JP2012119842A - Flat speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat speaker which can reproduce the sound quality of a conventional speaker, and can be made thin, compact and lightweight.SOLUTION: The flat speaker comprises a carrier wave generation unit which generates a carrier wave in an ultrasonic frequency band modulated by an acoustic signal in the audible frequency band, and a diaphragm 2 which is vibrated by the carrier wave and reproduces the acoustic signal. In the carrier wave generation unit, multiple ultrasonic wave generation elements are arranged in array and subjected to drive control according to the acoustic signal. The diaphragm 2 is vibrated by the carrier wave radiated from the carrier wave generation unit and propagated through a space between an ultrasonic wave generation element 7, and reflects the carrier wave.

Description

  The present invention relates to a flat speaker driven by a digital signal.

  In recent years, there has been an increasing demand for thinner, smaller, and lighter electronic devices equipped with speakers, and conventional cone-type speakers cannot satisfy these requirements. In addition, although digitization of signals is progressing, it is necessary to convert the digital signal into an analog signal and drive it when driving the speaker. On the other hand, a speaker that obtains sound in an audible frequency band by arranging transducers, which are ultrasonic generation elements, on an array and directly driving the digital signal with a clock frequency in the ultrasonic range has been proposed. For example, Patent Document 1 discloses a speaker that obtains analog audio by converting a normal digital signal into a binary digital signal and driving a plurality of transducers according to the number of bits of the signal in the positive or negative direction. Yes. For example, Patent Document 2 discloses a digital speaker having a configuration in which transducers formed by MEMS technology are arrayed and driven and controlled by digital signals.

  On the other hand, the transducers of the ultrasonic generators are arranged in an array, and the ultrasonic waves modulated by the acoustic signals in the audible frequency band are emitted from these, and the acoustic signals in the audible frequency band are reproduced by the nonlinear effect of the transmission medium (air). A technique for constructing a so-called parametric speaker is disclosed in Patent Document 3, for example.

  The difference between the above-mentioned digital speaker and parametric speaker is that, in the digital speaker, the ultrasonic waves radiated from the respective transducers are overlapped with each other. As a result, sound waves having an audible frequency are generated and function as a speaker. While the ultrasonic wave is propagating, the sound is obtained on a different principle that the modulation signal is self-demodulated by the non-linear effect of air and the sound in the audible range is reproduced.

Japanese Patent No. 3492698 US Patent No. 7089069 Japanese Patent No. 4285537

  In a conventional digital speaker, as described above, an ultrasonic wave is emitted from a plurality of micro transducers (ultrasonic wave generating elements), and an audio signal having an audible frequency is obtained by overlapping sound waves that vibrate in the ultrasonic region. It has become. Therefore, since ultrasonic waves are radiated into the air that is the transmission medium, the vibration in the air is different from the vibration of the original acoustic signal. In addition, there is a disadvantage that an acoustic reduction filter that removes ultrasonic waves to prevent adverse effects on animals and the like that cannot be heard by humans must be considered.

  In addition, the array requires a large number of transducers corresponding to the number of bits, requires an area, and does not operate with an operating ultrasonic generating element among a plurality of ultrasonic generating elements at a certain moment. There is an ultrasonic wave generating element, and the overlap of emitted ultrasonic waves changes for each reproduction time, and there is a problem that it is not localized at one point. Also, when approaching the minimum volume, the number of driven transducers in the array decreases, and the problem that the sound waves do not overlap easily tends to occur. Alternatively, each transducer is driven positively or negatively by a clock signal in the ultrasonic range, but is not driven constantly, so a wide flat frequency characteristic is required for the transducer, and usually a flat frequency characteristic is required. The transducer is difficult to obtain, which has the problem that it impairs sound fidelity.

  In conventional parametric speakers, reproduced sound is generated by the non-linear effect of the transmission medium, so that there is a problem that the sound pressure distribution is biased toward the negative sound pressure side, and the listener feels uncomfortable. In addition, sharp directivity determined by the propagation direction of ultrasonic waves is a feature, and it has a great advantage in the field that can make use of the feature of providing audio information to a specific person, but it is unspecified like ordinary analog speakers It could not be used for the purpose of telling many people.

  An object of the present invention is to provide a flat speaker that can solve the above-described problems, can reproduce the sound quality of a conventional analog speaker, and can be reduced in thickness, size, and weight.

  In order to achieve the above object, the invention according to claim 1 of the present application reproduces the acoustic signal by generating a carrier wave of an ultrasonic frequency band modulated by an acoustic signal of an audible frequency band, and vibrating by the carrier wave. A vibration plate, wherein the carrier wave generation unit is configured to arrange a plurality of ultrasonic wave generation elements in an array, and the ultrasonic wave generation elements are driven and controlled according to the acoustic signal, It is configured to vibrate by the carrier wave radiated from the carrier wave generation unit and propagated through the space between the ultrasonic wave generating element and the diaphragm and to reflect the carrier wave.

  The invention according to claim 2 of the present application is the flat speaker according to claim 1, wherein the ultrasonic wave generating element is formed on the first substrate and overlaps the first substrate or the first substrate. A switch element that connects the ultrasonic wave generating element and a driving power source is formed on the second substrate, and the ultrasonic vibration element is driven and controlled by controlling opening and closing of the switch element. .

  According to the present invention, an ultrasonic wave is not superimposed on a reproduced sound, and nonuniformity due to the superposition of ultrasonic waves can be eliminated, so that a speaker capable of faithfully reproducing an acoustic signal (original sound) is provided. Can do.

  The acoustic signal is reproduced by vibration of the diaphragm, and is not generated by the superposition of ultrasonic waves as in the conventional example. Therefore, the acoustic signal is desired regardless of the vibration frequency of the ultrasonic generator. There is an advantage that a reproduced sound of a certain band can be obtained. The reproduced sound does not cause the sound pressure distribution to be biased toward the negative sound pressure side due to the non-linear effect of the transmission medium, so that the listener does not feel uncomfortable.

  Furthermore, the ultrasonic wave generating element is formed on the first substrate, and the switch element formed between the ultrasonic power generating element and the drive power source supplied to the ultrasonic wave generating element is also formed on the same first substrate. Alternatively, since it can be formed on the second substrate overlapping the first substrate, it is suitable for reduction in thickness, size, and weight. In this case, since the drive control of the ultrasonic wave generation element may be control of the switch element, there is an advantage that adjustment is easy.

It is a figure explaining the planar speaker of this invention. It is another figure explaining the planar speaker of this invention.

  The flat speaker of the present invention generates a carrier wave (ultrasonic wave) in an ultrasonic frequency band in accordance with an acoustic signal in an audible frequency band such as a voice or an audio signal. The carrier wave generator has a plurality of ultrasonic wave generating elements arranged in an array. And a diaphragm is arrange | positioned at predetermined intervals so that a several ultrasonic wave generation element may be opposed. This diaphragm is made of a material that is greatly different from the acoustic impedance of the transmission medium between the ultrasonic generating elements, specifically, air. Further, the diaphragm is arranged so that the carrier wave (ultrasound) is reflected by the diaphragm and does not propagate toward the listener who can hear the reproduced sound.

  With this configuration, when a carrier wave (ultrasonic wave) modulated by an acoustic signal is emitted from the ultrasonic wave generating element, it propagates through the space in the vicinity and reaches the diaphragm. In this diaphragm, acoustic radiation pressure is generated due to the nonlinear effect of the carrier wave (ultrasonic wave). The magnitude of this acoustic radiation pressure is proportional to the energy intensity of the carrier wave (ultrasound). As a result, the diaphragm vibrates in the traveling direction of the carrier wave and reproduces an acoustic signal. At this time, since most of the ultrasonic waves are reflected from the difference in acoustic impedance, the ultrasonic waves do not reach the listener's ear.

  As described above, since the acoustic signal is reproduced by the displacement of the diaphragm, the change in the superposition of the ultrasonic waves due to the presence of the operating elements and the non-operating elements among the plurality of ultrasonic generating elements is as follows. It has no effect on the sound localization. Further, since the vibration frequency of the acoustic signal can be adjusted by the displacement of the diaphragm, there is an advantage that a broadband signal can be obtained without being limited by the vibration frequency of the ultrasonic wave generating element.

As described above, according to the present invention, the sound signal is reproduced by the displacement of the diaphragm like the conventional speaker, so that the sound quality of the conventional speaker can be reproduced, and the thickness and size are reduced. It is possible to reduce the weight.
Hereinafter, specific examples will be described in detail.

  FIG. 1 is an explanatory diagram of a flat speaker according to the present invention. FIG. 2 is an explanatory diagram of a part constituting the flat speaker of the present invention. As shown in the figure, reference numeral 1 is an ultrasonic wave generating element portion in which a plurality of ultrasonic wave generating elements are arranged in an array, 2 is a vibration plate, 3 is a housing, 4 is a displacement of the vibration plate 2 to the housing 3 The connecting portion to be held, 5 is a switch element portion, and 6 is a drive circuit portion. The ultrasonic wave generation element unit 1 includes a plurality of ultrasonic wave generation elements 7 and can be formed by cMUT (Capacitive Micromachined Ultrasonic Transducer) or the like as an example. The switch element unit 5 includes a plurality of switch elements 8 connected to each of the plurality of ultrasonic wave generating elements 7. The drive circuit unit 6 includes an ultrasonic generator power supply 9 for driving the ultrasonic generator 7 and a switch element controller 10 for controlling opening and closing of the switch element 8.

  As shown in FIG. 1, a diaphragm 2 is arranged in the traveling direction of a carrier wave (ultrasonic wave) radiated from the ultrasonic wave generating element unit 1 so as to block the traveling thereof. The diaphragm 2 is held so as to be displaceable by being connected to the housing 3 by a connecting portion 4 made of, for example, a weak spring. The dimension between the diaphragm 2 and the ultrasonic wave generating element unit 2 is adjusted so that the energy of the propagation wave (ultrasonic wave) can surely reach the diaphragm 2 and be reproduced faithfully. Further, the size of the diaphragm 2 is made larger than that of the ultrasonic wave generating element units 1 arranged in an array, so that the energy of the propagation wave (ultrasonic wave) can be reliably transmitted to the diaphragm 2. The diaphragm 2 is made of a material that is greatly different from the acoustic impedance of the space in which the carrier wave travels, and it is necessary to reproduce a good sound quality. Therefore, it is preferable to select a hard and light material like a conventional speaker.

  The ultrasonic generators 7 arranged in an array are driven and controlled by controlling the opening and closing of the switch elements 8 constituting the switch element unit 5.

  As shown in FIG. 2, when the ultrasonic wave generating element 7 is constituted by, for example, cMUT, an upper electrode, a lower electrode, and the like serving as a vibration film are formed on a silicon semiconductor substrate by using a normal semiconductor device processing technique. be able to. The ultrasonic wave generating element 7 is not limited to cMUT, and can be formed by processing a silicon substrate using a silicon micromachine technology. Similarly, when the switch element 8 is formed on the same silicon semiconductor substrate or formed on another silicon substrate overlapping the silicon semiconductor substrate and both are electrically connected, it is suitable for reduction in size, thickness and weight. .

  The drive control of the ultrasonic wave generating element unit 1 by the switch element unit 5 is configured such that one switching element 8 is connected to one ultrasonic wave generating element 7, but one ultrasonic element 7 is connected to one ultrasonic wave generating element 7. The switch element 8 may be connected. In the latter case, the number of switches can be a number corresponding to the number of bits of the digital signal, for example, 255 for 8 bits, 65,535 for 16 bits, or an integral multiple thereof.

  As shown in FIG. 2, the switch element controller 10 controls the opening and closing of the switch element 8, and a propagation wave (ultrasonic wave) is emitted into the space from the ultrasonic wave generation element 7 connected to the ultrasonic wave generation element power source 9. . The propagating wave (ultrasonic wave) released into the space reaches the diaphragm 2 and presses the diaphragm 2 with acoustic radiation pressure. The intensity of the propagating wave (ultrasonic wave) emitted at this time is proportional to the number of ultrasonic wave generating elements 7 connected to the ultrasonic wave generating element power source 9. Therefore, the connecting portion 4 may be adjusted so that the number of ultrasonic generating elements connected to the power supply for ultrasonic generating elements is proportional to the amount of displacement of the diaphragm 2. For example, when the connecting portion 4 is constituted by a spring, it may be adjusted so that the spring constant is in a range showing linear characteristics.

  Due to the temporal change in the displacement of the diaphragm 2, the air in the vicinity of the diaphragm 2 vibrates and an acoustic signal in an audible frequency band is reproduced. This is the same as the conventional speaker reproduction method, and reproduction can be realized as in the conventional method. At this time, the transmission wave (ultrasonic wave) that displaces the diaphragm 2 does not pass through the diaphragm 2. Therefore, since only the sound reproduced by the diaphragm 2 is transmitted in the air, the original acoustic signal can be faithfully reproduced.

  In order to uniformly vibrate the diaphragm 2, it is preferable to control so that the operating ultrasonic wave generating elements 7 among the ultrasonic wave generating elements 7 formed in an array are uniformly dispersed. In addition, the number of operating ultrasonic wave generating elements can be adjusted according to the frequency band of the acoustic signal to be reproduced, the volume, and the like.

  The ultrasonic wave generated from the ultrasonic wave generating element needs to be higher than the frequency of the signal for operating the switch element controller 10. However, the higher the frequency of ultrasonic waves, the greater the attenuation in the air.

  1: Ultrasonic wave generation element part, 2: Diaphragm, 3: Housing, 4: Connection part, 5: Switch element part, 6: Drive circuit part, 7: Ultrasonic wave generation element, 8: Switch element, 9: Ultra Power supply for sound wave oscillation element, 10: Switch element controller

Claims (2)

A carrier generation unit that generates a carrier wave in an ultrasonic frequency band modulated by an acoustic signal in an audible frequency band; and a diaphragm that vibrates by the carrier wave and reproduces the acoustic signal,
The carrier wave generation unit is configured to arrange a plurality of ultrasonic wave generation elements in an array, and the ultrasonic wave generation elements are driven and controlled according to the acoustic signal,
The diaphragm is configured to vibrate by the carrier wave radiated from the carrier wave generation unit and propagated through a space between the ultrasonic wave generating element and the diaphragm and to reflect the carrier wave. Flat speaker. The flat speaker according to claim 1, wherein
The ultrasonic wave generating element is formed on a first substrate,
On the first substrate or on the second substrate overlapping the first substrate, a switch element for connecting the ultrasonic wave generating element and the drive power source is formed,
A flat speaker, wherein the ultrasonic wave generating element is driven and controlled by controlling opening and closing of the switch element.

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