Sound elimination system

Abstract

To provide a sound elimination system including a piezoelectric film from which a sound wave for sound elimination is appropriately radiated.SOLUTION: A sound elimination system comprises at least one sound elimination speaker for radiating a sound wave for sound elimination. The at least one sound elimination speaker includes a piezoelectric loudspeaker 10. The piezoelectric loudspeaker 10 comprises a piezoelectric film 35, a fixation face 17 in contact with a support body for supporting the piezoelectric loudspeaker 10, and a film holding part 55 arranged between the piezoelectric film 35 and the fixation face 17. The film holding part 55 includes an adhesive layer 51 with the fixation face 17 formed on a surface of the adhesive layer 51, and further includes an intervention layer 40 which is a porous body layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sound deadening system, and in particular to a sound deadening system comprising at least one sound deadening speaker for emitting sound waves for sound deadening. [Background technology]

[0002] Speakers that use piezoelectric film (hereinafter referred to as piezoelectric speakers) are known. Piezoelectric speakers have the advantages of being small in volume and lightweight.

[0003] Patent Document 1 describes a noise reduction system that uses a piezoelectric speaker as a noise reduction speaker. Specifically, in this noise reduction system, a piezoelectric film is directly attached with adhesive to a wooden board that acts as a support and is used as a wall material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-236189 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-122187 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a sound absorbing system in which sound waves for absorbing noise are efficiently emitted from a piezoelectric film. [Means for solving the problem]

[0006] According to the inventors' research, if an appropriate layer is interposed between the piezoelectric film and the support, it becomes easier for the piezoelectric film to emit sound in the audible range. An adhesive for fixing the piezoelectric film is also interposed between the piezoelectric film and the support (Patent Document 1). However, because this adhesive is applied at the site where the noise reduction system is to be constructed, the manner in which it is interposed is poorly reproducible. For this reason, the adhesive applied to the piezoelectric film when fixing it to the support is not, at least by itself, suitable for improving a noise reduction system using a piezoelectric speaker.

[0007] The present invention provides 1. A noise reduction system comprising at least one noise reduction speaker for emitting noise reduction sound waves, the at least one muffled speaker includes a piezoelectric speaker; the piezoelectric speaker includes a piezoelectric film, a fixing surface in contact with a support that supports the piezoelectric speaker, and a film holding portion disposed between the piezoelectric film and the fixing surface; The present invention provides a sound-absorbing system, wherein (i) the film holding portion includes an adhesive layer and the fixing surface is formed by the surface of the adhesive layer, and / or (ii) the film holding portion includes a porous layer. [Effects of the Invention]

[0008] The above sound-deadening system is suitable for effectively radiating sound waves for sound mitigation from the piezoelectric film. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a piezoelectric speaker taken along a plane parallel to the thickness direction. [Figure 2] FIG. 2 is a top view of the piezoelectric speaker as viewed from the opposite side to the fixing surface. [Figure 3] FIG. 3 is a schematic diagram for explaining the noise reduction system. [Figure 4] FIG. 4 is a diagram showing a piezoelectric speaker according to another embodiment. [Figure 5]FIG. 5 is a diagram for explaining the structure produced in the example. [Figure 6] FIG. 6 is a diagram illustrating a configuration for measuring a sample. [Figure 7] FIG. 7 is a diagram illustrating a configuration for measuring a sample. [Figure 8] FIG. 8 is a block diagram of the output system. [Figure 9] FIG. 9 is a block diagram of the evaluation system. [Figure 10A] FIG. 10A is a table showing the evaluation results of the samples. [Figure 10B] FIG. 10B is a table showing the evaluation results of the samples. [Figure 11] FIG. 11 is a graph showing the relationship between the degree of constraint of the intermediate layer and the frequency at which sound begins to be produced. [Figure 12] FIG. 12 is a graph showing frequency characteristics of sound pressure levels of the samples of Example 1. [Figure 13] FIG. 13 is a graph showing frequency characteristics of sound pressure level of the sample of Example 2. [Figure 14] FIG. 14 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 3. [Figure 15] FIG. 15 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 4. [Figure 16] FIG. 16 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 5. [Figure 17] FIG. 17 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 6. [Figure 18] FIG. 18 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 7. [Figure 19] FIG. 19 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 8. [Figure 20] FIG. 20 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 9. [Figure 21]FIG. 21 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 10. [Figure 22] FIG. 22 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 11. [Figure 23] FIG. 23 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 12. [Figure 24] FIG. 24 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 13. [Figure 25] FIG. 25 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 14. [Figure 26] FIG. 26 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 15. [Figure 27] FIG. 27 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 16. [Figure 28] FIG. 28 is a graph showing the frequency characteristics of the sound pressure level of the sample of Example 17. [Figure 29] FIG. 29 is a graph showing frequency characteristics of sound pressure levels of the sample of Reference Example 1. [Figure 30] FIG. 30 is a graph showing frequency characteristics of the sound pressure level of background noise. [Figure 31] FIG. 31 is a diagram illustrating a support structure for a piezoelectric film. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the following is merely an example of an embodiment of the present invention and is not intended to limit the present invention.

[0011] [First embodiment] A piezoelectric speaker according to a first embodiment will be described with reference to Figures 1 and 2. The piezoelectric speaker 10 includes a piezoelectric film 35, a fixing surface 17, and a film holding portion 55. The fixing surface 17 can be used to fix the piezoelectric film 35 to a support body.

[0012] The film holding portion 55 is disposed between the piezoelectric film 35 and the fixing surface 17. The film holding portion 55 includes an intervening layer 40, an adhesive or bonding layer 51 (hereinafter sometimes simply referred to as the adhesive layer 51), and an adhesive or bonding layer 52 (hereinafter sometimes simply referred to as the adhesive layer 52). In the example of FIG. 1, the fixing surface 17 is formed by the surface (main surface) of the adhesive layer 51. In other words, the fixing surface 17 is an adhesive or bonding surface.

[0013] The piezoelectric film 35 includes a piezoelectric body 30, an electrode 61, and an electrode 62. The adhesive layer 51, the intervening layer 40, the adhesive layer 52, and the piezoelectric film 35 are laminated in this order.

[0014] Hereinafter, the adhesive layer 51 may be referred to as the first adhesive layer 51, the adhesive layer 52 may be referred to as the second adhesive layer 52, the electrode 61 may be referred to as the first electrode 61, and the electrode 62 may be referred to as the second electrode 62.

[0015] The piezoelectric body 30 has a film shape. The piezoelectric body 30 vibrates when a voltage is applied. The piezoelectric body 30 can be made of a ceramic film, a resin film, or the like. Examples of materials for the ceramic film 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 materials for the resin film piezoelectric body 30 include polyvinylidene fluoride and polylactic acid. The resin film piezoelectric body 30 can also be made of polyolefins such as polyethylene and polypropylene. The piezoelectric body 30 can be either non-porous or porous.

[0016] The thickness of the piezoelectric body 30 is, for example, in the range of 10 μm to 300 μm, and may be in the range of 30 μm to 110 μm.

[0017] 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 are in the form of a film. The first electrode 61 and the second electrode 62 are each connected to a lead wire (not shown). The first electrode 61 and the second electrode 62 can be formed on the piezoelectric body 30 by vapor deposition, plating, sputtering, or the like. Metal foils can also be used as the first electrode 61 and the second electrode 62. The metal foils can be attached to the piezoelectric body 30 using double-sided tape, pressure-sensitive adhesives, adhesives, or the like. Materials for the first electrode 61 and the second electrode 62 include metals, such as gold, platinum, silver, copper, palladium, chromium, molybdenum, iron, tin, aluminum, and nickel. Materials for the first electrode 61 and the second electrode 62 include carbon, conductive polymers, and the like. Materials for the first electrode 61 and the second electrode 62 also include alloys of these. The first electrode 61 and the second electrode 62 may contain a glass component, etc.

[0018] The thickness of each of the first electrode 61 and the second electrode 62 is, for example, in the range of 10 nm to 150 μm. The thickness is within this range, and may be in the range of 20 nm to 100 μm.

[0019] 1 and 2, the first electrode 61 covers the entirety of one main surface of the piezoelectric body 30. However, the first electrode 61 may cover only a portion of the one main surface of the piezoelectric body 30. The second electrode 62 covers the entirety of the other main surface of the piezoelectric body 30. However, the second electrode 62 may cover only a portion of the other main surface of the piezoelectric body 30.

[0020] The intervening layer 40 is disposed between the piezoelectric film 35 and the fixing surface 17. In this embodiment, the intervening layer 40 is disposed between the piezoelectric film 35 and the first adhesive layer 51. The intervening layer 40 may be a layer other than an adhesive layer or a pressure-sensitive adhesive layer, and may be an adhesive layer or a pressure-sensitive adhesive layer. The intervening layer 40 is a porous layer and / or a resin layer. Here, the resin layer is a concept that includes a rubber layer and an elastomer layer, and therefore the intervening layer 40 that is a resin layer may be a rubber layer or an elastomer layer. Examples of the intervening layer 40 that is a resin layer 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 urethane layer, and an acrylic resin layer. Examples of the intervening layer 40 that is a porous layer include a foam layer. Specifically, examples of the intervening layer 40, which is a porous layer and a resin layer, 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, and a urethane foam layer. Examples of the intervening layer 40 that is a resin layer but not a porous layer include an acrylic resin layer. Examples of the intervening layer 40 that is a porous layer but not a resin layer include a metal porous layer. Here, the term "resin layer" refers to a layer containing resin, and may include a layer containing 30% or more of resin, 45% or more of resin, 60% or more of resin, or 80% or more of 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, urethane layers, acrylic resin layers, metal layers, resin films, ceramic films, and the like. The intervening layer 40 may also be a blend layer of two or more materials.

[0021] The modulus of elasticity of the intermediate layer 40 is, for example, 10,000 N / m 2 ~20,000,000N / m 2 and 20000N / m 2 ~100,000N / m 2 may be.

[0022] In one example, the pore size of the intervening layer 40, which is a porous body layer, is 0.1 mm to 7.0 mm, or may be 0.3 mm to 5.0 mm. In another example, the pore size of the intervening layer 40, which is a porous body layer, is, for example, 0.1 mm to 2.5 mm, or may be 0.2 mm to 1.5 mm, or may be 0.3 mm to 0.7 mm. The porosity of the intervening layer 40, which is a porous body layer, is, for example, 70% to 99%, or may be 80% to 99%, or may be 90% to 95%.

[0023] A known foam can be used for the intervening layer 40 (for example, the foam disclosed in Patent Document 2). The intervening layer 40 may have an open-cell structure, a closed-cell structure, or a semi-closed semi-open-cell structure. An open-cell structure refers to a structure in which the open cell ratio is 100%. A closed-cell structure refers to a structure in which the open cell ratio is 0%. A semi-closed semi-open-cell structure refers to a structure in which the open cell ratio is greater than 0% and less than 100%. Here, the open cell ratio can be calculated, for example, by conducting a test in which the foam layer is submerged in water and using the formula: open cell ratio (%) = {(volume of absorbed water) / (volume of air bubble portion)} × 100. In one specific example, the "volume of absorbed water" is measured by submerging the foam layer in water and leaving it under a reduced pressure of -750 mmHg for 3 minutes, then measuring the mass of water that has replaced the air in the bubbles of the foam layer, and determining that the density of water is 1.0 g / cm. 3 This can be converted to volume as The "partial bubble volume" is calculated using the formula: partial bubble volume (cm 3 )={(Quality of foam layer "Material density" is the density of the matrix (solid) that forms the foam layer.

[0024] The foaming ratio (density ratio before and after foaming) of the intervening layer 40, which is a foam layer, is, for example, 5 to 40 times, and may be 10 to 40 times.

[0025] The thickness of the intervening layer 40 in the uncompressed state is, for example, in the range of 0.1 mm to 30 mm, or may be in the range of 1 mm to 30 mm, or may be in the range of 1.5 mm to 30 mm, or may be in the range of 2 mm to 25 mm. Typically, the intervening layer 40 is thicker than the piezoelectric film 35 in the uncompressed state. In the uncompressed state, the ratio of the thickness of the intervening layer 40 to the thickness of the piezoelectric film 35 is, for example, 3 times or more, or may be 10 times or more, or may be 30 times or more. Furthermore, typically, the intervening layer 40 is thicker than the first adhesive layer 51 in the uncompressed state.

[0026] The first adhesive layer 51 has a surface that forms the fixing surface 17. The first adhesive layer 51 is a layer that is bonded to the support. In the example of FIG. 1, the first adhesive layer 51 is bonded to the intervening layer 40. An example of the first adhesive layer 51 is a double-sided tape having a substrate and an adhesive applied to both sides of the substrate. An example of the substrate of the double-sided tape used as the first adhesive layer 51 is a nonwoven fabric. An example of the adhesive of the double-sided tape used as the first adhesive layer 51 is an adhesive containing an acrylic resin. However, the first adhesive layer 51 may also be an adhesive layer that does not have a substrate.

[0027] The thickness of the first adhesive layer 51 is, for example, 0.01 mm to 1.0 mm, and may be 0.05 mm to 0.5 mm.

[0028] The second adhesive layer 52 is disposed between the intervening layer 40 and the piezoelectric film 35. Specifically, the second adhesive layer 52 is bonded to the intervening layer 40 and the piezoelectric film 35. An example of the second adhesive layer 52 is a double-sided tape having a substrate and an adhesive applied to both sides of the substrate. An example of the substrate of the double-sided tape used as the second adhesive layer 52 is a nonwoven fabric. An example of the adhesive of the double-sided tape used as the second adhesive layer 52 is an adhesive containing an acrylic resin. However, the second adhesive layer 52 may be an adhesive layer without a substrate.

[0029] The thickness of the second adhesive layer 52 is, for example, 0.01 mm to 1.0 mm, and may be 0.05 mm to 0.5 mm.

[0030] In this embodiment, the adhesive surface or sticky surface comes into contact with the piezoelectric film 35, thereby integrating the piezoelectric film 35 with the layer on the fixing surface 17 side. Specifically, in this embodiment, the adhesive surface or sticky surface is a surface formed by the surface of the second sticky layer or adhesive layer 52.

[0031] The piezoelectric speaker 10 can be applied to a noise reduction system 500 shown in FIG. 3. The noise reduction system 500 is a system including at least one noise reduction speaker for emitting noise reduction sound waves. Specifically, the noise reduction sound waves are sound waves that have an opposite phase to the sound waves to be canceled in a predetermined area (area to be muted) 300. The noise reduction system 500 also includes a reference microphone 130, an error microphone 140, and a control device 110. Compared to a dynamic speaker, the piezoelectric speaker 10 has a shorter time (hereinafter sometimes referred to as delay time) between receiving an electrical signal and emitting sound. Therefore, the piezoelectric speaker 10 is suitable for configuring a compact noise reduction system not only because of its small size but also 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 attached to a single partition.

[0032] In the sound-cancelling system 500, at least one sound-cancelling speaker is provided. In this embodiment, the sound deadening system 500 includes a plurality of piezoelectric speakers 10. The sound deadening system 500 includes a support 80 that supports the piezoelectric speaker 35. The piezoelectric speaker 10 is fixed to the support 80. The fixing surface 17 is in contact with the support 80. The presence of a plurality of piezoelectric speakers 10 is advantageous from the viewpoint of implementing sound deadening over a wide area.

[0033] With the piezoelectric speaker 10 fixed to the support 80, a voltage is applied to the piezoelectric film 35 via the lead wires. This causes the piezoelectric film 35 to vibrate and radiate sound waves from the piezoelectric film 35. In the example of FIG. 3, the support 80 has a flat surface, the piezoelectric speaker 10 is fixed on that flat surface, and the piezoelectric film 35 extends in a planar shape. This configuration is advantageous from the viewpoint of making the sound waves radiated from the piezoelectric film 35 closer to plane waves. However, if the support 80 has a curved surface, the piezoelectric speaker 10 may be fixed on that curved surface.

[0034] As shown in Figure 3, a sound wave to be canceled arrives at region 300 from noise source 200 and has waveform 290 at region 300. Piezoelectric speaker 10 emits a sound wave that, when it arrives at region 300, has waveform 90, which is opposite in phase to waveform 290. These sound waves cancel each other at region 300. In other words, these sound waves combine at region 300 to produce a combined sound wave with waveform 390 whose amplitude is reduced to zero or a small level. This is how sound cancellation system 500 achieves sound cancellation.

[0035] In one specific example, each of the multiple piezoelectric speakers 10 generates a wavefront. These wavefronts are combined to form a composite wavefront that propagates into the area 300. The propagation direction of the composite wavefront can be controlled by controlling the phase difference between the voltages applied to each piezoelectric speaker 10.

[0036] 3 performs feedforward control using a reference microphone 130, an error microphone 140, and a control device 110. Specifically, the reference microphone 130 detects sound from a noise source 200. The reference microphone 130 is typically placed on the noise source 200 side as viewed from the piezoelectric speaker 10. Based on the sound detected by the reference microphone 130, the control device 110 adjusts the phase of the sound wave emitted from the piezoelectric speaker 10. Furthermore, the error microphone 140 is placed in an area 300 and detects sound in the area 300. Based on the sound detected by the error microphone 140, the control device 110 adjusts the amplitude of the sound wave emitted from the piezoelectric speaker 10 so as to reduce the amplitude of the composite sound wave in the area 300.

[0037] In the noise reduction system of this modified example, the reference microphone 130 is omitted. Instead, feedback control is performed using the error microphone 140 and the control device 110. Specifically, the error microphone 140 adjusts the phase and amplitude of the sound waves emitted from the piezoelectric speaker 10 so as to reduce the amplitude of the sound waves in the area 300. Even in this case, the sound waves from the noise source 200 end up being canceled out in the area 300 by the sound waves of the opposite phase generated by the piezoelectric speaker 10.

[0038] In the sound deadening system 500 of this embodiment, the support 80 is an article made for a purpose other than supporting the piezoelectric film 35, which is repurposed for supporting the piezoelectric film 35. Therefore, the sound deadening system 500 does not require a dedicated item for supporting the piezoelectric film 35. Such a system is advantageous from the viewpoint of eliminating space narrowing. Specifically, in this embodiment, the support 80 is: a) a partition wall separating a room including a space to be silenced by the sound deadening system 500 or a space to be prevented from leaking sound to the outside, from the outdoors or another room; b) a product that is immovably or movably installed indoors and performs a function other than a sound deadening speaker; c) a device or instrument designed to be portable or wearable by a person; or d) a sound insulating wall installed outdoors.

[0039] Examples of the support 80 in the above type a) include walls, ceilings, window glass, vehicle bodies, doors, and other barriers that define spaces where people enter. Examples of the support 80 in the above type b) include office furniture such as partitions, chairs, and tables, home appliances, sashes, etc. Examples of the support 80 in the above type c) include helmets, etc.

[0040] Typically, the area of ​​the surface of the support 80 facing the fixing surface 17 is equal to or greater than the area of ​​the fixing surface 17. The area of ​​the former is, for example, 1.0 times or more, or may be 1.5 times or more, or may be 5 times or more, of the area of ​​the latter. Typically, the support 80 has a greater rigidity (the product of Young's modulus and the moment of inertia), a greater Young's modulus, and / or a greater thickness than the intervening layer 40. However, the support 80 may have the same rigidity, Young's modulus, and / or thickness as the intervening layer 40, or may have a smaller rigidity, Young's modulus, and / or thickness than the intervening layer 40. The Young's modulus of the support 80 is, for example, 1 GPa or more, or may be 10 GPa or more, or may be 50 GPa or more. The upper limit of the Young's modulus of the support 80 is not particularly limited, but is, for example, 1000 GPa. Because various articles can be used as the support 80, it is difficult to specify a range for its thickness, but the thickness of the support 80 is, for example, 0.1 mm or more, or may be 1 mm or more, 10 mm or more, or 50 mm or more. There is no particular upper limit to the thickness of the support 80, but it is, for example, 1 mm. Typically, the position and / or shape of the support 80 is fixed regardless of the piezoelectric speaker 10. Typically, the support 80 is manufactured assuming that it will not be bent.

[0041] In one example, the sound deadening system 500 is used to muffle noise in an area where people are present. Specifically, the area 300 is the area where people are present. In another example, the sound deadening system 500 is used to prevent sound leakage from an area where people are present. Specifically, the area where people are present is the noise source 200. The size of the area 300 is not particularly limited; in one example, the area 300 is the entire room, and in another example, the area 300 is a part of the room.

[0042] The entire noise reduction system 500 according to this embodiment and its components will now be further described.

[0043] In the sound-absorbing system 500 , the film holding portion 55 is disposed between the piezoelectric film 35 and the support 80 .

[0044] In the sound absorbing system 500, (i) the film holding portion 55 includes an adhesive layer and the fixing surface 17 is formed by the surface of the adhesive layer, and / or (ii) the film holding portion 55 includes a porous layer.

[0045] Such a sound-absorbing system 500 is suitable for effectively emitting sound waves for sound absorption from the piezoelectric film 35. The first adhesive layer 51 may correspond to the adhesive layer in (i) above. The intervening layer 40 may correspond to the porous layer in (ii) above.

[0046] In the sound-deadening system 500 , the intervening layer 40 is disposed between the piezoelectric film 35 and the support 80 .

[0047] Although the details of the effect need to be studied further, it is possible that by appropriately restraining one main surface of the piezoelectric film 35 with the intervening layer 40, it becomes easier for the piezoelectric film 35 to generate low-frequency sounds in the audible range. Taking this into consideration, when the piezoelectric film 35 is observed in a planar view, the intervening layer 40 can be arranged in an area that occupies 25% or more of the area of ​​the piezoelectric film 35. When the piezoelectric film 35 is observed in a planar view, the intervening layer 40 can be arranged in an area that occupies 50% or more of the area of ​​the piezoelectric film 35. Alternatively, the intervening layer 40 may be disposed over 75% or more of the area of ​​the piezoelectric film 35, or the intervening layer 40 may be disposed over the entire area of ​​the piezoelectric film 35. Furthermore, 50% or more of the main surface 15 on the side opposite the fixing surface 17 of the piezoelectric speaker 10 may be made up of the piezoelectric film 35. 75% or more of the main surface 15 may be made up of the piezoelectric film 35, or the entire main surface 15 may be made up of the piezoelectric film 35.

[0048] In this embodiment, the second adhesive layer 52 prevents separation between the piezoelectric film 35 and the intervening layer 40. From the viewpoint of the above-mentioned "appropriate restraint," the second adhesive layer 52 and the intervening layer 40 can be arranged over 25% or more of the area of ​​the piezoelectric film 35 when observed in a planar view. When observed in a planar view, the second adhesive layer 52 and the intervening layer 40 may be arranged over 50% or more of the area of ​​the piezoelectric film 35, or over 75% or more of the area of ​​the piezoelectric film 35, or the second adhesive layer 52 and the intervening layer 40 may be arranged over the entire area of ​​the piezoelectric film 35.

[0049] Here, when the intervening layer 40 is porous, the proportion of the area where the intervening layer 40 is disposed is determined from a more macroscopic perspective, rather than a microscopic perspective that takes into account the pores resulting from the porous structure. For example, when the piezoelectric film 35, the porous intervening layer 40, and the second adhesive layer 52 are plate-like bodies that have a common outline in a planar view, it is expressed that the second adhesive layer 52 and the intervening layer 40 are disposed over 100% of the area of ​​the piezoelectric film 35.

[0050] In this embodiment, 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, 1×10 4 N / m 3 The degree of constraint of the intermediate layer 40 is preferably 5×10 8 N / m 3 More preferably, it is 2×10 or less. 8 N / m 3 or less, and more preferably 1×10 5 ~5×10 7 N / m 3 Here, the constraint degree (N / m 3 ) is calculated by the following formula: 2 ) and the surface filling rate of the intermediate layer 40. This is a value obtained by dividing by the thickness (m) of the intervening layer 40. The surface filling rate of the intervening layer 40 is the filling rate (1 minus the porosity) of the main surface of the intervening layer 40 facing the piezoelectric film 35. If the pores in the intervening layer 40 are evenly distributed, the surface filling rate can be considered to be equal to the three-dimensional filling rate of the intervening layer 40. Restraint degree (N / m 3 ) = Elastic modulus (N / m 2 ) × surface filling rate ÷ thickness (m)

[0051] The degree of constraint can be considered a parameter that represents the degree of constraint of the piezoelectric film 35 by the intervening layer 40. The above formula shows that the greater the elastic modulus of the intervening layer 40, the greater the degree of constraint. The above formula also shows that the greater the surface filling rate of the intervening layer 40, the greater the degree of constraint. The above formula also shows that the thinner the intervening layer 40, the greater the degree of constraint. Although the relationship between the degree of constraint of the intervening layer 40 and the sound generated by the piezoelectric film 35 needs further study, if the degree of constraint is excessively large, it is possible that the deformation of the piezoelectric film 35 necessary to generate low-frequency sound is hindered. Conversely, if the degree of constraint is excessively small, the piezoelectric film 35 does not deform sufficiently in its thickness direction, and expands and contracts only in its in-plane direction (direction perpendicular to the thickness direction), which may prevent the generation of low-frequency sound. By setting the degree of constraint of the intervening layer 40 within an appropriate range, the expansion and contraction of the piezoelectric film 35 in the in-plane direction is appropriately converted into deformation in the thickness direction, causing the piezoelectric film 35 to bend appropriately as a whole, making it easier to generate low-frequency sounds.

[0052] The support 80 may have a greater degree of constraint than the intermediate layer 40. Even in this case, low-frequency sound may be generated from the piezoelectric film 35 due to the contribution of the intermediate layer 40. However, the support 80 may have the same degree of constraint as the intermediate layer 40, or may have a smaller degree of constraint than the intermediate layer 40. Here, the degree of constraint (N / m 3 ) is a support 80 Elastic modulus (N / m 2 ) and the surface filling rate of the support 80, and divide the product by the thickness (m) of the support 80 The surface filling rate of the support 80 is the filling rate (a value obtained by subtracting the porosity from 1) of the main surface of the support 80 on the piezoelectric film 35 side.

[0053] In this embodiment, fixing surface 17 is arranged so that at least a portion of piezoelectric film 35 overlaps fixing surface 17 (overlapping with first adhesive layer 51 in the example of FIG. 1 ) when piezoelectric film 35 is observed in a plan view. From the perspective of stably fixing piezoelectric speaker 10 to support body 80, fixing surface 17 can be arranged to occupy 50% or more of the area of ​​piezoelectric film 35 when piezoelectric film 35 is observed in a plan view. Fixing surface 17 may also be arranged to occupy 75% or more of the area of ​​piezoelectric film 35, or may be arranged to occupy the entire area of ​​piezoelectric film 35 when piezoelectric film 35 is observed in a plan view.

[0054] In this embodiment, adjacent layers present between the piezoelectric film 35 and the fixing surface 17 are bonded together. Here, "between the piezoelectric film 35 and the fixing surface 17" includes the piezoelectric film 35 and the fixing surface 17. Specifically, the first adhesive layer 51 and the intervening layer 40 are bonded together, the intervening layer 40 and the second adhesive layer 52 are bonded together, and the second adhesive layer 52 and the piezoelectric film 35 are bonded together. This allows the piezoelectric film 35 to be stably positioned regardless of the mounting position on the support 80, and also makes it easy to mount the piezoelectric film 35 to the support 80. Furthermore, thanks to the contribution of the intervening layer 40, sound is emitted from the piezoelectric film 35 regardless of the mounting position. Therefore, in this embodiment, these features work together to realize a user-friendly piezoelectric speaker. Note that "adjacent layers are bonded together" means that the adjacent layers are fully or partially bonded together. In the illustrated example, adjacent layers are joined in a predetermined region that extends along the thickness direction of the piezoelectric film 35 and passes through the piezoelectric film 35, the intervening layer 40, and the fixing surface 17 in this order.

[0055] In this embodiment, the piezoelectric film 35 and the intervening layer 40 each have a substantially constant thickness. This is often advantageous from various perspectives, such as storage of the piezoelectric speaker 10, ease of use, and control of the sound emitted from the piezoelectric film 35. Note that "substantially constant thickness" refers to, for example, a minimum thickness value that is 70% or more and 100% or less of the maximum thickness. The piezoelectric film 35 and the intervening layer 40 each may have a minimum thickness value that is 85% or more and 100% or less of the maximum thickness.

[0056] In this embodiment, the piezoelectric film 35 and the film holding portion 55 each have a substantially constant thickness. The minimum thickness of the piezoelectric film 35 and the film holding portion 55 may be 85% or more and 100% or less of the maximum thickness.

[0057] Resin is a material that is less susceptible to cracking than ceramics and the like. In one specific example, the piezoelectric body 30 of the piezoelectric film 35 is a resin film, and the intervening layer 40 is a resin layer that does not function as a piezoelectric film. This is advantageous from the perspective of cutting the piezoelectric speaker 10 with scissors, by hand, or the like without causing cracks in the piezoelectric body 30 or the intervening layer 40 (the fact that the piezoelectric speaker 10 can be cut with scissors, by hand, or the like contributes to improving the design flexibility of the noise reduction system 500 and also makes it easier to construct the noise reduction system 500). This also makes it less likely that cracks will occur in the piezoelectric body 30 or the intervening layer 40 even when the piezoelectric speaker 10 is bent. Furthermore, having the piezoelectric body 30 be a resin film and the intervening layer 40 be a resin layer is advantageous from the perspective of fixing the piezoelectric speaker 10 to a curved surface without causing cracks in the piezoelectric body 30 or the intervening layer 40.

[0058] In the example of FIG. 1, the piezoelectric film 35, the intervening layer 40, the first adhesive layer 51, and the second adhesive layer 52 have an undivided, unframed plate-like shape, and their outlines coincide in a plan view. Some or all of these may have a frame shape, some or all of these may be divided into multiple parts, or their outlines may be misaligned.

[0059] 1, the piezoelectric film 35, the interposing layer 40, the first adhesive layer 51, and the second adhesive layer 52 are rectangular in shape having a short side direction and a long side direction in a plan view, but may also be square, circular, elliptical, or the like.

[0060] Furthermore, the piezoelectric speaker may include layers other than those shown in FIG.

[0061] Needless to say, the film holding portion 55 can be explained as including a layer that can be used as the intervening layer 40. This also applies to the second embodiment described below. For example, the film holding portion 55 can be explained as including a resin layer that does not function as the piezoelectric film 35. The film holding portion 55 can be explained as including a porous layer. The film holding portion 55 can be explained as including an ethylene propylene rubber foam layer.

[0062] Similarly, film holding portion 55 can be described as including a layer that can be employed as first adhesive layer 51. Film holding portion 55 can be described as including a layer that can be employed as second adhesive layer 52. For example, film holding portion 55 can be described as including an adhesive layer or a bonding layer.

[0063] [Second embodiment] A piezoelectric speaker 110 according to the second embodiment will be described below with reference to Fig. 4. In the following, descriptions of parts that are the same as those in the first embodiment may be omitted.

[0064] The piezoelectric speaker 110 includes a piezoelectric film 35, a fixing surface 117, and a film holding portion 155. The fixing surface 117 can be used to fix the piezoelectric film 35 to a support.

[0065] The film holding portion 155 is disposed between the piezoelectric film 35 and the fixing surface 117 (here, "between" includes the fixing surface 117; the same applies to the first embodiment). In the example of FIG. 4, the film holding portion 155 is formed by the intervening layer 140. The fixing surface 117 is formed by the surface (main surface) of the intervening layer 140.

[0066] The intervening layer 140 is a porous layer and / or a resin layer. The intervening layer 140 is an adhesive layer or a bonding layer. An adhesive containing an acrylic resin can be used as the intervening layer 140. Other adhesives, such as adhesives containing rubber, silicone, or urethane, may also be used as the intervening layer 140. The intervening layer 140 may also be a blend layer of two or more materials.

[0067] The modulus of elasticity of the intermediate layer 140 is, for example, 10,000 N / m 2 ~20,000,000N / m 2 and 20000N / m 2 ~100,000N / m 2 may be.

[0068] The thickness of the intervening layer 140 in the uncompressed state is, for example, in the range of 0.1 mm to 30 mm, or may be in the range of 1 mm to 30 mm, or may be in the range of 1.5 mm to 30 mm, or may be in the range of 2 mm to 25 mm. Typically, in the uncompressed state, the intervening layer 140 is thicker than the piezoelectric film 35. In the uncompressed state, the ratio of the thickness of the intervening layer 140 to the thickness of the piezoelectric film 35 is, for example, 3 times or more, or may be 10 times or more, or may be 30 times or more.

[0069] In this embodiment, 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 degree of constraint of the intermediate layer 140 is preferably 5×10 8 N / m 3 More preferably, it is 2×10 or less. 8 N / m 3 and Preferably 1 x 10 5 ~5×10 7 N / m 3 The definition of the constraint is as explained above. be.

[0070] In this embodiment, the adhesive or sticky surface comes into contact with the piezoelectric film 35, thereby integrating the piezoelectric film 35 with the layer on the fixing surface 117 side. Specifically, in this embodiment, the adhesive or sticky surface is a surface formed by the intervening layer 140.

[0071] The piezoelectric speaker 110 can also be fixed to the support 80 in Fig. 3 by the fixing surface 117. In this manner, a sound-canceling system 500 using the piezoelectric speaker 110 can be configured.

[0072] In the sound absorbing system 500, (i) the film holding portion 155 includes an adhesive layer and the fixing surface 117 is formed by the surface of the adhesive layer, and / or (ii) the film holding portion 155 includes a porous layer.

[0073] Such a sound-deadening system 500 is suitable for effectively emitting sound waves for sound mitigation from the piezoelectric film 35 . [Example]

[0074] The present invention will be described in detail with reference to examples, but the following examples are merely examples of the present invention and are not intended to limit the scope of the present invention.

[0075] Example 1 The structure shown in FIG. 5 was fabricated by attaching the fixing surface 17 of the piezoelectric speaker 10 to the fixed support member 680. Specifically, a 5 mm-thick stainless steel plate (SUS plate) was used as the support member 680. A 0.16 mm-thick adhesive sheet (double-sided tape) was used as the first adhesive layer 51, in which both sides of a nonwoven fabric were impregnated with an acrylic adhesive. A 3 mm-thick closed-cell foam was used as the intervening layer 40, in which a mixture containing ethylene propylene rubber and butyl rubber was foamed at an expansion ratio of approximately 10 times. A 0.15 mm-thick adhesive sheet (double-sided tape) was used as the second adhesive layer 52, in which a nonwoven fabric substrate was coated on both sides with an adhesive containing a solventless acrylic resin. A polyvinylidene fluoride film (total thickness 33 μm) with copper electrodes (containing nickel) vapor-deposited on both sides was used as the piezoelectric film 35. The first adhesive layer 51, interposition layer 40, second adhesive layer 52, and piezoelectric film 35 of Example 1 each have dimensions of 37.5 mm long x 37.5 mm wide in a plan view, and have an undivided, unframed, plate-like shape with overlapping contours in a plan view (the same applies to the examples and reference examples described below). The support member 680 has dimensions of 50 mm long x 50 mm wide in a plan view, and entirely covers the first adhesive layer 51. In this way, a sample of Example 1 having the configuration shown in FIG. 5 was produced.

[0076] Example 2 A 3 mm thick semi-closed, semi-open-cell foam was used as the intermediate layer 40. The foam was made by foaming a mixture containing ethylene propylene rubber at an expansion ratio of approximately 10. This foam contained sulfur. A sample of Example 2 was produced in the same manner as Example 1 except for the above.

[0077] Example 3 In Example 3, a foam having a thickness of 5 mm and made of the same material and structure as the intermediate layer 40 of Example 2 was used as the intermediate layer 40. Otherwise, the sample of Example 3 was produced in the same manner as Example 2.

[0078] Example 4 In Example 4, the intermediate layer 40 is made of the same material and has the same structure as the intermediate layer 40 in Example 2. A foam having a thickness of 10 mm was used. Except for this, a sample of Example 4 was produced in the same manner as in Example 2.

[0079] Example 5 In Example 5, a foam having a thickness of 20 mm and made of the same material and structure as the intermediate layer 40 of Example 2 was used as the intermediate layer 40. Otherwise, the sample of Example 5 was produced in the same manner as Example 2.

[0080] Example 6 A 20 mm thick semi-closed, semi-open cell foam was used as the intermediate layer 40, which was made by foaming a mixture containing ethylene propylene rubber at an expansion ratio of approximately 10. This foam did not contain sulfur and was more flexible than the foams used as the intermediate layer 40 in Examples 2 to 5. A sample of Example 6 was otherwise produced in the same manner as Example 1.

[0081] Example 7 A 20 mm thick semi-closed, semi-open cell foam obtained by foaming a mixture containing ethylene propylene rubber at an expansion ratio of approximately 20 was used as the intermediate layer 40. A sample of Example 7 was produced in the same manner as Example 1 except for the above.

[0082] Example 8 A metal porous body was used as the intermediate layer 40. This metal porous body was made of nickel, had a pore diameter of 0.9 mm, and was 2.0 mm thick. The same adhesive layer as the first adhesive layer 51 of Example 1 was used as the second adhesive layer 52. Otherwise, a sample of Example 8 was produced in the same manner as Example 1.

[0083] Example 9 The first adhesive layer 51 and the second adhesive layer 52 of Example 1 were omitted, and only the intervening layer 140 was interposed between the piezoelectric film 35 and the support 80. A substrate-less adhesive sheet made of an acrylic adhesive and having a thickness of 3 mm was used as the intervening layer 140. Otherwise, a sample of Example 9 was produced in the same manner as Example 1, having a configuration in which the laminate of FIG. 5 was attached to the support member 680 of FIG. 4.

[0084] Example 10 The same intermediate layer as the intermediate layer 140 of Example 9 was used as the intermediate layer 40. Otherwise, the sample of Example 10 was produced in the same manner as Example 8.

[0085] Example 11 A 5 mm thick urethane foam was used as the intermediate layer 40. A sample of Example 11 was produced in the same manner as Example 8 except for the above.

[0086] Example 12 A 10 mm thick urethane foam was used as the intermediate layer 40. This urethane foam had a smaller pore size than the urethane foam used as the intermediate layer 40 in Example 11. Otherwise, the sample of Example 12 was produced in the same manner as in Example 8.

[0087] Example 13 A closed-cell acrylonitrile butadiene rubber foam having a thickness of 5 mm was used as the intermediate layer 40. A sample of Example 13 was produced in the same manner as Example 8 except for the above.

[0088] Example 14 A closed-cell ethylene propylene rubber foam having a thickness of 5 mm was used as the intermediate layer 40. A sample of Example 14 was produced in the same manner as Example 8 except for the above.

[0089] Example 15 A 5 mm thick closed-cell foam made of a blend of natural rubber and styrene-butadiene rubber was used as the intermediate layer 40. A sample of Example 15 was produced in the same manner as Example 8 except for the above.

[0090] Example 16 A closed-cell silicone foam with a thickness of 5 mm was used as the intermediate layer 40. A sample of Example 16 was produced in the same manner as Example 8 except for the above.

[0091] Example 17 The intervening layer 40 was a 10 mm thick foam made of the same material and structure as the intervening layer 40 of Example 1. The second adhesive layer 52 was the same adhesive sheet as in Example 1. The piezoelectric element 30 of the piezoelectric film 35 was a 35 μm thick resin sheet made primarily of corn-derived polylactic acid. The first electrode 61 and the second electrode 62 of the piezoelectric film 35 were each 0.1 μm thick aluminum films formed by vapor deposition. In this way, a piezoelectric film 35 with a total thickness of 35.2 μm was obtained. Otherwise, a sample of Example 17 was produced in the same manner as Example 1.

[0092] (Reference example 1) The piezoelectric film 35 of Example 1 was used as the sample of Reference Example 1. In Reference Example 1, the sample was placed without adhesive on a table parallel to the ground.

[0093] The samples according to the examples and reference examples were evaluated as follows.

[0094] <Thickness of intervening layer (uncompressed state)> The thickness of the intervening layer was measured using a thickness gauge.

[0095] <Elastic modulus of intervening layer> Small pieces were cut out from the interposing layer. A compression test was performed on the cut pieces at room temperature using a tensile tester (TA Instruments "RSA-G2"), thereby obtaining a stress-strain curve. The elastic modulus was calculated from the initial slope of the stress-strain curve.

[0096] <Pore diameter of intervening layer> A magnified image of the intervening layer was obtained using a microscope. The magnified image was analyzed to determine the average pore size of the intervening layer. The average value thus determined was taken as the pore size of the intervening layer.

[0097] <Porosity of the intervening layer> A small rectangular piece was cut out from the intervening layer. The apparent density was calculated from the volume and mass of the cut piece. The apparent density was divided by the density of the base material (solid body) forming the intervening layer. This gave the packing ratio. The packing ratio was then subtracted from 1. This gave the porosity.

[0098] <Surface filling rate of the intervening layer> The above-mentioned filling rate was taken as the surface filling rate for Examples 2 to 16. In Examples 1 and 17, the intervening layer had a surface skin layer, so the surface filling rate was taken as 100%.

[0099] <Sample sound pressure level frequency characteristics> The setup for measuring the samples of Examples 1 to 8 and 10 to 17 is shown in Figure 6. Conductive copper foil tape 70 (CU-35C manufactured by 3M) with a thickness of 70 µm and dimensions of 5 mm length x 70 mm width was attached to the corners of both sides of piezoelectric film 35. In addition, a bagworm clip 75 was attached to each of these conductive copper foil tapes 70. The conductive copper foil tape 70 and bagworm clip 75 form part of the electrical path for applying an AC voltage to piezoelectric film 35.

[0100] The configuration for measuring the sample of Example 9 is shown in Figure 7. The configuration in Figure 7 does not have the first adhesive layer 51 and the second adhesive layer 52 in Figure 6. The configuration in Figure 7 has an intervening layer 140.

[0101] The setup for measuring the sample of Reference Example 1 was similar to that shown in Figures 6 and 7. Specifically, conductive copper foil tape 70 was attached to the corners on both sides of the piezoelectric film 35, and bagworm clips 75 were attached to these tapes 70, similar to Figures 6 and 7. The assembly thus obtained was placed, without adhesive, on a table parallel to the ground.

[0102] 8 and 9 show block diagrams for measuring the acoustic characteristics of a sample. Specifically, Fig. 8 shows the output system, and Fig. 9 shows the evaluation system.

[0103] 8, an audio output personal computer (hereinafter, the personal computer may be simply referred to as a PC) 401, an audio interface 402, a speaker amplifier 403, and a sample 404 (a piezoelectric speaker of the examples and reference examples) were connected in this order. The speaker amplifier 403 was also connected to an oscilloscope 405 so that the output from the speaker amplifier 403 to the sample 404 could be confirmed.

[0104] WaveGene was installed on the audio output PC 401. WaveGene is free software for generating test audio signals. A QUAD-CAPTURE manufactured by Roland Corporation was used as the audio interface 402. The sampling frequency of the audio interface 402 was 192 kHz. An A-924 manufactured by Onkyo Corporation was used as the speaker amplifier 403. A DPO2024 manufactured by Tektronix was used as the oscilloscope 405.

[0105] In the evaluation system shown in FIG. 9, a microphone 501, an acoustic evaluation device (PULSE) 502, and an acoustic evaluation PC 503 were connected in this order.

[0106] A Type 4939-C-002 manufactured by B&K was used as the microphone 501. The microphone 501 was placed at a position 1 m away from the sample 404. A Type 3052-A-030 manufactured by B&K was used as the acoustic evaluation device 502.

[0107] With the output system and evaluation system configured as described above, an AC voltage was applied from the audio output PC 401 to the sample 404 via the audio interface 402 and the speaker amplifier 403. Specifically, a test audio signal whose frequency swept from 100 Hz to 100 kHz over 20 seconds was generated using the audio output PC 401. At this time, the voltage output from the speaker amplifier 403 was confirmed using an oscilloscope 405. The sound generated from the sample 404 was also evaluated using the evaluation system. In this manner, a sound pressure frequency characteristic measurement test was performed.

[0108] The details of the settings for the output system and evaluation system are as follows.

[0109] [Output system settings] Frequency range: 100Hz~100kHz Sweep time: 20 seconds Effective voltage: 10V Output waveform: Sine wave

[0110] [Evaluation system settings] Measurement time: 22 seconds Peak hold Measurement range: 4Hz to 102.4kHz Number of lines: 6400

[0111] <Determining the frequency at which sound begins to be produced> The lower end of the frequency range where the sound pressure level is 3 dB or more higher than the background noise (excluding the steep peak area where the frequency range where the sound pressure level is maintained at 3 dB or more above the background noise is less than ±10% of the peak frequency (the frequency at which the sound pressure level peaks)) was determined to be the frequency at which sound begins to be heard.

[0112] The evaluation results of Examples 1 to 17 and Reference Example 1 are shown in Figures 10A to 29. The frequency characteristics of the sound pressure level of background noise are shown in Figure 30. In Figure 11, E1 to E17 correspond to Examples 1 to 17.

[0113] [Support structure of piezoelectric film and degree of freedom of vibration] 5, an example of a support structure for a piezoelectric speaker according to the present invention will be described. In the piezoelectric speaker 10, the entire surface of the piezoelectric film 35 is fixed to a support (support structure) 680 via adhesive layers 51 and 52 and an intervening layer 40.

[0114] In order to prevent the vibration of the piezoelectric film 35 from being hindered by the support 680, it is possible to support a portion of the piezoelectric film 35 and space it apart from the support 680. An example of a support structure based on this design concept is shown in Figure 31. In the imaginary piezoelectric speaker 108 shown in Figure 31, the frame 88 supports the peripheral portion of the piezoelectric film 35 at a position away from the support 680.

[0115] It is easy to ensure sufficient volume from a piezoelectric film that has been pre-bent to one side and has a fixed direction of curvature. For this reason, for example, in piezoelectric speaker 108, it is conceivable to place an inclusion with a convex upper surface and variable thickness in space 48 surrounded by piezoelectric film 35, frame 88, and support 680, thereby pushing up the center of piezoelectric film 35. However, such an inclusion would not be bonded to piezoelectric film 35 so as not to inhibit the vibration of piezoelectric film 35. Therefore, even if an inclusion is placed in space 48, only frame 88 supports piezoelectric film 35 in a manner that regulates its vibration.

[0116] As described above, the piezoelectric speaker 108 shown in FIG. 31 employs a localized support structure for the piezoelectric film 35. In contrast, as shown in FIG. 5, the piezoelectric speaker 10 does not support the piezoelectric film 35 at specific locations. Surprisingly, the piezoelectric speaker 10 exhibits practical acoustic characteristics, even though the entire surface of the piezoelectric film 35 is fixed to the support 80. Specifically, in the piezoelectric speaker 10, even the peripheral edge of the piezoelectric film 35 can vibrate up and down. The entire piezoelectric film 35 can also vibrate up and down. Therefore, compared to the piezoelectric speaker 108, the piezoelectric speaker 10 has a higher degree of vibration freedom and is relatively advantageous for achieving good sound generation characteristics.

Claims

[Claim 1] 1. A noise reduction system comprising: at least one noise reduction speaker for emitting noise reduction sound waves; at least one microphone; and a control device, the at least one muffled speaker includes a piezoelectric speaker; the piezoelectric speaker includes a piezoelectric film, a fixing surface in contact with a support that supports the piezoelectric speaker, and a film holding portion disposed between the piezoelectric film and the fixing surface in a thickness direction of the piezoelectric film; the piezoelectric speaker is configured such that the piezoelectric film expands in a planar shape when the piezoelectric speaker is fixed alone on a flat surface, the fixing surface is disposed so that at least a portion of the piezoelectric film overlaps with the fixing surface when the piezoelectric film is observed in a plan view; (i) the film holding portion includes a first adhesive layer, and the fixing surface is formed by a surface of the first adhesive layer, and / or (ii) the film holding portion includes a porous layer, The control device cooperates with the at least one microphone to control the sound waves emitted from the piezoelectric speaker, thereby eliminating noise.

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