JP4803246B2 - Ultrasonic speaker, audio signal reproduction method, superdirective acoustic system - Google Patents

Description

  The present invention relates to an electrostatic ultrasonic transducer having a sharp directivity that generates a constant high sound pressure over a wide frequency band, an ultrasonic speaker having a sharp directivity using the ultrasonic transducer, an audio signal reproducing method, The present invention relates to a directional acoustic system and a display device.

Most conventional ultrasonic transducers as acoustic radiation devices with sharp directivity are resonant types using piezoelectric ceramics.
Here, FIG. 9 shows a configuration of a conventional ultrasonic transducer. Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics as vibration elements. The ultrasonic transducer shown in FIG. 9 performs both the conversion from an electric signal to an ultrasonic wave and the conversion from an ultrasonic wave to an electric signal (transmission and reception of an ultrasonic wave) using a piezoelectric ceramic as a vibration element. The bimorph ultrasonic transducer shown in FIG. 9 includes two piezoelectric ceramics 61 and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67.

The piezoelectric ceramics 61 and 62 are bonded to each other, and a lead 65 and a lead 66 are connected to a surface opposite to the bonded surface, respectively.
Since the resonance type ultrasonic transducer uses the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are good in a relatively narrow frequency band around the resonance frequency.

Unlike the resonant ultrasonic transducer shown in FIG. 9 described above, an electrostatic ultrasonic transducer is conventionally known as a broadband oscillation ultrasonic transducer capable of generating a high sound pressure over a high frequency band. This electrostatic ultrasonic transducer is called a pull type because it works only in the direction in which the vibrating membrane is attracted to the fixed electrode side.
FIG. 10 shows a specific configuration of a broadband oscillation type ultrasonic transducer (Pull type).

  The electrostatic ultrasonic transducer shown in FIG. 10 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. An upper electrode 132 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 131 by a process such as vapor deposition, and a lower electrode 133 formed of brass is formed on the lower surface of the dielectric 131. It is provided so that it may contact a part. The lower electrode 133 is connected to a lead 152 and is fixed to a base plate 135 made of bakelite or the like.

  The upper electrode 132 is connected to a lead 153, and the lead 153 is connected to the DC bias power supply 150. The DC bias power supply 150 constantly applies a DC bias voltage for attracting the upper electrode of about 50 to 150 V to the upper electrode 132 so that the upper electrode 132 is attracted to the lower electrode 133 side. Reference numeral 151 denotes a signal source.

The dielectric 131, the upper electrode 132, and the base plate 135 are caulked by the case 130 together with the metal rings 136, 137, and 138 and the mesh 139.
On the surface of the lower electrode 133 on the dielectric 131 side, a plurality of minute grooves of about several tens to several hundreds μm having a non-uniform shape are formed. Since this minute groove becomes a gap between the lower electrode 133 and the dielectric 131, the electrostatic capacity distribution between the upper electrode 132 and the lower electrode 133 changes minutely.

  These random minute grooves are formed by manually roughing the surface of the lower electrode 133 with a file. In the electrostatic ultrasonic transducer, the frequency characteristics of the ultrasonic transducer shown in FIG. 9 are as shown by a curve Q1 in FIG. 10 by forming innumerable capacitors having different gap sizes and depths. It is broadband.

In the ultrasonic transducer having the above configuration, a rectangular wave signal (50 to 150 Vp-p) is applied between the upper electrode 132 and the lower electrode 133 in a state where a DC bias voltage is applied to the upper electrode 132. Yes. Incidentally, as shown by the curve Q2 in FIG. 11, the frequency characteristic of the resonance type ultrasonic transducer has a center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, and ± 5 kHz with respect to the center frequency that is the maximum sound pressure. -30 dB with respect to the maximum sound pressure at a frequency of.
On the other hand, the frequency characteristic of the broadband oscillation type ultrasonic transducer having the above configuration is flat from 40 kHz to near 100 kHz, and is about ± 6 dB compared to the maximum sound pressure at 100 kHz (see Patent Documents 1 and 2). .

As described above, unlike the resonant ultrasonic transducer shown in FIG. 9, the electrostatic ultrasonic transducer shown in FIG. 10 can generate a relatively high sound pressure over a wide frequency band. It is known as a broadband ultrasonic transducer (Pull type).
However, as shown in FIG. 11, the maximum value of the sound pressure is 120 dB or less for the electrostatic ultrasonic transducer as compared with the resonance ultrasonic transducer of 130 dB or more, and the sound pressure is low as an ultrasonic speaker. Sound pressure was slightly insufficient for use.

  Here, the ultrasonic speaker will be described. The ultrasonic wave was modulated with the audio signal of the signal source by applying AM modulation to the signal in the ultrasonic frequency band called carrier wave with audio signal (audible frequency band signal) and driving the ultrasonic transducer with this modulation signal. The sound wave of the state is radiated into the air, and the original audio signal is self-regenerated in the air due to the nonlinearity of air.

  In other words, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse parts of air appear prominently in the process of propagation of modulated ultrasonic waves. Since the speed of sound is slow in this part, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic wave) and an audible wave (original audio signal). This is the principle that only listening can be heard, and it is generally called the parametric array effect.

In order for the above parametric effect to appear sufficiently, an ultrasonic sound pressure of 120 dB or more is required. However, it is difficult to achieve this value with an electrostatic ultrasonic transducer, and ceramic piezoelectric elements such as PZT, PVDF, etc. The polymer piezoelectric element has been used as an ultrasonic transmitter.
However, since the piezoelectric element has a sharp resonance point regardless of the material, and is practically used as an ultrasonic speaker by being driven at the resonance frequency, the frequency region where a high sound pressure can be secured is extremely narrow. That is, it can be said that it is a narrow band.

  Generally, the maximum human audible frequency band is said to be 20 Hz to 20 kHz and has a band of about 20 kHz. That is, in an ultrasonic speaker, it is impossible to faithfully demodulate the original audio signal unless a high sound pressure is ensured over a frequency band of 20 kHz in the ultrasonic region. It can be easily understood that it is difficult to faithfully reproduce (demodulate) this wide band of 20 kHz with a resonance type ultrasonic speaker using a conventional piezoelectric element.

  Actually, in an ultrasonic speaker using a conventional resonance type ultrasonic transducer, (1) a narrow band and poor reproduction sound quality, (2) if the AM modulation degree is increased too much, the demodulated sound is distorted, so about 0.5 at the maximum. (3) When the input voltage is increased (when the volume is increased), the vibration of the piezoelectric element becomes unstable and the sound is broken. When the voltage is further increased, the piezoelectric element itself is liable to be destroyed, and (4) it is difficult to make an array, enlargement, and miniaturization.

On the other hand, the ultrasonic speaker using the electrostatic ultrasonic transducer (Pull type) shown in FIG. 10 can substantially solve the above-mentioned problems of the prior art, but can cover a wide band, but has sufficient demodulated sound. However, there was a problem that the absolute sound pressure was insufficient for the sound volume to be high.
Further, in the pull type electrostatic ultrasonic transducer, the electrostatic force works only in the direction of attracting only to the fixed electrode side, and the vibration symmetry of the vibration film (corresponding to the upper electrode 132 in FIG. 10) is not maintained. Therefore, when used for an ultrasonic speaker, there has been a problem that the vibration of the vibrating membrane directly generates an audible sound.

  On the other hand, we have already proposed an electrostatic ultrasonic transducer capable of generating an acoustic signal having a sufficiently high sound pressure level to obtain a parametric array effect over a wide frequency band (see Patent Document 3). . The configuration of this electrostatic ultrasonic transducer is shown in FIG. FIG. 12A shows the configuration of the electrostatic ultrasonic transducer, and FIG. 12B shows a plan view in which a part of the electrostatic ultrasonic transducer is broken. In FIG. 12, the electrostatic ultrasonic transducer 1 includes a pair of fixed electrodes 10 </ b> A and 10 </ b> B including a conductive member formed of a conductive material that functions as an electrode, and an electrode layer 121 sandwiched between the pair of fixed electrodes. The diaphragm 12 includes a member (not shown) that holds the pair of fixed electrodes 10 </ b> A and 10 </ b> B and the diaphragm 12.

  The vibration film 12 is formed of an insulator (insulating layer) 120 and has an electrode layer 121 formed of a conductive material. The electrode layer 121 is unipolar (positive polarity) by a DC bias power supply 16. DC bias voltage may be applied to the fixed electrode 10 </ b> A and the fixed electrode 10 </ b> B superimposed on the DC bias voltage and output from the signal source 18. The AC signals 18A and 18B whose phases are reversed from each other are applied between the electrode layer 121 and the AC signals 18A and 18B.

Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of through holes 14 at positions facing each other with the vibrating membrane 12 interposed therebetween. AC signals 18A and 18B whose phases are reversed from each other are applied. Reference numeral 16 denotes a DC bias power source.
The fixed electrode 10A and the electrode layer 121, and the fixed electrode 10B and the electrode layer 121 are each formed with a capacitor. Note that the configuration of a control unit that controls the signal source 18 and the DC bias power supply 16 and a storage unit that stores a table indicating the control characteristics of the control unit are omitted in FIG.
In this electrostatic ultrasonic transducer 1, a vibrating membrane 12 having a conductive layer 121 is sandwiched between a pair of fixed electrodes 10 </ b> A and 10 </ b> B in which through holes are formed at opposing positions. The AC signals 18A and 18B are applied from the signal source 18 to the pair of fixed electrodes 10A and 10B in a state where a bias voltage is applied.

  This electrostatic ultrasonic transducer is called a Push-Pull type electrostatic ultrasonic transducer, and an electrostatic attraction force is applied in a direction in which the vibration film sandwiched between a pair of fixed electrodes corresponds to the polarity of an AC signal. And electrostatic repulsion simultaneously in the same direction and at the same time, the vibration of the diaphragm can be made large enough to obtain the parametric array effect, and the symmetry of the vibration is ensured. High sound pressure can be generated over a wide frequency band as compared with the Pull type electrostatic ultrasonic transducer.

  As described above, as described above, as an ultrasonic transducer applied to an acoustic radiation device with sharp directivity (for example, an ultrasonic speaker), a piezoelectric method and an electrostatic method have been proposed. Since the resonance point is sharp and it is difficult to widen the band, the sound reproducibility is poor (see Patent Documents 4 and 5). On the other hand, the electrostatic method has the advantages that the vibration of the diaphragm itself is not sharp, and that it can be broadened by using the air column resonance phenomenon of the acoustic tube and has excellent sound reproducibility (good sound quality). (See Patent Document 3).

JP 2000-50387 A JP 2000-50392 A JP 2005-354472 A JP-A 61-296897 JP 2000-287297 A

However, when an ultrasonic transducer is applied to an ultrasonic speaker, the output sound pressure of the ultrasonic transducer is required to be high. However, even an electrostatic ultrasonic transducer that can obtain a relatively high sound pressure has a higher sound level. Pressure was desired.
Further, in an electrostatic ultrasonic transducer, a high voltage of 200 V or more is required to be applied between the electrodes in order to obtain a high sound pressure output.

  The present invention has been made in view of such circumstances, and an electrostatic ultrasonic transducer that achieves a low power consumption capable of obtaining a high sound pressure with a voltage applied between electrodes lower than that of the prior art. An object of the present invention is to provide an ultrasonic speaker, an audio signal reproduction method, a super-directional acoustic system, and a display device using the same.

  In order to achieve the above object, an electrostatic ultrasonic transducer of the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the first electrode. And the electrode has an electrode layer that is sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and a DC bias is applied to the electrode layer. And the pair of electrodes has an electrode layer at a position located at a peripheral edge of the through hole, and the electrode layer of the diaphragm is disposed between the pair of electrodes and the electrode layer of the diaphragm. An AC signal is applied. Here, in the specification and claims of the present application, the through hole refers to a columnar space through which sound waves pierced in the thickness direction of the first electrode and the second electrode pass. To do.

In the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) of the present invention having the above-described configuration, the pair of electrodes is located at the peripheral portion of the through hole, which is a location necessary for applying an electrostatic force. An electrode layer is formed at the place to be.
Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced. Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  The electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the second electrode. The through-hole is disposed so as to form a pair and is sandwiched between a pair of electrodes including the first electrode and the second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode layer. The pair of electrodes is made of a non-conductive material, and the pair of electrodes has a step portion at a peripheral edge of the through hole, and faces the electrode layer of the vibration film. The step surface has an electrode layer, and an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane.

In the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) of the present invention having the above-described configuration, the base material of the pair of electrodes is a non-conductive material, and is formed at the peripheral portion of the through hole of the pair of electrodes. A step portion is provided, and an electrode layer is provided on the surface of the step portion facing the electrode layer of the vibrating membrane.
Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  The electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the second electrode. The through-hole is disposed so as to form a pair and is sandwiched between a pair of electrodes including the first electrode and the second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode layer. The base material of the pair of electrodes is a conductive material, and the pair of electrodes has a convex shape only in the electrode portion, the base material having the through hole, and the insertion hole A pair of electrodes and an electrode layer of the vibrating membrane, each of which is formed by fitting a convex electrode portion of the base material into the insertion hole of the nonconductive member. An AC signal is applied between the two.

In the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) of the present invention having the above-described configuration, the base material of the pair of electrodes is a conductive material, and each of the pair of electrodes is formed of the vibrating membrane. Only the electrode portion for causing electrostatic force to act so as to take a long distance from the electrode layer is formed in a convex shape, and includes the base material having a through hole, and a non-conductive member having an insertion hole, The convex electrode portion of the base material is integrally formed by being fitted into the insertion hole of the non-conductive member.
Thereby, the distance between the electrode layer of the pair of electrodes other than the portion where the electrostatic force acts on the pair of electrodes and the electrode layer of the vibration film can be increased, and the pair of electrodes and the vibration film The capacitance formed by the electrode layer can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  The electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the second electrode. The through-hole is disposed so as to form a pair and is sandwiched between a pair of electrodes including the first electrode and the second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode layer. The pair of electrodes includes an electrode layer at a position located inside the through hole, and an AC signal is applied between the pair of electrodes and the electrode layer of the diaphragm. It is characterized by. Here, in the specification and claims of the present application, the inside of the through hole refers to the inside of a columnar space through which sound waves pierced in the thickness direction of the first electrode and the second electrode pass. Shall point to.

In the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) of the present invention having the above-described configuration, the pair of electrodes is located inside a through hole, which is a place necessary for applying an electrostatic force. An electrode layer is provided at a location.
Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced. Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  The electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the second electrode. The through-hole is disposed so as to form a pair and is sandwiched between a pair of electrodes including the first electrode and the second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode layer. The pair of electrodes is made of a non-conductive material, and the pair of electrodes is located inside the through hole and faces the electrode layer of the diaphragm. An electrode layer is provided on the surface of the material portion, and an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane.

In the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) of the present invention having the above-described configuration, the base material of the pair of electrodes is a non-conductive material and is positioned inside the through hole of the pair of electrodes. And it has an electrode layer on the surface of the base material portion formed in a bridge shape so as to face the electrode layer of the vibrating membrane.
Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  The electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the second electrode. The through-hole is disposed so as to form a pair and is sandwiched between a pair of electrodes including the first electrode and the second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode layer. The base material of the pair of electrodes is a conductive material, and the pair of electrodes is formed in a bridge shape so that only the electrode portion is convex and faces the electrode layer of the vibration film. The base material and a non-conductive member having an insertion hole, wherein the convex electrode portion of the base material is fitted into the insertion hole of the non-conductive member, and the pair An AC signal is applied between the electrode of the electrode and the electrode layer of the vibrating membrane And features.

In the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) of the present invention having the above-described configuration, the base material of the pair of electrodes is a conductive material, and the pair of electrodes are electrodes of the vibrating membrane. The base material formed in a bridge shape so that only the electrode portion for applying electrostatic force is convex and faces the electrode layer of the vibrating membrane so as to increase the distance from the layer, and the insertion hole is vacant The non-conductive member is integrally formed by fitting the convex electrode portion of the base material into the insertion hole of the non-conductive member.
Thereby, the distance between the electrode layer of the pair of electrodes other than the portion where the electrostatic force acts on the pair of electrodes and the electrode layer of the vibration film can be increased, and the pair of electrodes and the vibration film The capacitance formed by the electrode layer can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  The ultrasonic speaker according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the through hole of the second electrode. Are arranged so as to form a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and have an electrode layer, and a vibrating membrane to which a DC bias voltage is applied to the electrode layer; The pair of electrodes includes an electrode layer at a position located at a peripheral portion of the through hole, and an electrostatic type in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane Ultrasonic transducer, signal source for generating signal wave of audible frequency band, carrier wave supply means for generating and outputting carrier wave of ultrasonic frequency band, and audible frequency for outputting carrier wave from signal source Modulation means for modulating the signal wave of the band, Serial electrostatic ultrasonic transducer, characterized in that it is driven by a modulated signal output from said modulation means is applied between the electrode layer of the vibrating film and the electrode.

  In the ultrasonic speaker according to the present invention having the above-described configuration, the pair of electrodes in the electrostatic ultrasonic transducer to be used is located at the peripheral portion of the through hole, which is a place necessary for applying an electrostatic force. Therefore, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced. Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven. That is, the same sound pressure as that of a conventional ultrasonic speaker can be generated with less energy, and the power consumption of the ultrasonic speaker can be reduced.

  Also, the audio signal reproduction method using the electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the first electrode. And the electrode has an electrode layer that is sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and a DC bias is applied to the electrode layer. A vibration membrane to which a voltage is applied, the pair of electrodes has an electrode layer at a position located at a peripheral portion of the through hole, and an alternating current is provided between the pair of electrodes and the electrode layer of the vibration membrane. A procedure for using an electrostatic ultrasonic transducer to which a signal is applied, generating a signal wave in an audible frequency band by a signal source, and generating and outputting a carrier wave in an ultrasonic frequency band by a carrier wave supply means And the carrier by the modulation means. A procedure for generating a modulated signal obtained by modulating a wave with a signal wave in the audible frequency band, and applying the modulated signal between the electrode and the electrode layer of the vibrating membrane, the electrostatic ultrasonic transducer And a driving procedure.

In the audio signal reproduction method of the electrostatic ultrasonic transducer including such a procedure, an audible frequency band signal wave is generated by the signal source, and an ultrasonic frequency band carrier wave is generated by the carrier wave supply source and output. Is done. Then, the carrier wave is modulated by the signal wave in the audible frequency band by the modulating means, and this modulated signal is applied between the electrode and the electrode layer of the vibrating membrane, thereby driving the electrostatic ultrasonic transducer.
As a result, the electrostatic ultrasonic transducer having the above-described configuration can reduce the voltage applied between the electrodes and increase the membrane vibration, and an acoustic signal having a sufficiently high sound pressure level to obtain a parametric array effect over a wide frequency band. Can be output and an audio signal can be reproduced.

  Moreover, the super-directional acoustic system of the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the through of the second electrode. A vibration that is disposed so as to make a pair with a hole and is sandwiched between a pair of electrodes composed of the first electrode and the second electrode and has an electrode layer, and a DC bias voltage is applied to the electrode layer The pair of electrodes includes an electrode layer at a position located at a peripheral portion of the through hole, and an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane. An ultrasonic speaker configured to use an electric ultrasonic transducer to reproduce a mid-high range audio signal among audio signals supplied from an acoustic source, and a low-frequency audio signal among audio signals supplied from the acoustic source A low-frequency speaker for reproducing signals Wherein the ultrasonic speaker reproduces an audio signal supplied from the sound source, and forming a virtual sound source into a sound wave reflecting surface near the screen or the like.

In the superdirective acoustic system configured as described above, the first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode, and the through hole of the second electrode Are arranged so as to form a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and have an electrode layer, and a vibrating membrane to which a DC bias voltage is applied to the electrode layer; The pair of electrodes includes an electrode layer at a position located at a peripheral portion of the through hole, and an electrostatic type in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane An ultrasonic speaker composed of an ultrasonic transducer is used. The ultrasonic speaker reproduces an audio signal in the middle / high range among the audio signals supplied from the acoustic source. Further, among the audio signals supplied from the acoustic source, the audio signal in the low frequency range is reproduced by a low tone reproduction speaker.
Therefore, it has sufficient sound pressure and wideband characteristics in the state that the voltage applied between the electrodes of the electrostatic ultrasonic transducer is lowered and the sound pressure characteristics are improved. It can be reproduced so as to be emitted from a virtual sound source formed near the sound wave reflecting surface such as a screen. Further, since the sound in the low frequency range is directly output from the low sound reproduction speaker provided in the sound system, the low frequency range can be reinforced and a more realistic sound field environment can be created.

  The display device of the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the through hole of the second electrode. A vibrating membrane arranged in a pair and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer The pair of electrodes has an electrode layer at a position located in a peripheral portion of the through hole, and an electrostatic super-type is applied to which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane. An ultrasonic speaker that includes an acoustic wave transducer and reproduces an audio signal in an audible frequency band from an audio signal supplied from an acoustic source, and a projection optical system that projects an image on a projection surface.

In the display device having the above configuration, the first electrode having the through hole, the second electrode having the through hole, the through hole of the first electrode, and the through hole of the second electrode are paired. And a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer, The pair of electrodes has an electrode layer at a position located at a peripheral portion of the through hole, and an electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane The ultrasonic speaker comprised including is used. And the audio | voice signal supplied from an acoustic source is reproduced | regenerated by this ultrasonic speaker.
As a result, the sound signal can be reproduced so as to be emitted from a virtual sound source formed in the vicinity of a sound wave reflection surface such as a screen with sufficient sound pressure and wide band characteristics in a state where the sound pressure characteristics are improved. For this reason, it is possible to easily control the reproduction range of the acoustic signal. In addition, directivity control of sound radiated from the ultrasonic speaker can be performed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Configuration example of electrostatic ultrasonic transducer according to the present invention]
FIG. 1 shows the configuration of an electrostatic ultrasonic transducer according to the first embodiment of the present invention. FIG. 1A shows a configuration of an electrostatic ultrasonic transducer, and FIG. 1B shows a plan view in which a part of the ultrasonic transducer is broken.

  In FIG. 1, the electrostatic ultrasonic transducer 1 according to the first embodiment of the present invention includes a fixed electrode 10A (first electrode) having a through hole 14 and a through hole that forms a pair with the through hole 14 of the fixed electrode 10A. A vibrating electrode 12 having an electrode layer 121 sandwiched between a fixed electrode 10B (second electrode) having a hole 14, a pair of fixed electrodes 10A and 10B including the fixed electrode 10A and the fixed electrode 10B, and a pair of fixed electrodes 10A 10B and a member (not shown) for holding the vibration film.

The vibration film 12 is formed of an insulator (insulating layer) 120, and an electrode layer 121 formed of a conductive material is formed in an intermediate portion of the insulator (insulating layer) 120. Specifically, the vibration film 12 is a metal film processed on one side of a polymer film (insulator) having a thickness of several microns and laminated with an adhesive. As the material of the polymer film, for example, poly (ethylene terephthalate) (PET), aramid, poly ester, poly (ethylene naphthalate) (PEN), poly (phenylene sulfide) (PPS) or the like is used. Al is the most common material for metallization, and Ni, Cu, SUS, Ti, etc. may be used.
The thickness of the metallization is preferably about 500 mm to 1500 mm.

These electrode layers 121 are applied with a DC bias voltage having a single polarity (in this embodiment, positive polarity, but may be either positive polarity or negative polarity) by the DC bias power supply 16. ing. A DC bias voltage of 50 to 300 V is applied to the metallized portion (electrode layer 121) of the vibrating membrane 12 from the circuit side.
Further, AC signals 18A and 18B, which are output from the signal source 18 and are mutually phase-inverted, are applied between the plurality of electrode layers 121 on the fixed electrode 10A and the fixed electrode 10B so as to be superimposed on the DC bias voltage. It is like that.

Further, the pair of fixed electrodes 10 </ b> A and 10 </ b> B have the same number and a plurality of through holes 14 at positions facing each other with the vibration film 12 therebetween. The base material 100 of the pair of fixed electrodes 10A, 10B is a non-conductive material, and the pair of electrodes 10A, 10B has a step portion at the peripheral edge of the through hole 14 of the pair of electrodes 10A, 10B. The electrode layer 101 is formed of a conductive material on the surface of the step portion facing the electrode layer 121 of the vibrating membrane.
As the non-conductive material that is a base material of the pair of fixed electrodes 10A and 10B, for example, glass, glass fiber material, plastic, hard rubber, or the like can be used. As the conductive material for forming the electrode layer 101, copper, aluminum, nickel, gold, silver, chromium, or the like can be used. An electrode layer 101 is formed on the stepped surface of the pair of electrodes 10A, 10B formed of a base material by a technique such as plating, vapor deposition, printing, or the like.

AC signals 18A and 18B whose phases are reversed from each other by the signal source 18 are applied between the fixed electrode 10A and the electrode layer 121 of the vibrating membrane 12 and between the fixed electrode 10B and the electrode layer 121 of the vibrating membrane 12. It is like that. An AC voltage (AC signal) of about 100 to 300 V is applied to the pair of fixed electrodes 10A and 10B from the circuit side. Reference numeral 16 denotes a DC bias power source.
A capacitor is formed by the fixed electrode 10A and the electrode layer 121, and the fixed electrode 10B and the electrode layer 121, respectively. Note that the configuration of a control unit that controls the signal source 18 and the DC bias power supply 16 and a storage unit that stores a table indicating the control characteristics of the control unit are omitted in FIG.

In the above-described configuration, in the ultrasonic transducer 1, a single polarity (positive polarity in the present embodiment) DC bias voltage is applied to the electrode layer 121 of the vibrating membrane 12 from the DC bias power supply 16. The AC signals 18A and 18B which are output from the signal source 18 and whose phases are inverted with each other are applied in a superimposed state.
On the other hand, between the fixed electrode 10A and the vibrating membrane 12, and between the fixed electrode 10B and the electrode layer 121 in the vibrating membrane 12, AC signals 18A and 18B having their phases inverted from each other are applied from the signal source 18, respectively.

As a result, in the positive half cycle of the AC signal 18A output from the signal source 18, since a positive voltage is applied to the fixed electrode 10A, the surface portion 12A not sandwiched between the fixed electrodes of the vibrating membrane 12 is applied to the surface portion 12A. The electrostatic repulsive force acts, and the surface portion 12A is pulled downward in FIG.
At this time, since the AC signal 18B has a negative cycle and a negative voltage is applied to the opposed fixed electrode 10B, the back surface portion 12B, which is the back surface side of the surface portion 12A of the vibrating membrane 12, An electrostatic attraction force acts, and the back surface portion 12B is pulled downward in FIG.

  Therefore, the film portion not sandwiched between the pair of fixed electrodes 10 </ b> A and 10 </ b> B of the vibration film 12 receives an electrostatic attractive force and an electrostatic repulsive force (electrostatic repulsive force) in the same direction. Similarly, in the negative half cycle of the AC signal output from the signal source 18, the electrostatic attracting force is applied to the upper surface portion 12 </ b> A of the vibrating membrane 12 in FIG. In FIG. 1, the electrostatic repulsive force acts upward, and the film portion that is not sandwiched between the pair of fixed electrodes 10A and 10B of the vibrating membrane 12 receives the electrostatic attractive force and the electrostatic repulsive force in the same direction. In this way, the direction in which the electrostatic force changes alternately while the vibrating membrane 12 receives the electrostatic attractive force and the electrostatic repulsive force in the same direction according to the change in the polarity of the AC signal. An acoustic signal having a sound pressure level sufficient to obtain a parametric array effect can be generated.

As described above, the electrostatic ultrasonic transducer 1 according to the embodiment of the present invention is called a push-pull type because the vibrating membrane 12 vibrates by receiving a force from the pair of fixed electrodes 10A and 10B. ing.
The electrostatic ultrasonic transducer 1 according to the embodiment of the present invention has a broadband property and a high sound frequency as compared with a conventional electrostatic ultrasonic transducer (Pull type) in which only an electrostatic attraction force acts on a vibrating membrane. Has the ability to satisfy pressure simultaneously.

  FIG. 11 shows frequency characteristics of the ultrasonic transducer according to the embodiment of the present invention. In the figure, a curve Q3 is a frequency characteristic of the ultrasonic transducer according to the present embodiment. As can be seen from the figure, a higher sound pressure level can be obtained over a wider frequency band than the frequency characteristics of the conventional broadband electrostatic ultrasonic transducer. Specifically, it can be seen that a sound pressure level of 120 dB or higher that provides a parametric effect in a frequency band of 20 kHz to 120 kHz can be obtained.

  In the ultrasonic transducer 1 according to the embodiment of the present invention, the thin vibration film 12 sandwiched between the pair of fixed electrodes 10A and 10B receives both the electrostatic attractive force and the electrostatic repulsive force. In addition, since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide band.

  Here, an example of the structure of the fixed electrode 10A (first electrode) and the fixed electrode 10B (second electrode) in FIG. 1, which is a feature of the present invention, is shown in FIG. 2A is a plan view of one side of the fixed electrodes 10A and 10B, FIG. 2B is a cross-sectional view taken along the line XX ′ in FIG. 2A, and FIG. 2C is in 2A. It is a figure which shows the other example of the cross-section by a XX 'cut line. In FIG. 2, for convenience of explanation, only seven through holes from which sound is emitted are shown. As shown in FIG. 2, the base material 100 of a non-conductive material is processed so as to form a step portion 100A at the peripheral portion of the through hole 14, and the electrode layer 101 is formed on the surface of the step portion 100A.

The processing method of the base material is appropriately selected depending on the material such as pressing, injection molding, machining, and the like. Conventionally, in addition to the electrode layer, the base material portion was also a conductive material, so the capacitance value of the capacitance formed between the pair of fixed electrodes 10A, 10B and the electrode layer 121 of the vibrating membrane 12 is large, Low power consumption was difficult.
In the first embodiment of the present invention, the base material is made of a non-conductive material, so that the electrode area can be reduced and the capacitance value of the capacitance can be reduced. As a result, power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  In the electrode structure shown in FIGS. 2A and 2B, when the diameter of the through hole 14 is φ0.75 mm, the outer diameter of the electrode layer 101 is φ1.5 mm, and the through hole pitch is 1.625 mm, By configuring the base material 100 with a non-conductive material, the capacitance value of the capacitance can be reduced by 20%. This means that the current is also reduced by 20%, and the current that flows when a voltage equivalent to the conventional voltage is applied between the pair of fixed electrodes 10A, 10B and the electrode layer 121 of the vibrating membrane 12 is the conventional example. As a result, the power consumption can be reduced to 80% of the conventional example.

  FIG. 2C shows another example of the cross-sectional structure of the electrode taken along the line X-X ′ in FIG. 2A (modified example of the first embodiment). Since the configuration other than the fixed electrode of the electrostatic ultrasonic transducer is basically the same as that in FIG. 1, this modification will be described with reference to FIGS. 1 and 2C. 4 is another example of an electrode structure that reduces the capacitance value of the capacitance formed between the pair of fixed electrodes 10A and 10B and the electrode layer 121 of the vibrating membrane 12 in the electrostatic ultrasonic transducer 1. In FIG. 2C, the base material 110 of the pair of fixed electrodes 10A, 10B is a conductive material unlike the case of FIGS. 1, 2A, 2B, and the pair of fixed electrodes 10A, 10B. Each has a through-hole 14 so that the distance from the electrode layer 121 of the vibrating membrane 12 is increased, and a base material 110 in which only an electrode portion 110A for applying an electrostatic force is formed in a convex shape, and an insertion hole 112 and a non-conductive member 111 which is free. Each of the pair of fixed electrodes 10 </ b> A and 10 </ b> B is integrally configured by fitting the convex electrode portion 110 </ b> A of the base material 110 into the insertion hole 112 of the nonconductive member 111. Other configurations are the same as those in FIGS. 1 and 2A.

When the electrode structure shown in FIG. 2C is adopted with the above configuration, the electrode layers (electrode portions) of the pair of fixed electrodes 10A and 10B other than the portion where the electrostatic force acts on the pair of fixed electrodes 10A and 10B. 110A) and the vibrating membrane electrode layer 121 (see FIG. 1) can be increased, and the capacitance formed by the pair of fixed electrodes and the vibrating membrane electrode layer can be reduced. be able to.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  Next, an electrostatic ultrasonic transducer according to a second embodiment of the present invention will be described. The electrostatic ultrasonic transducer according to the second embodiment of the present invention is basically the same as that of the first embodiment except for the structure of the pair of fixed electrodes 10A and 10B in FIG. The electrostatic ultrasonic transducer according to the second embodiment will be described with reference to FIG. FIG. 3 shows the structure of the fixed electrode of the electrostatic ultrasonic transducer according to the second embodiment of the present invention. 3A is a plan view of one side of the fixed electrodes 10A and 10B, FIG. 3B is a cross-sectional view taken along the line YY ′ in FIG. 3A, and FIG. 3C is FIG. It is a figure which shows the other example of the cross-sectional structure by the YY 'cutting line in.

In FIG. 1 and FIGS. 3A and 3B, the base material 200 of the pair of fixed electrodes 10A and 10B is a non-conductive material and is located inside the through hole 214 of the pair of fixed electrodes 10A and 10B. An electrode layer 201 is formed on the surface of a base material portion 200 </ b> A formed in a bridge shape so as to face the electrode layer 121 of the vibration film 12.
Thereby, the electrode layer area of the pair of fixed electrodes in the electrostatic ultrasonic transducer can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  FIG. 3C shows another example of the cross-sectional structure of the electrode taken along the line Y-Y ′ in FIG. 3A (modified example of the second embodiment). 1 and 3C, the base material 210 of the pair of fixed electrodes 10A and 10B in the electrostatic ultrasonic transducer 1 is a conductive material, and each of the pair of fixed electrodes 10A and 10B is a vibrating membrane. The base material 210 is formed in a bridge shape so that only the electrode portion 210 </ b> A for applying an electrostatic force is convex and faces the electrode layer 121 of the vibrating membrane 12 so as to increase the distance from the 12 electrode layers 121. And the non-conductive member 211 having the insertion hole 212 open, and the convex electrode portion 210A of the base material 210 is integrally formed by being fitted into the insertion hole 212 of the non-conductive member 211. .

Thereby, the distance between the electrode layer (electrode portion 210A) of the pair of electrodes other than the portion where the electrostatic force acts on the pair of fixed electrodes 10A and 10B and the electrode layer 121 of the vibrating membrane 12 can be increased. In addition, the capacitance formed by the pair of electrodes 10A and 10B and the electrode layer 121 of the vibrating membrane 12 can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

As described above, according to the electrostatic ultrasonic transducer (Push-Pull ultrasonic transducer) according to the embodiment of the present invention, it is necessary to cause an electrostatic force to act on a pair of electrodes (fixed electrodes). An electrode layer is formed at a peripheral part of the through hole or a part located inside the through hole.
Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced.
Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven.

  In the embodiment of FIGS. 3A, 3B, and 3C, an electrode layer (electrode portion) is formed on a non-conductive material or a base material of a conductive material. You may comprise so that a through-hole may be bridged with a bridge-shaped electrode, without providing the base material for comprising. In this case, the same effect as that of the second embodiment can be obtained.

[Configuration Example of Ultrasonic Speaker According to the Present Invention]
Next, the configuration of the ultrasonic speaker according to the embodiment of the present invention is shown in FIG. The ultrasonic speaker according to the present embodiment uses the above-described electrostatic ultrasonic transducer (see FIG. 1) according to the present embodiment as the ultrasonic transducer 55.

In FIG. 4, an ultrasonic speaker 50 according to the present embodiment generates and outputs an audio frequency wave oscillation source (signal source) 51 that generates a signal wave in the audio frequency band and a carrier wave in the ultrasonic frequency band. A carrier wave oscillation source (carrier wave supply means) 52, a modulator (modulation means) 53, a power amplifier 54, and an ultrasonic transducer (electrostatic ultrasonic transducer) 55 are included.
The modulator 53 modulates the carrier wave output from the carrier wave oscillation source 52 with the signal wave of the audio frequency band output from the audio frequency wave oscillation source 51, and supplies the modulated wave to the ultrasonic transducer 55 via the power amplifier 54. To do.

  In the above configuration, the carrier wave in the ultrasonic frequency band output from the carrier wave oscillation source 52 by the signal wave output from the audible frequency wave oscillation source 51 is modulated by the modulator 53 and the modulated signal amplified by the power amplifier 54 is used. The ultrasonic transducer 55 is driven. As a result, the modulated signal is converted into a sound wave of a finite amplitude level by the ultrasonic transducer 55, and this sound wave is radiated into the medium (in the air), and the signal sound in the original audible frequency band due to the nonlinear effect of the medium (air). Is self-regenerating.

  In other words, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse portions of the air appear prominently in the process of propagation of the modulated ultrasonic waves, and the dense portions have high sound speed and sparseness. Since the sound speed of such a portion is slow, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic frequency band), and a signal wave (signal sound) in an audible frequency band is reproduced.

As described above, when a high sound pressure broadband property is ensured, it can be used as a speaker for various purposes. Ultrasound is strongly attenuated in the air and attenuates in proportion to the square of its frequency. Therefore, when the carrier frequency (ultrasonic wave) is low, it is possible to provide an ultrasonic speaker in which the sound reaches far as a beam with little attenuation.
On the contrary, if the carrier frequency is high, the attenuation is severe, so that the parametric array effect does not occur sufficiently and an ultrasonic speaker in which the sound spreads can be provided. These are very effective functions because the same ultrasonic speaker can be used according to the application.

  Also, dogs who often live with humans as pets can listen to sounds up to 40 kHz, and cats can listen to sounds up to 100 kHz, so if you use a carrier frequency higher than that, there will be no effect on the pet. There are also advantages. In any case, the fact that it can be used at various frequencies brings many advantages.

The ultrasonic speaker according to the embodiment of the present invention can generate an acoustic signal having a sufficiently high sound pressure level to obtain a parametric array effect over a wide frequency band.
Further, in the ultrasonic speaker of the present invention having the above-described configuration, the peripheral portion or the inside of the through hole, which is a place necessary for applying an electrostatic force, to the pair of electrodes in the electrostatic ultrasonic transducer to be used Since the electrode layer is formed at a position located in the region, the electrode layer area of the pair of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane can be reduced. be able to. Therefore, when an electrostatic ultrasonic transducer is used as a capacitive load, the load impedance increases and flows between each electrode of the pair of electrodes and the electrode layer of the vibrating membrane in the electrostatic ultrasonic transducer. The current is reduced, so that the voltage can be lowered and the power consumption can be reduced when the electrostatic ultrasonic transducer is driven. That is, the same sound pressure as that of a conventional ultrasonic speaker can be generated with less energy, and the power consumption of the ultrasonic speaker can be reduced.

[Description of configuration example of superdirective acoustic system according to the present invention]
Next, the electrostatic ultrasonic transducer of the present invention, that is, a first electrode having a through hole, a second electrode having a through hole paired with the through hole of the first electrode, and the first electrode A pair of electrodes composed of a first electrode and a second electrode and having an electrode layer, and a vibration film to which a DC bias voltage is applied to the electrode layer, and a peripheral portion of a through hole of the pair of electrodes or An electrode layer is formed at a location located inside, and a Push-Pull type electrostatic ultrasonic transducer is used in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane. A super-directional acoustic system using an ultrasonic speaker will be described.

Hereinafter, a projector will be described as an example of a superdirective acoustic system according to the present invention. Note that the super-directional acoustic system according to the present invention is not limited to a projector and can be widely applied to display devices that reproduce audio and video.
FIG. 5 shows a use state of the projector according to the present invention. As shown in the figure, the projector 301 is installed behind the viewer 303, projects an image on a screen 302 installed in front of the viewer 303, and uses the ultrasonic speaker mounted on the projector 301 to screen 302. A virtual sound source is formed on the projection plane and the sound is reproduced.

An external configuration of the projector 301 is shown in FIG. The projector 301 includes a projector main body 320 including a projection optical system that projects an image on a projection surface such as a screen, and ultrasonic transducers 324A and 324B that can oscillate sound waves in an ultrasonic frequency band, and is supplied from an acoustic source. And an ultrasonic speaker that reproduces a signal sound in an audible frequency band from a sound signal. In the present embodiment, in order to reproduce a stereo audio signal, ultrasonic transducers 324A and 324B constituting ultrasonic speakers are mounted on the left and right with a projector lens 331 constituting a projection optical system interposed therebetween in the projector body.
Further, a low-pitched sound reproduction speaker 323 is provided on the bottom surface of the projector main body 320. Reference numeral 325 denotes a height adjusting screw for adjusting the height of the projector main body 320, and reference numeral 326 denotes an exhaust port for the air cooling fan.

  Further, the projector 301 uses the Push-Pull electrostatic ultrasonic transducer according to the present invention as an ultrasonic transducer constituting the ultrasonic speaker, and a wide frequency band acoustic signal (sound wave in the ultrasonic frequency band). Can oscillate at high sound pressure. For this reason, by conventionally changing the frequency of the carrier wave to control the spatial reproduction range of the reproduction signal in the audible frequency band, an acoustic effect that can be obtained in a stereo surround system or 5.1ch surround system is conventionally required. Thus, it is possible to realize a projector that can be realized without requiring a large-scale sound system and is easy to carry.

  Next, an electrical configuration of the projector 301 is shown in FIG. The projector 301 includes an operation input unit 310, a reproduction range setting unit 312, a reproduction range control processing unit 313, an audio / video signal reproduction unit 314, a carrier wave oscillation source 316, modulators 318A and 318B, power amplifiers 322A and 322B, and static An ultrasonic speaker comprising electric ultrasonic transducers 324A and 324B, a high-pass filter 317A and 317B, a low-pass filter 319, an adder 321, a power amplifier 322C, a low-frequency sound reproduction speaker 323, and a projector main body 320 are provided. is doing. The electrostatic ultrasonic transducers 324A and 324B are Push-Pull electrostatic ultrasonic transducers according to the present invention.

  The projector main body 320 includes a video generation unit 332 that generates a video and a projection optical system 333 that projects the generated video on a projection surface. The projector 301 is configured by integrating an ultrasonic speaker and a bass reproduction speaker 323 and a projector main body 320.

  The operation input unit 310 has various function keys including a numeric keypad, numeric keys, and a power key for turning the power on and off. The reproduction range setting unit 312 can input data specifying a reproduction range of a reproduction signal (signal sound) by a user operating the operation input unit 310 with a key. The frequency of the carrier wave that defines the reproduction range of the signal is set and held. The reproduction range of the reproduction signal is set by designating a distance that the reproduction signal reaches in the radial axis direction from the sound wave emission surfaces of the ultrasonic transducers 324A and 324B.

The reproduction range setting unit 312 can set the frequency of the carrier wave by the control signal output from the audio / video signal reproduction unit 314 according to the video content.
Further, the reproduction range control processing unit 313 refers to the setting contents of the reproduction range setting unit 312 and changes the frequency of the carrier wave generated by the carrier wave oscillation source 316 so as to be within the set reproduction range. It has a function of controlling the oscillation source 316.
For example, when the distance corresponding to the carrier wave frequency of 50 kHz is set as the internal information of the reproduction range setting unit 312, the carrier wave oscillation source 316 is controlled to oscillate at 50 kHz.

The reproduction range control processing unit 313 stores in advance a table indicating the relationship between the distance that the reproduction signal reaches in the radial axis direction from the sound wave emitting surfaces of the ultrasonic transducers 324A and 324B that define the reproduction range and the frequency of the carrier wave. It has a storage part. The data in this table is obtained by actually measuring the relationship between the frequency of the carrier wave and the reach distance of the reproduction signal.
The reproduction range control processing unit 313 obtains the frequency of the carrier wave corresponding to the distance information set with reference to the table based on the setting content of the reproduction range setting unit 312 and oscillates the carrier wave so as to be the frequency. Control the source 316.

The audio / video signal reproduction unit 314 is, for example, a DVD player that uses a DVD as a video medium. Among the reproduced audio signals, the R channel audio signal is sent to the modulator 318A via the high-pass filter 317A. The signal is output to the modulator 318B via the high-pass filter 317B, and the video signal is output to the video generation unit 332 of the projector main body 320.
The R channel audio signal and the L channel audio signal output from the audio / video signal reproduction unit 314 are combined by the adder 321 and input to the power amplifier 322C via the low-pass filter 319. Yes. The audio / video signal reproduction unit 314 corresponds to an acoustic source.

The high-pass filters 317A and 317B have characteristics that allow only the frequency components in the middle and high frequencies in the R-channel and L-channel audio signals to pass, and the low-pass filters are low-frequency filters in the R-channel and L-channel audio signals. It has the characteristic of passing only the frequency component of the sound range.
Accordingly, among the R channel and L channel audio signals, the mid and high range audio signals are reproduced by the ultrasonic transducers 324A and 324B, respectively, and among the R channel and L channel audio signals, the low range audio signals are low frequencies. It is reproduced by the reproduction speaker 323.

  The audio / video signal reproduction unit 314 is not limited to a DVD player, and may be a reproduction device that reproduces a video signal input from the outside. In addition, the audio / video signal reproduction unit 314 instructs the reproduction range setting unit 312 to dynamically change the reproduction range of the reproduced sound in order to produce an acoustic effect corresponding to the reproduced video scene. Has a function of outputting a control signal.

The carrier wave oscillation source 316 has a function of generating a carrier wave having a frequency in the ultrasonic frequency band designated by the reproduction range setting unit 312 and outputting the carrier wave to the modulators 318A and 318B.
The modulators 318A and 318B AM modulate the carrier wave supplied from the carrier wave oscillation source 316 with the audio signal in the audible frequency band output from the audio / video signal reproduction unit 314, and each of the modulated signals is a power amplifier 322A. , 322B.

  The ultrasonic transducers 324A and 324B are driven by modulation signals output from the modulators 318A and 318B via the power amplifiers 322A and 322B, respectively, and convert the modulation signals into sound waves of a finite amplitude level and radiate them into the medium. And has a function of reproducing a signal sound (reproduction signal) in an audible frequency band.

The video generation unit 332 includes a display such as a liquid crystal display and a plasma display panel (PDP), a drive circuit that drives the display based on a video signal output from the audio / video signal reproduction unit 314, and the like. A video obtained from the video signal output from the audio / video signal reproduction unit 314 is generated.
The projection optical system 333 has a function of projecting an image displayed on the display onto a projection surface such as a screen installed in front of the projector main body 320.

  Next, the operation of the projector 301 having the above configuration will be described. First, data (distance information) instructing the reproduction range of the reproduction signal is set in the reproduction range setting unit 312 from the operation input unit 310 by the user's key operation, and a reproduction instruction is given to the audio / video signal reproduction unit 314.

As a result, distance information defining the reproduction range is set in the reproduction range setting unit 312, and the reproduction range control processing unit 313 takes in the distance information set in the reproduction range setting unit 312 and stores it in the built-in storage unit. The carrier wave oscillation source 316 is controlled so as to obtain the frequency of the carrier wave corresponding to the set distance information with reference to the set table and to generate the carrier wave of the frequency.
As a result, the carrier wave oscillation source 316 generates a carrier wave having a frequency corresponding to the distance information set in the reproduction range setting unit 312 and outputs the carrier wave to the modulators 318A and 318B.

  On the other hand, the audio / video signal reproduction unit 314 outputs the R channel audio signal of the reproduced audio signal to the modulator 318A via the high pass filter 317A, and the L channel audio signal to the modulator 318B via the high pass filter 317B. In addition, the R channel audio signal and the L channel audio signal are output to the adder 321, and the video signal is output to the video generation unit 332 of the projector main body 320.

Therefore, the high-pass filter 317A inputs the mid-high range audio signal of the R channel audio signal to the modulator 318, and the high-pass filter 317B converts the mid-high range audio signal of the L channel audio signal to the modulator 318B. Is input.
The R channel audio signal and the L channel audio signal are combined by an adder 321, and a low frequency audio signal of the R channel audio signal and the L channel audio signal is supplied to a power amplifier 322 C by a low pass filter 319. Entered.

The video generation unit 332 generates a video by driving the display based on the input video signal, and displays the video. The image displayed on the display is projected onto a projection surface, for example, the screen 302 shown in FIG. 5 by the projection optical system 333.
On the other hand, the modulator 318A AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the R channel audio signal output from the high-pass filter 317A, and outputs it to the power amplifier 322A. .
Further, the modulator 318B AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the L channel audio signal output from the high pass filter 317B, and outputs the result to the power amplifier 322B. .

The modulated signals amplified by the power amplifiers 322A and 322B are applied between the upper electrode 10A and the lower electrode 10B (see FIG. 1) of the ultrasonic transducers 324A and 324B, respectively, and the modulated signals have a finite amplitude level. The sound wave (acoustic signal) is converted and radiated to the medium (in the air), and the ultrasonic transducer 324A reproduces the mid-high range audio signal in the R channel audio signal, and the ultrasonic transducer 324B An audio signal in the middle and high range in the L channel audio signal is reproduced.
In addition, the low frequency sound signal in the R channel and the L channel amplified by the power amplifier 322C is reproduced by the low sound reproduction speaker 323.

  As described above, in the propagation of ultrasonic waves radiated into the medium (in the air) by the ultrasonic transducer, the sound speed increases at a portion where the sound pressure is high and the sound speed is slow at a portion where the sound pressure is low. Become. As a result, waveform distortion occurs.

  When a signal (carrier wave) in the radiated ultrasonic band is modulated (AM modulation) with a signal in the audible frequency band, the signal wave in the audible frequency band used for modulation is super It is formed so as to be self-demodulated separately from the carrier wave in the sonic frequency band. At this time, the spread of the reproduction signal becomes a beam shape due to the characteristics of ultrasonic waves, and the sound is reproduced only in a specific direction completely different from that of a normal speaker.

  The beam-like reproduction signal output from the ultrasonic transducer 324 constituting the ultrasonic speaker is radiated toward the projection surface (screen) on which the image is projected by the projection optical system 333, and is reflected and diffused by the projection surface. In this case, until the reproduction signal is separated from the carrier wave in the radial axis direction (normal direction) from the sound wave emitting surface of the ultrasonic transducer 324 according to the frequency of the carrier wave set in the reproduction range setting unit 312. And the beam width (beam divergence angle) of the carrier wave are different, the reproduction range changes.

  FIG. 8 shows a state in which a reproduction signal is reproduced by an ultrasonic speaker including the ultrasonic transducers 324A and 324B in the projector 301. In the projector 301, when the ultrasonic transducer is driven by the modulation signal obtained by modulating the carrier wave with the audio signal, if the carrier frequency set by the reproduction range setting unit 312 is low, the sound wave emitting surface of the ultrasonic transducer 324 To the direction of the radiation axis (the distance until the reproduction signal is separated from the carrier wave in the normal direction of the sound wave radiation surface, that is, the distance to the reproduction point becomes long.

  Accordingly, the reproduced beam of the reproduced signal in the audible frequency band reaches the projection plane (screen) 302 without being relatively expanded, and is reflected on the projection plane 302 in this state. Therefore, the reproduction range is as shown in FIG. Becomes a audible range A indicated by a dotted arrow, and a reproduction signal (reproduced sound) can be heard only in a relatively narrow and narrow range from the projection plane 302.

  On the other hand, when the carrier frequency set by the reproduction range setting unit 312 is higher than the case described above, the sound wave radiated from the sound wave emission surface of the ultrasonic transducer 324 is narrower than when the carrier frequency is low. However, the distance until the reproduction signal is separated from the carrier wave in the radial direction (normal direction of the acoustic wave emission surface) from the sound wave emission surface of the ultrasonic transducer 324, that is, the distance to the reproduction point is shortened.

  Therefore, the reproduced reproduction signal beam in the audible frequency band spreads before reaching the projection plane 302 and reaches the projection plane 302, and is reflected on the projection plane 302 in this state. 8, an audible range B indicated by a solid arrow indicates that a reproduction signal (reproduction sound) can be heard only in a relatively close and wide range from the projection plane 302.

As described above, the projector according to the present invention uses the ultrasonic speaker using the Push-Pull type or Pull type electrostatic ultrasonic transducer according to the present invention, and the acoustic signal is transmitted with sufficient sound pressure. It has a broadband characteristic and can be reproduced so as to be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen. For this reason, the reproduction range can be easily controlled. Further, as described above for the electrostatic ultrasonic transducer, the vibration region of the vibration film is divided into a plurality of blocks, and an alternating current is applied between the electrode layer of the vibration film and each block of the vibration electrode pattern. It is possible to control the directivity of the sound emitted from the ultrasonic speaker by controlling the phase of the signal so that a predetermined phase difference is provided between adjacent blocks.
Although the embodiments of the present invention have been described above, the electrostatic ultrasonic transducer and the ultrasonic speaker of the present invention are not limited to the above illustrated examples, and do not depart from the gist of the present invention. Of course, various changes can be made.

  The ultrasonic transducer according to the embodiment of the present invention can be used for various sensors, for example, a distance measuring sensor, and as described above, a sound source for a directional speaker and an ideal impulse signal generation source. Etc. are available. It is also useful for superdirective acoustic systems and display devices such as projectors.

The figure which shows the structure of the electrostatic ultrasonic transducer which concerns on embodiment of this invention. The top view and sectional drawing which show an example of the structure of the fixed electrode in FIG. Sectional drawing which shows the other example of the structure of the fixed electrode in FIG. The figure which shows the structural example of an ultrasonic speaker. FIG. 3 is a diagram illustrating a usage state of the projector according to the embodiment of the invention. FIG. 5 is a diagram showing an external configuration of the projector shown in FIG. 4. FIG. 5 is a block diagram showing an electrical configuration of the projector shown in FIG. 4. Explanatory drawing which shows the reproduction | regeneration state of the reproduction signal by an ultrasonic transducer. The figure which shows the structure of the conventional resonance type ultrasonic transducer. The figure which shows the specific structure of the conventional electrostatic broadband oscillation type ultrasonic transducer. The figure which showed the frequency characteristic of the electrostatic ultrasonic transducer which concerns on embodiment of this invention with the frequency characteristic of the conventional ultrasonic transducer. The figure which shows the structural example of the conventional electrostatic ultrasonic transducer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrostatic ultrasonic transducer, 10A, 10B ... Fixed electrode, 12 ... Vibration film, 12A ... Front surface part, 12B ... Back surface part, 14 ... Through-hole, 16 ... DC bias power supply, 18 ... Signal source, 50 ... Super Sound wave speaker, 51 ... audible frequency wave oscillation source, 52 ... carrier wave signal source, 53 ... modulator, 54 ... power amplifier, 55 ... ultrasonic transducer, 120 ... insulator, 121 ... electrode layer, 301 ... projector, 302 ... Screen (projection plane), 303 ... viewer, 310 ... operation input unit, 312 ... reproduction range setting unit, 313 ... reproduction range control processing unit, 314 ... audio / video signal reproduction unit, 316 ... carrier wave oscillation source, 317A, 317B: High pass filter (HPF), 318A, 318B ... Modulator, 319 ... Low pass filter (LPF), 320 ... Projector body, 3 1 ... adder, 322A, 322B, 322C ... power amplifier, 323 ... low-frequency sound reproducing speaker, 324A, 324B ... electrostatic ultrasonic transducer, 331 ... projector lens, 332 ... image generator, 333 ... projection optical system.

Claims (12)

A first electrode having a through hole, a second electrode having a transmural throughbore, with the through hole of the said through holes before Symbol first electrode and the second electrode are arranged in pairs and an electrode layer with sandwiched pair of electrodes consisting of the first electrode and the second electrode, and a vibrating membrane to which a DC bias voltage to the electrode layer is applied, prior Symbol pair of electrodes the base material is a non-conductive material, prior Symbol pair of electrodes has a step portion on the periphery of the through hole, have a electrode layer on the stepped portion surface facing the electrode layer of the vibrating film and the electrostatic ultrasonic transducer AC device signals is applied between the electrode layer of the vibrating film and before Symbol pair of electrodes,
A signal source for generating a signal wave in an audible frequency band;
A carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band;
Modulation means for modulating the carrier wave with an audible frequency band signal wave output from the signal source;
Have
The ultrasonic speaker according to claim 1, wherein the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means applied between the electrode and the electrode layer of the vibrating membrane .   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a non-conductive material, and the pair of electrodes has a step portion at a peripheral portion of the through hole, and has an electrode layer on the step portion surface of the vibrating membrane facing the electrode layer, and the pair of electrodes And using an electrostatic ultrasonic transducer in which an AC signal is applied between the electrode and the electrode layer of the vibrating membrane,
  Generating a signal wave of an audible frequency band by a signal source;
  A procedure for generating and outputting a carrier wave in the ultrasonic frequency band by the carrier wave supply means;
  Generating a modulated signal obtained by modulating the carrier wave with a signal wave in the audible frequency band by a modulation means;
  A procedure for driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode and the electrode layer of the vibrating membrane;
  A method for reproducing an audio signal using an electrostatic ultrasonic transducer.   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a non-conductive material, and the pair of electrodes has a step portion at a peripheral portion of the through hole, and has an electrode layer on the step portion surface of the vibrating membrane facing the electrode layer, and the pair of electrodes It is composed of an electrostatic ultrasonic transducer in which an AC signal is applied between the electrode of the diaphragm and the electrode layer of the vibrating membrane, and reproduces an audio signal in the mid-high range among audio signals supplied from an acoustic source An ultrasonic speaker,
  A low-pitched sound reproduction speaker that reproduces a low-frequency sound signal among the sound signals supplied from the acoustic source;
  Have
  A superdirective acoustic system, wherein an audio signal supplied from the acoustic source is reproduced by the ultrasonic speaker, and a virtual sound source is formed in the vicinity of a sound wave reflecting surface such as a screen. A first electrode having a through hole, a second electrode having a transmural throughbore, with the through hole of the said through holes before Symbol first electrode and the second electrode are arranged in pairs and an electrode layer with sandwiched pair of electrodes consisting of the first electrode and the second electrode, and a vibrating membrane to which a DC bias voltage to the electrode layer is applied, prior Symbol pair of electrodes the base material is a conductive material, before Symbol pair of electrodes, only the electrode portion has a convex shape, the said base material having a through hole consists of a non-conductive member vacant insertion hole , is constituted by the electrode portion of the convex shape of the base material is fitted in the insertion hole of said non-conductive member, an AC signal between the electrode layer before Symbol pair of electrodes and the vibrating film is applied and electrostatic ultrasonic transducer that will be,
A signal source for generating a signal wave in an audible frequency band;
A carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band;
Modulation means for modulating the carrier wave with an audible frequency band signal wave output from the signal source;
Have
The ultrasonic speaker according to claim 1, wherein the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means applied between the electrode and the electrode layer of the vibrating membrane .   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a conductive material, and the pair of electrodes has a convex shape only in the electrode portion, and is composed of the base material having the through hole and a non-conductive member having an insertion hole, The electrostatic superstructure is configured by fitting a convex electrode portion into the insertion hole of the non-conductive member, and applying an AC signal between the pair of electrodes and the electrode layer of the vibrating membrane. While using a sonic transducer,
  Generating a signal wave of an audible frequency band by a signal source;
  A procedure for generating and outputting a carrier wave in the ultrasonic frequency band by the carrier wave supply means;
  Generating a modulated signal obtained by modulating the carrier wave with a signal wave in the audible frequency band by a modulation means;
  A procedure for driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode and the electrode layer of the vibrating membrane;
  A method for reproducing an audio signal using an electrostatic ultrasonic transducer.   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a conductive material, and the pair of electrodes has a convex shape only in the electrode portion, and is composed of the base material having the through hole and a non-conductive member having an insertion hole, The electrostatic superstructure is configured by fitting a convex electrode portion into the insertion hole of the non-conductive member, and applying an AC signal between the pair of electrodes and the electrode layer of the vibrating membrane. It is composed of acoustic transducers and is an audio signal source from an acoustic source. An ultrasonic speaker for reproducing an audio signal of the mid-high range,
  A low-pitched sound reproduction speaker that reproduces a low-frequency sound signal among the sound signals supplied from the acoustic source;
  Have
  A superdirective acoustic system, wherein an audio signal supplied from the acoustic source is reproduced by the ultrasonic speaker, and a virtual sound source is formed in the vicinity of a sound wave reflecting surface such as a screen. A first electrode having a through hole, a second electrode having a transmural throughbore, with the through hole of the said through holes before Symbol first electrode and the second electrode are arranged in pairs and an electrode layer with sandwiched pair of electrodes consisting of the first electrode and the second electrode, and a vibrating membrane to which a DC bias voltage to the electrode layer is applied, prior Symbol pair of electrodes the base material is a non-conductive material, prior Symbol pair of electrodes, the electrodes on the surface of the base portion to be bridged to the bridge-shaped inside of the through hole so as to face the electrode layer before Symbol vibration film have a layer, and the electrostatic ultrasonic transducer AC device signals is applied between the electrode layer of the vibrating film and before Symbol pair of electrodes,
A signal source for generating a signal wave in an audible frequency band;
A carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band;
Modulation means for modulating the carrier wave with an audible frequency band signal wave output from the signal source;
Have
The ultrasonic speaker according to claim 1, wherein the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means applied between the electrode and the electrode layer of the vibrating membrane .   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a non-conductive material, and the pair of electrodes has an electrode layer on a surface of a base material portion bridged in a bridge shape inside the through hole so as to face the electrode layer of the vibrating membrane, While using an electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane,
  Generating a signal wave of an audible frequency band by a signal source;
  A procedure for generating and outputting a carrier wave in the ultrasonic frequency band by the carrier wave supply means;
  Generating a modulated signal obtained by modulating the carrier wave with a signal wave in the audible frequency band by a modulation means;
  A procedure for driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode and the electrode layer of the vibrating membrane;
  A method for reproducing an audio signal using an electrostatic ultrasonic transducer.   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a non-conductive material, and the pair of electrodes has an electrode layer on a surface of a base material portion bridged in a bridge shape inside the through hole so as to face the electrode layer of the vibrating membrane, An audio signal in the middle and high range among audio signals supplied from an acoustic source, which is configured using an electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane. An ultrasonic speaker for reproducing,
  A low-pitched sound reproduction speaker that reproduces a low-frequency sound signal among the sound signals supplied from the acoustic source;
  Have
  A superdirective acoustic system, wherein an audio signal supplied from the acoustic source is reproduced by the ultrasonic speaker, and a virtual sound source is formed in the vicinity of a sound wave reflecting surface such as a screen. A first electrode having a through hole, a second electrode having a transmural throughbore, with the through hole of the said through holes before Symbol first electrode and the second electrode are arranged in pairs and an electrode layer with sandwiched pair of electrodes consisting of the first electrode and the second electrode, and a vibrating membrane to which a DC bias voltage to the electrode layer is applied, prior Symbol pair of electrodes the base material is a conductive material, before Symbol pair of electrodes, and the base material in which only electrode portions are formed like a bridge so as to be opposed to the electrode layer of the convex a and the vibrating membrane, the insertion hole vacant consists of a non-conductive member, said electrode portion of the convex shape of the base material is formed by being fitted into the insertion hole of said non-conductive member, the electrodes of the previous SL pair of electrodes and the vibrating film and electrostatic ultrasonic transducer AC device signals is applied between the layers,
A signal source for generating a signal wave in an audible frequency band;
A carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band;
Modulation means for modulating the carrier wave with an audible frequency band signal wave output from the signal source;
Have
The ultrasonic speaker according to claim 1, wherein the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means applied between the electrode and the electrode layer of the vibrating membrane .   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a conductive material, and the pair of electrodes is a non-conductive material in which only the electrode portion has a convex shape and is formed in a bridge shape so as to face the electrode layer of the vibrating membrane, and an insertion hole is provided. A convex electrode portion of the base material is fitted into the insertion hole of the non-conductive member, and an alternating current is formed between the pair of electrodes and the electrode layer of the vibrating membrane. Using an electrostatic ultrasonic transducer to which the signal is applied,
  Generating a signal wave of an audible frequency band by a signal source;
  A procedure for generating and outputting a carrier wave in the ultrasonic frequency band by the carrier wave supply means;
  Generating a modulated signal obtained by modulating the carrier wave with a signal wave in the audible frequency band by a modulation means;
  A procedure for driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode and the electrode layer of the vibrating membrane;
  A method for reproducing an audio signal using an electrostatic ultrasonic transducer.   The first electrode having a through hole, the second electrode having a through hole, the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and A base material for the pair of electrodes, including a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having an electrode layer, and a DC bias voltage is applied to the electrode layer. Is a conductive material, and the pair of electrodes is a non-conductive material in which only the electrode portion has a convex shape and is formed in a bridge shape so as to face the electrode layer of the vibrating membrane, and an insertion hole is provided. A convex electrode portion of the base material is fitted into the insertion hole of the non-conductive member, and an alternating current is formed between the pair of electrodes and the electrode layer of the vibrating membrane. Consists of electrostatic ultrasonic transducers to which signals are applied, An ultrasonic speaker for reproducing an audio signal of the middle-to-high frequency range of the audio signal supplied from the scan,
  A low-pitched sound reproduction speaker that reproduces a low-frequency sound signal among the sound signals supplied from the acoustic source;
  Have
  A superdirective acoustic system, wherein an audio signal supplied from the acoustic source is reproduced by the ultrasonic speaker, and a virtual sound source is formed in the vicinity of a sound wave reflecting surface such as a screen.

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