JP2008244964A - Electrostatic ultrasonic transducer, electrostatic transducer, ultrasonic speaker, speaker device, audio signal reproduction method using electrostatic ultrasonic transducer, directional acoustic system, and display device - Google Patents

Abstract

An electrostatic ultrasonic transducer capable of increasing the sound pressure level of a radiated sound wave by causing a through hole provided in a fixed electrode to act as a resonance tube and increasing the sound pressure level over a wide band.
A first electrode having a through hole, a second electrode having a through hole, and the through hole of the first electrode and the through hole of the second electrode make a pair. And a vibration film sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, a DC bias voltage is applied to the vibration film, and An AC signal, which is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band, is applied to the electrode, and a through hole provided in at least one of the pair of electrodes is used as a resonance tube It is characterized by having a length of at least two kinds of resonance tubes.
[Selection] Figure 3

Description

  The present invention provides an electrostatic ultrasonic transducer, electrostatic transducer, ultrasonic speaker, speaker device, and audio signal reproduction method using an electrostatic ultrasonic transducer capable of increasing the sound pressure level of radiated sound waves over a wide band. The present invention relates to a directional acoustic system and a display device.

  The electrostatic transducer used for an ultrasonic speaker or the like includes an electrostatic transducer called a pull type shown in FIG. 14 (see, for example, Patent Document 1), and an electrostatic type called a push-pull type shown in FIG. There is a transducer (see, for example, Patent Document 2).

  The pull-type electrostatic transducer shown in the cross-sectional view of FIG. 14A includes a vibration film 31, a fixed electrode 51 formed of a conductor having a convex portion 51C in close contact with the vibration film 31, and a DC bias power source. 32 and a signal source for generating an AC signal 33. As shown in FIG. 14B, the vibration film 31 is formed by sandwiching a vibration electrode layer 31A, which is a conductive layer, with a dielectric film (insulating layer) 32B.

  A constant DC bias voltage is always applied between the vibrating electrode layer 31A and the fixed electrode 51 by a DC bias power source 32 that can adjust the voltage, and the convex portion of the fixed electrode 51 is generated by the electrostatic force generated by this electric field. The vibration electrode layer 31A is adsorbed by 51C, and is in close contact except for the cavity portion (electrostatic force generation portion) 52 formed between the vibration electrode layer 31A and the fixed electrode 51. The fixed electrode 51 is formed with a through hole 54 that communicates from the cavity 52 to the outside. The through hole 54 functions as a vent and also functions as a resonance tube (acoustic resonance tube) that improves the sound pressure level of the emitted sound wave.

  In the above configuration, when a DC bias voltage is applied between the vibrating electrode layer 31 </ b> A of the vibrating film 31 and the fixed electrode 51 by the DC bias power supply 32, the vibrating electrode layer 31 </ b> A of the vibrating film 31 is protruded from the fixed electrode 51. Adsorbed to 51C. In this state, the AC signal 33 is applied between the vibrating electrode layer 31A and the fixed electrode 51 so as to be superimposed on the DC bias voltage, whereby the electrode portions of the vibrating electrode layer 31A and the fixed electrode 51 (the vibrating portion of the vibrating membrane) are applied. Electrostatic force acts between the surface 53 and the vibration film 31, and the vibration film 31 is driven by the AC signal 33 and vibrates.

  FIG. 14C shows the vibration state of the vibration film 31 when the negative (−) side output of the AC signal 33 is applied to the vibration electrode layer 31A. FIG. 14D shows the AC signal. The vibration state of the vibration film 31 when 33 positive (+) side output is applied is shown.

  In the state shown in FIG. 14C, the potential difference between the fixed electrode 51 and the vibrating electrode layer 31A becomes large, and a strong electrostatic force (attraction force) acts between the fixed electrode 51 and the vibrating electrode layer 31A. The central portion of the vibrating electrode layer 31 </ b> A is drawn toward the fixed electrode 51. In the case of the state shown in FIG. 14D, the potential difference between the fixed electrode 51 and the vibrating electrode layer 31A is reduced, and the electrostatic force (attraction force) between the fixed electrode 51 and the vibrating electrode layer 31A is weakened. The central portion of the vibrating electrode layer 31A is pulled back in the direction opposite to the fixed electrode 51 by an elastic restoring force. In this way, the vibrating electrode layer 31A vibrates according to the AC signal 33 and outputs sound waves.

  As described above, the electrostatic transducer shown in FIG. 14 is called a pull-type electrostatic transducer because the vibrating membrane receives an electrostatic attractive force from one direction. The advantages of this pull type electrostatic transducer are that the opening area is large and that it is easy to obtain sound pressure, and the disadvantage is that the distortion of the output waveform is large. (Because it vibrates with electrostatic attractive force and elastic restoring force).

  A push-pull electrostatic transducer shown in FIG. 15A includes a vibrating membrane 31 having a vibrating electrode layer 31A, a front-side fixed electrode 51A provided to face each surface of the vibrating membrane 31, and It has a pair of fixed electrode which consists of back side fixed electrode 51B. As shown in FIG. 15B, the vibration film 31 is formed so that a vibration electrode layer 31A, which is a conductive layer, is sandwiched between dielectric films 31B.

  The front-side fixed electrode 51A that sandwiches the vibration film 31 is provided with a plurality of through holes 54A, and the back-side fixed electrode 51B is located at a position facing the through-hole 54A provided in the front-side fixed electrode 51A. A through hole 54B having the same shape is provided. The through hole 54 functions as a vent and also functions as a resonance tube that improves the sound pressure level of the radiated sound wave.

  The front-side fixed electrode 51A and the back-side fixed electrode 51B are in close contact with each other except for the cavity portions (electrostatic force generating portions) 52A and 52B formed between the vibrating electrode layer 31A and the fixed electrodes 51A and 51B. The vibrating membrane 31 and the fixed electrodes 51A and 51B are configured so as to face each other through the hollow portions 52A and 52B.

  Further, the DC bias power source 32 and the power source for applying a DC bias voltage to the vibrating electrode layer 31A, the AC signals 33A and 33B are signals applied between the front side fixed electrode 51A and the rear side fixed electrode 51B. It is. With the above configuration, the AC signals 33A and 33B having the same amplitude and the phases reversed from each other with respect to the center tap are applied to the front side fixed electrode 51A and the back side fixed electrode 51B. As a result, an electrostatic force acts between the vibrating electrode layer 31A and the electrode portions (surfaces facing the vibrating portion of the vibrating membrane) 53A and 53B of the fixed electrodes 51A and 51B, and the vibrating membrane 31 receives the AC signals 33A and 33B. Driven and vibrated.

  FIG. 15A shows the amplitude state of the vibrating membrane 31 when the AC signal is zero (0), and the vibrating membrane 31 is neutral (the middle between the front-side fixed electrode 51A and the rear-side fixed electrode 51B). In position.

  FIG. 15C is a diagram illustrating a vibration state of the vibrating membrane 31 when a positive voltage of an AC signal is applied to the front fixed electrode 51A and a negative voltage of the AC signal is applied to the rear fixed electrode 51B. Yes, the central portion of the vibrating electrode layer 31A of the vibrating membrane 31 has a back surface due to an electrostatic force (suction force) between the back side fixed electrode 51B and an electrostatic force (repulsive force) between the front side fixed electrode 51A. It is attracted in the direction of the side fixed electrode 51B.

FIG. 15D is a diagram illustrating a vibration state of the vibrating membrane 31 when a negative voltage of an AC signal is applied to the front fixed electrode 51A and a positive voltage of the AC signal is applied to the rear fixed electrode 51B. Yes, the central portion of the vibrating electrode layer 31A of the vibrating membrane 31 is on the front side due to the electrostatic force (attraction force) between the front side fixed electrode 51A and the electrostatic force (repulsive force) between the rear side fixed electrode 51B. It is drawn in the direction of the fixed electrode 51A.
In this way, the vibrating membrane 31 vibrates in accordance with the AC signal and outputs a sound wave, and the sound wave generated by the vibrating membrane 31 is released to the outside through the through holes 54A and 54B provided in the fixed electrodes 51A and 51B. .

As described above, the electrostatic transducer shown in FIG. 15 is called a push-pull electrostatic transducer because the vibrating membrane receives an electrostatic force from both the upper and lower fixed electrodes and vibrates. The advantage of this push-pull type electrostatic transducer is that the distortion of the output waveform is small (because the electrostatic force acts symmetrically between positive and negative).
JP 2005-117103 A JP 2005-354472 A

  In the electrostatic transducer described above, the through hole provided in the fixed electrode acts as a resonance tube to improve the sound pressure level of the emitted sound wave. However, in the conventional configuration, since the thickness of the fixed electrode, that is, the length of the acoustic tube is constant, the sound pressure level in the acoustic resonance frequency band is particularly improved. For this reason, there is a problem that it is difficult to perform a design for leveling the sound pressure to increase the sound pressure level in a wide band, or to make the sound pressure level peaks at a plurality of frequencies.

  The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a resonance tube (acoustic resonance tube) with a through hole (vent hole) provided in a fixed electrode in an electrostatic transducer or the like. Electrostatic ultrasonic transducers, electrostatic transducers, ultrasonic speakers, speaker devices, electrostatic ultrasonic waves that can increase the sound pressure level of radiated sound waves and increase the sound pressure level over a wide band An object is to provide an audio signal reproduction method using a transducer, a directional acoustic system, and a display device.

The present invention has been made to solve the above problems, and an electrostatic transducer according to the present invention includes a first electrode having a through hole, a second electrode having a through hole, and the first electrode. The through hole of the second electrode and the through hole of the second electrode are arranged so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode and have a conductive layer A DC bias voltage is applied to the vibrating membrane, and an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes. Alternatively, the DC bias voltage is applied to the pair of electrodes, the AC signal is applied to the vibrating membrane, and a through hole provided in at least one electrode of the pair of electrodes serves as a resonance tube. Let And having a length of at least two types of resonance tubes.
In the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, in the pair of electrodes arranged to face both surfaces of the vibrating membrane, a through hole provided in at least one of the electrodes is formed as a resonance tube (acoustic resonance tube). And at least two types of resonance tube lengths.
As a result, in an electrostatic ultrasonic transducer, the opening through which air is provided in the electrode acts as an acoustic resonance tube, and the sound pressure of the emitted sound wave is leveled, and the sound pressure level is increased in a wide band. Can do. Furthermore, since it has the length of two or more types of resonance tubes, it is possible to arbitrarily perform an optimization design such as generating a sound pressure level peak at a plurality of frequencies.

In the electrostatic ultrasonic transducer according to the present invention, the thickness of at least one of the pair of electrodes is changed stepwise, and the length of the resonance tube is gradually increased or decreased according to the step change. It is characterized by being set to gradually decrease.
In the electrostatic ultrasonic transducer of the present invention configured as described above, the length of the resonance tube (acoustic resonance tube) is set so as to gradually increase or decrease in accordance with the stepwise change in the thickness of the electrode.
Thus, by arranging a plurality of resonance tubes having different tube lengths over the entire electrode surface, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased in a wide band.

In the electrostatic ultrasonic transducer according to the present invention, at least one of the pair of electrodes has an inclined structure or a curved structure, and the length of the resonance tube is adjusted according to the inclined structure or the curved structure. It is characterized by being set to gradually increase or decrease.
In the electrostatic transducer of the present invention having the above-described configuration, the length of the resonance tube (acoustic resonance tube) is gradually increased or adjusted in accordance with the inclined structure or curved surface structure of one side of the electrode in at least one of the pair of electrodes. Set to decrease gradually.
Thus, by arranging a plurality of resonance tubes having different tube lengths over the entire electrode surface, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased in a wide band.

In addition, the electrostatic ultrasonic transducer of the present invention, 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 vibrating membrane disposed in a pair with a hole and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, and is provided on the pair of electrodes The ultrasonic wave emitted from each through hole on the back surface of the electrostatic transducer having the through hole functioning as a resonance tube and having at least two types of resonance tube lengths is applied to the electrostatic ultrasonic wave. An acoustic reflection plate that reflects on the front side of the transducer is installed.
In the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, in a pair of electrodes arranged to face both sides of the vibration film, a through hole provided in at least one of the electrodes acts as a resonance tube, and An acoustic system configured to have at least two types of tube lengths and to reflect ultrasonic waves radiated from the through holes on the back surface of the electrostatic ultrasonic transducer to the front surface side of the electrostatic ultrasonic transducer. Install a reflector.
As a result, in the electrostatic ultrasonic transducer, the opening through which air is provided in the electrode can act as a resonance tube, the sound pressure of the radiated sound wave can be leveled, and the sound pressure level can be increased over a wide band. . Further, by providing the acoustic reflector, it is possible to effectively use the ultrasonic waves emitted from both surfaces of the electrostatic ultrasonic transducer.

In the electrostatic ultrasonic transducer according to the present invention, the thickness of at least one of the pair of electrodes is changed stepwise, and the length of the resonance tube is gradually increased or decreased according to the step change. It is characterized by being set to gradually decrease.
In the electrostatic transducer according to the present invention having the above-described configuration, the through hole provided in the electrode acts as a resonance tube, and the thickness of at least one of the pair of electrodes is changed stepwise, The length of the resonance tube is gradually increased or decreased in accordance with the change in the frequency, and the ultrasonic waves radiated from the through-holes on the back surface of the electrostatic transducer are applied to the back surface of the electrostatic transducer. Install an acoustic reflector on the front side.
As a result, in the electrostatic ultrasonic transducer, the opening through which air is provided in the electrode can act as an acoustic resonance tube, and the sound pressure level of the radiated sound wave can be leveled to increase the sound pressure level in a wide band. Further, by providing the acoustic reflector, it is possible to effectively use the ultrasonic waves emitted from both surfaces of the electrostatic ultrasonic transducer.

In the electrostatic ultrasonic transducer according to the present invention, at least one of the pair of electrodes may have an inclined structure or a curved structure, and the length of the resonance tube may be adjusted to the inclined structure or the curved structure. Is set to gradually increase or decrease.
In the electrostatic transducer according to the present invention having the above-described configuration, in at least one of the pair of electrodes, a through hole provided in the electrode acts as a resonance tube, and at least one of the pair of electrodes One side of the resonance tube is formed as an inclined structure or a curved surface structure, and the length of the resonance tube is gradually increased or decreased in accordance with the inclined structure or the curved surface structure. An acoustic reflector is installed to reflect the ultrasonic wave radiated from the hole to the front side of the electrostatic ultrasonic transducer.
As a result, in the electrostatic ultrasonic transducer, the opening portion through which air is provided in the electrode can act as a resonance tube, and the sound pressure level of the radiated sound wave can be leveled to increase the sound pressure level in a wide band. Further, by providing the acoustic reflector, it is possible to effectively use the ultrasonic waves emitted from both surfaces of the electrostatic ultrasonic transducer.

The electrostatic 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 through hole of the second electrode. And a vibration film sandwiched between a pair of electrodes including the first electrode and the second electrode and having a conductive layer, and a DC bias voltage is applied to the vibration film. And an AC signal is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes, and the AC signal is applied to the vibrating membrane, and A through hole provided in at least one of the electrodes acts as a resonance tube, and has at least two types of resonance tube lengths.
In the electrostatic transducer of the present invention having the above-described configuration, in a pair of electrodes arranged to face both sides of the vibration membrane, a through hole provided in at least one of the electrodes acts as a resonance tube, and at least 2 It is configured to have more than one type of resonance tube length.
As a result, in the electrostatic transducer, the opening portion through which air is provided in the electrode can act as an acoustic resonance tube, and the sound pressure of the radiated sound wave can be leveled to increase the sound pressure level in a wide band. Furthermore, since it has the length of two or more types of resonance tubes, it is possible to arbitrarily perform an optimization design such as generating a sound pressure level peak at a plurality of frequencies.

In the electrostatic transducer according to the present invention, the thickness of at least one of the pair of electrodes is changed stepwise, and the length of the resonance tube is gradually increased or decreased in accordance with the step change. It is characterized by being set to.
In the electrostatic transducer of the present invention having the above-described configuration, the length of the resonance tube is set so as to gradually increase or decrease in accordance with the stepwise change in the thickness of the electrode.
Thus, by arranging a plurality of resonance tubes having different tube lengths over the entire electrode surface, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased in a wide band.

In the electrostatic transducer according to the present invention, one surface of at least one of the pair of electrodes may have an inclined structure or a curved structure, and the length of the resonance tube may be gradually increased according to the inclined structure or the curved structure. It is characterized by being set to gradually decrease.
In the electrostatic transducer of the present invention having the above-described configuration, the length of the resonance tube is set so as to gradually increase or decrease in accordance with the inclined structure or curved surface structure of one side of the electrode in at least one of the pair of electrodes. To do.
Thus, by arranging a plurality of resonance tubes having different tube lengths on the entire electrode surface, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased over a wide band.

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. And a vibrating membrane sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, and at least one electrode of the pair of electrodes An electrostatic ultrasonic transducer having a through-hole provided in the tube as a resonance tube and having at least two types of resonance tube lengths, a signal source for generating a signal wave in an audible frequency band, and an ultrasonic frequency A carrier wave supply means for generating and outputting a carrier wave of a band, and a modulation means for generating a modulated wave by modulating the carrier wave with a signal wave of the audible frequency band, and a DC bias voltage is provided to the diaphragm And said Driving the electrostatic ultrasonic transducer by applying the modulation wave to a pair of electrodes or applying the DC bias voltage to the pair of electrodes and applying the modulation wave to the vibrating membrane; It is characterized by.
In the ultrasonic speaker of the present invention having the above-described configuration, an ultrasonic speaker that modulates a carrier wave (carrier wave) in an ultrasonic frequency band with a signal wave in an audible frequency band and drives an electrostatic ultrasonic transducer with the modulated wave. The electrostatic ultrasonic transducer has a pair of electrodes arranged opposite to both surfaces of the vibrating membrane, wherein a through hole provided in at least one of the electrodes acts as a resonance tube, and at least two or more types The length of the resonance tube is set.
Thereby, it is possible to realize an ultrasonic speaker having a wide band and an increased sound pressure level.

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. And a vibrating membrane sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, the penetrating holes provided in the pair of electrodes An ultrasonic wave radiated from each through-hole on the back surface of the electrostatic transducer having a hole acting as a resonance tube and having at least two types of resonance tube lengths is applied to the back surface of the electrostatic ultrasonic transducer. An electrostatic ultrasonic transducer having an acoustic reflector that reflects on the front side, a signal source that generates an audible frequency band signal wave, a carrier wave supply means that generates and outputs a carrier wave in the ultrasonic frequency band, and The carrier wave Modulation means for generating a modulated wave by modulating with a signal wave in the audible frequency band, applying a DC bias voltage to the vibrating membrane and applying the modulated wave to the pair of electrodes, or The electrostatic ultrasonic transducer is driven by applying a DC bias voltage to the pair of electrodes and applying the modulated wave to the vibrating membrane.
In the ultrasonic speaker of the present invention having the above-described configuration, an ultrasonic speaker that modulates a carrier wave (carrier wave) in an ultrasonic frequency band with a signal wave in an audible frequency band and drives an electrostatic ultrasonic transducer with the modulated wave. The electrostatic ultrasonic transducer has a pair of electrodes arranged opposite to both surfaces of the vibrating membrane, wherein a through hole provided in at least one of the electrodes acts as a resonance tube, and at least two or more types The acoustic reflection is configured to have the length of the resonance tube, and reflects the ultrasonic wave radiated from each through-hole on the back surface of the electrostatic ultrasonic transducer to the front surface side of the electrostatic ultrasonic transducer. Install the board.
Thereby, it is possible to realize an ultrasonic speaker having a wide band and an increased sound pressure level. In addition, sound waves radiated from both surfaces of the electrostatic ultrasonic transducer can be used effectively.

The speaker 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 disposed in a pair and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, and at least one electrode of the pair of electrodes An electrostatic transducer having at least two types of resonance tube lengths, a signal source for generating an audible frequency band signal wave, and an output from the signal source And an amplifier that amplifies the signal wave to be reproduced, and the electrostatic transducer is driven by an output signal of the amplifier to reproduce a signal in an audible frequency band.
In the speaker device of the present invention having the above-described configuration, at least one of the pair of electrodes arranged to face both surfaces of the vibrating membrane of the electrostatic transducer by driving the electrostatic transducer with a signal wave in an audible frequency band, A through hole provided in one of the electrodes is made to act as a resonance tube, and has at least two types of resonance tube lengths.
As a result, it is possible to realize a loudspeaker device with a high sound pressure level in a wide band.

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. A vibrating membrane disposed in a pair with the through hole of the two electrodes and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, An electrostatic ultrasonic transducer having a through hole provided in at least one of the pair of electrodes as a resonance tube and having at least two types of resonance tube lengths is used, and an audible frequency is determined by a signal source. A procedure for generating a signal wave in a band, a procedure for generating and outputting a carrier wave in an ultrasonic frequency band by a carrier wave supply means, and a modulated wave obtained by modulating the carrier wave with a signal wave in the audible frequency band. Applying a DC bias voltage to the vibrating membrane and applying the modulation wave to the pair of electrodes, or applying the DC bias voltage to the pair of electrodes, and applying the modulation wave to the pair of electrodes. And a procedure for driving the electrostatic ultrasonic transducer by applying it to the vibration film.
In the audio signal reproducing method using the electrostatic ultrasonic transducer of the present invention including the above procedure, a carrier wave (carrier wave) in the ultrasonic frequency band is modulated by a signal wave in the audible frequency band, and the electrostatic ultrasonic wave is generated by the modulated wave. When driving a transducer, as the electrostatic ultrasonic transducer, in a pair of electrodes arranged to face both sides of the vibrating membrane, a through hole provided in at least one of the electrodes acts as a resonance tube, In addition, one having at least two types of resonance tube lengths is used.
As a result, when the electrostatic ultrasonic transducer is driven, the sound pressure of the emitted sound wave can be leveled and the sound pressure level can be increased over a wide band.

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. A vibrating membrane disposed in a pair with the through hole of the two electrodes and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, Ultrasonic waves radiated from the through holes on the back surface are applied to the back surface of the electrostatic transducer having the through holes provided in the pair of electrodes acting as a resonance tube and having at least two types of resonance tube lengths. A procedure for generating an audible frequency band signal wave by a signal source using a capacitive ultrasonic transducer having an acoustic reflector that reflects on the front side of the electrostatic ultrasonic transducer, and a carrier wave supply means A procedure for generating and outputting a carrier wave in an ultrasonic frequency band, a procedure for generating a modulated wave obtained by modulating the carrier wave with the signal wave, a DC bias voltage is applied to the vibrating membrane, and the pair of Applying the modulation wave to the electrodes, or applying the DC bias voltage to the pair of electrodes, and driving the electrostatic ultrasonic transducer by applying the modulation wave to the vibrating membrane; It is characterized by including.
In the audio signal reproducing method using the electrostatic ultrasonic transducer of the present invention including the above procedure, a carrier wave (carrier wave) in the ultrasonic frequency band is modulated by a signal wave in the audible frequency band, and the electrostatic ultrasonic wave is generated by the modulated wave. When driving a transducer, as the electrostatic ultrasonic transducer, in a pair of electrodes arranged to face both sides of the vibrating membrane, a through hole provided in at least one of the electrodes acts as a resonance tube, And at least two types of resonance tube lengths, and the ultrasonic wave radiated from each through-hole on the back surface of the electrostatic ultrasonic transducer is transmitted to the front surface of the electrostatic ultrasonic transducer. Use an acoustic reflector that reflects to the side.
As a result, when the electrostatic ultrasonic transducer is driven, the sound pressure of the emitted sound wave can be leveled and the sound pressure level can be increased over a wide band. Further, by providing the acoustic reflector, it is possible to effectively use the ultrasonic waves emitted from both surfaces of the electrostatic ultrasonic transducer.

Further, the 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 hole of the second electrode. And a vibration film sandwiched between a pair of electrodes including the first electrode and the second electrode and having a conductive layer, and a DC bias voltage is applied to the vibration film. And an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes. And the AC signal is applied to the vibrating membrane, and a through hole provided in at least one of the pair of electrodes is made to act as a resonance tube, and the length of at least two types of resonance tubes is increased. Electrostatic type An ultrasonic speaker configured to use an acoustic transducer to reproduce an audio signal in the first range among audio signals supplied from an acoustic source, and an audio signal in the second range among audio signals supplied from the acoustic source A low-frequency sound reproduction speaker for reproducing the sound signal supplied from an acoustic source by the ultrasonic speaker to form a virtual sound source in the vicinity of a sound wave reflection surface such as a screen.
In the directional acoustic system of the present invention having the above-described configuration, an electrostatic ultrasonic transducer is used for the ultrasonic speaker, and a pair of electrodes disposed opposite to both surfaces of the vibration film of the electrostatic ultrasonic transducer. In this embodiment, the through hole provided in at least one of the electrodes is made to act as a resonance tube, and has at least two types of resonance tube lengths. Then, a sound signal in the middle and high sound range (first sound range) among the sound signals supplied from the acoustic source is reproduced by an ultrasonic speaker using this electrostatic ultrasonic transducer. In addition, a sound signal in the low sound range (second sound range) among the sound signals supplied from the acoustic source is reproduced by a low sound reproduction speaker .
Thereby, in the electrostatic transducer used for the ultrasonic speaker, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased over a wide band. Therefore, an ultrasonic speaker using an electrostatic transducer with high efficiency and high sound quality can be realized. As a result, it is possible to reproduce the mid-high range sound so that it can be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen with sufficient sound pressure and wide band characteristics. 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.

Further, the 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 hole of the second electrode. And a vibration film sandwiched between a pair of electrodes including the first electrode and the second electrode and having a conductive layer, and a DC bias voltage is applied to the vibration film. And an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes. And the AC signal is applied to the vibrating membrane, the through-holes provided in the pair of electrodes act as a resonance tube, and the electrostatic transducer has at least two types of resonance tube lengths. Back of The electrostatic ultrasonic transducer is provided with an acoustic reflector provided with an acoustic reflector that reflects the ultrasonic wave radiated from each through hole on the back surface to the front side of the electrostatic ultrasonic transducer, and is supplied from an acoustic source. An ultrasonic speaker that reproduces an audio signal in the first range among the audio signals to be reproduced, and a speaker for low-frequency reproduction that reproduces an audio signal in the second range among the audio signals supplied from the acoustic source, An audio signal supplied from an acoustic source by the ultrasonic speaker is reproduced, and a virtual sound source is formed in the vicinity of a sound wave reflecting surface such as a screen.
In the directional acoustic system of the present invention having the above-described configuration, an electrostatic ultrasonic transducer is used for the ultrasonic speaker, and a pair of electrodes disposed opposite to both surfaces of the vibration film of the electrostatic ultrasonic transducer. The through hole provided in at least one of the electrodes acts as a resonance tube and has at least two types of resonance tube lengths, and the back surface of the electrostatic ultrasonic transducer An acoustic reflector is installed to reflect the ultrasonic wave radiated from each through hole to the front side of the electrostatic ultrasonic transducer. Then, a sound signal in the middle and high sound range (first sound range) among the sound signals supplied from the acoustic source is reproduced by an ultrasonic speaker using this electrostatic ultrasonic transducer. In addition, among the audio signals supplied from the acoustic source, an audio signal in a low sound range (second sound range) is reproduced by a low sound reproduction speaker.
Thereby, in the electrostatic transducer used for the ultrasonic speaker, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased over a wide band. In addition, it is possible to effectively use ultrasonic waves emitted from both surfaces of the electrostatic ultrasonic transducer by the acoustic reflector. Therefore, an ultrasonic speaker using an electrostatic transducer with high efficiency and high sound quality can be realized. As a result, it is possible to reproduce the mid-high range sound so that it can be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen with sufficient sound pressure and wide band characteristics. 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 disposed in a pair and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, and a DC bias voltage is applied to the vibrating membrane And an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes, The AC signal is applied to the vibrating membrane, and a through hole provided in at least one of the pair of electrodes is made to act as a resonance tube, and at least two types of resonance tube lengths are provided. Electric ultrasonic tiger It is configured to include a Sudeyusa, characterized in that it comprises an ultrasonic speaker for reproducing an acoustic signal in the audible frequency band from the audio signal supplied from the sound source, and a projection optical system for projecting an image onto a projection surface.
In the display device of the present invention having the above-described configuration, an electrostatic ultrasonic transducer is used for the ultrasonic speaker, and a pair of electrodes arranged to face both surfaces of the vibration film of the electrostatic ultrasonic transducer, A through hole provided in at least one of the electrodes is made to act as a resonance tube, and has at least two types of resonance tube lengths. And the audio | voice signal supplied from an acoustic source is reproduced | regenerated using the ultrasonic speaker comprised with this electrostatic type ultrasonic transducer.
Thereby, in the electrostatic ultrasonic transducer used for the ultrasonic speaker, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased in a wide band. Therefore, an ultrasonic speaker using an electrostatic ultrasonic transducer with high efficiency and high sound quality can be realized. As a result, an acoustic signal can be reproduced with a sufficient sound pressure and wideband characteristics 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, it is possible to easily control the reproduction range of the acoustic signal.

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 disposed in a pair and sandwiched between a pair of electrodes composed of the first electrode and the second electrode and having a conductive layer, and a DC bias voltage is applied to the vibrating membrane And an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes, The back surface of the electrostatic transducer having the AC signal applied to the vibrating membrane, the through holes provided in the pair of electrodes acting as a resonance tube, and having at least two types of resonance tube lengths On the back From an audio signal supplied from an acoustic source, including an electrostatic ultrasonic transducer provided with an acoustic reflector that reflects the ultrasonic wave radiated from each through hole to the front side of the electrostatic ultrasonic transducer An ultrasonic speaker that reproduces a signal sound in an audible frequency band and a projection optical system that projects an image on a projection surface are provided.
In the display device of the present invention having the above-described configuration, an electrostatic ultrasonic transducer is used for the ultrasonic speaker, and a pair of electrodes arranged to face both surfaces of the vibration film of the electrostatic ultrasonic transducer, A through hole provided in at least one of the electrodes is made to act as a resonance tube, and has at least two types of resonance tube lengths. An acoustic reflector is installed to reflect the ultrasonic wave radiated from the through hole to the front side of the electrostatic ultrasonic transducer. And the audio | voice signal supplied from an acoustic source is reproduced | regenerated using the ultrasonic speaker comprised with this electrostatic type ultrasonic transducer.
Thereby, in the electrostatic ultrasonic transducer used for the ultrasonic speaker, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased in a wide band. Therefore, an ultrasonic speaker using an electrostatic ultrasonic transducer with high efficiency and high sound quality can be realized. As a result, an acoustic signal can be reproduced with a sufficient sound pressure and wideband characteristics 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, it is possible to easily control the reproduction range of the acoustic signal.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment]
In the electrostatic transducer and the electrostatic ultrasonic transducer according to the present invention, the opening of the fixed electrode that passes through the air acts as an acoustic resonance tube, and these are used as different tube lengths to widen and optimize the emission sound wave.

FIG. 1 is a diagram showing the configuration of the lower fixed electrode (second electrode) of the electrostatic transducer according to the first embodiment of the present invention. The configuration of the upper fixed electrode (first electrode) is also the same.
As shown in FIG. 1A, the lower fixed electrode 11 of the electrostatic transducer of the present invention penetrates a conductive material of a plate-like metal (for example, aluminum alloy, stainless steel, etc.) whose thickness changes stepwise. Make a hole. In the example shown in FIG. 1, through holes 12A and 12B having different tube lengths are provided for regions A and B having different thicknesses of the lower fixed electrode 11. In addition, although the example shown in FIG. 1 has shown the example which provided only one through-hole for every area | region where plate | board thickness differs, the several through-hole is actually arranged. For example, they are arranged in accordance with the shape of the lower fixed electrode 11 such as series, parallel, circular, or honeycomb.

  Then, as shown in FIG. 1B, on the surface of the fixed electrode 11 on the plane side (the side facing the vibrating membrane), the electrode portion (including the through hole 12) covered with an epoxy insulating layer is covered. An epoxy insulating layer 13 is applied so as to provide an exposed electrode surface 14). For example, it is formed by pattern-printing an epoxy insulating layer on the surface of the lower fixed electrode 11 (side facing the vibration film) in the manner of resist printing on a printed board.

  FIG. 2 shows the configuration of the vibrating membrane. The vibrating membrane 31 has a configuration in which a vibrating electrode layer 31A (for example, an aluminum thin film formed by sputtering) is sandwiched between insulating dielectric films 31B.

FIG. 3 is a diagram showing the configuration of the electrostatic transducer according to the first embodiment of the present invention.
As shown in FIG. 3A, in the electrostatic transducer, the surface of the epoxy insulating layer 23 of the upper fixed electrode 21 is in close contact with the surface of the vibration film 31, and the surface of the epoxy insulating layer 13 of the lower fixed electrode 11 is It is configured to be in close contact with the surface of the vibration film 31. A cavity is provided between the electrode part 24 and the vibration film 31, and a cavity is provided between the electrode part 14 and the vibration film 31. The portion of the vibration film 31 facing the cavity (the portion not pressed by the epoxy insulating layer of the fixed electrode) becomes the vibration portion of the vibration film 31.

  With such a configuration, the vibrating membrane 31 and the electrode portion 14 of the lower fixed electrode 11 are opposed to each other through the cavity, and the electrostatic force is provided between the vibrating electrode layer 31 </ b> A of the vibrating membrane 31 and the electrode portion 14. Works. In addition, the vibrating membrane 31 and the electrode portion 24 of the upper fixed electrode 21 are opposed to each other through the cavity portion, and an electrostatic force acts between the vibrating electrode layer 31 </ b> A of the vibrating membrane 31 and the electrode portion 24.

  Then, a DC bias voltage is applied to the vibrating electrode layer 31A of the vibrating membrane 31 by the voltage variable DC bias power source 32, and AC signals 33A and 33B are applied to the upper fixed electrode 21 and the lower fixed electrode 11. As a result, AC signals 33A and 33B having the same amplitude and opposite phases are applied to the upper fixed electrode 21 and the lower fixed electrode 11. Therefore, an electrostatic force acts between the vibrating electrode layer 31A of the vibrating membrane 31 and the electrode portions (electrostatic force generating surfaces) 14 and 24 of the fixed electrodes 11 and 21, and the vibrating membrane 31 is driven by AC signals 33A and 33B. And vibrate. (This operation will be described in more detail in FIG. 4).

  As shown in FIG. 3B, a DC bias voltage is applied to the upper fixed electrode 21 and the lower fixed electrode 11 by the DC bias power supplies 32A and 32B, and an AC signal 33 is applied to the vibration film 31. Also good.

  FIG. 4 is a diagram for explaining the operation of the electrostatic transducer of the present invention. The operating principle of the electrostatic transducer of the present invention is basically the same as that of the conventional push-pull electrostatic transducer shown in FIG. 13, but the configuration of the through hole (resonance tube) in the fixed electrode is different.

  FIG. 4A shows the amplitude state of the vibrating membrane 31 when the AC signal is zero (0), and the vibrating membrane 31 is in a neutral position (middle of the upper fixed electrode 21 and the lower fixed electrode 11). It is in.

  FIG. 4B is a diagram illustrating a vibration state of the vibrating membrane 31 when a positive voltage of an AC signal is applied to the upper fixed electrode 21 and a negative voltage of the AC signal is applied to the lower fixed electrode 11. The central portion of the vibrating portion of the vibrating membrane 31 (the portion not fixed by the epoxy insulating layer of the fixed electrode) is an electrostatic force (attraction force) between the vibrating electrode layer 31A and the electrode portion 14 of the lower fixed electrode 11. Then, the electrostatic force (repulsive force) between the vibrating electrode layer 31 </ b> A and the electrode portion 24 of the upper fixed electrode 21 is attracted toward the lower fixed electrode 11.

FIG. 4C is a diagram illustrating a vibration state of the vibrating membrane 31 when a negative voltage of an AC signal is applied to the upper fixed electrode 21 and a positive voltage of the AC signal is applied to the lower fixed electrode 11. The central part of the vibration part of the vibration film 31 is the electrostatic force (attraction force) between the vibration electrode layer 31A and the electrode part 24 of the upper fixed electrode 21, and the electrode part of the vibration electrode layer 31A and the lower fixed electrode 11. 14 is attracted in the direction of the upper fixed electrode 21 by an electrostatic force (repulsive force) between them.
In this way, the vibrating membrane 31 vibrates in response to an AC signal and outputs a sound wave. 22 to the outside.

  At this time, since the thickness differs on the left and right sides of the fixed electrode shown in FIG. 4, that is, the length of the through hole (acoustic resonance tube) is different, the acoustic resonance frequency is also different. For example, if the resonance frequency of the left acoustic tube is 50 kHz and the resonance frequency of the right acoustic tube is 45 kHz, the sound pressure level in the two resonance frequency bands can be improved. Therefore, it is possible to improve the sound pressure in a wide band as compared with the case of having only one resonance frequency, that is, a fixed electrode having a uniform thickness facing each other.

  Furthermore, the sound pressure level in an arbitrary band can be improved depending on the number of types of acoustic tube lengths. For example, as shown in the specific example of the electrostatic transducer in FIG. 5, a plurality of different acoustic tubes can be arranged across the front surface of the fixed electrode. FIG. 5A is a view of the upper fixed electrode 21 (or the lower fixed electrode 11) viewed from the sound wave emitting surface side, and FIG. 5B is a cross-sectional view in the XX ′ direction. Thus, by arranging a plurality of different acoustic tubes on the entire surface of the fixed electrode, the sound pressure level of the radiated sound wave can be leveled and the sound pressure level can be increased over a wide band. In addition, by arranging a plurality of different acoustic tubes, it is possible to arbitrarily perform an optimization design such as generating a sound pressure level peak at a plurality of frequencies.

  Further, the shape, number and arrangement of the through holes are not limited to this, and can be changed without departing from the present invention. For example, it can be configured as shown in FIG.

  In the electrostatic transducer shown in FIG. 6A, the thickness of the upper fixed electrode 21 is changed stepwise so that the tube length of the through hole 22 is from one end (left end in the figure) to the other end (right end). The lower fixed electrode 11 has a constant thickness, and the through holes 12 have the same tube length.

  In the electrostatic transducer shown in FIG. 6B, the upper fixed electrode 21 has a tapered (inclined) upper surface, and the tube length of the through hole 22 gradually increases from one end (left end in the figure) to the other end (right end). Thus, the lower fixed electrode 11 has a constant thickness and the through holes 12 have the same tube length.

  6C shows a structure in which the upper surface of the upper fixed electrode 21 has a concave (curved surface) shape, and the tube length of the through hole 22 gradually increases from the central portion toward the end portion. The thickness is constant and the through holes 12 have the same tube length.

  Thus, by arranging a plurality of through holes (acoustic tubes) having different tube lengths in both or one of the fixed electrodes 11, 21, the sound pressure level of the radiated sound wave can be leveled and the sound pressure level can be increased in a wide band. . Moreover, the shape shown here and the combination of the upper fixed electrode and the lower fixed electrode are merely examples, and can be changed to teeth that do not depart from the present invention.

[Third Embodiment]
The configuration of the electrostatic transducer shown in FIG. 7 is the same as that of the electrostatic transducer shown in FIG. 6C except that the acoustic reflectors 103 and 104 are installed on the back surface of the electrostatic transducer. .

In FIG. 7, in the acoustic reflectors 103 and 104, all the ultrasonic waves radiated from the through holes 12 of the lower fixed electrode 11 of the electrostatic transducer are radiated to the front surface of the electrostatic transducer through a path having the same length. Are arranged as follows.
That is, one end of the acoustic reflector is located at the center position M of the back surface of the electrostatic transducer, and the other end of the acoustic reflector is disposed at an angle of 45 degrees with respect to both sides of the back surface of the electrostatic transducer with respect to the center position M. Is formed at a right angle with the pair of first reflectors 103 and 103 having a length matching the ends X1 and X2 of the electrostatic transducer and the ends of the pair of first reflectors 103 and 103. Each has a pair of second reflectors 104 and 104 connected to the outside of the first reflector and having a length equivalent to the length of the first reflector.

  In the above configuration, the first reflecting plates 103 and 103 are arranged at an angle of 45 degrees with respect to both sides of the center position M on the back surface of the electrostatic transducer, and the ends thereof coincide with the ends of the electrostatic transducer. The length of is required. The ultrasonic waves emitted from the back surface of the electrostatic transducer by the first reflecting plates 103 and 103 are reflected in the horizontal direction.

  Next, by connecting the second reflectors 104 and 104 connected at a right angle to the first reflectors 103 and 103 to the outside of the first reflectors 103 and 103, respectively, the ultrasonic waves are electrostatically charged. To the front of the mold transducer. The second reflector length is also required to be equal to the first reflector length. What is important here is that all the ultrasonic waves radiated from the back surface of the electrostatic transducer have paths of the same length. This is because the same path length means that the phases of the ultrasonic waves emitted from the back surface are all aligned.

  Further, the reason why the sound wave can be handled geometrically as shown in FIG. 7 is that the sound wave to be emitted is an ultrasonic wave and therefore has a very strong directivity. Another point that needs to be mentioned is the time difference between the ultrasonic wave emitted from the front surface of the electrostatic transducer and the ultrasonic wave reflected from the back surface and emitted to the front surface.

The ultrasonic wave emitted from a point a away from the center position M of the transducer is assumed to be circular and the radius is r, and the distance to reach the transducer front surface is approximately 2r, that is, the diameter of the transducer. . Of course, the distance a must satisfy the following equation.
0 ≦ a ≦ r (1)

  Now, assuming that the transducer diameter is about 10 cm and the sound velocity is 340 m / sec, the time difference between the ultrasonic wave emitted from the front surface and the ultrasonic wave emitted from the back surface and reaching the front surface is about 0.29 msec. There is no problem because it is a time difference that humans cannot perceive. That is, ultrasonic waves emitted from the front and back surfaces of the transducer can be used effectively.

[Fourth Embodiment]
Next, an ultrasonic speaker and a speaker device according to the fourth embodiment of the present invention will be described. FIG. 8A is a diagram showing a configuration of an ultrasonic speaker using the electrostatic transducer of the present invention. The ultrasonic speaker according to the present embodiment uses the above-described electrostatic transducer of the present invention. This electrostatic transducer is configured such that, in the upper fixed electrode and the lower fixed electrode, the through hole of at least one fixed electrode has two or more types of resonance tube lengths. As a result, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased over a wide band.
An electrostatic transducer driven by a signal wave in the ultrasonic frequency band is also called an electrostatic ultrasonic transducer.

In FIG. 8A, the ultrasonic speaker includes an audio frequency wave oscillation source 201 that generates a signal wave in the audio frequency band, and a carrier wave oscillation source that generates and outputs a carrier wave (carrier wave) in the ultrasonic frequency band. 202, a modulator 203, a power amplifier 204, and an electrostatic transducer 205A.
The modulator 203 modulates the carrier wave output from the carrier wave oscillation source 202 with the signal wave in the audible frequency band output from the audio frequency wave oscillation source 201, and transmits the modulated wave to the electrostatic transducer 205A via the power amplifier 204. Supply.

  In the above configuration, the carrier wave in the ultrasonic frequency band output from the carrier wave oscillation source 202 by the signal wave output from the audible frequency wave oscillation source 201 is modulated by the modulator 203 and the modulated signal amplified by the power amplifier 204 is used. The electrostatic transducer 205A is driven. As a result, the modulated signal is converted into a sound wave of a finite amplitude level by the electrostatic transducer 205A, and this sound wave is radiated into the medium (in the air) and the signal in the original audible frequency band due to the nonlinear effect of the medium (air). The sound is self-playing.

  In other words, sound waves are coarse and dense waves that propagate using air as a medium, so that in the process of modulated ultrasonic waves, the dense and sparse portions of air appear prominently, 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.

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 electrostatic transducer of the present invention can be used not only as an ultrasonic speaker but also as a normal speaker device. For example, as shown in FIG. 8B, the electrostatic transducer 205B is driven by a signal obtained by amplifying the signal wave output from the audible frequency wave oscillation source 201 by the power amplifier 204.

  As described above, in the ultrasonic speaker and the speaker device of the present invention, the electrostatic transducer of the present invention is used so that the through hole of the fixed electrode has two or more types of resonance tube lengths. It is configured. As a result, the sound pressure of the radiated sound wave can be leveled and the sound pressure level can be increased over a wide band, so that an acoustic signal can be reproduced with a sufficient sound pressure level and wide band characteristics. In particular, in an ultrasonic speaker, an acoustic signal 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 with a sufficient sound pressure level and wide band characteristics. For this reason, the reproduction range can be easily controlled.

[Fifth Embodiment]
Next, the electrostatic ultrasonic transducer of the present invention, that is, the through hole (resonance tube) provided in the fixed electrode is configured to have two or more types of lengths, and the sound pressure of the radiated sound wave is leveled. A directional acoustic system using an ultrasonic speaker composed of an electrostatic ultrasonic transducer capable of increasing the sound pressure level in a wide band will be described. Note that an electrostatic ultrasonic transducer driven by an ultrasonic frequency band signal is also simply referred to as an “ultrasonic transducer”.

  Hereinafter, a projector (display device) will be described as an example of a directional acoustic system according to the present invention. FIG. 9 shows a usage 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.

  In the projector 301, the electrostatic ultrasonic transducer according to the present invention is used as the ultrasonic transducers 324A and 324B constituting the ultrasonic speaker. This electrostatic ultrasonic transducer is configured so that the through hole (resonance tube) provided in the fixed electrode has two or more types of lengths, leveling the sound pressure of the radiated sound wave, and increasing the sound pressure level in a wide band An electrostatic ultrasonic transducer that can be enhanced. 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 a super The apparatus includes an ultrasonic speaker including sound wave transducers 324A and 324B, high-pass filters 317A and 317B, a low-pass filter 319, a mixer 321, a power amplifier 322C, a low-frequency sound reproduction speaker 323, and a projector main body 320.

  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 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.

Also, 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 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 mixer 321 and input to the power amplifier 322C via the low-pass filter 319. . The audio / video signal reproduction unit 314 corresponds to an acoustic source.

The high-pass filters 317A and 317B have a characteristic of allowing only the frequency components in the middle and high frequencies (first sound range) in the R-channel and L-channel audio signals to pass, respectively. Only the low frequency range (second range) frequency component of the audio signal of the channel is passed.
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 reproducing 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 mixer 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 318A, 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 synthesized by the mixer 321, and the low frequency audio signal of the R channel audio signal and the L channel audio signal is input to the power amplifier 322 C by the low pass filter 319. Is done.

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. 9 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 the result 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 to the ultrasonic transducers 324A and 324B, respectively, and the modulated signals are converted into sound waves (acoustic signals) having a finite amplitude level and emitted to the medium (in the air). Then, the ultrasonic transducer 324A reproduces the mid-high range audio signal in the R channel audio signal, and the ultrasonic transducer 324B reproduces the mid-high range audio signal in the L channel audio signal. .
Also, the low-frequency audio signals in the R channel and L channel amplified by the power amplifier 322C are reproduced by the low tone 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. 12 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.

Therefore, the reproduced reproduction signal beam 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. 12, an audible range B indicated by a solid arrow indicates that a reproduction signal (reproduced sound) can be heard only in a relatively close and wide range from the projection plane 302.

  As described above, in the projector according to the present invention, the electrostatic ultrasonic transducer according to the present invention is used as the ultrasonic transducer constituting the ultrasonic speaker. Since the pressure level can be increased, the sound signal can be reproduced with a sufficient sound pressure level and wide band characteristics 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.

  The projector described above is used for viewing images on a large screen. Recently, large-screen liquid crystal televisions and large-screen plasma televisions are rapidly spreading, and those large-screen televisions are also used. The ultrasonic speaker of the present invention can be used effectively.

  That is, by using the ultrasonic speaker according to the present invention for a large screen television, it becomes possible to radiate an audio signal locally toward the front of the large screen television.

  Although the embodiments of the present invention have been described above, the electrostatic ultrasonic transducer, electrostatic transducer, ultrasonic speaker, speaker device, and display device of the present invention are limited to the above-described illustrated examples. However, it goes without saying that various changes can be made without departing from the scope of the present invention.

The block diagram of the lower side fixed electrode of the electrostatic transducer which concerns on 1st Embodiment. The figure which shows the structure of a diaphragm. It is sectional drawing which shows the structure of an electrostatic transducer. Operation | movement explanatory drawing of an electrostatic transducer. The figure which shows the specific example of an electrostatic transducer. The figure which shows the other specific example of an electrostatic transducer. The figure which shows the example which provided the reflecting plate in the back surface of the electrostatic transducer. The figure which shows the structure of the ultrasonic speaker by this invention, and a speaker apparatus. The figure which shows the use condition of the projector by this invention. FIG. 11 is a diagram showing an external configuration of the projector shown in FIG. 10. FIG. 11 is a block diagram showing an electrical configuration of the projector shown in FIG. 10. Explanatory drawing of the reproduction | regeneration state of the reproduction signal by an ultrasonic transducer. The figure which shows the structure of the conventional pull type electrostatic transducer. The figure which shows the structure of the conventional push pull type electrostatic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Lower fixed electrode, 12, 12A, 12B ... Through-hole (resonance tube), 13 ... Epoxy insulating layer, 14 ... Electrode part, 21 ... Upper fixed electrode, 22, 22A , 22B ... through-hole (resonance tube), 31 ... vibrating membrane, 31A ... vibrating electrode layer, 31B ... dielectric film, 32 ... DC bias power source, 33, 33A, 33B ... AC signal, 103, 104 ... acoustic reflector, 201 ... audible frequency wave oscillation source, 202 ... carrier wave oscillation source, 203 ... modulator, 204 ... power amplifier, 205A, 205B ... Electrostatic transducer, 301 ... Projector, 302 ... Screen (projection surface), 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, 318A, 318B ... modulator, 319 ... low pass filter, 320 ... projector body, 321 ... Mixer, 322A, 322B ... Power amplifier, 322C ... Power amplifier, 323 ... Low-frequency sound reproduction speaker, 324, 324A, 324B ... Ultrasonic transducer, 331 ... Projector lens, 332: Image generation unit, 333: Projection optical system

Claims (18)

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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
A DC bias voltage is applied to the vibrating membrane, and an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias A voltage is applied to the pair of electrodes and the alternating signal is applied to the vibrating membrane;
An electrostatic ultrasonic transducer characterized in that a through hole provided in at least one of the pair of electrodes acts as a resonance tube and has at least two types of resonance tube lengths. The thickness of at least one of the pair of electrodes is changed stepwise, and the length of the resonance tube is set to gradually increase or decrease in accordance with the step change. 2. The electrostatic ultrasonic transducer according to 1. One surface of at least one of the pair of electrodes has an inclined structure or a curved surface structure, and the length of the resonance tube is set to be gradually increased or decreased in accordance with the inclined structure or the curved surface structure. The electrostatic ultrasonic transducer according to claim 1. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
Ultrasonic waves radiated from the through holes on the back surface of the electrostatic transducer having the through holes provided in the pair of electrodes acting as resonance tubes and having at least two types of resonance tube lengths An acoustic reflection plate is provided that reflects an acoustic reflection plate on the front side of the electrostatic ultrasonic transducer. The thickness of at least one of the pair of electrodes is changed stepwise, and the length of the resonance tube is set to gradually increase or decrease in accordance with the step change. 4. The electrostatic ultrasonic transducer according to 4. One surface of at least one of the pair of electrodes has an inclined structure or a curved surface structure, and the length of the resonance tube is set to be gradually increased or decreased in accordance with the inclined structure or the curved surface structure. The electrostatic ultrasonic transducer according to claim 4. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
A DC bias voltage is applied to the diaphragm and an AC signal is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes and the AC signal is applied to the diaphragm. And
An electrostatic transducer characterized in that a through hole provided in at least one of the pair of electrodes acts as a resonance tube and has at least two types of resonance tube lengths. 8. The thickness of at least one of the pair of electrodes is changed stepwise, and the length of the resonance tube is set to gradually increase or decrease in accordance with the step change. The electrostatic transducer according to 1. One surface of at least one of the pair of electrodes has an inclined structure or a curved surface structure, and the length of the resonance tube is set to be gradually increased or decreased in accordance with the inclined structure or the curved surface structure. The electrostatic transducer according to claim 7. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
An electrostatic ultrasonic transducer having a through hole provided in at least one of the pair of electrodes as a resonance tube and having at least two types of resonance tube lengths;
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 a signal wave in the audible frequency band to generate a modulated wave;
With
A DC bias voltage is applied to the diaphragm and the modulated wave is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes and the modulated wave is applied to the diaphragm. Thus, the ultrasonic speaker is driven by the electrostatic ultrasonic transducer. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
Ultrasonic waves radiated from the through holes on the back surface of the electrostatic transducer having the through holes provided in the pair of electrodes acting as resonance tubes and having at least two types of resonance tube lengths An electrostatic ultrasonic transducer having an acoustic reflector that reflects the front side of the electrostatic ultrasonic transducer;
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 a signal wave in the audible frequency band to generate a modulated wave;
With
A DC bias voltage is applied to the diaphragm and the modulated wave is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes and the modulated wave is applied to the diaphragm. Thus, the ultrasonic speaker is driven by the electrostatic ultrasonic transducer. 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 make a pair, and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode And a vibrating membrane having a conductive layer,
Including
An electrostatic transducer having a through hole provided in at least one of the pair of electrodes as a resonance tube and having at least two types of resonance tube lengths;
A signal source for generating a signal wave in an audible frequency band;
An amplifier for amplifying a signal wave output from the signal source;
With
A speaker device that reproduces an audible frequency band signal by driving the electrostatic transducer with an output signal of the amplifier. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
Using an electrostatic ultrasonic transducer having a through-hole provided in at least one of the pair of electrodes as a resonance tube and having at least two types of resonance tube lengths;
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 wave obtained by modulating the carrier wave with a signal wave in the audible frequency band;
A DC bias voltage is applied to the diaphragm and the modulated wave is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes and the modulated wave is applied to the diaphragm. A procedure for driving the electrostatic ultrasonic transducer by
A method of reproducing an audio signal using an electrostatic ultrasonic transducer. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
Ultrasonic waves radiated from the through holes on the back surface of the electrostatic transducer having the through holes provided in the pair of electrodes acting as resonance tubes and having at least two types of resonance tube lengths And using an electrostatic ultrasonic transducer provided with an acoustic reflector that reflects the front surface side of the electrostatic ultrasonic 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 wave obtained by modulating the carrier wave with the signal wave;
A DC bias voltage is applied to the diaphragm and the modulated wave is applied to the pair of electrodes, or the DC bias voltage is applied to the pair of electrodes and the modulated wave is applied to the diaphragm. A procedure for driving the electrostatic ultrasonic transducer by
A method of reproducing an audio signal using an electrostatic ultrasonic transducer. 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
A DC bias voltage is applied to the vibrating membrane, and an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias A voltage is applied to the pair of electrodes and the alternating signal is applied to the vibrating membrane;
A through-hole provided in at least one electrode of the pair of electrodes serves as a resonance tube, and is configured using an electrostatic ultrasonic transducer having at least two types of resonance tube lengths. An ultrasonic speaker for reproducing an audio signal in a first range among the supplied audio signals;
A bass reproduction speaker for reproducing an audio signal in the second range among audio signals supplied from an acoustic source;
Have
A directional acoustic system characterized in that an audio signal supplied from an acoustic source by the ultrasonic speaker is reproduced, 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 through hole;
The through hole of the first electrode and the through hole of the second electrode are disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
A DC bias voltage is applied to the vibrating membrane, and an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias A voltage is applied to the pair of electrodes and the alternating signal is applied to the vibrating membrane;
Ultrasonic waves radiated from the through holes on the back surface of the electrostatic transducer having the through holes provided in the pair of electrodes acting as resonance tubes and having at least two types of resonance tube lengths Of the first ultrasonic range among the audio signals supplied from the acoustic source. An ultrasonic speaker to play,
A bass reproduction speaker for reproducing an audio signal in the second range among audio signals supplied from an acoustic source;
Have
A directional acoustic system characterized in that an audio signal supplied from an acoustic source by the ultrasonic speaker is reproduced, 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 through hole;
The through hole of the first electrode and the through hole of the second electrode are disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
A DC bias voltage is applied to the vibrating membrane, and an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias A voltage is applied to the pair of electrodes and the alternating signal is applied to the vibrating membrane;
An electrostatic ultrasonic transducer having a through-hole provided in at least one electrode of the pair of electrodes as a resonance tube and having at least two types of resonance tube lengths is provided. An ultrasonic speaker that reproduces a signal sound of an audible frequency band from a supplied audio signal;
A projection optical system that projects an image onto a projection surface;
A display device comprising: 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 disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer;
Including
A DC bias voltage is applied to the vibrating membrane, and an AC signal that is a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied to the pair of electrodes, or the DC bias A voltage is applied to the pair of electrodes and the alternating signal is applied to the vibrating membrane;
Ultrasonic waves radiated from the through holes on the back surface of the electrostatic transducer having the through holes provided in the pair of electrodes acting as resonance tubes and having at least two types of resonance tube lengths Including an electrostatic ultrasonic transducer provided with an acoustic reflector that reflects the front side of the electrostatic ultrasonic transducer, and reproduces an audio frequency band signal from an audio signal supplied from an acoustic source An ultrasonic speaker,
A projection optical system that projects an image onto a projection surface;
A display device comprising:

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