JP2005033488A - Ultrasonic speaker and method for reproducing signal sound of ultrasonic speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic speaker and an ultrasonic speaker signal sound reproducing method capable of reproducing sound that does not accompany sense of incongruity to listeners. <P>SOLUTION: This ultrasonic speaker has: an audio frequency wave oscillation source 10 for generating a signal wave of an audio frequency band; a carrier wave oscillation source 12 for generating and outputting a carrier wave; a modulator 14 for modulating the carrier wave with the signal wave; and an ultrasonic transducer 18 which is driven by a modulated signal outputted from the modulator 14, converts the modulated signal into an acoustic wave at a limited amplitude level and radiates the resultant acoustic wave into a medium. The ultrasonic speaker emits a reproduced signal being a signal sound of an audible wave frequency band, and has a sound pressure level regulator 20 for shifting the sound pressure level of the modulated signal to be applied to the ultrasonic transducer 18 so as to make the sound pressure distribution of the signal sound to be symmetrical in the positive and negative directions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic speaker that reproduces signal sound in an audible frequency band using nonlinearity of a medium (air) with respect to ultrasonic waves, and a signal sound reproducing method for the ultrasonic speaker.
[0002]
[Prior art]
Conventionally, it is known that an ultrasonic speaker using the nonlinearity of a medium (air) with respect to ultrasonic waves can reproduce a signal in an audible frequency band having a much sharper directivity than a normal speaker ( For example, see Patent Document 1.)
The configuration of a conventional ultrasonic speaker is shown in FIG. The ultrasonic speaker has an audio frequency wave oscillation source 10 that generates an audio frequency band signal, a carrier wave oscillation source 12 that generates a carrier wave, a modulator 14, a power amplifier 16, and an ultrasonic transducer 18. is doing.
[0003]
In the above configuration, the carrier wave in the ultrasonic frequency band output from the carrier wave oscillation source 12 by the signal wave output from the audible frequency wave oscillation source 10 is modulated by the modulator 14 and the modulated signal amplified by the power amplifier 16 is used. The ultrasonic transducer 18 is driven. As a result, the modulated signal is converted into a sound wave of a finite amplitude level by the ultrasonic transducer 18, and this sound wave is radiated into the medium (in the air), and the signal sound in the original audible frequency band is generated by the nonlinear effect of the medium (air). Is to be played.
In this case, the reproduction range of the reproduction signal in the audible frequency band is a beam-shaped range from the ultrasonic transducer 18 to the emission axis direction.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 58-119293
[Problems to be solved by the invention]
However, in the above-described conventional ultrasonic speaker, the signal sound of the audible frequency band to be reproduced tends to be biased toward the negative sound pressure side instead of being symmetric with respect to the positive and negative sound pressures due to the non-linear characteristics. There has been a problem that it is recognized as a sound with a sense of incongruity for the listener as compared with the signal sound of the frequency.
[0006]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an ultrasonic speaker and a method for reproducing a signal sound of an ultrasonic speaker that can reproduce a sound that does not cause a sense of incongruity for a listener. To do.
[0007]
[Means for Solving the Problems]
The point of the present invention is that in order to improve the phenomenon that the sound pressure distribution of the reproduced sound that is uncomfortable for the listener is biased toward the negative sound pressure side, a signal radiated from the ultrasonic transducer constituting the ultrasonic speaker is fixed in advance. It is in the point corrected by the rule. By doing so, it is possible to make the sound pressure distribution of the reproduced sound heard by the listener symmetric, and the listener can listen as a reproduction signal in a normal audible frequency band. Since it is a reproduction signal in a normal audible frequency band, there is no sense of incongruity in listening, and the quality of the reproduction sound output from the ultrasonic speaker can be improved.
[0008]
In other words, in order to achieve the above object, the invention according to claim 1 modulates a carrier wave with a signal wave output from a signal source that generates a signal wave in an audible frequency band, and uses the modulated signal to generate a wide frequency band. An ultrasonic speaker signal sound reproduction method for reproducing an audio frequency band signal sound by driving an ultrasonic transducer capable of oscillating an acoustic signal, wherein the sound pressure distribution of the signal sound is subject to positive and negative The sound pressure level of the modulation signal applied to the ultrasonic transducer is shifted.
[0009]
According to a second aspect of the present invention, in the method for reproducing a signal sound of the ultrasonic speaker according to the first aspect, the sound pressure level of the modulation signal is shifted in the positive direction in advance.
[0010]
According to a third aspect of the present invention, in the method of reproducing a signal sound of the ultrasonic speaker according to any one of the first or second aspect, the amount of shift of the sound pressure level of the modulation signal is set as the sound wave radiation of the ultrasonic transducer. It adjusts according to the distance from a surface to a reproduction | regeneration point in a radial direction.
[0011]
According to a fourth aspect of the present invention, in the method of reproducing a signal sound of the ultrasonic speaker according to any one of the first or second aspect, a shift amount of the sound pressure level of the modulation signal is set as a sound wave radiation of the ultrasonic transducer. It is characterized by a fixed value regardless of the distance from the surface to the reproduction point.
[0012]
According to a fifth aspect of the present invention, there is provided a signal source for generating an audible frequency band signal wave, a carrier wave supply means for generating and outputting a carrier wave, and a modulation means for modulating the carrier wave with the signal wave And an ultrasonic transducer that is driven by the modulation signal output from the modulation means and converts the modulation signal into a sound wave of a finite amplitude level and radiates it into the medium, and reproduces a signal sound in an audio frequency band An ultrasonic speaker for outputting a signal, comprising sound pressure level adjusting means for shifting the sound pressure level of the modulation signal applied to the ultrasonic transducer so that the sound pressure distribution of the signal sound is a target of positive and negative. It is characterized by.
[0013]
According to a sixth aspect of the present invention, in the ultrasonic speaker according to the fifth aspect of the present invention, the sound pressure level adjusting means determines the shift amount of the sound pressure level of the modulated wave from the sound wave emitting surface of the ultrasonic transducer. It can be adjusted according to the distance to the reproduction point in the radial axis direction.
[0014]
The invention according to claim 7 is the ultrasonic speaker according to claim 5, wherein the sound pressure level adjusting means is a reproduction point in a radial axis direction from a sound wave emitting surface of the ultrasonic transducer. A table that stores in advance a table showing the relationship between the distance to the sound pressure distribution and the amount of shift in the sound pressure level of the modulation signal required to make the sound pressure distribution of the signal sound positive and negative, and input from the outside The distance information from the sound wave emitting surface of the ultrasonic transducer to the reproduction point in the radial axis direction is fetched, the table is referred to, the shift amount of the sound pressure level of the modulation signal according to the distance information is obtained, A shift amount selection unit that outputs a shift amount; and a sound pressure level adjustment unit that shifts and outputs the sound pressure level of the modulation signal by the shift amount input from the shift amount selection unit. The features.
[0015]
The invention of claim 8 provides the ultrasonic speaker according to claim 5, wherein the sound pressure level adjusting means, the shift amount to shift advance in the positive direction of the sound pressure level of the modulation signal is fixed It is characteristically set.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of an ultrasonic speaker according to an embodiment of the present invention. In the figure, the ultrasonic speaker has an audible frequency wave oscillation source 10, a carrier wave oscillation source 12, a modulator 14, a sound pressure level adjuster 20, a power amplifier 16, and an ultrasonic transducer 18. Yes.
[0017]
The audio frequency wave oscillation source 10 has a function of generating a signal wave in the audio frequency band.
The carrier wave oscillation source 12 has a function of generating a carrier wave having a frequency in the ultrasonic frequency band and supplying the carrier wave to the modulator 14.
Each of the modulators 14 has a function of AM-modulating the carrier wave output from the carrier wave oscillation source 12 with the signal wave output from the audio frequency wave oscillation source 10 and outputting a modulated signal.
The audio frequency wave oscillation source 10 corresponds to the signal source of the present invention, the carrier wave oscillation source 12 corresponds to the carrier wave supply means of the present invention, and the modulator 14 corresponds to the modulation means of the present invention.
[0018]
The sound pressure level adjuster 20 has a function of shifting the sound pressure level of the modulation signal applied to the ultrasonic transducer so that the sound pressure distribution of the signal sound becomes a positive / negative target. Specifically, the correction to the acoustic signal radiated from the ultrasonic transducer 18 has a tendency that the sound pressure distribution of the signal sound (reproduced signal) is not symmetric with respect to the negative sound pressure due to the characteristic of the nonlinearity of the medium. In order to respond, the entire modulation signal is adjusted in advance so as to shift to the positive sound pressure side. In other words, the sound pressure level adjuster 20 adjusts the shift amount so that the result of the sound wave radiated from the ultrasonic transducer 18 being biased toward the negative sound pressure side as it propagates through the medium becomes symmetrical.
[0019]
However, in non-linear propagation, the sound pressure of the reproduced signal in the audible frequency band varies depending on the reproduction position of the signal sound, that is, the listening position (distance from the ultrasonic transducer) . Therefore, in order to be reliably positive-negative symmetrical distribution of sound pressure signals sound, ultrasonic transducers shift amount of the sound pressure level of the modulated signal output from the modulator 14 is applied to the ultrasonic transducer 18 It is necessary to adjust according to the distance from the 18 sound wave emitting surfaces to the reproduction point in the radial axis direction. However, the sound pressure of the playback signal may be considered constant after a certain distance, and the discomfort felt by the listener even if there is no reliable symmetry is much smaller than the playback sound of a conventional ultrasonic speaker. .
[0020]
Next, an example of a specific configuration of the sound pressure level adjuster 20 is shown in FIG. In the figure, the sound pressure level adjuster 20 includes a storage unit 201, a shift amount selection unit 202, and a sound pressure level adjustment unit 203.
The storage unit 201 includes a modulation signal (output of the modulator 14) necessary for setting the distance from the sound wave emission surface of the ultrasonic transducer 18 to the reproduction point in the radial axis direction and the sound pressure distribution of the signal sound as a positive / negative target. A table showing the relationship between the shift amount of the sound pressure level of the (signal) and the sound pressure level is stored in advance.
[0021]
The shift amount selection unit 202 takes in distance information from the sound wave emitting surface of the ultrasonic transducer 18 to the reproduction point in the radial axis direction inputted from the outside by an operation means or the like, refers to the table, and corresponds to the distance information It has a function of obtaining the shift amount of the sound pressure level of the modulation signal and outputting the shift amount.
The sound pressure level adjustment unit 203 has a function of shifting and outputting the sound pressure level of the modulation signal by the shift amount input from the shift amount selection unit 202.
The sound pressure level adjuster 20 corresponds to the sound pressure level adjusting means of the present invention.
[0022]
The power amplifier 16 amplifies the power of the modulation signal output from the sound pressure level adjuster and outputs the amplified signal to the ultrasonic transducer 18.
The ultrasonic transducer 18 is driven by the modulation signal output from the power amplifier 16, converts the modulation signal into a sound wave of a finite amplitude level, radiates it into the medium, and reproduces the signal sound (reproduction signal) in the audible frequency band. Has the function of As the ultrasonic transducer 18 , for example, an electrostatic transducer that can oscillate an acoustic signal in a wide frequency band is used.
The present invention can also be applied to an ultrasonic transducer that oscillates a resonance-type acoustic signal in a narrow frequency band. As an ultrasonic transducer to be applied, a wide frequency band oscillation type is a narrow frequency band type. There is no question.
[0023]
An example of a specific configuration of the ultrasonic transducer 18 is shown in FIG. The electrostatic ultrasonic transducer shown in FIG. 3 uses a dielectric 31 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. An upper electrode 32 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 31 by a process such as vapor deposition, and a lower electrode 33 formed of brass is formed on the lower surface of the dielectric 31. It is provided so that it may contact a part. The lower electrode 33 is connected to a lead 52 and is fixed to a base plate 35 made of bakelite or the like.
[0024]
The upper electrode 32 is connected to a lead 53, and the lead 53 is connected to a DC bias power supply 50. A DC bias voltage for upper electrode adsorption of about 50 to 150 V is always applied to the upper electrode 32 by the DC bias power source 50 so that the upper electrode 32 is attracted to the lower electrode 33 side. Reference numeral 51 denotes an AC signal source, which corresponds to the output (AC 50 to 150 Vp-p) of the power amplifier 16 in FIG.
The dielectric 31, the upper electrode 32, and the base plate 35 are caulked by the case 30 together with the metal rings 36, 37, and 38 and the mesh 39.
[0025]
On the surface of the lower electrode 33 on the dielectric 31 side, a plurality of minute grooves of about several tens to several hundreds μm having a non-uniform shape are formed. Since this minute groove becomes a gap between the lower electrode 33 and the dielectric 31, the electrostatic capacity distribution between the upper electrode 32 and the lower electrode 33 changes minutely. These random minute grooves are formed by manually rubbing the surface of the lower electrode 33 with a file. In the electrostatic ultrasonic transducer, the frequency characteristics of the ultrasonic transducer are widened as shown by the curve Q1 in FIG. 4 by forming innumerable capacitors having different gap sizes and depths. Yes.
[0026]
In the ultrasonic transducer 18 having the above configuration, a modulation signal (output of the power amplifier 16) is applied between the upper electrode 31 and the lower electrode 33 in a state where a DC bias voltage is applied to the upper electrode 32. Yes. Incidentally, as shown by the curve Q2 in FIG. 4, the frequency characteristic of the resonance type ultrasonic transducer has a center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, and a maximum sound pressure at ± 5 kHz with respect to the center frequency. On the other hand, it is -30 dB. On the other hand, the frequency characteristics of the broadband oscillation type ultrasonic transducer having the above configuration are flat from 40 kHz to around 100 kHz, and are about ± 6 dB compared to the maximum sound pressure at 100 kHz.
[0027]
The operation of the ultrasonic speaker according to the embodiment of the present invention having the above configuration will be described. The audio frequency wave oscillation source 10 generates an audio frequency band signal wave and outputs the signal wave to the modulator 14.
The carrier wave oscillation source 12 generates a carrier wave having a frequency in the ultrasonic frequency band and supplies the carrier wave to the modulator 14.
The modulator 14 AM modulates the carrier wave output from the carrier wave transmission source 12 with the signal wave output from the audible frequency wave oscillation source 10 and outputs the modulated signal to the sound pressure level adjuster 20.
[0028]
On the other hand, in the sound pressure level adjuster, the shift amount selection unit 202 takes in the distance information from the sound wave emitting surface of the ultrasonic transducer 18 to the reproduction point in the radial axis direction inputted by the operation means and stores it in the storage unit 201. The shift amount of the sound pressure level of the modulation signal corresponding to the distance information is obtained by referring to the table, and the shift amount is output to the volume level adjustment unit 203.
The sound pressure level adjustment unit 203 shifts the sound pressure level of the modulation signal input from the modulator 14 in the positive direction by the shift amount input from the shift amount selection unit 202, and outputs it to the power amplifier 16.
The modulation signal amplified by the power amplifier 16 is applied between the upper electrode 32 and the lower electrode 33 of the ultrasonic transducer 18 , and the modulation signal is converted into a sound wave (acoustic signal) having a finite amplitude level, and the medium ( (In the air).
[0029]
Here, the nonlinear effect of the medium (air) will be briefly described. In the propagation of the ultrasonic wave radiated into the medium (in the air) by the ultrasonic transducer, the sound speed is increased at the portion where the sound pressure is high due to the propagation. The sound speed becomes higher and the sound speed becomes slower in the part where the sound pressure is low. As a result, it is known that waveform distortion occurs. When a signal in the ultrasonic band to be radiated (referred to as a carrier wave) is modulated (AM modulation) with a signal in the audible frequency band, the signal wave in the audible frequency band used for modulation is obtained based on the result of the waveform distortion. It is also known that is formed in a form that self-demodulates. 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.
[0030]
Next, the effect of the ultrasonic speaker according to the embodiment of the present invention will be described with reference to FIGS.
FIG. 5 shows the characteristics of the conventional ultrasonic speaker (FIG. 7), and FIG. 6 shows the characteristics of the ultrasonic speaker (FIG. 1) according to the present invention. 5 and 6 both show a modulated wave (FIG. 5 (a), FIG. 6 (a)) and a propagation wave (FIG. 5) when the frequency of the carrier wave is 40 kHz and the frequency of the signal wave in the audible frequency band is 2 kHz. 5 (b) and FIG. 6 (b)) and the waveform of the reproduction signal (FIG. 5 (c) and FIG. 6 (c)) are shown.
[0031]
As is clear from these figures, since the conventional ultrasonic speaker does not adjust the sound pressure level of the modulation signal, the sound pressure level distribution of the reproduction signal is on the negative sound pressure side as shown in FIG. It turns out that it is biased to. Therefore, the reproduced sound is recognized as a sound with a sense of incongruity for the listener.
On the other hand, in the ultrasonic speaker according to the present invention (FIG. 1), the sound pressure level of the modulator is set to the positive sound pressure side in advance by the sound pressure level adjuster 20 so that the sound pressure level of the reproduction signal is symmetrical. Since the shift is adjusted so that the shift amount is 0.8% of the maximum amplitude of the modulation signal in FIG. 6A, for example, the sound pressure level of the reproduction signal is as shown in FIG. Symmetry is positive and negative, and it is possible to reproduce a sound that is comfortable for the listener.
[0032]
In this embodiment, the sound pressure level adjuster 20 sets the shift amount of the sound pressure level of the modulation signal that is the output of the modulator 14 to the distance from the sound wave emitting surface of the ultrasonic transducer to the reproduction point in the radial axis direction. However, as described above, since there is an improvement effect even when it is not strictly positive-negative symmetric, the shift amount of the sound pressure level of the modulation signal is set to the sound wave emitting surface of the ultrasonic transducer. It may be a fixed value that shifts in advance to the positive sound pressure side regardless of the distance from to the reproduction point.
[0033]
According to this embodiment, a carrier wave is modulated by a signal wave output from a signal source that generates a signal wave in an audible frequency band, and an ultrasonic transducer that can oscillate an acoustic signal in a wide frequency band is driven by the modulated signal. As a result, the sound pressure level of the modulation signal applied to the ultrasonic transducer is shifted so that the sound pressure distribution of the signal sound is subject to positive and negative in the ultrasonic speaker that reproduces the signal sound in the audible frequency band. Therefore, it is possible to reproduce the sound without a sense of incongruity for the listener.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an ultrasonic speaker according to an embodiment of the present invention.
2 is a block diagram showing an example of a specific configuration of a sound pressure level adjuster in the ultrasonic speaker according to the embodiment of the present invention shown in FIG. 1;
FIG. 3 is a diagram showing a specific configuration of an ultrasonic transducer in the ultrasonic speaker according to the embodiment of the present invention shown in FIG. 1;
4 is a characteristic diagram showing frequency characteristics of the ultrasonic transducer shown in FIG. 3; FIG.
FIG. 5 shows the characteristics of a conventional ultrasonic speaker, and shows waveforms of a modulated signal (FIG. 5A), a propagation wave (FIG. 5B), and a reproduction signal (FIG. 5C). Figure.
FIG. 6 shows the characteristics of the ultrasonic speaker according to the present invention, and each waveform of the modulation signal (FIG. 6 (a)), the propagation wave (FIG. 6 (b)), and the reproduction signal (FIG. 6 (c)). FIG.
FIG. 7 is a block diagram showing a configuration of a conventional ultrasonic speaker.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Audio frequency wave oscillation source 12 ... Carrier wave oscillation source 14 ... Modulator 16 ... Power amplifier 18 ... Ultrasonic transducer 20 ... Sound pressure level adjuster

Claims (8)

A carrier wave is modulated by a signal wave output from a signal source that generates a signal wave in an audible frequency band, and an ultrasonic transducer capable of oscillating an acoustic signal in a wide frequency band is driven by the modulated signal. An ultrasonic speaker signal sound reproducing method for reproducing a signal sound,
A signal sound reproduction method of an ultrasonic speaker, wherein a sound pressure level of a modulation signal applied to the ultrasonic transducer is shifted so that a sound pressure distribution of the signal sound is a target of positive and negative. 2. The method for reproducing signal sound of an ultrasonic speaker according to claim 1, wherein the sound pressure level of the modulation signal is shifted in the positive direction in advance. The amount of shift of the sound pressure level of the modulation signal is adjusted according to the distance from the sound wave emission surface of the ultrasonic transducer to the reproduction point in the radial axis direction. A method for reproducing sound signals of an ultrasonic speaker. 3. The ultrasonic wave according to claim 1, wherein a shift amount of a sound pressure level of the modulation signal is set to a fixed value regardless of a distance from a sound wave emitting surface of the ultrasonic transducer to a reproduction point. A method for reproducing signal sound of a speaker. 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;
Modulation means for modulating the carrier wave with the signal wave;
An ultrasonic transducer that is driven by the modulation signal output from the modulation means and converts the modulation signal into a sound wave of a finite amplitude level and radiates it into the medium, and a reproduction signal that is a signal sound in an audible frequency band An ultrasonic speaker for output,
An ultrasonic speaker comprising sound pressure level adjusting means for shifting a sound pressure level of a modulation signal applied to the ultrasonic transducer so that a sound pressure distribution of the signal sound is a target of positive and negative. The sound pressure level adjusting means can adjust the shift amount of the sound pressure level of the modulated wave according to the distance from the sound wave emitting surface of the ultrasonic transducer to the reproduction point in the radial axis direction. Item 6. The ultrasonic speaker according to Item 5. The sound pressure level adjusting means is
The relationship between the distance from the sound wave emitting surface of the ultrasonic transducer to the reproduction point in the radial axis direction and the amount of shift in the sound pressure level of the modulation signal necessary for making the sound pressure distribution of the signal sound positive or negative A storage unit in which a table to be stored is stored in advance;
The distance information from the sound wave emitting surface of the ultrasonic transducer input from the outside to the reproduction point in the radial axis direction is taken in, the table is referred to, and the shift amount of the sound pressure level of the modulation signal according to the distance information is calculated. A shift amount selection unit for obtaining and outputting the shift amount;
A sound pressure level adjustment unit that shifts and outputs the sound pressure level of the modulation signal by the shift amount input from the shift amount selection unit;
The ultrasonic speaker according to claim 5 or 6, characterized by comprising: 6. The ultrasonic speaker according to claim 5, wherein the sound pressure level adjusting means has a fixed shift amount so as to shift the sound pressure level of the modulation signal in a positive direction in advance.

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