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JP2008011340

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DESCRIPTION JP2008011340
The present invention provides an acoustic speaker with reduced sound distortion and good
sound quality. SOLUTION: An acoustic speaker 10 has a diaphragm 11 made of a rectangular flat
plate, an auxiliary plate 12 provided on one main surface 11a of the diaphragm 11, and an
output rod 14 in contact with the diaphragm 12. And an actuator for driving the output rod 14
based on the acoustic signal to vibrate the diaphragm 11. The auxiliary plate 11 is provided to
cover a flat area on the diaphragm 11 including the contact point P of the output rod 14 and the
strain points S1 and S2 on the diaphragm 11. With such a configuration, the strain points S1 and
S2 on the diaphragm 11 and the contact points of the output rod 14 can be vibrated together.
[Selected figure] Figure 1
Acoustic speaker
[0001]
The present invention relates to an acoustic speaker, and more particularly to the structure of a
diaphragm driven by a giant magnetostrictive actuator.
[0002]
Recently, acoustic speakers utilizing giant magnetostrictive actuators have attracted attention.
The giant magnetostrictive actuator is an actuator utilizing the property of the giant
magnetostrictive element in which the dimension is expanded by a change in magnetic field. The
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giant magnetostrictive element generates a displacement of 1000 to 2000 ppm due to magnetic
field changes, has a high response speed, and can be driven at a low voltage, so it is used as an
actuator to drive a diaphragm to realize a high-performance speaker It is a thing. In the
conventional acoustic speaker, the rod portion of the giant magnetostrictive actuator is brought
into contact with the diaphragm, and the giant magnetostrictive actuator is driven based on the
acoustic signal to vibrate the diaphragm, thereby converting the acoustic signal into mechanical
vibration. It was made to output as (refer to patent documents 1). Patent No. 3615883
[0003]
However, just as in the conventional acoustic speaker described above, simply contacting the rod
portion of the giant magnetostrictive actuator with the diaphragm causes a distortion point in the
vibration on the diaphragm, which is output as distortion of sound. There was a problem. Such a
problem is a problem that may occur not only when using a giant magnetostrictive actuator as a
drive element of an acoustic speaker but also when using other types of actuators.
[0004]
The present invention has been made to solve such problems, and an object of the present
invention is to provide an acoustic speaker with reduced sound distortion and good sound
quality.
[0005]
The above object of the present invention is provided with a diaphragm, and an actuator having
an output rod in direct or indirect contact with the diaphragm and driving the output rod based
on the acoustic signal to vibrate the diaphragm. This is achieved by the acoustic speaker
characterized in that the elasticity of the flat region on the diaphragm including the contact point
of the above and the strain point on the diaphragm is suppressed more than the elasticity of the
other regions.
[0006]
In the present invention, the elasticity of the flat region is preferably suppressed by an auxiliary
plate provided on at least one of the main surfaces of the diaphragm.
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According to this, the strength of the diaphragm can be enhanced with a very simple
configuration.
[0007]
In the present invention, the length of the auxiliary plate is preferably 38% or more of the length
of the diaphragm, and particularly preferably 48 to 68%.
If the ratio of the length of the auxiliary plate to the diaphragm is 38% or more, the distorted
sound can be suppressed to such an extent that ordinary people can not perceive it, and if it is 48
to 68%, the hearing ability is very high. Since the distorted sound can be suppressed to such an
extent that even a superior person can not feel it, it is possible to reproduce a good quality sound
without distortion.
[0008]
As described above, according to the present invention, distortion of sound can be sufficiently
reduced, and an acoustic speaker with extremely good sound quality can be provided.
[0009]
Hereinafter, preferred embodiments of the present invention will be described in detail with
reference to the accompanying drawings.
[0010]
FIG. 1 is a schematic perspective view showing the configuration of an acoustic speaker
according to a first embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view taken along the line Y-Y of FIG.
[0011]
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As shown in FIG. 1, this acoustic speaker 10 includes a diaphragm 11, an auxiliary plate 12
provided at a substantially central portion on one main surface 11 a of the diaphragm 11, and a
super magnetostrictive actuator that vibrates the diaphragm 11. It has 13 and.
The giant magnetostrictive actuator 13 is also referred to as an exciter, and has an output rod 14
in contact with the surface of the auxiliary plate 12 and vibrates the diaphragm 11 together with
the auxiliary plate 12 by driving the output rod 14 based on the acoustic signal.
[0012]
The diaphragm 11 is a rectangular flat plate, and a point 11p near the upper end of the
diaphragm 11 and two points 11q and 11r near the lower end are fixed to a speaker housing
(not shown). As a material of the diaphragm 11, for example, an acrylic plate can be used. The
planar dimensions of the diaphragm 11 can be appropriately set according to the purpose of the
speaker. As an example, the width W1 of the diaphragm 11 can be set to 135 mm, and the length
L1 can be set to 480 mm. Further, the thickness T1 of the diaphragm 11 is not particularly
limited as long as it can be vibrated by the driving of the super magnetostrictive actuator 13. For
example, T1 can be set to 10 mm.
[0013]
The auxiliary plate 12 is a smaller and elongated member than the diaphragm 11. The auxiliary
plate 12 of the present embodiment is a member different from the diaphragm 11 and is
adhesively fixed to a substantially central portion of the diaphragm 11. The auxiliary plate 12
may be the same material as the diaphragm 11 or may be another material. Although details will
be described later, the auxiliary plate 12 is provided so as to cover a flat area on the diaphragm
11 including the contact point P of the output rod 14 and the strain points S1 and S2 on the
diaphragm 11. For that purpose, the length L2 of the auxiliary plate 12 is preferably 38% or
more of the length L1 of the diaphragm 11, and particularly preferably 48 to 68%. If L2 / L1 ≧
38%, the distortion sound can be suppressed to a low level to which normal people can not
perceive it, so good quality sound can be reproduced, and 48% ≦ L2 / L1 ≦ 68%. If so, the
distortion sound is suppressed to such an extent that even a person with very high hearing can
not feel it, so it is possible to reproduce a high quality sound without distortion. Further, the
width W2 and the thickness T2 of the auxiliary plate 12 are not particularly limited, and can be
appropriately determined within the practical range.
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[0014]
The giant magnetostrictive actuator 13 is provided on one main surface 11 a side of the
diaphragm 11, and the tip of the output rod 14 is in contact with the surface of the auxiliary
plate 12. Therefore, the vibration of the output rod 14 is supplied to the diaphragm 11 via the
auxiliary plate 12. The contact point P of the output rod 14 is provided slightly closer to the
upper end than the center of the main surface of the diaphragm 11 in the plane region of the
diaphragm 11. This is because the vicinity of the upper end of the diaphragm 11 is fixed at one
point, and the vicinity of the lower end is fixed at two points, so that the balance of vibration of
the whole diaphragm is considered. A slight recess 12 d is formed on the surface of the auxiliary
plate 12, and the tip of the output rod 14 is fitted in the recess 12 d to prevent displacement of
the output rod 14.
[0015]
When mechanical vibration is applied from the output rod 14 of the giant magnetostrictive
actuator 13 to one point on the diaphragm 11, several strain points are generated on the
diaphragm 11. In particular, in the acoustic speaker 10 of the present embodiment, the first
distortion point S1 is on the center line (Y-Y line) extending in the longitudinal direction of the
diaphragm 11 and closer to the upper end than the contact point P of the output rod 14 As a
result, a second strain point S2 is generated on the lower end side of the contact point P of the
output rod 14. The auxiliary plate 12 reduces distortion on the diaphragm 11 by fixing the strain
points S1 and S2 and the contact point of the output rod 14 together.
[0016]
FIG. 3 is a schematic cross-sectional view showing the configuration of the giant magnetostrictive
actuator 13. As shown in FIG.
[0017]
As shown in FIG. 3, the giant magnetostrictive actuator 13 applies a magnetic field in the axial
direction to the housing 21, the giant magnetostrictive shaft 22 provided in the housing 21, and
the giant magnetostrictive shaft 22 to thereby obtain the giant magnetostrictive shaft 22. A coil
23 to be expanded, a bobbin 24 around which the coil 23 is wound, a cylindrical bias magnet 25
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provided on the outer periphery of the bobbin 24, and an output rod 14 vibrating in conjunction
with expansion and contraction of the giant magnetostrictive shaft 22; The output rod 14 and the
elastic member 26 for applying a preload to the giant magnetostrictive shaft 22 are provided.
These members are accommodated in the housing 21 with the back cover 21a provided on the
bottom surface of the housing 21 removed, and the back cover 21a is fixed by screws 21b.
[0018]
The giant magnetostrictive shaft 22 is a substantially columnar member made of a giant
magnetostrictive material. The giant magnetostrictive material has a characteristic that the
permeability changes when an external stress is applied, and the amount of magnetostriction
changes when an external magnetic field is applied. The super magnetostrictive material is not
particularly limited, but a material having Tb0.34-Dy0.66-Fe1.90 as a central composition can be
used. The dimensions of the giant magnetostrictive shaft 22 may be appropriately selected in
accordance with the target amount of magnetostriction. For example, in the case where the giant
magnetostrictive shaft 22 is formed using a material capable of obtaining a magnetostriction
amount of about 1000 ppm, if the expansion and contraction of about 10 μm is desired, the
length of the giant magnetostrictive shaft 22 may be about 1 cm.
[0019]
The coil 23 is disposed on the outer periphery of the giant magnetostrictive shaft 22 in a state of
being wound around the bobbin 24. That is, the giant magnetostrictive shaft 22 is inserted into
the hollow portion of the bobbin 24 around which the coil 23 is wound. A bias magnetic field is
previously applied to the giant magnetostrictive shaft 22 by the bias magnet 25. Even if a
magnetic field from the coil 23 is applied to the giant magnetostrictive shaft 22 placed in a
magnetic field, the giant magnetostrictive shaft 22 only stretches, but the bias magnetic field is
applied in advance. Both stretching and contraction are possible.
[0020]
The output rod 14 is a member that vibrates in accordance with the expansion and contraction of
the giant magnetostrictive shaft 22. The front end of the output rod 14 is in contact with the
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auxiliary plate 12, and the rear end of the output rod 14 is in contact with the front end of the
giant magnetostrictive shaft 22. The output rod 14 is provided with a flange portion 14 a, and
the elastic member 26 is sandwiched between the flange portion 14 a and the inner wall surface
of the housing 21. The output rod 14 is biased by the elastic member 26 in a direction to press
the tip of the giant magnetostrictive shaft 22.
[0021]
In the above configuration, when a drive current is applied to the coil 23 to change the magnetic
field penetrating the giant magnetostrictive shaft 22, the giant magnetostrictive shaft 22 expands
and contracts, and the output rod 14 vibrates. Further, when the current supply to the coil 23 is
stopped, the output rod 14 is pushed back to the original position by the biasing force of the
elastic member 26. Therefore, when the giant magnetostrictive actuator 13 is driven by an
acoustic signal, the acoustic signal can be converted into mechanical vibration, and the
diaphragm 11 can be vibrated by the vibration modulated by the acoustic signal.
[0022]
As described above, according to the present embodiment, the auxiliary plate 12 is provided so
as to cover the planar region on the diaphragm 11 including the contact point P of the output
rod 14 and the strain points S1 and S2 on the diaphragm 11. Because of this, the strain points S1
and S2 on the diaphragm 11 and the contact points of the output rod 14 can be vibrated
together. Therefore, distortion of the sound radiated from the diaphragm 11 can be sufficiently
reduced, and a very good acoustic speaker with high sound quality can be realized.
[0023]
FIG. 4 is a schematic cross-sectional view showing the configuration of an acoustic speaker
according to a second embodiment of the present invention.
[0024]
As shown in FIG. 4, the characteristic of this acoustic speaker 30 is that the super
magnetostrictive actuator 13 is provided on the other main surface 11 b side of the diaphragm
11, and the tip of the output rod 14 is the other main surface of the diaphragm 11. It is in
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contact with 11b.
That is, the vibration from the output rod 14 is directly supplied to the diaphragm 11 without the
aid of the auxiliary plate 12. The other configuration is substantially the same as that of the first
embodiment, and thus the description thereof is omitted.
[0025]
Also in the present embodiment, when mechanical vibration is applied from the output rod 14 of
the giant magnetostrictive actuator 13 to one point on the diaphragm 11, strain points S1 and S2
are generated at the widthwise center (Y-Y line) of the diaphragm 11. However, since the
auxiliary plate 12 is provided so as to cover a flat region on the diaphragm 11 including the
contact point P of the output rod 14 and the strain points S1 and S2 on the diaphragm 11, And
the contact points of the output rod 14 can be vibrated together. Therefore, distortion of the
sound radiated from the diaphragm 11 can be sufficiently reduced, and a very good acoustic
speaker with high sound quality can be realized.
[0026]
The present invention is not limited to the above embodiments, and various modifications can be
made without departing from the scope of the present invention, and these are also included in
the scope of the present invention. Needless to say.
[0027]
For example, in the above embodiment, the auxiliary plate 12 has a shape elongated in the
longitudinal direction of the diaphragm 11, but may have another shape such as a circular shape
or an elliptical shape.
Furthermore, as the shape of the auxiliary plate 12, the thickness near the contact point P of the
output rod 14 may be thick, and the thickness may be linear or curvilinearly thinner toward the
outer side. The point is that the shape of the auxiliary plate 12 is not particularly limited, and can
be freely set in accordance with the shape of the diaphragm 11 and the generation position of
the strain point. That is, the auxiliary plate 12 may be provided so as to cover a flat area on the
diaphragm 11 including the contact point of the output rod 14 and the strain point generated on
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the diaphragm 11.
[0028]
Moreover, in the said embodiment, although the auxiliary plate 12 is a member different from
the diaphragm 11, and adhesively fixed to the approximate center part of the diaphragm 11, the
diaphragm 11 and the auxiliary plate 12 are integrally shape ¦ molded. It may be done.
[0029]
In the above embodiment, the contact point P of the output rod is set slightly above the center of
the flat area of the diaphragm 11, but the contact point of the output rod 14 is the center of the
diaphragm 11. And may be set to other points.
Even in such a configuration, the elasticity of the flat region on the diaphragm 11 including the
contact point of the output rod 14 and the strain point generated on the diaphragm 11 of the
auxiliary plate 12 is higher than the elasticity of other regions. It is possible to sufficiently reduce
the distortion of the sound if it is suppressed.
[0030]
In the above embodiment, the giant magnetostrictive actuator 13 is used as an actuator for
driving the diaphragm 11. However, the present invention is not limited to such a case, and
various actuators may be targeted. Can.
[0031]
The first embodiment will be described first.
In Example 1, distortion distribution of the diaphragm 11 was measured. In the measurement of
strain distribution, first, the diaphragm 11 to be measured was prepared. The dimensions of the
diaphragm 11 were, as shown in FIG. 5, a length L1 = 480 mm, a width W1 = 135 mm, and a
thickness D1 = 10 mm. The center in the width direction of the upper end of such a diaphragm
11 is defined as a zero point, the width direction is defined as an X axis, the longitudinal direction
as a Y axis, and the center (X, Y) of the diaphragm 11 = (0, 240 mm) The contact point P of the
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output rod of the actuator. Then, while applying a sine wave signal of 1570 Hz as a drive signal
to the giant magnetostrictive actuator, the distortion factor at each point on the diaphragm was
determined. The measurement results are shown in FIG.
[0032]
FIG. 6 is a graph showing the measurement results, in which the horizontal axis represents the
distance (mm) in the Y direction, and the vertical axis represents the strain rate (%).
[0033]
As shown in FIG. 6, it was found that in the case of X = 37.5 mm and 57.5 mm, the distortion
factor on the diaphragm 11 was 0.2% or less over the entire Y-axis direction.
On the other hand, in the case of X = 0 mm, it was found that there are two peaks with a strain
rate of 0.3% or more on both sides of the contact point P (Y = 240 mm) of the output rod. In
particular, in the present embodiment, the first peak occurs at the point of Y = 200 mm, and the
second peak occurs at the point of Y = 320 mm. This is, as shown in FIG. 1, on the center line (YY line) extending in the longitudinal direction of the diaphragm 11, and on the upper end side
and the lower end side of the contact point P of the output rod 14, respectively. It means that S1
and S2 are generated. The positions of the strain points S1 and S2 are generated at positions
different from the nodes of the diaphragm 11 generated when the diaphragm 11 is vibrated.
[0034]
A second embodiment will now be described. In Example 2, the relationship between the length
of the auxiliary plate 12 and the distortion factor (THD) was measured. In this measurement,
first, a diaphragm 11 having the same dimensions (135 mm × 480 mm × 10 mm) as in
Example 1 was prepared, and various auxiliary plates 12 having different lengths L2 were
adhesively fixed to the diaphragm 11. In particular, in the present embodiment, the length L2 of
the auxiliary plate 12 is variable, and the width W2 = 30 mm and the thickness T2 = 10 mm.
Then, vibration due to the giant magnetostrictive actuator to which a 1570 Hz sine wave signal
was applied was applied to the diaphragm 11 provided with such an auxiliary plate 12, and the
maximum value of the distortion factor on the Y axis obtained at this time was determined. . The
measurement results are shown in FIG.
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[0035]
FIG. 7 is a graph showing the measurement results, where the abscissa represents the ratio (L2 /
L1) of the length L1 of the diaphragm to the length L2 of the auxiliary plate, and the ordinate
represents the maximum value (%) of the distortion factor. Each is shown.
[0036]
As shown in FIG. 7, it was found that the maximum value of the distortion factor is 10% or less
when L2 / L1 is 38% or more, and 5% or less when 48 to 68%.
It was found that if L2 / L1> 38%, a good quality sound without distortion could be reproduced,
since a distortion of 10% or less would result in a distorted sound that would not be perceived by
ordinary people. . Furthermore, if the distortion ratio is 5% or less, distortion sounds that can not
be perceived even by a person with very high hearing ability, so if L2 / L1 is 48 to 68%, good
quality without distortion It turned out that you can play a good sound.
[0037]
A third embodiment will now be described. In Example 3, the relationship between the width W2
of the auxiliary plate 12 and the distortion factor (THD) was measured. In this measurement, a
diaphragm 11 having the same dimensions (L1 = 480 mm, W1 = 135 mm, T1 = 10 mm) as in
Example 1 was prepared, and various auxiliary plates 12 having different widths W2 were
adhesively fixed to the diaphragm 11. . At this time, the length L2 of the auxiliary plate 12 was
250 mm, and the thickness T2 was 10 mm. Then, vibration due to the giant magnetostrictive
actuator to which a 1570 Hz sine wave signal was applied was applied to the diaphragm 11
provided with such an auxiliary plate 12, and the maximum value of the distortion factor on the
Y axis obtained at this time was determined. . The measurement results are shown in FIG.
[0038]
FIG. 8 is a graph showing the measurement results, where the abscissa represents the ratio (W2 /
W1) between the width W1 of the diaphragm and the width W2 of the auxiliary plate, and the
ordinate represents the maximum value (%) of the distortion factor. ing.
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[0039]
As shown in FIG. 8, it was found that the maximum value of the distortion factor was 10% or less
regardless of the value of W2 / W1.
If the distortion factor is 10% or less, it becomes a distorted sound that can not be perceived by
ordinary people, and it has been found that good sound with little distortion can be reproduced
over the entire range of W2 / W1. That is, it has been found that the width W2 of the auxiliary
plate 12 does not significantly affect the distortion generated on the diaphragm 11, and it may
be set to any value as long as W2 <W1.
[0040]
FIG. 1 is a schematic perspective view showing the configuration of an acoustic speaker
according to a first embodiment of the present invention. FIG. 2 is a schematic sectional view
taken along the line Y-Y of FIG. FIG. 3 is a schematic cross-sectional view showing the
configuration of the giant magnetostrictive actuator 13. As shown in FIG. FIG. 4 is a schematic
cross-sectional view showing the configuration of an acoustic speaker according to a second
embodiment of the present invention. FIG. 4 is a schematic view for explaining measurement of
strain distribution on the diaphragm. FIG. 6 is a graph showing the measurement results
according to Example 1. The horizontal axis represents distance in the Y direction (mm), and the
vertical axis represents strain rate (%). FIG. 7 is a graph showing the measurement results
according to Example 2. The abscissa represents the ratio (L2 / L1) between the length L1 of the
diaphragm and the length L2 of the auxiliary plate, and the ordinate represents the maximum
value of the distortion factor. (%) Is shown respectively. FIG. 8 is a graph showing the
measurement results according to Example 3. The horizontal axis represents the ratio (W2 / W1)
of the width W1 of the diaphragm to the width W2 of the auxiliary plate, and the vertical axis
represents the maximum value of distortion factor (%) ) Are shown respectively.
Explanation of sign
[0041]
DESCRIPTION OF SYMBOLS 10 Acoustic speaker 11 Diaphragm 11a One main surface 11b of
the diaphragm 11b The other main surface 11p of the diaphragm 11 Fixing point of the
diaphragm 11q Fixing point of diaphragm 11r Fixing point of diaphragm 12 Auxiliary plate 12d
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Recess 13 Super magnetostrictive actuator 14 Output rod 14a Flange portion 14 Diaphragm 21
Housing 21a Back cover 21b Screw 22 super magnetostrictive shaft 23 coil 24 bobbin 25 bias
magnet 26 elastic member 30 acoustic speaker P contact point of output rod S1 strain point S2
strain point
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