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JP2005223720

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DESCRIPTION JP2005223720
PROBLEM TO BE SOLVED: To reduce variation in magnetic flux density at a coil position and to
suppress non-uniform vibration of a diaphragm which causes a decrease in sound pressure and
an increase in distortion. SOLUTION: A magnet 17 is disposed in a yoke 16 consisting of a
bottom surface portion 16a and a peripheral wall portion 16b surrounding the periphery, a
magnetic gap 18 is formed between the peripheral wall portion 16b and the magnet 17, and the
magnetic gap 18 In the flat coil speaker in which the spiral coil 14 formed on the surface of the
diaphragm 13 is positioned on the upper surface of the peripheral wall portion 16b facing the
coil 14 from the outer peripheral side to the inner peripheral side, It comprises the inclined
surface 16c which inclines so that it may separate gradually. As compared with the case where
the end face of the peripheral wall portion 16b is not inclined, the magnetic flux lines are laid
down, so the component of the magnetic flux density in the coil outer peripheral portion in the
direction parallel to the plate surface of the diaphragm 13 becomes large. Variations in magnetic
flux density from the side to the outer periphery are reduced. [Selected figure] Figure 1
フラットコイルスピーカ
[0001]
The present invention relates to a flat coil type speaker in which a coil (voice coil) is formed in a
spiral shape on a plate surface of a diaphragm.
[0002]
FIG. 7 shows the structure of a flat coil speaker of this type which has been proposed
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conventionally, and in this example, it has a cylindrical lower frame 11 and an upper frame 12,
and the diaphragm 13 has peripheral edges thereof. 11 and the upper frame 12 so as to be
supported.
The lower frame 11 and the upper frame 12 are made of resin, for example. The diaphragm 13
includes a flat plate portion 13a, an edge portion 13b supporting the periphery of the flat plate
portion 13a, and a fixing portion 13c positioned around the edge portion 13b and sandwiched
between the lower frame 11 and the upper frame 12 The edge portion 13 b is configured to have
a cross-sectional dome shape in the radial direction.
[0003]
The diaphragm 13 is formed of, for example, an insulating film such as polyethylene
terephthalate (PET), and a coil 14 having a spiral shape is pattern-formed on a plate surface of
the flat plate portion 13a and provided as a flat coil. An opening 15 is provided in the closed
lower end face of the lower frame 11, and a yoke 16 made of a soft magnetic material such as
soft iron is disposed in the opening 15. The yoke 16 is composed of a bottom surface portion 16
a and a cylindrical peripheral wall portion 16 b surrounding the periphery, and the bottom
surface portion 16 a is attached to the lower frame 11 with the outer side.
[0004]
A disc-shaped magnet 17 is disposed on the inner surface of the bottom surface portion 16 a of
the yoke 16, and the magnet 17 and the yoke 16 constitute a magnetic circuit. The magnet 17 is,
for example, a neodymium magnet. The flat plate portion 13a of the diaphragm 13 is opposed to
the tip end surface of the peripheral wall portion 16b of the magnet 17 and the yoke 16, and the
coil 14 is positioned on the magnetic gap 18 annularly formed between the peripheral wall
portion 16b and the magnet 17. It is done. A baffle 19 is attached to the open upper end face of
the upper frame 12. In FIG. 7, 19a indicates a hole for sound emission. In the flat coil speaker
having the above structure, the coil 14 is placed in a magnetic field generated in the magnetic
gap 18, and an electric signal is supplied to the coil 14, whereby the coil 14 is vibrated by the
electromagnetic induction action. Thus, the diaphragm 13 vibrates to emit a sound wave, and a
speaker having a structure in which a flat coil is provided on the plate surface of the diaphragm
as described above is also described in, for example, Patent Document 1 and the like. Japanese
Patent Application Laid-Open No. 9-130892
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[0005]
By the way, in the flat coil speaker as described above, there is a problem that it is generally
difficult to obtain a uniform magnetic flux density distribution at the coil position. FIGS. 8A and
8B show this state in contrast to a normal speaker in which the coil is not a flat coil but is wound
in a direction perpendicular to the plate surface of the diaphragm to form a cylindrical shape,
and is shown in FIG. 8A. In the flat coil speaker, as compared with the normal speaker structure
shown in FIG. 8B, since the magnetic flux lines 21 crossing the coil 14 become large flux lines,
the variation of the magnetic flux density tends to be large. In addition, 22 in FIG. 8B shows a
pole piece.
[0006]
Further, in the normal speaker shown in FIG. 8B, the upper end of the coil 14 is coupled to the
diaphragm 13, and the diaphragm 13 is driven at one upper end, whereas the flat coil speaker
shown in FIG. 8A. In this case, since the driving force proportional to the magnetic flux density at
that position is applied to each point of the coil 14, the variation of the magnetic flux density
directly becomes the variation of the diaphragm driving force. Vibration causes a decrease in
sound pressure and an increase in distortion. An object of the present invention is, in view of the
above-mentioned problems, to provide a flat coil speaker capable of reducing non-uniform
vibration of a diaphragm by reducing variations in magnetic flux density at coil positions.
[0007]
According to the invention of claim 1, the magnet is disposed in the yoke formed of the bottom
surface portion and the peripheral wall portion surrounding the periphery, a magnetic gap is
formed between the peripheral wall portion and the magnet, and vibration is generated on the
magnetic gap In a flat coil speaker in which a spiral coil formed on a surface of a plate is
positioned, a tip surface of the peripheral wall facing the coil is inclined so as to be gradually
separated from the coil from the outer peripheral side toward the inner peripheral side It is
assumed that it is constituted by the inclined surface. According to the invention of claim 2, in
the invention of claim 1, the magnetic circuit composed of the yoke and the magnet is disposed
to face each other with the diaphragm interposed therebetween, and the coils are formed on both
sides of the diaphragm.
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[0008]
According to the invention of claim 3, in the invention of claim 1 or 2, the inclination angle of the
inclined surface with respect to the plate surface of the diaphragm is set to 20 ° or more and 60
° or less.
[0009]
According to the present invention, the variation in the magnetic flux density at the coil position
which contributes as the driving force to the diaphragm in the direction parallel to the plate
surface of the diaphragm from the inner circumference side to the outer circumference side is
reduced compared to the prior art. Thus, it is possible to suppress the non-uniform vibration of
the diaphragm which leads to a decrease in sound pressure and an increase in distortion, and a
flat coil speaker having good performance in that respect can be obtained.
[0010]
The best mode for carrying out the present invention will be described by way of example with
reference to the drawings.
FIG. 1A shows the structure of one embodiment of the flat coil speaker according to the present
invention, and the parts corresponding to FIG. 7 are assigned the same reference numerals and
detailed explanations thereof will be omitted.
In this example, the end surface of the peripheral wall portion 16b of the yoke 16 facing the coil
14 is constituted by an inclined surface 16c which is inclined so as to be gradually separated
from the coil 14 from the outer peripheral side toward the inner peripheral side. By setting the
tip end surface of the portion 16b as the inclined surface 16c, the variation in the magnetic flux
density at the coil position can be reduced.
[0011]
FIG. 2A shows the magnetic flux line distribution in the case where the tip end surface of the
peripheral wall portion 16b of the yoke 16 is thus the inclined surface 16c and the inclination is
given by simulation, and FIG. The magnetic flux line distribution of the conventional structure
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shown in FIG. 7 having no inclination on the tip end surface of is shown for comparison. In the
figure, dotted lines indicate magnetic flux lines. In FIG. 2A, the inclination angle θ (see FIG. 1B)
of the inclined surface 16c with respect to the plate surface of the diaphragm 13 is 30 °. In the
flat coil speaker, what contributes as a driving force to the diaphragm is a component in a
direction parallel to the plate surface of the diaphragm of the magnetic flux crossing the coil
(hereinafter referred to as a horizontal component). )である。 When there is no inclination in
the yoke tip surface, as shown in FIG. 2B, the magnetic flux lines pass in a direction substantially
perpendicular to the plate surface of the diaphragm 13 at the right end (outer periphery) of the
coil 14. Is small. On the other hand, in the case where the end face of the yoke shown in FIG. 2A
is inclined, the magnetic flux lines lie down, and the component in the horizontal direction
increases accordingly. However, the magnetic flux density itself becomes low at the left end side
(inner peripheral side) of the coil 14 due to the inclination of the yoke tip surface.
[0012]
FIG. 3 shows the distribution of the horizontal component of the magnetic flux density from the
inner periphery to the outer periphery at the coil position when the inclination angle θ is 0 °,
20 °, 60 ° and 75 ° by simulation. The following values were used for the dimensions of each
part in the simulation. In addition, each symbol in the following is shown in FIG. 1B. Coil Outer
diameter φ1 = 11.5 mm Thickness t1 = 0.045 mm Inner diameter φ2 = 9.25 mm Yoke Outer
diameter φ3 = 11.5 mm Thickness t2 = 0.5 mm Inner diameter φ4 = 10.5 mm Height H = 1. 45
mm · Magnet outer diameter φ 5 = 9.5 mm Thickness t 3 = 0.75 mm · Yoke, magnet level
difference D = 0.2 mm · Yoke, diaphragm gap S = 0.4 mm As apparent from FIG. In the horizontal
direction component, the maximum value decreases as the inclination angle θ increases, while
the minimum value increases and exhibits a gentle tendency as a whole.
[0013]
Table 1 summarizes the average value of the magnetic flux density at the coil position and the
ratio of the maximum value to the minimum value of the magnetic flux density in the table due to
the difference of the inclination angle θ.
[0014]
When the inclination angle θ is 45 °, the average magnetic flux density is maximum, and when
the inclination angle θ is 75 °, the average magnetic flux density is smaller than when the
inclination angle θ is 0 °.
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On the other hand, when the inclination angle θ is 0 °, the maximum value and the minimum
value of the magnetic flux density at the coil position differ by 7 times or more, which indicates
that the driving force applied to the diaphragm also differs 7 times or more depending on the
place. On the other hand, as the inclination angle θ is increased, the ratio between the maximum
value and the minimum value decreases, that is, the variation of the magnetic flux density from
the inner circumferential side to the outer circumferential side of the coil decreases.
[0015]
Therefore, by making the tip end surface of the peripheral wall portion 16b of the yoke 16
inclined as the inclined surface 16c as in this example, the variation in magnetic flux density can
be reduced without reducing the average magnetic flux density at the coil position. By reducing
the variation of the magnetic flux density in this manner, a uniform and favorable vibration state
of the diaphragm can be obtained. In addition, it is preferable to make the magnitude | size of
inclination | tilt angle (theta) into the range of 20 degrees-60 degrees from ratio of the maximum
value of magnetic flux density, and the minimum value. FIG. 4 shows an example in which the
coil 14 is formed on both sides of the diaphragm 13, the yoke 16 and the magnet 17 are
disposed facing each other with the diaphragm 13 interposed, and the magnetic circuit is
provided on both sides of the diaphragm 13. In addition to the single-sided magnetic circuit
configuration shown in FIG. In this example, the upper frame 12 is provided with an opening 31
at the closed upper end face thereof, and the yoke 16 is disposed in the opening 31 similarly to
the lower frame 11. In the figure, 32 indicates a hole for sound emission.
[0016]
FIG. 5 shows the magnetic flux line distribution obtained by simulation in the same manner as
FIG. 2 as in FIG. 6 shows the horizontal direction component of the magnetic flux density from
the inner periphery to the outer periphery at the coil position when the inclination angle θ is set
to 0 °, 20 °, 60 °, 75 ° as in FIG. Shows the distribution of In the simulation, the dimensions
of each part are the same as in the case of FIG. 3, and the magnetic circuit is arranged
symmetrically with respect to the diaphragm 13. When there are magnetic circuits on both sides
of the diaphragm 13 as shown in FIG. 5, the magnetic flux lines from both magnetic circuits repel
each other, so the magnetic flux lines are parallel to the plate surface of the diaphragm 13 at the
coil portion. Will be able to take out the driving force efficiently. As a result, the horizontal
component of the magnetic flux density at the coil position on the side of the diaphragm is
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approximately doubled as compared with FIG. 3 as shown in FIG. 6, and the coils 14 are on both
sides of the diaphragm 13. The convenience 4 times the sensitivity improvement will be
expected. Therefore, such a configuration in which magnetic circuits are arranged on both sides
is useful particularly when high sensitivity is required.
[0017]
Table 2 summarizes the ratio of the average value of the magnetic flux density at the coil position
and the maximum value to the minimum value of the magnetic flux density in this double-sided
magnetic circuit configuration in a table.
[0018]
In this example, when the inclination angle θ is 60 °, the average magnetic flux density is
maximum, and as the inclination angle θ is increased, the ratio of the maximum value to the
minimum value decreases and the variation in magnetic flux density decreases. Know that
The magnitude of the inclination angle θ is set in the range of 20 ° to 60 °, as in the case of
the one-sided magnetic circuit.
[0019]
A is sectional drawing which shows one Example of the flat coil speaker by this invention, B is the
elements on larger scale. A is a diagram showing magnetic flux line distribution in a coil portion
of the flat coil speaker shown in FIG. 1, and B is a diagram showing magnetic flux line
distribution in a coil portion of a conventional flat coil speaker shown in FIG. 7 for comparison.
The graph which shows the magnetic flux density distribution in the coil position by the
difference in inclination-angle (theta) of the flat coil speaker shown in FIG. FIG. 7 is a crosssectional view showing another embodiment of the flat coil speaker according to the present
invention. The figure which shows the magnetic flux line distribution in the coil part of the flat
coil speaker shown in FIG. The graph which shows the magnetic flux density distribution in the
coil position by the difference in inclination-angle (theta) of the flat coil speaker shown in FIG.
Sectional drawing which shows the structure of the flat coil speaker currently proposed
conventionally. Fig. 7A is a diagram showing magnetic flux lines crossing coils in the flat coil
speaker shown in Fig. 7; Fig. 8B is a diagram showing magnetic flux lines crossing coils in a
normal speaker that is not a flat coil for comparison;
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