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JP2004312394

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DESCRIPTION JP2004312394
The present invention provides an electroacoustic transducer for parametric speakers and a
parametric speaker that is excellent in conversion efficiency when converting an electrical signal
into ultrasonic waves and that is advantageous for downsizing. An electroacoustic transducer for
a parametric speaker is used for a parametric speaker, converts an input electric signal into an
ultrasonic wave, and emits the ultrasonic wave. The electroacoustic transducer 2 for a parametric
speaker has a long shape, and a piezoelectric actuator 3 that vibrates in the longitudinal direction
when an electric signal is input and a base 4 that supports the base end of the piezoelectric
actuator 3 And the diaphragm 5 having the vibration portion 51 disposed on the tip end side of
the piezoelectric actuator 3 and vibrating so as to generate an ultrasonic wave along with the
expansion and contraction vibration of the piezoelectric actuator 3 and the ultrasonic wave
generated by the diaphragm 5 as a resonance And a resonator 6. [Selected figure] Figure 2
Electroacoustic transducer for parametric speaker and parametric speaker
TECHNICAL FIELD [0001] The present invention relates to an electroacoustic transducer for
parametric speakers and a parametric speaker. [0002] There is known a parametric speaker (also
commonly referred to as an audio spotlight) that can obtain high directivity in the direction in
which sound is directed (see, for example, Non-Patent Document 1). The parametric speaker
includes an electroacoustic transducer that converts an electrical signal into an ultrasonic wave
and emits the ultrasonic wave, and emits an amplitude-modulated ultrasonic wave from the
electroacoustic transducer according to the audio signal, and the ultrasonic wave travels through
the air The audible sound produced by being self-demodulated by the non-linear phenomenon of
sound waves during propagation is heard by the human ear. Thus, the parametric speaker can
generate an audible sound by emitting a sound wave in a highly directional ultrasonic band, and
thus has high directivity in the direction in which the sound is directed. However, in the
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conventional parametric speaker, the conversion efficiency of the electroacoustic transducer as
an ultrasonic source is poor and large. Therefore, the conventional parametric speaker has many
drawbacks such as heavy weight, large size, large power consumption, poor sound quality, high
manufacturing cost and the like. And, since the parametric speaker is low in energy efficiency
due to the loss caused when it is converted to an audible sound by self-demodulation, it is
extremely difficult to overcome the above-mentioned drawbacks. Non-Patent Document 1 M.
Yoneyama, et al. , J. Acoust. Soc. Am v 73 1532-1536 (1983) SUMMARY OF THE
INVENTION It is an object of the present invention to provide a parametric speaker which is
excellent in conversion efficiency at the time of converting an electric signal into an ultrasonic
wave and which is advantageous for downsizing. An electroacoustic transducer and a parametric
speaker. Such objects are achieved by the present invention described below. The electroacoustic
transducer for parametric speakers according to the present invention is an electroacoustic
transducer for parametric speakers that is used for parametric speakers and converts an input
electric signal into an ultrasonic wave and emits the ultrasonic wave, and has a long shape, A
piezoelectric actuator that vibrates in the longitudinal direction when an electric signal is input, a
base that supports a base end of the piezoelectric actuator, a distal end of the piezoelectric
actuator, and the vibration of the piezoelectric actuator Along with this, it is characterized by
comprising: a diaphragm having a vibration unit that vibrates so as to generate an ultrasonic
wave; and a resonator for resonating the ultrasonic wave generated by the diaphragm.
As a result, it is possible to provide an electroacoustic transducer for a parametric speaker that is
excellent in conversion efficiency when converting an electrical signal into an ultrasonic wave
and that is advantageous for downsizing. With a parametric speaker using this electroacoustic
transducer for parametric speaker, reduction of power consumption, downsizing, weight
reduction and cost reduction can be achieved. In the electroacoustic transducer for parametric
speakers of the present invention, it is preferable that the resonator has a resonance chamber
and a sound output hole communicating with the resonance chamber. As a result, the sound
pressure of the ultrasonic wave can be emitted more strongly, and further excellent conversion
efficiency can be obtained, and the directivity of the sound, which is a feature of the parametric
speaker, can be fully utilized. In the electroacoustic transducer for parametric speakers of the
present invention, preferably, the sound emission hole is formed at a position not facing the tip
surface of the piezoelectric actuator. Thereby, when arranging several electroacoustic
transducers for parametric speakers side by side, arrangement | positioning of the sound
emission hole of each electroacoustic transducer for parametric speakers can be determined with
high freedom. In the electroacoustic transducer for parametric speakers of the present invention,
the piezoelectric actuator preferably has a portion in which a piezoelectric material and a
conductive material are alternately laminated in layers. As a result, the piezoelectric actuator can
obtain a large displacement amount even at a relatively low voltage and is excellent in
controllability (responsiveness), so that a further excellent conversion efficiency can be obtained,
and when used for a parametric speaker, Excellent sound quality is obtained. In addition, since
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the processability of the piezoelectric actuator can be made excellent, it is suitable for mass
production and can be manufactured at lower cost. In the electroacoustic transducer for
parametric speakers of the present invention, it is preferable that the piezoelectric material and
the conductive material are stacked in parallel with the expansion and contraction direction of
the piezoelectric actuator. This provides the piezoelectric actuator with higher energy efficiency
compared to other vibration modes. In the electroacoustic transducer for parametric speakers of
the present invention, it is preferable that the piezoelectric material and the conductive material
be stacked perpendicularly to the expansion and contraction direction of the piezoelectric
actuator. Thereby, the piezoelectric actuator can be stacked in more layers and can be driven at a
lower voltage. In the electroacoustic transducer for parametric speakers of the present invention,
preferably, the base and the resonator are fixed via a fixing member.
As a result, the piezoelectric actuator can be accurately positioned relative to the resonator
(diaphragm) by adjusting the relative positional relationship between the fixing member and the
base during manufacturing (assembly), and manufacturing is easy. be able to. In the
electroacoustic transducer for parametric speakers according to the present invention, a sound
output plate that is overlapped and joined to the diaphragm is provided, and is formed on at least
one of the bonding surface side of the diaphragm and the sound output plate. Preferably, the
recess forms a resonance chamber of the resonator. Thereby, manufacture (assembly) of a
resonator part can be performed easily. In the electroacoustic transducer for parametric speakers
according to the present invention, the diaphragm, the spacer plate, and the sound output plate
are stacked and joined in this order, and the spacer plate and the sound output plate are
connected by the spacer plate. Preferably, at least a part of the resonance chamber of the
resonator is formed by the space formed between. Thereby, manufacture (assembly) of a
resonator part can be performed easily. In the electroacoustic transducer for parametric speakers
of the present invention, it is preferable that the piezoelectric actuator is fixed so that a plane
parallel to the expansion and contraction direction overlaps the base. Thus, the piezoelectric
actuator can be easily and firmly fixed to the base. In the electroacoustic transducer for
parametric speakers of the present invention, the length of the base in the expansion and
contraction direction of the piezoelectric actuator is preferably longer than the length of the
piezoelectric actuator. Thereby, manufacture (assembly) of the electroacoustic transducer for
parametric speakers can be performed easily. The parametric speaker according to the present
invention comprises at least one electroacoustic transducer for parametric speakers according to
the present invention, an oscillator for generating a signal whose voltage oscillates at a frequency
in an ultrasonic band, and the signal based on an audio signal. And an amplifier for amplifying
the modulated signal modulated by the amplitude modulator, wherein the modulated signal
amplified by the amplifier is input to the electroacoustic transducer for parametric speakers and
It is characterized by emitting a sound wave. As a result, it is possible to provide a parametric
speaker capable of achieving reduction in power consumption, reduction in size and weight, and
cost reduction. In the parametric speaker of the present invention, it is preferable that the natural
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frequency of the expansion and contraction vibration of the piezoelectric actuator of the
electroacoustic transducer for parametric speaker and the oscillation frequency of the oscillator
be in the vicinity.
As a result, the piezoelectric actuator can be vibrated with a larger amplitude by the resonance
phenomenon, so that the conversion efficiency of the electroacoustic transducer can be further
improved, and the reduction of the power consumption, the miniaturization and the weight
reduction can be achieved. In the parametric speaker according to the present invention, it is
preferable that a resonance frequency of a resonator of the electroacoustic transducer for
parametric speakers and an oscillation frequency of the oscillator be close to each other or close
to an overtone relationship. As a result, since the ultrasonic waves generated by the diaphragm
can be resonated more strongly, the conversion efficiency of the electroacoustic transducer can
be further improved, and further reduction in power consumption, size reduction and weight
reduction can be achieved. In the parametric speaker according to the present invention, it is
preferable that the natural frequency of the expansion / contraction vibration of the piezoelectric
actuator of the electroacoustic transducer for parametric speaker and the resonance frequency of
the resonator be in the vicinity or in the vicinity of harmonics. . As a result, since the ultrasonic
waves generated by the diaphragm can be resonated more strongly, the conversion efficiency of
the electroacoustic transducer can be further improved, and further reduction in power
consumption, size reduction and weight reduction can be achieved. BEST MODE FOR CARRYING
OUT THE INVENTION Hereinafter, the electroacoustic transducer for parametric speakers and
the parametric speaker of the present invention will be described in detail based on preferred
embodiments shown in the attached drawings. 1 and 2 are a perspective view and a crosssectional side view respectively showing an embodiment of the electroacoustic transducer for
parametric speakers of the present invention. In the following, for convenience of explanation,
the upper side in FIGS. 1 and 2 is referred to as the “tip”, and the lower side is referred to as
the “proximal”. An electroacoustic transducer 2 for parametric speakers (hereinafter simply
referred to as “electroacoustic transducer 2”) shown in FIG. 1 and FIG. 2 is used for parametric
speakers, and it is possible to It is converted into sound waves (ultrasonic vibrations) and emitted
into the air. In addition, the whole structure of the parametric speaker 1 provided with the
electroacoustic transducer 2 is mentioned later. The electro-acoustic transducer 2 includes a
piezoelectric actuator (piezoelectric vibrator) 3 having an elongated shape (elongated shape), a
base 4 supporting a base end (fixed end) portion of the piezoelectric actuator 3, and the
piezoelectric actuator 3. The diaphragm 5 installed on the end (free end) side of the above, the
resonator 6 for resonating the ultrasonic wave generated by the diaphragm 5, and the fixing
member 7 are provided. As shown in FIG. 1, in this embodiment, a configuration in which a
plurality of electroacoustic transducers 2 arranged in n rows × 2 columns (n is an integer of 2 or
more) is integrated (electroacoustic transducer array )It has become.
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In the electro-acoustic transducer array, the base 4, the diaphragm 5, the resonator 6, and the
fixing member 7 (the fixing member 7 is omitted in FIG. 1) are integrated into each electroacoustic transducer 2. Is formed. As shown in FIG. 2, the electro-acoustic transducers 2 in the left
row and the electro-acoustic transducers 2 in the right row in FIG. In addition, the plurality of
electroacoustic transducers 2 in each row have the same structure. Therefore, in the following,
one electro-acoustic transducer 2 will be representatively described. The piezoelectric actuator 3
stretches and vibrates in the longitudinal direction when an electric signal (oscillation voltage) is
input (applied). The piezoelectric actuator 3 has a portion in which a piezoelectric material and a
conductive material are alternately stacked in layers. Further, in the present embodiment, the
piezoelectric material and the conductive material are stacked in parallel to the expansion and
contraction direction (longitudinal direction) of the piezoelectric actuator 3. Hereinafter, although
an example of a method of manufacturing the piezoelectric actuator 3 will be described,
illustration of a manufacturing process is omitted. Further, the following example is an example
in which a plurality of piezoelectric actuators 3 aligned in the column direction (direction
perpendicular to the paper surface of FIG. 2) are simultaneously manufactured. A piezoelectric
material (for example, a lead zirconate titanate composite perovskite ceramic material) prepared
in a paste form is thinly applied on a platen to form a first piezoelectric material layer 31, and for
example, evaporation or conduction is performed on the surface The first conductive layer 32 is
formed to leave an exposed portion on a part of the first piezoelectric material layer 31 by a
method such as application of a conductive paint, and further, the first conductive layer 32 and
the first piezoelectric layer are formed. A piezoelectric material is thinly applied to the surface of
the material layer 31 with the exposed portion to form a second piezoelectric material layer 33,
and a second conductive layer 34 is formed on the second piezoelectric material layer 33 on a
side different from the first conductive layer 32. Repeat the process of forming as many times as
necessary. After forming a predetermined number of layers in this manner, it is dried, and is fired
at a temperature of 1000 to 1200 ° C. for about 1 hour in a state where pressure is applied to
the plate-like ceramic (piezoelectric plate) Finished. Then, a conductive paint is applied to one
end where each first conductive layer 32 is exposed, and one collector electrode 35 is also
provided, and the other end where each second conductive layer 34 is exposed. A conductive
paint is applied to form a collector 36. The piezoelectric plate formed in this manner is fixed to
the projection 41 of the base 4 (the aggregate of the base 4) using, for example, a conductive
adhesive or the like, up to the vicinity of the surface of the base 4 at a predetermined width
interval. Cut (divide) with a diamond cutter etc.
A plurality of piezoelectric actuators 3 are formed by separating the piezoelectric plate into a
plurality of elongated members by slits generated by this tooth split processing (cutting). The
piezoelectric actuator 3 can be manufactured relatively easily and at low cost, for example, by the
method described above. In such a piezoelectric actuator 3, the plurality of first conductive layers
32 and the plurality of second conductive layers 34 function as a pair of comb electrodes. In the
electro-acoustic transducer 2, conductive materials (conductive members) (not shown) are
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connected to the collecting electrodes 35 and 36 respectively, and the first conductive layer 32
and the second conductive as a pair of comb electrodes An electric signal (voltage) can be input
(applied) to the layer 34. When the diaphragm 5 is made of a conductive material, the diaphragm
5 may function as a conductive member for the collecting electrode 35. In the piezoelectric
actuator 3 shown in FIG. 2, the piezoelectric material and the conductive material (electrode) are
disposed parallel to the expansion and contraction direction (longitudinal direction), whereby
higher energy efficiency can be obtained as compared to other vibration modes. . The
piezoelectric actuator 3 preferably has a natural frequency 11 of 20 kHz to 800 kHz, and more
preferably 40 kHz to 400 kHz. Further, as described later, it is more preferable that the natural
frequency 11 be in the vicinity of the oscillation frequency 22 of the oscillator 11 of the
parametric speaker 1. Further, it is more preferable that the natural frequency 11 and the
resonance frequency 共鳴 3 of the resonator 6 be in the vicinity or in the vicinity of the overtone
relationship. FIG. 3 is a perspective view showing another configuration example of the
piezoelectric actuator in the present invention. In the piezoelectric actuator 3 'shown in FIG. 3,
the piezoelectric material and the conductive material are stacked perpendicularly to the
expansion and contraction direction (longitudinal direction) of the piezoelectric actuator 3'. In the
present invention, the piezoelectric actuator 3 ′ may be used instead of the piezoelectric
actuator 3. In the piezoelectric actuator 3 'shown in FIG. 3, since the piezoelectric material and
the conductive material can be stacked in more layers, they can be driven at a lower voltage. As
shown in FIG. 2, the base 4 has a protrusion 41 projecting in the lateral direction for fixing the
piezoelectric actuator 3 in a portion on the base end side. The distal end (distal end surface) of
the piezoelectric actuator 3 is joined to the diaphragm 5, and the base end is fixed to the
projection 41 of the base 4.
In the present invention, since the base end of the piezoelectric actuator 3 is fixed to the base 4,
the strength (rigidity) of the base 4 does not require the piezoelectric actuator 3 to have such a
large strength, so that the manufacture is easy. It is also advantageous for miniaturization.
Further, in the illustrated configuration, the piezoelectric actuator 3 is fixed so that a plane
parallel to the expansion and contraction direction (longitudinal direction) thereof overlaps the
projection 41 of the base 4. Thereby, the said effect is exhibited more notably. The base 4 is
configured such that the position of its distal end substantially coincides with the distal end
surface of the piezoelectric actuator 3 and the position of its proximal end projects in the
proximal direction beyond the proximal end of the piezoelectric actuator 3. ing. That is, the
length of the base 4 in the expansion and contraction direction of the piezoelectric actuator 3 is
longer than the length of the piezoelectric actuator 3. The base 4 is fixed at its base end (base
end face) to the fixing member 7. Further, the tip (tip surface) of the base 4 is joined (fixed) to the
diaphragm 5. The fixing member 7 supports the diaphragm 5 and the resonator 6 and makes the
tip of the piezoelectric actuator 3 abut on the diaphragm 5 via the base 4. A diaphragm 5 for
separating a resonance chamber 63 described later and the piezoelectric actuator 3 is fixed to
the front end surface of the base 4. The vibrating plate 5 has a vibrating portion 51 joined (fixed
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or abutted) to the end surface of the piezoelectric actuator 3. Further, the diaphragm 5 has a
thin-walled portion formed by the concave portions 52 and 53 provided in the vicinity of the
vibrating portion 51. As a result, the vibration unit 51 can reliably follow and vibrate by the
vibration of the piezoelectric actuator 3. The constituent material of the diaphragm 5 is not
particularly limited. For example, stainless steel, silicon, epoxy resin, acrylic resin, diglycol dialkyl
carbonate resin, unsaturated polyester resin, polyurethane resin, polyimide resin, melamine resin,
Various metal materials such as phenol resin, urea resin silicon nitride, zirconia, and partially
stabilized zirconia, various resin materials, and various ceramics can be used. A resonator 6
having a resonance chamber 63 is installed on the front end surface side of the diaphragm 5. The
resonator 6 functions as a Helmholtz resonator. The resonator 6 is a spacer plate (spacer
member) 62 overlapped and joined (fixed) on the front end surface side of the diaphragm 5, and
a sound emission plate overlapped and connected (fixed) on the front end surface side of the
spacer plate 62. And 61.
The spacer plate 62 has a recess 621 formed on the side of the bonding surface to the
diaphragm 5 and a through hole 622 penetrating from the recess 621 to the tip side. A space (a
gap) is formed between the diaphragm 5 and the sound output plate 61 by the recess 621, and
the space in the recess 621 constitutes a resonance chamber 63. A sound emission hole 64
communicating with the resonance chamber 63 via the through hole 622 is formed in the sound
emission plate 61. The sound release hole 64 and the through hole 622 constitute a port portion
in the Helmholtz resonator. In the illustrated configuration, the sound output holes 64 and the
through holes 622 are formed at positions not facing the tip surface of the piezoelectric actuator
3. Thereby, the degree of freedom of the arrangement position of the sound output holes 64 can
be enhanced, and it becomes possible to arrange the sound output holes 64 of each row close to
each other as in this embodiment, for example (see FIG. 1). . When an electric signal (oscillation
voltage) whose voltage vibrates at a frequency in the ultrasonic band is input to the piezoelectric
actuator 3 of the electroacoustic transducer 2 as described above, the piezoelectric actuator 3
stretches and vibrates in its longitudinal direction. Accordingly, the vibrating portion 51 of the
diaphragm 5 vibrates to generate an ultrasonic wave. The ultrasonic waves generated by the
diaphragm 5 resonate in the resonator 6 and are emitted upward in FIG. The constituent
materials of the base 4, the sound release plate 61, the spacer plate 62, and the fixing member 7
are not particularly limited, and for example, stainless steel, silicon, SiO 2, polyimide, polysulfone,
negative type or positive type Various metal materials such as photosensitive resin materials
(epoxy resin, acrylic resin, diglycol dialkyl carbonate resin, unsaturated polyester resin,
polyurethane resin, polyimide resin, melamine resin, phenol resin, urea resin etc.), various resin
materials, Various glasses and various ceramics can be used. In the electro-acoustic transducer 2
of the present invention, the provision of the resonator 6 makes it possible to resonate and emit
ultrasonic waves, thereby converting an input electric signal into ultrasonic waves (acoustic
energy). Conversion efficiency (hereinafter sometimes referred to simply as “conversion
efficiency”) is high. Therefore, in the parametric speaker using the electroacoustic transducer 2,
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since an ultrasonic wave can be emitted with sufficient strength even with a relatively low
voltage electric signal, power consumption can be reduced. Furthermore, the electro-acoustic
transducer 2 of the present invention is extremely advantageous for downsizing, and in the case
of arranging a large number of electro-acoustic transducers 2 in a matrix, for example, the
number of arrangement per unit area is extremely increased. be able to.
Therefore, even with a relatively small parametric speaker, an audible sound with sufficient
strength can be obtained, and the miniaturization and weight reduction of the parametric speaker
can be achieved. In particular, in the present embodiment, by providing the sound emission hole
64 in the resonator 6, the ultrasonic wave resonates more strongly, and further excellent
conversion efficiency is obtained, and the sound pressure of the ultrasonic wave is made
stronger. It can radiate. Therefore, the above-described effects (reduction in power consumption,
reduction in size and weight) can be more remarkably exhibited, and the directivity of the sound,
which is a feature of the parametric speaker, can be fully utilized. The resonator 6 preferably
satisfies the following conditions in order to obtain a better resonance state. The resonance
frequency 33 of the resonator 6 is preferably 10 kHz to 200 kHz, and more preferably 20 kHz to
100 kHz. As will be described later, the resonance frequency 33 is closer to the natural
frequency 伸縮 1 of the expansion / contraction vibration of the piezoelectric actuator 3 and the
oscillation frequency 22 of the oscillator 11 of the parametric speaker 1 or closer to the overtone
relationship. preferable. Since the resonator 6 satisfies the above conditions, in the parametric
speaker using the electroacoustic transducer 2, the effect of the resonator 6 described above is
more prominent. In general, a Helmholtz resonator has a resonance frequency ν shown by the
following equation. Where, in the above equation, c is the speed of sound, S is the opening area
of the port portion (sound emission hole), and V is the resonance chamber. , L is the length of the
port portion (length indicated by L in FIG. 2). Hereinafter, based on the above equation, for
example, the resonance frequency に お け る in one embodiment is calculated. Considering a
resonator of S = 50 μm × 50 μm, L = 50 μm, V = 100 μm × 100 μm × 1.5 mm, the
resonance frequency は is about 99 kHz. In this case, energy can be transmitted to air with
higher efficiency by using the oscillation frequency 22 near the resonance frequency ν in the
parametric speaker 1 described later. However, since the actual resonator 6 has a complicated
geometrical structure, the calculated values as described above are only a guide, and it is
desirable to fit in the real thing. In this way, a low power (low power consumption) and highly
efficient parametric speaker can be obtained.
Further, in the electroacoustic transducer 2, since the piezoelectric actuator 3 can be positioned
with respect to the resonator 6 (diaphragm 5) via the base 4, the relative positional relationship
between the fixing member 7 and the base 4 The piezoelectric actuator 3 can be accurately
positioned with respect to the resonator 6 (the diaphragm 5) by adjusting. Therefore, the tip end
of the piezoelectric actuator 3 can be brought into contact with the vibrating portion 51 with
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high positional accuracy. Further, since it is possible to perform positioning after fixing the base
end side of the piezoelectric plate to the base 4 in the fixed member 7, it is possible to position
the fragile piezoelectric actuator 3 through the base 4 having high mechanical strength. Since
positioning can be performed, handling at the time of positioning to the resonator 6 (diaphragm
5) can be facilitated, and the base 4 and the fixing member 7 can be configured as separate
members, materials meeting the respective purposes, That is, the base 4 can be made of a
material having high rigidity enough to receive the reaction force from the piezoelectric actuator
3, and the fixing member 7 can be made of a polymer material etc. which can be manufactured
by injection molding or the like. . From such a thing, in the electroacoustic transducer 2,
coexistence with high performance (high conversion efficiency improvement) and reduction of
manufacturing cost can be achieved at a high level. Further, in the present embodiment, the
piezoelectric actuator 3 has a stacked structure as described above, so that a large amount of
displacement can be obtained even at a relatively low voltage, and the controllability
(responsiveness) is excellent. . As a result, the electro-acoustic transducer 2 of the present
embodiment can obtain more excellent conversion efficiency, and when used for a parametric
speaker, more excellent sound quality can be obtained. Further, the piezoelectric actuator 3
having the laminated structure as described above is excellent in processability, suitable for mass
production, can be manufactured at a lower cost, and has high durability. FIG. 4 is a perspective
view showing another embodiment according to the electroacoustic transducer for parametric
speakers of the present invention. In the electro-acoustic transducer 2 'shown in FIG. 4, unlike
the electro-acoustic transducer 2, the resonator 6 does not have the spacer plate 62, and the
sound emission plate 61' is superposed on and joined (fixed) to the diaphragm 5 '. It is done. And
the resonance chamber 63 of the resonator 6 is formed of the recessed parts 54 and 55 and the
recessed part 65 which were each formed in the joint surface side of a diaphragm and a sound
emission plate. In the illustrated configuration, the concave portions 54 and 55 communicate
with each other of the electroacoustic transducers 2 ′, but in order to make them independent
as resonators, separation by forming a partition is more preferable. desirable.
In the embodiment shown in FIG. 4, the spacer plate 62 is not required, and the assembly process
can be simplified. The electroacoustic transducer 2 ′ is the same as the electroacoustic
transducer 2 except for the above point. FIG. 5 is a block diagram showing an embodiment of the
parametric speaker of the present invention, and FIG. 6 is a diagram for explaining the principle
of the parametric speaker. Hereinafter, based on the figure, the embodiment of the parametric
speaker of the present invention is described. The parametric speaker (parametric array speaker)
1 shown in FIG. 5 includes the aforementioned electroacoustic transducer 2, an oscillator (carrier
generation means) 11, an amplitude modulator (amplitude modulation means) 12, an amplifier
(amplification means) 13, and , And an audio input interface 14. The parametric speaker 1
radiates to the air a carrier wave (signal) having an ultrasonic band frequency amplitude
modulated by an audible sound (voice signal) into the air, and demodulates the audible sound by
using the non-linear characteristic of air (self It is a speaker that can perform highly directional
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acoustic radiation by performing demodulation). Although the number of the electroacoustic
transducers 2 installed in the parametric speaker 1 may be one, it is preferable to be plural. By
adjusting the number of installed devices, an audible sound with a sufficient magnitude (sound
pressure) can be generated. As described above, since the electro-acoustic transducer 2 of the
present invention is advantageous for downsizing, a large number of electro-acoustic transducers
2 can be arranged with high integration (density). The oscillator 11 generates (generates) a
signal (carrier wave) whose voltage oscillates at a frequency (about 20 kHz or more) of the
ultrasonic band. The oscillation frequency (carrier wave frequency) 2 2 of the oscillator 11 is not
particularly limited as long as it is an ultrasonic wave band, but is preferably about 20 kHz to
400 kHz, and more preferably about 40 kHz to 100 kHz. An audio signal generated by an audio
generator (not shown) is input to the amplitude modulator 12 through the audio input interface
14. The amplitude modulator 12 amplitude modulates the signal oscillated from the oscillator 11,
that is, the carrier wave, based on the voice signal. The amplitude modulation system in the
amplitude modulator 12 is not particularly limited, and may be an ordinary amplitude
modulation system, or may be an envelope modulation system in which amplitude modulation is
performed with an envelope of a signal. The modulated signal modulated by the amplitude
modulator 12 is input to the amplifier 13 and amplified to a level at which the electroacoustic
transducer 2 can be driven.
The modulated signal amplified by the amplifier 13 is input to the electroacoustic transducer 2.
The electroacoustic transducer 2 converts the input signal into an ultrasonic wave, and radiates it
in the air with directivity (upward in FIG. 2). The ultrasonic wave (modulated wave) radiated from
the electroacoustic transducer 2 into air becomes a distorted wave due to the non-linear
characteristic of air, and is demodulated into the audible sound of the original sound signal while
propagating through the air. Since the demodulated audible sound has superdirective
characteristics of the original ultrasonic wave, the parametric speaker 1 can emit acoustic
radiation only in a desired specific space (specific direction). The principle of the parametric
speaker 1 as described above will be further described based on FIG. FIG. 6 (a) is a waveform of a
transmission wave, that is, an audio signal output from an audio generator. FIG. 6 (b) shows the
waveform of the signal (carrier wave) generated by the oscillator 11. By placing the carrier wave
on the transmission wave, the transmission wave is converted into a modulated wave (modulated
signal) as shown in FIG. 6 (c). When this modulated wave is radiated into the air, the sound wave
is distorted as shown in FIG. 6 (d) because it travels fast when air vibrates in the forward
direction due to the non-linear characteristic of air and travels slowly when air travels in the
reverse direction. The original audible sound is demodulated (FIG. 6 (e)). This demodulated
audible sound has superdirective characteristics of the original ultrasound. In such a parametric
speaker 1, it is preferable that the natural frequency 1 1 of the expansion and contraction
vibration of the piezoelectric actuator 3 of the electroacoustic transducer 2 and the oscillation
frequency 2 2 of the oscillator 11 be in the vicinity. Here, that ν1 and 22 are in the vicinity
means that the relationship of preferably 0.8 ≦ 1/1 / ν2 ≦ 1.2, more preferably 0.9 ≦ ν1 /
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ν2 ≦ 1.1 is satisfied. . However, since the natural frequency 11 slightly changes due to heat
generation during driving, it is actually preferable to select a condition that stabilizes as a result
by slightly shifting the oscillation frequency 22. By satisfying the conditions as described above,
the piezoelectric actuator 3 can be vibrated at a relatively large voltage even with a relatively low
voltage due to a resonance phenomenon, so that the conversion efficiency of the electroacoustic
transducer 2 can be further improved. In the parametric speaker 1, it is preferable that the
oscillation frequency 周波 数 2 of the oscillator 11 and the resonance frequency 周波 数 3 of the
resonator 6 of the electroacoustic transducer 2 be in the vicinity or in the vicinity of the
harmonics relationship. Here, that ν 2 and 3 3 are in the vicinity means that the relationship of
preferably 0.8 ≦ 2 2 / ν 3 ≦ 1.2, more preferably 0.9 ≦ ν 2 / ν 3 ≦ 1.1 is satisfied. .
Further, that ν2 and 33 are in the vicinity of a harmonic relationship means that m × ν2 and n
× ν3 are in the same manner as described above, where m and n are positive integers,
respectively. Thereby, since the ultrasonic wave generated by the diaphragm 5 can be resonated
more strongly, the conversion efficiency of the electroacoustic transducer 2 can be further
improved. Further, in the parametric speaker 1, it is preferable that the resonance frequency 3 3
of the resonator 6 and the natural frequency 1 1 of the piezoelectric actuator 3 be in the vicinity
or in the vicinity of the overtone relationship. Here, that ν3 and 11 are in the vicinity means that
the relationship satisfying 0.8 ≦ ν3 // 1 ≦ 1.2, more preferably 0.9 ≦ ν3 / ν1 ≦ 1.1 is
satisfied. . Further, that ν3 and 11 are in the vicinity of a harmonic relationship means that i ×
ν3 and j × ν1 are in the same manner as described above, where i and j are positive integers,
respectively. Thereby, since the ultrasonic wave generated by the diaphragm 5 can be resonated
more strongly, the conversion efficiency of the electroacoustic transducer 2 can be further
improved. Furthermore, in the parametric speaker 1, the natural frequency 11 of the
piezoelectric actuator 3, the oscillation frequency 22 of the oscillator 11, and the resonance
frequency 33 of the resonator 6 are in the vicinity of each other or in the vicinity of the overtone
relationship. Most preferred. In addition, when such a parametric speaker 1 is what has several
electroacoustic transducers 2, you may radiate | emit the ultrasonic wave of mutually different
frequency from multiple (multiple sets) electroacoustic transducer 2. As shown in FIG. The
electroacoustic transducer for parametric speakers and the parametric speaker according to the
present invention have been described above with reference to the illustrated embodiment, but
the present invention is not limited to this, and the electroacoustic transducers for parametric
speakers and parametric Each part which comprises a speaker can be substituted by the thing of
arbitrary structures which can exhibit the same function. Also, any component may be added.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of
the electroacoustic transducer for parametric speakers of the present invention. FIG. 2 is a crosssectional side view showing an embodiment of the electroacoustic transducer for parametric
speakers of the present invention. FIG. 3 is a perspective view showing another configuration
example of the piezoelectric actuator in the present invention. FIG. 4 is a perspective view
showing another embodiment of the electroacoustic transducer for parametric speakers of the
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present invention. FIG. 5 is a block diagram illustrating an embodiment of a parametric speaker
of the present invention.
FIG. 6 is a diagram for explaining the principle of a parametric speaker. [Description of the code]
1 ....... Parametric speaker 11 ...... Oscillator 12 ...... Amplitude modulator 13 ...... Amplifier 14 ......
Voice input interface 2, 2 ..... Electroacoustic transducer for parametric speaker 3, 3 .....
Piezoelectric Actuator 31 first piezoelectric material layer 32 first conductive layer 33 second
piezoelectric material layer 34 second conductive layer 35, 36 collector electrode 4 base 41
Protrusions 5, 5 '...... diaphragm 51 部 vibrating portion 52, 53, 54, 55 凹 部 recess 6 61
resonator 61, 61' 放 sound emitting plate 62 ス ペ ー サ spacer plate 621 凹 部 recess 622 ... ...
through hole 63 ... resonance chamber 64 ... sound emitting hole 65 ... recess 7 ... fixed member
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