Transducer and transducer array

Abstract

This transducer performs electro-acoustic conversion and comprises: a diaphragm that can vibrate in a plate thickness direction; a driver that causes the diaphragm to vibrate by electrical energy; and a first lid body that covers the diaphragm. The first lid body has formed therein a through hole that allows sound waves from the diaphragm, which is a surface sound source, to be emitted to the outside as a point or line sound source by causing an internal space formed between the first lid body and the diaphragm to communicate with the outside. By forming a plurality of through holes, the sound waves from the point or line sound source are combined, and the widths and depths of the plurality of through holes are set such that, of maximum values of the volume of air blown out from or sucked into an internal space which are obtained on the basis of the vibration amplitude and the vibration frequency of the diaphragm, the maximum volume of air in terms of the vibration frequency can pass through the through holes.

Description

Transducers and Transducer Arrays

[0001] The present disclosure relates to transducers and transducer arrays.

[0002] As a transducer for electroacoustic conversion, a MEMS (Micro Electro Mechanical Systems) speaker has many advantages such as power saving, and has been widely used in earphones and the like in recent years (see Patent Documents 1 and 2).

[0003] JP 2021-44762 A JP 2021-52305 A

[0004] [Summary] However, small speakers such as MEMS speakers have a problem in that they have a low output sound pressure level due to their small size.

[0005] An object of the present disclosure is to provide a transducer and a transducer array that can increase the output sound pressure level.

[0006] In order to solve the above-mentioned problems, one aspect of the present disclosure is a transducer that performs electro-acoustic conversion, comprising a diaphragm that can vibrate in the plate thickness direction, a driver that vibrates the diaphragm using electric energy, and a first lid that covers the diaphragm. The first lid has through-holes that communicate an internal space formed between the first lid and the diaphragm with the outside, thereby emitting sound waves from the diaphragm, which is a surface sound source, to the outside as a point or line sound source. By forming multiple through-holes, sound waves from the point or line sound sources are combined, and the widths and depths of the multiple through-holes are set so that a maximum volume of air can pass through at the vibration frequency, relative to the maximum volume of air pushed out or sucked into the internal space that is determined based on the vibration amplitude and vibration frequency of the diaphragm.

[0007] FIG. 1 is a front view of a transducer according to a first embodiment. FIG. 2 is a cross-sectional view taken along the cutting line II-II in FIG. 1. FIG. 3 is a front view of a transducer according to a second embodiment. FIG. 4 is a cross-sectional view taken along the cutting line IV-IV in FIG. 3. FIG. 5 is a front view of a transducer according to a third embodiment. FIG. 6 is a cross-sectional view taken along the cutting line VI-VI in FIG. 5. FIG. 7 is a cross-sectional view schematically showing the structure of a transducer according to a fourth embodiment. FIG. 8 is a schematic front view of a transducer array according to a fifth embodiment.

[0008] [Detailed Description] Next, embodiments will be described with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and planar dimensions of each component may differ from the actual relationship. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings may include parts with different dimensional relationships and ratios.

[0009] Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical ideas, and do not specify the materials, shapes, structures, arrangements, etc. of each component part. Various modifications can be made to the embodiments within the scope of the claims.

[0010] (First embodiment) Fig. 1 is a front view of a transducer 1 according to a first embodiment, and Fig. 2 is a cross-sectional view schematically showing the structure of the transducer 1 of Fig. 1. Fig. 2 is a cross-sectional view taken along the cutting line II-II of Fig. 1. The transducer 1 according to this embodiment performs electro-acoustic conversion by vibrating a diaphragm 2a with electrical energy using a driver such as a piezoelectric element 3. The transducer 1 is realized (commercialized) as a speaker, earphones, or the like.

[0011] The transducer 1 comprises a vibration plate 2a capable of vibrating in the thickness direction, a piezoelectric element 3 formed on a first surface 2a1 of the vibration plate 2a, and a first cover 4 covering the vibration plate 2a.

[0012] The piezoelectric element 3 includes a piezoelectric film 3a and a pair of electrodes 3b, 3c formed on the front and back of the piezoelectric film 3a. The piezoelectric film 3a is made of ceramics formed by depositing PZT (lead zirconate titanate) using a sol-gel method, sputtering, or other methods. Other materials that can be used for the piezoelectric film 3a include aluminum nitride (AlN), zinc oxide (ZnO), and lead titanate (PbTiO3). Each of the pair of electrodes 3b, 3c is formed using a thin film of a conductive metal such as platinum, molybdenum, iridium, or titanium. The piezoelectric element 3 can be formed by depositing the electrode 3b, piezoelectric film 3a, and electrode 3c on the diaphragm 2a and then patterning them into a desired planar shape.

[0013] When a voltage is applied between the electrodes 3b and 3c, the piezoelectric film 3a contracts in the plane direction of the piezoelectric film 3a. Due to the contraction of the piezoelectric film 3a, the diaphragm 2a receives stress in the plane direction and vibrates in the thickness direction. The vibration of the diaphragm 2a becomes a vibration of the air, and the transducer 1 can perform electro-acoustic conversion. Such a transducer 1 can be used to form a MEMS speaker.

[0014] In this embodiment, the piezoelectric element 3 is formed in a circular plate shape when viewed from the vibration direction of the diaphragm 2a, and the diaphragm 2a is a circular diaphragm type diaphragm. The piezoelectric element 3 is mounted on a first surface 2a1 of the diaphragm 2a.

[0015] The transducer 1 has a vibrating unit 2. The diaphragm 2a is a part of the vibrating unit 2. The vibrating unit 2 further includes a plate support 2b that supports the diaphragm 2a. The plate support 2b is formed in a cylindrical shape, with the diaphragm 2a attached to one end and the other end open. An open space is formed inside the plate support 2b on the other end side of the plate support 2b. The vibrating unit 2 can be formed from a semiconductor substrate such as silicon. For example, the diaphragm 2a and the plate support 2b can be integrally formed by etching the silicon substrate from the side opposite the first surface 2a1 of the diaphragm 2a. The provision of the plate support 2b enables the diaphragm 2a to vibrate in the thickness direction. A MEMS speaker in which the diaphragm 2a is a circular diaphragm-type diaphragm that can be displaced in the thickness direction is highly versatile, can be manufactured at low cost, and can be made strong, making it suitable for MEMS speakers.

[0016] The second surface 2a2 of the diaphragm 2a, which faces the first surface 2a1, emits sound waves that are out of phase with the sound waves emitted from the first surface 2a1. The out-of-phase sound waves may be absorbed by a sound-absorbing material or reflected back toward the first surface 2a1 by a reflecting material so that they are in phase with the sound waves emitted from the first surface 2a1. Alternatively, the emission of out-of-phase sound waves may be suppressed by preventing sound extracted from an opening formed in the mounting substrate of the transducer 1 (not shown) from leaking to the back side of the mounting substrate in a sealed space. The mounting substrate may be, for example, a printed circuit board such as a printed wiring board (PWB) or a printed circuit board (PCB). Wiring to the electrodes 3b and 3c is routed on the mounting substrate, and a drive circuit (not shown) that applies voltage to the electrodes 3b and 3c via the wiring is also mounted on the mounting substrate.

[0017] The first lid 4 covers the diaphragm 2a. The first lid 4 has a plurality of (seven in FIG. 1 ) through-holes 50, 51, 52, 53, 54, 55, and 56 (hereinafter collectively referred to as through-holes 5). The first lid 4 has a plate-shaped first lid portion 4a and a first cylindrical portion 4b connecting an outer edge 4a1 of the first lid portion 4a to an outer edge 2a3 of the diaphragm 2a. In this embodiment, the through-holes 5 are formed in the first lid portion 4a. The first lid 4 may be formed by stacking silicon thin plates with through-holes 5 formed therein, or by forming through-holes 5 in a resin plate such as polycarbonate or a metal plate.

[0018] An internal space 6 is formed between the first cover 4 and the diaphragm 2a, and the internal space 6 is connected to the outside via the through-hole 5. Meanwhile, the through-hole 5 is formed to have a predetermined smaller area than the area of ​​the diaphragm 2a when viewed from the vibration direction of the diaphragm 2a. This allows the through-hole 5 to emit sound waves from the diaphragm 2a, which is a surface sound source, to the outside as sound waves from a point sound source. In other words, instead of the diaphragm 2a, which is a surface sound source, the through-hole 5 becomes a new point sound source, which re-radiates the sound waves. Therefore, in the transducer 1 of this embodiment, the through-hole 5 can be considered as a minute point speaker.

[0019] By providing multiple through holes 5, the transducer 1 of this embodiment has a single diaphragm 2a, but is equipped with multiple point sound sources, and serves as a speaker with a microarray structure that can combine sound waves radiated from the multiple point sound sources. This allows the transducer 1 of this embodiment to increase its directivity and output sound pressure level. In other words, the transducer 1 of this embodiment can cause sound waves to travel as plane waves with a certain width without being carelessly diffused.

[0020] Here, the through-holes 5, which serve as the point sound source, will be described in detail. If the opening area of ​​the through-holes 5 as viewed in the vibration direction of the diaphragm 2a is small, or if the number of through-holes 5 is small, and the total area of ​​the through-holes 5, i.e., the above-mentioned predetermined small area, is small, the air in the internal space 6 is not completely pushed out or sucked in during half a cycle of the vibration of the diaphragm 2a. As a result, the first cover 4 functions as a damper (a buffer device). In other words, the volume of air corresponding to the stroke of the diaphragm 2a moving at one time is compressed or expanded at the speed (frequency) of the diaphragm 2a moving. It is desirable that the through-holes 5 have a diameter and depth sufficient to allow the flow of air with the outside to alleviate the pressure difference with the outside caused by the compression or expansion within a predetermined time, i.e., within the speed (frequency) of the diaphragm 2a moving.

[0021] Conversely, if the opening area of ​​the through holes 5 is large, or if there are many of them and the total area of ​​the through holes 5 is large, the through holes 5 simply pass through the sound from the diaphragm 2a, which is a surface sound source, and the through holes 5 are less effective as point sound sources. An example of such a case is a mesh-like speaker cover for dust prevention or protection. Furthermore, the thicker the first lid 4, the more effective it is at shielding the internal space 6 from the outside, and the more effective the through holes 5 are as point sound sources. However, if the first lid 4 is thick, the depth d of the through holes 5 becomes deep, so that the air that should be pushed out or sucked in does not completely escape and instead remains in the through holes 5, causing the through holes 5 to act as orifices (restrictions). In other words, the flow resistance of the through holes 5 increases, and as a result, the through holes 5 restrict the movement of the diaphragm 2a.

[0022] Therefore, in this embodiment, the diameter and depth of each of the plurality of through-holes 50-56 are set so that the maximum volume of air can pass through in a half cycle of the vibration frequency at which the maximum volume of air is pushed out or sucked into the internal space 6, which is determined based on the vibration amplitude and vibration frequency of the diaphragm 2a. Specifically, the parameters are the viscosity of the filler (air), the area of ​​the piston (diaphragm 2a), the speed of the piston (diaphragm 2a) (frequency and volume of the sound wave), and the size (diameter, number, and hole depth) of the orifice (through-hole 5).

[0023] To satisfy the above conditions, three or more through holes 5 may be formed at equal intervals in the first lid portion 4a of the first lid body 4. In the example shown in FIG. 1, the number of through holes 5 is seven, including through hole 50 located at the center of the circular diaphragm-type diaphragm 2a and through holes 51-56 located on the outer periphery of the diaphragm 2a. The through holes 50-56 are arranged at equal intervals r. In the example shown in FIG. 1, two circumferentially adjacent through holes 50 and 51-56 are arranged at the vertices of an equilateral triangle. Therefore, the through holes 51-56 on the outer periphery are arranged at equal angles θ=60° in the circumferential direction around through hole 50. In the example shown in FIG. 1, each through hole 5 is shown as a circular hole, but it may also be a polygonal hole. Furthermore, the through holes 5 may be arranged in a matrix rather than at the vertices of an equilateral triangle.

[0024] Generally, sound waves from a point sound source spread out spherically, but by arranging three or more through holes 5 at equal intervals r in the first lid portion 4a as described above, the sound waves can be propagated in a manner similar to a plane wave. Therefore, within the propagation width of the plane wave, the sound can be heard in the same way even if it is shifted from the front of the transducer 1, and unnecessary sound leakage can be prevented outside the propagation width of the plane wave.

[0025] The width of the through hole 5 is determined taking into consideration the depth d of the through hole 5. The depth d of the through hole 5 is determined by the thickness of the first lid portion 4a. As an example, if the thickness of the first lid portion 4a is about 250 μm, which is sufficient in terms of strength, and the width of the through hole 5 is 20 μm or more, it becomes possible to extract sound waves from the internal space 6, and the through hole 5 can function as a point sound source as described above. When the through hole 5 is a round hole as shown in FIG. 1 , the width refers to the diameter φ.

[0026] On the other hand, if the diameter φ of the through-hole 5 is too small, a damping effect occurs in which the through-hole 5 acts as a brake to restrict the movement of the diaphragm 2a. Therefore, in order to prevent this damping effect from occurring, the diameter φ of the through-hole 5 should be set to the above-mentioned 20 μm or more, for example, 50 μm. With a diameter of about 50 μm, the damping effect is not generated and the effect as a point sound source can be exhibited.

[0027] Since the deflection of the circular diaphragm diaphragm 2a is greater closer to the center, the volume of the internal space 6 can be calculated by dividing the diaphragm 2a into small compartments and integrating the volume of air pushed out or sucked in by each small compartment at maximum deflection across all compartments. The through-holes 5 may be tapered or widened outward (or widened in the case of round holes as described above). This provides a horn effect and improves the linearity of sound waves from a point sound source.

[0028] Second Embodiment Fig. 3 is a front view of a transducer 11 according to a second embodiment, and Fig. 4 is a cross-sectional view schematically showing the structure of the transducer 11 of Fig. 3. Fig. 4 is a cross-sectional view taken along the cutting line IV-IV in Fig. 3. In the transducer 11 according to this embodiment, the vibrating section 2 and the piezoelectric element 3 are the same as those in the transducer 1 shown in Figs. 1 and 2, but the structure of the first lid 14 that covers the diaphragm 2a is different.

[0029] The first lid 14 of this embodiment includes a first lid portion 14a and a first cylindrical portion 14b that connects an outer edge 14a1 of the first lid portion 14a to an outer edge 2a3 of the diaphragm 2a. The first lid 14 of this embodiment has a plurality of parallel slits (long holes) (three in FIGS. 3 and 4 ) formed therein as through-holes 15. Like the first lid 4, the first lid 14 may be formed by stacking thin silicon plates with through-holes 15 formed therein, or by forming through-holes 15 in a resin plate such as polycarbonate or a metal plate.

[0030] In a small transducer 11 such as a MEMS type, assuming that the air pressure inside the first cover 14 is uniform, the slit (long hole) through-holes 15 form a line sound source, and the transducer 11 can achieve the same function as a line array speaker in which point sound sources are arranged linearly, i.e., one-dimensionally, without gaps. The length L of the through-holes (slits) 15 is, for example, λ / 4. In the case of a line sound source, the radiated sound usually diffuses cylindrically. However, as in the transducer 11 of this embodiment, the slits (through-holes 15) of the line sound source are arranged in parallel with each other at equal intervals W shorter than λ / 4, so that the radiated sound is combined and has high linearity.

[0031] (Third embodiment) Fig. 5 is a front view of a transducer 21 according to a third embodiment, and Fig. 6 is a cross-sectional view schematically showing the structure of the transducer 21 in Fig. 5. Fig. 6 is a cross-sectional view taken along the cutting line VI-VI in Fig. 5.

[0032] In the transducer 21 of this embodiment, the piezoelectric element 23 and the vibration plate 22a are formed in a rectangular shape when viewed from the vibration direction of the vibration plate 22a. The piezoelectric element 23 serving as a driver has a piezoelectric film 23a and a pair of electrodes 23b, 23c that sandwich the piezoelectric film 23a from the front and back, similar to the piezoelectric element 3 described above. The vibration section 22, like the vibration section 2, is formed by etching silicon or the like, and includes a thin vibration plate 22a and a plate support section 22b hanging down from the outer periphery thereof.

[0033] The first cover 24 includes a first cover portion 24a and a first cylindrical portion 24b that connects an outer edge 24a1 of the first cover portion 24a to an outer edge 22a3 of the vibration plate 22a. The first cover portion 24a is formed in a rectangular plate shape, and the first cylindrical portion 24b is formed in a square cylindrical shape, corresponding to the rectangular piezoelectric element 23 and vibration plate 22a. In the example shown in FIGS. 5 and 6 , the outer shapes of the first cover portion 24a and the first cylindrical portion 24b are square when viewed from the vibration direction of the vibration plate 22a. The inner periphery of the first cylindrical portion 24b is also square when viewed from the vibration direction of the vibration plate 22a.

[0034] The first cover 24 has through-holes 25 that penetrate the first cylindrical portion 24b in a direction perpendicular to the vibration direction of the diaphragm 22a. The through-holes 25 are elongated holes (slits), and the longitudinal direction of the through-holes 25 is aligned with the circumferential direction of the first cylindrical portion 24b. In the example shown in FIGS. 5 and 6 , the through-holes 25 are provided in pairs on two opposing wall surfaces 24c, 24d of the first cylindrical portion 24b. However, the through-holes 25 may be formed on one, three, or all of the wall surfaces of the first cylindrical portion 24b. The number, shape, depth d, and length L of the through-holes 25 may be determined appropriately depending on the maximum volume of air that can be pushed out or sucked in from the internal space 6.

[0035] Here, at a wavelength λ (17.2 mm) of 20 kHz, which is the upper limit of audible sound, λ / 4 is 4.3 mm. At a wavelength of 2 kHz, which is perceived as a somewhat high-pitched sound by the ear, λ / 4 is 10 times that, or 43 mm. On the other hand, in the case of a MEMS speaker, the height H of the first cover 24 forming the front chamber is extremely thin, ranging from several tens to 500 μm. Therefore, even if the through-hole 25, which serves as an entrance and exit for the air compressed or expanded by the diaphragm 22 a, is provided in the first cylindrical portion 24 b, which is the side surface of the first cover 24, the through-hole 25 can be considered a sound source. Furthermore, by forming the through-hole 25 as a long hole (slit), a line sound source can be constructed. Furthermore, by forming the through-hole 25 as a long hole (slit) in the circumferential direction of the rectangular cylindrical first cylindrical portion 24 b, a linear, long line sound source can be realized. A similar effect can be achieved by arranging multiple holes in a straight line instead of the through-hole 25.

[0036] On the other hand, consider a combination of a first cover 24 having a rectangular cylindrical first cylindrical portion 24b, which can realize the above-mentioned linear, long sound source, and a circular diaphragm 2a, such as the transducer shown in Figures 1 and 3, as the diaphragm 22a of this embodiment. In this case, a large amount of unnecessary space is created around the periphery 22c of the diaphragm 22a (especially the corners of the rectangular cylinder). The presence of such unnecessary space reduces the pressure change in the internal space 6 caused by the vibration of the diaphragm 22a. In other words, if the diaphragm 22a is considered a piston, many gaps will exist around its periphery, reducing the amount of air pushed out or sucked in by the through-holes 25.

[0037] Therefore, as in this embodiment, a rectangular diaphragm 22a is combined with a first cover 24 having a square-tubular first cylindrical portion 24b. This reduces unnecessary space generated at the peripheral portion 22a4 of the diaphragm 22a, thereby enhancing the effectiveness as a line sound source. Combining a circular diaphragm 2a shown in Figures 1 and 3 with a first cover 4, 14 having a cylindrical inner periphery also reduces unnecessary space, enhancing the effectiveness as a sound source or line sound source. Furthermore, by forming the through-hole 25 extending in the circumferential direction of the first cylindrical portion 24b, the above-mentioned linear, long line sound source can be realized.

[0038] The diaphragm 22a is not limited to a doubly supported type, but may also be a cantilever type. Furthermore, the circular diaphragm type diaphragm 2a may be a voice coil type speaker using a permanent magnet and a coil. Furthermore, instead of elongated holes (slits), the through holes 25 may be multiple circular or polygonal holes arranged along the circumferential direction of the first cylindrical portion 24b. This allows for multiple point sound sources arranged along the circumferential direction. By satisfying the same conditions as the through holes 5 described above, the multiple circular or polygonal holes can further enhance their effectiveness as point sound sources.

[0039] 7 is a cross-sectional view schematically showing the structure of a transducer 31 according to a fourth embodiment. The transducer 31 has a second cover 34 added to the transducer 1 shown in FIGS. 1 and 2. That is, the structure of the transducer 31 other than the second cover 34, specifically the structures of the vibration section 2, the piezoelectric element 3, and the first cover 4, are the same as those of the transducer 1.

[0040] The second lid 34 includes a second lid portion 34a and a second cylindrical portion 34b that connects an outer edge 34a1 of the second lid portion 34a to an outer edge 2a3 (plate support portion 2b) of the diaphragm 2a. Seven through holes 35 may be formed in the second lid portion 34a, similar to the through holes 5 in FIG. 1. The through holes 35 may be formed as slits (long holes), similar to the through holes 15 in FIG. 4. The second lid 34 may be formed by laminating thin silicon plates with through holes 35 formed therein, or by forming through holes 35 in a resin plate such as polycarbonate or a metal plate, similar to the first lids 4 and 14 in FIGS. 1 to 4.

[0041] No piezoelectric element 3 is provided on the second surface 2a2 of the diaphragm 2a. Therefore, the plate support portion 2b only needs to be formed to a height that can absorb the stroke (vibration) of the diaphragm 2a. The second lid 34, which is placed over the second surface 2a2 side of the diaphragm 2a, may also be formed with the second cylindrical portion 34b as low as possible. This allows the internal space 36 formed by the diaphragm 2a and the second lid 34 to be reduced, making it easier to extract pressure changes in the internal space 36 due to vibration of the diaphragm 2a through the through-hole 35. In other words, by reducing the internal space 36, the effectiveness of the through-hole 35 as a point sound source can be enhanced.

[0042] With this configuration, the transducer 31 can radiate sound waves from both sides of the diaphragm 2a as a point sound source or a line sound source. Therefore, the transducer 31 can radiate sound waves from one side of the diaphragm 2a by appropriately adjusting the phase and combining them with sound waves from the other side, thereby increasing the output sound pressure level. Alternatively, for example, sound waves from the first side 2a1 of the diaphragm 2a can be radiated forward through the first cover 4, and sound waves from the second side 2a2 can be radiated backward through the second cover 34 while being appropriately muted as necessary, thereby realizing earphones that prevent sound leakage to the surroundings. In this case, by forming a through hole 35 in the second cylindrical portion 34b of the second cover 34, sound waves of opposite phase can be radiated to the sides of the earphones. Furthermore, by forming a through hole 35 in the second lid portion 34a and also forming a through hole 25 in the second cylindrical portion 34b, it is possible to more accurately muffle sound around the earphone, i.e., prevent sound leakage.

[0043] The second cover 34 added to the transducer 31 may not have the effect of a point sound source as described above, but may function only as a damper to suppress unnecessary vibrations when the diaphragm 2a resonates.

[0044] Fifth Embodiment Fig. 8 is a schematic front view of a transducer array 10 according to a fifth embodiment. This transducer array 10 is configured by arranging a plurality of transducers 1 (5 x 5 in Fig. 8) shown in Figs. 1 and 2 in an array. The transducer array 10 may use the transducers 11 shown in Figs. 3 and 4.

[0045] As mentioned above, each transducer 1 has a plurality of through holes 5 that function as point sound sources, and the radiated sound waves are combined. This transducer array 10 further arranges a plurality of such transducers 1 in a line or plane (the 5 × 5 plane in the example of FIG. 8), thereby further improving the directivity and output sound pressure level.

[0046] In Japanese Patent No. 7171156, a cylindrical substrate is placed on the front surface (sound emission surface) of a MEMS speaker, and a baffle plate is placed on top of that. The publication then adjusts the resonant frequency of the cavity formed by these components to the set frequency of the MEMS speaker. Furthermore, the publication also devisees a design for the through-holes in the baffle plate to increase the output sound pressure level at the set frequency and adjust harmonic distortion.

[0047] However, in the conventional technology of this publication, the sound is emitted as it is from the surface sound source, which is different from the present embodiment.

[0048] The technical ideas that can be understood from the present disclosure are described in the following appendices. Note that, for the purpose of aiding understanding and not intending to be limiting, the components described in the appendices are given the reference numerals of the corresponding components in the embodiments. The reference numerals are shown as examples to aid understanding, and the components described in each appendix should not be limited to the components indicated by the reference numerals.

[0049] <Supplementary Note 1> The transducers 1, 11, 21, and 31 are transducers that perform electroacoustic conversion and include a diaphragm 2a (22a) that can vibrate in the thickness direction, a driver (3, 23) that vibrates the diaphragm 2a (22a) using electrical energy, and a first lid 4, 14, or 24 that covers the diaphragm 2a (22a). The first lid 4, 14, or 24 has through-holes 5, 15, or 25 that communicate an internal space 6 formed between the first lid 4, 14, or 24 and the diaphragm 2a (22a) with the outside, thereby emitting sound waves from the diaphragm 2a (22a), which is a surface sound source, to the outside as a point or line sound source. By forming a plurality of through-holes 5, 15, or 25, sound waves from the point or line sound sources are combined. The width (diameter) φ and depth d of the plurality of through holes 5, 15, 25 are set so that the maximum volume of air can pass through at the vibration frequency, relative to the maximum volume of air pushed out or sucked into the internal space 6, which is determined based on the vibration amplitude and vibration frequency of the diaphragms 2 a, 22 a. The transducers 1, 11, 21, 31 convert a surface sound source into a point or line sound source, arrange a plurality of such point or line sound sources, and combine the radiated sound waves, thereby increasing the directivity and output sound pressure level.

[0050] <Supplementary Note 2> In the transducer 1, 11, 31 described in Supplementary Note 1, the first lid body 4, 14 has a first lid portion 4a, 14a facing the diaphragm 2a and a first cylindrical portion 4b, 14b connecting an outer edge 4a1, 14a1 of the first lid portion 4a, 14a to an outer edge 2a3 of the diaphragm 2a. A plurality of through holes 5, 15 are arranged in a planar or linear pattern in the first lid portion 4a, 14a. The transducer 1, 11, 31 can realize a point or line sound source by the through holes 5, 15 formed in the first lid portion 4a, 14a.

[0051] <Supplementary Note 3> In the transducer 21 described in Supplementary Note 1, the first cover 24 has a first cover portion 24a facing the diaphragm 22a and a first cylindrical portion 24b connecting an outer edge 24a1 of the first cover portion 24a to an outer edge 22a3 of the diaphragm 22a. The plurality of through holes 25 are linearly arranged in the first cylindrical portion 24b. The transducer 21 can realize a linear sound source that emits sound from the side.

[0052] <Supplementary Note 4> In the transducer 31 described in any one of Supplementary Notes 1 to 3, the first lid 4, 14, 24 faces and covers the first surface 2a1 of the diaphragm 2a, 22a. The transducer 31 further includes a second lid 34 facing and covering the second surface 2a2 of the diaphragm 2a, 22a, opposite the first surface 2a1. The transducer 31 can radiate sound waves from both sides of the diaphragm 2a, 22a using a point sound source or a line sound source. Therefore, sound waves from the second surface 2a2 side of the diaphragm 2a, 22a can be appropriately attenuated or phase-adjusted and radiated to the surroundings or rear, thereby realizing earphones that prevent sound leakage. The second lid 34 may have a second lid portion 34a facing the diaphragms 2a and 22a, and a second cylindrical portion 34b connecting the outer edge of the second lid portion 34a to the outer edge 2a3 of the diaphragms 2a and 22a. The plurality of through holes 35 may be arranged in a planar or linear pattern in the second lid portion 34a.

[0053] <Supplementary Note 5> In the transducers 1, 11, 21, and 31 described in any one of Supplementary Notes 1 to 4, the driver is a piezoelectric element 3 or 23. In the transducers 1, 11, 21, and 31 that perform electroacoustic conversion, the piezoelectric element 3 or 23 is suitable as a driver for the diaphragm 2 a or 22 a because it has high energy conversion efficiency, a simple mechanical structure, and can produce greater power (output sound pressure level) than a capacitance element.

[0054] <Supplementary Note 6> In the transducers 1, 11, 21, and 31 described in Supplementary Note 5, the piezoelectric elements 3 and 23 have piezoelectric films 3a and 23a and pairs of electrodes 3b and 3c, 23b and 23c formed on the front and back of the piezoelectric films 3a and 23a. The transducers 1, 11, 21, and 31 have a simple structure and can be easily manufactured at low cost. Furthermore, the amount of air pushed out or sucked into the transducers 1, 11, 21, and 31 can be increased, and the volume of sound produced by the transducers 1, 11, 21, and 31 can be increased.

[0055] <Supplementary Note 7> In the transducers 1, 11, 21, and 31 described in Supplementary Note 5 or Supplementary Note 6, the driver (3, 23) is a MEMS. Transducers with a MEMS structure can be easily produced using semiconductor manufacturing technology, and have many advantages such as being extremely small and power-saving, but have a low output sound pressure level. Therefore, the transducers 1, 11, 21, and 31, which have a large effect of improving the output sound pressure level as described above, are suitable for transducers with a MEMS structure.

[0056] <Supplementary Note 8> In the transducers 1, 11, 21, and 31 described in any one of Supplementary Notes 1 to 7, the number of through holes 5 is three or more, and the through holes 5 are formed in the first lid portion 4a at equal intervals r. The transducers 1, 11, 21, and 31 can cause sound waves to travel in a form that is relatively close to a plane wave.

[0057] <Supplementary Note 9> In the transducer 1, 31 described in any one of Supplementary Notes 1 to 8, the diaphragm 2a is a circular diaphragm type diaphragm. The transducer 1, 31 can be manufactured at low cost as a general-purpose MEMS speaker, and can also be made strong.

[0058] <Supplementary Note 10> In the transducer 21 described in Supplementary Note 3, the diaphragm 22a has a rectangular shape when viewed from the vibration direction, the first lid portion 24a has a rectangular shape when viewed from the vibration direction, the first cylindrical portion 24b has a square cylindrical shape, and the through-hole 25 is formed in the first cylindrical portion 24b in a linear shape extending in the circumferential direction. The transducer 21 can reduce unnecessary space generated in the peripheral portion 22c of the diaphragm 22a, thereby improving its effectiveness as a line sound source. Furthermore, by forming the through-hole 25 to extend in the circumferential direction of the first cylindrical portion 24b, a long, straight line sound source can be realized.

[0059] <Supplementary Note 11> In the transducer 1 described in any one of Supplementary Notes 1 to 10, the through hole 5 is widened outward. The transducer 1 can obtain an effect as a horn, and can increase the linearity of sound waves from a point sound source.

[0060] <Supplementary Note 12> The transducer array 10 according to Supplementary Note 12 has a plurality of transducers 1, 11, 21, 31 according to any one of Supplementary Notes 1 to 11 arranged linearly or planarly. The transducer array 10 can further increase the directivity and the output sound pressure level.

[0061] 1, 11, 21, 31 Transducer 2, 22 Vibration part 2a, 22a Vibration plate 2a1 First surface 2a2 Second surface 2a3 Outer edge 22a4 Peripheral edge part 2b, 22b Plate support part 24c, 24d Wall surface 3, 23 Piezoelectric element 3a, 23a Piezoelectric film 3b, 3c; 23b, 23c Electrode 4, 14, 24 First lid body 4a, 14a, 24a First lid part 4a1, 14a1, 24a1 Outer edge 4b, 14b, 24b First cylindrical part 34 Second lid body 34a Second lid part 34a1 Outer edge 34b Second cylindrical part 5; 50, 51, 52, 53, 54, 55, 56; 15; 25; 35 Through hole 6, 36 Internal space 10 Transducer array

Claims

1. A transducer for electroacoustic conversion, comprising: a diaphragm capable of vibrating in a thickness direction; a driver for vibrating the diaphragm with electrical energy; and a first lid placed over the diaphragm, wherein the first lid has a through hole formed therein that connects an internal space formed between the first lid and the diaphragm with the outside, thereby emitting sound waves from the diaphragm, which is a surface sound source, to the outside as a point or line sound source, and a plurality of the through holes are formed so that sound waves from the point or line sound sources are combined, and the width and depth of the plurality of through holes are set so that a maximum volume of air can pass through at the vibration frequency, relative to a maximum volume of air pushed out or sucked into the internal space that is determined based on the vibration width and vibration frequency of the diaphragm.

2. A transducer as described in claim 1, wherein the first lid body has a first lid portion facing the vibration plate and a first cylindrical portion connecting the outer edge of the first lid portion and the outer edge of the vibration plate, and the multiple through holes are arranged in a planar or linear pattern in the first lid portion.

3. A transducer as described in claim 1, wherein the first lid body has a first lid portion facing the vibration plate and a first cylindrical portion connecting an outer edge of the first lid portion and an outer edge of the vibration plate, and the multiple through holes are arranged linearly in the first cylindrical portion.

4. A transducer as claimed in any one of claims 1 to 3, wherein the first lid is placed opposite to a first surface of the diaphragm, and further comprising a second lid placed opposite to a second surface of the diaphragm opposite to the first surface.

5. A transducer as claimed in any one of claims 1 to 4, wherein the driver is a piezoelectric element.

6. A transducer according to claim 5, wherein said piezoelectric element comprises a piezoelectric film and a pair of electrodes formed on the front and back sides of said piezoelectric film.

7. A transducer according to claim 5 or 6, wherein the driver is a MEMS.

8. A transducer as claimed in any one of claims 1 to 7, wherein the number of said through holes is three or more, and said through holes are formed at equal intervals in said first lid portion.

9. A transducer according to any one of claims 1 to 8, wherein the diaphragm is a circular diaphragm type diaphragm.

10. A transducer as described in claim 3, wherein the vibration plate has a rectangular shape when viewed in the vibration direction, the first lid portion has a rectangular shape when viewed in the vibration direction, the first cylindrical portion has a square cylindrical shape, and the through hole is formed linearly in the first cylindrical portion, extending circumferentially.

11. A transducer according to any one of claims 1 to 10, wherein the through hole is widened outwardly.

12. A transducer array comprising a plurality of transducers according to any one of claims 1 to 11 arranged in a line or plane.

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