JP4785647B2 - Super directional acoustic device - Google Patents

Description

  The present invention relates to a superdirective acoustic device that emits audible sound in a narrow area.

A super-directional acoustic device that radiates audible sound within a limited area using a carrier wave in the ultrasonic band by utilizing a nonlinear phenomenon of air, an amplitude modulator generates a carrier wave signal generated by a high-frequency generator. Amplitude modulation is performed with a sound signal representing audible sound, and an emitter generates an ultrasonic wave based on the modulation signal output from the amplitude modulator. The emitter used in such a device has sound pressure frequency characteristics including a steep peak. In a typical apparatus, the emitter resonance frequency at which the characteristic curve has a peak in the sound pressure frequency characteristic of the emitter is used as the frequency of the carrier wave.
In addition, some parametric speakers or emitters are operated to obtain a sufficient volume. When configured and operated in this way, a significant phase difference occurs in the acoustic output of each emitter, and the output and directivity become lower than theoretically. For this reason, there is a technique that uses a carrier wave having a frequency shifted by 1 to 5% from the maximum resonance frequency of the emitter so that the output phases of the emitters coincide with each other (see, for example, Patent Document 1).

Japanese translation of PCT publication No. 2003-513576 (pages 12-13, FIG. 2)

Since the conventional superdirective acoustic device is configured as described above, the carrier wave of the emitter resonance frequency is modulated with audible sound, so the relationship between the sound pressure frequency characteristic of the emitter and the carrier wave and sidebands, There was a problem that the sound pressure of the audible sound self-demodulated from the ultrasonic wave emitted from the emitter was reduced.
In addition, if the sound pressure level of audible sound is improved by using a plurality of emitters, the configuration of the apparatus becomes complicated and the cost is increased, and processing for aligning the output phase of each emitter is required, and the operation is also complicated. There was a problem.

  The present invention has been made to solve the above-described problems. When an ultrasonic wave is amplitude-modulated with an audible voice and the ultrasonic wave is radiated, the sound pressure of the audible voice is self-demodulated from the ultrasonic wave. An object of the present invention is to obtain a super-directional acoustic device that can improve the sound efficiency efficiently.

  In the superdirective acoustic device according to the present invention, the amplitude modulation means includes the sound pressure of the carrier wave in the sound pressure frequency characteristic of the emitter and the sound pressure of the sideband when the carrier wave is amplitude-modulated with an audio signal. A carrier wave signal having a frequency that increases the product is generated.

  According to the present invention, a carrier wave signal having a frequency at which the product of the sound pressure of the carrier wave and the sound pressure of the sideband when the carrier wave is amplitude-modulated with the sound signal in the sound pressure frequency characteristic of the emitter is increased. Since the amplitude modulation means is generated, it is possible to increase the sound pressure of the audible sound that is self-demodulated from the carrier wave and the side band of the ultrasonic band emitted from the emitter without complicating the device configuration. There is.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a superdirective acoustic device according to Embodiment 1 of the present invention. The illustrated superdirective acoustic apparatus includes a sound generator 1 that generates a sound signal indicating audible sound, an amplitude modulator 2 that receives the sound signal and generates an amplitude modulation signal, an amplifier 3 that amplifies the amplitude modulation signal, and an amplifier. 3 is formed by an emitter 4 that receives the amplitude-modulated signal amplified by 3 and generates ultrasonic waves.
The amplitude modulator 2 inputs a high-frequency generator 21 that generates a signal indicating a carrier wave in the ultrasonic band, a carrier wave signal from the high-frequency generator 21 and an audio signal from the audio generator 1, and outputs these signals. The multiplier 22 is configured to perform multiplication processing. The emitter 4 that emits ultrasonic waves is provided with an ultrasonic vibrator made of an organic hard piezoelectric material such as lead zirconate titanate, that is, PZT.

FIG. 2 is a block diagram showing a configuration of an amplitude modulator provided in the superdirective acoustic device according to the first embodiment. The same parts as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. This diagram shows a schematic configuration of the amplitude modulator 2 when the superdirective acoustic device shown in FIG. 1 is a device that performs single side band (hereinafter referred to as SSB) modulation that can be processed relatively efficiently. It is shown. The amplitude modulator 2 that performs SSB modulation is a multiplier 22 that multiplies the audio signal from the audio generator 1 and the carrier wave signal from the high-frequency generator 21 shown in FIG. 1 and the signal processed by the multiplier 22. A filter 23 that performs filtering on frequency components, an attenuator 24 that inputs a carrier wave signal from the high-frequency generator 21 and adjusts the level of the signal, and an output signal of the filter 23 and an output signal of the attenuator 24 are added to perform amplitude modulation. The adder 25 outputs a signal.
For example, when performing SSB modulation having an upper side band, the filter 23 suppresses a carrier wave and a side band in a frequency band lower than the carrier wave, and has a filter characteristic that passes a side band in a frequency band higher than the carrier wave. It is what you have. In addition, when performing SSB modulation having a lower sideband, a filter having a filter characteristic that passes a sideband in a frequency band lower than that of the carrier wave is used.

Next, the operation will be described.
The sound generator 1 shown in FIG. 1 generates a sound signal indicating sound in an audible band. This audio signal is input to the multiplier 22 of the amplitude modulator 2. In the amplitude modulator 2, the high frequency generator 21 generates a carrier wave signal indicating a carrier wave in the ultrasonic band. The carrier wave signal generated here represents an ultrasonic wave having a frequency different from the resonance frequency of the emitter 4 as described later, that is, a frequency shifted from the emitter resonance frequency. This carrier wave signal is also input to the multiplier 22 in the same manner as the audio signal described above. The multiplier 22 performs a multiplication process on the audio signal and the carrier wave signal, and generates an amplitude modulation signal obtained by amplitude-modulating the carrier wave signal with the audio signal. In order to set the modulation rate to 100%, for example, an adder for inputting an audio signal (not shown) or the like so that the sideband level generated by amplitude modulation is “−6 dB” with respect to the carrier wave level. The multiplication process is performed by adjusting the level of the audio signal by the processing operation.

  The amplifier 3 to which the amplitude modulation signal is input from the amplitude modulator 2 amplifies the amplitude modulation signal to a level at which the emitter 4 can be driven. The emitter 4 generates an ultrasonic wave according to the amplitude modulation signal input from the amplifier 3. The ultrasonic wave radiated from the emitter 4 is self-demodulated into an audible voice represented by the above-mentioned voice signal by a non-linear interaction when propagating in the air. In this way, an audible sound that can be heard only within a limited area, for example, in the form of a beam, is emitted.

When the superdirective acoustic device shown in FIG. 1 operates, for example, by performing SSB modulation, modulation is performed by the amplitude modulator 2 shown in FIG. The amplitude modulator 2 outputs an audio signal output from the audio generator 1 and a carrier wave signal having a frequency shifted from the emitter resonance frequency fe in the same manner as described above, output from the high frequency generator 21. Input to the multiplier 22 to perform multiplication processing. Next, the output signal of the multiplier 22 is input to the filter 23.
For example, when performing SSB modulation having an upper side band, the filter 23 acts as a high-pass filter as described above, and attenuates the carrier wave and the lower side band of the carrier wave from the output signal of the multiplier 22. And pass the sideband component of the upper band.
On the other hand, the carrier wave signal output from the high frequency generator 21 is input to the attenuator 24. The attenuator 24 attenuates the level of the input carrier wave signal and adjusts the level so that it matches the signal level output from the filter 23, that is, ensures a high modulation rate and does not cause distortion due to modulation. I do.
The output signal of the filter 23 and the output signal of the attenuator 24 are input to the adder 25, and the addition processing of these signals is performed to generate a modulation signal composed of the upper side band and the carrier wave. The modulation signal subjected to the SSB modulation having the upper side band in this way is input to the amplifier 3 and amplified to a level at which the emitter 4 can be driven. The emitter 4 is driven to emit ultrasonic waves by SSB modulation.

FIG. 3A is an explanatory diagram illustrating an operation of a superdirective acoustic apparatus that performs double side band (hereinafter referred to as DSB) modulation. FIG. 3B is an explanatory diagram illustrating the operation of the superdirective acoustic device that performs SSB modulation. In these drawings, the same or corresponding parts will be described using the same reference numerals.
As described above, the emitter 4 generates ultrasonic waves by using an ultrasonic transducer made of an organic hard piezoelectric material, and generally has a plurality of sound pressure peaks as sound pressure frequency characteristics. The emitter 4 illustrated here has a sound pressure frequency characteristic having two sound pressure peaks, and this characteristic is the sound pressure frequency characteristic A of the characteristic curve shown in FIGS. It is expressed as follows. In the illustrated sound pressure frequency characteristic A, a portion where the sound pressure is highest is defined as a first peak, and a sound pressure peak having a frequency higher than the emitter resonance frequency fe in the drawing is defined as a second peak. Here, the frequency of the first peak is described as the emitter resonance frequency fe. In the graphs shown in FIGS. 3A and 3B, the vertical axis represents the sound pressure [dB] of the ultrasonic wave radiated from the radiator, that is, the emitter 4, and the horizontal axis represents the frequency [Hz]. It represents the frequency of the band.

There are two types of amplitude modulation: DSB modulation and SSB modulation. The ones shown in FIGS. 3A and 3B represent operations when amplitude modulation is performed using the emitter resonance frequency fe as the frequency of the carrier wave B. ing.
When DSB modulation is performed, sidebands C are generated in the upper and lower frequency bands around the carrier wave B as shown in FIG.
When the SSB modulation is performed, the sideband C exists in either the higher frequency band or the lower frequency band than the carrier wave B. For example, when the upper side band, that is, the amplitude modulation having the USB is performed, FIG. As shown in -2, a sideband C is generated in a frequency band higher than the carrier wave B. Further, when amplitude modulation having a lower sideband, that is, LSB is performed, a sideband C is generated in a frequency band lower than the carrier wave B.
Note that SSB modulation can reduce the amount of data processing required for modulation compared to DSB modulation, and is advantageous when processing a digital data audio signal or carrier wave signal. In addition, SSB modulation theoretically does not generate second-order harmonic distortion and can reduce harmonic distortion, so that modulation efficiency can be improved.

  When audible sound is radiated from the emitter 4 as an ultrasonic wave as a carrier wave, self-demodulation is performed from the ultrasonic wave to the audible sound by the interaction between the frequency component of the carrier wave and the frequency component of the sideband. That is, the sideband component radiated from the emitter 4 affects the sound pressure level of the audible sound that is self-demodulated. Therefore, as illustrated in FIG. 3-2, when the SBS modulation is performed with the emitter resonance frequency fe as the frequency of the carrier wave B to perform superradiant acoustic radiation, when a general emitter 4 is used, The sound pressure level of the side band C is considerably lower than the sound pressure level of the carrier wave B, and the sound pressure level of the carrier wave B and the sound pressure level of the side band C are within the sound pressure frequency characteristics A of the emitter 4. The product becomes a small value and the sound pressure level of the audible sound demodulated from the ultrasonic wave is lowered. When the emitter resonance frequency fe is set as the frequency of the carrier wave B as shown in FIGS. 3A and 3B, especially when SSB modulation is used, the carrier depends on the sound pressure frequency characteristic A of the emitter 4 described above. The product of the sound pressure of the wave B and the sound pressure of the sideband C becomes a small value.

  Therefore, the amplitude modulator 2 according to the first embodiment sets the frequency of the carrier wave B to be higher or lower than the emitter resonance frequency fe so as to output audible sound with high sound pressure. When the product of the sound pressure level of the carrier wave B depending on the sound pressure frequency characteristic A of the emitter 4 and the sound pressure level of the sideband C is obtained, this value uses at least the emitter resonance frequency fe as the frequency of the carrier wave B. Amplitude modulation is performed by setting the frequency of the carrier wave B so as to be larger than the product of the sound pressure of the carrier wave B and the sound pressure of the sideband C in the sound pressure frequency characteristic A. Such an operation is particularly effective when performing SSB modulation. When the amplitude modulation handles an audible voice band, the side band C is approximately “+20 kHz” from the frequency of the carrier wave B in the SSB modulation having the upper side band, for example. Further, in the SSB modulation having the lower sideband, the sideband C is approximately “−20 kHz” from the frequency of the carrier wave B.

  FIG. 4A is an explanatory diagram of an operation of the superdirective acoustic device according to the first embodiment. FIG. 4B is an explanatory diagram illustrating the operation of amplitude modulation. In these drawings, the same reference numerals are used for the same or corresponding parts as those shown in FIG. 3B, and the description thereof is omitted. The vertical axis shown in FIGS. 4A and 4B represents the sound pressure [dB] of the ultrasonic wave radiated from the emitter 4, and the horizontal axis represents the frequency [Hz]. In particular, the frequency in the ultrasonic band is shown. Represents. FIG. 4-1 shows the sound pressure frequency characteristic A of the emitter 4 constituting the superdirective acoustic device according to Embodiment 1, the carrier wave B and the sideband when the amplitude modulator 2 performs SSB modulation having the upper sideband. An example of the relationship with C is shown. FIG. 4B illustrates an example of the relationship between the sound pressure frequency characteristic A, the carrier wave B, and the sideband C that cannot increase the sound pressure of audible sound when SSB modulation is performed.

The high-frequency generator 21 shown in FIG. 1 and FIG. 2 is a carrier wave indicating an ultrasonic wave having a frequency higher or lower than the emitter resonance frequency fe that forms the peak of the sound pressure in the sound pressure frequency characteristic A of the emitter 4. Generate a signal. This carrier wave signal has a frequency included in the range from the emitter resonance frequency fe to approximately 20% of the emitter resonance frequency fe.
Since the sound pressure peak occurs at the emitter resonance frequency fe as described above, the emitter 4 has a lower side wave when the amplitude modulator 2 uses, for example, a carrier wave B having a frequency higher than the emitter resonance frequency fe for amplitude modulation. SSB modulation with band or LSB is performed. As a result, the frequency of the carrier wave B and the frequency band of the sideband C sandwich the emitter resonance frequency fe, and the sound pressure of the carrier wave B and the sound pressure of the sideband C It becomes the sound pressure on both sides of the pressure peak, and the product of the sound pressure of the carrier wave B and the sound pressure of the sideband C in the sound pressure frequency characteristic A can be increased.
Further, when the carrier wave B having a frequency lower than the emitter resonance frequency fe is used, SSB modulation having an upper side band, that is, USB is performed. Also in this case, the sound pressure of the carrier wave B and the sound pressure of the sideband C become the sound pressures on both sides of the sound pressure peak in the sound pressure frequency characteristic A, as described above, and the sound pressure frequency In the characteristic A, the product of the sound pressure of the carrier wave B and the sound pressure of the sideband C can be set to a large value.

The frequency of the carrier wave signal generated by the high frequency generator 21 is set according to the sound pressure frequency characteristic A of the emitter 4 provided in the superdirective acoustic device. When the slope of the characteristic curve of the sound pressure frequency characteristic A is gentle in a band higher than the emitter resonance frequency fe, the frequency of the carrier wave B is set higher than the emitter resonance frequency fe. When SSB modulation with LSB is performed as described above, the sound pressure level of the sideband C becomes relatively high in the sound pressure frequency characteristic A, and the sound pressure of the carrier wave B and the sideband C The product with the sound pressure of becomes a large value.
Further, when the slope of the characteristic curve of the sound pressure frequency characteristic A is gentle in a band lower than the emitter resonance frequency fe, the frequency of the carrier wave B is set lower than the emitter resonance frequency fe. When SSB modulation with USB is performed as described above, the sound pressure level of the sideband C becomes relatively high in the sound pressure frequency characteristic A, and the sound pressure of the carrier wave B and the sideband C The product with the sound pressure of becomes a large value.

  For example, the sound pressure frequency characteristic A of the emitter 4 changes similarly in the upper and lower frequency bands of the emitter resonance frequency fe, that is, the characteristic curve of the sound pressure frequency characteristic A has substantially the same slope on both sides of the emitter resonance frequency fe. 2 is configured so that the characteristics of the filter 23 shown in FIG. 2 can be switched according to the setting from the outside, and the frequency of the carrier wave B is set to a frequency higher than the emitter resonance frequency fe in conjunction with this switching setting, Alternatively, the high frequency generator 21 is configured so as to generate a carrier wave signal by setting one of the low frequencies, and the amplitude modulator 2 is operated so as to operate by selecting either modulation using USB or modulation using LSB. May be configured.

  Further, as described above, the frequency of the carrier wave B is set to a value moved within a range of approximately 20% from the emitter resonance frequency fe. However, if the carrier wave B is moved more greatly than the emitter resonance frequency fe, the sound pressure is increased. In the frequency characteristic A, the sound pressure level of the carrier wave B becomes low, the product of the sound pressure level of the carrier wave B and the sound pressure level of the sideband C becomes a small value, and the ultrasonic wave radiated from the emitter 4 is reduced. The sound pressure level when self-demodulating to become audible sound is also lowered. Therefore, the frequency of the carrier wave B is set to a frequency shifted in a range smaller than 20% of the emitter resonance frequency fe, that is, a frequency included in the range from the emitter resonance frequency fe to about 20% of the emitter resonance frequency fe.

  FIG. 5 is an explanatory diagram illustrating the operation of the superdirective acoustic device according to the first embodiment. This figure is a graph showing the sound pressure frequency characteristics of an audible sound that is amplified by an amplifier 3 to emit an ultrasonic wave from the emitter 4 and self-demodulates in the air. The axis represents sound pressure [dB], and the horizontal axis represents frequency [Hz], particularly the frequency of the audible voice band. A characteristic curve D indicated by a one-dot broken line in the figure represents a sound pressure frequency characteristic of audible sound that is self-demodulated when the carrier wave B having the emitter resonance frequency fe is used. A characteristic curve E indicated by a broken line in the figure shows a sound pressure frequency characteristic of an audible sound that is self-demodulated when a carrier wave B having a frequency lower than the emitter resonance frequency fe is used. A characteristic curve F indicated by a solid line in the figure shows a sound pressure frequency characteristic of an audible sound that is self-demodulated when a carrier wave B having a frequency higher than the emitter resonance frequency fe is used.

A characteristic curve D in FIG. 5 represents a sound pressure frequency characteristic of audible sound when the ultrasonic wave composed of the carrier wave B and the sideband C shown in FIG. 3-2 is radiated from the emitter 4. E is a sound pressure frequency characteristic of the audible sound when the ultrasonic wave composed of the carrier wave B and the sideband C shown in FIG. The product of the sound pressure of the carrier wave B and the sound pressure of the sideband C in FIG. 4-2 is a smaller value than that shown in FIG. 3-2. Therefore, the characteristic curve E is almost all audible sounds. The band is below the characteristic curve D, and the sound pressure level of the audible sound self-demodulated from the ultrasonic wave is low.
A characteristic curve F represents an audible sound pressure frequency characteristic that is self-demodulated when the ultrasonic wave composed of the carrier wave B and the sideband C shown in FIG. is there. The sound pressure level of the carrier wave B shown in FIG. 4A is lower than the sound pressure of the carrier wave B and the sound pressure of the side band C shown in FIG. Since the pressure level is high, the product of the sound pressure of the carrier wave B and the sound pressure of the sideband C in FIG. 4-1 is higher than that shown in FIGS. 3-2 and 4-2 above. Great value. When the carrier wave B and the sideband C ultrasonic waves having the frequencies shown in FIG. 4A are radiated from the emitter 4, the sound pressure level of the audible sound demodulated from the ultrasonic waves, that is, the characteristic curve F is the characteristic curve D or the characteristic curve F. The value is higher than the sound pressure level indicated by the curve E, particularly from the low to mid range to the high range.

  Further, when the emitter resonance frequency fe is used as a carrier wave, the impedance of the emitter 4 is lowered. However, when a carrier wave having a frequency deviated from the emitter resonance frequency fe described so far is used, the impedance of the emitter 4 is The load on the amplifier 3 driving the emitter 4 can be reduced.

As described above, according to the first embodiment, the frequency of the carrier wave B is set to a frequency shifted within a range smaller than 20% from the emitter resonance frequency fe based on the sound pressure frequency characteristic A of the emitter 4, and the sound In the frequency characteristic A, the high frequency generator 22 generates a carrier wave signal by setting a frequency at which the product of the sound pressure of the carrier wave B and the sound pressure of the sideband C is large, and the amplitude modulator 2 Since the amplitude modulation signal is generated using the carrier wave signal, when the emitter 4 emits an ultrasonic wave based on the amplitude modulation signal, the sound pressure of the audible sound self-demodulated from the ultrasonic wave is improved. There is an effect that can be.
Further, since the amplitude modulation signal is generated by adapting the setting of the frequency of the carrier wave signal generated by the high frequency generator 22 to the sound pressure frequency characteristic A of the emitter 4, the emitter 4 can be generated without complicating the configuration. There is an effect that the sound pressure of the audible sound emitted can be increased.

It is a block diagram which shows the structure of the super-directional sound apparatus by Embodiment 1 of this invention. 3 is a block diagram showing a configuration of an amplitude modulator provided in the superdirective acoustic device according to Embodiment 1. FIG. It is explanatory drawing which shows operation | movement of the super-directional sound apparatus which performs DSB modulation. It is explanatory drawing which shows operation | movement of the super-directional sound apparatus which performs SSB modulation. FIG. 6 is an explanatory diagram illustrating an operation of the superdirective acoustic device according to the first embodiment. It is explanatory drawing which shows the operation | movement of amplitude modulation. FIG. 6 is an explanatory diagram illustrating an operation of the superdirective acoustic device according to the first embodiment.

Explanation of symbols

1 sound generator, 2 amplitude modulator, 3 amplifier, 4 emitter, 21 high frequency generator, 22 multiplier, 23 filter, 24 attenuator, 25 adder.

Claims (5)

An audio signal generating means for generating an audio signal indicating an audible sound; and an amplitude-modulated signal by generating a carrier wave signal indicating a carrier wave in an ultrasonic band and amplitude-modulating the carrier wave signal with the audio signal inputted from the audio generating means Superdirective sound comprising: amplitude modulation means for generating amplifying means; amplification means for amplifying the amplitude modulation signal; and an emitter for emitting audible sound using ultrasonic waves as carrier waves based on the amplitude modulation signal from the amplifier In the device
The amplitude modulation means includes a carrier wave having a frequency in which the product of the sound pressure of the carrier wave and the sound pressure of the sideband when the carrier wave is amplitude-modulated with an audio signal in the sound pressure frequency characteristics of the emitter is increased. A super-directional acoustic device characterized by generating a signal.   2. The superdirective sound according to claim 1, wherein the amplitude modulation means generates a carrier wave signal having a frequency higher than the resonance frequency of the emitter and performs SSB modulation having a lower sideband of the carrier wave signal. apparatus.   The superdirective acoustic device according to claim 1, wherein the amplitude modulation means generates a carrier wave signal having a frequency lower than the resonance frequency of the emitter and performs SSB modulation having an upper side band of the carrier wave signal. .   The amplitude modulation means performs SSB modulation having a lower sideband of the carrier wave signal when set to generate a carrier wave signal having a frequency higher than the resonance frequency of the emitter from the outside, or the resonance frequency of the emitter The superdirective acoustic device according to claim 1, wherein when set to generate a carrier wave signal having a lower frequency, SSB modulation having an upper side band of the carrier wave signal is performed. The amplitude modulation means generates a carrier wave signal having a frequency shifted from a resonance frequency of the emitter within a range smaller than 20% of the resonance frequency. The superdirective acoustic device described.

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