JP2022021931A - Method for sound pressure improvement of parametric speaker, and parametric speaker - Google Patents

Abstract

To provide a parametric speaker which improves the sound pressure of a demodulation tone of the parametric speaker.SOLUTION: A method for sound pressure improvement of the parametric speaker comprises modulating the amplitude or frequency of a carrier in response to the target signal 60 of an audible sound and outputting a modulated signal 65 generated by the modulation, from an ultrasonic wave generation element 30. The carrier is a pulse modulation carrier 62.SELECTED DRAWING: Figure 1

Description

Application for application of Article 30, Paragraph 2 of the Patent Law has been applied. March 2, 2nd year of Reiwa, Institute of Electronics, Information and Communication Engineers Kansai Branch 25th Student Association Research Presentation Lecture Proceedings

The present disclosure relates to a method for improving the sound pressure of a parametric speaker and a parametric speaker.

Patent Document 1 discloses a parametric speaker. The parametric speaker is configured to radiate a modulated signal in which carriers in the ultrasonic band are modulated according to a target signal which is an audible sound through an ultrasonic generating element. The radiated modulation signal is demodulated by self-demodulating based on the non-linearity of the air. The parametric speaker is configured to convey the demodulated sound, which is the audible sound produced by the demodulated modulated signal.

Japanese Unexamined Patent Publication No. 2004-349816

Since the parametric speaker self-demodulates the modulated signal based on the non-linearity of air, there is a problem that the demodulated sound pressure is small. Therefore, it is desired to improve the sound pressure of the demodulated sound in the parametric speaker.

One aspect of the present disclosure is a method of improving the sound pressure of a parametric speaker. The disclosed method for improving the sound pressure of a parametric speaker comprises modulating the amplitude or frequency of a carrier according to a target signal which is an audible sound, and outputting the modulated signal generated by the modulation from an ultrasonic generating element. The carrier is a pulse modulation carrier.

Another aspect of the disclosure is a parametric speaker. The disclosed parametric speakers include a carrier generator that generates carriers, a modulation circuit that modulates the amplitude or frequency of the carriers according to an audible target signal, and ultrasonic generation that emits a modulation signal modulated by the modulation circuit. It is equipped with an element. The carrier generator is a pulse modulation carrier generator that generates a pulse modulation carrier.

Further details will be described in the embodiments described below.

FIG. 1 is a block diagram showing a schematic configuration of a parametric speaker according to the first embodiment. FIG. 2 is a schematic diagram showing a reproduction principle (modulated wave output method) of a target signal (audible sound) in the parametric speaker of FIG. FIG. 3 is a block diagram showing a schematic configuration of a parametric speaker according to the second embodiment. FIG. 4 is a schematic diagram showing a reproduction principle (modulated wave output method) of a target signal (audible sound) in the parametric speaker of FIG. FIG. 5 is a schematic diagram of an amplitude modulation method and a frequency modulation method when a pure tone (cosine wave) carrier is used as the carrier of the parametric speaker. FIG. 6 is a diagram showing the energy of the carrier waveform of a pure tone (cosine wave). FIG. 7 is a diagram showing the energy of the waveform of the carrier of pulse modulation. FIG. 8 is a diagram showing the relationship between the sound pressure of the carrier and the sound pressure of the demodulated sound in the modulated wave. FIG. 9 is a graph showing the sound pressure level of the demodulated sound in each modulation method in the evaluation experiment. FIG. 10 is a schematic diagram showing an amplitude modulation method when a triangular wave carrier is used as the carrier of the parametric speaker. FIG. 11 is a diagram showing a comparison result of the sound pressure level of the demodulated sound in each carrier in the verification experiment 1. FIG. 12 is a diagram showing a comparison result of the sound pressure level of the demodulated sound in each carrier in the verification experiment 2. FIG. 13 is a diagram showing the harmonic distortion factor in each modulation method in the verification experiment 3. FIG. 14 is a diagram showing the PESQ value of the male voice in each modulation method in the verification experiment 4. FIG. 15 is a diagram showing the PESQ value of the female voice in each modulation method in the verification experiment 4.

<1. How to improve the sound pressure of parametric speakers and overview of parametric speakers>

(1) The method for improving the sound pressure of the parametric speaker according to the embodiment is to modulate the amplitude or frequency of the carrier according to the target signal of the audible sound, and output the modulated signal generated by the modulation from the ultrasonic generating element. , Equipped with. The carrier is a pulse modulation carrier. Since the waveform energy of the pulse modulation carrier is large, the sound pressure of the carrier increases by making the carrier a pulse modulation carrier. As a result, the sound pressure of the generated modulated signal is amplified. As a result, the sound pressure of the audible sound generated from the ultrasonic wave generating element can be improved.

(2) The modulation is pulse amplitude modulation that changes the amplitude of the pulse modulation carrier according to the target signal. In this case, pulse amplitude modulation produces a modulated signal with amplified sound pressure. As a result, the modulated signal with amplified sound pressure is input to the ultrasonic wave generating element. As a result, the sound pressure of the audible sound generated from the ultrasonic wave generating element can be improved.

(3) The parametric speaker according to the embodiment includes a carrier generator that generates a carrier, a modulation circuit that modulates the amplitude or frequency of the carrier according to a target signal of an audible sound, and a modulation signal modulated by the modulation circuit. It comprises an ultrasonic generator that emits radiation, and the carrier generator is characterized in that it generates a pulse modulation carrier. The pulse modulation carrier generator generates a pulse modulation carrier that amplifies the sound pressure, so that the sound pressure of the modulated signal modulated by the modulation circuit is also amplified. As a result, the sound pressure of the audible sound generated from the ultrasonic wave generating element can be improved.

<2. How to improve the sound pressure of parametric speakers and examples of parametric speakers>

<2.1 First Embodiment>

<Structure in the first embodiment>

FIG. 1 shows a parametric speaker according to the first embodiment. The first parametric speaker 1 shown in FIG. 1 is configured to radiate a modulated signal 65 obtained by modulating a carrier in the ultrasonic band according to the amplitude of a target signal 60 which is an audible sound. In the first embodiment, the carrier is modulated in amplitude according to the amplitude of the target signal 60.

The first parametric speaker 1 includes a plurality of ultrasonic wave generating elements 30. Each of the plurality of ultrasonic wave generating elements 30 emits a modulated signal 65. The radiated modulation signal 65 is demodulated by self-demodulation due to the influence of the non-linearity of air, and a demodulated sound 70 which is an audible sound is generated. As the carrier, a pulse modulation carrier 62 is used.

The first parametric speaker 1 includes a signal processing circuit 10 that generates a modulation signal 65 radiated from the ultrasonic wave generating element 30. The signal processing circuit 10 includes a pulse modulation carrier generator 11. The pulse modulation carrier generator 11 generates the pulse modulation carrier 62. The pulse modulation carrier generator 11 includes, for example, a high frequency oscillator using a crystal oscillator or the like.

The signal processing circuit 10 includes a pulse amplitude modulation circuit 13. The pulse amplitude modulation circuit 13 receives the input of the pulse modulation carrier 62 from the pulse modulation carrier generator 11 and also receives the input of the target signal 60. The pulse amplitude modulation circuit 13 modulates the amplitude of the pulse modulation carrier 62 based on the amplitude of the target signal 60 to generate the pulse amplitude modulation signal 65.

The pulse amplitude modulation circuit 13 may be configured by, for example, a digital circuit or an analog circuit. The digital circuit is composed of a processor such as a CPU and a computer provided with a memory, for example. The processor executes a computer program stored in memory. The computer program is configured to cause the computer to function, for example, as a pulse amplitude modulation circuit 13.

The pulse amplitude modulation circuit 13 is connected to the amplifier 20. The amplifier 20 receives the input of the pulse amplitude modulation signal 65 from the pulse amplitude modulation circuit 13. The amplifier 20 amplifies the pulse amplitude modulation signal 65, and inputs the amplified pulse amplitude modulation signal 65 to the ultrasonic generation element 30. The amplifier 20 is configured by using, for example, an operational amplifier having good amplification characteristics in the ultrasonic band. The pulse amplitude modulation signal 65 amplified by the amplifier 20 is input to the ultrasonic wave generating element 30 and radiated from the ultrasonic wave generating element 30.

<Modulated wave output in the first embodiment>

FIG. 2 shows the principle of the parametric speaker 1 in the first embodiment. The first parametric speaker 1 uses a pulse amplitude modulation method as the modulation method.

The target signal 60 is a signal representing a sound in the audible range. The audible range indicates a range of frequencies (low sound 20 [Hz] to high sound 20 [kHz]). The target signal 60 is also referred to as an acoustic signal.

The pulse modulation carrier 62 is a carrier used for pulse modulation. Pulse modulation is to modulate the amplitude or frequency of a pulsed carrier. The pulse modulation carrier has a larger carrier energy than the carrier of the cosine wave. The pulse modulation carrier is, for example, a square wave. The carrier of the square wave has a larger carrier energy than the carrier of the cosine wave. The pulse modulation carrier may be a trapezoidal wave in which the rising and falling edges of the waveform are gentler than those of the rectangular wave. The trapezoidal wave also has a larger carrier energy than the carrier of the cosine wave. The rising and falling edges may be linear or curved. A pulsed carrier such as a square wave or a trapezoidal wave has a section where the value is almost constant between the rising edge and the falling edge of the waveform, and a section where the value is almost constant between the falling edge and the rising edge. Have.

On the other hand, the carrier of the triangular wave is not pulsed and has a smaller carrier energy than the carrier of the cosine wave. Not included in pulsed carriers. The energy of the carrier waveform will be described later.

The pulse amplitude modulation signal 65 is generated by a pulse amplitude modulation method that modulates the amplitude of the pulse modulation carrier 62 based on the amplitude of the target signal 60. The pulse amplitude modulation signal 65 is input to the plurality of ultrasonic wave generating elements 30 and radiated into the air. The pulse amplitude modulation signal 65 radiated into the air is distorted due to the non-linearity of the air in the process of propagating in the air, and is self-demodulated by this distortion. As a result, the pulse amplitude modulated signal 65 radiated into the air becomes a demodulated sound 70 that can be perceived by humans as sound.

<2.2 Second Embodiment>

<Structure in the second embodiment>

FIG. 3 shows the parametric speaker 1 according to the second embodiment. The parametric speaker 1 according to the second embodiment is configured to radiate a modulated signal 67 in which the frequency of the carrier in the ultrasonic band is modulated by the frequency of the pulse modulation carrier 62 according to the amplitude of the target signal 60 which is an audible sound. Has been done.

The parametric speaker 1 according to the second embodiment includes a pulse frequency modulation circuit 15 in place of the pulse amplitude modulation circuit 13 of the parametric speaker 1 according to the first embodiment. The second embodiment is the same as the first embodiment in that the description is omitted.

The pulse frequency modulation circuit 15 receives the input of the pulse modulation carrier 62 from the pulse modulation carrier generator 11 and also receives the input of the target signal 60. The pulse frequency modulation circuit 15 modulates the frequency of the pulse modulation carrier 62 based on the amplitude of the target signal 60 to generate the pulse frequency modulation signal 67.

The pulse frequency modulation circuit 15 may be configured by, for example, a digital circuit or an analog circuit. The digital circuit is composed of a processor such as a CPU and a computer provided with a memory, for example. The processor executes a computer program stored in memory. The computer program is configured to cause the computer to function, for example, as a pulse frequency modulation circuit 15.

The pulse frequency modulation circuit 15 is connected to the amplifier 20 as in the first embodiment. The amplifier 20 receives the input of the pulse frequency modulation signal 67 from the pulse frequency modulation circuit 15. The amplifier 20 amplifies the pulse frequency modulation signal 67, and inputs the amplified pulse frequency modulation signal 67 to the ultrasonic generation element 30. The pulse frequency modulation signal 67 amplified by the amplifier 20 is input to the ultrasonic wave generating element 30 and radiated from the ultrasonic wave generating element 30.

<Modulated wave output method in the second embodiment>

FIG. 4 shows the principle of the parametric speaker 1 in the second embodiment. The parametric speaker 1 uses a pulse frequency modulation method as the modulation method.

The target signal 60 is the same signal as in the first embodiment.

The pulse modulation carrier 62 is a carrier used for pulse modulation as in the first embodiment.

The pulse frequency modulation signal 67 is generated by a pulse frequency modulation method that modulates the frequency of the pulse modulation carrier 62 based on the amplitude of the target signal 60. The pulse frequency modulation signal 67 is input to the plurality of ultrasonic wave generating elements 30 and radiated into the air. The pulse frequency modulation signal 67 radiated into the air is distorted due to the non-linearity of the air in the process of propagating in the air, and is self-demodulated by this distortion. As a result, the pulse frequency modulation signal 67 radiated into the air becomes a demodulated sound 70 that can be perceived by humans as sound.

<3. Energy of carrier waveform>

In addition to the pulse modulation carrier 62, the carrier used in the parametric speaker 1 includes, for example, a pure tone (cosine wave) carrier 82. In the following, the energy of the pure tone (cosine wave) carrier 82, the pulse modulation carrier 62, and the energy of each waveform will be compared with respect to the energy of the carrier waveform. The energy of the carrier waveform indicates the strength of the carrier waveform. The strength of the carrier waveform indicates the sound pressure of the carrier.

First, FIG. 5 shows an amplitude modulation method and a frequency modulation method when a pure tone (cosine wave) carrier 82 is used as the carrier of the parametric speaker 1. The target signal 60 is a signal similar to the first embodiment and the second embodiment.

The pure tone (cosine wave) carrier 82 has a wave motion that periodically draws a cosine waveform. The pure tone carrier may draw a complete cosine waveform or may draw an approximate waveform of the cosine waveform. A pure tone is a sound that draws a complete sine and cosine waveform (cosine waveform) at a single frequency, and is, for example, a sound emitted by a tuning fork or a vacuum tube oscillator.

The amplitude modulation signal 85 is generated by an amplitude modulation method that modulates the amplitude of the pure tone (cosine wave) carrier 82 based on the amplitude of the target signal 60. Further, the frequency modulation signal 87 is generated by a frequency modulation method that modulates the frequency of the pure tone (cosine wave) carrier 82 based on the amplitude of the target signal 60.

FIG. 6 shows an equation representing the waveform of the pure tone (cosine wave) and the energy E1 of the waveform of the pure tone (cosine wave) based on the pure tone (cosine wave) carrier 82. Here, assuming that the length (time) of one cycle of the waveform is N and the maximum amplitude of the waveform is _AC , the energy E1 of the waveform of a pure tone (cosine wave) can be expressed by the equation (1). As shown in the equation (1), the energy E1 (cosine wave energy) of the waveform of the pure tone (cosine wave) is N / _2AC ² .

FIG. 7 shows a square wave waveform and an equation representing the energy E2 (square wave energy) of the square wave waveform based on the pulse modulation carrier 62. Here, assuming that the length (time) of one cycle of the waveform is N and the maximum amplitude of the waveform is _AC , the energy E2 of the waveform of the square wave can be expressed by the equation (2). As shown in the equation (2), the energy E2 of the rectangular wave waveform is _NAC ² .

Even if the maximum amplitudes _AC of the pure tone (cosine wave) waveform and the rectangular wave waveform are the same, the energy E2 of the rectangular wave waveform is twice the energy E1 of the pure tone (cosine wave) waveform. From this, it can be seen that the waveform of the rectangular wave has a larger energy than the waveform of the pure tone (cosine wave). That is, the waveform of the square wave indicates that the sound pressure is larger than that of the waveform of the pure tone (cosine wave).

Therefore, the pulse amplitude modulation signal 65 and the pulse frequency modulation signal 67 generated by using the pulse modulation carrier 62 have a large sound pressure. As a result, the sound pressures of the pulse amplitude modulation signal 65 and the pulse frequency modulation signal 67 radiated from the plurality of ultrasonic generation elements 30 also increase. As a result, the sound pressure of the demodulated sound 70, which can be perceived by humans as sound, increases. In other words, as the energy of the carrier waveform increases, the sound pressure of the carrier increases. As the sound pressure of the carrier increases, the sound pressure of the demodulated sound increases. That is, as the energy of the carrier waveform increases, the sound pressure of the demodulated sound 70 increases. As a result, the sound pressure of the demodulated sound 70 is improved.

By comparing the waveform energy of the carrier of pure tone (cosine wave) with the waveform energy of the pulse modulation carrier 62, as shown in FIG. 8, as the sound pressure of the carrier increases, the sound pressure of the demodulated sound also increases. Recognize. In the graph shown in FIG. 8, the horizontal axis shows the sound pressure level [dB] of the carrier, and the vertical axis shows the sound pressure level [dB] of the demodulated sound 70.

The sound pressure level represents the strength of the sound pressure, which is the amount of pressure change from the atmospheric pressure. A high sound pressure level means that the sound pressure is high.

<4. Evaluation experiment>

The inventor of the present application conducted an evaluation experiment to confirm that the pulse modulation carrier 62 is effective in improving the sound pressure of the demodulated sound 70 of the parametric speaker 1. Specifically, a sound wave including the demodulated sound 70 radiated from the parametric speaker 1 was recorded by a microphone, and the magnitude of the sound pressure of the recorded demodulated sound 70 was calculated as the sound pressure level [dB].

The microphones were placed at a distance of 0.8 m from the parametric speaker 1. Other experimental conditions are as follows. The experimental environment is an anechoic chamber, the reverberation time is 0.15 [s], the background noise level is 21.0 [dB], the temperature and humidity are 20.3 degrees and 38.7%, and the sound source is white noise (0 to 8 [0-8 []. kHz]), the input voltage was 10 [V].

The following three modulation methods were tested. Experimental Example 1 is an amplitude modulation method using a pure tone (cosine wave) carrier 82. Experimental Example 2 is a frequency modulation method using a pure tone (cosine wave) carrier 82. Experimental Example 3 is a pulse amplitude modulation method using a pulse modulation carrier 62.

FIG. 9 shows the sound pressure level [dB] of the demodulated sound 70 in each modulation method. The horizontal axis shows each modulation method in Experimental Examples 1, 2 and 3. The vertical axis indicates the sound pressure level [dB] of the demodulated sound 70. The values entered in the graphs of the experimental examples indicate the values of the sound pressure level [dB] of the demodulated sound 70. In FIG. 9, it is shown that the larger the value of the sound pressure level [dB] of the demodulated sound 70 is, the more the sound pressure of the demodulated sound 70 is improved.

As shown in FIG. 9, the highest sound pressure level [dB] among Experimental Examples 1, 2 and 3 is the pulse modulation of Experimental Example 3 in which the sound pressure level of the demodulated sound is 77.4 [dB]. It turns out that it is a method. This is because the sound pressure level [dB] of the demodulated sound 70 of the pulse amplitude modulation method using the pulse modulation carrier 62 is the demodulated sound 70 of the amplitude modulation method or the frequency modulation method using the pure sound (cosine wave) carrier 82. It shows that it is larger than the sound pressure level [dB] of. In other words, it can be seen that by using the pulse modulation carrier 62 having a large carrier waveform energy, the sound pressure of the carrier is increased and the sound pressure of the demodulated sound 70 is further improved. From this result, it was shown that the sound pressure of the demodulated sound also increased as the sound pressure of the carrier increased.

As a result of comparing the amplitude modulation method using the pure tone (cosine wave) carrier 82 and the frequency modulation method with respect to the sound pressure level [dB] of the demodulated sound 70, the sound pressure level [dB] of the demodulated sound 70 of the frequency modulation method The result was larger. However, surprisingly, as a result of comparing the pulse amplitude modulation method using the pulse modulation carrier 62 and the frequency modulation method using the pure sound (cosine wave) carrier 82, the pulse amplitude modulation method using the pulse modulation carrier 62 was obtained. The result was that the sound pressure level [dB] of the demodulated sound 70 was exceeded.

The sound pressure level [dB] of the demodulated sound 70 of the pulse frequency modulation method using the pulse modulation carrier 62 is the sound pressure of the demodulated sound 70 of the amplitude modulation method using the pure sound (cosine wave) carrier 82 or the frequency modulation method. It becomes larger than the level [dB]. Further, the sound pressure level [dB] of the demodulated sound 70 of the pulse frequency modulation method using the pulse modulation carrier 62 is higher than the sound pressure level [dB] of the demodulated sound 70 of the pulse amplitude modulation method using the pulse modulation carrier 62. growing.

As a result of calculating the magnitude of the sound pressure of the demodulated sound 70 recorded using each carrier as the sound pressure level [dB], the pulse modulation carrier 62 is effective in improving the sound pressure of the demodulated sound 70. It was shown to be. Furthermore, it was shown that as the sound pressure of the carrier increases, the sound pressure of the demodulated sound also increases (see FIG. 8).

<5. Verification experiment ＞
The inventor of the present application conducted a verification experiment to confirm that the pulse modulation carrier 65 used for the parametric speaker 1 is effective in improving the sound pressure of the demodulated sound 70 of the parametric speaker 1.

<5.1 Verification experiment 1>

Carriers used in the parametric speaker 1 include, for example, a triangular wave carrier 83 in addition to the pulse modulation carrier 62 and the pure tone (cosine wave) carrier 82. FIG. 10 shows a triangular wave amplitude modulated signal 86 generated by modulating the amplitude of the triangular wave carrier 83 based on the amplitude of the target signal 60.

First, FIG. 10 shows a triangular wave amplitude modulation method when the triangular wave carrier 83 is used as the carrier of the parametric speaker 1. The target signal 60 is a signal similar to the first embodiment and the second embodiment. The triangular wave amplitude modulation signal 86 is generated by the triangular wave amplitude modulation method that modulates the amplitude of the triangular wave carrier 83 based on the amplitude of the target signal 60.

In the verification experiment 1, specifically, a sound wave including a pure tone (cosine wave) carrier 82 and a demodulated sound 70 generated by the triangular wave amplitude modulation method when the triangular wave carrier 83 is used as the carrier of the parametric speaker 1 is used. Recorded with a microphone. The magnitude of the sound pressure of the demodulated sound 70 recorded by the microphone was calculated as the sound pressure level [dB].

The microphones were placed at a distance of 0.8 m from the parametric speaker 1 as in the evaluation experiment. Other experimental conditions are as follows. The experimental environment is an office environment, the noise level is 36.6 [dB], the temperature and humidity are 24.9 degrees and 69.3%, the sampling frequency is 192 [kHz], and the sound source is a TSP signal (0 to 8 [kHz]). , The input voltage was 16 [V].

There are two carriers used in the experiment, the first carrier and the second carrier. The first carrier is a pure tone (cosine wave) carrier 82 (see FIG. 5). The second carrier is a triangular wave carrier 83 (see FIG. 10).

FIG. 11 shows the sound pressure level [dB] of the demodulated sound 70 in each carrier. The horizontal axis indicates each carrier such as the first carrier and the second carrier. The vertical axis indicates the sound pressure level [dB] of the demodulated sound 70. The value entered in the graph of each carrier indicates the value of the sound pressure level [dB] of the demodulated sound 70. In FIG. 11, it is shown that the larger the value of the sound pressure level [dB] of the demodulated sound 70 is, the more the demodulated sound 70 is improved.

As shown in FIG. 11, the sound pressure level of the demodulated sound 70 of the second carrier, which is the triangular wave carrier 83, is 63.3 [dB], and the demodulated sound 70 of the first carrier, which is the pure tone (cosine wave) carrier 82. It was found that the sound pressure level was lower than 71.9 [dB]. This indicates that the energy of the waveform of the triangular wave carrier 83 is smaller than the energy of the waveform of the pure tone (cosine wave) carrier 82. That is, when the energy of the carrier waveform decreases, the sound pressure of the carrier also decreases, indicating that the sound pressure of the demodulated sound 70 decreases.

From the verification experiment 1, it was shown that the triangular wave carrier 83 is not effective in improving the sound pressure of the demodulated sound 70. Furthermore, it was shown that as the sound pressure of the carrier increases, the sound pressure of the demodulated sound also increases (see FIG. 8).

<5.2 Verification experiment 2>

In the verification experiment 2, specifically, the demodulation generated by the sawtooth wave amplitude modulation method when the pulse modulation carrier 62, the pure tone (cosine wave) carrier 82, and the sawtooth wave carrier are used as the carriers of the parametric speaker 1. Sound waves including sound 70 were recorded with a microphone. The magnitude of the sound pressure of the demodulated sound 70 recorded by the microphone was calculated as the sound pressure level [dB].

The microphones were placed at a distance of 0.8 m from the parametric speaker 1 as in the evaluation experiment. Other experimental conditions are as follows. The experimental environment is an office environment, the noise level is 25.7 [dB], the temperature and humidity are 20.2 degrees and 64.1%, the sampling frequency is 192 [kHz], the number of quantization bits is 16 bits (output), and 32 bits (recording). ), The sound source was white noise (0 to 8 [kHz]), and the input voltage was 10 [V].

The carriers used in the experiment are the first carrier, the second carrier, and the third carrier. The first carrier is a pure tone (cosine wave) carrier 82. The second carrier is a sawtooth carrier. The third carrier is a pulse modulation carrier 62.

FIG. 12 shows the sound pressure level [dB] of the demodulated sound 70 in each carrier. The horizontal axis indicates a first carrier, a second carrier, and a third carrier. The vertical axis indicates the sound pressure level [dB] of the demodulated sound 70. The value entered in the graph of each carrier indicates the value of the sound pressure level [dB] of the demodulated sound 70. In FIG. 12, it is shown that the larger the value of the sound pressure level [dB] of the demodulated sound 70 is, the more the demodulated sound 70 is improved.

As shown in FIG. 12, among the first carrier, the second carrier, and the third carrier, the sound pressure level [dB] of the demodulated sound 70 is the highest because the sound pressure level of the demodulated sound is 129.9 [dB]. It turned out to be the third carrier.

That is, it is shown that the sound pressure level [dB] of the demodulated sound 70 of the pulse amplitude modulation method using the pulse modulation carrier 62 is larger than that of the amplitude modulation method using the pure tone (cosine wave) carrier 82. Further, the sound pressure level [dB] of the demodulated sound 70 of the pulse amplitude modulation method using the pulse modulation carrier is higher than the sound pressure level [dB] of the demodulated sound 70 of the sawtooth wave amplitude modulation method using the sawtooth wave carrier. , Indicates a greater value.

The energy of the waveform of the pulse modulation carrier 62 is larger than the energy of the waveform of the pure tone (cosine wave) carrier 82. Further, the energy of the waveform of the pulse modulation carrier 62 is larger than the energy of the waveform of the sawtooth wave carrier. This indicates that when the energy of the waveform is amplified, the sound pressure of the demodulated sound 70 is also amplified.

From the verification experiment 2, it was shown again that the pulse modulation carrier 62 is effective in improving the sound pressure of the demodulated sound 70. Furthermore, it was shown that as the sound pressure of the carrier increases, the sound pressure of the demodulated sound also increases (see FIG. 8).

<5.3 Verification experiment 3>

Specifically, in the verification experiment 3, a sound wave including the demodulated sound 70 emitted from the parametric speaker 1 was recorded with a microphone, and the harmonic distortion factor [dB] in the recorded demodulated sound 70 was calculated.

The harmonic distortion factor is the magnitude of the harmonic distortion component and the noise component excluding the high frequency component by removing only the high frequency waveform as the ratio to the fundamental wave.

The microphones were placed at a distance of 0.8 m from the parametric speaker 1 as in the evaluation experiment. Other experimental conditions are as follows. The experimental environment is an office environment, the noise level is 36.6 [dB], the temperature and humidity are 24.9 degrees and 69.3%, the sampling frequency is 192 [kHz], and the sound source is Log-upTSP (0-8 [kHz]. ), The input voltage was 16 [V].

The following three modulation methods were tested. Experimental Example 1 is an amplitude modulation method using a pure tone (cosine wave) carrier 82. Experimental Example 2 is a frequency modulation method using a pure tone (cosine wave) carrier 82. Experimental Example 3 is a pulse amplitude modulation method using a pulse modulation carrier 62.

FIG. 13 shows the harmonic distortion factor [dB] of the demodulated sound 70 in each modulation method. The horizontal axis shows each modulation method in Experimental Examples 1, 2 and 3. The vertical axis shows the harmonic distortion factor [dB] of the demodulated sound 70 in each modulation method. The numerical value entered in the graph of each modulation method shows the value of the harmonic distortion rate [dB] of the demodulated sound 70 in each modulation method. Therefore, in FIG. 13, it is shown that the smaller the value of the harmonic distortion factor [dB] is, the lower the harmonic distortion factor [dB] is, and the demodulated sound 70 is not adversely affected.

As shown in FIG. 13, the value of the harmonic distortion factor [dB] is the lowest among Experimental Example 1, Experimental Example 2, and Experimental Example 3 because the value of the harmonic distortion factor is −8.18 [dB]. It was found that it was Experimental Example 3. This indicates that the harmonic distortion rate [dB] of the pulse amplitude modulation method using the pulse modulation carrier 62 is smaller than that of the amplitude modulation method using the pure tone (cosine wave) carrier 82. Further, it is shown that the harmonic distortion rate [dB] of the pulse amplitude modulation method using the pulse modulation carrier 62 is smaller than the harmonic distortion rate [dB] of the frequency modulation method.

From this result, it can be seen that the demodulated sound 70 using the pulse modulation carrier 62 has the lowest harmonic distortion factor [dB]. That is, it was shown that the harmonic distortion factor [dB] did not adversely affect the improvement of the demodulated sound 70.

From the verification experiment 3, it was shown that the pulse modulation carrier 62 is effective in improving the sound pressure of the demodulated sound 70 from the viewpoint of the harmonic distortion factor [dB].

<5.4 Verification Experiment 4>

Specifically, in the verification experiment 4, the demodulated sound 70 radiated from the parametric speaker 1 was recorded with a microphone, and the sound quality of the recorded demodulated sound 70 was evaluated.

As an evaluation index of voice quality, an objective voice quality evaluation method called PESQ (Perceptual Assessment of Speech Quality) was used. This is an internationally standardized quality evaluation standard for telephone voice, and the index is distributed in the range of -0.5 to 4.5, and it is said that the larger the value of the index, the better the quality.

The microphones were placed at a distance of 0.8 m from the parametric speaker 1 as in the evaluation experiment. Other experimental conditions are as follows. The experimental environment is an office environment, the noise level is 36.6 [dB], the temperature and humidity are 24.9 degrees and 69.3%, the sampling frequency is 192 [kHz], and the sound source is explained focusing on the experimental conditions different from the evaluation experiment. do. The sound sources were a male voice (3 speakers x 5 sound sources), a female voice (3 speakers x 5 sound sources), and an input voltage of 16 [V].

The following three modulation methods were tested. Experimental Example 1 is an amplitude modulation method using a pure tone (cosine wave) carrier. Experimental Example 2 is a frequency modulation method using a pure tone (cosine wave) carrier. Experimental Example 3 is a pulse amplitude modulation method using a pulse modulation carrier.

FIG. 14 shows the PESQ value of the male voice in each modulation method, and FIG. 15 shows the PESQ value of the female voice in each modulation method. The horizontal axis shows each modulation method in Experimental Examples 1, 2 and 3. The vertical axis shows the PESQ value. The numerical value entered in the graph shows the PESQ value in each modulation method. Further, the graph shows whether or not there is a significant difference of 1% between Experimental Examples 1 to 3 respectively.

As shown in FIG. 14, it was determined that there was a significant difference of 1% between Experimental Example 1 and Experimental Example 3, or Experimental Example 2 and Experimental Example 3. The highest PESQ value among male voices was the pulse amplitude modulation method using the pulse modulation carrier of Experimental Example 3, which was 2.79.

As shown in FIG. 15, it was determined that Experimental Example 1 and Experimental Example 3 had a significant difference of 1%, and Experimental Example 2 and Experimental Example 3 did not have a significant difference of 1%. The highest PESQ value among female voices was the pulse amplitude modulation method using the pulse modulation carrier of Experimental Example 3, which was 2.59.

In this way, the PESQ value in the pulse amplitude modulation method using the pulse modulation carrier 62 is higher than the PESQ value in the amplitude modulation method using the pure tone (cosine wave) carrier 82 or the frequency modulation method for both male and female voices. , About 0.1 improvement. From this, it can be seen that the demodulated sound 70 in the pulse amplitude modulation method using the pulse modulation carrier 62 is perceived by humans as sound without deteriorating the sound quality.

From the verification experiment 4, it was shown that the pulse modulation carrier 62 is effective in improving the sound pressure of the demodulated sound 70 from the viewpoint of voice quality.

<6. Addendum>
The present invention is not limited to the above embodiment, and various modifications are possible.

1 Parametric speaker, 1st parametric speaker, 2nd parametric speaker 10 Signal processing circuit 11 Pulse modulation carrier generator 13 Pulse amplitude modulation circuit 20 Amplifier 30 Ultrasonic generator 15 Pulse frequency modulation circuit 60 Target signal (audible sound)
62 Pulse modulation carrier 65 Pulse amplitude modulation signal 67 Pulse frequency modulation signal 70 Demodulation sound 82 Pure sound (cosine wave) carrier 85 Vibration modulation signal 87 Frequency modulation signal 83 Triangular wave carrier 86 Triangular wave amplitude modulation signal E1 Pure sound (cosine wave) waveform energy E2 pulse modulation wave waveform energy

Claims (3)

Modulate the carrier amplitude or frequency according to the target signal of the audible sound,
It comprises outputting the modulation signal generated by the modulation from the ultrasonic wave generating element.
The carrier is a method for improving the sound pressure of a parametric speaker which is a pulse modulation carrier. The method for improving the sound pressure of a parametric speaker according to claim 1, wherein the modulation is pulse amplitude modulation in which the amplitude of the pulse modulation carrier is changed according to the target signal. A carrier generator that generates carriers and
A modulation circuit that modulates the amplitude or frequency of the carrier according to the target signal of the audible sound.
An ultrasonic generating element that radiates a modulated signal modulated by the modulation circuit is provided.
The carrier generator is a parametric speaker which is a pulse modulation carrier generator that generates a pulse modulation carrier.

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