Parametric speaker, signal processing device, and signal processing method

Abstract

A parametric speaker 10 comprises: a plurality of ultrasonic wave generation elements 23A, 23B arranged side by side in a first direction R1; and a modulation circuit 32 that generates a modulation signal by modulating an audible sound with a carrier wave. The ultrasonic wave generation elements include a first ultrasonic wave generation element 23A included in a first region which is at least one of opposite end regions in the first direction, and second ultrasonic wave generation elements 23B included in a second region located between the opposite end regions. The modulation circuit generates a first modulation signal SG1 to be applied to the first ultrasonic wave generation element and a second modulation signal SG2 to be applied to the second ultrasonic wave generation elements. The first modulation signal is a signal obtained by shifting the phase of a carrier wave and / or a sideband wave of the second modulation signal by a prescribed phase shifting amount.

Description

[Technical Field]

[0001] This disclosure relates to a parametric speaker, a signal processing device, and a signal processing method. This application claims priority under Japanese application No. 2021-092599 filed on June 1, 2021, and incorporates all the provisions of the said Japanese application. [Background technology]

[0002] Conventionally, parametric speakers that achieve high directivity using ultrasound are known (see, for example, Patent Document 1). Parametric speakers emit a modulated wave, which is a carrier wave in the ultrasonic band modulated with an audio signal, and transmit sound by self-demodulating the modulated wave due to the nonlinear characteristics of the air. The audible range of a parametric speaker exists in a straight line due to the high directivity of the modulated wave (ultrasound). Therefore, it is possible to deliver sound only to those who are in the straight line of the audible range. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-349816 [Overview of the Initiative]

[0004] Regarding parametric speakers, there is a demand for delivering sound to a more limited range. Therefore, one of the objectives of this disclosure is to provide a parametric speaker, a signal processing device, and a signal processing method that can change the range of audible sound.

[0005] According to one embodiment, the parametric speaker comprises a plurality of ultrasonic generating elements arranged in a first direction, and a modulation circuit that generates a modulated signal obtained by modulating an audible sound with a carrier wave. The plurality of ultrasonic generating elements include a first ultrasonic generating element included in a first region which is at least one of the end regions in the first direction, and a second ultrasonic generating element included in a second region which is between the end regions. The modulation circuit generates a first modulated signal to be supplied to the first ultrasonic generating element and a second modulated signal to be supplied to the second ultrasonic generating element. The first modulated signal is a signal in which at least one of the carrier wave and sideband wave of the second modulated signal is phase-shifted by a predetermined amount.

[0006] According to one embodiment, the signal processing device is a signal processing device used in a parametric speaker having a plurality of ultrasonic generating elements arranged in a first direction, which generates a modulated signal obtained by modulating an audible sound with a carrier wave, and generates a first modulated signal to be applied to a first ultrasonic generating element included in a first region which is at least one of the end regions in the first direction of the plurality of ultrasonic generating elements, and a second modulated signal to be applied to a second ultrasonic generating element included in a second region which is between the end regions, wherein the first modulated signal is a signal in which at least one of the carrier wave and sideband wave of the second modulated signal is shifted in phase by a predetermined amount.

[0007] According to one embodiment, the signal processing method is a signal processing method for generating a modulated signal obtained by modulating an audible sound with a carrier wave in a parametric speaker having a plurality of ultrasonic generating elements arranged in a first direction, comprising: generating a first modulated signal to be applied to a first ultrasonic generating element included in a first region which is at least one of the end regions in the first direction of the plurality of ultrasonic generating elements, and generating a second modulated signal to be applied to a second ultrasonic generating element included in a second region located between the end regions, wherein the first modulated signal is a signal in which at least one of the carrier wave and sideband wave of the second modulated signal is shifted in phase by a predetermined amount.

[0008] Further details will be described in the embodiments below. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram of an acoustic system equipped with a parametric speaker according to an embodiment. [Figure 2] Figure 2 is a front view diagram of the speaker unit. [Figure 3] Figure 3 is an explanatory diagram illustrating the principle of a parametric speaker. [Figure 4] Figure 4 is a flowchart illustrating an example of a signal processing method according to an embodiment. [Figure 5] Figure 5 shows the results of the first experiment under condition 1 in the verification experiment of the parametric speaker according to the embodiment. [Figure 6] Figure 6 shows the results of the first experiment under condition 2 in the verification experiment of the parametric speaker according to the embodiment. [Figure 7] Figure 7 shows the results of the first experiment under condition 3 in the verification experiment of the parametric speaker according to the embodiment. [Figure 8] Figure 8 shows the results of the first experiment under condition 4 in the verification experiment of the parametric speaker according to the embodiment. [Figure 9] Figure 9 shows the results of the first experiment under condition 5 in the verification experiment of the parametric speaker according to the embodiment. [Figure 10] Figure 10 shows the results of the first experiment under condition 6 in the verification experiment of the parametric speaker according to the embodiment. [Figure 11] Figure 11 shows the results under conditions 1 to 5 in the first experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 12] Figure 12 shows the results under condition 7 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 13]FIG. 13 is a diagram showing the results of Condition 8 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 14] FIG. 14 is a diagram showing the results of Condition 9 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 15] FIG. 15 is a diagram showing the results of Condition 10 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 16] FIG. 16 is a diagram showing the results of Condition 11 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 17] FIG. 17 is a diagram showing the results of Condition 12 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 18] FIG. 18 is a diagram showing the results of Conditions 7 to 11 in the second experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 19] FIG. 19 is a diagram showing the results of Condition 13 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 20] FIG. 20 is a diagram showing the results of Condition 14 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 21] FIG. 21 is a diagram showing the results of Condition 15 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 22] FIG. 22 is a diagram showing the results of Condition 16 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 23] FIG. 23 is a diagram showing the results of Condition 17 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 24] FIG. 24 is a diagram showing the results of Condition 18 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Figure 25]Figure 25 shows the results under conditions 13 to 17 in the third experiment of the verification experiment of the parametric speaker according to the embodiment. [Modes for carrying out the invention]

[0010] <1. Overview of Parametric Speaker, Signal Processing Device, and Signal Processing Method>

[0011] (1) The parametric speaker according to the embodiment comprises a plurality of ultrasonic generating elements arranged in a first direction, and a modulation circuit that generates a modulated signal obtained by modulating an audible sound with a carrier wave, wherein the plurality of ultrasonic generating elements include a first ultrasonic generating element included in a first region which is at least one of the end regions of the first direction, and a second ultrasonic generating element included in a second region which is between the end regions, and the modulation circuit generates a first modulated signal to be given to the first ultrasonic generating element and a second modulated signal to be given to the second ultrasonic generating element, wherein the first modulated signal is a signal obtained by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal by a predetermined phase shift amount.

[0012] The first modulated signal may be a signal in which only the sidebands of the second modulated signal are phase-shifted. The inventors have experimentally verified that this can narrow the width of the audible range in the first direction obtained by the self-demodulation of the modulated wave radiated from the parametric speaker.

[0013] The first modulated signal may be a signal in which only the carrier wave of the second modulated signal is phase-shifted. The inventors have experimentally verified that this can shorten the length in the second direction perpendicular to the first direction of the audible range, that is, the distance that the audible sound can travel.

[0014] The first modulated signal may be the carrier wave of the second modulated signal and a signal with a phase shift of the carrier wave. The inventors have verified through experiments that this makes it possible to narrow the width of the audible range in the first direction while shortening the length in the second direction perpendicular to the first direction, that is, the distance that the audible sound can travel.

[0015] Therefore, the range of audible sound can be changed by using a parametric speaker in which the first modulated signal is a signal in which at least one of the carrier wave and sideband of the second modulated signal is shifted in phase by a predetermined amount.

[0016] (2) Preferably, generating the second modulated signal in the modulation circuit includes inverting the phase of the carrier wave of the first modulated signal and not changing the phase of the sidebands. Because the carrier wave of the first modulated signal is out of phase with the carrier wave of the second modulated signal, the radiated waves cancel each other out near the boundary between the modulated wave radiated from the first ultrasonic generating element and the modulated wave radiated from the second ultrasonic generating element, which is thought to make the width of the audible range in the first direction smaller. Therefore, inverting the phase of the carrier wave causes more cancellation and makes the width of the audible range in the first direction smaller.

[0017] (3) Preferably, generating the second modulated signal in the modulation circuit includes inverting the phase of the sidebands of the first modulated signal and not changing the phase of the carrier wave. Because the sidebands of the first modulated signal are out of phase with the sidebands of the second modulated signal, the number of ultrasonic generating elements emitting the modulated wave of the second modulated signal is reduced. As a result, it is thought that the range of the audible sound is shortened. Therefore, by inverting the phase of the sidebands, the number of ultrasonic generating elements emitting the modulated wave of the second modulated signal can be further reduced, and the range of the audible sound can be shortened even further.

[0018] (4) Preferably, generating a second modulated signal in the modulation circuit includes inverting the phase of both the sidebands and carrier of the first modulated signal. This shortens the range of the audible sound by inverting the phase of the sidebands of the modulated wave, and further, by inverting the phase of the carrier of the modulated wave for the ultrasonic generating elements at both ends of the first direction, it becomes possible to deliver sound more narrowly and sharply in the first direction.

[0019] (5) The signal processing device according to the embodiment is a signal processing device used in a parametric speaker having a plurality of ultrasonic generating elements arranged in a first direction, which generates a modulated signal obtained by modulating an audible sound with a carrier wave, and generates a first modulated signal to be applied to a first ultrasonic generating element included in a first region which is at least one of the end regions in the first direction of the plurality of ultrasonic generating elements, and generates a second modulated signal to be applied to a second ultrasonic generating element included in a second region which is between the end regions, wherein the first modulated signal is a signal in which at least one of the carrier wave and sideband wave of the second modulated signal is shifted in phase by a predetermined amount. This makes it possible to change the range in which an audible sound can reach in a parametric speaker.

[0020] (6) The signal processing method according to the embodiment is a signal processing method for generating a modulated signal obtained by modulating an audible sound with a carrier wave in a parametric speaker having a plurality of ultrasonic generating elements arranged in a first direction, comprising: generating a first modulated signal to be applied to a first ultrasonic generating element included in a first region which is at least one of the end regions in the first direction of the plurality of ultrasonic generating elements, and generating a second modulated signal to be applied to a second ultrasonic generating element included in a second region which is between the end regions, wherein the first modulated signal is a signal obtained by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal by a predetermined phase shift amount. This makes it possible to change the range in which audible sound can reach in the parametric speaker.

[0021] <2. Examples of parametric speakers, signal processing devices, and signal processing methods>

[0022] Figure 1 is a schematic diagram of an acoustic system 10 equipped with a parametric speaker according to an embodiment. Referring to Figure 1, the acoustic system 10 comprises a signal generating device 11 and a parametric speaker 12.

[0023] The signal generation device 11 comprises a signal source 13 and a filter processing unit 14. The signal source 13 generates sound wave signals in the audible range, such as voice signals or audio signals, and outputs them to the filter processing unit 14. The filter processing unit 14 imparts predetermined characteristics to the signal wave and then outputs the signal wave to the parametric speaker 12.

[0024] The parametric speaker 12 comprises a speaker body 21 and a signal processing unit 22. The signal processing unit 22 may be mounted in the same device as the speaker body 21, or it may be configured as a separate signal processing unit from the speaker body 21, connected to the speaker body 21 by wire or wireless, and transmitting the generated signals to the speaker body 21. The signal processing unit 22, as a signal processing unit, may be implemented by, for example, a computer. The computer may be, for example, a smartphone.

[0025] Figure 2 is a front view of the speaker body 21. The speaker body 21 is equipped with multiple ultrasonic generating elements 23 that emit ultrasonic waves. The multiple ultrasonic generating elements 23 are arranged on the support substrate 24 in a first direction R1, which corresponds to the left-right direction in Figure 2, with N elements (where N is multiple). In Figure 2, 15 ultrasonic generating elements 23 (N=15) are arranged in the first direction R1 with intervals d.

[0026] Preferably, multiple ultrasonic generating elements 23 are also arranged in a second direction R2 that is perpendicular to the first direction R1, which corresponds to the vertical direction in Figure 2. In Figure 2, 10 ultrasonic generating elements 23 are arranged in the second direction R2. That is, preferably, multiple ultrasonic generating elements 23 are provided in a planar arrangement on the support substrate 24, and in Figure 2, they are arranged in 10 vertically and 15 horizontally.

[0027] The plurality of ultrasonic generating elements 23 arranged in the first direction R1 include a first ultrasonic generating element 23A included in the first region A1, which is at least one of the end regions of the first direction R1, and a second ultrasonic generating element 23B included in the second region A2, which is located between the end regions. As an example, both end regions of the first direction R1 are defined as the first region A1.

[0028] Specifically, in the example shown in Figure 2, of the 15 columns in the left-right direction, the three columns on each end are designated as the first ultrasonic generating elements 23A, and the multiple columns inside them are designated as the second ultrasonic generating elements 23B. If we number the columns from right to left as 1 to 15, the ultrasonic generating elements 23 located in columns 1 to 3 and columns 13 to 15 are designated as the first ultrasonic generating elements 23A, and the ultrasonic generating elements 23 located in columns 4 to 12 are designated as the second ultrasonic generating elements 23B. In Figure 1, each column is schematically represented by one ultrasonic generating element 23, with one on each side designated as the first ultrasonic generating elements 23A, and the multiple ultrasonic generating elements 23 inside them designated as the second ultrasonic generating elements 23B.

[0029] Figure 3 is an explanatory diagram illustrating the principle of the parametric speaker 12. The parametric speaker 12 generates ultrasonic waves, which are imperceptible to humans as sound, at high frequencies of 20 kHz or higher, as a carrier wave. The carrier wave is amplitude-modulated by a sound wave signal, which is an audible sound generated by the signal generator 11, and the resulting modulated wave is radiated into the air. As the radiated modulated wave propagates through the air, it undergoes distortion due to the nonlinearity of the air, and this distortion causes the audible sound to self-demodulate.

[0030] The signal processing unit 22 includes a carrier wave generation unit 31, a modulation unit 32, and an amplification unit 35. The signal processing unit 22 generates a first modulation signal SG1 to be supplied to the first ultrasonic generating element 23A and a second modulation signal SG2 to be supplied to the second ultrasonic generating element 23B.

[0031] The carrier wave generation unit 31 generates a carrier wave consisting of ultrasonic waves of a predetermined frequency and outputs it to the modulation unit 32. This carrier wave generation unit 31 is configured to include a high-frequency oscillator, for example, using a quartz crystal oscillator. In this embodiment, the carrier wave generation unit 31 generates a 40 kHz carrier wave and outputs it to the modulation unit 32.

[0032] The modulation unit 32 generates an amplitude-modulated wave by amplitude-modulating the carrier wave input from the carrier wave generation unit 31 using the sound wave signal input from the signal generation device 11. The amplification unit 35 is configured using, for example, an operational amplifier with good amplification characteristics in the ultrasonic band, and amplifies the modulated wave generated by the modulation unit 32.

[0033] More specifically, the carrier wave vc(t) can be expressed by the following equation (1), using the carrier wave frequency fc, time t, and the maximum amplitude Ac of the carrier wave. Furthermore, the audible sound vs(t) can be expressed by the following equation (2), using the frequency fs of the sound wave signal generated by the signal generator 11 and the maximum amplitude As of the audible sound. vc(t)=Ac·cos(2πfct) …Equation (1) vs(t)=As·cos(2πfst) …Equation (2)

[0034] The modulation unit 32 amplitude modulates the carrier wave vc(t) with the audible sound vs(t). The modulated wave v generated by the modulation unit 32 M (t) can be expressed by the following equation (3), using the modulation index m (m ≤ 1), which indicates the amount of audible sound. Note that the modulation index m is expressed by the following equation (4). v M (t)=(1+m vs(t))vc(t)) …Equation (3) m = As / Ac …Equation (4)

[0035] From equation (3), the modulated wave v M (t) can be expressed by the following equation (5). v M (t)=vc(t)+m vs(t) vc(t) …Equation (5)

[0036] From equation (5), the modulated wave v M It can be seen that (t) is composed of a carrier wave vc(t) and sidebands m·vs(t)·vc(t). The sidebands m·vs(t)·vc(t) may be both a sideband having the frequency of the sum of the carrier wave frequency fc and the frequency of the audible sound wave signal fs (fc+fs) and a sideband having the difference frequency (fc-fs), or one of these may be removed using a filter or the like. Such a modulated wave v M When (t) is radiated into the air at high sound pressure from the parametric speaker 12, the modulated wave is distorted due to the nonlinearity of the air, and the difference tone between the carrier wave and the sidebands is reproduced as an audible sound.

[0037] The modulated wave amplified by the amplification unit 35 is passed to the second ultrasonic generating element 23B as the second modulated signal SG2. Meanwhile, the modulated wave amplified by the amplification unit 35 is also passed to the phase adjustment unit 33. The phase adjustment unit 33 adjusts the phase of the modulated wave to generate the first modulated signal SG1, which is then passed to the first ultrasonic generating element 23A.

[0038] The phase adjustment unit 33 generates the first modulated signal SG1 by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal SG2 by a predetermined phase shift amount. In other words, the first modulated signal SG1 is a signal obtained by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal SG2, i.e., the amplified modulated wave, by a predetermined phase shift amount.

[0039] The phase adjustment unit 33 may be implemented by a phase shifter, including a temporary phase shift circuit also known as an all-pass filter. Alternatively, the phase adjustment unit 33 may be implemented by computer-based phase processing.

[0040] The predetermined phase shift amount is preferably the shift amount at which the phase is inverted. Thereby, the first modulation signal SG1 becomes a signal obtained by inverting the phase of at least one of the carrier wave and the sideband wave of the second modulation signal SG2. The predetermined phase shift amount is preferably 180° for inverting the phase, but is not particularly limited, and may be, for example, within the range of 90° to 270°. As another example, the predetermined phase shift amount may be within the range of 135° to 225° for inverting the phase.

[0041] As an example, the phase adjustment unit 33 generates a signal that inverts the phase of the carrier wave of the second modulation signal SG2 and does not change the phase of the sideband wave, and uses it as the first modulation signal SG1. The modulated wave v M 1(t) can be expressed by the following equation (6) from equation (5). v M 1(t)=-vc(t)+m·vs(t)·vc(t) … Equation (6)

[0042] As another example, the phase adjustment unit 33 generates a signal that inverts the phase of the sideband wave of the second modulation signal SG2 and does not change the phase of the carrier wave, and uses it as the first modulation signal SG1. The modulated wave M 2(t) can be expressed by the following equation (7) from equation (5). v M 2(t)=vc(t)-m·vs(t)·vc(t) … Equation (7)

[0043] As another example, the phase adjustment unit 33 generates a signal that inverts the phases of both the sideband wave and the carrier wave of the second modulation signal SG2, and uses it as the first modulation signal SG1. The modulated wave M 3(t) can be expressed by the following equation (8) from equation (5). v M 3(t)=-vc(t)-m·vs(t)·vc(t) … Equation (8)

[0044] Figure 4 is a flowchart illustrating an example of a signal processing method according to the embodiment. Referring to Figure 4, the audible frequency sound wave signal generated by the signal generation device 11 is input to the signal processing unit 22 (step S101).

[0045] In the signal processing unit 22, a 40 kHz carrier wave is generated (step S103). The carrier wave is amplitude-modulated by the sound wave signal input from the signal generator 11 (step S105). The amplitude-modulated wave generated in step S105 is output to the second ultrasonic generating element 23B as the second modulation signal SG2 (step S107).

[0046] In the signal processing unit 22, the first modulated signal SG1 is generated by inverting the phase of at least one of the carrier wave and sideband wave of the amplitude modulated wave, and is passed to the first ultrasonic generating element 23A (step S109).

[0047] Verification experiments were conducted to investigate the effect of the signal generated by the signal processing method according to the embodiment on the radiation characteristics from the parametric speaker 12. For the verification experiments, a parametric speaker 12 was used, as shown in Figure 2, in which ultrasonic generating elements 23 were arranged in 10 vertical and 15 horizontal rows.

[0048] The effects on radiation characteristics were measured by sound pressure level, directivity angle, and sound pressure attenuation. The sound pressure level was measured by recording sound waves (modulated waves) emitted from the parametric speaker 12 with multiple microphones, calculating the sound pressure level of the recorded audible sound, and determining its distribution. As an example, a predetermined number of microphones were arranged vertically and horizontally at predetermined intervals (e.g., 0.1m intervals), and the speaker body 21 of the parametric speaker 12 was placed at a position where the width and depth (distance) were 0m (coordinate (0,0)).

[0049] The directivity angle is the angle at which ultrasonic waves spread. The inventor measured the directivity angle at a distance of 1 m from the speaker body 21 (1m directivity angle) and at a distance of 2 m (2m directivity angle). A larger directivity angle indicates a wider audible range, meaning that sound is delivered over a wider area, while a smaller directivity angle indicates a narrower listening range, meaning that sound is delivered over a narrower area.

[0050] Sound pressure attenuation is the amount of sound pressure attenuation at a predetermined distance. The inventor measured the sound pressure attenuation from a distance of 0.5m to 2.5m from the speaker body 21 (0.5→2.5m sound pressure attenuation), and the sound pressure attenuation from a distance of 0.5m to 3.5m (0.5→3.5m sound pressure attenuation). A smaller sound pressure attenuation value indicates a longer distance from the parametric speaker 12 in the audible range, meaning the sound can travel further. A larger value indicates a shorter distance from the parametric speaker 12 in the audible range, meaning the sound can travel shorter.

[0051] In the first experiment, the ultrasonic generating elements 23 located in the left and right rows of the speaker body 21, i.e., the 1st and 15th rows, were designated as the first ultrasonic generating elements 23A, and the ultrasonic generating elements 23 located in the 2nd to 14th rows were designated as the second ultrasonic generating elements 23B. In this state, the inventor measured the sound pressure level, directivity angle, and sound pressure attenuation for each of the following conditions 1 to 3. Condition 1: The first modulated signal SG1 is a signal that inverts the phase of the carrier wave of the second modulated signal SG2, but does not change the phase of the sideband (v in equation (6)). M When 1(t) Condition 2: The first modulated signal SG1 is a signal that inverts the phase of the sideband of the second modulated signal SG2 and does not change the phase of the carrier wave (v in equation (7)). M When 2(t) Condition 3: The first modulated signal SG1 is obtained by inverting the phase of both the sideband and carrier wave of the second modulated signal SG2 (v in equation (8)). M When 3(t)

[0052] Furthermore, as a comparative experiment, the inventors used the same parametric speaker 12 to output only the second modulated signal SG2, in which neither the carrier wave nor the sidebands were changed in their transport, and measured the sound pressure level, directivity angle, and sound pressure attenuation for each of the conditions 4 to 6 below. Condition 4: When all modulation signals of the first ultrasonic generating element 23A and the second ultrasonic generating element 23B are set to the second modulation signal SG2. Condition 5: When only the second ultrasonic generating element 23B is used as the second modulation signal SG2. Condition 6: When only the first ultrasonic generating element 23A is used as the second modulation signal SG2.

[0053] Figures 5 to 7 show the measurement results of sound pressure levels under conditions 1 to 3, respectively, and Figures 8 to 10 show the measurement results of sound pressure levels under conditions 4 to 6, respectively. Figure 11 shows the measurement results of directivity angle and sound pressure attenuation under conditions 1 to 5. In Figures 5 to 10, the X-axis represents the first direction R1 (left-right direction), and the Y-axis represents the second direction R2 (up-down direction). The X-axis is aligned with the surface of the speaker body 21, and the position of Y-axis 0, X-axis 0 is set to the center of the first direction R1 of the speaker body 21, i.e., the 7th column. Therefore, the larger the Y-axis value, the further away it is from the front of the speaker body 21, and the larger the Y-axis value, the further to the right it is, and the smaller the Y-axis value, the further to the left it is. Figures 5 to 11 show the sound pressure level of audible sound at each position represented by the YX coordinates.

[0054] In the second experiment, the ultrasonic generating elements 23 located in two rows on each side of the speaker body 21, i.e., in the 1st and 2nd rows and the 14th and 15th rows, were designated as the first ultrasonic generating elements 23A, and the ultrasonic generating elements 23 located in the 3rd to 13th rows were designated as the second ultrasonic generating elements 23B. In this state, the inventor measured the sound pressure level, directivity angle, and sound pressure attenuation for each of the following conditions 7 to 9. Condition 7: The first modulated signal SG1 is a signal that inverts the phase of the carrier wave of the second modulated signal SG2, but does not change the phase of the sideband (v in equation (6)). M When 1(t) Condition 8: The first modulated signal SG1 is a signal that inverts the phase of the sideband of the second modulated signal SG2, but does not change the phase of the carrier wave (v in equation (7)). M When 2(t) Condition 9: The first modulated signal SG1 is obtained by inverting the phase of both the sideband and carrier wave of the second modulated signal SG2 (the v of equation (8)). M When 3(t)

[0055] Furthermore, as a comparative experiment, the inventors used the same parametric speaker 12 to output only the second modulated signal SG2, in which neither the carrier wave nor the sidebands were changed in their transport, and measured the sound pressure level, directivity angle, and sound pressure attenuation for each of the conditions 9 to 12 below. Condition 10: When all modulation signals of the first ultrasonic generating element 23A and the second ultrasonic generating element 23B are set to the second modulation signal SG2. Condition 11: When only the second ultrasonic generating element 23B is used as the second modulation signal SG2. Condition 12: When only the first ultrasonic generating element 23A is used as the second modulation signal SG2.

[0056] Figures 12 to 14 show the sound pressure level measurement results for conditions 7 to 9, respectively, and Figures 15 to 17 show the sound pressure level measurement results for conditions 10 to 12, respectively. Figure 18 shows the measurement results for the directivity angle and sound pressure attenuation for conditions 7 to 11.

[0057] In the third experiment, the ultrasonic generating elements 23 located in three rows on each side of the speaker body 21, i.e., rows 1, 2, and 3 and rows 13, 14, and 15, were designated as the first ultrasonic generating elements 23A, and the ultrasonic generating elements 23 located in rows 4 to 12 were designated as the second ultrasonic generating elements 23B. In this state, the inventor measured the sound pressure level, directivity angle, and sound pressure attenuation for each of the following conditions 13 to 15. Condition 13: The first modulated signal SG1 is a signal that inverts the phase of the carrier wave of the second modulated signal SG2, but does not change the phase of the sideband (v in equation (6)). M When 1(t) Condition 14: The first modulated signal SG1 is a signal that inverts the phase of the sideband of the second modulated signal SG2 and does not change the phase of the carrier wave (v in equation (7)). M When 2(t) Condition 15: The first modulated signal SG1 is obtained by inverting the phase of both the sideband and carrier wave of the second modulated signal SG2 (the v of equation (8)). M When 3(t)

[0058] Furthermore, as a comparative experiment, the inventors used the same parametric speaker 12 to output only the second modulated signal SG2, in which neither the carrier wave nor the sidebands were changed in their transport, and measured the sound pressure level, directivity angle, and sound pressure attenuation for each of the conditions 16 to 18 below. Condition 16: When all modulation signals of the first ultrasonic generating element 23A and the second ultrasonic generating element 23B are set to the second modulation signal SG2. Condition 17: When only the second ultrasonic generating element 23B is used as the second modulation signal SG2. Condition 18: When only the first ultrasonic generating element 23A is used as the second modulation signal SG2.

[0059] Figures 19 to 21 show the sound pressure level measurement results for conditions 13 to 15, respectively, and Figures 22 to 24 show the sound pressure level measurement results for conditions 16 to 18, respectively. Figure 23 shows the measurement results for the directivity angle and sound pressure attenuation for conditions 13 to 17.

[0060] In the first to third experiments, under conditions 6, 12, and 18, which were performed for comparison and involved emitting modulated waves based on the second modulated signal SG2 only at the left and right ends, it can be seen from Figures 10, 17, and 24 that the sound pressure level was extremely low at all positions relative to the speaker body 21. Therefore, it was considered that an effective audible range could not be obtained under conditions 6, 12, and 18. Accordingly, measurements of the directivity angle and sound pressure attenuation were not performed for these conditions.

[0061] In the first experiment, comparing the sound pressure levels of condition 1 and condition 4, Figures 5 and 8 show that the width of the first direction R1 (X-axis direction) of the audible range was smaller in condition 1 than in condition 4. Similarly, comparing conditions 7 and 10 in the second experiment, and conditions 13 and 16 in the third experiment, Figures 12 and 15, and 19 and 12 show that the width of the first direction R1 of the audible range was smaller in condition 7 than in condition 10, and the width of the first direction R1 of the audible range was smaller in condition 13 than in condition 16.

[0062] This is also shown by the fact that in all of the measurement results of the beam angle in the first to third experiments (Figures 11, 18, and 25), the 1m beam angle and 2m beam angle for conditions 1 and 4, 7 and 10, and 13 and 16 are smaller for conditions 1, 7, and 13 than for conditions 4, 10, and 16, respectively.

[0063] Therefore, it was verified that by radiating the carrier wave of the modulated wave with the ultrasonic generating elements 23 at both ends of the first direction R1 having their phases reversed, the width of the audible range in the first direction R1 can be reduced compared to when all ultrasonic generating elements 23 radiate modulated waves without reversing the carrier wave's phase. In other words, it was verified that by reversing the phase of the carrier wave of the modulated wave from the ultrasonic generating elements 23 at both ends of the first direction R1, it becomes possible to deliver sound in a narrower and sharper direction R1.

[0064] Here, comparing the measurement results of the directivity angles for conditions 1, 7, and 13 with those for conditions 5, 11, and 17, respectively, Figures 11, 18, and 25 show that the directivity angles for conditions 1, 7, and 13 are smaller than those for conditions 5, 11, and 17. This trend is particularly pronounced at greater distances from the speaker body 21. The phases of the carrier wave of the modulated wave radiated from the first ultrasonic generating element 23A and the carrier wave of the modulated wave radiated from the second ultrasonic generating element 23B are reversed. Therefore, it is thought that the radiated waves cancel each other out near the boundary between the modulated wave radiated from the first ultrasonic generating element 23A and the modulated wave radiated from the second ultrasonic generating element 23B.

[0065] As a result, the first modulated signal SG1 may be a signal in which the phase of the carrier wave of the second modulated signal SG2 is shifted by a predetermined phase shift amount, and the predetermined phase shift amount only needs to be greater than 0. Preferably, it is a shift amount that inverts the phase. As a result, it is thought that the modulated waves radiated from the first ultrasonic generating element 23A and the modulated waves radiated from the second ultrasonic generating element 23B cancel each other out more near the boundary between them, and the width of the first direction R1 of the audible range can be made smaller.

[0066] Comparing the measurement results of the directional angle for each of the conditions 1, 7, and 13, Figures 11, 18, and 25 show that the directional angle was smaller for condition 7 than for condition 1, and smaller for condition 13 than for condition 7. Therefore, it was verified that for the ultrasonic generating elements 23 at both ends of the first direction R1, having two rows on each end instead of one row on each end, and three rows on each end instead of two rows, makes it possible to deliver sound more narrowly and sharply in the first direction R1.

[0067] Therefore, in order to narrow the width of the first direction R1 of the audible range, it was verified that it is effective to invert the phase of the carrier wave of the modulated wave for at least one row at both ends of the first direction R1 of the speaker body 21, preferably a number of rows of ultrasonic generating elements 23 that represent approximately 20% of the total number of ultrasonic generating elements 23 arranged in the first direction R1 of the speaker body 21.

[0068] Next, comparing the sound pressure levels of conditions 2, 8, and 14 with those of conditions 4, 10, and 13, respectively, Figures 6, 8, 13, 15, 20, and 22 show that the length of the second direction R2 (Y-axis direction) in the audible range is greater for conditions 2, 8, and 14 than for conditions 4, 10, and 13.

[0069] Comparing the sound pressure attenuation measurement results from the first to third experiments (Figures 11, 18, and 25), the sound pressure attenuation from 0.5 to 2.5 m was greater for conditions 2, 8, and 14 than for conditions 4, 10, and 16, respectively. However, the sound pressure attenuation from 0.5 to 3.5 m was smaller for conditions 2, 8, and 14 than for conditions 4, 10, and 16, respectively. Therefore, it was found that the sound pressure attenuates more in conditions 2, 8, and 14 as the distance from the speaker body 21 increases.

[0070] Furthermore, comparing the measurement results of sound pressure attenuation under conditions 2, 8, and 14, Figures 11, 18, and 25 show that under condition 8, the sound pressure attenuation from 0.5 to 2.5 m and from 0.5 to 3.5 m were greater than under condition 2, and under condition 14, the sound pressure attenuation from 0.5 to 2.5 m and from 0.5 to 3.5 m were greater than under condition 8.

[0071] This is likely because conditions 2, 8, and 14 have fewer second ultrasonic generating elements 23B than conditions 4, 10, and 16, meaning there are fewer ultrasonic generating elements 23 that emit the modulated wave of the second modulated signal SG2.

[0072] As a result, the first modulated signal SG1 may be a signal in which the phase of the sideband of the second modulated signal SG2 is shifted by a predetermined phase shift amount, and the predetermined phase shift amount only needs to be greater than 0. Preferably, it is a shift amount that inverts the phase. This makes it possible to further reduce the number of ultrasonic generating elements 23 that radiate the modulated wave of the second modulated signal SG2, and it is thought that the length of the second direction R2 in the audible range can be made smaller.

[0073] Therefore, it was verified that by radiating the sidebands of the modulated wave with the ultrasonic generating elements 23 at both ends of the first direction R1 of the speaker body 21 while inverting the phase of the sidebands, the length of the second direction R2 in the audible range can be reduced compared to the case where modulated waves with uninverted sideband phases are radiated from all ultrasonic generating elements 23. In other words, it was verified that by inverting the phase of the sidebands of the modulated wave from the ultrasonic generating elements 23 at both ends of the first direction R1, it becomes possible to deliver sound over a shorter distance in the second direction R2.

[0074] Furthermore, comparing the measurement results of the directivity angles for conditions 8 and 9, and conditions 14 and 15, it was found that the directivity angle was smaller for condition 9 than for condition 8, and smaller for condition 15 than for condition 14. Therefore, it was verified that by inverting the phase of the sidebands in the modulated wave to reduce the length of the second direction R2 of the audible range for the ultrasonic generating elements 23 at both ends of the first direction R1 of the speaker body 21, and further inverting the phase of the carrier wave of the modulated wave for the ultrasonic generating elements 23 at both ends of the first direction R1, it becomes possible to deliver sound more narrowly and sharply in the first direction R1.

[0075] In the above explanation, the ultrasonic generating elements 23 at both ends of the speaker body 21 in the first direction R1 are assumed to have their phase shifted (inverted) by a predetermined amount for at least one of the carrier wave and sidebands of the modulated wave. However, the same method may be used for the ultrasonic generating elements 23 at both ends of the second direction R2, where the phase shift is predetermined for at least one of the carrier wave and sidebands of the modulated wave. The results of the above experiment have verified that by swapping the first direction R1 and the second direction R2, the range of audible sound can be similarly changed in the second direction R2. Furthermore, it is considered that the range of audible sound can be changed by shifting the phase of at least one of the carrier wave and sidebands of the modulated wave by a predetermined amount for both the first direction R1 and the second direction R2, using the ultrasonic generating elements 23 at both ends.

[0076] The present invention is not limited to the above embodiments, and various modifications are possible. [Explanation of Symbols]

[0077] 10: Sound System 11:Signal generation device 12: Parametric speaker 13: Signal source 14: Filtering section 21: Speaker unit 22: Signal Processing Unit 23: Ultrasonic generating element 23A: First ultrasonic generating element 23B: Second ultrasonic generating element 24: Support substrate 31: Carrier wave generation unit 32: Modulation section 33: Phase adjustment section 34: Phase control unit 35: Amplification section A1: 1st area A2:Second area R1: First direction R2: Second direction SG1: First Modulated Signal SG2: Second modulation signal

Claims

1. Multiple ultrasonic generating elements arranged in the first direction, It comprises a modulation circuit that generates a modulated signal by modulating an audible sound with a carrier wave, The plurality of ultrasonic generating elements include a first ultrasonic generating element included in a first region which is at least one of the two end regions in the first direction, and a second ultrasonic generating element included in a second region which is between the two end regions. The modulation circuit described above is The first modulation signal supplied to the first ultrasonic generating element, The second modulation signal is supplied to the second ultrasonic generating element, and a second modulation signal is generated. The first modulated signal is a signal obtained by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal by a predetermined phase shift amount. Parametric speaker.

2. Generating the second modulated signal in the modulation circuit includes inverting the phase of the carrier wave of the first modulated signal and not changing the phase of the sideband wave. The parametric speaker according to claim 1.

3. Generating the second modulated signal in the modulation circuit includes inverting the phase of the sideband of the first modulated signal and not changing the phase of the carrier wave. The parametric speaker according to claim 1.

4. Generating the second modulated signal in the modulation circuit includes inverting the phase of both the sideband and the carrier wave of the first modulated signal. The parametric speaker according to claim 1.

5. A signal processing device for generating a modulated signal obtained by modulating an audible sound with a carrier wave, used in a parametric speaker having a plurality of ultrasonic generating elements arranged in a first direction, A first modulation signal is generated to a first ultrasonic generating element that is included in the first region, which is at least one of the end regions in the first direction, among the plurality of ultrasonic generating elements. A second modulation signal is generated which is applied to a second ultrasonic generating element located in a second region between the two end regions, The first modulated signal is a signal obtained by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal by a predetermined phase shift amount. Signal processing device.

6. A signal processing method for generating a modulated signal obtained by modulating an audible sound with a carrier wave in a parametric speaker having a plurality of ultrasonic generating elements arranged in a first direction, A first modulation signal is generated to a first ultrasonic generating element that is included in the first region, which is at least one of the end regions in the first direction, among the plurality of ultrasonic generating elements. The system generates a second modulation signal that is supplied to a second ultrasonic generating element located in a second region between the two end regions, The first modulated signal is a signal obtained by shifting the phase of at least one of the carrier wave and sideband wave of the second modulated signal by a predetermined phase shift amount. Signal processing method.

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