Sound systems and in-car communication support systems

Abstract

We provide an "acoustic system and in-vehicle communication support system" that increases the audible sound playback level while suppressing the disadvantages of ultrasonic radiation using a parametric speaker. [Solution] Ultrasound amplitude-modulated by audible sound emitted from a parametric speaker 1 is incident with high directionality on an audible sound collector 2. Of the incident ultrasound and audible sound self-demodulated from the ultrasound, the audible sound collector 2 attenuates the ultrasound and reflects the audible sound to collect it at a position near the user. The audible sound collector 2 can be composed of a reflector 21 with a reflective surface of a paraboloid of revolution and a sound absorber 22 that absorbs the ultrasound, and the sound absorber 22 can be composed of a sound-absorbing material using phononic crystals or a resonance tube 221.

Description

[Technical Field]

[0001] The present invention relates to a technique for performing local reproduction using a parametric speaker. [Background technology]

[0002] A known technique for localized reproduction using a parametric speaker is to amplitude-modulate an ultrasonic signal with an audible signal, and then use the amplitude-modulated signal to drive a highly directional ultrasonic transducer array to emit ultrasonic waves, thereby reproducing audible sounds with high directivity as audible sounds that are self-demodulated as the ultrasonic waves propagate through the air (for example, Patent Document 1).

[0003] Also, a technique is known for making the direction of directivity of such a parametric speaker variable and controlling the direction of the directivity (for example, Patent Document 2). There is also known a technology in which ultrasonic waves that have been amplitude-modulated with an audible sound signal are reflected by a reflector having a paraboloid or ellipsoid as a reflecting surface, and the sound is collected at a position near the user to reproduce the audible sound (for example, Patent Documents 3 and 4). As a technique related to the present invention, a sound absorbing material made of phononic crystals that absorbs only the ultrasonic components emitted from a parametric speaker is known (Non-Patent Document 1). Further, known technologies related to the present invention include ultrasonic sound-absorbing materials with a cellular structure (for example, Patent Document 5) and a technology in which closed resonance tubes, each open at one end and closed at the other, are arranged to absorb noise in the resonance frequency band of the resonance tubes (for example, Patent Document 6). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-234248 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-349816 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-158788 [Patent Document 4] Japanese Patent Application Publication No. 7-107588 [Patent Document 5] Utility Model Registration No. 3128029 [Patent Document 6] Japanese Patent Application Publication No. 07-302087 [Non-patent literature]

[0005] [Non-Patent Document 1] Akiko Sugawara, Hyojin Lee, Shinichi Sakamoto, and Shigeto Takeoka, "Study on reducing ultrasonic waves in measuring architectural acoustic characteristics using a parametric loudspeaker," Proceedings of the Autumn Meeting of the Acoustical Society of Japan, pp.1061-1062, September 2017 Summary of the Invention [Problem to be solved by the invention]

[0006] Reproducing audible sound via ultrasound using a parametric loudspeaker generally presents the following problems to be solved: That is, there are problems such as the level of the reproduced audible sound being low compared to the level of the ultrasonic waves, the radiation of high-level ultrasonic waves toward the user, and the reproduction of audible sounds at the destination of the reflected ultrasonic waves. The problem of audible sound levels can be improved by providing a reflector that collects the ultrasound emitted from the parametric speaker at a position close to the user, but this can result in higher levels of ultrasound being emitted toward the user, and can also cause problems with the reproduction of audible sounds at the reflection point of the higher levels of ultrasound.

[0007] Therefore, an object of the present invention is to increase the reproduction level of audible sound while suppressing the disadvantages caused by the emission of ultrasonic waves when audible sound is reproduced via ultrasonic waves by a parametric speaker. [Means for solving the problem]

[0008] To achieve the above object, the present invention provides an acoustic system equipped with a parametric speaker that emits ultrasonic waves modulated with audible sound as output sound waves, and an audible sound collector into which the output sound waves emitted by the parametric speaker are incident. The audible sound collector includes a reflector with a reflective surface that reflects sound waves incident from the same direction as the output sound waves are incident, and a sound absorber. The sound absorber is positioned closer to the direction in which the output sound waves are incident than the reflective surface of the reflector, and attenuates the ultrasonic components of the output sound waves that reach the reflective surface. The reflective surface of the reflector is self-demodulated by the output sound waves, and reflects the audible sound components that are incident on the audible sound collector to collect them at a predetermined sound collection position.

[0009] Here, in this acoustic system, the shape of the reflecting surface of the reflector may be a paraboloid of revolution. In this acoustic system, the sound absorber may be a sound absorbing material that uses a phononic crystal and absorbs ultrasonic waves. In this acoustic system, the sound absorber may include a plurality of closed resonance tubes that absorb ultrasonic waves. In this acoustic system, the sound collection position may be located in a direction shifted from the direction in which the emitted sound waves are incident, as viewed from the audible sound collector. The present invention also provides an in-car communication support system equipped with the above acoustic system and mounted on an automobile, the in-car communication support system including a microphone for collecting speech from a user seated in a first seat of the automobile, the parametric speaker emitting ultrasonic waves modulated by the speech collected by the microphone as output sound waves, and the sound collection position where the audible sound collector of the acoustic system collects the audible sound components is a position near the user seated in a second seat of the automobile.

[0010] According to the acoustic system described above, the sound absorber of the audible sound collector absorbs ultrasonic components so as to prevent them from reaching the reflective surface, and the reflective surface collects the audible sound components at the sound collection position, so it is possible to increase only the level of the audible sound. This prevents problems such as the emission of higher-level ultrasonic waves to the user and the reproduction of audible sounds at the reflection destination of higher-level ultrasonic waves. [Effects of the Invention]

[0011] As described above, according to the present invention, in reproducing audible sound via ultrasonic waves using a parametric speaker, it is possible to increase the reproduction level of the audible sound while suppressing the disadvantages caused by the emission of ultrasonic waves. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a configuration of an audio system according to an embodiment of the present invention. [Figure 2] 1 is a diagram illustrating an example of the configuration of an audible sound collector according to an embodiment of the present invention. FIG. [Figure 3] 1 is a diagram illustrating an example of the configuration of an audible sound collector according to an embodiment of the present invention. FIG. [Figure 4] 1 is a diagram illustrating an application example of an acoustic system according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating an application example of an acoustic system according to an embodiment of the present invention. [Figure 6] FIG. 10 is a diagram illustrating another exemplary configuration of an acoustic system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described. FIG. 1 shows the configuration of an audio system according to this embodiment. As shown in the figure, the acoustic system includes a parametric speaker 1 and an audible sound collector 2 . The parametric speaker 1 has an oscillator 11 that generates a carrier signal, which is an AC signal with a frequency in the ultrasonic band (for example, 40 kHz), a modulator 12 that amplitude-modulates the carrier signal with an input audible sound signal, a driver 13, and an ultrasonic transducer array 14. The driver 13 drives the ultrasonic transducer array 14 with a drive signal that has been phase-adjusted for amplifying the modulated signal amplitude-modulated by the modulator 12 and for directional control, and the ultrasonic transducer array 14 emits amplitude-modulated ultrasonic waves with high directivity in a predetermined directional direction.

[0014] The direction of the amplitude-modulated ultrasound emitted from the ultrasound transducer array 14 is toward the audible sound collector 2, and the amplitude-modulated ultrasound and audible sound self-demodulated from the ultrasound in space are incident on the audible sound collector 2. The audible sound collector 2 attenuates the ultrasonic waves and reflects the audible sounds, out of the incident ultrasonic waves and audible sounds, and collects them at a sound collection position CP near the user. FIG. 2 shows an example of the configuration of the audible sound collector 2. As shown in FIG. 2a, the audible sound collector 2 includes a reflector 21 having a reflecting surface of a paraboloid of revolution, and a sound absorber 22 that absorbs ultrasonic waves. Here, Figure 2a shows the shape of the audible sound collector 2 as viewed from the opening side of the direction of the rotation axis of the paraboloid of revolution, Figure 2b shows the shape of the audible sound collector 2 as viewed from a direction perpendicular to the rotation axis of the paraboloid of revolution, and Figure 2c shows a cross section along line AA in Figure 2a. As shown in the figure, the reflector 21 has a parabolic antenna shape, and a sound absorber 22 is disposed in a recess on the inner side of the reflecting surface so as to cover the reflecting surface. The sound absorber 22 has a function of absorbing incident ultrasonic waves or reflecting them so that they do not reach the reflecting surface, and a function of transmitting incident audible sounds. Therefore, as shown in Figure 2d, the audible sound collector 2 reflects only the audible sound of the incident ultrasonic waves and audible sounds, collects and amplifies it at a sound collection point CP near the user, thereby increasing the volume of the audible sound heard by the user and suppressing the emission of ultrasonic waves to the user.

[0015] For example, the gain of a parabolic antenna is G=(πd / λ) 2 e A However, d: diameter, λ: wavelength, e A : Coefficient (aperture efficiency) Therefore, if the diameter of the reflecting surface is 15 cm, the gain of 1 kHz audible sound is GA = 1.92e A This becomes:

[0016] If the sound absorber 22 is not provided, the gain of the carrier wave, which is an ultrasonic wave of 40 kHz, is GC=3073.58e A As a result, ultrasonic waves that are amplified 1600 times (32 dB) more than audible sounds are emitted toward the user. However, in this embodiment, in which the sound absorber 22 is provided, the emission of such highly amplified ultrasonic waves is suppressed.

[0017] In this embodiment, the collection point CP of the audible sound collector 2 is set in a direction diagonally shifted from the incident direction of the modulated ultrasound, similar to an offset parabolic antenna, so that the ultrasound modulated by the user is not obstructed from entering the audible sound collector 2. As such a sound absorber 22, for example, a sound absorbing material using a phononic crystal can be used. When using a phononic crystal, as shown in Figure 2e, if the structural period is a and the incident angle of the sound wave is θ, the center frequency fc of the sound reflection band is expressed as follows, where C is the sound velocity: fc=nC / (2acosθ) n=1, 2, 3, ... This becomes:

[0018] Therefore, for example, if the sound speed C is 340 m / s, and the sound absorber 22 is positioned so that a=4 mm and the incident angle θ is 0°, then when n=1, fc=42.5 kHz can be obtained. Therefore, when a 40 kHz carrier wave is used as the sound absorber 22, a sound absorbing material using a phononic crystal can be used to reflect ultrasonic waves incident on the audible sound collector 2 so that they do not reach the reflecting surface. Furthermore, even when the incident angle θ is not 0°, by setting the structural period a so that nC / (2acosθ) is approximately 40 kHz, when a 40 kHz carrier wave is used, ultrasonic waves incident on the audible sound collector 2 can be reflected so that they do not reach the reflecting surface. The center frequency fc of a similar sound reflection band can be obtained. Here, the sound absorber 22 is not limited to sound absorbing materials using phononic crystals, but may be any sound absorbing material that absorbs ultrasonic waves, such as sound absorbing materials with a bubble structure that absorbs ultrasonic waves, or other acoustic metamaterials. Furthermore, the sound absorber 22 may be positioned in any way that covers the reflecting surface when viewed from the incident side, and may be positioned only on the opening side of the recess inside the reflecting surface as shown in Figure 2f, or in front of the reflector 21 as shown in Figure 2g. As the sound absorber 22, a sound absorber 22 using a closed-tube resonance tube can be used. Here, when a sound absorber 22 using a closed-tube resonance tube is used, the shape of the audible sound collector 2 as seen from the opening side of the direction of the rotation axis of the paraboloid of revolution is shown in Figure 3a, the shape of the audible sound collector 2 as seen from a direction perpendicular to the rotation axis of the paraboloid of revolution is shown in Figure 3b, and a cross section along line AA in Figure 3a is shown in Figure 3c.

[0019] As shown in the figure, this audible sound collector 2 has a configuration in which a sound absorber 22 having an array of closed-tube resonance tubes 221 is arranged so as to cover the opening of a recess on the inner side of the reflecting surface of a reflector 21. As shown in Figure 3d, when the length L and diameter a of a closed tube are determined, the length L of a closed tube with a natural vibration of wavelength λ is L = λ / 4. Furthermore, the tube diameter a must satisfy the relationship a ≦ 0.586λ where λ is the wavelength. If the natural vibration is a 40 kHz carrier wave with a wavelength λ, the tube length L is approximately 2.1 mm, since λ = C / fc, assuming the speed of sound C is 340 m / s. Furthermore, the tube diameter is a ≦ 0.586λ = 0.004891, so it should be approximately 4.9 mm or less.

[0020] Therefore, by using a sound absorber 22 in which resonance tubes 221 with a length of approximately 2.1 mm and a tube diameter of 4.9 mm or less are arranged, ultrasonic waves incident on the audible sound collector 2 can be reflected so as not to reach the reflecting surface. Furthermore, even when using a sound absorber 22 that uses a resonance tube 221, the sound absorber 22 may be positioned in any manner that covers the reflective surface when viewed from the incident side, such as being positioned in front of the reflector 21 as shown in Figure 3e, or being positioned so as to cover the reflective surface as shown in Figure 3f. The acoustic system of the present invention has been described above. Such an acoustic system can be applied to a variety of systems. As an example, we will show an application of the acoustic system to an ICC (In Car Communication) system that supports voice communication between users inside a passenger car. Figure 4a shows the configuration of the ICC system. As shown in the figure, the ICC system includes multiple microphones 401, a selector 402, a signal processing unit 403, a parametric speaker group 404 consisting of one or more parametric speakers 1, an ICC control unit 405, and multiple audible sound collectors 2. Here, the parametric speaker group 404 and the multiple audible sound collectors 2 constitute a configuration corresponding to the above acoustic system.

[0021] 5a1, for example, a plurality of microphones 401 are provided corresponding to the respective seats of a passenger vehicle, and each is disposed near the corresponding seat so as to pick up the speech of the user seated in the corresponding seat. However, the microphones 401 may be provided so as to be shared by a plurality of seats, for example, one for each row of seats.

[0022] Furthermore, the parametric speaker group 404 is disposed, for example, at the rear of the vehicle, and a plurality of audible sound collectors 2 are provided corresponding to the respective seats, each provided in front of the corresponding seat. Each audible sound collector 2 reflects the audible sound that has been self-demodulated from the ultrasound that has been amplitude-modulated with the audible sound and that has been emitted from the parametric speaker group 404 toward itself, toward the rear, and collects the sound toward the user seated in the corresponding seat.

[0023] Here, as shown in FIG. 5a2, the parametric speaker group 404 and the plurality of audible sound collectors 2 can be arranged on the ceiling of the vehicle interior. Returning to FIG. 4, the ICC control unit 405 controls the operation of emitting ultrasound amplitude-modulated by audio input from one or more microphones 401 to one or more audible sound mufflers in accordance with a preset response or a response selected by the user. For example, when ultrasound amplitude-modulated with sound input from the ith microphone 401 is to be emitted to the jth audible sound collector 2, the selector 402 outputs the output of the ith microphone 401 as sound i to the signal processing unit 403, and the signal processing unit 403 performs echo cancellation processing and gain adjustment on the sound i before outputting it to the parametric speaker group 404. Then, in the parametric speaker 1 of the parametric speaker group 404 whose directivity direction is in the direction of the jth audible sound collector 2, a carrier wave which is ultrasound is amplitude-modulated with sound i and emitted to the jth audible sound collector 2.

[0024] Here, as the parametric speaker 1 having a direction of direction toward the jth audible sound collector 2, parametric speakers 1 each having a fixed direction of direction toward each audible sound collector 2 may be prepared in advance, and the parametric speaker 1 having a direction of direction toward the jth audible sound collector 2 may be used from among them, or a parametric speaker 1 whose direction of direction can be changed may be prepared, and when emitting amplitude-modulated ultrasound to the jth audible sound collector 2, the ICC control unit 405 may control the direction of the parametric speaker 1 to the direction of the jth audible sound collector 2 and use it.

[0025] Similarly, when ultrasound amplitude-modulated with sound input from the ith microphone 401 is to be emitted to the j, k, m, n...th audible sound collectors 2, the selector 402 outputs the output of the ith microphone 401 as sound i to the signal processing unit 403, which then performs echo cancellation and gain adjustment on the sound i before outputting it to the parametric speaker group 404. Then, in the four parametric speakers 1 of the parametric speaker group 404 whose directivity directions are in the directions of the j, k, m, n...th audible sound collectors 2, a carrier wave which is ultrasound is amplitude-modulated with sound i and emitted to the j, k, m, n...th audible sound collectors 2.

[0026] Here, as the parametric speaker 1 having a directional direction in the direction of the j, k, m, n...th audible sound collector 2, parametric speakers 1 having a fixed directional direction in the direction of each audible sound collector 2 may be prepared in advance, and from among these, the parametric speaker 1 having a directional direction in the direction of the j, k, m, n...th audible sound collector 2 may be used; alternatively, parametric speakers 1 with changeable directional directions may be prepared in the same number as the audible sound collectors 2 that may be used simultaneously, and when emitting amplitude-modulated ultrasound to the j, k, m, n...th audible sound collector 2, the ICC control unit 405 may control the directional direction of the parametric speakers 1 for the j, k, m, n...th audible sound collector 2 to the direction of the j, k, m, n...th audible sound collector 2.

[0027] Next, the operation of emitting ultrasound amplitude-modulated with sound input from the a, b, c, d...th microphones 401 to the j-th audible sound collector 2 and the operation of emitting ultrasound amplitude-modulated with sound input from the j, k, m, n...th audible sound collectors 2 in the above description is an operation in which, in the parametric speaker 1, instead of sound i input from the ith microphone 401, a carrier wave, which is ultrasound, is amplitude-modulated with sound synthesized by the signal processing unit 403 from the sound input from the a, b, c, d...th microphones 401.

[0028] As described above, the number of parametric speakers 1 required for the parametric speaker group 404 is the number of audible sound collectors 2 that may be used simultaneously when using parametric speakers 1 with changeable directional directions, and is the number of audible sound collectors 2 that may be used simultaneously or not when using parametric speakers 1 with fixed directional directions. However, when a parametric speaker 1 capable of setting multiple changeable directional directions is used and multiple audible sound collectors 2 are used simultaneously, the same parametric speaker 1 may be shared by two or more audible sound collectors 2.

[0029] In such an ICC system, when the parametric speaker group 404 includes multiple parametric speakers 1, the parametric speakers 1 may be arranged in different positions. For example, as shown in Fig. 5b, a parametric speaker 1 for an audible sound collector corresponding to the seats in the first row may be provided at the rear of the seats in the first row, a parametric speaker 1 for an audible sound collector corresponding to the seats in the second row may be provided at the rear of the seats in the second row, and a parametric speaker 1 for an audible sound collector corresponding to the seats in the third row may be provided at the rear of the seats in the third row.

[0030] In addition, at least some of the audible sound collectors 2 may be placed on the seats. For example, as shown in Figures 5c1 and 5c2, the audible sound collectors 2 corresponding to the seats in the second row may be placed on the headrests of the seats in the first row, and the audible sound collectors 2 corresponding to the seats in the third row may be placed on the headrests of the seats in the second row.

[0031] Also, as shown in Figure 5c1, the parametric speaker group 404 may be placed at the front of the vehicle, and an audible sound collector 2 corresponding to each seat may be placed behind each seat, and the audible sound collector 2 may reflect the audible sound that is self-demodulated from the ultrasound that is amplitude-modulated with audible sound and emitted from the parametric speaker group 404 toward itself, forward, and collected toward the user sitting in the corresponding seat.

[0032] In this example, as shown in FIG. 5c2, an audible sound collector 2 corresponding to each seat is provided on the headrest of that seat. Next, the configuration of the acoustic system according to this embodiment can also be configured as shown in Figures 6a and 6b, in which the parametric speaker 1 and the audible sound collector 2 are arranged coaxially, and the audible sound collector 2 collects audible sound at a position near a user who is between the parametric speaker 1 and the audible sound collector 2.

[0033] Figure 6a shows a case where modulated ultrasound is emitted to the audible sound collector 2 while avoiding the user, and Figure 6b shows a case where modulated ultrasound is emitted to the audible sound collector 2 while allowing some of it to be emitted to the user. Even in the case of Figure 6b, it is expected that the level of audible sound heard by the user will be small due to direct waves, and will be dominated by the audible sound collected by the audible sound collector 2. In addition, the ultrasonic waves radiated to the user will be limited to a portion of the emitted ultrasonic waves. In the above embodiment, the reflecting surface of the reflector 21 is a paraboloid of revolution, but the reflecting surface may have a shape that can appropriately collect an appropriate audible sound depending on the incident angle and the spread of the incident angle of the modulated ultrasonic wave. In other words, the shape of the reflecting surface may be, for example, an ellipsoid of revolution or another concave surface. [Explanation of symbols]

[0034] 1...parametric speaker, 2...audible sound collector, 11...oscillator, 12...modulator, 13...driver, 14...ultrasonic transducer array, 21...reflector, 22...sound absorber, 221...resonator tube, 401...microphone, 402...selector, 403...signal processing unit, 404...parametric speaker group, 405...ICC control unit.

Claims

1. An acoustic system including a parametric speaker that emits ultrasonic waves modulated with audible sound as output sound waves, an audible sound collector into which the sound waves emitted by the parametric speaker are incident, The audible sound collector includes a reflector having a reflective surface that reflects sound waves incident from the same direction as the incident direction of the outgoing sound waves, and a sound absorber, the sound absorber is disposed on the side of the reflecting surface of the reflector in the direction in which the emitted sound waves are incident, and attenuates ultrasonic components of the emitted sound waves that reach the reflecting surface; An acoustic system characterized in that the reflecting surface of the reflector is self-demodulated by the emitted sound waves, reflects audible sound components incident on the audible sound collector, and collects the sound at a predetermined sound collection position.

2. 2. The acoustic system of claim 1, An acoustic system characterized in that the shape of the reflecting surface of the reflector is a paraboloid of revolution.

3. 2. The acoustic system of claim 1, An acoustic system characterized in that the sound absorber is a sound absorbing material that uses phononic crystals to absorb ultrasonic waves.

4. 2. The acoustic system of claim 1, The acoustic system is characterized in that the sound absorber has a plurality of closed resonance tubes that absorb ultrasonic waves.

5. 2. The acoustic system of claim 1, An acoustic system characterized in that the sound collection position is located in a direction shifted from the direction in which the emitted sound waves are incident, as viewed from the audible sound collector.

6. An in-car communication support system installed in a vehicle, an acoustic system according to claim 1, 2, 3, 4 or 5; a microphone that collects a speech of a user seated in a first seat of the vehicle, the parametric speaker emits ultrasonic waves modulated by the speech sound collected by the microphone as output sound waves; An in-vehicle communication support system characterized in that the sound collection position where the audible sound collector of the acoustic system collects the audible sound components is a position near a user seated in a second seat of the automobile.

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