Parametric speaker system

Abstract

To provide a parametric speaker system configured to reduce noise sound at a difference frequency generated in an audible region.SOLUTION: A parametric speaker system 100 includes: a first speaker 50 that emits carrier waves in an ultrasonic range toward a target point F, the first speaker having a plurality of first ultrasonic vibrators 70 arranged in a first arrangement region 51; and a plurality of second speakers 60 that emit side band waves generated by performing amplitude modulation on carrier waves with signal waves in an audible range, the second speakers having a plurality of second ultrasonic vibrators 70 arranged in a second arrangement region 61. The side band wave emitted from each of the second speakers is emitted toward the target point from each of emission regions arranged on an arrangement circle 54 centered on an arrangement point CP on a first reference line CL1 that connects the target point and the first speaker.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a parametric speaker system.

Background Art

[0002] When a modulated wave obtained by amplitude-modulating a carrier wave in the ultrasonic range with a signal wave in the audible range is radiated from a speaker at a large sound pressure, self-demodulation occurs due to distortion caused by non-linear propagation, and an audible sound is generated in a limited area away from the speaker. A parametric speaker is known. Patent Document 1 discloses a parametric speaker (device) including a first speaker (ultrasonic amplification means) that radiates a modulated wave and a second speaker that radiates a carrier wave. Audible sound is generated in an area where the radiation area of the modulated wave radiated from the first speaker and the radiation area of the carrier wave radiated from the second speaker overlap.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a need for a parametric speaker system that can generate audible sound with good sound quality even when a signal wave includes a plurality of frequency components having different frequencies.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms.

[0006] According to one aspect of the present disclosure, a parametric speaker system (4A parametric speaker system (100) is provided. This parametric speaker system includes a first speaker (50) that radiates a carrier wave in the ultrasonic range toward a target point (F), the first speaker having a plurality of first ultrasonic vibrators (70) arranged in a first arrangement region (51); and a plurality of second speakers (60) that radiate sideband waves generated by amplitude-modulating the carrier wave with a signal wave in the audible range, the plurality of second speakers each having a plurality of second ultrasonic vibrators (70) arranged in a second arrangement region (61). An acoustic output unit (104) that outputs a modulated wave generated by amplitude-modulating the carrier wave with a predetermined sound, and a third speaker (90) that radiates the modulated wave toward the target point. The sideband waves radiated from each of the plurality of second speakers are radiated toward the target point from each of a plurality of radiation regions arranged on an arrangement circle (54) centered on an arrangement point (CP) on a first reference line (CL1) connecting the target point and the first speaker. The sound includes frequency components included in each of a plurality of divided bands obtained by dividing a band of 300 Hz or more and 3400 Hz or less into a plurality of bands.

[0007] According to this type of parametric speaker system, a plurality of radiation regions for radiating sideband waves are arranged with respect to one first speaker that radiates a carrier wave such that the distances from the target point are equal. Therefore, generation of sound at difference frequencies in the audible range can be reduced. Thus, it is possible to provide a parametric speaker system that can generate audible sound with good sound quality even when a plurality of frequency components having different frequencies are included in the signal wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Embodiments for Carrying Out the Invention

[0009] A. First Embodiment: As shown in FIG. 1, the parametric speaker system 100 includes a signal input unit 101 and a speaker unit 102. The speaker unit 102 has a first speaker 50 and a plurality of second speakers 60. A carrier wave is radiated from the first speaker 50 toward the target point F shown in FIG. 2. From the plurality of second speakers 60, sideband waves generated from modulated waves obtained by amplitude-modulating the carrier wave with a signal wave in the audible range are radiated toward the target point F. The carrier wave radiated from the first speaker 50 and the sideband waves radiated from the second speakers 60 are ultrasonic waves with high sound pressure. Due to the interference and non-linear propagation between the carrier wave and the sideband waves, audible sound is generated in the audible region RA shown in FIG. 4 centered on the target point F. As a result, the subject can hear the target audible sound having the difference frequency between the carrier wave and the sideband waves in the audible region RA.

[0010] As shown in FIG. 1, the signal input unit 101 includes an amplitude modulator 10, a filter 20, and a plurality of amplifiers 30. A carrier wave amplified in voltage by the amplifier 30 is input to the first speaker 50. The amplitude modulator 10 inputs a modulated wave obtained by amplitude-modulating the input carrier wave with the input signal wave to the filter 20. The filter 20 passes only a frequency component of either the upper sideband or the lower sideband among the frequency components of the carrier wave, the upper sideband, and the lower sideband included in the modulated wave, and inputs it to each amplifier 30. In the present embodiment, the upper sideband is input to each amplifier 30. An upper sideband amplified in voltage by the amplifier 30 is input to the second speaker 60. By radiating only one sideband from the second speaker 60, it is possible to suppress deterioration of the sound quality of the target audible sound due to the generation of a difference-frequency sound between the upper sideband and the lower sideband.

[0011] In the present embodiment, the signal wave input to the amplitude modulator 10 includes a plurality of frequency components having different frequencies from each other. The inventors have found a problem that when the signal wave includes a plurality of frequency components, a difference-frequency sound between the plurality of frequency components is generated in the audible range RA. For example, when a 40.3 kHz carrier wave is radiated from the first speaker 50 and a sideband generated by amplitude-modulating the 40.3 kHz carrier wave with a signal wave having a 1 kHz frequency component and a 1.7 kHz frequency component is radiated from the second speaker 60, in addition to the 1 kHz audible sound and the target 1.7 kHz audible sound, a 0.7 kHz audible sound, which is the difference frequency between 1.7 kHz and 1 kHz, is also generated. Furthermore, the inventors have found that the sound pressure of the audible sound having a difference frequency increases as the sound pressure of the sideband is increased with respect to the sound pressure of the carrier wave. The audible sound having a difference frequency is noise that is not the target frequency and preferably should not be generated. Therefore, the inventors have devised the specifications and arrangement modes of each of the first speaker 50 and the second speaker 60. As a result, it is possible to reduce the generation of the difference-frequency sound in the audible range RA.

[0012] As shown in FIG. 3, the first speaker 50 and the second speaker 60 each have a plurality of ultrasonic transducers 70. In FIG. 2, the illustration of the ultrasonic transducers 70 is omitted. In FIGS. 2 to 4, XYZ axes, which are three spatial axes orthogonal to each other, are drawn. The directions in which the arrows of the X-axis, Y-axis, and Z-axis point indicate the positive directions along the X-axis, Y-axis, and Z-axis, respectively. The positive directions along the X-axis, Y-axis, and Z-axis are defined as the +X direction, +Y direction, and +Z direction, respectively. The directions opposite to the directions in which the arrows of the X-axis, Y-axis, and Z-axis point are the negative directions along the X-axis, Y-axis, and Z-axis, respectively. The negative directions along the X-axis, Y-axis, and Z-axis are defined as the -X direction, -Y direction, and -Z direction, respectively. Directions along the X-axis, Y-axis, and Z-axis regardless of positive or negative are called the X direction, Y direction, and Z direction, respectively. The same applies to the figures and explanations shown hereinafter.

[0013] The ultrasonic transducer 70 has a cylindrical shape and emits ultrasonic waves from a circular radiation surface. The plurality of ultrasonic transducers 70 constituting the first speaker 50 are arranged at equal intervals in a regular hexagonal first arrangement region 51. The shape of the first arrangement region 51 is a regular hexagon that encloses all the arranged ultrasonic transducers 70 and is in contact with the outermost ultrasonic transducers 70. The plurality of ultrasonic transducers 70 are arranged such that six ultrasonic transducers 70 surrounding one ultrasonic transducer 70 are located at the vertices of a regular hexagon. Further, the radiation surfaces of the plurality of ultrasonic transducers 70 constituting the first speaker 50 are arranged on substantially the same plane.

[0014] The plurality of ultrasonic transducers 70 that constitute the second speaker 60 are arranged at equal intervals in a rectangular second arrangement region 61. The shape of the second arrangement region 61 is a rectangle that encloses all of the arranged ultrasonic transducers 70 and is in contact with the ultrasonic transducers 70 on the outer periphery. The plurality of ultrasonic transducers 70 are arranged such that six ultrasonic transducers 70 surrounding one ultrasonic transducer 70 are located at the vertices of a hexagon. The radiating surfaces of the plurality of ultrasonic transducers 70 that constitute the second speaker 60 are arranged on substantially the same plane. Here, the virtual plane on which the radiating surfaces of the plurality of ultrasonic transducers 70 that constitute the first speaker 50 are arranged is referred to as the first radiating surface 52. As shown in FIG. 4, the virtual plane on which the radiating surfaces of the plurality of ultrasonic transducers 70 that constitute the second speaker 60 are arranged is referred to as the second radiating surface 62. The ultrasonic transducers 70 arranged in the first arrangement region 51 of the first speaker 50 are also referred to as first ultrasonic transducers. The ultrasonic transducers 70 arranged in the second arrangement region 61 of the second speaker 60 are also referred to as second ultrasonic transducers. All of the first ultrasonic transducers radiate carrier waves having the same phase with each other. All of the second ultrasonic transducers radiate sideband waves having the same phase with each other.

[0015] As shown in FIG. 2, each of the first speaker 50 and the second speaker 60 is arranged to emit ultrasonic waves toward a preset target point F. Specifically, the first speaker 50 is arranged such that a first reference line CL1 passing through the centroid CG of the first radiation surface 52 and perpendicular to the first radiation surface 52 passes through the target point F. The second speaker 60 is arranged such that a second reference line CL2 passing through the centroid CG of the second radiation surface 62 and perpendicular to the second radiation surface 62 passes through the target point F. Note that the first reference line CL1 connecting the target point F and the first speaker 50 is parallel to the Z direction. The first radiation surface 52 is parallel to the XY plane. The angle θ formed by the first reference line CL1 and the second reference line CL2 is 45 degrees or less. Thereby, the carrier wave and the sideband wave interfere well, and audible sound with good sound pressure can be generated in the audible region RA. Also, since a plurality of second speakers 60 are arranged to emit sideband waves having different angles with respect to the first reference line CL1, the audible region RA can be formed three-dimensionally. Therefore, even when the subject moves unintentionally not only in the Y direction and the Z direction but also in the X direction, the generated audible sound can be heard.

[0016] In the present embodiment, eight second speakers 60 are arranged surrounding the first speaker 50. As shown in FIG. 3, the eight second speakers 60 are arranged such that the centroid CG of the second radiation surface 62 of each second speaker 60 is located on an arrangement circle 54 centered on an arrangement point CP which is a point on the first reference line CL1. In the present embodiment, the centroid CG of the second radiation surface 62 of each second speaker 60 is located at the vertex of a regular octagon centered on the arrangement point CP. Each of the eight second speakers 60 is a rotation object centered on the arrangement point CP with respect to each other. That is, the sideband waves radiated from each of the second speakers 60 are radiated from a plurality of second radiation surfaces 62 as a plurality of radiation regions arranged on the arrangement circle 54 toward the target point F. In this way, by providing a plurality of second speakers 60 that emit sideband waves with respect to one first speaker 50 that emits a carrier wave such that the distances from the target point F are equal, the generation of sound of the difference frequency in the audible region RA can be reduced.

[0017] The sound pressure of the carrier wave radiated from the first speaker 50 is greater than the sound pressure of the sideband wave radiated from the second speaker 60. Thereby, generation of sound of the difference frequency in the audible range RA can be reduced.

[0018] In the present embodiment, as shown in FIG. 4, the second speaker 60 is arranged at a position closer to the target point F than the first speaker 50 in the Z direction parallel to the first reference line CL1. The distance between the center of gravity CG of the first radiation surface 52 of the first speaker 50 and the target point F is equal to or less than the Rayleigh length of the first speaker 50, which is a criterion for forming a far-field. Thereby, audible sound can be generated well in the audible range RA. The inventors have experimentally confirmed that when a modulated wave is radiated from a parametric speaker whose radiation surface is rectangular, in the internal space of a quadrangular prism drawn with the radiation surface of the parametric speaker as the bottom surface and the direction perpendicular to the radiation surface as the height direction, in a space where at least the distance in the height direction is within the Rayleigh length, audible sound with good sound pressure is demodulated. Note that the modulated wave is specifically a modulated wave obtained by amplitude-modulating a carrier wave in the ultrasonic range with a signal wave in the audible range. Therefore, by setting the position of the target point F to a position equal to or less than the Rayleigh length of the first speaker 50, audible sound with good sound pressure can be generated.

[0019] As shown by the broken line in FIG. 4, the carrier wave is radiated from the first speaker 50 from the first radiation surface 52 toward the target point F. The sideband wave is radiated from the second speaker 60 from the second radiation surface 62 toward the target point F. Then, in the audible range RA centered on the target point F, which is a region where the region where the carrier wave is radiated and the region where the sideband wave is radiated overlap, audible sound, which is the difference frequency between the carrier wave and the sideband wave, is generated by self-demodulation due to interference between the carrier wave and the sideband wave and distortion due to non-linear propagation.

[0020] As shown in FIG. 3, the size of the first speaker 50 is larger than the size of the second speaker 60. Specifically, the diameter of the first circle 53 circumscribing the first arrangement region 51 which is a regular hexagon is larger than the diameter of the second circle 63 circumscribing the second arrangement region 61 which is a rectangle. Thereby, the size of the audible region RA can be defined by the size of the second speaker 60. Thus, the audible region RA can be appropriately set.

[0021] As described above, the audible region RA is formed in a region where the region where the carrier wave is radiated and the region where the sideband wave is radiated overlap. For this reason, in the plane passing through the target point F, when the region where the carrier wave is radiated is smaller than the region where the sideband wave is radiated, the range of the audible region RA becomes smaller than the region where the sideband wave is radiated. Therefore, if the region where the carrier wave is radiated is enlarged with respect to the region where the sideband wave is radiated, the range of the audible region RA is not limited by the region where the carrier wave is radiated, and thus can be defined by the region where the sideband wave is radiated.

[0022] The inventors have found by experiments described later that the size of the audible region RA is smaller than the size of the second speaker 60. Therefore, by making the size of the first speaker 50 larger than the size of the second speaker 60, the region where the carrier wave is radiated can be enlarged with respect to the region where the sideband wave is radiated. Thus, by setting the size of the second speaker 60 to a size such that the sideband wave can be radiated to the target audible region RA, and further setting the size of the first speaker 50 to be larger than the size of the second speaker 60, the target audible region RA can be generated.

[0023] According to the first embodiment described above, the parametric speaker system 100 includes a first speaker 50 and a plurality of second speakers 60. Each of the plurality of second speakers 60 is arranged on an arrangement circle 54 centered on an arrangement point CP on the first reference line CL1. That is, a plurality of second radiation surfaces 62 as a plurality of radiation surfaces are arranged on the arrangement circle 54. Therefore, even when the sideband wave includes a plurality of frequency components in the audible region RA centered on the target point F, the generation of the difference frequency sound in the audible region RA can be reduced.

[0024] Also, the sound pressure of the carrier wave radiated from the first speaker 50 is greater than the sound pressure of the sideband wave radiated from the second speaker 60. Thereby, the generation of the difference frequency sound in the audible region RA can be reduced. Further, the angle θ formed by the first reference line CL1 and the second reference line CL2 is 45 degrees or less. Thereby, in the audible region RA, an audible sound with good sound pressure can be generated. Also, the distance between the center of gravity CG of the first radiation surface 52 of the first speaker 50 and the target point F is equal to or less than the Rayleigh length of the first speaker 50. Thereby, in the audible region RA, an audible sound can be generated well. Also, the size of the first arrangement region 51 is larger than the size of the second arrangement region 61. Thereby, the size of the audible region RA can be defined by the size of the second speaker 60.

[0025] B. Second Embodiment: The parametric speaker system 2100 according to the present embodiment shown in FIG. 5 is different from the first embodiment in that it includes an angle changing unit 103. Also, the second speaker 60 according to the present embodiment is different from the first embodiment in that it has a rotation mechanism for rotating the second speaker 60 with respect to a support portion (not shown) so that the orientation of the second radiation surface 62 can be changed. Thereby, the angle formed by the second reference line CL2 and the first reference line CL1 can be changed. Since the other configurations are the same as those of the first embodiment, the description thereof is omitted. For convenience, in FIG. 5, only two of the eight second speakers 60 that are located on a line parallel to the X direction passing through the first speaker 50 are shown.

[0026] When the angle change unit 103 receives an instruction to change the position of the target point F, it changes the orientation of the second speaker 60 so that a sideband wave is radiated from the second speaker 60 toward the changed target point F. Specifically, the parametric speaker system 2100 has a button for receiving an instruction to change the position of the target point F. Then, through the operation of the button, an instruction to change the position of the target point F is received. For example, when the changed target point F is the changed target point Fa, the angle formed by the second reference line CL2 and the first reference line CL1 is changed to be an angle θa larger than the angle θi before the change. Thereby, the position of the audible region RA centered on the target point F can be freely changed.

[0027] According to the second embodiment described above, the parametric speaker system 2100 includes an angle change unit 103. When the angle change unit 103 receives an instruction to change the position of the target point F, it changes the orientation of the second speaker 60 so that a sideband wave is radiated toward the changed target point F. Thereby, the position of the audible region RA centered on the target point F can be freely changed.

[0028] C. Third Embodiment: As shown in FIG. 6, the parametric speaker system 3100 according to this embodiment is different from the first embodiment in that a phase control unit 80 is provided in the signal input unit 3101. Further, the parametric speaker system 3100 according to this embodiment is different from the first embodiment in that the second radiation surface 62 of the second speaker 60 shown in FIG. 7 is provided parallel to the XY plane. Since the other configurations are the same as those of the first embodiment, the description thereof is omitted.

[0029] As shown in FIG. 6, the phase control unit 80 is provided between the filter 20 and the amplifier 30. The phase control unit 80 controls the phase of the sideband wave input to each of the ultrasonic transducers 70 that make up the second speaker 60 as a plurality of second ultrasonic transducers so that the radiation direction of the sideband wave is directed toward the target point F. Specifically, the phase control unit 80 changes the phase of the sideband wave input to each of the ultrasonic transducers 70 arranged in a straight line among the ultrasonic transducers 70 that make up the second speaker 60, thereby operating the radiation direction of the sideband wave radiated from the second speaker 60. The phase control unit 80 inputs the sideband wave with the changed phase to each amplifier 30. As shown by the arrows in FIG. 7, the radiation direction of the sideband wave radiated from each second speaker 60 is a direction toward the target point F. Thereby, audible sound can be generated in the audible region RA centered on the target point F.

[0030] According to the third embodiment described above, the parametric speaker system 3100 includes a phase control unit 80. The phase control unit 80 controls the phase of the sideband wave input to each of the ultrasonic transducers 70 included in the second speaker 60 so that the radiation direction of the sideband wave is directed toward the target point F. Thereby, the degree of freedom in the orientation of the second speaker 60 with respect to the position of the target audible region RA can be improved.

[0031] D. Fourth Embodiment The parametric speaker system 4100 according to the present embodiment shown in FIG. 8 differs from the parametric speaker system 100 according to the first embodiment in that it includes an acoustic output unit 104 and a third speaker 90 that radiates a modulated wave. Since the other configurations are the same as those of the first embodiment, the description thereof is omitted.

[0032] The audio output unit 104 amplifies and outputs a modulated wave generated by amplitude-modulating a carrier wave with audio using an amplifier 30. The audio includes frequency components included in each of a plurality of divided bands DB obtained by dividing a band from 300 Hz to 3400 Hz into a plurality of bands. The modulated wave output by the audio output unit 104 is input to the third speaker 90, and the input modulated wave is radiated toward the target point F. As a result, in the audible region RA, self-demodulation occurs and audio is generated.

[0033] The audio in the present embodiment has frequency components included in the divided bands DB obtained by dividing the band from 300 Hz to 3400 Hz into five bands, as illustrated in FIG. 9. The audio includes a plurality of frequency components. And each of the plurality of divided bands DB obtained by dividing the band from 300 Hz to 3400 Hz into a plurality of bands includes any one of the plurality of frequency components of the audio. As a result, in the audible region RA, the audio obtained by demodulating the modulated wave radiated from the third speaker 90 can be heard. Therefore, since the audible sound of the difference frequency is masked by the audio radiated from the third speaker 90, the target audible sound can be made easier to hear.

[0034] As the audio, music or white noise can be used. When the audible sound generated in the audible region RA is speech, music without speech is preferable. By using music without speech, the audible sound generated in the audible region RA can be made easier to hear.

[0035] The sound pressure of the modulated wave radiated from the third speaker 90 is smaller than the sound pressure of the sideband wave radiated from the second speaker 60 and is large enough for the audio generated in the audible region RA to be heard by the subject. As a result, the subject can hear the target audible sound without being inhibited by the audio.

[0036] According to the fourth embodiment described above, the parametric speaker system 4100 includes an acoustic output unit 104 and a third speaker 90 that radiates the sound input from the acoustic output unit 104. As a result, the sound includes a plurality of frequency components, and the plurality of frequency components are distributed over the entire band from 300 Hz to 3400 Hz, so that the target audible sound can be made easier to hear.

[0037] E. Other Embodiments: (E1) In the first embodiment described above, since the plurality of second speakers 60 are arranged on the arrangement circle 54, sideband waves are radiated from the plurality of radiation regions arranged on the arrangement circle 54 toward the target point F. The configuration of radiating sideband waves from the plurality of radiation regions arranged on the arrangement circle 54 toward the target point F is not limited to the configuration of arranging the second speakers 60 on the arrangement circle 54. The second speaker 60 may be arranged at a position different from the arrangement circle 54, and the sideband waves radiated from the second speaker 60 may be reflected to radiate sideband waves from the radiation regions on the arrangement circle 54. Specifically, a reflector that reflects ultrasonic waves may be arranged on the arrangement circle 54, and the sideband waves, which are ultrasonic waves radiated from the second speaker 60, may be reflected by the reflector toward the target point F.

[0038] (E2) In the parametric speaker system 100 according to the first embodiment described above, the second speaker 60 is arranged at a position closer to the target point F than the first speaker 50 in the Z direction. The second speaker 60 may be arranged at the same position as the first speaker 50 in the Z direction, or may be arranged at a position farther from the target point F than the first speaker 50. Regardless of the arrangement position of the second speaker 60 in the Z direction, since the plurality of second speakers 60 are arranged on the arrangement circle 54 centered on the arrangement point CP, the generation of sound with a difference frequency in the audible region RA can be reduced. Further, the shapes of the first arrangement region 51 and the second arrangement region 61 are not limited to the above.

[0039] (E3) The parametric speaker system 100 according to the first embodiment includes eight second speakers 60. The number of the second speakers 60 is not limited to eight. Also, the plurality of second speakers 60 may not be arranged at equal intervals on the arrangement circle 54. By arranging at least two or more second speakers 60 on the arrangement circle 54, generation of sound of a difference frequency in the audible region RA can be reduced.

[0040] (E4) In the parametric speaker system 3100 according to the third embodiment, the second speaker 60 is provided such that the second radiation surface 62 is arranged parallel to the XY plane. The orientation of the second speaker 60 is not limited to the case where it is parallel to the XY plane. By combining the orientation of the second speaker 60 with the operation by phase control, the radiation direction of the sideband wave radiated from the second speaker 60 can be set.

[0041] (E5) In the first embodiment, the upper sideband wave among the sideband waves on both sides is radiated from the second speaker 60. The sideband wave radiated from the second speaker 60 may be the lower sideband wave instead of the upper sideband wave, or the sideband waves on both sides may be radiated.

[0042] The present disclosure is not limited to the above-described embodiments and modifications, and can be realized in various configurations without departing from the gist thereof. For example, the embodiments and modifications corresponding to the technical features in each of the forms described in the summary of the invention can be appropriately replaced or combined in order to solve part or all of the above-described problems or to achieve part or all of the above-described effects. Also, if the technical feature is not described as essential in this specification, it can be appropriately deleted.

[0043] F. Experimental Example: F1. First Experiment: Number of Second Speakers and Sound Pressure: In the first experiment, as shown in FIGS. 10 and 11, up to three second speakers 60 were arranged around the first speaker 50. The angle θ formed by the first reference line CL1 and the second reference line CL2 shown in FIG. 11 is 30 degrees. The distance L1 from the center of gravity CG of the first radiation surface 52 of the first speaker 50 to the target point F is 40 cm. The distance L2 from the center of gravity CG of the second radiation surface 62 of the second speaker 60 to the target point F is 30 cm.

[0044] A carrier wave of 40.3 kHz was input to the first speaker 50. An upper sideband wave generated by amplitude-modulating a signal wave including a frequency component of 1 kHz and a frequency component of 1.7 kHz with a carrier wave of 40.3 kHz was input to the second speaker 60. Therefore, in the audible region RA, an audible sound of 1 kHz and an audible sound of 1.7 kHz are generated. The same applies to the second to fourth experiments hereinafter.

[0045] In this experiment, a microphone was placed at the target point F, the sound pressure of an audible sound, which is a noise of 0.7 kHz, which is the difference frequency between 1 kHz and 1.7 kHz, was set to a predetermined value, and the number of second speakers 60 was changed to measure the sound pressure of the audible sounds of 1 kHz and 1.7 kHz, which are the target audible sounds. The horizontal axis of FIG. 12 showing the results is the number of second speakers 60. As shown in FIG. 12, in both cases of 1 kHz and 1.7 kHz, the sound pressure level increased as the number of speakers, that is, the number of second speakers 60 increased. From this, it can be seen that by increasing the number of second speakers 60, the sound pressure of the noise can be made relatively smaller with respect to the sound pressure of the target audible sound.

[0046] F2. Second Experiment: Size of Second Speaker and Audible Region: In the second experiment, using one second speaker 60, the size of the second speaker 60 and the size of the audible region RA where audible sound is generated were examined. As shown in FIG. 13, the second speaker 60 is arranged such that the second reference line CL2 is orthogonal to the first reference line CL1. The second speaker 60 has its long side arranged parallel to the X-axis. The size of the first speaker 50, specifically, the diameter L3 of the circumscribed circle of the first arrangement region 51 which is a regular octagon, is 15 cm. The length L4 of the long side of the second speaker 60 is 10 cm. The distance L5 between the centroid CG of the first radiation surface 52 shown in FIG. 14 and the target point F is 20 cm. The distance L6 between the centroid CG of the second radiation surface 62 and the target point F is 20 cm. The angle θ formed between the second reference line CL2 and the first reference line CL1 is 90 degrees. The Rayleigh length of the first speaker 50 is approximately 2 m. Note that the Rayleigh length is calculated by dividing the area of the speaker by the wavelength of the sound wave. Therefore, the target point F is set within the range of the Rayleigh length of the first speaker 50.

[0047] In this experiment, measurements were taken by placing a microphone on a line parallel to the X-axis passing through the target point F. The frequency of the audible sound for which the sound pressure level was measured was 1 kHz. The horizontal axis of FIG. 15 showing the results is the position with the +X direction being positive with the target point F as the origin. As shown in FIG. 15, within the range of -2.5 cm or more and +2.5 cm or less centered on the origin, a sound pressure level of 40 dB or more was measured. And when it was outside the range of -2.5 cm or more and +2.5 cm or less centered on the origin, the sound pressure level dropped sharply. From this, it can be seen that audible sound is being generated well within a limited range centered on the origin. The range in which good demodulation occurs is a range narrower than the length L4 which is the size of the second speaker 60. Therefore, by making the size of the first speaker 50 larger than that of the second speaker 60, it can be seen that the range of the audible region RA is not restricted by the region where the carrier wave is radiated, and thus the range of the audible region RA can be defined by the region where the sideband wave is radiated.

[0048] F3. Third Experiment: Output of the Second Speaker and Sound Pressure: In the third experiment, with the voltage of the carrier wave input to the first speaker 50 kept constant, the sound pressure level of the target audible sound in the audible range RA was measured when the voltage of the sideband wave input to the second speaker 60 was changed. In this experiment, three second speakers 60 arranged in the same manner as in the first experiment were used. Fig. 16 shows the result of measuring the sound pressure level while changing the input voltage of the ultrasonic oscillator 70 constituting the second speaker 60 in the range of approximately 3.0 Vpp to 14 Vpp with the input voltage of the ultrasonic oscillator 70 constituting the first speaker 50 being 14 Vpp. Fig. 17 shows the result of measuring the sound pressure level while changing the input voltage of the ultrasonic oscillator 70 constituting the second speaker 60 in the range of approximately 0.4 Vpp to 28 Vpp with the input voltage of the ultrasonic oscillator 70 constituting the first speaker 50 being 28 Vpp. As shown in Fig. 16 and Fig. 17, when the input voltage of the second speaker 60 is 10% or less of the input voltage of the first speaker 50, the sound pressure level of 0.7 kHz which is noise is sufficiently small compared to the sound pressure levels of 1 kHz and 1.7 kHz which are the target audible sounds. And as the voltage of the input signal of the second speaker 60 approaches the voltage of the input signal of the first speaker 50, the sound pressure level of 0.7 kHz which is noise increases. When the voltage of the input signal of the second speaker 60 becomes the same as the voltage of the input signal of the first speaker 50, the sound pressure level of 0.7 kHz becomes the same level as the target audible sound. Therefore, it can be seen that by making the voltage of the input signal to the second speaker 60 at least smaller than the voltage of the input signal to the first speaker 50, the sound pressure level of the difference frequency which becomes noise can be reduced.

[0049] F4. Fourth Experiment: Arrangement Position of the Second Speaker: In the fourth experiment, the arrangement position of the second speaker 60, specifically, the angle θ formed between the first reference line CL1 and the second reference line CL2 was changed, and the sound pressure level of 1 kHz which is the target audible sound was measured. The horizontal axis of Fig. 18 showing the measurement result is the angle of the formed angle θ, and the vertical axis is the sound pressure level. When the formed angle θ exceeds 45 degrees, the sound pressure level decreases. Therefore, it can be seen that by setting the formed angle θ to 45 degrees or less, an audible sound with good sound pressure can be generated.

Explanation of Signs

[0050] 50…First speaker, 51…First placement area, 53…Placement circle, 60…Second speaker, 61…Second placement area, 70…Ultrasonic vibrator, 80…Phase control unit, 90…Third speaker, 100, 2100, 3100, 4100…Parametric speaker system, 103…Angle change unit, 104…Acoustic output unit, CL1…First reference line, CL2…Second reference line, CP…Placement center, F…Target point, RA…Audible area

Claims

1. A first speaker (50) that radiates an ultrasonic carrier wave toward a target point (F), the first speaker having a plurality of first ultrasonic vibrators (70) arranged in a first arrangement region (51); A plurality of second speakers (60) that radiate sideband waves generated by amplitude-modulating the carrier wave with a signal wave in the audible range, the plurality of second speakers each having a plurality of second ultrasonic vibrators (70) arranged in a second arrangement region (61); An acoustic output unit (104) that outputs a modulated wave generated by amplitude-modulating the carrier wave with a predetermined sound; A third speaker (90) that radiates the modulated wave toward the target point, comprising: The sideband waves radiated from each of the plurality of second speakers are radiated toward the target point from each of a plurality of radiation regions arranged on an arrangement circle (54) centered on an arrangement point (CP) on a first reference line (CL1) connecting the target point and the first speaker; The sound includes frequency components included in each of a plurality of divided bands obtained by dividing a band of 300 Hz or more and 3400 Hz or less into a plurality of bands, a parametric speaker system (4100).

2. The parametric speaker system according to claim 1, wherein the sound pressure of the carrier wave is greater than the sound pressure of the sideband wave, a parametric speaker system.

3. The parametric speaker system according to claim 1 or 2, wherein an angle formed by the first reference line and a second reference line connecting the target point and the plurality of radiation regions is 45 degrees or less, a parametric speaker system.

4. The parametric speaker system according to any one of claims 1 to 3, wherein the target point is set within a range of a Rayleigh length of the first speaker, a parametric speaker system.

5. The parametric speaker system according to any one of claims 1 to 4, wherein each of the plurality of second speakers is arranged on the arrangement circle, and the plurality of radiation regions are a plurality of radiation surfaces of the plurality of second speakers, a parametric speaker system.

6. The parametric speaker system according to claim 5, wherein the size of the first arrangement region is larger than the size of the second arrangement region, a parametric speaker system.

7. The parametric speaker system according to claim 5 or 6, Each of the plurality of second speakers is provided so that its orientation can be changed. Further, a parametric speaker system comprising an angle changing unit (103) that, when receiving an instruction to change the position of the target point, changes the orientation of each of the plurality of second speakers so as to radiate the sideband wave toward the target point after the change. **Claim 8** The parametric speaker system according to any one of claims 5 to 7, further comprising: a parametric speaker system comprising a phase control unit (80) that controls the phase of the sideband wave input to each of the plurality of second ultrasonic transducers so that the radiation direction of the sideband wave is directed toward the target point.

Images