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JP2018019386

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DESCRIPTION JP2018019386
Abstract: To provide an electroacoustic transducer capable of improving acoustic characteristics.
An electro-acoustic transducer includes a housing and a piezoelectric speaker. The piezoelectric
speaker 32 has a first diaphragm 321 having a peripheral portion supported directly or
indirectly by the housing and a piezoelectric element 322 disposed on at least one surface of the
first diaphragm. The rigidity is asymmetrically configured with respect to the central axis C1 of
the first diaphragm. [Selected figure] Figure 3
Electro-acoustic transducer
[0001]
The present invention relates to an electroacoustic transducer applicable to, for example,
earphones, headphones, portable information terminals, and the like.
[0002]
The piezoelectric sounding element is widely used as a simple electroacoustic conversion means,
and is widely used as, for example, an acoustic device such as an earphone or a headphone, and
further as a speaker of a portable information terminal.
The piezoelectric sound emitting element typically has a configuration in which a piezoelectric
element is bonded to one side or both sides of a diaphragm (see, for example, Patent Document
1).
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[0003]
On the other hand, Patent Document 2 describes a headphone including a dynamic driver and a
piezoelectric driver, and by driving these two drivers in parallel, reproduction with a wide
bandwidth is possible. The piezoelectric driver is provided at the center of the inner surface of a
front cover that closes the front surface of the dynamic driver and functions as a diaphragm, and
is configured to function as the high-range driver.
[0004]
Unexamined-Japanese-Patent No. 2013-150305 Unexamined-Japanese-Patent No. 62-68400
[0005]
In recent years, further improvement in sound quality has been required for acoustic devices
such as earphones and headphones.
For this reason, in the piezoelectric sound element, it is considered essential to improve the
characteristics of the electroacoustic conversion function. In addition, high sound pressure in the
high range when combined with a dynamic type speaker is desired.
[0006]
In view of the circumstances as described above, an object of the present invention is to provide
an electroacoustic transducer capable of improving acoustic characteristics.
[0007]
In order to achieve the above object, an electroacoustic transducer according to an aspect of the
present invention comprises a housing and a piezoelectric speaker.
The piezoelectric speaker has a first diaphragm having a peripheral portion supported directly or
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indirectly by the casing, and a piezoelectric element disposed on at least one surface of the first
diaphragm. The rigidity is asymmetrically configured with respect to the central axis of the first
diaphragm.
[0008]
In the above-described electroacoustic transducer, since the piezoelectric speaker has a structure
in which the rigidity is asymmetric with respect to the central axis of the first diaphragm, the
vibration mode of the first diaphragm becomes uneven in a plane. As a result, the sound pressure
level in the high region becomes broad, and the sound pressure characteristic is improved, so
that good sound quality can be reproduced.
[0009]
The piezoelectric element may be arranged at an eccentric position with respect to the first
diaphragm. Thereby, the vibration mode of the first diaphragm can be made asymmetric with
respect to the central axis.
[0010]
The piezoelectric speaker may further include a passage portion penetrating the first diaphragm
in the thickness direction. The passage portion may include at least one opening provided in the
plane of the first diaphragm, or may include at least one notch provided in the peripheral
portion.
[0011]
The electro-acoustic transducer may further include an electromagnetic speaker that includes a
second diaphragm. In this case, the housing has a first space portion and a second space portion.
The electromagnetic speaker is disposed in the first space portion. The second space portion
communicates with the first space portion via the passage portion, and has a sound conduction
path for guiding the sound wave generated by the piezoelectric sounding body and the
electromagnetic sounding body to the outside. .
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[0012]
The passage may include a plurality of passages. In this case, the sound introducing path is
provided at a position facing the passage part having the largest opening area among the
plurality of passage parts. As a result, since the sound waves generated from the electromagnetic
speaker can be efficiently guided to the sound introducing path, the acoustic characteristics of
the electromagnetic speaker can be improved.
[0013]
The planar shapes of the first diaphragm and the piezoelectric element are not particularly
limited. Typically, the planar shape of the first diaphragm is circular, and the planar shape of the
piezoelectric element is rectangular.
[0014]
The piezoelectric speaker may further include an annular member.
The annular member is fixed to the housing and supports the peripheral portion of the first
diaphragm. As a result, the assembling workability of the piezoelectric speaker with respect to
the housing is improved, and the adjustment of the distance between the first diaphragm and the
second diaphragm is facilitated.
[0015]
The distance between the first diaphragm and the second diaphragm is not particularly limited,
and can be appropriately set according to the size of each diaphragm, the desired acoustic
characteristics, and the like. For example, the ratio of the distance between the first diaphragm
and the second diaphragm to the diameter of the second diaphragm can be set to not less than
0.152 and not more than 0.212. Thereby, the drop of the sound pressure characteristic around 8
kHz can be improved.
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[0016]
The first diaphragm may be disposed at a position eccentric to the second diaphragm. This
configuration also makes it possible to improve the acoustic characteristics.
[0017]
As described above, according to the present invention, acoustic characteristics can be improved.
[0018]
FIG. 1 is a schematic side sectional view showing an electro-acoustic transducer according to an
embodiment of the present invention.
It is a schematic sectional side view which shows the electromagnetic sounding body in the said
electroacoustic transducer. It is a schematic bottom view which shows the piezoelectric type
sounding body in the said electroacoustic transducer. It is a schematic sectional side view of the
piezoelectric element in the said piezoelectric type sounding body. It is a schematic plan view
explaining two piezoelectric sounding bodies from which composition differs. It is a simulation
result which compares and shows the frequency characteristic of two said piezoelectric sounding
bodies. It is an experimental result which shows the frequency characteristic of the said
electroacoustic transducer. It is a top view which shows one structural example of the
piezoelectric type sounding body demonstrated in the 2nd Embodiment of this invention. It is a
top view which shows the other structural example of the said piezoelectric type sounding body.
It is a top view which shows the other structural example of the said piezoelectric type sounding
body. It is a top view which shows the other structural example of the said piezoelectric type
sounding body. It is a top view which shows the modification of a structure of FIG. It is a top view
which shows the modification of a structure of FIG. It is a top view which shows the modification
of a structure of FIG. It is an experimental result which compares and shows the frequency
characteristic of the electromagnetic sounding body in the electroacoustic transducer provided
with the piezoelectric sounding body shown to FIG. 10 and FIG. It is a schematic sectional side
view which shows the structure of the electroacoustic transducer based on the 3rd Embodiment
of this invention. It is an experimental result which shows the sound pressure characteristic of
the said electroacoustic transducer. According to an experimental result showing a relationship
between a ratio of the distance (h) between the first and second diaphragms to the diameter (d)
of the second diaphragm and the sound pressure in a predetermined frequency band in the
above-mentioned electroacoustic transducer is there.
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[0019]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0020]
First Embodiment FIG. 1 is a schematic side sectional view showing a configuration of an
earphone 100 as an electro-acoustic transducer according to an embodiment of the present
invention.
In the figure, the X-axis, the Y-axis and the Z-axis indicate three axis directions orthogonal to
each other.
[0021]
[Overall Configuration of Earphone] The earphone 100 has an earphone body 10 and an earpiece
20. The earpiece 20 is attached to the sound guiding path 41 of the earphone body 10 and
configured to be attachable to the user's ear.
[0022]
The earphone body 10 has a sound generation unit 30 and a housing 40 for housing the sound
generation unit 30. The sound production unit 30 has an electromagnetic sounding body 31 and
a piezoelectric sounding body 32.
[0023]
[Case] The case 40 has an internal space that accommodates the sound generation unit 30, and is
configured by a two-split structure that can be separated in the Z-axis direction. The bottom
portion 410 of the housing 40 is provided with a sound guide path 41 for guiding the sound
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wave generated by the sound generation unit 30 to the outside.
[0024]
The housing 40 has a support portion 411 for supporting the peripheral portion of the
piezoelectric speaker 32. The support portion 411 is formed in an annular shape, and is provided
so as to protrude upward from the peripheral portion of the bottom portion 410. In the figure,
the upper surface of the support portion 411 is formed as a plane parallel to the XY plane, and
supports the peripheral portion of the piezoelectric sounding body 32 described later directly or
indirectly via another member.
[0025]
The internal space of the housing 40 is divided by the piezoelectric speaker 32 into a first space
portion S1 and a second space portion S2. An electromagnetic speaker 31 is disposed in the first
space S1. The second space portion S2 is a space portion communicating with the sound
introducing path 41, and is formed between the piezoelectric sounding body 32 and the bottom
portion 410 of the housing 40. The first space S1 and the second space S2 communicate with
each other through the openings 331 to 337 (see FIG. 3) of the piezoelectric speaker 32.
[0026]
[Electromagnetic Sounding Body] The electromagnetic sounding body 31 is configured of a
dynamic type speaker unit that functions as a woofer that reproduces a low tone range. In the
present embodiment, for example, a dynamic speaker that mainly generates a sound wave of 7
kHz or less, a mechanical unit 311 including a vibrating body such as a voice coil motor
(electromagnetic coil), and a pedestal unit 312 that vibratably supports the mechanical unit 311.
And.
[0027]
The configuration of the mechanical portion 311 of the electromagnetic speaker 31 is not
particularly limited. FIG. 2 is a cross-sectional view of an essential part showing one structural
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example of the mechanical part 311. As shown in FIG. The mechanical section 311 has a
diaphragm E1 (second diaphragm) vibratably supported by the pedestal portion 312, a
permanent magnet E2, a voice coil E3, and a yoke E4 supporting the permanent magnet E2. The
diaphragm E1 is supported by the pedestal portion 312 by the peripheral edge thereof being
sandwiched between the bottom portion of the pedestal portion 312 and the annular fixture 310
integrally assembled thereto.
[0028]
The voice coil E3 is formed by winding a conducting wire around a bobbin serving as a winding
core, and is joined to the central portion of the diaphragm E1. Also, the voice coil E3 is disposed
perpendicularly to the direction of the magnetic flux of the permanent magnet E2. When an
alternating current (voice signal) is supplied to the voice coil E3, an electromagnetic force acts on
the voice coil E3, so the voice coil E3 vibrates in the Z-axis direction in the figure in accordance
with the signal waveform. This vibration is transmitted to the diaphragm E1 connected to the
voice coil E3, and the air in the first space portion S1 (FIG. 1) is vibrated to generate a sound
wave in the low frequency range.
[0029]
The electromagnetic speaker 31 is fixed to the inside of the housing 40 by an appropriate
method. A circuit board 33 constituting an electric circuit of the sound generation unit 30 is
fixed to the upper portion of the electromagnetic sounding body 31. The circuit board 33 is
electrically connected to the cable 50 introduced through the lead portion 42 of the housing 40,
and an electrical signal is sent to the electromagnetic sounding body 31 and the piezoelectric
sounding body 32 through a wiring member (not shown). Output.
[0030]
[Piezoelectric Sounding Body] The piezoelectric sounding body 32 constitutes a speaker unit that
functions as a tweeter that reproduces a high sound range. In the present embodiment, the
oscillation frequency is set so as to mainly generate, for example, a sound wave of 7 kHz or more.
The piezoelectric speaker 32 includes a vibrating plate 321 (first vibrating plate) and a
piezoelectric element 322.
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[0031]
The diaphragm 321 is made of a conductive material such as metal (for example, 42 alloy) or an
insulating material such as a resin (for example, liquid crystal polymer), and its planar shape is
formed in a circle. The outer diameter and thickness of the diaphragm 321 are not particularly
limited, and are appropriately set according to the size of the housing 40, the frequency band of
the reproduced sound wave, and the like. In the present embodiment, a diaphragm having a
diameter of about 8 to 12 mm and a thickness of about 0.2 mm is used.
[0032]
The diaphragm 321 has a first major surface 32 a facing the sound introducing path 41 and a
second major surface 32 b facing the electromagnetic sounding body 31. In the present
embodiment, the piezoelectric speaker 32 has a unimorph structure in which the piezoelectric
element 322 is bonded only to the first major surface 32 a of the diaphragm 321. The invention
is not limited to this, and the piezoelectric element 322 may be joined to the second main surface
32 b of the diaphragm 321. In addition, the piezoelectric speaker 32 may have a bimorph
structure in which piezoelectric elements are respectively bonded to both main surfaces 32 a and
32 b of the diaphragm 321.
[0033]
The diaphragm 321 has a peripheral portion 321 c supported by the support portion 411 of the
housing 40. The peripheral portion 321 c is elastically supported by the support portion 411 via
the adhesive layer. It is preferable that the said adhesive material layer has moderate elasticity.
As a result, the diaphragm 321 is elastically supported with respect to the support portion 411,
so that vibration of resonance of the diaphragm 321 is suppressed, and stable resonance
operation of the diaphragm 321 is secured.
[0034]
In addition, the diaphragm 321 may be fixed to the support part 411 via the annular member
which supports the peripheral part 321c. The annular member is preferably made of an elastic
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material such as rubber or resin, whereby the same effects as those described above can be
obtained. Alternatively, the annular member may be made of a relatively rigid material, and may
be bonded to the support 411 through the adhesive layer.
[0035]
FIG. 3 is a plan view (or a bottom view) of the piezoelectric speaker 32. FIG. As shown in the
figure, the piezoelectric sounding body 32 is configured to be asymmetric in rigidity with respect
to the central axis C1 of the diaphragm 321 (an axis parallel to the Z-axis direction passing
through the center of the diaphragm 321).
[0036]
Here, that the rigidity is asymmetric with respect to the central axis C1 means that the structure,
shape, physical properties, etc. is asymmetric with respect to the central axis C1, and in
particular, the vibration mode becomes asymmetric with respect to the central axis C1 when the
diaphragm 321 oscillates Say the form.
[0037]
In the present embodiment, the planar shape of the piezoelectric element 322 is rectangular, and
the central axis C2 of the piezoelectric element 322 (an axis parallel to the Z axis passing the
center of the piezoelectric element 322) is greater than the central axis C1 of the diaphragm 321.
It is displaced by a predetermined amount in the X axis direction.
That is, the piezoelectric element 322 is disposed at a position eccentric to the diaphragm 321.
As a result, the vibration center of the diaphragm 321 shifts to a position different from the
central axis C1, so that the vibration mode of the piezoelectric speaker 32 is asymmetric with
respect to the central axis C1.
[0038]
Furthermore, as shown in FIG. 3, the diaphragm 321 has a shape (a form (shape) in a right half
area and a left half area bordering on a center line CL (a line parallel to the Y axis direction
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passing the center of the diaphragm 321). ) Has anisotropy. That is, the piezoelectric speaker 32
has a plurality of openings 331 to 337 (passage portions) penetrating the diaphragm 321 in the
thickness direction, and the openings 331 to 337 are formed in the following manner. , And
asymmetrically with respect to the center line CL.
[0039]
The opening 331 is formed in a semicircular or semicircular shape in a region between the
peripheral edge 321 c of the diaphragm 321 and one side of the piezoelectric element 322, and
has the largest opening area among the openings 331 to 337. . The piezoelectric speaker 32 is
assembled on the support 411 so that the opening 331 faces the inlet of the sound guide 41 (see
FIG. 1).
[0040]
The openings 332 to 335 are formed by circular holes provided in the region between the
peripheral portion 321 c and the piezoelectric element 322. Among them, the openings 332 and
333 are provided on the center line CL at symmetrical positions with respect to the central axis
C1, respectively, and the openings 334 and 335 are provided between the opening 331 and the
openings 332 and 333, respectively. Each of the openings 332 to 335 is formed by a round hole
of the same diameter (for example, about 1 mm in diameter), but of course is not limited thereto.
[0041]
On the other hand, the openings 336 and 337 are respectively provided between the openings
332 and 333 and the piezoelectric element 322, and are formed in a rectangular shape having a
long side in the X-axis direction. The openings 336 and 337 are formed along the periphery of
the piezoelectric element 322, and a part of them is partially covered on the periphery of the
piezoelectric element 322. The openings 336 and 337 also have a function to prevent a short
circuit between two external electrodes of the piezoelectric element 322 as described later, in
addition to the function as a passage passing through the front and back of the diaphragm 321.
[0042]
FIG. 4 is a schematic cross-sectional view showing the internal structure of the piezoelectric
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element 322. As shown in FIG.
[0043]
The piezoelectric element 322 has an element body 328, and first and second outer electrodes
326a and 326b opposed to each other in the Y-axis direction.
In addition, the piezoelectric element 322 has a first main surface 322a and a second main
surface 322b perpendicular to the Z-axis facing each other. The second main surface 322 b of
the piezoelectric element 322 is configured as a mounting surface facing the first main surface
32 a of the diaphragm 321.
[0044]
Element body 328 has a structure in which ceramic sheet 323 and internal electrode layers 324a
and 324b are stacked in the Z-axis direction. That is, the internal electrode layers 324a and 324b
are alternately stacked with the ceramic sheet 323 interposed therebetween. The ceramic sheet
323 is formed of, for example, a piezoelectric material such as lead zirconate titanate (PZT) or an
alkali metal-containing niobium oxide. The internal electrode layers 324a and 324b are formed
of a conductive material such as various metal materials.
[0045]
The first inner electrode layer 324a of the element body 328 is connected to the first outer
electrode 326a, and is insulated from the second outer electrode 326b by the margin portion of
the ceramic sheet 323. The second inner electrode layer 324 b of the element body 328 is
connected to the second outer electrode 326 b and insulated from the first outer electrode 326 a
by the margin portion of the ceramic sheet 323.
[0046]
In FIG. 4, the uppermost layer of the first internal electrode layer 324a constitutes a first
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extraction electrode layer 325a partially covering the surface (upper surface in FIG. 4) of the
element body 328, and the second internal electrode layer The lowermost layer of 324 b
constitutes a second extraction electrode layer 325 b partially covering the back surface (the
lower surface in FIG. 4) of the element body 328. The first lead-out electrode layer 325a has a
terminal portion 327a of one of the poles electrically connected to the circuit board 33 (FIG. 1),
and the second lead-out electrode layer 325b is through an appropriate bonding material. It is
electrically and mechanically connected to the first major surface 32 a of the diaphragm 321.
When the diaphragm 321 is made of a conductive material, a conductive bonding material such
as a conductive adhesive or solder may be used as the bonding material, and in this case, the
terminal portion of the other electrode is a diaphragm 321 can be provided.
[0047]
The first and second outer electrodes 326a and 326b are formed of conductive materials such as
various metal materials at substantially central portions of both end surfaces of the element body
328 in the Y-axis direction. The first outer electrode 326a is electrically connected to the first
inner electrode layer 324a and the first lead-out electrode layer 325a, and the second outer
electrode 326b is electrically connected to the second inner electrode layer 324b and the second
lead-out. It is electrically connected to the electrode layer 325b.
[0048]
With such a configuration, when an AC voltage is applied between the external electrodes 326a
and 326b, the ceramic sheets 323 between the internal electrode layers 324a and 324b expand
and contract at a predetermined frequency. Thus, the piezoelectric element 322 can generate a
vibration to be applied to the diaphragm 321.
[0049]
Here, as shown in FIG. 4, the first and second outer electrodes 326a and 326b respectively
project from each of the end faces of the base body 328. At this time, the first and second outer
electrodes 326a and 326b may be formed with raised portions 329a and 329b protruding
toward the first major surface 32a of the diaphragm 321. Thus, the openings 336 and 337
described above are formed to be sized to accommodate the raised portions 329a and 329b.
Thereby, the electrical short circuit between the external electrodes 326a and 326b due to the
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contact between the raised portions 329a and 329b and the diaphragm 321 is prevented.
[0050]
[Operation of Earphone] Subsequently, a typical operation of the earphone 100 of the present
embodiment configured as described above will be described.
[0051]
In the earphone 100 of the present embodiment, a reproduction signal is input to the circuit
board 33 of the sound generation unit 30 via the cable 50.
The reproduction signal is input to the electromagnetic speaker 31 and the piezoelectric speaker
32 through the circuit board 33. As a result, the electromagnetic sounding body 31 is driven to
generate a sound wave mainly in the low frequency range of 7 kHz or less. On the other hand, in
the piezoelectric sounding body 32, the diaphragm 321 vibrates by the expansion and
contraction operation of the piezoelectric element 322, and a high frequency sound wave of 7
kHz or more is mainly generated. The generated sound waves of each band are transmitted to the
user's ear via the sound guide path 41. Thus, the earphone 100 functions as a hybrid speaker
having a sound producing body for the low frequency band and a sound producing body for the
high frequency band.
[0052]
On the other hand, the sound wave generated by the electromagnetic sounding body 31 causes
the diaphragm 321 of the piezoelectric sounding body 32 to vibrate and propagates to the
second space portion S2, and the second sound wave component via the openings 331 to 337. It
is formed of a synthetic wave with a sound wave component propagating to the space portion S2.
Therefore, by optimizing the size, the number, and the like of the openings 331 to 337, the sound
wave in the low sound range output from the piezoelectric sounding body 32 has a frequency
such that a sound pressure peak can be obtained in a predetermined low sound band, for
example. It becomes possible to adjust or tune to the characteristics.
[0053]
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In the present embodiment, the piezoelectric speaker 32 is configured to be asymmetric in
rigidity with respect to the central axis C1. Specifically, the piezoelectric element 322 is disposed
at a position eccentric to the diaphragm 321, and the shapes and the number of the openings
331 to 337 are asymmetric with respect to the Y-axis direction of the diaphragm 321. (See
Figure 3). For this reason, the vibration mode of the diaphragm 321 becomes uneven in the
plane. As a result, the sound pressure level in the high region becomes broad, and the sound
pressure characteristic is improved, so that good sound quality can be reproduced.
[0054]
As an example, two piezoelectric sound generator samples 11A and 11B shown in FIGS. 5A and
5B were produced, and their frequency characteristics were compared. As a result, simulation
results as shown in FIGS. 6A and 6B were obtained. Here, although each of the samples 11A and
11B has the circular diaphragm 12 and the rectangular piezoelectric element 13 disposed
thereon, in the sample 11A, the piezoelectric element 13 is disposed at the center of the
diaphragm 12 On the other hand, the sample 11B differs in that the piezoelectric element 13 is
disposed at an eccentric position with respect to the diaphragm 12. A rectangular opening 14
wider than the piezoelectric element 13 is provided at the center of the diaphragm 12, the
piezoelectric element 13 is disposed at the center of the opening 14 in the sample 11A, and the
piezoelectric element 13 in the sample 11B. Are disposed eccentrically to the opening 14.
[0055]
FIG. 6A shows the frequency characteristics near the resonance frequency of the samples 11A
and 11B, and FIG. 6B shows the frequency characteristics in each of the higher order modes. A
large difference was not found in the resonance frequency (natural frequency) of the samples
11A and 11B, and it was confirmed that the resonance frequency of the sample 11B slightly
decreased (FIG. 6A). The symmetry of the sample 11B with respect to the central axis of the
diaphragm 12 is broken compared to the sample 11A, leading to a decrease in resonant
frequency due to multiple reasons such as a shift in the maximum amplitude position and a
decrease in the amplitude of the center position. It is presumed that. On the other hand, it was
confirmed that the difference in frequency characteristics between the samples 11A and 11B
clearly starts to appear when the resonance becomes higher (for example, 30 kHz or more) (FIG.
6B).
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[0056]
As described above, when the symmetry of the piezoelectric speaker 32 with respect to the
central axis C1 is broken, the decrease in the resonance point in the higher order mode becomes
large. It is assumed that such a tendency becomes more remarkable as the degree of the
asymmetry becomes larger. Therefore, by adjusting the above-mentioned asymmetry of the
piezoelectric speaker 32 arbitrarily, it is possible to realize a desired high frequency
characteristic. Further, as the asymmetry of the piezoelectric speaker increases, the resistance
element of vibration increases, and the mechanical sharpness (Q value) of resonance decreases,
so that the sound quality can be improved.
[0057]
On the other hand, it has been confirmed that the above-mentioned asymmetry of the
piezoelectric sounding body 32 promotes the improvement of the sound pressure level
particularly in the high range when it is combined with the electromagnetic sounding body 31.
FIG. 7 shows an experimental result showing frequency characteristics of the reproduction sound
of the earphone 100 of the present embodiment. As a comparative example, a frequency
characteristic when a piezoelectric speaker (sample 11A) shown in FIG. 5A is set in the housing
40 instead of the piezoelectric speaker 32 of the present embodiment is shown by a solid line.
[0058]
According to the present embodiment, as shown in FIG. 7, the sound pressure level can be raised
in the high frequency range of 10 kHz or more as compared with the comparative example. This
is because the asymmetry of the piezoelectric speaker 32 according to the present embodiment
causes the maximum amplitude position of the diaphragm 321 to be shifted from the center of
the diaphragm 321, thereby canceling out the sound waves in the high sound band. As a result of
the relaxation, it is presumed that it led to the improvement of the sound pressure characteristic.
In addition, since a rise in sound pressure level is recognized in a band exceeding an audible
range of 20 kHz or more, it is possible to reproduce a sound with a sense of depth.
[0059]
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Furthermore, according to the present embodiment, since the opening 331 of the piezoelectric
sounding body 32 is disposed to face the sound conduction path 41, the reproduction sound of
the electromagnetic sounding body 31 is efficiently guided to the sound conduction path 41. It
becomes possible. As a result, as shown in FIG. 7, the sound pressure level in the low tone range
(7 kHz or less) is also improved, so that the sound pressure characteristic can be improved from
the low tone range to the high tone range.
[0060]
Second Embodiment FIGS. 8 to 15 are schematic plan views (or bottom views) showing the
configuration of a piezoelectric electronic speaker according to a second embodiment of the
present embodiment. Hereinafter, the configuration different from the first embodiment will be
mainly described, and the same configuration as that of the first embodiment is denoted by the
same reference numeral, and the description thereof will be omitted or simplified.
[0061]
The piezoelectric speaker according to this embodiment differs from the first embodiment in the
configuration of the diaphragm as in each of the configuration examples described below. In the
following description, although an example in which the piezoelectric element 322 is disposed at
the center of the diaphragm will be described, the present invention is of course not limited
thereto, and the position where the piezoelectric element 322 is decentered with respect to the
diaphragm as in the first embodiment. It may be located at
[0062]
Configuration Example 1 The piezoelectric speaker 500 shown in FIG. 8 includes a plurality of
(four in this example) notched portions 522 to 525 as passage portions provided in the
peripheral portion 521c of the circular diaphragm 521; It has two openings 526, 527 formed in
the plane of the diaphragm 521. The openings 526 and 527 are for preventing a short circuit
between the external electrodes of the piezoelectric element 322, but also function as a sound
passage (passage).
[0063]
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The notched portions 522 to 525 are provided at an interval of 90 °, at such a depth that they
can form a passage portion that allows the first space portion S1 and the second space portion
S2 of the housing 40 to communicate with each other. The same depth is formed from the
peripheral portion 521 c toward the central axis C. Among them, the notch 522 is formed to have
an opening width larger than the other notches 523 to 525, and the other notches 523 to 525
are all formed to have the same opening width. Thus, the diaphragm 521 is formed in an
asymmetrical shape with respect to the center line CL parallel to the Y-axis direction.
[0064]
Since the piezoelectric speaker 500 having such a configuration has an asymmetric structure
with respect to the central axis C1, the same effects as those of the first embodiment described
above can be obtained. Furthermore, in FIG. 8, the asymmetry of the piezoelectric speaker 500
can be further enhanced by decentering the piezoelectric element 322 to, for example, the right
side of the center line CL. In the present embodiment, it is preferable that the piezoelectric
sounding body 500 be installed in the housing 40 such that the notch 522 having the largest
area of the passage portion faces the sound conduction path 41 (FIG. 1).
[0065]
Configuration Example 2 The piezoelectric speaker 600 shown in FIG. 9 includes a plurality of
(five in this example) notched portions 622 to 626 as passage portions provided in the
peripheral portion 621c of the circular diaphragm 621; And the openings 526 and 527
described above.
[0066]
The notches 622 to 626 are provided at unequal angular intervals and have a depth that can
form a passage that allows the first space S1 and the second space S2 of the housing 40 to
communicate with each other. Thus, they are formed at an arbitrary depth from the peripheral
portion 621c toward the central axis C.
[0067]
In the present configuration example, the number, the distribution, and the like of the notched
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portions 622 to 625 are set asymmetrically with respect to the center line CL parallel to the Yaxis direction.
Since the piezoelectric speaker 600 having such a configuration has an asymmetrical structure
with respect to the central axis C1, the same function and effect as those of the first embodiment
described above can be obtained.
Further, in FIG. 9, the asymmetry of the piezoelectric speaker 600 can be further enhanced by
decentering the piezoelectric element 322, for example, to the right of the center line CL. In this
example, the piezoelectric sounding body 600 is installed in the housing 40 so that the formation
portions of the notches 625, 626, 622 where the passage portions are densely face the sound
conduction path 41 (FIG. 1). Is preferred.
[0068]
Configuration Example 3 A piezoelectric speaker 700 shown in FIG. 10 has an opening 722 as a
passage provided in the surface of a circular diaphragm 721, and openings 526 and 527 for
short circuit prevention.
[0069]
The opening 722 is formed in a semicircular or semi-circular shape similar to the opening 331 in
the first embodiment.
In the present example, the opening 722 is formed continuously with the one opening 526 for
preventing short circuit, but the invention is not limited to this, and the opening 722 may be an
opening independent of the opening 526.
[0070]
In the peripheral portion 721 c of the diaphragm 721, four concave portions 731 and 732 are
provided at intervals of 90 °. The recesses 731 and 732 are used for positioning the support 40
with respect to the housing 40. In particular, as shown in the drawing, by making one recess 732
out of the four recesses different in shape from the other three recesses 731, a pointer indicating
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the directivity of the diaphragm 721 can be obtained. There is an advantage that the assembly
can be prevented.
[0071]
In this configuration example, the position of the opening 722 is set asymmetrically with respect
to the center line CL parallel to the Y-axis direction. Since the piezoelectric speaker 700 having
such a configuration has an asymmetrical structure with respect to the central axis C1, the same
effects as those of the first embodiment described above can be obtained. Further, in FIG. 10, the
asymmetry of the piezoelectric speaker 700 can be further enhanced by decentering the
piezoelectric element 322, for example, to the right of the center line CL. In the present
embodiment, the piezoelectric speaker 700 is preferably installed in the housing 40 such that the
opening 722 functioning as a passage portion faces the sound conduction path 41 (FIG. 1).
[0072]
Configuration Example 4 The piezoelectric speaker 800 shown in FIG. 11 includes a notch 822
as a passage provided at the peripheral portion 821c of the circular diaphragm 821, and an
opening 526, 527 for short circuit prevention. Have.
[0073]
In the present configuration example, the notch 822 has a shape similar to that obtained by
cutting out the peripheral portion 721 c of the diaphragm 721 adjacent to the arc portion of the
opening 722 in the configuration example 3.
Also in such a configuration, the same function and effect as in the configuration example 3 can
be obtained.
[0074]
In the present embodiment, for example, in the vibration plate 721 of the configuration example
3 (FIG. 10), the recessed portions 731 and 732 for positioning are respectively provided in the
peripheral portion 721c, but as shown in FIG. , 732, a plurality of (four in this example) incisions
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741 may be further provided. Each incised portion 741 is a peripheral portion 321c of the
diaphragm 321, and is provided at an interval of 90 °, for example, at a position offset by 45 °
in the circumferential direction from the recessed portions 731 and 732. These positions
correspond to positions radially opposed to the four corners of the piezoelectric element 322.
Therefore, when the piezoelectric element 322 is bonded onto the diaphragm 321, the relative
position of the diaphragm 321 and the piezoelectric element 322 can be confirmed on the basis
of the cutouts 741.
[0075]
Configuration Example 5 In the piezoelectric speaker 700, 800 according to Configuration
Example 3 (FIG. 10) and Configuration Example 4 (FIG. 11), even if a plurality of openings are
further provided in the plane of the diaphragm 721, 821. Good. FIGS. 13 and 14 respectively
show piezoelectric sounding bodies 710 and 810 provided with a plurality of openings 528 in
the plane of the diaphragms 721 and 821. The openings 528 are circular through holes and are
formed at symmetrical positions with respect to the center line CL of the diaphragms 721 and
821, respectively.
[0076]
The number and size of the openings 528 are not particularly limited, and in the illustrated
example, the openings 528 each having a diameter of about 1 mm are provided at four
symmetrical positions with respect to the center line CL and the piezoelectric element 322.
Assuming that the diameter of the diaphragms 721 and 821 is 12 mm, for example, the four
positions are positions where the opposing distance perpendicular to the center line CL is 3.2
mm and the opposing distance parallel to the center line CL is 8.6 mm. It is assumed.
[0077]
Also in the piezoelectric speaker 700, 800 having such a configuration, the same effect as in the
third and fourth embodiments can be obtained. Further, according to this configuration example,
each opening 528 effectively functions as a passage through which the sound wave generated
from the electromagnetic sounding body passes, so as shown in FIG. 15, for example, in the high
frequency band of the electromagnetic sounding body. Sound pressure characteristics can be
improved.
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[0078]
In FIG. 15, the white solid line shows the frequency characteristics when only the piezoelectric
sounding body is driven in the earphone provided with the piezoelectric sounding body 710
shown in FIG. 13, and the white dashed dotted line is shown in FIG. 18 shows frequency
characteristics when only the piezoelectric sounding body is driven in the earphone provided
with the piezoelectric sounding body 700. FIG. As shown in the figure, according to the
piezoelectric sounding body 710, sound pressure characteristics can be improved at 10 to 20
kHz as compared with the piezoelectric sounding body 700.
[0079]
Third Embodiment FIG. 16 is a schematic side sectional view showing a configuration of an
electroacoustic transducer according to a third embodiment of the present invention. Hereinafter,
the configuration different from the first embodiment will be mainly described, and the same
configuration as that of the first embodiment is denoted by the same reference numeral, and the
description thereof will be omitted or simplified.
[0080]
The earphone 300 of the present embodiment includes a housing 340, a piezoelectric speaker
350, and an electromagnetic speaker 360, as in the first embodiment.
[0081]
The housing 340 includes a first support 341 having a sound conduction path (not shown) and
an internal space for accommodating the piezoelectric sounding body 350, a second support 342
for supporting the electromagnetic sounding body 360, and And a third support 343 for joining
the first support 341 and the second support 342 to each other, and constitutes a housing
portion of the earphone.
The third support 343 has a plate shape in which a through hole 343a is bored in the center, and
prevents mutual contact between the diaphragm 351 of the piezoelectric speaker 350 and the
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diaphragm 361 of the electromagnetic speaker 360. Configured as a protector. The second
support 342 may be a part of the electromagnetic speaker 360.
[0082]
The piezoelectric speaker 350 has a diaphragm 351 (first diaphragm) and a piezoelectric
element 352, and the rigidity is asymmetric with respect to the central axis C1 of the diaphragm
351 as in the first embodiment. Ru. That is, the piezoelectric element 352 is disposed at a
position eccentric to the diaphragm 351. In the illustrated example, the central axis C2 of the
piezoelectric element 352 is predetermined in the X axis direction with respect to the central axis
C1 of the diaphragm 351. The distance of
[0083]
The diaphragm 351 is provided with a plurality of openings 353 and 354 as a passage. One
opening 353 corresponds to the openings 332 to 335 (see FIG. 3) in the first embodiment, and
the other opening 354 corresponds to the openings 336 and 337 in the first embodiment (see
FIG. 3). It corresponds to
[0084]
In the present embodiment, the piezoelectric speaker 350 further includes a mount ring 353
(annular member). The mount ring 353 is fixed to the housing 340 (third support 343) via the
bonding layer 356, and supports the peripheral portion of the diaphragm 351 of the
piezoelectric speaker 350. In the present embodiment, the mount ring 353 includes a pedestal
353 a that supports the diaphragm 351 on the upper surface, and a peripheral wall 353 b that
positions the peripheral edge of the diaphragm 351.
[0085]
The support structure of the diaphragm 351 by the mount ring 353 is not particularly limited,
and an adhesive, a double-sided adhesive tape, or the like can be used. The bonding layer 356 is
preferably made of an adhesive material having appropriate elasticity, whereby the piezoelectric
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speaker 350 is elastically supported with respect to the housing 340.
[0086]
Since the piezoelectric sounding body 350 has the mount ring 353, the assembling workability of
the piezoelectric sounding body 350 with respect to the housing 430 is improved, and further,
adjustment of the relative position of the piezoelectric sounding body 350 with respect to the
electromagnetic sounding body 360 is easy. It becomes. Typically, the diaphragm 351 is
disposed concentrically with the diaphragm 361 of the electromagnetic speaker 360, but the
diaphragm 351 may be disposed at an eccentric position with respect to the diaphragm 361.
[0087]
In the present embodiment, as shown in FIG. 16, the central axis C1 of the diaphragm 351 is
disposed at a position away from the central axis C3 of the diaphragm 361 by a predetermined
distance in the X-axis direction. The acoustic characteristics of the piezoelectric speaker 350 can
be improved by arranging the piezoelectric speaker 350 asymmetrically with respect to the
electromagnetic speaker 360 as described above. Such a configuration can be adopted as
appropriate depending on the shape and size of the housing 430, the position of the sound guide
path, and the like.
[0088]
Furthermore, according to the present embodiment, by adjusting the thickness (height) of the
pedestal 353 a of the mount ring 353, the relative distance of the piezoelectric speaker 350 to
the electromagnetic speaker 360 can be set. Adjustment of the said distance can be performed
easily. Further, by optimizing the distance, it is possible to optimize the sound pressure
characteristics in the predetermined frequency band.
[0089]
For example, in FIG. 17, the earphones shown in FIG. 16 are manufactured using two mount
rings 353 having different thicknesses of the pedestal portion 353a, and experimental results of
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frequency characteristics of reproduced sound for each are compared and shown. In FIG. 17, the
white solid line indicates the sound pressure characteristics when the first mount ring having a
thickness of the pedestal 353 a of 1.4 times the unit length (t) is applied, and the white two-dot
chain line indicates The sound pressure characteristic at the time of applying the 2nd mount ring
whose thickness of pedestal part 353a is twice the unit length (t) is shown. The unit length (t) is
1 mm in this example.
[0090]
As shown in FIG. 17, according to the electroacoustic transducer to which the first mount ring is
applied, sound in the range of approximately 5 kHz to 9 kHz is compared with the
electroacoustic transducer to which the second mount ring is applied. Pressure is improved. This
occurs in the electromagnetic speaker 360 because the volume of the space between them
decreases as the distance between the diaphragm 351 of the piezoelectric speaker 350 and the
diaphragm 361 of the electromagnetic speaker 360 decreases. It is considered that the generated
sound wave is likely to be emitted to the outside through the piezoelectric speaker 350.
[0091]
The frequency band in which the improvement of the sound pressure is observed in the distance
between the piezoelectric speaker 350 and the electromagnetic speaker 360 is mainly
determined by the diameter (d) of the diaphragm 361 of the electromagnetic speaker 360. For
example, in order to improve the sound pressure at 6 kHz to 9 kHz, the diameter (d) of the
diaphragm 361 is, for example, 7.5 mm to 13.5 mm. Then, assuming that the distance from the
upper surface of the diaphragm 361 to the lower surface of the diaphragm 351 of the
piezoelectric speaker 350 is h, the predetermined (h / d) of the distance (h) to the diameter (d)
decreases. The sound pressure can be improved in the frequency band of
[0092]
FIGS. 18A and 18B are experimental results showing the relationship between the sound
pressure of 7.5 kHz and the (h / d) value and the relationship between the average sound
pressure of 5 to 9 kHz and the (h / d) value, respectively. Here, in all cases, the value of the
diameter d is 9.2 mm, and the diameter of the diaphragm 351 of the piezoelectric speaker 350 is
8 mm. As shown in FIGS. 18A and 18B, the upper limit of the (h / d) value at which improvement
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in sound pressure can be obtained compared to when the second mount ring is applied (open
two-dot chain line in FIG. 14) is 0.212 or less (H = 1.908 mm or less).
[0093]
The lower limit of the (h / d) value is not particularly limited, but can be set to an appropriate
value such that the diaphragms 351 and 361 do not interfere with each other (or do not contact
the third support 343). In this example, the value (0.152 (h = 1.368 mm)) at the time of
application of the first mount ring (white two-dot chain line in FIG. 14) is set.
[0094]
As described above, in the present embodiment, the sound pressure observed at 5 kHz to 9 kHz
can be obtained by selecting the thickness of the pedestal portion 353a of the mount ring 353
such that 0.152 ≦ (h / d) ≦ 0.212. It is possible to improve the sound pressure characteristics
by improving the dip of the Although not shown, even when the diameter of the diaphragm 351
of the piezoelectric speaker 350 is 12 mm in the experiments of the present inventors, it is
possible to adjust the (h / d) value in the same manner as described above. It has been confirmed
that the sound pressure drop at 9 kHz can be improved.
[0095]
As mentioned above, although embodiment of this invention was described, this invention is not
limited only to the above-mentioned embodiment, of course, a various change can be added.
[0096]
For example, in the first and second embodiments described above, in order to realize the
asymmetric structure of the piezoelectric speaker, the shape of the diaphragm is made
asymmetric with respect to the central axis, or in addition to this, the piezoelectric element is
However, the present invention is not limited to this. Even if the piezoelectric element is disposed
at an eccentric position with respect to the diaphragm, the same effect as described above can be
obtained.
[0097]
In the above embodiments, the shape, position, size and number of the opening or notch forming
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the passage of the piezoelectric sound generation unit are not particularly limited, and the
opening or notch forming the passage is There should be at least one.
[0098]
DESCRIPTION OF SYMBOLS 10 ... Earphone main body 20 ... Earpiece 30 ... Sounding unit 31,
360 ... Electromagnetic sounding body 32, 350, 500, 600, 700, 710, 800, 810 ... Piezoelectric
sounding body 40, 340 ... Casing 321, 351, 521 , 621, 721, 821 ... Vibrating plate (first vibrating
plate) 322, 352 ... Piezoelectric elements 331 to 337, 354, 353, 526, 527, 528, 722 ... Openings
522 to 525, 622 to 626 ... Notches Part 100, 300 ... earphones (electro-acoustic transducer) E 1,
361 ... diaphragm (second diaphragm)
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