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JP2004312561

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DESCRIPTION JP2004312561
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 2
for parametric speaker is used for parametric speaker, converts an input electric signal into an
ultrasonic wave and emits it, and it is possible to use Coulomb force generated by inputting the
electric signal. A diaphragm 41 that vibrates as a result and generates an ultrasonic wave, and a
resonator 6 that resonates the generated ultrasonic wave are provided. The resonator 6 has a
resonance chamber 61 and a sound emission hole 62 communicating with the resonance
chamber 61. Further, the electrode 71 is disposed to face the diaphragm 41 via a gap, and the
coulomb force acts between the diaphragm 41 and the electrode 71. [Selected figure] Figure 1
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
conventional parametric speaker, the conversion efficiency of the electroacoustic transducer as
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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 the electric signal is
input A vibrating plate that vibrates and generates an ultrasonic wave due to a Coulomb force
generated thereby, and a resonator that resonates the generated ultrasonic wave. 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 ultrasonic waves can be resonated more strongly,
and further excellent conversion efficiency can be obtained, and the ultrasonic waves can be
emitted more strongly directivity. Therefore, the directivity of the sound, which is a feature of the
parametric speaker, can be more fully utilized. The electroacoustic transducer for parametric
speakers according to the present invention comprises an electrode disposed opposite to the
diaphragm via a gap, and the coulomb force acts between the diaphragm and the electrode. Is
preferred. Thereby, the structure can be further simplified, and further miniaturization, weight
reduction and cost reduction can be achieved. The electroacoustic transducer for parametric
speakers of the present invention has a structure in which a first plate, a second plate, and a third
plate are stacked in this order, and a part of the second plate The diaphragm is formed, the first
plate and the second plate define a resonance chamber of the resonator, and an electrode facing
the diaphragm is provided on the third plate Is preferred. As a result, the structure is easier to
manufacture, can be made more suitable for mass production, and further miniaturization,
weight reduction, and cost reduction can be achieved. In the electroacoustic transducer for
parametric speakers of the present invention, the sound emission hole communicated with the
resonance chamber by the groove portion formed on the side of the joint surface of at least one
of the first plate and the second plate. Is preferably configured. As a result, the ultrasonic waves
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can be made to resonate more strongly by the presence of the sound emission holes, and further
excellent conversion efficiency can be obtained, and the ultrasonic waves can be emitted with a
stronger directivity. Further, the sound emission hole can be easily formed at the time of
manufacture. In the electroacoustic transducer for parametric speakers according to the present
invention, it is preferable that a sound emission hole communicating with the resonance chamber
is formed in the first plate. As a result, the ultrasonic waves can be made to resonate more
strongly by the presence of the sound emission holes, and further excellent conversion efficiency
can be obtained, and the ultrasonic waves can be emitted with a stronger directivity.
Further, the sound emission hole can be easily formed at the time of manufacture. In the
electroacoustic transducer for parametric speakers of the present invention, it is preferable that
the second plate and the third plate be joined by anodic bonding. As a result, manufacturing
(assembly) can be performed more easily, and the second plate and the third plate can be joined
firmly and with high adhesion. 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 of
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
frequency of the diaphragm of the electroacoustic transducer for parametric speakers and the
oscillation frequency of the oscillator be close to each other. As a result, the diaphragm 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 further reduction of power
consumption, downsizing and 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 of the present invention, it is preferable that the natural frequency of the diaphragm of
the electroacoustic transducer for parametric speakers and the resonance frequency of the
resonator be in the vicinity or in the vicinity of the harmonics 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. BEST MODE FOR
CARRYING OUT THE INVENTION Hereinafter, the electroacoustic transducer for parametric
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speakers and the parametric speaker of the present invention will be described in detail based on
preferred embodiments shown in the attached drawings.
FIG. 1 is a cross-sectional side view 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 FIG. 1 is referred to as “upper” and the lower side as “lower”. An
electroacoustic transducer for parametric speakers (hereinafter simply referred to as
“electroacoustic transducer”) 2 shown in FIG. 1 is used for a parametric loudspeaker, and an
inputted electric signal is an ultrasonic wave (ultrasonic wave) It is converted to vibration and
emitted to 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 vibrates
(flexural vibration) due to a coulomb force (electrostatic force) generated by the input of an
electric signal, and generates a vibration plate 41, and the vibration plate And a resonator 6 for
resonating the generated ultrasonic waves. Further, the resonator 6 has a resonance chamber 61
and a sound emission hole 62 communicating with the resonance chamber 61. The electroacoustic transducer 2 of the present embodiment has a first plate (first substrate) 3 made of
silicon on the upper side, sandwiching a second plate (second substrate) 4 made of silicon. And,
the lower side has a three-layer structure in which a third plate (third substrate) 5 made of
borosilicate glass having a thermal expansion coefficient close to that of silicon is laminated,
respectively. In the present embodiment, each of these plates is long and continuous in the
direction perpendicular to the paper surface of FIG. Then, on each of these plates, a plurality of
electroacoustic transducers 2 aligned in a direction perpendicular to the paper surface of FIG. 1
are formed to constitute an electroacoustic transducer array, but each electroacoustic transducer
2 Since the configurations are the same as each other, one electro-acoustic transducer 2 will be
representatively described below. The constituent materials of the first plate 3, the second plate
4 and the third plate 5 are not limited to those described above, and for example, stainless steel,
silicon, SiO 2, polyimide, polysulfone, etc. Various metal materials such as epoxy resin, acrylic
resin, diglycol dialkyl carbonate resin, unsaturated polyester resin, polyurethane resin, polyimide
resin, melamine resin, phenol resin, urea resin silicon nitride, zirconia, partially stabilized
zirconia, various resins Materials and various ceramics can be used. The central second plate 4
has a recess formed on the side in contact with the first plate 3. The recess can be formed, for
example, by performing an etching process on the surface of the second plate 4.
The space in the recess is to be the resonance chamber 61. That is, the first plate 3 and the
second plate 4 define the resonance chamber 61. Thus, the resonator 6 is composed of the first
plate 3 and a part of the second plate 4. The resonance chamber 61 is formed in a rectangular
parallelepiped shape long in the left-right direction in FIG. The resonator 6 functions as a
Helmholtz resonator. Further, the second plate 4 has a groove portion formed on the end surface
of the second plate 4 from the resonance chamber 61 on the side of the bonding surface with the
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first plate 3. A sound output hole 62 communicating with the resonance chamber 61 is formed
by the groove portion. The sound release hole 62 constitutes a port portion in the Helmholtz
resonator. The bottom wall (lower portion) of the portion of the second plate 4 facing the
resonance chamber 61 is formed thinner than the other portions, and the diaphragm 41 is
configured by this thin portion . The diaphragm 41 functions as a diaphragm (diaphragm) which
can be elastically deformed (elastically displaced) in the vertical direction in FIG. The volume of
the resonance chamber 61 changes due to the vibration (displacement) of the diaphragm 41. The
diaphragm 41 has conductivity and also functions as an electrode. In the present embodiment,
the diaphragm 41 has conductivity by injecting impurities into the second plate 4 to impart
conductivity to the second plate 4 itself. Also, unlike such a configuration, for example, a thin film
of a conductive material such as gold or copper may be formed on one surface of the diaphragm
41, in which case lower electrical resistance (with higher efficiency It is possible to supply a
voltage (charge) to the diaphragm 41. This thin film may be formed, for example, by vapor
deposition or sputtering. The vibration plate 41 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. In the present invention, the structure is not limited to the
illustrated structure, and for example, a groove (concave portion) is formed in a portion around
the diaphragm 41 of the second plate 4 as a structure that facilitates the diaphragm 41 to vibrate
with a larger displacement. Or a structure in which the diaphragm 41 is supported in a cantilever
manner.
The third plate 5 has a shallow concave portion 51 at a position corresponding to the resonance
chamber 61 on the side of the joint surface with the second plate 4. The bottom (bottom) 52 of
the recess 51 is positioned to face the diaphragm 41 with a gap. The recess 51 can be formed,
for example, by etching or the like. The internal space of the recess 51 communicates with the
outside. Thereby, the pressure in the recess 51 can be prevented from suppressing the vibration
of the diaphragm 41. An electrode 71 facing the diaphragm 41 is formed on the bottom surface
52. In addition, this electrode 71 is a segment electrode provided separately for each of the
electroacoustic transducer 2 in the electroacoustic transducer array. Further, the electrode 71 is
covered from the upper side by an insulating layer (insulating film) 72 made of an oxide film (SiO
2) of silicon. The insulating layer 72 has a function of protecting the electrode 71 and a function
of preventing a short circuit with the diaphragm 41. The insulating layer 72 may be provided on
the lower surface of the diaphragm 41. The electrode 71 and the insulating layer 72 are
positioned between the diaphragm 41 and the gap (air gap). As described above, the diaphragm
41 and the electrode 71 constitute a pair of opposing electrodes facing each other with the gap
and the insulating layer 72 interposed therebetween. The third plate 5 is formed with an input
terminal 73 electrically connected to the electrode 71. Further, the second plate 4 is formed with
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an input terminal 74 electrically connected to the diaphragm 41. The electroacoustic transducer
2 can input (apply) an electrical signal (voltage) between the diaphragm 41 and the electrode 71
through the input terminals 73 and 74. As described above, since the second plate 4 itself has
conductivity, the diaphragms 41 of the respective electroacoustic transducer 2 of the
electroacoustic transducer array serve as common electrodes electrically connected to each
other. Thus, one input terminal 74 can conduct electricity to each of the diaphragms 41. Here, an
example of a method of manufacturing the electroacoustic transducer 2 will be described. When
the first plate 3 and the second plate 4 are made of silicon, silicon is single crystal, so anisotropic
etching is possible. For example, when the (100) plane is etched, it is in the direction of 55 ° It
can etch regularly. In the (111) plane, etching can be performed in the 90 ° direction.
Therefore, by using this characteristic, each portion such as the sound output hole 62 and the
resonance chamber 61 can be formed in the first plate 3 or the second plate 4 with high
accuracy.
Then, the third plate 5 in which the electrode 71 and the insulating layer 72 are formed on the
lower surface side of the second plate 4 (a glass or an insulating material having a thermal
expansion coefficient close to that of silicon in the constituent material of the third plate 5 Is
preferably heated to a temperature of, for example, 300 to 500 ° C., and a voltage of about
several hundred volts is applied, with the second plate 4 side as an anode and the third plate 5
side as a cathode. By anodically bonding, the second plate 4 and the third plate 5 can be bonded
easily with high adhesion. A conductive film used as an electrode in the anodic bonding is formed
on the upper surface side of the second plate 4, and this conductive film can be used as it is as an
input terminal 74 to the diaphragm 41. In the present invention, for example, the input terminal
74 may be omitted, and the method of bonding the second plate 4 and the third plate 5 is not
limited to anodic bonding. When a voltage is applied between the vibrating plate 41 and the
electrode 71 of the electro-acoustic transducer 2 as described above, the vibrating plate 41 and
the electrode 71 are charged and an attractive force due to the Coulomb force is generated
between them. Is generated, and the diaphragm 41 is bent to the electrode 71 side by this
attractive force. In this state, when the voltage application to the diaphragm 41 and the electrode
71 is released, the coulomb force disappears, and the diaphragm 41 is restored upward in FIG. It
is further displaced upward in FIG. 1 beyond the state shown in FIG. When an electrical signal
(oscillation voltage) whose voltage oscillates at the frequency in the ultrasonic band is input
between the diaphragm 41 and the electrode 71, the displacement of the diaphragm 41 as
described above is repeatedly generated, and the diaphragm 41 is flexurally oscillated And
generate ultrasound. The ultrasonic waves generated by the diaphragm 41 resonate in the
resonator 6, and are emitted from the sound emission hole 62 in the left direction in FIG. In the
electroacoustic transducer 2 of the present invention, the provision of the resonator 6 makes it
possible to resonate and emit ultrasonic waves, so that the input electric signal is converted into
ultrasonic waves (acoustic energy). Conversion efficiency (hereinafter sometimes referred to
simply as “conversion efficiency”) is high. Therefore, in the parametric speaker using the
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electroacoustic transducer 2, since an ultrasonic wave can be emitted with sufficient strength
even with a relatively low voltage electric signal, power consumption can be reduced.
Furthermore, since the electroacoustic transducer 2 can be manufactured by laminating the first
plate 3, the second plate 4 and the third plate 5 as described above, the size is extremely
reduced. It is advantageous.
Therefore, when arranging a large number of electroacoustic transducers 2 in a matrix, for
example, the number of arrangement per unit area can be extremely increased. 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 output hole 62 in the
resonator 6, the ultrasonic waves resonate more strongly, and further excellent conversion
efficiency is obtained, and the sound pressure of the ultrasonic waves 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
described later, it is more preferable that the resonance frequency 33 be in the vicinity of the
natural frequency 11 of the diaphragm 41 and the oscillation frequency 22 of the oscillator 11
of the parametric speaker 1 or in the vicinity of overtone relationship. 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 (the 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, since the electroacoustic transducer 2 vibrates (displaces) the diaphragm 41
by the coulomb force (electrostatic force), the displacement amount is large even when driven at
a low voltage, and high controllability can be obtained. Therefore, in the parametric speaker
using the electroacoustic transducer 2, high sound quality can be obtained while reducing the
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power consumption. Furthermore, it has excellent durability and processability, and is suitable
for mass production. FIG. 2 is a cross-sectional side view showing another embodiment of the
electroacoustic transducer for parametric speakers of the present invention. Hereinafter,
although it demonstrates based on FIG. 2, it demonstrates focusing on difference with
embodiment mentioned above, and the description is abbreviate | omitted about the same matter.
An electroacoustic transducer 2 'shown in FIG. 2 is the same as the electroacoustic transducer 2
except that the sound emitting hole 62 of the resonator 6 is formed by a through hole formed in
the first plate 3. It is. In the electro-acoustic transducer 2 ′, the sound output hole 62 is formed
at a position facing the diaphragm 41. Then, ultrasonic waves are emitted upward in FIG. 2 from
the sound release holes 62. Further, in the resonator 6 in the present embodiment, the length
indicated by L in FIG. 2 is the length of the port portion. FIG. 3 is a block diagram showing an
embodiment of the parametric speaker of the present invention, and FIG. 4 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. 3 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 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 (the
frequency of the carrier wave) of the oscillator 11 is not particularly limited as long as it is an
ultrasonic 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
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electroacoustic transducer 2 converts the input signal into an ultrasonic wave, and radiates it in
the air with directivity (left direction in FIG. 1). 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. 4A shows a
transmission wave, that is, the waveform of the audio signal output from the audio generator.
FIG. 4B 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. 4 (c). When this modulated wave is radiated
into the air, the sound wave is distorted as shown in FIG. 4 (d) because it travels faster when air
vibrates in the forward direction due to the non-linear characteristic of air and travels later when
air travels in the reverse direction. The original audible sound is demodulated (FIG. 4 (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 diaphragm 41 of the
electroacoustic transducer 2 and the oscillation frequency 2 2 of the oscillator 11 be close to
each other.
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 / ν2 ≦ 1.1 is satisfied. . Thereby, since the diaphragm
41 can be vibrated with a larger amplitude by the resonance phenomenon, the conversion
efficiency of the electroacoustic transducer 2 can be further improved. Further, in the parametric
speaker 1, it is preferable that the oscillation frequency 発 振 器 2 of the oscillator 11 and the
resonance frequency 3 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, the ultrasonic waves generated by the diaphragm 41 can
be resonated more strongly, so that the conversion efficiency of the electroacoustic transducer 2
can be further improved. In the parametric speaker 1, it is preferable that the resonance
frequency 3 3 of the resonator 6 and the natural frequency 振動 1 of the diaphragm 41 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, the ultrasonic waves generated by the diaphragm 41 can be
resonated more strongly, so that the conversion efficiency of the electroacoustic transducer 2
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can be further improved. Furthermore, in the parametric speaker 1, the natural frequency 1 1 of
the diaphragm 41, the oscillation frequency 2 2 of the oscillator 11, and the resonance frequency
3 3 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. Although
the electroacoustic transducer for parametric speakers and the parametric speaker according to
the present invention have been described with reference to the illustrated embodiment, 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 cross-sectional side view showing another
embodiment of the electroacoustic transducer for parametric speakers of the present invention.
FIG. 3 is a block diagram illustrating an embodiment of a parametric speaker of the present
invention. FIG. 4 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 ...
Audio input interface 2, 2 ........ Electroacoustic transducer for parametric speaker 3 ... First plate
4 第 second plate 41 振動 diaphragm 5 第 third plate 51 凹 部 recess 52 底面 bottom 6 共鳴
resonator 61 共鳴 resonance chamber 62 放 sound emitting hole 71 電極 electrode 72 ......
Insulating layer 73, 74 ... input terminal
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