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JPH1051892

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DESCRIPTION JPH1051892
[0001]
TECHNICAL FIELD The present invention relates to a headphone driver.
[0002]
[Prior Art] Headphones have the disadvantage of having to wear a headband on the head, etc.,
but have the advantage of being less affected by the room than speakers, or relatively less
annoying to others There are also good conditions for watching music carefully. In particular, the
intention of designing as an acoustic device is that it is not necessary to be affected by the room,
it is annoyed by the problem of setting and tuning, and in many cases the problem that the
developed intention is not accurately reproduced. There is an advantage that it is easy to convey
the user directly to the user, and also the user can feel it straight and can judge it.
[0003]
FIG. 11 is a cross-sectional view of a headphone driver in the conventional example. In the figure,
21 is a diaphragm, 3 is a voice coil, 4 is a frame, a yoke, 5 is a pole piece, and 6 is a magnet.
[0004]
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For the diaphragm 21 of this conventional headphone driver, a polymer film such as polyester is
widely used. This is because the dome portion of the diaphragm 21 needs to have a certain
degree of hardness and rigidity, while the film is thermoplastic and can be relatively easily
formed, and the shape rigidity by the formation can be obtained. In addition, by making the film
thinner, the compliance can be increased (f0 is lowered), so that the bass reproduction can be
extended. A polyester film is relatively suitable as a material to be thinned. Paper and metal are
not suitable in that they are thin and soft. Paper can not be made very thin, and aluminum can
not achieve the required compliance even if it is made thin.
[0005]
However, when viewed as a material, most polymer films have a specific gravity of 1 or more, so
the Young's modulus as the material is not very high, and a material having a relatively high
Young's modulus, such as PPTA, is used. However, the propagation velocity (E / ρ) 1/2 is less
than 4000 m / s, the value of the square root of flexural rigidity (E / ρ3) 1/2 is lower than that
of wood pulp, and the high-frequency regeneration and high fidelity are sufficient. Regeneration
can not be expected. However, symbol E is Young's modulus and ρ is density. The resonance
frequency f is proportional to the product of the square root of flexural rigidity (E / ρ3) 1/2 and
the mass m. That is, it can be represented by the following equation (1). f ∝ m (E / ρ 3) 1/2
··············· (1)
[0006]
Therefore, it is conceivable to use a metal or ceramic with a high Young's modulus for the dome
or to deposit it on the surface of the polymer film, but when using these materials alone, the
internal loss (tan δ) is low. Since the material has a tone specific to the material and the tone
changes even when deposited, the actual propagation speed is dominated by the substrate, so f
often hardly changes as well.
[0007]
More recently, materials using cellulose or the like produced from living things or these to form a
diaphragm, materials with low specific gravity, high Young's modulus, and appropriate internal
loss are used, but the compliance as a diaphragm Since the Young's modulus is high in order to
obtain H, the diaphragm is made extremely thin, and as a result, there is a problem that the
rigidity as the diaphragm is reduced.
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[0008]
The present invention has been made in view of such a point, and achieves the performance
required for the diaphragm body corresponding to the dome portion in an extremely wellbalanced manner, and the edge portion is made of a material different from the diaphragm body.
It is an object of the present invention to provide a headphone driver having a diaphragm that
can be used to obtain appropriate compliance.
Another object of the present invention is to provide a headphone driver having a sufficiently low
energy band and extremely low distortion over the entire band.
[0009]
SUMMARY OF THE INVENTION According to the present invention, it is intended to achieve wellbalanced properties such as Young's modulus, density, internal loss, flexural rigidity, etc. of
physical properties required for the diaphragm body of a diaphragm, and to provide an edge
separately. Thus, a high compliance material can be used without making the diaphragm
extremely thin.
That is, by adding carbon fiber to the disintegrated biocellulose, it is possible to lower the density
and to increase the Young's modulus, and it is possible to obtain higher propagation speed and
higher bending rigidity than in the case of biocellulose alone. In addition, although the Young's
modulus is further increased by increasing the mixing ratio of carbon fibers mixed with
biocellulose, the internal loss is also reduced, so by setting the mixing ratio of carbon fibers to
50% or less by weight ratio, The required performance is achieved in an extremely well-balanced
manner. Furthermore, by using the dual magnetic gap in combination, the coils can be push-pull
operated by the increase in the driving force, the vertical symmetry of the magnetic flux density
distribution, and the reverse winding direction of the upper and lower coils, thereby further
improving the performance.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION The headphone driver of the present
invention has a diaphragm having a two-piece structure of a diaphragm body portion and an
edge portion, and a material of the diaphragm body portion has biocellulose as a base material
and a tensile modulus of elasticity. It is characterized in that a carbon fiber of 40,000 Kgf / mm 2
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or more is mixed with 15 to 50% by weight as a reinforcing material.
[0011]
Further, in the headphone driver according to the present invention, the ring-shaped pole pieces
are disposed respectively on the upper and lower surfaces of the ring-shaped magnet, and the
magnetic circuit is configured to form a dual magnetic gap from these pole pieces and the ringshaped yoke. It has a feature.
[0012]
Furthermore, the headphone driver according to the present invention has a diaphragm having a
two-piece structure of a diaphragm body portion and an edge portion, biocellulose as a base
material, and a carbon fiber having a tensile modulus of 40,000 Kgf / mm 2 or more as a
reinforcing material. It is characterized in that a diaphragm body using a material mixed with 15
to 50% by weight and a magnetic circuit forming a dual magnetic gap are used.
[0013]
[Examples] In the present invention, by mixing carbon fiber with disintegrated biocellulose,
propagation speed (E / ρ) 1/2 or square root of flexural rigidity (E / ρ3) as compared with
biocellulose alone. It is raising the half further.
However, if the carbon fiber mixing ratio is increased, the Young's modulus becomes high and at
the same time the internal loss becomes low, so the optimum range of the ratio of carbon fibers
is determined and adopted.
[0014]
In order to expand the bass range, it is necessary to increase the edge compliance.
In the case of an integral diaphragm, this problem is dealt with by reducing the thickness of the
diaphragm.
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However, because the disintegrated biocellulose has a high Young's modulus, the required
compliance can not be obtained even with a thickness of 40 microns. If the thickness is further
reduced, the advantages of the material as the diaphragm are lost. Integral diaphragms are
required to have opposite physical properties such as rigidity and compliance, but generally a
polyester film or the like is used to find a compromise point.
[0015]
Further, by providing the edge portion separately, high compliance can be obtained without
extremely thinning the diaphragm body portion, and therefore, the performance of the material
can be sufficiently extracted. In the free edge type, this problem can be solved by using a rigid
body material for the diaphragm body portion and another material soft for the edge portion, for
example, using a thin urethane elastomer film.
[0016]
By mixing carbon fiber with the disintegrated biocellulose, the density is lowered and the
bending rigidity is raised. Sound quality is effective in both bending stiffness and propagation
speed, the speed of sound needs a material with high propagation speed, and it is necessary to
lower the density for distortion and increase the bending stiffness. A suitable balance of physical
properties such as internal loss, propagation speed, bending stiffness, etc. is taken into
consideration so as not to deteriorate sound quality and the like.
[0017]
Basically, biocellulose is the main component of the diaphragm body. If there is no carbon fiber
mixing, the high frequency band is insufficient, and if the carbon fiber mixing is too large, a peak
appears in the high frequency. Therefore, the range is defined in relation to the acoustic
characteristics that are derived from physical properties.
[0018]
However, in the diaphragm of the headphone driver, when the ratio of carbon fibers is 50% or
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more, the carbon fibers are entangled with each other, bonding increases, and uniform dispersion
does not occur. Since entanglement occurs, unevenness in papermaking and unevenness in
carbon fiber can be made, and thick and thin areas can be formed. After all, if it is made as thin
as possible, pinholes will occur. When the ratio of carbon fiber is high, weight reduction can not
be performed.
[0019]
Therefore, various physical property values are made optimum values by adding a predetermined
amount of carbon fiber. Physical property values include density, sound velocity, Young's
modulus and the like. Basically, the density is 1 or less, the internal loss is about 0.03, and the
speed of sound or bending rigidity is increased.
[0020]
The greater the thickness, the stronger the bending stiffness, which is very effective for the
vibration of the axisymmetric mode. This is less effective when the diaphragm body is made
deeper, and requires a low density material whose weight does not increase much even if it is
made thicker. The split resonance of the axis-oriented mode is particularly related to odd-order
harmonic distortion, third-order, and fifth-order, and if there is a large amount of harmonic
distortion, it will be extremely disturbing in listening to music. Therefore, without removing it, a
high quality diaphragm can not be obtained.
[0021]
If it is only bending rigidity, it will become high if it thickens even with paper. However, although
the diaphragm body made of thick paper has high bending rigidity, it becomes heavy and the
sensitivity is lowered. In headphones, it is necessary to increase the sensitivity without increasing
the size of the magnetic circuit, so a light and rigid material is required for the vibration system.
For example, carbon cloth is relatively lightweight and highly rigid, but there is a limit to weight
reduction per grammage. Therefore, we aim to reduce weight and improve bending rigidity by
supplementing biocellulose with carbon fiber with high elasticity.
[0022]
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FIG. 9 is a view showing the relationship between the carbon fiber mixing ratio to biocellulose
and the square root of flexural rigidity. When the mixing ratio for mixing carbon fiber with
biocellulose is 0%, the square root of flexural rigidity is 3.1, 5 for mixing ratio 10%, and 8.3 for
mixing ratio 20%. The resonant frequency is proportional to this value. For example, when the
mixing ratio of carbon fibers is increased from 0% to 20%, the resonance frequency is
approximately tripled (8.3 / 3.1). As the frequency of the split resonance mode increases,
harmonic distortion moves to a higher frequency by that much, and the amount of distortion
decreases.
[0023]
The square root of the flexural rigidity of the polyester film in the conventional example is 1.5.
The square root of flexural rigidity of biocellulose is 3, twice that of polyester film, and when
carbon fiber is mixed with biocellulose at 15%, the square root of flexural rigidity is about 4
times at 6.5.
[0024]
FIG. 10 is a graph showing the relationship between the carbon fiber mixing ratio to biocellulose
and the internal loss. If the internal loss changes by about 0.005, you can clearly see the
evaluation difference in sound quality by ear. In that sense, the difference between 20% and 40%
of the carbon fiber mixing ratio is also large.
[0025]
The internal loss is lowest at a carbon fiber mixing ratio of 40 to 50%. The internal loss of carbon
fiber alone is very low at 0.0001 and even lower than that of aluminum. In addition, if the
internal loss itself possessed by biocellulose is a very large value (0.037) and it is a composite
material made by dispersing carbon fibers of about 3 mm in which biocellulose is cut as matrix
material, The polyester film has a larger than 0.02. Therefore, the internal loss is a larger value
than conventional materials, and a large bending stiffness can be obtained. From the nature of
the original carbon fiber, the internal loss can be maintained as large as two orders of magnitude.
This is basically due to the effect of biocellulose.
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[0026]
On the other hand, if the carbon fiber mixing ratio is 50% or more, the internal loss increases, the
binding property is lost, and a large amount of rattling noise due to rubbing of the carbon fibers
becomes unpleasant sound. Sound quality seems to be cold compared to the one with a carbon
fiber mixing ratio of 0%. In addition, the uniformity of papermaking also deteriorates. Therefore,
if the mixing ratio of around 20% to 30% is selected from the balance with the bending rigidity,
the resonance frequency is 4 times or more and there is a considerable effect.
[0027]
First Embodiment An embodiment of the present invention will be described below with
reference to the drawings. FIG. 1 is a cross-sectional view of a headphone driver according to a
first embodiment of the present invention. In the figure, 1 is a diaphragm body, 2 is an edge, 3 is
a voice coil, 4 is a frame, a yoke, 5 is a pole piece, 6 is a magnet, and 10 is a diaphragm
comprising a diaphragm body 1 and an edge 2 It is. The diameter of the headphone driver was
φ50 mm.
[0028]
The material of the diaphragm body 1 specifies a carbon fiber mixing ratio to biocellulose as
20%, and is in a range where it can be made light and thin.
[0029]
The Young's modulus of the material of the edge part 2 was 450 MPa or less, and what shape ¦
molded the urethane-elastomer sheet (Bridgestone URS-B2) was used.
[0030]
FIG. 2 is a diagram showing comparison of frequency characteristics and second harmonic
distortion in the first embodiment of the present invention and the conventional example, and is
a measurement result in an anechoic chamber.
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In the figure, the solid line A1 is the frequency characteristic in the first embodiment, and the
broken line B is the frequency characteristic in the conventional example shown in FIG.
A polyester film was used for the diaphragm 21 in the conventional example. The solid line A12
is the second harmonic distortion in the first embodiment, and the broken line B2 is the second
harmonic distortion in the prior art. It can be seen from the solid line A12 that the improvement
result appears in the second harmonic distortion at a frequency of 200 Hz or more. The solid line
A12 is higher in level than the broken line B2 at a frequency of 200 Hz or less for measurement
in the anechoic chamber.
[0031]
FIG. 3 is a diagram showing a comparison of frequency characteristics and third harmonic
distortion in the first embodiment of the present invention and the conventional example, which
are measurement results in an anechoic chamber. In the figure, the solid line A1 is the frequency
characteristic in the first embodiment, and the broken line B is the frequency characteristic in the
conventional example shown in FIG. A polyester film was used for the diaphragm 21 in the
conventional example. The solid line A13 is the third harmonic distortion in the first
embodiment, and the broken line B3 is the third harmonic distortion in the prior art. It can be
seen from the solid line A13 that the improvement result appears in the third harmonic
distortion at a frequency of 200 Hz or more.
[0032]
Second Embodiment FIG. 4 is a cross-sectional view of a headphone driver according to a second
embodiment of the present invention. In addition, what attached ¦ subjected the code ¦ symbol
same as FIG. 1 has shown the same element, respectively, and abbreviate ¦ omits description. In
the figure, 13 is a voice coil, 14 is a frame and yoke, 15a is an upper pole piece, and 15b is a
lower pole piece. In this second embodiment, the diaphragm 10 comprising the diaphragm body
1 and the edge portion 2 is the same as that in the first embodiment, but the magnetic circuit is
different. The diameter of the headphone driver was φ50 mm.
[0033]
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By using a neodymium magnet with a very high energy product for the magnetic circuit forming
the dual magnetic gap, it was possible to make the utilization efficiency relatively thin and
compact. The dual magnetic gap is not limited to the inner magnetic type in the embodiment, but
may have the same function and effect even if it is an outer magnetic type.
[0034]
1. The magnetic flux density distribution is vertically symmetrical because the upper and
lower magnetic circuits can be perfectly symmetrical. 2. There is an advantage that the coils
can be push-pull operated by reversing the winding direction of the coils with respect to each
gap.
[0035]
FIG. 5 is a diagram showing a comparison of frequency characteristics and second harmonic
distortion in the second embodiment of the present invention and the conventional example,
which are measurement results in an anechoic chamber. In the figure, the solid line A2 is the
frequency characteristic in the second embodiment, and the broken line B is the frequency
characteristic in the conventional example shown in FIG. A polyester film was used for the
diaphragm 21 in the conventional example. The solid line A22 is the second harmonic distortion
in the second embodiment, and the solid line B2 is the second harmonic distortion in the
conventional example. It can be seen from the solid line A22 that the improvement result
appears in the second harmonic distortion at a frequency of 200 Hz or more. The solid line A22
is higher in level than the broken line B2 at frequencies below 200 Hz for measurement in the
anechoic chamber.
[0036]
FIG. 6 is a diagram showing a comparison of frequency characteristics and third harmonic
distortion in the second embodiment of the present invention and the conventional example,
which are measurement results in an anechoic chamber. In the figure, the solid line A2 is the
frequency characteristic in the second embodiment, and the broken line B is the frequency
characteristic in the conventional example shown in FIG. A polyester film was used for the
diaphragm 21 in the conventional example. The solid line A23 is the third harmonic distortion in
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the second embodiment, and the solid line B3 is the third harmonic distortion in the conventional
example. It can be seen from the solid line A23 that the improvement result appears in the third
harmonic distortion at a frequency of 200 Hz or more.
[0037]
FIG. 7 is a view showing a comparison of second harmonic distortion in the first embodiment and
the second embodiment of the present invention, which are measurement results in an anechoic
chamber. In the figure, the solid line A is the frequency characteristic in the embodiment, the
broken line A12 is the second harmonic distortion in the first embodiment, and the solid line A22
is the second harmonic distortion in the second embodiment. As is apparent from the figure, the
effect of the magnetic circuit forming the dual magnetic gap in the second embodiment is
remarkable.
[0038]
FIG. 8 is a diagram showing a comparison of third harmonic distortion in the first embodiment
and the second embodiment of the present invention, which are measurement results in an
anechoic chamber. In the figure, the solid line A is the frequency characteristic in the
embodiment, the broken line A13 is the third harmonic distortion in the first embodiment, and
the solid line A23 is the third harmonic distortion in the second embodiment. As is apparent from
the figure, the effect of the magnetic circuit forming the dual magnetic gap in the second
embodiment is remarkable.
[0039]
As described above, in the headphone driver according to the present invention, the diaphragm
has a two-piece structure of the diaphragm body portion and the edge portion, and the material
of the diaphragm body portion is made of biocellulose. Since a carbon fiber with a tensile elastic
modulus of 40,000 Kgf / mm 2 or more is mixed with 15 to 50% by weight as a reinforcing
material, the driver for headphones according to the present invention can Since the magnetic
circuit is configured to arrange each piece and to form a dual magnetic gap from the pole piece
and the ring yoke, the headphone driver of the present invention further includes the diaphragm
as the diaphragm body portion and the edge portion And a biocellulose-based material with a
carbon fiber with a tensile modulus of 40,000 Kgf / mm2 or more as a reinforcing material Since
the diaphragm body using the material mixed with 15 to 50% by weight and the magnetic circuit
forming the dual magnetic gap are used, the performance required for the diaphragm body is
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achieved in an extremely well-balanced manner. Edges can be made highly compliant, have
sufficiently low energy, and can have very low distortion across all bands.
[0040]
Brief description of the drawings
[0041]
1 is a cross-sectional view of the headphone driver in the first embodiment of the present
invention.
[0042]
2 is a diagram showing a comparison of the frequency characteristics and the second harmonic
distortion in the first embodiment of the present invention and the conventional example.
[0043]
3 is a diagram showing a comparison of the frequency characteristics and the third harmonic
distortion in the first embodiment of the present invention and the conventional example.
[0044]
4 is a cross-sectional view of a headphone driver according to a second embodiment of the
present invention.
[0045]
5 is a diagram showing a comparison of the frequency characteristics and the second harmonic
distortion in the second embodiment of the present invention and the conventional example.
[0046]
6 is a diagram showing a comparison of the frequency characteristics and the third harmonic
distortion in the second embodiment of the present invention and the conventional example.
[0047]
7 is a diagram showing a comparison of the second harmonic distortion in the first embodiment
and the second embodiment of the present invention.
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[0048]
8 is a diagram showing a comparison of the third harmonic distortion in the first embodiment
and the second embodiment of the present invention.
[0049]
FIG. 9 is a view showing the relationship between the carbon fiber mixing ratio of biocellulose
and the square root of flexural rigidity.
[0050]
10 is a diagram showing the relationship between the carbon fiber mixing ratio of the
biocellulose and the internal loss.
[0051]
11 is a cross-sectional view of a headphone driver in the conventional example.
[0052]
Explanation of sign
[0053]
DESCRIPTION OF SYMBOLS 1 diaphragm body 2 edge part 3 voice coil 4 frame, yoke 5 pole
piece 6 magnet 10 diaphragm 13 voice coil 14 frame, yoke 15 a upper pole piece 15 b lower
pole piece 21 diaphragm A frequency characteristic in the embodiment A1 Frequency
characteristic A12 in the embodiment Second harmonic distortion characteristic A13 in the first
embodiment Third harmonic distortion characteristic A2 in the first embodiment Frequency
characteristic A22 in the second embodiment Second harmonic distortion characteristic A23 in
the second embodiment Third harmonic distortion characteristic B in the second embodiment.
Frequency characteristic B2 in the conventional example Second harmonic distortion
characteristic in the embodiment B3 Third harmonic distortion characteristic in the prior
example
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