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JP2014039093

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DESCRIPTION JP2014039093
Abstract: PROBLEM TO BE SOLVED: To reduce variation in sound pressure in frequency
characteristics of sound pressure. SOLUTION: A sound generator comprises a film 3, a frame
member 5a provided on the outer peripheral portion of the film 3, a piezoelectric element 1
provided on the film 3 in the frame of the frame member 5, and the piezoelectric element 1 and
the resin layer 20 filled in the frame of the frame member 5, and the L / W ratio of the length L
and the width W of the region formed inside the frame member 5a is 1.4 The frame member 5a
is formed so as to be -2.33. [Selected figure] Figure 1A
Acoustic generator, acoustic generator and electronic device
[0001]
The present invention relates to a sound generator, a sound generator and an electronic device.
[0002]
Conventionally, an acoustic generator represented by a piezoelectric speaker is known as a smallsized, low-current-driven acoustic device using a piezoelectric body as an electroacoustic
transducer, and, for example, a small electronic device such as a mobile computing device It is
used as a built-in sound generator.
[0003]
In general, an acoustic generator using a piezoelectric body as an electroacoustic conversion
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element has a structure in which a piezoelectric element in which an electrode made of a silver
thin film or the like is formed is attached to a metal diaphragm.
The sound generation mechanism of an acoustic generator using a piezoelectric body as an
electroacoustic transducer generates a shape distortion in the piezoelectric element by applying
an alternating voltage to both surfaces of the piezoelectric element, and causes the shape
distortion of the piezoelectric element to be a metal diaphragm The sound is generated by
transmitting it to and vibrating it.
[0004]
However, since an acoustic generator having a structure in which a piezoelectric element is
attached to a metal diaphragm is such that area bending vibration is generated by restraining a
piezoelectric element that spreads and vibrates with a metal plate whose area does not change. It
has been difficult to provide sound pressure characteristics with low conversion efficiency, small
size, and low resonance frequency.
[0005]
With respect to such a problem, the present applicant has proposed a sound generating device in
which a resin film is applied as a diaphragm instead of a metal diaphragm (see, for example,
Patent Document 1).
[0006]
In this sound generator, a bimorph-type laminated piezoelectric element is sandwiched between a
pair of resin films in the thickness direction, and the resin film is fixed to a frame member in a
tensioned state.
Thereby, the sound conversion efficiency is improved, and high sound pressure can be generated.
[0007]
JP, 2010-177867, A
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[0008]
However, the above-mentioned sound generator is required to improve the variation in sound
pressure in the frequency characteristic of sound pressure.
[0009]
This invention is made in view of the above, Comprising: It aims at providing the sound generator
which can reduce the dispersion ¦ variation in the sound pressure in the frequency characteristic
of sound pressure, a sound generator, and an electronic device.
[0010]
The sound generator according to the present invention comprises a film, a frame member
provided on an outer peripheral portion of the film, a piezoelectric element provided on the film
in the frame of the frame member, and the piezoelectric element embedded therein. The frame
member is formed so that the ratio of the length and the width of the region formed inside the
frame member is 1.4 to 2.33. Be done.
[0011]
According to one aspect of the sound generator according to the present invention, it is possible
to reduce the variation in sound pressure in the frequency characteristic of sound pressure.
[0012]
FIG. 1A is a plan view showing a first embodiment of a sound generator.
FIG. 1B is a cross-sectional view showing a first embodiment of a sound generator.
FIG. 2 is a plan view showing a sound generator of a second embodiment.
FIG. 3 is a plan view showing a third embodiment of the sound generator.
FIG. 4 is a graph showing an example of sound pressure frequency characteristics.
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FIG. 5 is a graph showing an example of the frequency characteristic of sound pressure.
FIG. 6 is a graph showing an example of frequency characteristics of sound pressure.
FIG. 7 is a graph showing an example of the frequency characteristic of sound pressure. FIG. 8 is
a graph showing an example of the frequency characteristic of sound pressure. FIG. 9 is a graph
showing an example of the frequency characteristic of sound pressure. FIG. 10 is a graph
showing an example of the frequency characteristic of sound pressure. FIG. 11 is a graph
showing an example of sound pressure frequency characteristics.
[0013]
Hereinafter, embodiments of a sound generator, a sound generator and an electronic device
according to the present invention will be described in detail based on the drawings. Note that
this embodiment does not limit the present invention. And each form illustrated below as an
embodiment can be combined suitably in the range which does not contradict the shape and size
of each member which constitute a sound generator.
[0014]
(1) First Embodiment [Configuration of Sound Generator] First, a first embodiment of a sound
generator will be described based on FIGS. 1A and 1B. FIG. 1A is a plan view showing the sound
generator of the first embodiment, and FIG. 1B is a cross-sectional view showing the sound
generator of the first embodiment. Note that FIG. 1B illustrates a cross-sectional view along the
line AA shown in FIG. 1A. Moreover, in FIG. 1B, in order to facilitate understanding, the thickness
direction (y direction) of the laminated piezoelectric element 1 is shown enlarged.
[0015]
The sound generator of the first embodiment shown in FIGS. 1A and 1B includes a laminated
piezoelectric element 1 on the upper surface of a film 3 serving as a support plate sandwiched by
a pair of frame-like frame members 5. ing. That is, as shown in FIG. 1B, the sound generator of
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the first embodiment holds the film 3 between the first and second frame members 5a and 5b in
a tensioned state, so that the film 3 becomes the first and the second. It is fixed to the second
frame members 5 a and 5 b, and the laminated piezoelectric element 1 is disposed on the upper
surface of the film 3.
[0016]
Among these, the piezoelectric element 1 is formed in a plate shape and the upper and lower
main surfaces are formed in a rectangular shape. The piezoelectric element 1 includes a laminate
13 formed by alternately laminating four piezoelectric layers 7 made of ceramic and three
internal electrode layers 9, and surface electrodes formed on both upper and lower surfaces of
the laminate 13. Layers 15 a and 15 b and a pair of external electrodes 17 and 19 provided at
both ends in the longitudinal direction x of the laminate 13 are included.
[0017]
The external electrode 17 is connected to the surface electrode layers 15a and 15b and the one
internal electrode layer 9b. In addition, the external electrode 19 is connected to the two internal
electrode layers 9a and 9c. The piezoelectric layer 7 is polarized as shown by the arrow in FIG.
1B, and when the piezoelectric layers 7a and 7b contract, the piezoelectric layers 7c and 7d
extend or the piezoelectric layers 7a and 7b extend. In this case, a voltage is applied to the
external electrodes 17 and 19 so that the piezoelectric layers 7c and 7d contract.
[0018]
The upper and lower end portions of the external electrode 19 are extended to the upper and
lower surfaces of the laminated body 13 to form folded external electrodes 19 a, and these
folded external electrodes 19 a are surface electrodes formed on the surface of the laminated
body 13. A predetermined distance is extended between the surface electrode layers 15a and
15b so as not to contact the layers 15a and 15b.
[0019]
The four layers of the piezoelectric layer 7 and the three layers of the internal electrode layer 9
are simultaneously fired in the laminated state, and the surface electrode layers 15 a and 15 b
are formed of the laminated body 13. After that, it is formed by applying and baking a paste.
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[0020]
In the piezoelectric element 1, the main surface on the film 3 side and the film 3 are bonded by
the adhesive layer 21.
The thickness of the adhesive layer 21 between the piezoelectric element 1 and the film 3 is set
to 20 μm or less.
In particular, the thickness of the adhesive layer 21 is desirably other than 10 μm. As described
above, when the thickness of the adhesive layer 21 is 20 μm or less, the vibration of the
laminate 13 is easily transmitted to the film 3.
[0021]
As an adhesive for forming the adhesive layer 21, known materials such as epoxy resin, silicon
resin, polyester resin and the like can be used. As a method of curing the resin used for the
adhesive, the vibrator can be produced by any method such as heat curing, light curing,
anaerobic curing and the like.
[0022]
Furthermore, in the sound generator of the first embodiment, the resin is filled inside the frame
member 5 a so that the piezoelectric element 1 is embedded, and the resin layer 20 is formed. In
FIG. 1A, illustration of the resin layer is omitted to facilitate understanding.
[0023]
For example, an epoxy resin, an acrylic resin, a silicon resin, or a rubber can be employed as the
resin layer 20. Moreover, it is preferable that the resin layer 20 be apply ¦ coated in the state
which covers the piezoelectric element 1 completely from a viewpoint of suppressing a spurious.
Furthermore, since the film 3 serving as the support plate also vibrates integrally with the
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piezoelectric element 1, the region of the film 3 not covered by the piezoelectric element 1 is also
covered with the resin layer 20.
[0024]
As described above, in the acoustic generator of the first embodiment, by embedding the
piezoelectric element 1 with the resin layer 20, it is possible to induce an appropriate damping
effect with respect to the peak dip accompanying the resonance phenomenon of the piezoelectric
element 1. By such a damping effect, it is possible to suppress the resonance phenomenon and to
suppress the peak dip small. As a result, it is possible to reduce the frequency dependency of the
sound pressure.
[0025]
As the piezoelectric layer 7, existing piezoelectric ceramics such as lead-free piezoelectric
materials such as lead zirconate (PZ), lead zirconate titanate (PZT), Bi layer compounds, tungsten
bronze structure compounds, etc. can be used. . The thickness of the piezoelectric layer 7 is 10 to
100 μm from the viewpoint of low voltage driving.
[0026]
It is desirable that the internal electrode layer 9 include a metal component composed of silver
and palladium and a material component constituting the piezoelectric layer 7. By causing the
internal electrode layer 9 to contain the ceramic component that constitutes the piezoelectric
layer 7, it is possible to reduce the stress due to the thermal expansion difference between the
piezoelectric layer 7 and the internal electrode layer 9, and obtain the piezoelectric element 1
free from stacking faults. Can. The internal electrode layer 9 is not particularly limited to the
metal component consisting of silver and palladium, and may be another metal component, and
is limited to the material component constituting the piezoelectric layer 7 as a ceramic
component. Other ceramic components may be used.
[0027]
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It is desirable that the surface electrode layers 15a and 15b and the external electrodes 17 and
19 contain a glass component in the metal component made of silver. As described above, by
containing the glass component, a strong adhesion can be obtained between the piezoelectric
layer 7 or the internal electrode layer 9 and the surface electrode layer 15 or the external
electrodes 17 and 19.
[0028]
As shown in FIG. 1B, the frame member 5 has a rectangular shape, and is configured by bonding
two rectangular frame-shaped frame members 5a and 5b, and a film 3 is formed between the
frame members 5a and 5b. The outer peripheral part of is sandwiched and fixed in a state where
tension is applied. The frame members 5a and 5b are made of, for example, stainless steel having
a thickness of 100 to 1000 μm. The material of the frame members 5a and 5b is not limited to
stainless steel, and may be any material that is less deformable than the resin layer 20. For
example, hard resin, plastic, engineering plastic, ceramics, etc. can be used. In the embodiment,
the material, thickness and the like of the frame members 5a and 5b are not particularly limited.
Furthermore, the frame shape is not limited to a rectangular shape, and a part of the inner
peripheral portion or the outer peripheral portion may be curved or rectangular.
[0029]
The film 3 is fixed to the frame members 5a and 5b in a state in which the film 3 is tensioned in
the surface direction by sandwiching the outer peripheral part of the film 3 between the frame
members 5a and 5b, and the film 3 serves as a diaphragm Plays. The thickness of the film 3 is,
for example, 10 to 200 μm, and the film 3 is made of, for example, a resin such as polyethylene,
polyimide, polypropylene, polystyrene, polystyrene or the like, or paper made of pulp, fibers or
the like. Peak dip can be suppressed by using these materials.
[0030]
[L / W Ratio] Subsequently, the ratio of the length L and the width W of the region formed inside
the frame member 5a of the sound generator of the first embodiment of the present embodiment
will be described. In the present embodiment, a rectangular shape is exemplified as an example
of the shape of the inner peripheral portion when the frame member 5a is viewed from the
stacking direction, but the shape of the inner peripheral portion is a polygon other than
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rectangular or one of the inner peripheral portions. It is also possible to curve the part.
[0031]
Here, in the sound generator of the first embodiment, as shown in FIG. 1A, the ratio of the length
L and the width W of the rectangular region formed inside the frame member 5a is 1.4 to 2.33.
The inner peripheral portion of the frame member 5a is formed to be as follows. Hereinafter, the
ratio obtained by dividing the length L of the region formed on the inner peripheral portion of
the frame member 5 a by the width W may be referred to as L / W ratio .
[0032]
As described above, when the L / W ratio is set to 1.4 to 2.33, compared to the case where the L
/ W ratio is smaller than 1.4 or the case where the L / W ratio is larger than 2.33. Also, with
respect to the peak dip associated with the resonance phenomenon of the piezoelectric element
1, a large damping effect can be induced. Although the details will be described later with
reference to FIGS. 4 to 9, in particular, when the L / W ratio is about 1.8, a more remarkable
damping effect can be obtained. Due to the damping effect, in the sound generator of the first
embodiment, it is possible to suppress the resonance phenomenon and to suppress the peak dip
small.
[0033]
Therefore, according to the sound generator of the first aspect, the variation in sound pressure in
the frequency characteristic of sound pressure can be reduced.
[0034]
[Manufacturing method] The manufacturing method of the sound generator of the present
invention will be described.
[0035]
First, a bimorph-type piezoelectric element 1 is prepared.
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The piezoelectric element 1 mixes the powder of the piezoelectric material with a binder, a
dispersant, a plasticizer, and a solvent to prepare a slurry.
As a piezoelectric material, any of lead-based and non-lead-based can be used.
[0036]
Next, the above slurry is formed into a sheet to obtain a green sheet, and an internal electrode
paste is printed on the green sheet to form an internal electrode pattern, and the green sheet on
which the electrode pattern is formed is Only one green sheet is laminated on the uppermost
layer and a laminated molded body is manufactured.
[0037]
Next, the laminate molded body is degreased and fired, and cut into a predetermined size,
whereby the laminate 13 can be obtained.
The laminate 13 is processed at its outer peripheral portion as necessary, and the paste of the
surface electrode layers 15 a and 15 b is printed on the main surface of the laminate 13 in the
laminate direction of the laminate 13. By printing the external electrodes 17 and 19 on both end
faces of x and baking the electrodes at a predetermined temperature, it is possible to obtain the
bimorph-type piezoelectric element 1 shown in FIGS. 1A and 1B.
[0038]
Next, in order to impart piezoelectricity to the bimorph piezoelectric element 1, a direct current
voltage is applied through the surface electrode layers 15 a and 15 b or the external electrodes
17 and 19 to form the piezoelectric layer 7 of the bimorph piezoelectric element 1. Do the
polarization. This polarization is performed by applying a DC voltage so as to be in the direction
indicated by the arrow in FIG. 1B.
[0039]
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Next, a film 3 to be a support is prepared, and the outer peripheral portion of the film 3 is
sandwiched between the frame members 5a and 5b, and the film 3 is fixed in a tensioned state.
After that, an adhesive is applied to the film 3, the surface electrode 15a side of the bimorph
piezoelectric element 1 is pressed against the film 3, and then the adhesive is cured by
irradiating heat or ultraviolet light. Then, a resin is poured inside the frame member 5a, the
bimorph-type piezoelectric element 1 is completely embedded, and the resin layer 20 is cured,
whereby the acoustic generator of the first embodiment can be obtained.
[0040]
The sound generator configured as described above has an inner peripheral portion of the frame
member 5a such that the ratio of the length L and the width W of the region formed inside the
frame member 5a is 1.4 to 2.33. Is formed. For this reason, the damping which is larger for the
peak dip due to the resonance phenomenon of the piezoelectric element 1 than for an acoustic
generator having an L / W ratio smaller than 1.4 or an acoustic generator having an L / W ratio
larger than 2.33. It can trigger an effect. As a result of the damping effect, the resonance
phenomenon can be suppressed and the peak dip can be suppressed to be small. As a result, the
variation of the sound pressure in the frequency characteristic of the sound pressure can be
reduced.
[0041]
(2) Second Embodiment Subsequently, a sound generator according to a second embodiment of
the present embodiment will be described. FIG. 2 is a plan view showing a sound generator of a
second embodiment. The sound generator of the second embodiment shown in FIG. 2 is longer
than the boundary between the film 3 formed on the inner periphery of the frame member 5a
and the sound generator of the first embodiment shown in FIG. 1A. The difference is that the
boundary of the direction is formed by a curve of a predetermined curvature. For example, as
shown in FIG. 2, it is formed by a curve curving in a concave shape inside the frame member 5a.
[0042]
Here, the boundary in the longitudinal direction is formed as a curve because the asymmetry can
be increased as compared with the case where the inner peripheral portion of the frame member
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5a is rectangular. That is, according to the shape of FIG. 2, it is possible to suppress the
degeneracy of the resonance frequency and disperse it, thereby suppressing the height of the
resonance peak and widening the width. By increasing the asymmetry in this manner, the
resonance phenomenon can be suppressed and the peak dip can be suppressed smaller than in
the case where only the L / W ratio is set to the optimum range of 1.4 to 2.33. For this reason,
according to the sound generator of the second embodiment, it is possible to more effectively
reduce the variation in sound pressure in the frequency characteristic of sound pressure.
[0043]
Furthermore, as shown in FIG. 2, the boundary line in the longitudinal direction is curved such
that the distance between the inner edge and the outer edge of the frame member 5a is closer as
the corner portion of the frame member 5a is approached to the central portion. As described
above, the boundary line in the length direction of the inner peripheral portion of the frame
member 5a is a curve that curves toward the outer peripheral portion even if the area of the film
3 vibrating integrally with the piezoelectric element 1 changes. This is to maintain the width of
the frequency range in which the sound pressure is obtained by the bending deflection vibration
of the film 3, that is, the so-called reproduction frequency band, in the same bandwidth as the
case where the inner peripheral portion of the frame member 5a is rectangular.
[0044]
As the L / W ratio, 1.4 to 2.33 is employed as in the first embodiment. Here, the length L and the
width W represent the longest distance among the distance in the length direction or the
distance in the width direction. In the example of FIG. 2, the distance between lines in the width
direction is used as the value of the length L, and the distance between the central portions of the
curve is used as the value of the width W.
[0045]
(3) Third Embodiment Next, a sound generator according to a third embodiment of the present
embodiment will be described. FIG. 3 is a plan view showing a third embodiment of the sound
generator. The sound generator of the third embodiment shown in FIG. 3 has a load on the film 3
by pressing the film 3 to a predetermined position on the surface of the resin layer 20 as
compared with the sound generator of the first embodiment shown in FIG. The difference is that
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the load member 30 to be applied is further adhered. As the L / W ratio, 1.4 to 2.33 is employed
as in the first embodiment.
[0046]
It is desirable that the load member 30 have physical properties that are soft and easily
deformable, and, for example, a rubber material such as urethane rubber can be employed. In
particular, porous rubber materials such as urethane foam can be suitably used.
[0047]
Here, the load member 30 is attached to the surface of the resin layer 20 at a position where the
amplitude is maximized by the resonance phenomenon caused by the vibrating member
including the film 3 and the resin layer 20 vibrating integrally with the piezoelectric element 1. Is
preferred. For example, since the central portion of the film 3 has the largest amplitude in a
plurality of frequency bands included in the frequency region in which a predetermined sound
pressure can be obtained by the vibration of the vibrator, the load member 30a is , 30b is
attached.
[0048]
As described above, by attaching the load members 30a and 30b to the position including the
central portion of the film 3, the third sound generation is more than in the case where only the L
/ W ratio is in the optimum range of 1.4 to 2.33. It is possible to reduce abrupt changes in
amplitude in a plurality of frequency bands included in the reproduction frequency band of the
device and to flatten the amplitude in each frequency band. For this reason, according to the
sound generator of the third aspect, it is possible to more effectively reduce the variation in
sound pressure in the frequency characteristic of sound pressure. Here, the case where the load
member 30 is provided at a position where the amplitude is maximum in a plurality of frequency
bands included in the reproduction frequency band of the third sound generator has been
illustrated, but the amplitude is maximum in at least one frequency band. The amplitude of the
frequency band can also be flattened by mounting the load member 30 at the position where
[0049]
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Furthermore, the load members 30 a and 30 b are formed of a vibrating body that vibrates
integrally with the piezoelectric element 1, that is, a material that is softer and easier to deform
than the film 3 and the resin layer 20. The term "soft and easily deformed" as used herein means
that the film is smaller in elasticity and rigidity than the film 3 and the resin layer 20, and is
easily deformed by an external force. As described above, a vibrator including the piezoelectric
element 1, the film 3, the resin layer 20 and the like in a portion where the load member 30 is
attached by forming the load members 30 a and 30 b by a material softer and easier to deform
than the vibrator. It is possible to reduce the inhibition of the deformation of the vibrator and to
deform the vibrator smoothly. This can reduce distortion of the sound generated by the vibration
of the vibrating body.
[0050]
(4) Fourth Embodiment The embodiments of the present invention have been described above.
However, the present invention may be implemented in various different embodiments other
than the above-described embodiments. Therefore, other embodiments included in the present
invention will be described below.
[0051]
[Scope of Application] For example, in the first embodiment described above, the bimorph-type
piezoelectric element is illustrated, but the present invention is not limited to this. That is, the
present invention is not limited to the case where the piezoelectric element is a bimorph type,
and even if it is a unimorph type, the same effect can be obtained by adopting the same L / W
ratio as the above first embodiment. .
[0052]
[Speaker Device] For example, the sound generator described in the first to third embodiments
described above is a sound generator, so-called speaker device , by being housed in a housing
for housing the sound generator, a so-called resonance box. It can also be configured as For
example, if it can be configured as a large-sized speaker device used for a television, a personal
computer, etc., medium-sized or small-sized mounted on mobile terminals such as smartphones,
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mobile phones, PHS (Personal Handyphone System), PDA (Personal Digital Assistants), etc. It can
also be configured as a speaker device of In addition, a speaker apparatus is not limited to said
application, It can comprise as a speaker apparatus mounted in arbitrary electronic devices, such
as a vacuum cleaner, a washing machine, and a refrigerator.
[0053]
[Electronic Device] Further, the sound generator described in the first to third modes described
above includes at least an electronic circuit connected to the sound generator, and a housing for
housing the electronic circuit and the sound generator. It can also be configured as an electronic
device having a function of generating sound from the sound generator. Examples of such
electronic devices include televisions, personal computers, and various mobile terminals.
[0054]
Now, in the present embodiment, in order to clarify that the optimum range of the L / W ratio is
1.4 to 2.33, the frequency characteristics of sound pressure when various L / W ratios are
adopted will be described. Do. 4-9 is a graph which shows an example of the frequency
characteristic of sound pressure. The graph of the frequency characteristic of the sound pressure
regarding the sound generator with the load member 30 which all showed in these FIGS. 4-9 is
shown by FIG.
[0055]
The graph of FIG. 4 refers to that of an acoustic generator with an L / W ratio of 1.33 , and
the graph of FIG. 5 refers to that of an acoustic generator with an L / W ratio of 1.4 . In the
graph of FIG. 6, the graph of FIG. 6 refers to the one of the sound generator whose L / W ratio is
1.83 , and the graph of FIG. 7 shows that of the sound generator whose L / W ratio is
2.00 . The graph of FIG. 8 refers to the one of the sound generator having an L / W ratio of
2.33 , and the graph of FIG. 9 has an L / W ratio of 2.5 . It refers to that of the sound
generator. The horizontal axes of the graphs shown in FIG. 4 to FIG. 9 indicate the frequency
[kHz], and the vertical axes of the graph indicate the sound pressure [dB].
[0056]
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Among the six graphs shown in FIGS. 4 to 9 described above, the graphs of FIGS. 4 and 9 in
which the L / W ratio of the sound generator is not in the optimum range of 1.4 to 2.33 are L /
W ratios of the sound generator. The variation in sound pressure is large as compared with the
graphs of FIGS. 5 to 8 in which the W ratio is included in the optimum range of 1.4 to 2.33.
[0057]
To explain this specifically, as shown in FIG. 4, when the L / W ratio of the sound generator is
1.33, a peak dip which reaches 30.6 dB at maximum occurs.
In the example shown in FIG. 4, it can be seen that a peak dip exceeding 25 dB occurs in the
frequency band 41 before 1 kHz and the frequency band 42 from 2 kHz to 4 kHz. Furthermore,
in the example shown in FIG. 4, in the frequency band 43 of 7 kHz to 10 kHz, the sound pressure
is reduced to around 80 dB. Further, as shown in FIG. 9, when the L / W ratio of the sound
generator is 2.5, a peak dip reaching 31.2 dB occurs at the maximum. In the example shown in
FIG. 9, it can be seen that a peak dip of about 30 dB is generated in the frequency band 91 of 1
kHz before and the frequency band 92 of 2 kHz to 4 kHz. As shown in FIGS. 4 and 9, when the L
/ W ratio of the sound generator is not in the optimum range of 1.4 to 2.33, peak dips exceeding
25 dB occur in a plurality of frequency bands. The resonance frequency due to the resonance
phenomenon becomes peaky, and the flatness of the frequency characteristic is also deteriorated.
[0058]
On the other hand, as shown in FIG. 5, when the L / W ratio of the sound generator is 1.4, only a
peak dip of up to 16 dB occurs. In the example shown in FIG. 5, compared to the examples shown
in FIGS. 4 and 9, it can be seen that the peak dip in the frequency band 51 before 1 kHz and the
frequency band 52 between 2 kHz and 4 kHz is improved to about 15 dB. Furthermore, it can be
seen that in the example shown in FIG. 5, a sound pressure of around 95 dB is obtained in the
frequency band 53 of 7 kHz to 10 kHz as compared with the examples shown in FIG. 4 and FIG.
Further, as shown in FIG. 7, even when the L / W ratio of the sound generator is 2.00, only a
peak dip of up to 17.6 dB occurs. In the example shown in FIG. 7, compared to the examples
shown in FIG. 4 and FIG. 9, it can be seen that the peak dip in the frequency band 71 before 1
kHz and in the frequency band 72 between 2 kHz and 4 kHz is improved to about 15 dB.
Furthermore, it can be seen that in the example shown in FIG. 7, a sound pressure of around 95
dB is obtained in the frequency band 73 of 7 kHz to 10 kHz as compared with the examples
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shown in FIG. 4 and FIG. Furthermore, as shown in FIG. 8, even when the L / W ratio of the sound
generator is 2.33, only a peak dip of up to 20.2 dB occurs. In the example shown in FIG. 8, it can
be understood that the peak dip in the frequency band 81 before 1 kHz and the frequency band
82 in 2 kHz to 4 kHz is improved to about 20 dB as compared with the examples shown in FIG. 4
and FIG. Furthermore, it can be seen that in the example shown in FIG. 8, a sound pressure of
around 95 dB is obtained in the frequency band 83 of 7 kHz to 10 kHz as compared with the
examples shown in FIG. 4 and FIG.
[0059]
In addition, as shown in FIG. 6, when the L / W ratio of the sound generator is 1.83, the peak dip
can be suppressed to at most 4.6 dB. In the example shown in FIG. 6, not only the example shown
in FIG. 4 and FIG. 9, but also the frequency band 61 before 1 kHz and the frequency band of 2
kHz to 4 kHz as compared with the examples shown in FIG. It can be seen that the peak dip at 62
is dramatically improved to about 5 dB. Furthermore, it can be seen that in the example shown in
FIG. 6, a sound pressure of around 95 dB is obtained in the frequency band 63 of 7 kHz to 10
kHz as compared with the examples shown in FIG. 4 and FIG.
[0060]
As described above, in the sound generator having the L / W ratio of 1.4 to 2.33 shown in FIGS.
5 to 8, the sound generation having the L / W ratio of less than 1.4 shown in FIG. 4 is generated.
The flatness of the frequency characteristic is improved by the suppression of the resonance
phenomenon and the peak dip can be reduced and the frequency of the sound pressure is
reduced, as compared with the sound generator having the L / W ratio greater than 2.33 shown
in FIG. It can be said that the variation in sound pressure in the characteristics can be reduced.
[0061]
Although the embodiment has been described in the case where the load member 30 is provided
in the sound generator, the L / W ratio is 1.4 to 2.33 even when the load member 30 is not
provided. Of the sound pressure in the frequency characteristic of the sound pressure, as
compared with the sound generator having the L / W ratio smaller than 1.4 and the sound
generator having the L / W ratio larger than 2.33. It goes without saying that it is possible to
reduce the
[0062]
By the way, although said Example 1 demonstrated the Example of the sound generator in which
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the load member 30 was provided, in a present Example, the boundary line with the film 3
formed in the inner peripheral part of the frame member 5a The difference in the frequency
characteristics of the sound pressure between the sound generator in which the boundary in the
length direction is formed by a curve having a predetermined curvature and the sound generator
in which the inner peripheral portion of the frame member 5a is rectangular will be described.
[0063]
FIG.10 and FIG.11 is a graph which shows an example of the frequency characteristic of sound
pressure.
In FIG. 10, the frequency characteristic of the sound pressure related to the sound generator in
which the inner peripheral portion of the frame member 5a is rectangular is shown, while in FIG.
11, the boundary line in the length direction is formed by a curve. The frequency characteristics
of the sound pressure for the sound generator are shown.
In FIGS. 10 and 11, the frequency of the sound pressure measured by the sound generator
having the frame member 5a having the L / W ratio 2.0 of the length L 60 mm and the
width W 30 mm The characteristics are shown.
The horizontal axis of the graph indicates frequency [kHz], and the vertical axis of the graph
indicates sound pressure [dB].
[0064]
As shown in FIG. 10, in the case of an acoustic generator in which the inner peripheral portion of
the frame member 5a is rectangular, a peak dip exceeding 20 dB occurs in a frequency band 101
before 1 kHz and a frequency band 102 of 2 kHz to 4 kHz. It can also be seen that a peak dip of
about 15 dB occurs at Furthermore, in the example shown in FIG. 10, in the frequency band of 7
kHz to 10 kHz, the sound pressure is reduced to about 90 dB. On the other hand, as shown in
FIG. 11, in the case of an acoustic generator in which the boundary in the length direction is
formed by a curve, the peak dip in the frequency band 111 of 1 kHz before and the frequency
band 112 of 2 kHz to 4 kHz is about 5 dB. It turns out that it has improved dramatically.
Furthermore, in the example shown in FIG. 11, it can be seen that a sound pressure of about 95
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dB is obtained even in the frequency band of 7 kHz to 10 kHz.
[0065]
As described above, the sound generator in which the boundary in the length direction shown in
FIG. 11 is formed by a curve has a resonance compared to the sound generator in which the
inner peripheral portion of the frame member 5a shown in FIG. By suppressing the phenomenon,
it is possible to improve the flatness of the frequency characteristic and to suppress the peak dip
small, and it is possible to reduce the variation in sound pressure in the frequency characteristic
of sound pressure.
[0066]
DESCRIPTION OF SYMBOLS 1 Piezoelectric element 3 Film 5, 5a, 5b Frame member 7, 7a, 7b, 7c,
7d Piezoelectric material layer 9, 9a, 9b, 9c Internal electrode layer 13 Laminated body 15a, 15b
Surface electrode layer 17, 19 External electrode 20 Resin Layer 30, 30a, 30b Load member x
Longitudinal direction of stack y Thickness direction of piezoelectric element
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