrating part 133 can be formed such
that its cross section has a generatrix in a shape which is
an arc-curved cone, a flat cone formed in a shape of a straight
line, a parabolic cone or the like.
[ 0084]
Here, the diaphragm 122 having the above-described
structure vibratably supports the voice coil 123 near the end
of the plate 64, . In addition, as described above, the
diaphragm 122 in the concave part located between the voice
coil bobbin 132 and the conical vibrating part 133 is formed
widely extending from the bottom of the concave part to an
upper opening side thereof, thereby the diaphragm 122 is
formed easily.
[ 0085]
As shown in Fig.18, the edge 134 has an engaging portion
134a for engaging with the stepped portion 121b of the frame
121. Therefore, it is possible to perform a positioning of
the diaphragm 122 with respect to the speaker magnetic circuit
88 and the frame 121 by performing an engagement between the
stepped portion 121b of the frame 121 and the engaging portion
134a of the edge 134. In the speaker device described above,
the voice coil 123 is supported by the diaphragm 122 at a
specified position within a magnetic flux distribution formed

with the outer magnets 71-74, the inner magnet 75, the plate
64, and the yoke 86.
[ 0086]
When an audio signal (audio current) is supplied to the
speaker device having the structure described above, the audio
current is supplied through a pair of lead wires (not shown)
to the voice coil 123. At this time, the outer magnets 71-74
are magnetized in an oblique direction with respect to their
thickness direction, while the inner magnet 75 is magnetized
in a direction generally parallel to its thickness direction.
Therefore, the magnetic flux generated from the inner magnet
75 flows towards the outer magnets 71-74. As a result, the
magnetic flux is collected efficiently at or near the voice
coil position where the adequate vibration amplitude of the
voice coil 123 can be ensured.
[ 0087]
Thus, under an electromagnetic force (Lorentz force)
produced by an interaction between the magnetic flux generated
from the outer magnets 71-7 4 and the inner magnet 7 5
constituting the speaker magnetic circuit 88 on one hand and
the audio current flowing to the voice coil 123 on the other,
the driving force in the axial direction of the speaker device
is induced on the voice coil 123. With the driving force, the
voice coil bobbin 132 on which the voice coil is mounted ,
vibrates in the vertical direction in the drawing, thereby
causing the vibrations of the dome-shaped vibrating part 131
and the conical vibrating part 133 accordingly. Under the
vibrations of the dome-shaped vibrating part 131 and the
conical vibrating part 133, the speaker device emits an
acoustic wave corresponding to the audio current to the front
space (in sound emission direction) , thereby exhibiting two
characteristics, with one provided by a dome-shaped speaker
device and the other by a cone-shaped speaker device.
[ 0088]
As described above, the speaker device according to
embodiment 13 of the present invention comprises the speaker
magnetic circuit 88, the frame 121, the diaphragm 122, and
the voice coil 123. The speaker magnetic circuit 88 comprises
the outer magnets 71-74, the inner magnet 75, the plate 64
arranged on one pole side of the inner magnet 75, and the yoke
86 arranged on the other pole side of the inner magnet 75.

The outer magnets 71-74 are magnetized in an oblique direction
with respect to their thickness direction. The outer magnets
71-74 are arranged around the inner magnet 75. The inner
magnet 75 is magnetized in a direction generally parallel to
its thickness direction. In fact, the inner magnet 75 and the
plate 64 are stacked on the yoke 86 in an order of at first
the inner magnet 75 and then the plate 64.
[ 0089]
Further, the diaphragm 122 comprises the dome-shaped
vibrating part 131, the voice coil bobbin 132, the conical
vibrating part 133, and the edge 134. The diaphragm 122 and
the voice coil 123 together form the diaphragm body. In fact,
the diaphragm 122 is supported by the frame 121 via the edge
134. The voice coil 123 is mounted near the end of the plate
64 of the speaker magnetic circuit 88. The diaphragm 122
supports vibratably the voice coil 123 near the end of the
plate 64.
[ 0090]
Therefore, in a speaker device having the above-described
structure, since it is possible to prevent a decrease of the
magnetic flux density within the magnetic gap 65, it is
possible to ensure a great magnetic flux density in the
magnetic gap 65. In addition, since the magnetization
direction of the outer magnets 72, 74 and other two outer
magnets {not shown) is different from the magnetization
direction of the inner magnet 75, it is possible to ensure
the peak of the magnetic flux density near a position where
the voice coil 123 is supported. In addition, even if the
speaker device is formed thin in thickness and compact in size,
it is still possible to ensure a great magnetic flux density.
[ 0091]
The diaphragm 122 comprises: the dome-shaped vibrating
part (a first vibrating part) 131 formed on the center of the
diaphragm 122; the conical vibrating part (a second vibrating
part) 133 having an outer circumference supported by the frame
121 directly or indirectly; and the voice coil bobbin 132
formed between the dome-shaped vibrating part 131 and the
conical vibrating part 133, with the voice coil 123 arranged
on the voice coil bobbin 132 . Since the dome-shaped vibrating
part 131, the conical vibrating part 133, and the voice coil
bobbin 132 can be formed integrally, by press molding,

injection molding or the like, it is possible to easily obtain
the diaphragm 122.
[ 0092]
The diaphragm 122 has an engaging portion 134a formed at
the end of the diaphragm 122 for engaging with the stepped
portion 121b (to be embedded) formed on the frame 121. As the
diaphragm 122 and the frame 121 engage between the stepped
portion 121b of the frame 121 and the engaging portion 134a
of the diaphragm 122 and are positioned, it is easy to
position the diaphragm 122 and the frame 121..
[ 0093]
Thus, since the dome-shaped vibrating part 131, the voice
coil bobbin 132, and the conical vibrating part 133 are formed
integrally, it becomes possible to highly accurately put the
respective essential elements in the predetermined positions .
In particular, according to the above structure and an easy
attachment step, it is possible to highly accurately put the
voice coil bobbin 132 at the predetermined position near the
end of the plate 64.
[ 0094]
Moreover, an effective vibration area can be increased and
thus the sound pressure can be increased simply by fixing the
inner side surface of the end of the diaphragm 122 to the outer
side surface of the stepped portion 121b of the frame 121.
In addition, the voice coil 123 can be easily attached on the
voice coil bobbin 132 by fixing the voice coil 123 to the side
face part of the L-shaped cross section part of the voice coil
bobbin 132 with an adhesive agent.
[ 0095]
While the above description has been given in detail to
explain the embodiments of the present invention with
reference to the accompanying drawings, the detailed
constitutions should not be limited to those embodiments. In
fact, various variations and modifications can be included
in the present invention without departing from the gist of
the invention.
[ 0096]
For example, though the above-discussed embodiment 1 shows
an example in which the diaphragm 32 has a conical longitudinal

cross sectional shape, the present invention is not limited
to this. For example, the diaphragm32 can have the
longitudinal cross section to be generally dome-shaped,
protruding to the front side (sound wave emission side) of
speaker device.
[ 0097]
Further, though the above-discussed embodiment 4 shows an
example in which the voice coil 123 is mounted on the inner
side of the voice coil bobbin 132, the present invention is
not limited to this. For example, it is also possible for the
voice coil 123 to be attached on the outside of the voice coil
bobbin 132.
Moreover, as to the above-discussed embodiment 14, it is
also possible to provide a magnetic fluid between the plate
64 and the voice coil bobbin 132 or the voice coil 123. If
the magnetic fluid is arranged in such a manner, it is possible
to increase the electromagnetic force acting on the voice coil
123, and to transfer the heat (Joule heat) produced on the
voice coil 123 to the plate 64 and then dissipate the same.
[ 0093]
In the embodiments described above, the polarities of the
magnets are in directions indicated by the arrows shown in
Fig.2(b), Fig.5-Fig.10, Fig.11(b), Fig.12-Fig.15, and
Fig.16(b). However, the present invention is not limited to
this. For example, it is also possible for the polarities
to be in directions opposite to those arrows shown in the
drawings.
In addition, the above-discussed various embodiments are
applicable to one another, provided that there are no
contradictions in their objects and constitutions.

WE CLAIM
1. A speaker magnetic circuit comprising a magnet and a yoke,
wherein
a magnetic orientation of the magnet is in an oblique
direction with respect to the thickness direction of the
magnet, the magnetic orientations in said magnet are
substantially the similar in said thickness direction,
a magnetic flux generated from the magnet passes
through a position separated from an upper surface of the
yoke and being on the side of the magnet.
2. The speaker magnetic circuit according to claim 1,
comprising a plurality of magnets including said magnet
and a plate, wherein
among an inner magnet and an outer magnet included in
the plurality of magnets, the plate is arranged on one of
the magnets and the other of the magnets is said magnet,
a magnetic orientation of the one of the magnets is in
its thickness direction and a magnetic orientation of the
other of the magnets is in an oblique direction with respect
to its thickness direction,
the magnetic orientations in the other of the magnets
are substantially the similar in said thickness direction,
a magnetic gap arranged between said plate and the other
of the magnets is on side of said plate or the other of the
magnets with respect to a bottom portion of the yoke, and
located in a position separated from the bottom portion of
the yoke.
3. The speaker magnetic circuit according to claim 2, wherein
an outer side surface and an inner side surface of the inner
magnet and the outer magnet extend in a direction
substantially perpendicular to said yoke.

4. The speaker magnetic circuit according to claim 3, wherein
the bottom portion of the yoke has a tabular shape.
5. The speaker magnetic circuit according to claim 4, wherein
a lower surface of the outer magnet connects to the yoke,
from an inner side surface to an outer side surface of the
outer magnet.
6. The speaker magnetic circuit according to claim 5, wherein
the inner magnet has a planar surface defined by a long axis
and a short axis, a plurality of rod-like magnets serving
as the outer magnet are arranged along the long axis or the
short axis of the inner magnet and the inner magnet is
arranged between the outer magnets.
7. The speaker magnetic circuit according to claim 6, wherein
the upper surface of the outer magnet is located at a lower
position with respect to the upper surface of the plate.
8. The speaker magnetic circuit according to claim 7, wherein
a peak position of the magnetic flux density within the
magnet gap is near a height at which the upper surface of
the plate is arranged.
9. A speaker device comprising: a speaker magnetic circuit
according to claim 8; a frame; and a diaphragm body,
wherein
the diaphragm body includes a diaphragm and a tubular
voice coil supported by the diaphragm,
a lower end of the voice coil is located at a lower position
with respect to the upper surface of the plate,
a central position of the voice coil is located at a
position which is substantially the same as or lower than
the upper surface of the plate,
a magnet gap is arranged at a position where the voice

coil is arranged.
10. The speaker device according to claim 9, wherein the peak
position of the magnetic flux density within the magnetic
gap is near the central position of the voice coil.
11. The speaker device according to claim 10, wherein the
diaphragm body has an edge for supporting the diaphragm on
the frame, wherein
the diaphragm has a dome-like shape or a tabular shape,
the diaphragm body or the speaker magnetic circuit has a
planar shape defined by a short axis and a long axis.
12. The speaker magnetic circuit according to claim 1,
comprising an outer magnet and an inner magnet serving as
said magnet, wherein
a magnetic orientation of the inner magnet and a magnetic
orientation of the outer magnet are in an oblique direction
with respect to the thickness direction of the magnets,
the magnetic orientations in the inner and outer magnets
are substantially the same in the thickness direction of
the inner and outer magnets,
a magnetic gap arranged between the inner and outer
magnets is on side of the inner magnet or the outer magnet
with respect to the yoke, and located in a position separated
from the yoke.
13. The speaker magnetic circuit according to claim 12, wherein
inner and outer side surfaces of the inner and outer magnets
extend in a direction substantially perpendicular to a
surface of the yoke facing the bottom surfaces of the inner
and outer magnets.
14. The speaker magnetic circuit according to claim 13, wherein
the yoke includes a tabular bottom portion and an outer
circumferential side portion surrounding the bottom

portion,
the inner and outer magnets connect to the outer
circumferential side portion of the yoke,
a predetermined gap is provided between the bottom
surfaces of the inner and outer magnets on one hand and the
yoke on the other.
15. The speaker magnetic circuit according to claim 14, wherein
the bottom portion of the yoke to which the bottom surfaces
of the inner and outer magnets connect, has a tabular shape.
16. The speaker magnetic circuit according to claim 15, wherein
the position of a upper surface of the inner magnet is
substantially the same as that of the outer magnet,
the magnetic gap is arranged near the positions of the
upper surfaces of the inner and outer magnets.
17. The speaker magnetic circuit according to claim 16, wherein
the upper surface of the inner magnet is at a higher
position with respect to the upper surface of the outer
magnet,
the magnetic gap is arranged near the position of the upper
surface of the inner magnet.
18. The speaker magnetic circuit according to claim 17, wherein
the upper surface of the outer magnet is at a higher position
with respect to the upper surface of the inner magnet, the
magnetic gap is arranged near the position of the upper
surface of the outer magnet.
19. The speaker magnetic circuit according to claim 18, wherein
the outer diameter of the outer magnet is substantially the
same as the outer diameter of the bottom portion of the yoke.
20. The speaker magnetic circuit according to claim 1, wherein
the yoke has a tabular bottom portion to which the lower

surface of said magnet connect, and a side portion facing
the inner or outer side surface of the magnet,
a magnetic gap arranged between the magnet and the side
portion of the yoke is on the side of the magnet with respect
to the yoke, and located in a position separated from the
yoke.
21. The speaker magnetic circuit according to claim 1,
comprising a plurality of magnets including said magnet and
a plate, wherein
among an inner magnet and an outer magnet included in the
plurality of magnets, the plate is arranged on one of the
magnets and the other of the magnets is said magnet,
a magnetic orientation of one of the magnets is in its
thickness direction and a magnetic orientation of the other
of the magnets is in an oblique direction with respect to
its thickness direction,
magnetic orientations in the other of the magnets are
substantially the same in said thickness direction,
a magnetic gap arranged between said plate and the other
of the magnets is on side of said plate or the other of the
magnets with respect to the yoke, and located in a position
separated from the yoke.
22 . The speaker magnetic circuit according to claim 21, wherein
a position of a upper surface of the plate is substantially
the same as a position of the upper surface of the other
of the magnets,
the magnetic gap is arranged near the position of the upper
surfaces of the plate and the other of the magnets.
23. A speaker device comprising a speaker magnetic circuit
according to claim 1, a frame, and a diaphragm body, wherein
the speaker magnetic circuit has a plurality of magnets
including said magnet and a plate,
a plate is arranged on an inner magnet included in the

plurality of magnets, an outer magnet is said magnet,
a magnetic orientation of the inner magnet is in its
thickness direction
a magnetic orientation of an outer magnet is in an oblique
direction with respect to its thickness direction,
magnetic orientations in the outer magnets are
substantially the same in said thickness direction,
the diaphragm body includes a diaphragm, an edge for
supporting the diaphragm on the frame, and a voice coil
supported by the diaphragm,
the diaphragm supports vibratably the voice coil near an
outer end of the plate.
24. The speaker device according to claim 23, wherein
the diaphragm has a conical shape, a dome-like shape, or
a tabular shape,
the diaphragm has a voice coil housing part for housing
the voice coil,
an outer circumferential portion of the edge connects to
a stepped portion arranged on an outer circumferential
portion of the frame.
25. An electronic apparatus including a speaker device
according to claim 9.
26. A method of manufacturing a speaker magnetic circuit
including a yoke and a magnet,
wherein the speaker magnetic circuit is so formed that
a magnetic orientation of the magnet is in an oblique
direction with respect to its thickness direction , the
magnetic orientations in the magnet are substantially the
same in its thickness direction ,
the method comprises:
a magnetizing step for applying a magnetic field
including a predetermined direction to the magnet; and
a magnet fixing step for fixing the magnet on the yoke;

wherein a magnetic flux generated from the magnet passes
through a position separated from the upper surface of the yoke
and being on the side of the magnet.
27. A method of manufacturing a speaker magnetic circuit
according to claim 26, comprising a magnet formation step
for applying a pressing force to a magnetic powder in a
magnetic field having a predetermined direction,
wherein said predetermined direction is oblique with
respect to the thickness direction of the magnet.

The present invention is to provide a speaker magnetic
circuit which, even if small in its thickness, can reduce an
occurrence of magnetic flux leakage so as to obtain a
sufficient magnetic flux density in a magnetic gap,
particularly in a position where a voice coil is supported.
The speaker magnetic circuit (11) comprises a yoke (12) and
a magnet group (13). The magnet group (13) comprises outer
magnets (21-24) and inner magnets (25-28) . The outer magnets
(21-24) and the inner magnets (25-28) are magnetized in an
oblique direction with respect to their thickness direction.