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DESCRIPTION JP2012217096

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DESCRIPTION JP2012217096
The present invention provides a parametric speaker capable of preventing a cancellation of
sound waves generated by a plurality of ultrasonic wave generation elements, and obtaining a
sufficient sound pressure stably. SOLUTION: The parametric speaker 100 imparts directivity by
ultrasonic waves and transmits acoustic information, and an oscillator 101 which oscillates a
signal at a predetermined frequency in an ultrasonic band, and a modulator 102 which
modulates the oscillation signal by an audio signal. And a plurality of ultrasonic wave generating
elements 110 each having a resonance frequency on one side of high and low sides with respect
to a predetermined frequency and generating an ultrasonic wave based on the modulation signal.
Thereby, cancellation of the sound waves generated by the plurality of ultrasonic wave
generation elements 110 can be prevented, and a stable sound pressure can be obtained.
[Selected figure] Figure 3
パラメトリックスピーカ
[0001]
The present invention relates to a parametric speaker that imparts directivity to ultrasonic waves
and conveys acoustic information.
[0002]
Conventionally, parametric speakers that transmit information in a specific direction or position
using a highly directional ultrasonic signal have been put to practical use.
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1
A parametric speaker is a device utilizing a phenomenon in which a modulated ultrasonic signal
having a relatively high sound pressure is self-demodulated to an audible sound by the nonlinearity of air. For example, Patent Document 1 proposes a parametric speaker that changes the
frequency of an ultrasonic wave to control the distance of demodulation to an audible sound.
[0003]
JP 2004-349817 A
[0004]
Such a parametric speaker is configured by arranging a plurality of ultrasound generating
elements in order to enhance the directivity and sound pressure of the ultrasound.
And in order to mutually raise the sound pressure of the ultrasonic wave which generate | occur
| produces in each, it is necessary to vibrate each ultrasonic wave generation element by the
same phase.
[0005]
However, since each of the ultrasonic wave generating elements has its own resonance frequency
and each resonance frequency is different, for example, as shown in FIG. 6, when the drive
frequency is the same as the resonance frequency fb, the resonance frequency lower than that
The phase of the sound wave generated from the ultrasonic wave generating element having fa is
largely different from the phase of the sound wave generated from the ultrasonic wave
generating element having a higher resonance frequency fc.
[0006]
As a result, the sound waves generated by the ultrasonic wave generation element having the
resonance frequency fa lower than the drive frequency and the ultrasonic wave generation
element having the resonance frequency fc higher than the drive frequency cancel each other, so
that sufficient sound pressure can not be obtained. .
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Also, as shown by the curve Q in FIG. 7, the phase largely moves with respect to the change of
frequency near the resonance point where the peak of the curve P, so that the sound pressure
fluctuates due to the fluctuation of temperature etc. Can not demonstrate.
[0007]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide a parametric speaker which can prevent the cancellation of sound
waves generated by a plurality of ultrasonic wave generating elements and can obtain sufficient
sound pressure stably. With the goal.
[0008]
(1) In order to achieve the above object, the parametric speaker of the present invention is a
parametric speaker that imparts directivity by ultrasonic waves and transmits acoustic
information, and an oscillator that oscillates a signal at a predetermined frequency in an
ultrasonic band A modulator for modulating the oscillation signal with an audio signal, and a
plurality of ultrasonic wave generating elements each having a resonant frequency on one side
high or low with respect to the predetermined frequency and generating an ultrasonic wave
based on the modulation signal And are characterized.
[0009]
As described above, in the parametric speaker of the present invention, all of the plurality of
ultrasonic wave generating elements have a resonant frequency on one side of high or low with
respect to a predetermined driving frequency.
Thereby, cancellation of the sound waves generated by the plurality of ultrasonic wave
generation elements can be prevented, and a stable and sufficient sound pressure can be
obtained.
[0010]
(2) Further, the parametric speaker of the present invention is characterized in that each of the
plurality of ultrasonic wave generating elements has a resonance frequency lower than the
predetermined frequency.
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As a result, the heat generation of the ultrasonic wave generation element can be suppressed
more than in the case where the plurality of ultrasonic wave generation elements have a
resonant frequency higher than a predetermined frequency. Once the heat is generated, the
resonant frequency of the element is shifted to the lower side, which makes it easy to prevent the
cancellation of the sound waves. Further, by suppressing the heat generation, the shift of the
resonant frequency can be reduced, and an ultrasonic wave generating element with a resonant
frequency closer to the drive frequency can be used.
[0011]
(3) Further, the parametric speaker of the present invention is characterized in that each of the
plurality of ultrasonic wave generating elements has a resonance frequency lower than the
predetermined frequency at -40 ° C. Thereby, cancellation of sound waves can be reliably
prevented, and a stable and sufficient sound pressure can be obtained.
[0012]
According to the present invention, cancellation of sound waves generated by a plurality of
ultrasonic wave generation elements can be prevented, and a sufficient sound pressure can be
stably obtained.
[0013]
(A), (b) is the front view and side view which show the parametric speaker of this invention,
respectively.
It is a sectional view showing an ultrasonic wave generation element. It is a block diagram which
shows the electric constitution of the parametric speaker of this invention. It is a graph which
shows the relationship of the amplitude with respect to the frequency of an ultrasonic wave
generation element. It is a graph which shows the characteristic to the frequency of an ultrasonic
wave generation element. It is a graph which shows the relationship of the amplitude with
respect to the frequency of an ultrasonic wave generation element. It is a graph which shows the
characteristic to the frequency of an ultrasonic wave generation element.
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[0014]
Next, embodiments of the present invention will be described with reference to the drawings. In
order to facilitate understanding of the description, the same reference numerals are given to the
same components in the respective drawings, and the overlapping description will be omitted.
[0015]
(Configuration of Parametric Speaker) FIGS. 1A and 1B are a front view and a side view showing
the parametric speaker 100, respectively. The parametric speaker 100 generates an ultrasonic
wave modulated by a strong sound pressure, and an audible sound appears due to the non-linear
characteristic of the propagation of the ultrasonic wave in the air. In this way, it is possible to
identify the direction or distance, give directivity, and transmit acoustic information. As shown in
FIG. 1, the parametric speaker 100 is configured by providing a plurality of ultrasonic wave
generating elements 110 on a substrate 120. The ultrasonic wave generation element 110
generates an ultrasonic wave based on the modulation signal. The substrate 120 fixes and
supports the ultrasonic wave generating element 110. Note that FIG. 1 shows the external
configuration, and the electrical configuration is omitted.
[0016]
(Configuration of Ultrasonic Wave Generating Element) FIG. 2 is a cross-sectional view showing
the ultrasonic wave generating element 110. The ultrasonic wave generating element 110 is
composed of a metal plate 111, a piezoelectric element 112, lead wires 113 and 114, a parabolic
body 115 and a support 118. The metal plate 111 is formed in a disk shape, for example, by a
metal such as brass, 42 alloy, SUS 304 or aluminum.
[0017]
The piezoelectric element 112 is formed in a disk shape, and is adhered to one main surface of
the metal plate 111 and installed. The other main surface of the metal plate 111 is a vibrating
surface, and the piezoelectric element 112 can transmit and receive ultrasonic waves by the
parabolic body 115 via the vibrating surface. Electrodes are respectively formed on both main
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5
surfaces of the piezoelectric element 112, and the piezoelectric body of the main body portion is
polarized. The resonant frequency of the ultrasonic wave generating element 110 varies
depending on the shape, Young's modulus, weight and other characteristics of the vibrating part
in the ultrasonic wave generating element 110, that is, the shape, weight and material of the
metal plate 111, the piezoelectric element 112 and the parabola body 115 Do. The ultrasonic
wave generating element 110 is designed in advance to have a constant resonance frequency.
[0018]
Such a design is made to have a resonant frequency on either side of high or low with respect to
a predetermined drive frequency for any of the ultrasonic wave generating elements 110. That is,
the resonance frequency of all the ultrasonic wave generation elements 110 is higher than the
drive frequency, or the resonance frequency of all the ultrasonic wave generation elements 110
is lower than the drive frequency. Thereby, cancellation of the sound waves generated by the
plurality of ultrasonic wave generation elements 110 can be prevented, and a stable sound
pressure can be obtained.
[0019]
Furthermore, it is preferable that the plurality of ultrasound generating elements 110 be
designed to have a resonant frequency lower than a predetermined frequency. Thereby, heat
generation of the ultrasonic wave generation element 110 can be suppressed more than the case
where the plurality of ultrasonic wave generation elements 110 have a resonant frequency
higher than a predetermined frequency. Once the heat is generated, the resonance frequency of
the ultrasonic wave generating element 110 is shifted to the lower side, so that it is easy to
prevent the cancellation of the sound waves. Further, by suppressing the heat generation, the
shift of the resonant frequency can be reduced, and the ultrasonic wave generating element 110
with a resonant frequency closer to the drive frequency can be used.
[0020]
Further, it is more preferable that each of the plurality of ultrasonic wave generating elements
110 have a resonance frequency lower than a predetermined frequency at -40 ° C. Thereby,
cancellation of sound waves can be reliably prevented, and a stable and sufficient sound pressure
can be obtained. Details of the design of the resonant frequency will be described later.
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[0021]
The lead wires 113 and 114 are connected to the circuit on the substrate 120 so that voltage
application and detection are possible. The lead wire 113 is connected to an electrode on the
metal plate 111 side of the piezoelectric element 112 on one main surface side of the metal plate
111 via the metal plate 111. The lead wire 114 is connected to an electrode on the substrate 120
side of the piezoelectric element 112. Such a configuration makes it possible to transmit an
electrical signal to the piezoelectric element 112 and generate an ultrasonic wave.
[0022]
The parabola body 115 is formed in a parabola shape, for example, of metal, and is fixed on the
metal plate 111. By providing the parabolic body 115 on the metal plate 111, the sound pressure
of the generated ultrasonic wave is increased. The parabolic body 115 is preferably formed of a
light material such as aluminum or an aluminum-magnesium alloy.
[0023]
The support 118 is provided at several places on the substrate 120 side of the piezoelectric
element 112, and is formed of an elastic material such as silicon rubber, for example, to support
the ultrasonic wave generating element 110. The support 118 is provided at the position of the
node of vibration of the substrate 120. This prevents the vibration from the ultrasonic wave
generation element 110 from being transmitted to the substrate 120. A hole is provided at the
center of the arrangement position of the ultrasonic wave generating element 110 of the
substrate 120, and the sound absorbing material 121 is filled in the hole. The sound absorbing
material 121 is formed of a sponge-like material, and blocks the sound transmitted from the
ultrasonic wave generating element 110 to the back side. The above ultrasonic wave generating
element 110 is only an example, and the present invention can be applied as long as the
resonance frequency can be adjusted by design.
[0024]
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(Electrical Configuration of Parametric Speaker) FIG. 3 is a block diagram showing an electrical
configuration of the parametric speaker 100. As shown in FIG. As shown in FIG. 3, the parametric
speaker 100 includes an oscillator 101, a modulator 102, an amplifier 105, and an ultrasonic
wave generation element 110, and generates an ultrasonic wave through these. The oscillator
101 oscillates a signal at a predetermined frequency in the ultrasonic band. The frequency to be
oscillated is a drive frequency for driving the piezoelectric element 112 when the oscillation
signal is transmitted to the ultrasonic wave generation element 110, and is determined in
advance according to the application of the parametric speaker 100.
[0025]
The modulator 102 AM modulates the oscillation signal with the audio signal. The modulation
may be DSB modulation, SSB modulation, or FM modulation instead of AM modulation. The
amplifier 105 amplifies the modulated oscillation signal and outputs the amplified oscillation
signal to the ultrasonic wave generation element 110. The ultrasonic wave generation element
110 converts the amplified oscillation signal into a sound wave.
[0026]
(Operation of Parametric Speaker) The parametric speaker 100 configured as described above
oscillates a signal of a frequency of an ultrasonic band, modulates the oscillation signal with a
desired audio signal, amplifies the modulation signal, and generates an ultrasonic wave. The
element 110 converts it into a sound wave and emits it. In this way, highly directional ultrasound
can be emitted. In this way, for example, since information can be selectively sent to people in a
narrow area, it can be used for museums, aquariums, museums, amusement facilities and the like.
In the future, it can also be used as traffic information.
[0027]
(Design of Resonant Frequency) FIG. 4 is a graph showing the relationship of the amplitude to
the frequency of the ultrasonic wave generating element 110. As shown in FIG. 4, the ultrasonic
wave generating element 110 is designed such that the drive frequency is slightly higher than
the highest of the respective resonance frequencies. Such a design makes it possible to prevent
the sound waves from canceling each other because the ultrasonic waves generated from the
ultrasonic wave generating elements 110 are in phase with each other. For example, as shown in
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FIG. 4, when forming the parametric speaker 100 by arranging the ultrasonic wave generating
elements 110 having the resonance frequencies of f1, f2 and f3 and f1 <f2 <f3, f3 is slightly
higher than the drive frequency The ultrasonic wave generating element 110 is designed to be
lower.
[0028]
How much lower the frequency is set with respect to the drive frequency is mainly determined
by the temperature fluctuation of the ultrasonic wave generating element 110. Usually, it is
known that the resonant frequency of each ultrasonic wave generating element 110 decreases as
the temperature of the ultrasonic wave generating element 110 rises, and, for example, the
environmental temperature of the vehicle (-40 ° C to 85 ° C) In consideration of the above, it is
a standard that the resonance frequency fc does not become higher than the drive frequency
even when it becomes -40.degree.
[0029]
FIG. 5 is a graph showing the characteristics of the ultrasonic wave generating element 110 with
respect to the frequency. As shown by the curve R in FIG. 5, when the ultrasonic wave generating
element 110 is designed so that the resonant frequency is higher than the drive frequency, heat
generation is higher than in the case where the resonant frequency is shifted to the same degree
lower. It tends to grow. Therefore, designing the resonance frequency lower has the effect of
suppressing heat generation. Furthermore, once heat generation occurs, the resonance frequency
of the ultrasonic wave generation element 110 is shifted to the lower side, so that the heat
generation can be reduced and the shift of the resonance frequency can be reduced by driving in
a direction higher than the resonance frequency. be able to. In addition, there is also an effect
that it is possible to set the drive frequency closer to the resonance frequency.
[0030]
DESCRIPTION OF SYMBOLS 100 parametric speaker 101 oscillator 102 modulator 105 amplifier
110 ultrasonic wave generating element 111 metal plate 112 piezoelectric element 113, 114
lead wire 115 parabola body 118 support body 120 board 121 sound absorbing material
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