Active Noise Control System

Abstract

A loudspeaker (10) includes a radiation surface (15). The radiation surface (15) has a first region (15a), a second region (15b), and a third region (15c), wherein the third region (15c) is a region between the first region (15a) and the second region (15b). When an axis passing through the third region (15c) and extending away from the radiation surface (15) is defined as a reference axis (10X), the loudspeaker (10) forms a first wavefront (16a) that propagates from the first region (15a) toward the reference axis (10X) and a second wavefront (16b) that propagates from the second region (15b) toward the reference axis (10X).

Description

Technical Field

[0001] The present invention relates to active noise control systems. Background Art

[0002] An active noise control system (hereinafter sometimes referred to as an ANC system) is known. In an ANC system, noise is reduced by using sounds of opposite phases. Patent Document 1 describes an example of an ANC system.

[0003] Patent Document 1 describes an ANC system that reduces noise diffracted and propagated above a soundproof wall. Specifically, the ANC system of Patent Document 1 employs speakers with line-source characteristics mounted on the soundproof wall. Patent Document 1 describes line-source characteristics as the property in which radiated sound waves propagate in a cylindrical shape centered around a linear sound source.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-004583

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-122187 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] If a structure exists in the noise propagation path, diffraction may occur at the opposing first and second ends of the structure. The wavefronts generated by diffraction at these ends propagate by wrapping around behind the structure. Specifically, the wavefronts generated by diffraction at the first end and the wavefronts generated by diffraction at the second end propagate toward an axis passing between these ends and extending away from the structure. The line source characteristics of Patent Document 1 are not suitable for reducing diffracted sound generated at the first and second ends.

[0010] Technical solutions to problems

[0011] The present invention provides an active noise control system, which has:

[0012] structures; and

[0013] a loudspeaker, mounted on the structure,

[0014] The speaker comprises a radiating surface,

[0015] The radiation surface has a first area, a second area, and a third area, and the third area is an area between the first area and the second area.

[0016] When an axis passing through the third area and extending away from the radiation surface is defined as a reference axis, the speaker forms a first wavefront that propagates toward the reference axis from the first area and a second wavefront that propagates toward the reference axis from the second area.

[0017] Effects of the Invention

[0018] When the aforementioned structure is located on the noise propagation path, diffraction may occur at the opposing first and second ends of the structure. The wavefronts generated by diffraction at the first end and the wavefronts generated by diffraction at the second end of the structure propagate toward the reference axis. On the other hand, in the aforementioned ANC system, a first wavefront propagates from the first region toward the reference axis, and a second wavefront propagates from the second region toward the reference axis. Thus, the wavefronts diffracted from the first end and the second end share common propagation directions with the first and second wavefronts from the ANC system. This is suitable for reducing diffracted sound generated by noise diffracted at the first and second ends. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an illustration of the ANC system.

[0020] Figure 2 This is an illustration of diffraction waves.

[0021] Figure 3 This diagram illustrates the wavefront formed by the speakers of the ANC system.

[0022] Figure 4 This is an explanatory diagram of the wavefront formed by a conventional dynamic speaker.

[0023] Figure 5 This is an explanatory diagram of the wavefront formed by a conventional flat speaker.

[0024] Figure 6A This diagram illustrates the vibration of the radiating surface of a speaker.

[0025] Figure 6B This is an explanatory diagram of the support structure of the piezoelectric film.

[0026] Figure 7 It is a perspective view for explaining the first and second margins.

[0027] Figure 8 It is a top view for explaining the first and second margins.

[0028] Figure 9 It is a top view for explaining the first and second margins.

[0029] Figure 10 It is a top view for explaining the first and second margins.

[0030] Figure 11 It is a top view for explaining the first and second margins.

[0031] Figure 12 It is a top view for explaining the first and second margins.

[0032] Figure 13A It is the structural diagram of the feedforward control ANC system.

[0033] Figure 13B This is a structural diagram of a single-channel ANC system.

[0034] Figure 13C It is a structural diagram of a multi-channel ANC system.

[0035] Figure 13D It is a structural diagram of the control device.

[0036] Figure 14A It is a structural diagram of the feedback ANC system.

[0037] Figure 14B This is a structural diagram of a single-channel ANC system.

[0038] Figure 14C It is a structural diagram of a multi-channel ANC system.

[0039] Figure 14D It is a structural diagram of the control device.

[0040] Figure 15 This is a cross-sectional view of a section parallel to the thickness direction of the piezoelectric speaker.

[0041] Figure 16 This is a top view of the piezoelectric speaker as viewed from the side opposite to the fixing surface.

[0042] Figure 17 It is a diagram showing another structural example of a piezoelectric speaker.

[0043] Figure 18 It is a figure for demonstrating the structure of the sample produced.

[0044] Figure 19 This is a diagram for explaining the structure for measuring a sample.

[0045] Figure 20 This is a diagram for explaining the structure for measuring a sample.

[0046] Figure 21 It is a block diagram of the output system.

[0047] Figure 22 It is a block diagram of the evaluation system.

[0048] Figure 23A This is a table showing the evaluation results of the samples.

[0049] Figure 23B This is a table showing the evaluation results of the samples.

[0050] Figure 24 This is a graph showing the relationship between the degree of restraint of the middle layer and the frequency at which sound starts to be emitted.

[0051] Figure 25 This is a graph showing the frequency characteristics of the sound pressure level of sample E1.

[0052] Figure 26 This is a graph showing the frequency characteristics of the sound pressure level of sample E2.

[0053] Figure 27 This is a graph showing the frequency characteristics of the sound pressure level of sample E3.

[0054] Figure 28 This is a graph showing the frequency characteristics of the sound pressure level of sample E4.

[0055] Figure 29 This is a graph showing the frequency characteristics of the sound pressure level of Sample E5.

[0056] Figure 30 This is a graph showing the frequency characteristics of the sound pressure level of sample E6.

[0057] Figure 31 This is a graph showing the frequency characteristics of the sound pressure level of Sample E7.

[0058] Figure 32 This is a graph showing the frequency characteristics of the sound pressure level of Sample E8.

[0059] Figure 33 This is a graph showing the frequency characteristics of the sound pressure level of Sample E9.

[0060] Figure 34 This is a graph showing the frequency characteristics of the sound pressure level of sample E10.

[0061] Figure 35 This is a graph showing the frequency characteristics of the sound pressure level of sample E11.

[0062] Figure 36 This is a graph showing the frequency characteristics of the sound pressure level of sample E12.

[0063] Figure 37This is a graph showing the frequency characteristics of the sound pressure level of sample E13.

[0064] Figure 38 This is a graph showing the frequency characteristics of the sound pressure level of sample E14.

[0065] Figure 39 This is a graph showing the frequency characteristics of the sound pressure level of sample E15.

[0066] Figure 40 This is a graph showing the frequency characteristics of the sound pressure level of sample E16.

[0067] Figure 41 This is a graph showing the frequency characteristics of the sound pressure level of sample E17.

[0068] Figure 42 This is a graph showing the frequency characteristics of the sound pressure level of sample R1.

[0069] Figure 43 This is a graph showing the frequency characteristics of the sound pressure level of background noise.

[0070] Figure 44 This is a structural diagram of the ANC evaluation system.

[0071] Figure 45A This diagram shows the sound pressure distribution when the speaker is turned off.

[0072] Figure 45B This diagram shows the sound pressure distribution when the speaker is turned off.

[0073] Figure 45C This diagram shows the sound pressure distribution when the speaker is turned off.

[0074] Figure 46 This diagram shows the propagation of wavefronts when the speaker is turned off.

[0075] Figure 47A This diagram shows the sound pressure distribution when the speaker is turned off.

[0076] Figure 47B This diagram shows the sound pressure distribution when the speaker is turned off.

[0077] Figure 47C This diagram shows the sound pressure distribution when the speaker is turned off.

[0078] Figure 48 This diagram shows the propagation of wavefronts when the speaker is turned off.

[0079] Figure 49A This is a diagram showing the sound pressure distribution from the piezoelectric speaker.

[0080] Figure 49BThis is a diagram showing the sound pressure distribution from the piezoelectric speaker.

[0081] Figure 49C This is a diagram showing the sound pressure distribution from the piezoelectric speaker.

[0082] Figure 50 This is a diagram showing the propagation of a wavefront from a piezoelectric speaker.

[0083] Figure 51A This is a diagram showing the sound pressure distribution from the piezoelectric speaker.

[0084] Figure 51B This is a diagram showing the sound pressure distribution from the piezoelectric speaker.

[0085] Figure 51C This is a diagram showing the sound pressure distribution from the piezoelectric speaker.

[0086] Figure 52 This is a diagram showing the propagation of a wavefront from a piezoelectric speaker.

[0087] Figure 53A This is a diagram showing the sound pressure distribution from a dynamic speaker.

[0088] Figure 53B This is a diagram showing the sound pressure distribution from a dynamic speaker.

[0089] Figure 53C This is a diagram showing the sound pressure distribution from a dynamic speaker.

[0090] Figure 54 This is a diagram showing the propagation of wavefronts from a dynamic speaker.

[0091] Figure 55A This is a diagram showing the sound pressure distribution from a dynamic speaker.

[0092] Figure 55B This is a diagram showing the sound pressure distribution from a dynamic speaker.

[0093] Figure 55C This is a diagram showing the sound pressure distribution from a dynamic speaker.

[0094] Figure 56 This is a diagram showing the propagation of wavefronts from a dynamic speaker.

[0095] Figure 57A This is a diagram showing the sound pressure distribution from a planar speaker.

[0096] Figure 57B This is a diagram showing the sound pressure distribution from a planar speaker.

[0097] Figure 57C This is a diagram showing the sound pressure distribution from a planar speaker.

[0098] Figure 58 This is a diagram showing the propagation of wavefronts from a flat speaker.

[0099] Figure 59A This is a diagram showing the sound pressure distribution from a planar speaker.

[0100] Figure 59B This is a diagram showing the sound pressure distribution from a planar speaker.

[0101] Figure 59C This is a diagram showing the sound pressure distribution from a planar speaker.

[0102] Figure 60 This is a diagram showing the propagation of wavefronts from a flat speaker.

[0103] Figure 61A This is an illustration of the noise cancellation effect.

[0104] Figure 61B This is an illustration of the noise cancellation effect.

[0105] Figure 61C This is an illustration of the noise cancellation effect.

[0106] Figure 62A This is an illustration of the noise cancellation effect.

[0107] Figure 62B This is an illustration of the noise cancellation effect.

[0108] Figure 62C This is an illustration of the noise cancellation effect. DETAILED DESCRIPTION

[0109] Hereinafter, the embodiment of the present invention will be described with reference to the accompanying drawings, but the following is merely an illustration of the embodiment of the present invention and is not intended to limit the present invention. In addition, in the following, the same or similar components are sometimes marked with the same reference numerals and their description is omitted.

[0110] [Active Noise Control System]

[0111] Figure 1 2 shows an active noise control system (ANC system) 500 according to an embodiment. The ANC system 500 includes a structure 80 and a speaker 10. The speaker 10 is attached to the structure 80.

[0112] In the illustrated example, structure 80 is a plate-shaped structure. For example, the plate-shaped structure 80 has a longitudinal dimension of 20 cm to 600 cm (or 20 cm to 200 cm), a lateral dimension of 20 cm to 600 cm (or 20 cm to 200 cm), and a width dimension of 0.1 cm to 15 cm. The longitudinal, lateral, and width directions are orthogonal to each other. The longitudinal and lateral dimensions may be the same or different.

[0113] A specific example of the structure 80 is a partition.

[0114] The speaker 10 has a radiation surface 15. The radiation surface 15 radiates sound waves by vibrating. These sound waves reduce noise. In the example shown in the figure, the radiation surface 15 is a continuous radiation surface.

[0115] Specifically, the structure 80 has opposite ends 81 and 82. The ANC system 500 is suitable for reducing diffracted sound generated at the ends 81 and 82. Figure 2 and Figure 3 Provide explanation.

[0116] like Figure 2 As shown, noise from noise source 200 propagates toward structure 80. In this case, diffraction may occur at first end 81 and second end 82. The wavefronts generated by diffraction at ends 81 and 82 propagate by wrapping around behind structure 80. Specifically, wavefront 81w generated by diffraction at first end 81 and wavefront 82w generated by diffraction at second end 82 propagate toward axis 80X. Here, axis 80X is an axis passing between first end 81 and second end 82 and extending away from structure 80. Specifically, axis 80X is perpendicular to the mounting surface of speaker 10 on structure 80. Axis 80X may also pass through the center of the mounting surface.

[0117] The ANC system 500 is suitable for reducing the diffracted sound thus generated at the ends 81 and 82. Specifically, Figure 3 As shown, the radiation surface 15 has a first area 15a, a second area 15b, and a third area 15c. The third area 15c is an area between the first area 15a and the second area 15b. The speaker 10 forms a first wavefront 16a that propagates from the first area 15a toward the reference axis 10X and a second wavefront 16b that propagates from the second area 15b toward the reference axis 10X. Specifically, in this embodiment, the first wavefront 16a and the second wavefront 16b are formed by the vibration of the radiation surface 15. Here, the reference axis 10X is an axis that passes through the third area 15c and extends away from the radiation surface 15. It should be noted that a wavefront refers to a surface formed by connecting points where the phases of the waves are equal.

[0118] It can also be said that the wavefront 81w on the first end 81 and the wavefront 82w on the second end 82 are caused by diffraction and are close to each other. Figure 3 The diffracted wavefront 81w at the first end 81 and the diffracted wavefront 82w at the second end 82 therefore have common propagation directions with the first wavefront 16a and the second wavefront 16b originating from the ANC system 500. This is effective in reducing diffracted sound generated by noise diffracting at the first end 81 and the second end 82.

[0119] It's possible to mount two separate speakers on structure 80, with one speaker forming a wavefront equivalent to first wavefront 16a and the other speaker forming a wavefront equivalent to second wavefront 16b. However, in this case, it would be necessary to adjust the phase difference between the sounds output from the two speakers. In contrast, in this embodiment, first wavefront 16a and second wavefront 16b can be formed by radiating surface 15 on a single speaker 10 (in the illustrated example, a connected radiating surface). This is advantageous from the perspective of simplifying the control of speaker 10.

[0120] In this embodiment, the reference axis 10X is orthogonal to the third region 15c when not vibrating. The offset angle θ1 of the propagation direction of the first wavefront 16a relative to the reference axis 10X is, for example, in the range of 5° to 85°, can be in the range of 15° to 75°, or can be in the range of 25° to 65°. The offset angle θ2 of the propagation direction of the second wavefront 16b relative to the reference axis 10X is, for example, in the range of 5° to 85°, can be in the range of 15° to 75°, or can be in the range of 25° to 65°. The third region 15c can also be a plane when not vibrating. In addition, the entire radiation surface 15 can also be a plane when not vibrating. The reference axis 10X can also be an axis passing through the center of the radiation surface 15.

[0121] Figure 4 The conventional dynamic speaker 610 shown radiates a substantially hemispherical wave from its radiation surface. The wavefront 610w of the substantially hemispherical wave is also substantially hemispherical. Figure 4 In FIG. 6 , the axis 610X is an axis that passes through the radiation surface of the dynamic speaker 610 and extends away from the radiation surface.

[0122] Figure 5 The conventional planar speaker 620 shown radiates a substantially planar wave from its radiation surface. The wavefront 620w of the substantially planar wave is also substantially planar. Figure 5 In FIG. 6 , the axis 620X is an axis that passes through the radiation surface of the planar speaker 620 and extends away from the radiation surface.

[0123] Depend on Figure 3 、 Figure 4 as well as Figure 5 It can be seen that the combination of the first wavefront 16a propagating from the first area 15a toward the reference axis 10X and the second wavefront 16b propagating from the second area 15b toward the reference axis 10X in this embodiment cannot be obtained in the conventional speakers 610 and 710. Figure 6A As shown, the speaker 10 of this embodiment is configured so that the ends of the radiating surface 15 can also vibrate satisfactorily. The radiating surface 15 as a whole has a high degree of freedom of vibration. Further research is needed to determine the details, but this may contribute to the formation of the first wavefront 16a and the second wavefront 16b. Furthermore, the radiating surface 15 may vibrate in a mode somewhat close to the free-end vibration mode. Specifically, the radiating surface 15 may vibrate in a mode somewhat close to the primary free-end vibration mode.

[0124] The superiority of the noise cancellation effect of the speaker 10 over the conventional speakers 610 and 710 tends to be more apparent when the frequency of the noise from the noise source 200 is high.

[0125] In a typical example, a portion of the end portion of the radiation surface 15 is formed in the first region 15a, and a portion of the end portion of the radiation surface 15 is formed in the second region 15b.

[0126] Here, consider a situation where loudspeaker 10 is not vibrating and ANC system 500 is not performing its noise cancellation function. In this situation, although it depends on the size of structure 80 and the wavelength of the noise from noise source 200, due to the diffraction of the noise from noise source 200 at first end 81 and second end 82 of structure 80, there may be periods in which the phase of the sound wave in first region 15a and the phase of the sound wave in second region 15b are the same in sign, the phase of the sound wave in first region 15a and the phase of the sound wave in third region 15c are opposite in sign, and the phase of the sound wave in second region 15b and the phase of the sound wave in third region 15c are opposite in sign.

[0127] In this embodiment, there occurs a period in which the phases of the first sound wave and the second sound wave are of the same sign, the phases of the first sound wave and the third sound wave are opposite in sign, and the phases of the second sound wave and the third sound wave are opposite in sign. Here, the first sound wave is the sound wave in first area 15a formed by speaker 10. The second sound wave is the sound wave in second area 15b formed by speaker 10. The third sound wave is the sound wave in third area 15c formed by speaker 10. According to this embodiment, in first area 15a, second area 15b, and third area 15c, the noise originating from noise source 200 having the above-described phase distribution can be reduced by the sound originating from ANC system 500.

[0128] As described above, the first sound wave is the sound wave in first area 15a formed by speaker 10. The first sound wave is a concept that includes sound waves at a location that is infinitely close to first area 15a in a space facing first area 15a. Therefore, the first sound wave can be measured by measuring the sound wave at this "infinitely close location." The same applies to the second and third sound waves.

[0129] Furthermore, the fact that the phase distributions of the first acoustic wave, the second acoustic wave, and the third acoustic wave described above can be obtained matches the assumption that the radiation surface 15 is vibrated in a mode that is somewhat close to the first free-end vibration mode.

[0130] In this embodiment, ANC system 500 includes control device 110. A certain frequency range is set in control device 110. Control device 110 controls the frequency of the sound output from speaker 10 to a value within this frequency range. This frequency range is, for example, 20 Hz to 20,000 Hz, or may be 20 Hz to 6,000 Hz.

[0131] In this embodiment, when viewed from above, the radiating surface 15 has a first end 15j and a second end 15k that are opposed to each other. When viewed from above, the first distance M1 between the first end 15j and the end of the structure 80 is greater than zero and less than 1 / 10 of the reference wavelength. When viewed from above, the second distance M2 between the second end 15k and the end of the structure 80 is greater than zero and less than 1 / 10 of the reference wavelength. The reference wavelength is the wavelength of sound at the upper limit of the aforementioned frequency range. This is suitable for reducing diffracted sound generated by noise diffracting at the first and second ends 81 and 82. The 1 / 10 ratio stems from the fact that the typical ANC silencing zone is 1 / 10 of the wavelength of the noise being controlled.

[0132] Furthermore, in reality, for the sake of product development, it may be necessary to increase the first and second margins M1, M2 to a certain extent. Taking this into account, the upper limits of the first and second margins M1, M2 can be set to greater than 1 / 10 of the reference wavelength. To achieve the desired effect of reducing diffraction sound while ensuring reasonable product development, for example, the first margin M1 can be set to be greater than zero and less than 1 / 3 of the reference wavelength. Furthermore, when viewing the radiating surface 15 from above, the second margin M2 can be set to be greater than zero and less than 1 / 3 of the reference wavelength.

[0133] The first margin M1 is, for example, 0 cm to 50 cm, or may be 0 cm to 10 cm. The second margin M2 is, for example, 0 cm to 50 cm, or may be 0 cm to 10 cm.

[0134] The first margin M1 is the distance (specifically, the shortest distance) between the first end 15j of the radiating surface 15 and the end of the structure 80 when viewed from above. The second margin M2 is the distance (specifically, the shortest distance) between the second end 15k of the radiating surface 15 and the end of the structure 80 when viewed from above. In this embodiment, the first margin M1 is the distance between the first end 15j and the first end 81 of the radiating surface 15 when viewed from above. In this embodiment, the second margin M2 is the distance between the second end 15k and the second end 82 of the radiating surface 15 when viewed from above.

[0135] Reference Figures 7 to 12 , the first margin M1 and the second margin M2 are further described. Figures 8 to 12 , the long side direction 80L and the short side direction 80S of the structure 80 when the radiation surface 15 is viewed from above are shown. Figures 8 to 12 In the figure, the control device 110 is omitted.

[0136] exist Figure 7 and Figure 8 In the illustrated example, when the radiation surface 15 is viewed from above, the periphery of the radiation surface 15 completely coincides with the periphery of the structure 80. Therefore, the first margin M1 and the second margin M2 are zero.

[0137] exist Figures 9 to 12 In the example shown, the first margin M1 and the second margin M2 are greater than zero.

[0138] exist Figure 9 In the example, when the radiating surface 15 is viewed from above, at any portion of the outer periphery of the radiating surface 15, the distance between that portion and the end of the structure 80 is 1 / 3 or less of the reference wavelength. Specifically, when the radiating surface 15 is viewed from above, at any portion of the outer periphery of the radiating surface 15, the distance between that portion and the end of the structure 80 is 1 / 10 or less of the reference wavelength.

[0139] exist Figure 10 In the example of FIG, when the radiation surface 15 is viewed from above, the long side direction of the radiation surface 15 is the same as the short side direction 80S of the structure 80. The first margin M1 and the second margin M2 are the margins in the short side direction 80S. Figure 10 In the example of FIG, when the radiation surface 15 is viewed from above, the distance between the end of the structure 80 and the end of the radiation surface 15 in the longitudinal direction 80L is larger than 1 / 3 of the reference wavelength.

[0140] exist Figure 11 In the example of FIG, when the radiation surface 15 is viewed from above, the longitudinal direction of the radiation surface 15 is the same as the longitudinal direction 80L of the structure 80. The first margin M1 and the second margin M2 are the margins in the longitudinal direction 80L. Figure 11 In the example of FIG, when the radiation surface 15 is viewed from above, the distance between the end of the structure 80 and the end of the radiation surface 15 in the short-side direction 80S is larger than 1 / 3 of the reference wavelength.

[0141] Although not shown in the figure, in another example, when viewing the radiating surface 15 from above, the longitudinal direction of the radiating surface 15 differs from both the longitudinal direction 80L and the transverse direction 80S of the structure 80. The first margin M1 and the second margin M2 are the margins in the transverse direction 80S. On the other hand, in this other example, when viewing the radiating surface 15 from above, the margin between the end of the structure 80 in the transverse direction 80L and the end of the radiating surface 15 is greater than 1 / 3 of the reference wavelength.

[0142] In one specific example, Figures 7-11 In the example and the above-mentioned other example, the components of the structure 80 and the speaker 10 are configured so that the short side direction 80S is parallel to the horizontal direction and the long side direction 80L is parallel to the vertical direction. In another specific example, the components are configured so that the short side direction 80S is parallel to the vertical direction and the long side direction 80L is parallel to the horizontal direction. In yet another specific example, the components are configured so that the short side direction 80S is parallel to the direction inclined from the horizontal direction and the vertical direction, and the long side direction 80L is also parallel to the direction inclined from the horizontal direction and the vertical direction. For reference, Figure 12 The tilt configuration is applied to Figure 10 The situation of the components. Figure 12 In the figure, the symbol HD refers to the horizontal direction, and the symbol VD refers to the vertical direction.

[0143] The first margin M1 and the second margin M2 may be the same or different. One of the first margin M1 and the second margin M2 may be zero, and the other may be larger than zero.

[0144] The longitudinal and lateral dimensions of the radiating surface 15, when viewed from above, may be the same. In this case, the "longitudinal direction of the radiating surface 15" and "shortitudinal direction of the radiating surface 15" in the above description can be understood as the "first direction of the radiating surface 15" and the "second direction of the radiating surface 15." With this understanding, the first and second directions may be orthogonal to each other.

[0145] When viewing the radiating surface 15 from above, the longitudinal and lateral dimensions of the structure 80 may be the same. In this case, the "longitudinal direction of the structure 80" and "shortitudinal direction of the structure 80" in the above description can be understood as the "third direction of the structure 80" and the "fourth direction of the structure 80." In this understanding, the third and fourth directions may be orthogonal to each other.

[0146] From the reference Figures 7 to 12 As can be seen from the above description, there is no particular limitation on the mounting direction of the loudspeaker 10 relative to the structure 80. Of course, this also applies when the structure 80 is a partition.

[0147] [Feedforward control ANC system]

[0148] In a specific example, the ANC system 500 performs feedforward control. Hereinafter, the ANC system 500 that performs feedforward control may be referred to as a feedforward control ANC system 500A or ANC system 500A. In addition, the control device 110 in the ANC system 500A may be referred to as a control device 110A. Figures 13A to 13D An example ANC system 500A is described.

[0149] like Figure 13A As shown, the feedforward control ANC system 500A includes a reference microphone 130 , an error microphone 140 , and a control device 110A.

[0150] like Figure 13A As shown, a sound wave to be canceled arrives from noise source 200 in region 300 and has waveform 290 in region 300. Upon reaching region 300, speaker 10 radiates a sound wave having waveform 90 that is in phase opposite to waveform 290. These sound waves cancel each other out in region 300. In other words, these sound waves are combined in region 300, generating a composite sound wave having waveform 390 whose amplitude is reduced to zero or a small level. This achieves sound cancellation in ANC system 500A.

[0151] exist Figure 13AIn the illustrated ANC system 500A, feedforward control is performed using a reference microphone 130, an error microphone 140, and a control device 110A. Specifically, reference microphone 130 is positioned on the noise source 200 side as viewed from loudspeaker 10. Reference microphone 130 senses sound from noise source 200. Error microphone 140 is positioned in area 300 and senses sound within area 300. Control device 110A adjusts the sound waves radiated from loudspeaker 10 based on the sound sensed by reference microphone 130 and error microphone 140.

[0152] exist Figure 13A In the example shown in FIG, the number of error microphones 140 included in the ANC system 500A is 1. Such an ANC system 500A may be referred to as a single-channel ANC system 500A.

[0153] The ANC system 500A may include a plurality of error microphones 140. Such an ANC system 500A may be referred to as a multi-channel ANC system 500A.

[0154] Figure 13B A single-channel ANC system 500A is schematically shown in FIG. Figure 13C A multi-channel ANC system 500A is schematically shown in FIG. Single-channel ANC system 500A is advantageous from the perspective of achieving simple control. Meanwhile, multi-channel ANC system 500A can reduce noise at each error microphone 140 point. Providing multiple points (control points) where noise can be reduced by multiple error microphones 140 is advantageous from the perspective of achieving sound cancellation in a wide space.

[0155] Figure 13D is a block diagram of an exemplary control device 110A. Control device 110A includes a preamplifier (hereinafter sometimes referred to as an amplifier) ​​111, a low-pass filter 112, an analog-to-digital converter (hereinafter sometimes referred to as an AD converter) 113, a power amplifier 114, a low-pass filter 115, a digital-to-analog converter (hereinafter sometimes referred to as a DA converter) 116, a preamplifier 117, a low-pass filter 118, an AD converter 119, and a computing unit 120A.

[0156] Preamplifier 111 amplifies the output signal of reference microphone 130. Low-pass filter 112 passes the low-frequency components of the output signal of preamplifier 111. AD converter 113 converts the output signal of low-pass filter 112 into a digital signal. Thus, AD converter 113 outputs reference signal x(n) at time n.

[0157] Preamplifier 117 amplifies the output signal of error microphone 140. Low-pass filter 118 passes the low-frequency components of the output signal of preamplifier 117. AD converter 119 converts the output signal of low-pass filter 118 into a digital signal. Thus, AD converter 119 outputs error signal e(n) at time n.

[0158] Calculation unit 120A generates control signal y(n) at time n based on reference signal x(n) and error signal e(n). Calculation unit 120A is comprised of, for example, a DSP (Digital Signal Processor) or an FPGA (Field-Programmable Gate Array). Calculation unit 120A operates, for example, based on the filtered-x algorithm.

[0159] DA converter 116 converts control signal y(n) into an analog signal. Low-pass filter 115 passes the low-frequency components of the output signal from DA converter 116. Power amplifier 114 amplifies the output signal from low-pass filter 115. The signal output from power amplifier 114 is sent to speaker 10 as a control signal. Based on this signal, sound is output from radiating surface 15.

[0160] As can be seen from the above description, ANC system 500A includes error microphone 140, reference microphone 130, and control device 110A. Reference microphone 130, structure 80, loudspeaker 10, and error microphone 140 are arranged in this order. Control device 110A performs feedforward control of the sound output from loudspeaker 10 based on the output signals of reference microphone 130 and error microphone 140. This feedforward control can cancel not only periodic signals but also non-periodic signals.

[0161] [Feedback ANC system]

[0162] In a specific example, the ANC system 500 performs feedback control. Hereinafter, the ANC system 500 that performs feedback control may be referred to as a feedback ANC system 500B or an ANC system 500B. In addition, the control device 110 in the ANC system 500B may be referred to as a control device 110B. Figures 14A to 14D An example ANC system 500B is described.

[0163] like Figure 14A As shown, the feedback ANC system 500B includes an error microphone 140 and a control device 110B.

[0164] like Figure 14AAs shown, a sound wave to be canceled arrives from noise source 200 in region 300 and has waveform 290 in region 300. Upon reaching region 300, speaker 10 radiates a sound wave having waveform 90, which is in phase opposite to waveform 290. These sound waves cancel each other out in region 300. In other words, these sound waves are combined in region 300, generating a composite sound wave having waveform 390 whose amplitude is reduced to zero or a small level. This achieves sound cancellation in ANC system 500B.

[0165] exist Figure 14A In the illustrated ANC system 500B, feedback control is performed using error microphone 140 and control device 110B. Specifically, error microphone 140 is located in area 300 and senses sound in area 300. Control device 110B adjusts the sound waves radiated from speaker 10 based on the sound sensed by error microphone 140.

[0166] exist Figure 14A In the example of FIG, the number of error microphones 140 included in the ANC system 500B is 1. Such an ANC system 500B may be referred to as a single-channel ANC system 500B.

[0167] The ANC system 500B may include a plurality of error microphones 140. Such an ANC system 500B may be referred to as a multi-channel ANC system 500B.

[0168] Figure 14B A single-channel ANC system 500B is schematically shown in FIG. Figure 14C A multi-channel ANC system 500B is schematically shown in FIG. Single-channel ANC system 500B is advantageous from the perspective of achieving simple control. On the other hand, multi-channel ANC system 500B can reduce noise at each error microphone 140 point. Using multiple error microphones 140 to establish multiple control points is advantageous from the perspective of achieving sound cancellation in a wide space.

[0169] Figure 14D 2 shows a configuration diagram of an exemplary control device 110B. The control device 110B includes a power amplifier 114, a low-pass filter 115, a DA converter 116, a preamplifier 117, a low-pass filter 118, an AD converter 119, and a computing unit 120B.

[0170] Preamplifier 117 amplifies the output signal of error microphone 140. Low-pass filter 118 passes the low-frequency components of the output signal of preamplifier 117. AD converter 119 converts the output signal of low-pass filter 118 into a digital signal. Thus, AD converter 119 outputs error signal e(n) at time n.

[0171] The calculation unit 120B generates a control signal y(n) at time n based on the error signal e(n). The calculation unit 120B is composed of, for example, a DSP or an FPGA. The calculation unit 120B operates based on, for example, a filtered-x algorithm.

[0172] DA converter 116 converts control signal y(n) into an analog signal. Low-pass filter 115 passes the low-frequency components of the output signal from DA converter 116. Power amplifier 114 amplifies the output signal from low-pass filter 115. The signal output from power amplifier 114 is sent to speaker 10 as a control signal. Based on this signal, sound is output from radiating surface 15.

[0173] As can be seen from the above description, the ANC system 500B includes the error microphone 140 and the control device 110B. The structure 80, the speaker 10, and the error microphone 140 are arranged in this order. The control device 110B performs feedback control to control the sound output from the speaker 10 based on the output signal of the error microphone 140. According to the feedback control, there is no need Figure 13A The reference microphone 130 can eliminate the periodic signal.

[0174] As can be seen from the description of ANC systems 500A and 500B, control device 110 of ANC system 500 may include at least one amplifier. Control device 110 may include at least one low-pass filter. Control device 110 may include at least one AD converter. Control device 110 may include at least one DA converter. These elements contribute to controlling the sound output from speaker 10.

[0175] ANC system 500 can be installed in an office or the like. In a specific example, speaker 10 is mounted on structure 80 serving as a partition. Noise source 200 is a person in a conference room. Area 300 is another conference room.

[0176] [First Configuration Example of Speaker 10]

[0177] use Figure 15 and Figure 16 A first structural example of speaker 10 will be described. In the first structural example, speaker 10 is a piezoelectric speaker including a piezoelectric film. Hereinafter, speaker 10 of the first structural example may be referred to as piezoelectric speaker 10.

[0178] The piezoelectric speaker 10 includes a piezoelectric film 35, a first bonding layer 51, an intermediate layer 40, and a second bonding layer 52. The first bonding layer 51, the intermediate layer 40, the second bonding layer 52, and the piezoelectric film 35 are stacked in this order.

[0179] The piezoelectric film 35 includes a piezoelectric body 30 , a first electrode 61 , and a second electrode 62 .

[0180] The piezoelectric body 30 has a thin film shape. The piezoelectric body 30 vibrates by applying a voltage. As the piezoelectric body 30, a ceramic film, a resin film, etc. can be used. Examples of the material of the ceramic film, i.e., the piezoelectric body 30, include lead zirconate, lead zirconate titanate, lead lanthanum zirconate titanate, barium titanate, Bi layered compounds, tungsten bronze structure compounds, and solid solutions of barium titanate and bismuth ferrite. Examples of the material of the resin film, i.e., the piezoelectric body 30, include polyvinylidene fluoride, polylactic acid, etc. The material of the resin film, i.e., the piezoelectric body 30, can also be a polyolefin such as polyethylene or polypropylene. In addition, the piezoelectric body 30 can be a non-porous body or a porous body.

[0181] The thickness of the piezoelectric body 30 is, for example, in the range of 10 μm to 300 μm, or may be in the range of 30 μm to 110 μm.

[0182] The first electrode 61 and the second electrode 62 are in contact with the piezoelectric body 30 so as to sandwich the piezoelectric body 30. The first electrode 61 and the second electrode 62 have a thin film shape. The first electrode 61 and the second electrode 62 are respectively connected to leads (not shown). The first electrode 61 and the second electrode 62 can be formed on the piezoelectric body 30 by evaporation, plating, sputtering, etc. Metal foil can be used as the first electrode 61 and the second electrode 62. The metal foil can be affixed to the piezoelectric body 30 using double-sided tape, adhesive, bonding agent, etc. Examples of materials for the first electrode 61 and the second electrode 62 include metals, specifically gold, platinum, silver, copper, palladium, chromium, molybdenum, iron, tin, aluminum, nickel, etc. Examples of materials for the first electrode 61 and the second electrode 62 include carbon, conductive polymers, etc. Examples of materials for the first electrode 61 and the second electrode 62 include alloys thereof. The first electrode 61 and the second electrode 62 may also contain glass components, etc.

[0183] The thickness of the first electrode 61 and the second electrode 62 are each within a range of, for example, 10 nm to 150 μm, or may be within a range of 20 nm to 100 μm.

[0184] exist Figure 15 and Figure 16 In the example shown, the first electrode 61 covers the entirety of one principal surface of the piezoelectric body 30. However, the first electrode 61 may cover only a portion of the one principal surface of the piezoelectric body 30. The second electrode 62 covers the entirety of the other principal surface of the piezoelectric body 30. However, the second electrode 62 may cover only a portion of the other principal surface of the piezoelectric body 30.

[0185] In the first structural example, the intermediate layer 40 is arranged between the piezoelectric film 35 and the first bonding layer 51. The intermediate layer 40 can be a layer other than the adhesive layer and the bonding layer, or it can be an adhesive layer or the bonding layer. In the first structural example, the intermediate layer 40 is a porous layer and / or a resin layer. Here, the resin layer is a concept including a rubber layer and an elastomer layer. Therefore, the intermediate layer 40 as a resin layer can also be a rubber layer or an elastomer layer. Examples of the resin layer, i.e., the intermediate layer 40, include an ethylene propylene rubber layer, a butyl rubber layer, a nitrile rubber layer, a natural rubber layer, a styrene butadiene rubber layer, a silicone layer, a polyurethane layer, an acrylic resin layer, etc. Examples of the porous layer, i.e., the intermediate layer 40, include a foam layer, etc. Specifically, examples of the porous layer and the resin layer, i.e., the intermediate layer 40, include an ethylene propylene rubber foam layer, a butyl rubber foam layer, a nitrile rubber foam layer, a natural rubber foam layer, a styrene butadiene rubber foam layer, a silicone foam layer, a polyurethane foam layer, etc. Examples of the intermediate layer 40 that is not a porous body layer but a resin layer include an acrylic resin layer. Examples of the intermediate layer 40 that is not a resin layer but a porous body layer include a metal porous body layer. Here, the resin layer refers to a layer containing resin, and refers to a layer that can contain more than 30% resin, more than 45% resin, more than 60% resin, or more than 80% resin. The same applies to rubber layers, elastomer layers, ethylene propylene rubber layers, butyl rubber layers, nitrile rubber layers, natural rubber layers, styrene butadiene rubber layers, silicone layers, polyurethane layers, acrylic resin layers, metal layers, etc. In addition, the same applies to resin films, ceramic films, etc. that can be used as piezoelectric bodies 30. The intermediate layer 40 can be a mixed layer of two or more materials.

[0186] The elastic modulus of the intermediate layer 40 is, for example, 10000 N / m 2 ~20000000N / m 2 , or 20000N / m 2 ~100000N / m 2 .

[0187] In one example, the pore diameter of the intermediate layer 40, which is a porous layer, is 0.1 mm to 7.0 mm, or 0.3 mm to 5.0 mm. In another example, the pore diameter of the intermediate layer 40, which is a porous layer, is, for example, 0.1 mm to 2.5 mm, or 0.2 mm to 1.5 mm, or 0.3 mm to 0.7 mm. The porosity of the intermediate layer 40, which is a porous layer, is, for example, 70% to 99%, or 80% to 99%, or 90% to 95%.

[0188] As the foam layer, i.e., the middle layer 40, a known foam can be used (for example, the foam of Patent Document 2 can be used). The middle layer 40 as the foam layer can have a continuous bubble structure, an independent bubble structure, or a semi-independent semi-continuous bubble structure. A continuous bubble structure refers to a structure with a continuous bubble rate of 100%. An independent bubble structure refers to a structure with a continuous bubble rate of 0%. A semi-independent semi-continuous bubble structure refers to a structure with a continuous bubble rate greater than 0% and less than 100%. Here, the continuous bubble rate can be calculated, for example, by conducting a test of submerging the foam layer in water and using the formula: continuous bubble rate (%) = {(volume of water absorbed) / (partial volume of bubbles)} × 100. In a specific example, the "volume of water absorbed" is obtained by submerging the foam layer in water and placing it under a reduced pressure of -750 mmHg for 3 minutes, measuring the mass of water replaced with air in the bubbles of the foam layer, and taking the density of water as 1.0 g / cm 3 The "bubble partial volume" is calculated using the formula: bubble partial volume (cm 3 ) = {(mass of foam layer) / (apparent density of foam layer)} - {(mass of foam layer) / (material density)}. "Material density" is the density of the base material (solid body) forming the foam layer.

[0189] The expansion ratio (density ratio before and after foaming) of the intermediate layer 40 as the foam layer is, for example, 5 to 40 times, or may be 10 to 40 times.

[0190] The thickness of the intermediate layer 40 in the uncompressed state is, for example, in the range of 0.1 mm to 30 mm, and may be in the range of 1 mm to 30 mm, 1.5 mm to 30 mm, or 2 mm to 25 mm. Typically, in the uncompressed state, the intermediate layer 40 is thicker than the piezoelectric film 35. In the uncompressed state, the ratio of the thickness of the intermediate layer 40 to the thickness of the piezoelectric film 35 is, for example, 3 times or more, 10 times or more, or 30 times or more. Furthermore, typically, in the uncompressed state, the intermediate layer 40 is thicker than the first bonding layer 51.

[0191] The first bonding layer 51 forms the fixing surface 17 on its surface. The first bonding layer 51 is a layer that is bonded to the structure 80. Figure 15 In the example shown in FIG. 5 , the first bonding layer 51 is bonded to the intermediate layer 40 .

[0192] In the first structural example, the first bonding layer 51 is an adhesive or cohesive layer. In other words, the first bonding layer 51 is an adhesive layer or cohesive layer. The fixing surface 17 is an adhesive surface or cohesive surface. The first bonding layer 51 can be attached to the structure 80. Figure 1 In the example, the first bonding layer 51 is in contact with the intermediate layer 40 .

[0193] The first bonding layer 51 may be a double-sided tape having a base material and an adhesive applied to both sides of the base material. Examples of the base material for the double-sided tape used as the first bonding layer 51 include non-woven fabrics, etc. Examples of the adhesive for the double-sided tape used as the first bonding layer 51 include acrylic resin adhesives, etc. However, the first bonding layer 51 may also be an adhesive layer without a base material.

[0194] The thickness of the first bonding layer 51 is, for example, 0.01 mm to 1.0 mm, or may be 0.05 mm to 0.5 mm.

[0195] The second bonding layer 52 is disposed between the intermediate layer 40 and the piezoelectric film 35. In the first structural example, the second bonding layer 52 is an adhesive or cohesive layer. In other words, the second bonding layer 52 is an adhesive layer or cohesive layer. Specifically, the second bonding layer 52 is bonded to the intermediate layer 40 and the piezoelectric film 35.

[0196] The second bonding layer 52 may be a double-sided tape having a substrate and an adhesive applied to both sides of the substrate. Examples of the substrate for the double-sided tape used as the second bonding layer 52 include non-woven fabrics, etc. Examples of the adhesive for the double-sided tape used as the second bonding layer 52 include adhesives containing acrylic resins, etc. However, the second bonding layer 52 may also be an adhesive layer without a substrate.

[0197] The thickness of the second bonding layer 52 is, for example, 0.01 mm to 1.0 mm, or 0.05 mm to 0.5 mm.

[0198] In the first structural example, the piezoelectric film 35 is integrated with the layer on the fixed surface 17 side by the adhesive surface or adhesive surface contacting the piezoelectric film 35. Specifically, in the first structural example, the adhesive surface or adhesive surface is formed by the surface of the second adhesive layer or adhesive layer 52.

[0199] The piezoelectric speaker 10 is suitable for use in the ANC system 500. Compared to dynamic speakers, the time it takes for an electrical signal to reach the piezoelectric speaker 10 before sound is emitted (hereinafter sometimes referred to as latency) is shorter. Therefore, the piezoelectric speaker 10 is not only compact in size but also suitable for compact ANC system configurations because the distance between the reference microphone 130 and the piezoelectric speaker 10 can be shortened. For example, the reference microphone 130, the control device 110, and the piezoelectric speaker 10 can be mounted on a single partition.

[0200] When the piezoelectric speaker 10 is fixed to the structure 80 , a voltage is applied to the piezoelectric film 35 via the lead wires. This causes the piezoelectric film 35 to vibrate, and acoustic waves are radiated from the piezoelectric film 35 .

[0201] The piezoelectric speaker 10 and the ANC system 500 to which the piezoelectric speaker 10 is applied will be further described.

[0202] The piezoelectric speaker 10 can be fixed to the structure 80 via the fixing surface 17. In this manner, the ANC system 500 using the piezoelectric speaker 10 can be configured. In the ANC system 500, the intermediate layer 40 is disposed between the piezoelectric film 35 and the structure 80.

[0203] While further research is needed to determine the details of this function, by appropriately constraining one principal surface of the piezoelectric film 35 with the intermediate layer 40, it is possible that the piezoelectric film 35 can easily produce low-frequency sounds within the audible range. With this in mind, the intermediate layer 40 can be arranged in an area that covers at least 25% of the area of ​​the piezoelectric film 35 when viewed from above. Alternatively, the intermediate layer 40 can be arranged in an area that covers at least 50% of the area of ​​the piezoelectric film 35 when viewed from above, or at least 75% of the area of ​​the piezoelectric film 35 when viewed from above, or even the entire area of ​​the piezoelectric film 35. Furthermore, the piezoelectric film 35 can constitute at least 50% of the principal surface 38 of the piezoelectric speaker 10 opposite the fixing surface 17. Alternatively, the piezoelectric film 35 can constitute at least 75% of the principal surface 38, or even the entire principal surface 38.

[0204] In the first structural example, the second bonding layer 52 prevents separation of the piezoelectric film 35 and the intermediate layer 40. From the perspective of "appropriate restraint" described above, the second bonding layer 52 and the intermediate layer 40 can be arranged in an area that is at least 25% of the area of ​​the piezoelectric film 35 when viewed from above. When viewed from above, the second bonding layer 52 and the intermediate layer 40 can be arranged in an area that is at least 50% of the area of ​​the piezoelectric film 35, can be arranged in an area that is at least 75% of the area of ​​the piezoelectric film 35, or can be arranged in the entire area of ​​the piezoelectric film 35.

[0205] Here, when the intermediate layer 40 is a porous body, the ratio of the area where the intermediate layer 40 is disposed is determined not by the microscopic viewpoint of the pores of the porous structure, but by a more macroscopic viewpoint. For example, when the piezoelectric film 35, the porous intermediate layer 40, and the second bonding layer 52 are plate-like bodies with a common outline when viewed from above, the second bonding layer 52 and the intermediate layer 40 are disposed in an area that accounts for 100% of the area of ​​the piezoelectric film 35.

[0206] In the first structural example, the constraint degree of the intermediate layer 40 is 5×10 9 N / m 3 The degree of constraint of the intermediate layer 40 is, for example, 1×104 N / m 3 The constraint degree of the intermediate layer 40 is preferably 5×10 8 N / m 3 Below, more preferably 2×10 8 N / m 3 Below, more preferably 1×10 5 ~5×10 7 N / m 3 Here, the constraint degree (N / m 3 ) is expressed as follows: the elastic modulus (N / m 2 ) and the surface filling rate of the intermediate layer 40, divided by the thickness (m) of the intermediate layer 40. The surface filling rate of the intermediate layer 40 is the filling rate of the main surface of the intermediate layer 40 on the piezoelectric film 35 side (the value of subtracting the porosity from 1). When the pores in the intermediate layer 40 are evenly distributed, the surface filling rate can be considered to be equal to the three-dimensional filling rate of the intermediate layer 40.

[0207] Constraint (N / m 3 ) = elastic modulus (N / m 2 )×surface filling rate÷thickness (m)

[0208] The degree of constraint can be considered a parameter that indicates the degree of constraint imposed by the intermediate layer 40 on the piezoelectric film 35. The greater the elastic modulus of the intermediate layer 40, the greater the degree of constraint, as expressed by the above equation. The greater the surface fill factor of the intermediate layer 40, the greater the degree of constraint, as expressed by the above equation. The smaller the thickness of the intermediate layer 40, the greater the degree of constraint, as expressed by the above equation. The relationship between the degree of constraint of the intermediate layer 40 and the sound generated by the piezoelectric film 35 requires further research, but if the constraint is too high, it may hinder the deformation of the piezoelectric film 35 required to produce low-frequency sound. Conversely, if the constraint is too low, the piezoelectric film 35 does not deform sufficiently in its thickness direction, expanding and contracting only in its in-plane direction (a direction perpendicular to the thickness direction), potentially hindering the production of low-frequency sound. It is believed that by setting the degree of constraint of the intermediate layer 40 to an appropriate range, the expansion and contraction of the piezoelectric film 35 in the in-plane direction is appropriately converted to deformation in the thickness direction, allowing the piezoelectric film 35 to bend appropriately as a whole, making it easier to produce low-frequency sound.

[0209] As is clear from the above description, a layer different from the intermediate layer 40 may be provided between the piezoelectric film 35 and the fixed surface 17 . This different layer is, for example, the second adhesive layer 52 .

[0210] The structure 80 may have a greater degree of restraint than the intermediate layer 40. Even in this case, the intermediate layer 40 can generate low-frequency sound from the piezoelectric film 35. However, the structure 80 may have the same degree of restraint as the intermediate layer 40 or may have a smaller degree of restraint than the intermediate layer 40. Here, the degree of restraint of the structure 80 (N / m 3 ) is the elastic modulus of the structure 80 (N / m 2 ) and the surface filling rate of the structure 80 divided by the thickness (m) of the structure 80. The surface filling rate of the structure 80 is the filling rate of the main surface of the structure 80 on the piezoelectric film 35 side (the value of subtracting the porosity from 1).

[0211] Typically, the structure 80 has a greater rigidity (the product of Young's modulus and the second moment of area), a greater Young's modulus, and / or a greater thickness than the intermediate layer 40. However, the structure 80 may have the same rigidity, Young's modulus, and / or thickness as the intermediate layer 40, or may have a smaller rigidity, Young's modulus, and / or thickness than the intermediate layer 40. The Young's modulus of the structure 80 is, for example, 1 GPa or greater, 10 GPa or greater, or 50 GPa or greater. The upper limit of the Young's modulus of the structure 80 is not particularly limited and is, for example, 1000 GPa.

[0212] In the illustrated example, the piezoelectric film 35 is not completely surrounded by the intermediate layer 40. In the illustrated example, an imaginary straight line exists that passes through the intermediate layer 40 and the piezoelectric film 35 in sequence, then reaches the exterior of the speaker 10 without passing through the intermediate layer 40. Here, "an imaginary straight line exists" means that such a straight line can be drawn. In the illustrated example, the intermediate layer 40 extends only toward the fixing surface 17 side, as viewed from the piezoelectric film 35.

[0213] In the illustrated example, the principal surface 38 of the piezoelectric film 35 on the side opposite the fixed surface 17 constitutes the radiating surface 15. In other words, the principal surface 38 of the piezoelectric film 35 on the side opposite the intermediate layer 40 constitutes the radiating surface 15. In this structure, the principal surface of the piezoelectric film 35 on the intermediate layer 40 side is constrained by the intermediate layer 40, allowing the in-plane expansion and contraction of the piezoelectric film 35 to be appropriately converted into deformation in the thickness direction. However, other configurations are also possible.

[0214] Specifically, a first layer may be provided on the side of the piezoelectric film 35 opposite the intermediate layer 40. For example, the first layer serves to protect the piezoelectric film 35. In this case, the main surface of the first layer may constitute the radiating surface 15. Alternatively, a second layer other than the first layer may constitute the radiating surface 15.

[0215] The thickness of the first layer is, for example, 0.05 mm to 5 mm. The material of the first layer is, for example, a polyester-based material. Here, the polyester-based material refers to a material containing polyester, which refers to a material that can contain more than 30% polyester, more than 45% polyester, more than 60% polyester, or more than 80% polyester. In one example, the material of the intermediate layer 40 is different from the material of the first layer. When the material of the intermediate layer 40 is different from the material of the first layer, the degree to which the main surface of the intermediate layer 40 side of the piezoelectric film 35 is constrained can be different from the degree to which the main surface of the first layer side of the piezoelectric film 35 is constrained. This can appropriately convert the in-plane expansion and contraction of the piezoelectric film 35 into deformation in the thickness direction. The degree of constraint of the intermediate layer 40 may also be different from the degree of constraint of the first layer. Here, the degree of constraint of the first layer (N / m 3 ) is the elastic modulus of the first layer (N / m 2 ) and the surface filling rate of the first layer divided by the thickness (m) of the first layer. The surface filling rate of the first layer is the filling rate of the main surface of the piezoelectric film 35 side of the first layer (the value of subtracting the porosity from 1). The degree of constraint of the intermediate layer 40 is different from that of the first layer, which can appropriately convert the expansion and contraction in the in-plane direction of the piezoelectric film 35 into deformation in the thickness direction. In a specific example, the degree of constraint of the intermediate layer 40 is greater than that of the first layer. The first layer can have a thin film shape. The first layer can be a non-woven fabric.

[0216] In the first structural example, when the piezoelectric film 35 is viewed from above, at least a portion of the piezoelectric film 35 overlaps with the fixing surface 17 (in the Figure 15 In the example of FIG, the fixing surface 17 is arranged so as to overlap with the first bonding layer 51. From the perspective of stably fixing the piezoelectric speaker 10 to the structure 80, the fixing surface 17 can be arranged in a region that is at least 50% of the area of ​​the piezoelectric film 35 when viewed from above. When viewed from above, the fixing surface 17 can be arranged in a region that is at least 75% of the area of ​​the piezoelectric film 35, or can be arranged in the entire area of ​​the piezoelectric film 35.

[0217] In the first structural example, adjacent layers between the piezoelectric film 35 and the fixed surface 17 are bonded. Here, "between the piezoelectric film 35 and the fixed surface 17" includes both the piezoelectric film 35 and the fixed surface 17. Specifically, the first bonding layer 51 is bonded to the intermediate layer 40, the intermediate layer 40 is bonded to the second bonding layer 52, and the second bonding layer 52 is bonded to the piezoelectric film 35. Therefore, regardless of the mounting posture on the structure 80, the piezoelectric film 35 can be stably positioned, and installation on the structure 80 is also easy. Furthermore, due to the action of the intermediate layer 40, sound is emitted from the piezoelectric film 35 regardless of the mounting posture. Therefore, in the first structural example, these complement each other, achieving a piezoelectric speaker with excellent usability. Furthermore, "adjacent layers are bonded" means that adjacent layers are bonded in whole or in part. In the illustrated example, adjacent layers are bonded in a predetermined region extending along the thickness direction of the piezoelectric film 35 and sequentially passing through the piezoelectric film 35, the intermediate layer 40, and the fixed surface 17.

[0218] In the first structural example, the thickness of each of the piezoelectric film 35 and the intermediate layer 40 is substantially constant. This is often advantageous from various perspectives, such as storage and usability of the piezoelectric speaker 10, and control of the sound emitted by the piezoelectric film 35. Furthermore, "substantially constant thickness" means, for example, that the minimum thickness is 70% or more and 100% or less of the maximum thickness. Alternatively, the minimum thickness of the piezoelectric film 35 and the intermediate layer 40 may each be 85% or more and 100% or less of the maximum thickness.

[0219] Furthermore, resin is a material that is less likely to crack than ceramics and the like. In a specific example, the piezoelectric body 30 of the piezoelectric film 35 is a resin film, and the intermediate layer 40 is a resin layer that does not function as a piezoelectric film. This arrangement is advantageous from the perspective of not being able to cut the piezoelectric speaker 10 with scissors, human hands, or the like without causing cracks in the piezoelectric body 30 or the intermediate layer 40 (being able to cut the piezoelectric speaker 10 with scissors, human hands, or the like helps to increase the design freedom of the ANC system 500, and also makes it easier to construct the ANC system 500). Furthermore, if this arrangement is used, even if the piezoelectric speaker 10 is bent, cracks are less likely to occur in the piezoelectric body 30 or the intermediate layer 40. Furthermore, the piezoelectric body 30 being a resin film and the intermediate layer 40 being a resin layer is advantageous from the perspective of fixing the piezoelectric speaker 10 on a curved surface without causing cracks in the piezoelectric body 30 or the intermediate layer 40.

[0220] exist Figure 15 In the example shown in FIG, the piezoelectric film 35, the intermediate layer 40, the first bonding layer 51, and the second bonding layer 52 have the same outlines when viewed from above. However, these outlines may be offset.

[0221] exist Figure 15In the example shown in FIG, the piezoelectric film 35, the intermediate layer 40, the first bonding layer 51, and the second bonding layer 52 are rectangular with short and long sides in a plan view. However, they may also be square, circular, elliptical, or the like.

[0222] In addition, the piezoelectric speaker 10 may also include Figure 15 Layers other than those shown. Figure 15 Layers other than the layers shown are, for example, the first layer and the second layer described above.

[0223] [Second Configuration Example of Speaker 10]

[0224] Below, use Figure 17 A second configuration example of a piezoelectric speaker 110 will be described. Hereinafter, descriptions of the same parts as those of the first configuration example may be omitted.

[0225] The piezoelectric speaker 110 includes a piezoelectric film 35 , a fixing surface 117 , and an intermediate layer 140 . The fixing surface 117 can be used to fix the piezoelectric film 35 to the structure 80 .

[0226] The intermediate layer 140 is disposed between the piezoelectric film 35 and the fixed surface 117 (here, “between” includes the fixed surface 117 . This also applies to the first structural example). The fixed surface 117 is formed by the surface (main surface) of the intermediate layer 140 .

[0227] Intermediate layer 140 is a porous layer and / or a resin layer. Intermediate layer 140 is an adhesive layer or bonding layer. Adhesives containing acrylic resins can be used as intermediate layer 140. Other adhesives, such as rubber, silicone, or polyurethane, can also be used as intermediate layer 140. Intermediate layer 140 may also be a mixed layer of two or more materials.

[0228] The elastic modulus of the intermediate layer 140 is, for example, 10,000 N / m 2 ~20000000N / m 2 , or 20000N / m 2 ~100000N / m 2 .

[0229] The thickness of the intermediate layer 140 in the uncompressed state is, for example, in the range of 0.1 mm to 30 mm, and may be in the range of 1 mm to 30 mm, 1.5 mm to 30 mm, or 2 mm to 25 mm. Typically, in the uncompressed state, the intermediate layer 140 is thicker than the piezoelectric film 35. In the uncompressed state, the ratio of the thickness of the intermediate layer 140 to the thickness of the piezoelectric film 35 is, for example, 3 times or more, 10 times or more, or 30 times or more.

[0230] In the second structural example, the constraint degree of the intermediate layer 140 is 5×10 9 N / m 3 The degree of constraint of the intermediate layer 140 is, for example, 1×10 4 N / m 3 The constraint degree of the intermediate layer 140 is preferably 5×10 8 N / m 3 Below, more preferably 2×10 8 N / m 3 Below, more preferably 1×10 5 ~5×10 7 N / m 3 The definition of constraint degree is as explained above.

[0231] In the second configuration example, the piezoelectric film 35 is integrated with the layer on the fixed surface 117 side by the adhesive surface or the bonding surface being in contact with the piezoelectric film 35. Specifically, in the second configuration example, the adhesive surface or the bonding surface is a surface formed by the intermediate layer 140.

[0232] The piezoelectric speaker 110 may also be fixed to the structure 80 via the fixing surface 117. In this manner, the ANC system 500 using the piezoelectric speaker 110 can be configured.

[0233] Example

[0234] The present invention will be described in detail with reference to Examples. However, the following Examples are merely examples of the present invention, and the present invention is not limited to the following Examples.

[0235] (Sample E1)

[0236] By pasting the fixed surface 17 of the piezoelectric speaker 10 on the fixed support member 680, a Figure 18The structure shown. Specifically, as the supporting part 680, a stainless steel flat plate (SUS flat plate) with a thickness of 5 mm was used. As the first bonding layer 51, an adhesive sheet (double-sided tape) with a thickness of 0.16 mm impregnated with an acrylic adhesive on both sides of a non-woven fabric was used. As the intermediate layer 40, a foamed body of an independent bubble type with a thickness of 3 mm, which was formed by foaming a mixture of ethylene propylene rubber and butyl rubber at a foaming ratio of about 10 times, was used. As the second bonding layer 52, an adhesive sheet (double-sided tape) with a thickness of 0.15 mm, the substrate of which was a non-woven fabric and the adhesive comprising a solvent-free acrylic resin was coated on both sides of the substrate, was used. As the piezoelectric film 35, a polyvinylidene fluoride film (total thickness 33 μm) with copper electrodes (containing nickel) evaporated on both sides was used. The first bonding layer 51, the intermediate layer 40, the second bonding layer 52, and the piezoelectric film 35 of the sample E1 have a size of 37.5 mm in length and 37.5 mm in width when viewed from above, and have a non-divided and non-frame-shaped plate shape with a repeated outline when viewed from above (the same is true for the samples E2 to E17 and R1 described later). The supporting member 680 has a size of 50 mm in length and 50 mm in width when viewed from above, and covers the first bonding layer 51 as a whole. In this way, a Figure 18 The structure of sample E1 is shown.

[0237] (Sample E2)

[0238] As the intermediate layer 40, a semi-closed and semi-open cell foam having a thickness of 3 mm was used, which was made by expanding a mixture containing ethylene propylene rubber at an expansion ratio of approximately 10. This foam contained sulfur. Sample E2 was prepared, which was identical to Sample E1 except for these features.

[0239] (Sample E3)

[0240] In Sample E3, a foam having a thickness of 5 mm and made of the same material and having the same structure as the intermediate layer 40 of Sample E2 was used as the intermediate layer 40. Sample E3 was prepared in the same manner as Sample E2 except for these points.

[0241] (Sample E4)

[0242] In Sample E4, a foam having a thickness of 10 mm and made of the same material and having the same structure as the intermediate layer 40 of Sample E2 was used as the intermediate layer 40. Sample E4 was prepared in the same manner as Sample E2 except for these points.

[0243] (Sample E5)

[0244] In Sample E5, a foam having a thickness of 20 mm and made of the same material and having the same structure as the intermediate layer 40 of Sample E2 was used as the intermediate layer 40. Sample E5 was prepared in the same manner as Sample E2 except for these points.

[0245] (Sample E6)

[0246] As the intermediate layer 40, a 20 mm thick semi-closed, semi-open cell foam was used, made by expanding a mixture containing ethylene propylene rubber at an expansion ratio of approximately 10. This foam does not contain sulfur and is softer than the foam used as the intermediate layer 40 in samples E2 to E5. Sample E6 was prepared in the same manner as sample E1 except for these features.

[0247] (Sample E7)

[0248] A semi-closed and semi-open cell foam having a thickness of 20 mm, obtained by foaming a mixture containing ethylene propylene rubber at an expansion ratio of about 20, was used as the intermediate layer 40. Sample E7 was prepared which was identical to Sample E1 except for this.

[0249] (Sample E8)

[0250] A porous metal body was used as the intermediate layer 40. The porous metal body was made of nickel, had a pore diameter of 0.9 mm, and a thickness of 2.0 mm. The second bonding layer 52 was the same adhesive layer as the first bonding layer 51 of Sample E1. Sample E8 was prepared, identical to Sample E1 except for these features.

[0251] (Sample E9)

[0252] The first bonding layer 51 and the second bonding layer 52 of sample E1 were omitted, and only the intermediate layer 140 was interposed between the piezoelectric film 35 and the structure 80. As the intermediate layer 140, a 3 mm thick base-free adhesive sheet made of an acrylic adhesive was used. Figure 18 The support member 680 is installed with Figure 17 The structure of the laminated body of sample E9.

[0253] (Sample E10)

[0254] The same intermediate layer as the intermediate layer 140 of the sample E9 was used as the intermediate layer 40. A sample E10 similar to the sample E8 was prepared except for the above.

[0255] (Sample E11)

[0256] Polyurethane foam having a thickness of 5 mm was used as the intermediate layer 40. Sample E11 was prepared which was the same as Sample E8 except for the above.

[0257] (Sample E12)

[0258] A polyurethane foam having a thickness of 10 mm was used as the intermediate layer 40. This polyurethane foam had a smaller pore size than the polyurethane foam used as the intermediate layer 40 of sample E11. Sample E12 was prepared in the same manner as sample E8 except for these points.

[0259] (Sample E13)

[0260] A closed-cell acrylonitrile-butadiene rubber foam with a thickness of 5 mm was used as the intermediate layer 40. Sample E13 was prepared which was the same as Sample E8 except for the above.

[0261] (Sample E14)

[0262] A closed-cell ethylene-propylene rubber foam with a thickness of 5 mm was used as the intermediate layer 40. Sample E14 was prepared which was the same as Sample E8 except for the above.

[0263] (Sample E15)

[0264] A closed-cell foam having a thickness of 5 mm and a mixture of natural rubber and styrene-butadiene rubber was used as the intermediate layer 40. Sample E15 was prepared which was the same as Sample E8 except for the above.

[0265] (Sample E16)

[0266] A closed-cell silicone foam with a thickness of 5 mm was used as the intermediate layer 40. Sample E16 was prepared which was the same as Sample E8 except for the above.

[0267] (Sample E17)

[0268] As the intermediate layer 40, a foam with a thickness of 10 mm was used, which was made of the same material and had the same structure as the intermediate layer 40 of sample E1. As the second bonding layer 52, the same adhesive sheet as that of sample E1 was used. As the piezoelectric body 30 of the piezoelectric film 35, a resin sheet with a thickness of 35 μm and a main raw material of polylactic acid derived from corn was used. The first electrode 61 and the second electrode 62 of the piezoelectric film 35 were each an aluminum film with a thickness of 0.1 μm, formed by vapor deposition. In this way, a piezoelectric film 35 with a total thickness of 35.2 μm was obtained. Sample E17, which was the same as sample E1 except for this, was produced.

[0269] (Sample R1)

[0270] The piezoelectric film 35 of the sample E1 is referred to as the sample R1. The sample R1 is placed on a table parallel to the ground without adhesive.

[0271] Samples E1 to E17 and R1 were evaluated as follows.

[0272] <Thickness of the middle layer (uncompressed state)>

[0273] The thickness of the intermediate layer was measured using a thickness gauge.

[0274] <Elastic modulus of the middle layer>

[0275] Small pieces were cut from the intermediate layer. The cut pieces were subjected to compression testing at room temperature using a tensile testing machine ("RSA-G2" manufactured by TA Instruments). A stress-strain curve was obtained. The elastic modulus was calculated based on the initial slope of the stress-strain curve.

[0276] <Pore diameter of the middle layer>

[0277] An enlarged image of the intermediate layer was obtained using a microscope. The enlarged image was analyzed to determine the average pore size of the intermediate layer. The average value was used as the pore size of the intermediate layer.

[0278] <Porosity of the middle layer>

[0279] Cut a small rectangular piece from the intermediate layer. Calculate the apparent density based on the volume and mass of the cut piece. Divide the apparent density by the density of the base material (solid body) forming the intermediate layer. From this, calculate the filling rate. Then, subtract the filling rate from 1. This gives the porosity.

[0280] <Surface filling rate of the middle layer>

[0281] The above filling ratios were defined as the surface filling ratios for Samples E2 to 16. In Samples E1 and 17, since the intermediate layer had a surface layer, the surface filling ratios were defined as 100%.

[0282] <Frequency characteristics of the sound pressure level of the sample>

[0283] exist Figure 19 The structure used for measuring samples E1 to E8 and E10 to E17 is shown in the figure. Conductive copper foil tapes 70 (CU-35C, manufactured by 3M) with a thickness of 70 μm and a length of 5 mm and a width of 70 mm were attached to the corners of the piezoelectric film 35. Alligator clips 75 were also attached to each of these conductive copper foil tapes 70. The conductive copper foil tapes 70 and alligator clips 75 formed part of the circuit for applying an AC voltage to the piezoelectric film 35.

[0284] exist Figure 20 The structure used for measuring sample E9 is shown in FIG. Figure 20 The structure does not have Figure 19 The first bonding layer 51 and the second bonding layer 52. Figure 20 The structure includes an intermediate layer 140 .

[0285] The structure of sample R1 used for measurement is modeled after Figure 19 and Figure 20 Specifically, following the Figure 19 and Figure 20Conductive copper foil tapes 70 are attached to the corners of both surfaces of the piezoelectric film 35, and alligator clips 75 are attached to these tapes 70. The assembly obtained in this manner is placed on a table parallel to the ground without bonding.

[0286] exist Figure 21 and Figure 22 A block diagram for measuring the acoustic characteristics of a sample is shown in FIG. Figure 21 Shows the output system, Figure 22 An evaluation system is shown.

[0287] exist Figure 21 The output system shown here consists of a personal computer (hereinafter sometimes referred to as a PC) 401 for sound output, an audio interface 402, a speaker amplifier 403, and a sample 404 (samples E1 to E17 and the piezoelectric speaker R1). Speaker amplifier 403 is also connected to an oscilloscope 405 to verify the output from speaker amplifier 403 to sample 404.

[0288] WaveGene is installed on the audio output PC 401. WaveGene is free software for generating test audio signals. A QUAD-CAPTURE manufactured by Roland DG Corporation is used as the audio interface 402. The sampling frequency of audio interface 402 is set to 192 kHz. An A-924 manufactured by Onkyo Co., Ltd. is used as the speaker amplifier 403. A DPO2024 manufactured by Tektronix is ​​used as the oscilloscope 405.

[0289] exist Figure 22 In the illustrated evaluation system, a microphone 501, an acoustic evaluation device (PULSE) 502, and a PC 503 for acoustic evaluation are connected in this order.

[0290] A Type 4939-C-002 manufactured by B&K was used as the microphone 501. The microphone 501 was placed at a distance of 4041 m from the sample. A Type 3052-A-030 manufactured by B&K was used as the acoustic evaluation device 502.

[0291] With the output system and evaluation system configured in this manner, an AC voltage was applied to sample 404 from sound output PC 401 via audio interface 402 and speaker amplifier 403. Specifically, a test sound signal was generated using sound output PC 401, with the frequency sweeping from 100 Hz to 100 kHz over 20 seconds. The voltage output from speaker amplifier 403 was then confirmed using oscilloscope 405. Furthermore, the sound generated by sample 404 was evaluated using the evaluation system. A sound pressure-frequency characteristic measurement test was conducted in this manner.

[0292] The details of the output system and evaluation system settings are as follows.

[0293] [Output system settings]

[0294] Frequency range: 100Hz~100kHz

[0295] Scan time: 20 seconds

[0296] Effective voltage: 10V

[0297] Output waveform: sine wave

[0298] [Evaluation system settings]

[0299] Measurement time: 22 seconds

[0300] Peak hold

[0301] Measurement range: 4Hz~102.4kHz

[0302] Line count: 6400

[0303] <Judging the frequency of the sound start>

[0304] The lower end of the frequency range where the sound pressure level is 3dB or more higher than the background noise (excluding steep peaks such as the frequency range where the sound pressure level remains above +3dB of the background noise and does not meet ±10% of the peak frequency (the frequency at which the sound pressure level reaches its peak)) is judged as the frequency at which the sound starts to be emitted.

[0305] exist Figures 23A to 42 The evaluation results of samples E1 to 17 and sample R1 are shown in FIG. Figure 43 The frequency characteristics of the sound pressure level of the background noise are shown in FIG. Figure 24 , E1 to E17 correspond to samples E1 to 17.

[0306] (ANC system evaluation)

[0307] The same piezoelectric speaker 10 as that of sample E1 was used except that the size in plan view was changed to 35 cm in length and 50 cm in width. Figure 44 An ANC evaluation system 800 is shown.

[0308] The piezoelectric speaker 10 is mounted on a spacer 780. The noise source 700, reference microphone 730, the center of the spacer 780, the center of the piezoelectric speaker 10, and the error microphone 735 are arranged in a straight line. Furthermore, a control area 790 is defined on the piezoelectric speaker 10 side as viewed from the spacer 780. A measurement microphone 740 is located in the control area 790.

[0309] exist Figure 44 , the x-direction is the longitudinal direction of the control region 790. The y-direction is the lateral direction of the control region 790. The z-direction is the depth direction of the control region 790. The x-direction, the y-direction, and the z-direction are mutually orthogonal directions.

[0310] The z direction is also the direction in which the noise source 700, the reference microphone 730, the center of the diaphragm 780, the center of the piezoelectric speaker 10, and the error microphone 735 are arranged. The z direction is also the direction in which the radiation surface 15 of the piezoelectric speaker 10 faces.

[0311] The noise source 700 used was the Eclipse TD508MK3 manufactured by Fujitsu Ten Co., Ltd. The partition 780 used was the desktop side screen R manufactured by Mihashi Industrial Co., Ltd. The reference microphone 730 used was the ECM-PC60 manufactured by Sony Corporation. The error microphone 735 used was the ECM-PC60 manufactured by Sony Corporation. The measurement microphone 740 used was the ECM-PC60 manufactured by Sony Corporation.

[0312] The distance between the noise source 700 and the reference microphone 730 is 5 cm. The distance between the reference microphone 730 and the spacer 780 is 60 cm. The distance between the radiation surface 15 of the piezoelectric speaker 10 and the error microphone 735 is 17.5 cm. These distances are the dimensions in the z direction.

[0313] Partition 780 has a rectangular plate-like shape when viewed from above. The dimensions of partition 780 are 60 cm in length, 45 cm in width, and 0.5 cm in width. The dimensions of control area 790 are 60 cm in length, 45 cm in width, and 60 cm in depth. The longitudinal direction is the x-direction. The transverse direction is the y-direction. The width or depth direction is the z-direction.

[0314] In the ANC evaluation system 800 , the first margin M1 is 5 cm, and the second margin M2 is 5 cm. These margins are dimensions in the x-direction.

[0315] The ANC evaluation system 800 uses an output signal PC (personal computer) 750, a measurement PC 760, and a control device 710. The output signal PC 750 is connected to the noise source 700 and the measurement PC 760.

[0316] Output signal PC 750 sends a noise signal to noise source 700. Thus, output signal PC 750 causes noise source 700 to radiate a sine wave. In addition, output signal PC 750 sends a trigger signal to measurement PC 760. The trigger signal can provide a common reference time for each measurement data. Specifically, for the 176 measurement points described later, sound pressure data with a consistent time axis can be obtained. This makes it possible to perform the following Figures 45A to 60 Map of the sound pressure distribution is shown.

[0317] The reference microphone 730 senses sound from the noise source 700. An output signal of the reference microphone 730 is transmitted to the control device 710.

[0318] The error microphone 735 senses sound in the control area 790. An output signal of the error microphone 735 is sent to the control device 710.

[0319] The control device 710 transmits a control signal to the piezoelectric speaker 10 based on the output signals of the reference microphone 730 and the error microphone 735. Thus, the control device 710 controls the sound waves radiated from the piezoelectric speaker 10.

[0320] The measurement microphone 740 detects sound at the position where the measurement microphone 740 is disposed, and an output signal from the measurement microphone 740 is sent to the measurement PC 760 .

[0321] The measurement PC 760 receives a trigger signal from the signal output PC 750 and an output signal from the measurement microphone 740 .

[0322] Control region 790 has a measurement cross section 790CS extending in the x- and z-directions. In ANC evaluation system 800, measurement cross section 790CS is provided with 176 measurement points. Specifically, measurement cross section 790CS is divided into 11 equal sections in the x-direction and 16 equal sections in the z-direction. The number of 176 measurement points is the product of the number of sections in the x-direction (11) and the number of sections in the z-direction (16). The position of measurement cross section 790CS in the y-direction is the same as the center position of radiating surface 15 in the y-direction. An error microphone 735 is provided on measurement cross section 790CS.

[0323] In ANC evaluation system 800, measurement microphone 740 is sequentially moved to 176 measurement points. In this manner, microphone 740 and measurement PC 760 collaborate to measure the sound pressure at each of the 176 measurement points. Specifically, measurement PC 760 maps the distribution of the sound pressure at each of the 176 measurement points. This mapping visualizes the sound field of measurement cross section 790CS.

[0324] Below, refer to Figures 45A to 62C , and provide an explanation based on the measured data. Figures 45A to 62C In, omitted Figure 44 An illustration of a portion of the control area 790 away from the partition 780 is shown. Figures 45A to 45C 、 Figures 47A to 47C 、 Figures 49A to 49C 、 Figures 51A to 51C 、 Figures 53A to 53C 、 Figures 55A to 55C 、 Figures 57A to 57C as well as Figures 59A to 59C The value of the color bar indicates the sound pressure level, and its unit is Pascal (Pa). A positive value indicates positive sound pressure, and a negative value indicates negative sound pressure.

[0325] (Reference Example 1: Measurement of Diffraction Sound)

[0326] Under the condition that the piezoelectric speaker 10 does not produce any sound and the noise source 700 radiates a sine wave, the sound pressure at 176 measurement points of the measurement cross section 790CS is measured and mapped. Figures 45A to 48 The sound pressure distribution obtained by mapping is shown in Figures 45A-48 In order to make it easier to intuitively understand that the diffracted sound is being measured, the piezoelectric speaker 10 is not shown in the figure. However, the measurement of Reference Example 1 is performed with the piezoelectric speaker 10 attached to the spacer 780, similar to Example 1 described below.

[0327] Specifically, Figures 45A to 45C The figure shows the sound pressure distribution from the noise source 700 at different times when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 45A to 45C Arranged in time series order. Figure 46 The series of lines represents the propagation over time of a wavefront generated by a noise source 700 radiating a 500 Hz sine wave. Figures 47A to 47C The figure shows the sound pressure distribution from the noise source 700 at different times when the frequency of the sine wave radiated by the noise source 700 is 800 Hz. Figures 47A to 47C Arranged in time series order. Figure 48 The series of lines represents the propagation over time of a wavefront generated by a noise source 700 radiating an 800 Hz sine wave.

[0328] exist Figure 46 In the diagram, a series of lines represent the position of a wavefront at different times. In general, Figure 46 In FIG. 1 , of the two adjacent lines, the line farther from the partition plate 78 represents a “certain wavefront” at a more advanced time. Figure 46 The block arrows indicate the direction of propagation of the wavefront. These instructions related to a series of lines and block arrows are about Figure 48 、 Figure 50 、 Figure 52 、 Figure 54 、 Figure 56 、 Figure 58 as well as Figure 60 The same is true.

[0329] also, Figure 46 The following steps are used to make it. First, obtain multiple Figures 45A to 45CSimilarly, based on the measured sound pressure distribution diagrams related to different moments, a line corresponding to a certain wavefront is manually drawn in each of these multiple sound pressure distribution diagrams. Then, the multiple sound pressure distribution diagrams with the drawn lines are overlapped. Thus, Figure 46 The diagram shown depicts a series of lines representing the propagation of the wavefront. These descriptions of the steps involved in making the diagram are related to Figure 48 、 Figure 50 、 Figure 52 、 Figure 54 、 Figure 56 、 Figure 58 as well as Figure 60 The same is true.

[0330] Figures 45A to 48 Indicates that diffraction occurs at the opposite ends of the partition 780. In addition, Figures 45A to 48 This shows that the wavefronts generated by diffraction at these ends propagate in a manner that wraps around behind the partition 780. Specifically, Figures 45A to 48 This shows a case where the wavefronts generated by diffraction at these ends propagate in a manner that passes through the center of the partition plate 780 and approaches the axis extending in the z direction. Figures 45A to 48 The propagation of the wavefront shown is similar to Figure 2 same.

[0331] (Example 1: Measurement of Sound Emitted by Piezoelectric Speaker 10)

[0332] As in Reference Example 1, while noise source 700 is radiating a sinusoidal wave, control device 710 is used to vibrate piezoelectric speaker 10, generating a sound wave for noise cancellation. At this time, control device 710 stores a control signal to be sent to piezoelectric speaker 10. Then, while noise source 700 is not radiating sound, control device 710 transmits the stored control signal to piezoelectric speaker 10. In this manner, while noise source 700 is not radiating sound, the vibration of piezoelectric speaker 10 is reproduced, and the sound pressure at 176 measurement points on measurement cross section 790CS is measured and mapped. Figures 49A to 52 The sound pressure distribution obtained by mapping is shown in FIG.

[0333] Specifically, Figures 49A to 49C The figure shows the sound pressure distribution from the piezoelectric speaker 10 at different times when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 49A to 49C Arranged in time series order. Figure 50 The series of lines represents the propagation of a certain wavefront generated by the piezoelectric speaker 10 over time when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 51A to 51CThe figure shows the sound pressure distribution from the piezoelectric speaker 10 at different times when the frequency of the sine wave radiated by the noise source 700 is 800 Hz. Figures 51A to 51C Arranged in time series order. Figure 52 The series of lines shows the propagation of a certain wavefront generated by the piezoelectric speaker 10 over time when the frequency of the sine wave radiated by the noise source 700 is 800 Hz.

[0334] Figures 49A to 52 The diagram shows a state where a wavefront propagates from two outer regions sandwiching the central region of the radiation surface 15 of the piezoelectric speaker 10 , passes through the central region, and approaches an axis extending in the z direction. Figures 49A to 52 The propagation of the wavefront shown is similar to Figure 3 Specifically, the wavefront of the diffracted wave generated by the noise from the noise source 700 diffracting at the diaphragm 780 and the wavefront from the piezoelectric speaker 10 are the same in that they propagate while approaching the above-mentioned axis.

[0335] In addition, by Figures 45A to 48 It can be seen that due to the diffraction on the partition 780, there is a period in which the phase of the sound wave in the first area 15a is the same as the phase of the sound wave in the second area 15b, the phase of the sound wave in the first area 15a is opposite to the phase of the sound wave in the third area 15c, and the phase of the sound wave in the second area 15b is opposite to the phase of the sound wave in the third area 15c (for regions 15a, 15b and 15c, please refer to Figures 1 to 3 and related instructions). Figures 49A to 52 It can be seen that, through the piezoelectric speaker 10, there is a period in which the phases of the first sound wave and the second sound wave are the same in sign, the phases of the first sound wave and the third sound wave are opposite in sign, and the phases of the second sound wave and the third sound wave are opposite in sign (for the first sound wave, the second sound wave and the third sound wave, please refer to the reference Figures 1 to 3 Regarding the phase distributions in the first region 15 a , the second region 15 b , and the third region 15 c , commonality is also observed between the noise from the noise source 700 and the sound from the piezoelectric speaker 10 .

[0336] (Comparative Example 1: Measurement of Sound Emitted by Dynamic Speaker 610)

[0337] The piezoelectric speaker 10 of Example 1 was replaced with a dynamic speaker 610. This dynamic speaker 610 was a Fostex P650K manufactured by Fostex Electric Co., Ltd. Except for this replacement, the sound pressures at 176 measurement points on the measurement cross section 790CS of the dynamic speaker 610 were measured and mapped in the same manner as in Example 1. Figures 53A to 56The sound pressure distribution obtained by mapping is shown in . In addition, the dynamic speaker 610 is embedded in the partition plate 780 .

[0338] Specifically, Figures 53A to 53C The figure shows the sound pressure distribution from the dynamic speaker 610 at different times when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 53A to 53C Arranged in time series order. Figure 54 The series of lines represents the propagation of a wavefront over time generated by the dynamic loudspeaker 610 when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 55A to 55C The figure shows the sound pressure distribution from the dynamic speaker 610 at different times when the frequency of the sine wave radiated by the noise source 700 is 800 Hz. Figures 55A to 55C Arranged in time series order. Figure 56 A series of lines illustrate the propagation of a wavefront over time generated by the dynamic speaker 610 when the frequency of the sine wave radiated by the noise source 700 is 800 Hz.

[0339] Figures 53A to 56 This shows a case where a substantially hemispherical wave is radiated from the radiation surface of the dynamic speaker 610 and the wavefront of the substantially hemispherical wave is also substantially hemispherical. Figures 53A to 56 The propagation of the wavefront shown is similar to Figure 4 same.

[0340] (Comparative Example 2: Measurement of Sound Emitted by Planar Speaker 620)

[0341] The piezoelectric speaker 10 of Example 1 was replaced with a planar speaker 620. This planar speaker 620 was FPS2030M3P1R manufactured by FPS Co., Ltd. Except for this replacement, the sound pressures at 176 measurement points on the measurement cross section 790CS of the planar speaker 620 were measured and mapped in the same manner as in Example 1. Figures 57A to 60 The sound pressure distribution obtained by mapping is shown in FIG.

[0342] Specifically, Figures 57A to 57C The sound pressure distribution from the planar speaker 620 at different times is shown when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 57A to 57C Arranged in time series order. Figure 58 The series of lines represent the propagation of a certain wavefront generated by the planar speaker 620 over time when the frequency of the sine wave radiated by the noise source 700 is 500 Hz. Figures 59A to 59CThe sound pressure distribution from the planar speaker 620 at different times is shown when the frequency of the sine wave radiated by the noise source 700 is 800 Hz. Figures 59A to 59C Arranged in time series order. Figure 60 The series of lines represents the propagation of a certain wavefront generated by the planar speaker 620 over time when the frequency of the sine wave radiated by the noise source 700 is 800 Hz.

[0343] Figures 57A to 60 This shows a case where a substantially plane wave is radiated from the radiation surface of the planar speaker 620 and the wavefront of the substantially plane wave is also substantially planar. Figures 57A to 60 The propagation of the wavefront shown is similar to Figure 5 same.

[0344] (Noise reduction effect)

[0345] use Figures 61A to 62C The difference in noise cancellation effects between Example 1 and Comparative Example 2 will be described. In the following description, the terms "speaker on" and "speaker off" may be used. "Speaker on" refers to when the speaker is radiating noise cancellation sound. "Speaker off" refers to when the speaker is not radiating noise cancellation sound.

[0346] Figure 61A and Figure 62A The color map shows the silencing state at a certain moment when a sine wave is radiated from the noise source 700. Figure 61A and Figure 62A , the color map on the left shows the noise cancellation state of the piezoelectric speaker 10 of Example 1. The color map on the right shows the noise cancellation state of the flat speaker 620 of Comparative Example 2. Figure 61A The sound pressure distribution at a certain time when the frequency of the sine wave radiated by the noise source 700 is 500 Hz is shown. Figure 62A The sound pressure distribution at a certain time when the frequency of the sine wave radiated by the noise source 700 is 800 Hz is shown.

[0347] exist Figure 61A and Figure 62A The value to the right of the color bar indicates the amplification factor, expressed in dB. An amplification factor of X indicates that the sound pressure when the speaker is turned on is amplified by X dB, relative to the sound pressure when the speaker is turned off. A negative amplification factor indicates a noise cancellation effect. A positive amplification factor indicates that the noise is amplified, conversely. The reduction area (RA) indicates the proportion of the area in the measurement cross-section 790CS where the amplification factor is -6 dB or less (i.e., the area where the noise cancellation effect is good). The amplification area (AA) indicates the proportion of the area in the measurement cross-section 790CS where the amplification factor is greater than 0 dB (i.e., the area where the noise is amplified).

[0348] Figure 61B Yes Figure 61A In the figure, areas with amplification less than 0 dB are shaded lightly, and areas with amplification greater than 0 dB are shaded thickly. Figure 62B Yes Figure 62A The area with amplification less than 0dB is shaded lightly, and the area with amplification greater than 0 is shaded thickly. Figure 61B and Figure 62B In the , the noise reduction area is given a thin shading, and the magnified area is given a thick shading. Figure 61B and Figure 62B The shadows in the Figure 61A and Figure 62A The rough shadows are added by manual work. Figure 61C and Figure 62C The same is true for .

[0349] Figure 61C Yes Figure 61A In the figure, areas with amplification of -6dB or less are shaded lightly, and areas with amplification greater than 0 are shaded thickly. Figure 62C Yes Figure 62A In the figure, the area with amplification of -6dB or less is shaded lightly, and the area with amplification greater than 0 is shaded thickly. Figure 61C and Figure 62C In the , thin shading is applied to the reduced area and thick shading is applied to the enlarged area.

[0350] like Figures 61A to 62C As shown, when the piezoelectric speaker 10 of Example 1 is used, the noise reduction area and the reduction area are larger, and the amplification area is smaller, compared with the case of using the flat speaker 620 of Comparative Example 2.

[0351] Specifically, when using piezoelectric speaker 10 of Example 1, when the frequency of the sine wave radiated by noise source 700 is 500 Hz, the reduced area is approximately 58%, and the amplified area is approximately 18%. When the frequency of the sine wave radiated by noise source 700 is 800 Hz, the reduced area is approximately 27%, and the amplified area is approximately 18%.

[0352] On the other hand, when using the planar speaker 620 of Comparative Example 2, when the frequency of the sine wave radiated by the noise source 700 is 500 Hz, the reduced area is approximately 38%, and the amplified area is approximately 21%. When the frequency of the sine wave radiated by the noise source 700 is 800 Hz, the reduced area is approximately 13%, and the amplified area is approximately 61%.

[0353] according to Figures 61A to 62CThe superiority of the noise reduction effect of the piezoelectric speaker 10 over the planar speaker 620 is more significant when the frequency of the sine wave radiated by the noise source 700 is 500 Hz and 800 Hz.

[0354] Furthermore, when the dynamic speaker 610 of Comparative Example 1 is used, it can be expected that the noise reduction area and the noise reduction area become smaller and the amplification area becomes larger compared to the case of using the planar speaker 620 of Comparative Example 2.

[0355] [Piezoelectric film support structure and vibration freedom]

[0356] Referring to an example of the support structure of the piezoelectric speaker of the present invention. Figure 6A 、 Figure 15 、 Figure 17 、 Figure 18 As can be seen from the related descriptions, in the piezoelectric speaker 10 , the entire surface of the piezoelectric film 35 is fixed to the structure 80 via the bonding layers 51 and 52 and the intermediate layer 40 .

[0357] In order to prevent the vibration of the piezoelectric film 35 from being inhibited by the structure 80 , it is conceivable to support a portion of the piezoelectric film 35 so as to be separated from the structure 80 . Figure 6B The supporting structure based on this design concept is illustrated in . Figure 6B In the illustrated imaginary piezoelectric speaker 108 , the frame 88 supports the peripheral edge portion of the piezoelectric film 35 at a position spaced apart from the structure 80 .

[0358] A piezoelectric film that is pre-curved and fixed in its curved direction easily ensures sufficient sound volume. Therefore, for example, in piezoelectric speaker 108, it is conceivable to place an inclusion with a convex upper surface and uneven thickness in the space 48 surrounded by the piezoelectric film 35, the frame 88, and the structure 80, thereby pushing the center of the piezoelectric film 35 upward. However, such an inclusion does not bond to the piezoelectric film 35 in a manner that would hinder its vibration. Therefore, even if an inclusion is placed in space 48, only the frame 88 supports the piezoelectric film 35 in a manner that regulates its vibration.

[0359] As mentioned above, in Figure 6B In the piezoelectric speaker 108 shown in FIG. 1 , a local support structure of the piezoelectric film 35 is adopted. Figure 6AIn the piezoelectric speaker 10, the piezoelectric membrane 35 is not supported by a specific portion. Surprisingly, despite the entire surface of the piezoelectric membrane 35 being fixed to the structure 80, the piezoelectric speaker 10 exhibits practical acoustic properties. Specifically, in the piezoelectric speaker 10, the entire periphery of the piezoelectric membrane 35 can vibrate up and down. The entire piezoelectric membrane 35 can also vibrate up and down. Therefore, compared to the piezoelectric speaker 108, the piezoelectric speaker 10 has a higher degree of freedom of vibration and is relatively advantageous in achieving good sound production characteristics.

[0360] As reference Figure 6A As described above, the high degree of freedom of vibration may contribute to the formation of the first wavefront 16a and the second wavefront 16b. Figure 6A In the figure, the speaker 10 is depicted as Figure 15 The case of the piezoelectric speaker 10 shown. Figure 6A In the figure, the first bonding layer 51 and the second bonding layer 52 are omitted. Figure 17 Even in the case of the piezoelectric speaker 110 shown, a high degree of freedom of vibration can be obtained.

[0361] According to the research of the present inventors, the intermediate layer is a porous body layer and / or a resin layer suitable for ensuring the degree of freedom of vibration. Figures 25 to 41 As shown in FIG. 1 , in samples E1 to E17 in which the intermediate layer is a porous layer and / or a resin layer, practical acoustic characteristics are exhibited even though the entire surface of the piezoelectric film 35 is fixed to the support member 680. Therefore, it is believed that in the ANC evaluation system 800, even if the piezoelectric speaker 10 is changed from the piezoelectric speaker 10 of sample E1 with different dimensions to the piezoelectric speaker 10 of samples E2 to E17 with different dimensions, the same acoustic characteristics will be observed. Figures 49A to 52 Sound pressure distribution with the same tendency.

[0362] The ANC system 500 of the present invention can also be explained as follows:

[0363] The ANC system 500 includes:

[0364] structure 80; and

[0365] The speaker 10 is mounted on the structure 80.

[0366] in,

[0367] The speaker 10 includes a radiation surface 15, a piezoelectric film 35 and an intermediate layer 40 (or 140).

[0368] The intermediate layer 40 is disposed between the structure 80 and the piezoelectric film 35.

[0369] The intermediate layer 40 is a porous body layer and / or a resin layer.

Claims

1. An active noise control system comprising: structures; and a loudspeaker, mounted on the structure, in, The speaker comprises a radiating surface, The radiation surface has a first area, a second area, and a third area, and the third area is an area between the first area and the second area. When an axis passing through the third area and extending away from the radiation surface is defined as a reference axis, the speaker forms a first wavefront that propagates from the first area toward the reference axis and a second wavefront that propagates from the second area toward the reference axis. The radiation surfaces are connected together. When the sound waves in the first area formed by the speaker are defined as a first sound wave, the sound waves in the second area formed by the speaker are defined as a second sound wave, and the sound waves in the third area formed by the speaker are defined as a third sound wave, there is a period during which the phases of the first sound wave and the second sound wave are of the same sign, the phases of the first sound wave and the third sound wave are opposite in sign, and the phases of the second sound wave and the third sound wave are opposite in sign, The active noise control system comprises a control device, In the control device, a certain frequency range is set. The control device controls the frequency of the sound output from the speaker to a value within the frequency range. When the wavelength of the sound at the upper limit of the frequency range is defined as a reference wavelength and the radiation surface is viewed from above, The radiating surface has a first end and a second end opposite to each other, A first margin between the first end and the end of the structure is greater than or equal to zero and less than or equal to 1 / 3 of the reference wavelength. A second margin between the second end and the end of the structure is greater than or equal to zero and less than or equal to 1 / 3 of the reference wavelength. The active noise control system comprises an error microphone, a reference microphone and a control device, The reference microphone, the structure, the speaker and the error microphone are arranged in sequence, The control device performs feedforward control for controlling the sound output from the speaker based on the output signal of the reference microphone and the output signal of the error microphone.

2. The active noise control system according to claim 1, wherein: The speaker includes a piezoelectric film.

3. The active noise control system according to claim 2, wherein: The loudspeaker comprises a middle layer, The intermediate layer is arranged between the structure and the piezoelectric film, The intermediate layer is a porous body layer and / or a resin layer.

4. The active noise control system according to claim 3, wherein: There is an imaginary straight line that passes through the intermediate layer and the piezoelectric film in sequence and then reaches the outside of the speaker without passing through the intermediate layer.

5. The active noise control system according to claim 3, wherein: The main surface of the piezoelectric film on the side opposite to the intermediate layer constitutes the radiation surface, or A first layer is provided on a side of the piezoelectric film opposite to the intermediate layer. The material of the first layer is different from that of the intermediate layer.

6. The active noise control system according to claim 1, wherein: The control device includes at least one amplifier, at least one low-pass filter, at least one analog-to-digital converter, and at least one digital-to-analog converter.

7. The active noise control system according to claim 1, wherein: The structure is a plate-shaped body.

8. An active noise control system comprising: structures; and a loudspeaker, mounted on the structure, in, The speaker comprises a radiating surface, The radiation surface has a first area, a second area, and a third area, and the third area is an area between the first area and the second area. When an axis passing through the third area and extending away from the radiation surface is defined as a reference axis, the speaker forms a first wavefront that propagates from the first area toward the reference axis and a second wavefront that propagates from the second area toward the reference axis. The radiation surfaces are connected together. When the sound waves in the first area formed by the speaker are defined as a first sound wave, the sound waves in the second area formed by the speaker are defined as a second sound wave, and the sound waves in the third area formed by the speaker are defined as a third sound wave, there is a period during which the phases of the first sound wave and the second sound wave are of the same sign, the phases of the first sound wave and the third sound wave are opposite in sign, and the phases of the second sound wave and the third sound wave are opposite in sign, The active noise control system comprises a control device, In the control device, a certain frequency range is set. The control device controls the frequency of the sound output from the speaker to a value within the frequency range. When the wavelength of the sound at the upper limit of the frequency range is defined as a reference wavelength and the radiation surface is viewed from above, The radiating surface has a first end and a second end opposite to each other, A first margin between the first end and the end of the structure is greater than or equal to zero and less than or equal to 1 / 3 of the reference wavelength. A second margin between the second end and the end of the structure is greater than or equal to zero and less than or equal to 1 / 3 of the reference wavelength. The active noise control system includes an error microphone and a control device, The structure, the speaker and the error microphone are arranged in sequence, The control device performs feedback control for controlling the sound output from the speaker based on the output signal of the error microphone.

9. The active noise control system according to claim 8, wherein: The speaker includes a piezoelectric film.

10. The active noise control system according to claim 9, wherein: The loudspeaker comprises a middle layer, The intermediate layer is arranged between the structure and the piezoelectric film, The intermediate layer is a porous body layer and / or a resin layer.

11. The active noise control system according to claim 10, wherein: There is an imaginary straight line that passes through the intermediate layer and the piezoelectric film in sequence and then reaches the outside of the speaker without passing through the intermediate layer.

12. The active noise control system according to claim 10, wherein: The main surface of the piezoelectric film on the side opposite to the intermediate layer constitutes the radiation surface, or A first layer is provided on a side of the piezoelectric film opposite to the intermediate layer. The material of the first layer is different from that of the intermediate layer.

13. The active noise control system according to claim 8, wherein: The control device includes at least one amplifier, at least one low-pass filter, at least one analog-to-digital converter, and at least one digital-to-analog converter.

14. The active noise control system according to claim 8, wherein: The structure is a plate-shaped body.

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