Acoustic unit, headphone, and speaker

Abstract

This acoustic unit 10 comprises: an acoustic radiator 11 that is formed in a plate shape having a first surface 11a and a second surface 11b facing the opposite side of the first surface, radiates sound to at least the first surface side by vibrating in an intersecting direction Dv intersecting the first surface and the second surface, and includes a first portion 21 and a second portion 22 that vibrate in the intersecting direction in opposite phases to each other; and an acoustic metamaterial 16 that is disposed on the first surface side and suppresses transmission of a second sound generated accompanying the vibration of the second portion to a space S1 on the first surface side of the first portion from which a first sound generated accompanying the vibration of the first portion is radiated.

Description

Acoustic Unit, Headphones, and Speaker

[0001] The present invention relates to an acoustic unit, headphones, and a speaker.

[0002] Patent Document 1 discloses headphones provided with ear pads for attenuating an external sound source (leakage of parasitic sound). In the headphones of Patent Document 1, an acoustic resonator for attenuating an external sound source (leakage of parasitic sound) is provided in the ear pads.

[0003] Japanese Patent Translation No. 2024-510627

[0004] By the way, headphones, speakers, etc. have an acoustic unit that outputs sound. The acoustic unit has an acoustic radiator (vibrating plate) that radiates sound by vibrating in the thickness direction, for example. In such an acoustic radiator, in a specific frequency band, two parts of the acoustic radiator may vibrate in opposite phases to each other. In this case, for example, since sounds that are in opposite phases to each other are radiated to the same side of the acoustic radiator in a specific frequency band, these two types of sounds are mixed. Therefore, there is a problem that it is difficult to control the frequency characteristics of the sound output from the acoustic unit.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an acoustic unit, headphones, and a speaker capable of easily controlling the frequency characteristics of the sound output from the acoustic unit by suppressing the mixing of sounds that are in opposite phases to each other and are radiated to the same side of the acoustic radiator even when two parts of the acoustic radiator vibrate in opposite phases to each other.

[0006] A first aspect of the present invention is an acoustic unit including: an acoustic radiator formed in a plate shape having a first surface and a second surface facing the opposite side of the first surface, radiating sound at least to the first surface side by vibrating in an intersection direction intersecting the first surface and the second surface, and including a first part and a second part vibrating in the intersection direction in opposite phases to each other; and an acoustic metamaterial disposed on the first surface side and suppressing transmission of a second sound generated along with vibration of the second part of the sound to a space on the first surface side of the first part where the first sound generated along with vibration of the first part of the sound is radiated.

[0007] A second aspect of the present invention is a pair of headphones equipped with the aforementioned acoustic unit.

[0008] A third aspect of the present invention is a speaker equipped with the aforementioned acoustic unit.

[0009] According to the present invention, even if two parts of the acoustic radiator constituting the acoustic unit vibrate in opposite phases to each other, the mixing of sounds radiated from the same side of the acoustic radiator that are in opposite phases can be suppressed, and the frequency characteristics of the sound output from the acoustic unit can be easily controlled.

[0010] This is a partially broken diagram showing an acoustic unit according to the first embodiment of the present invention. This is a cross-sectional view showing the acoustic unit of Figure 1. This is a cross-sectional view taken along the line III-III in Figure 2. This is an enlarged cross-sectional view showing the main part of the acoustic unit of Figure 2. This is a schematic cross-sectional view showing Figure 4. This is a cross-sectional view taken along the line VI-VI in Figure 5. This is a cross-sectional view showing a modified example of Figure 5. This is a perspective view showing headphones according to the second embodiment of the present invention. This is a partially broken diagram showing the main part of the headphones of Figure 8. This is a partially broken diagram showing a speaker according to the third embodiment of the present invention. This is an enlarged cross-sectional view showing the main part of the speaker of Figure 10.

[0011] [First Embodiment] The first embodiment of the present invention will be described below with reference to Figures 1 to 6. As shown in Figures 1 and 2, the acoustic unit 10 of this embodiment is a driver unit provided in headphones, speakers, etc. The acoustic unit 10 comprises an acoustic radiator 11, a frame 13, a voice coil 14, a magnetic path forming section 15, and an acoustic metamaterial 16.

[0012] The acoustic radiator 11 is formed in a plate shape having a first surface 11a and a second surface 11b facing the opposite side of the first surface 11a. The term "plate shape" includes not only plate shapes but also film shapes.

[0013] The acoustic radiator 11 vibrates in an intersecting direction that crosses the first surface 11a and the second surface 11b, thereby radiating sound at least towards the first surface 11a. In this embodiment, the acoustic radiator 11 also radiates sound towards the second surface 11b by vibrating in the intersecting direction. The "intersecting direction" in which the acoustic radiator 11 vibrates includes orthogonal directions perpendicular to the first surface 11a and the second surface 11b, and inclined directions that are inclined relative to the first surface 11a and the second surface 11b. In the following description, the direction in which the acoustic radiator 11 vibrates will be referred to as the vibration direction Dv.

[0014] As shown in Figures 2, 4, and 5, the acoustic radiator 11 includes a first portion 21 and a second portion 22 that vibrate in opposite phases and in intersecting directions. The first portion 21 and the second portion 22 vibrate in opposite phases, for example, in a specific frequency band. The specific frequency band is, for example, the circumplex band that includes the resonant frequency of the acoustic radiator 11. The first portion 21 and the second portion 22 also vibrate in the same phase, for example, in a frequency band other than the specific frequency band. The acoustic radiator 11 has a nodal portion 23 located between the first portion 21 and the second portion 22. The nodal portion 23 is a portion that does not vibrate, or vibrates with an extremely small amplitude compared to the first portion 21 and the second portion 22, when the first portion 21 and the second portion 22 vibrate in opposite phases.

[0015] These first portion 21, second portion 22, and nodal portion 23 are aligned along the first surface 11a and second surface 11b of the acoustic radiator 11. In this embodiment, in a plan view from the vibration direction Dv, the second portion 22 is formed in an annular shape surrounding the first portion 21. Therefore, the nodal portion 23 is also formed in an annular shape similar to the second portion 22 (see Figure 3). In this embodiment, "annular" refers to a circular annular shape, but it may also refer to a polygonal annular shape, for example.

[0016] Although not shown in the figures, the acoustic radiator 11 of this embodiment consists of a first portion 21 and a second portion 22 that are formed separately and then fixed to each other. For this reason, the first portion 21 and the second portion 22 may be formed from materials having different properties, or they may be formed from the same material, for example. Alternatively, the first portion 21 and the second portion 22 may be formed integrally from the same material, for example.

[0017] As shown in Figures 4 and 5, in the acoustic radiator 11 having a first part 21 and a second part 22, the first sound generated by the vibration of the first part 21 is radiated into the space on the first surface 11a side of the first part 21 (first space S1). The second sound generated by the vibration of the second part 22 of the acoustic radiator 11 is radiated into the space on the first surface 11a side of the second part 22 (second space S2). In this embodiment, these first and second sounds are also radiated to the second surface 11b side of the acoustic radiator 11. The first and second sounds generated when the first part 21 and the second part 22 vibrate in opposite phases are sounds with opposite phases. The sounds generated when the first part 21 and the second part 22 vibrate in the same phase are sounds with the same phase.

[0018] As shown in Figures 1 and 2, the frame 13 holds the acoustic radiator 11 and the magnetic path forming section 15 at appropriate locations. The frame 13 in this embodiment has a cylindrical body 31, a shielding top wall 32, and a flange portion 33. The cylindrical body 31 is formed in a cylindrical shape with the vibration direction Dv as its axial direction. The periphery of the aforementioned acoustic radiator 11 is held on the inner circumference of the cylindrical body 31. In this embodiment, the periphery of the acoustic radiator 11 is held at an intermediate point in the cylindrical body 31 in the axial direction. Therefore, the cylindrical body 31 extends on both sides of the acoustic radiator 11 in its axial direction.

[0019] In the vibration direction Dv, the portion of the cylindrical body 31 extending toward the first surface 11a side of the acoustic radiator 11 is the shielding side wall 34. The shielding side wall 34 is positioned adjacent to the acoustic radiator 11 such that the second portion 22 is located between it and the first portion 21 of the acoustic radiator 11.

[0020] The shielding ceiling wall 32 is provided at the first end of the cylindrical body 31 in the axial direction. The first end of the cylindrical body 31 forms the tip in the extension direction of the shielding side wall 34. Therefore, the shielding ceiling wall 32 is positioned on the first surface 11a side of the sound radiator 11. The shielding ceiling wall 32 faces the second portion 22 of the sound radiator 11, that is, it is positioned at a distance from the second portion 22 in the vibration direction Dv. The shielding ceiling wall 32 does not face at least the portion of the first portion 21 that is far from the second portion 22. As shown in Figures 4 and 5, in this embodiment, the shielding ceiling wall 32 faces the first adjacent portion 21A of the first portion 21 that is adjacent to the nodal portion 23, and does not face any other portion of the first portion 21.

[0021] Furthermore, the shielding ceiling wall 32 does not have to face the entire first section 21, for example; that is, it may cover only the second section 22 and the nodal section 23. Also, the shielding ceiling wall 32 may cover only the second section 22, or it may cover only the portion of the second section 22 excluding the second adjacent section 22A adjacent to the nodal section 23. The "first adjacent section 21A" and "second adjacent section 22A" described above are the parts of the first section 21 and second section 22 adjacent to the nodal section 23, which vibrate more than the nodal section 23, but have a smaller amplitude compared to other parts of the first section 21 and second section 22.

[0022] As shown in Figures 1 and 2, the flange portion 33 is formed in a ring shape that protrudes radially inward from the second end of the cylindrical body 31 in the axial direction. The flange portion 33 faces the second surface 11b of the acoustic radiator 11 held by the cylindrical body 31 in the axial direction of the cylindrical body 31. Multiple first ventilation holes 35 are formed in the flange portion 33 and penetrate through it. The multiple first ventilation holes 35 are arranged at intervals in the circumferential direction of the flange portion 33. The multiple first ventilation holes 35 open the space on the second surface 11b side of the acoustic radiator 11 to the outside of the frame 13.

[0023] A first ventilation member 36 is positioned on the flange portion 33, overlapping it from the outside of the frame 13. The first ventilation member 36 is formed in a ring shape corresponding to the flange portion 33. As a result, the first ventilation member 36 covers the multiple first ventilation holes 35 of the flange portion 33 from the outside of the frame 13. The first ventilation member 36 is made of a mesh material or a woven fabric such as plain weave, and does not obstruct air from entering and exiting the inside of the frame 13 through the multiple first ventilation holes 35 of the flange portion 33.

[0024] The voice coil 14 is attached to a cylindrical bobbin 25 provided on the second surface 11b of the acoustic radiator 11.

[0025] The magnetic path forming section 15 is provided on the second surface 11b side of the acoustic radiator 11 and forms a magnetic field on the inside and outside of the voice coil 14. In this embodiment, the magnetic path forming section 15 is attached to the inside of the flange portion 33 of the frame 13. The magnetic path forming section 15 has a second ventilation hole 51 formed therein to open the space on the second surface 11b side of the acoustic radiator 11 to the outside of the frame 13. A second ventilation member 52 is arranged on the outer surface of the magnetic path forming section 15 to cover the second ventilation hole 51. The second ventilation member 52 is made of a mesh material or a woven fabric such as plain weave, similar to the first ventilation member 36, and does not obstruct air from entering and exiting the inside of the frame 13 through the second ventilation hole 51 of the magnetic path forming section 15.

[0026] As shown in Figures 2, 4, and 5, the acoustic metamaterial 16 is positioned on the first surface 11a side of the acoustic radiator 11. The acoustic metamaterial 16 suppresses the transmission of the second sound, which is radiated on the first surface 11a side of the acoustic radiator 11 in conjunction with the vibration of the second part 22 of the acoustic radiator 11, from the second space S2 to the first space S1.

[0027] As shown in Figures 2 and 3, the acoustic metamaterial 16 of this embodiment has a plurality of resonators 60 arranged on the first surface 11a side of the acoustic radiator 11. Each resonator 60 has one opening 61. The resonators 60 in this embodiment are Helmholtz resonators. The resonators 60 may also be, for example, resonant tubes with one end in the longitudinal direction closed. In this embodiment, the shapes and sizes of the plurality of resonators 60 are equal to each other.

[0028] As shown in Figures 2, 4, and 5, the openings 61 of each resonator 60 are oriented toward the nodal portions 23 of the acoustic radiator 11. Also, as shown in Figures 3 and 6, the openings 61 of the multiple resonators 60 are spaced apart in the direction in which the nodal portions 23 extend. In this embodiment, the openings 61 of the multiple resonators 60 are spaced equally apart in the direction in which the nodal portions 23 extend. Also, as shown in Figure 3, the nodal portions 23 in this embodiment are formed in an annular shape. Therefore, the openings 61 of the multiple resonators 60 are arranged in an annular shape along the nodal portions 23.

[0029] As shown in Figures 4 and 5, the resonator 60 of this embodiment has a cavity 62 and a passage 63 extending from the cavity 62. The volume of the passage 63 is smaller than the volume of the cavity 62 and is elongated. The tip of the passage 63 in the direction of extension constitutes the opening 61 of the resonator 60. In this embodiment, the passage 63 extends in the vibration direction Dv, but is not limited to this. The passage 63 may be inclined with respect to the vibration direction Dv, for example. In this embodiment, the acoustic metamaterial 16 including the plurality of resonators 60 described above is integrally provided on the frame 13. Specifically, the acoustic metamaterial 16 is integrally provided on the shielding ceiling wall 32.

[0030] As described above, the acoustic unit 10 of the first embodiment includes an acoustic metamaterial 16 that suppresses the transmission of a second sound, which is radiated into the second space S2 on the first surface 11a side of the acoustic radiator 11 in conjunction with the vibration of the second portion 22 of the acoustic radiator 11, to the first space S1 on the first surface 11a side (the space from which the first sound is radiated from the first portion 21). Therefore, it is possible to suppress the mixing of the second sound radiated from the second portion 22 to the first surface 11a side with the first sound radiated from the first portion 21 to the first surface 11a side. For example, it is possible to suppress the attenuation of the first sound by the second sound which is out of phase with the first sound. This makes it possible to easily control the frequency characteristics of the sound output from the acoustic unit 10.

[0031] Furthermore, in the acoustic unit 10 of the first embodiment, a plurality of resonators 60 constituting the acoustic metamaterial 16 are arranged on the first surface 11a side of the acoustic radiator 11, and the opening 61 of each resonator 60 faces the nodal portion 23 of the acoustic radiator 11. The openings 61 of the plurality of resonators 60 are spaced apart in the direction in which the nodal portion 23 extends. As a result, the second sound radiated from the second portion 22 to the first surface 11a side of the acoustic radiator 11 is attenuated by the action of the plurality of resonators 60 arranged in the direction in which the nodal portion 23 of the acoustic radiator 11 extends, as it travels from the second space S2 on the second portion 22 to the first space S1 on the first portion 21. This effectively suppresses the second sound from reaching the first space S1.

[0032] Furthermore, in the acoustic unit 10 of the first embodiment, the nodal portion 23 of the acoustic radiator 11 is formed in an annular shape. The openings 61 of the multiple resonators 60 are arranged in an annular shape along the nodal portion 23. This allows the first sound to be efficiently radiated from the first portion 21 located inside the nodal portion 23.

[0033] Furthermore, the acoustic unit 10 of the first embodiment is positioned adjacent to the acoustic radiator 11 such that the second portion 22 is located between it and the first portion 21, and further comprises a shielding side wall 34 extending toward the first surface 11a side of the acoustic radiator 11, and a shielding top wall 32 provided at the tip of the extension of the shielding side wall 34 so as to be positioned toward the first surface 11a side and facing the second portion 22. However, the shielding top wall 32 does not face at least the portion of the first portion 21 that is far from the second portion 22. With this configuration, the shielding side wall 34 and the shielding top wall 32 can prevent the second sound emitted from the second portion 22 from being emitted to areas other than the first space S1 on the first portion 21 on the first surface 11a side of the acoustic radiator 11. As mentioned above, the acoustic metamaterial 16 suppresses the second sound emitted from the second portion 22 from reaching the space on the first portion 21. Based on the above, it is possible to actively radiate only the first sound emitted from the first part 21 of the acoustic radiator 11 towards the first surface 11a of the acoustic radiator 11.

[0034] By radiating only the first sound from the first surface 11a side of the acoustic radiator 11, the frequency characteristics of the sound output from the acoustic unit 10 can be easily controlled. This point will be explained below. When the first and second sounds, which are out of phase with respect to each other in a specific frequency band, are radiated from the first surface 11a side of the acoustic radiator 11 and mixed, the sound output (sound pressure) in a specific frequency band may become smaller or larger than the sound output (sound pressure) in other frequency bands.

[0035] For example, when a first sound and a second sound, which are out of phase with respect to each other, are mixed, these first and second sounds cancel each other out, causing the sound pressure in a particular frequency band to be lower than the sound pressure in other frequency bands. Also, for example, if the amplitude of the second part 22 in a particular frequency band is significantly larger than the amplitude of the first part 21, and further significantly larger than the amplitude of the acoustic radiator 11 in other frequency bands, the sound pressure of the second sound in that particular frequency band becomes dominant, and as a result, the sound pressure in that particular frequency band becomes higher than the sound pressure in other frequency bands. For these reasons, when a first sound and a second sound, which are out of phase with respect to each other in a particular frequency band, are radiated to the first surface 11a side of the acoustic radiator 11 and mixed, it is difficult to control the frequency characteristics of the sound output from the acoustic unit 10.

[0036] In contrast, as in this embodiment, when only the first sound is radiated from the first surface 11a side of the acoustic radiator 11, the first sound and the second sound do not mix, making it possible to reduce the difference between the sound pressure in a specific frequency band and the sound pressure in other frequency bands. In other words, the sound pressure in a specific frequency band and the sound pressure in other frequency bands become equal. This makes it possible to easily control the frequency characteristics of the sound output from the acoustic unit 10.

[0037] Furthermore, in the acoustic unit 10 of the first embodiment, the acoustic metamaterial 16 is integrally provided with the frame 13, which is a common component of the driver unit. This makes it possible to appropriately control the frequency characteristics of the sound output from the acoustic unit 10 without increasing the number of components of the driver unit.

[0038] In the first embodiment, the opening 61 of each resonator 60 may face the first adjacent portion 21A of the first portion 21, for example, as shown in Figure 7. Alternatively, the opening 61 of each resonator 60 may face the second adjacent portion 22A of the second portion 22. Even with this configuration, similar to the first embodiment, the second sound radiated from the second portion 22 towards the first surface 11a of the acoustic radiator 11 is attenuated by the action of the multiple resonators 60 arranged in the direction in which the nodal portion 23 of the acoustic radiator 11 extends, thereby effectively suppressing its arrival at the first space S1 on the first portion 21. However, having the opening 61 of the resonator 60 face the nodal portion 23 of the acoustic radiator 11 is more effective in suppressing the second sound radiated from the second portion 22 from reaching the space on the first portion 21 than having the opening 61 of the resonator 60 face the first and second adjacent portions 21A and 22A of the nodal portion 23.

[0039] In Figure 7, the shielding ceiling wall 32 covers the portion of the first portion 21 that is further away from the second portion 22 and the nodal portion 23 than the first adjacent portion 21A, but it is preferable that the area of ​​the first portion 21 covered by the shielding ceiling wall 32 is small.

[0040] [Second Embodiment] Next, a second embodiment of the present invention will be described with reference to Figures 8 and 9. In the second embodiment described below, components common to the first embodiment are denoted by the same reference numerals in the figures and their descriptions are omitted.

[0041] As shown in Figures 8 and 9, the headphones 1 of the second embodiment include an acoustic unit 10D, a housing 71, ear pads 72, and a headband 73. The headphones 1 have two acoustic units 10D, two housings 71, and two ear pads 72.

[0042] The acoustic unit 10D of the second embodiment further includes a protector 17D in addition to the components of the acoustic unit 10 of the first embodiment. The protector 17D is disposed on the first surface 11a side of the acoustic radiator 11 and protects the first surface 11a side of the acoustic radiator 11 so as not to interfere with the vibration of the acoustic radiator 11. In the second embodiment, the protector 17D is attached to the frame 13. A plurality of openings 171D are formed in the protector 17D. This does not prevent air from entering and leaving the space between the protector 17D and the first surface 11a of the acoustic radiator 11 through the plurality of openings 171D of the protector 17D.

[0043] The housing 71 houses the acoustic unit 10D. Among the acoustic units 10D housed in the housing 71, the protector 17D (the first surface 11a side of the acoustic radiator 11) is exposed outside the housing 71 through an opening 74 formed in the opposing surface 71a of the housing 71 that faces the ear of the user wearing the headphones 1. The earpad 72 is attached to a region around the opening 74 (acoustic unit 10D) on the opposing surface 71a of the housing 71.

[0044] The headband 73 is curved in its longitudinal direction and has an arc-shaped appearance. The above-described housing 71 is attached to both ends in the longitudinal direction of the headband 73. The specific configuration of the headband 73 is not limited to that illustrated in FIG. 8 and may be arbitrary.

[0045] According to the headphones 1 of the second embodiment, the same effects as those of the first embodiment are achieved. Thereby, it is possible to provide headphones 1 including an acoustic unit 10D that can appropriately control the frequency characteristics of the output sound.

[0046] Further, in the headphones 1 of the second embodiment, the acoustic metamaterial 16 is provided integrally with the frame 13, which is a general component of the driver unit of the headphones 1. Thereby, the frequency characteristics of the sound output from the acoustic unit 10D can be appropriately controlled without increasing the components of the headphones 1.

[0047] In the acoustic unit 10D of the second embodiment, the acoustic metamaterial 16 may be provided, for example, on the protector 17D.

[0048] In the acoustic unit 10D of the second embodiment, the shielding ceiling wall 32, or the shielding side wall 34 and the shielding ceiling wall 32 may be formed separately from the frame 13, for example, and may be integrally formed on the protector 17D.

[0049] [Third Embodiment] Next, referring to FIGS. 10 and 11, a third embodiment of the present invention will be described. In the third embodiment described below, components common to the first embodiment are denoted by the same reference numerals in the drawings, and their description will be omitted.

[0050] As shown in FIGS. 10 and 11, the speaker 2 of the third embodiment includes an acoustic unit 10E and a housing 81.

[0051] The acoustic unit 10E of the third embodiment includes an acoustic radiator 11, a frame 13E, a voice coil 14, a magnetic circuit forming portion 15E, a connection ring 18E, a damper 19E, and an acoustic metamaterial 16. The acoustic radiator 11, the voice coil 14, and the acoustic metamaterial 16 are the same as those in the first embodiment.

[0052] As shown in FIG. 11, the frame 13E holds the acoustic radiator 11 and the magnetic circuit forming portion 15E at appropriate positions, similar to the first embodiment. The frame 13E of the third embodiment is integrally formed of a first ring portion 37E, a second ring portion 38E, and a plurality of connection portions 39E. The first ring portion 37E and the second ring portion 38E are each formed in an annular shape with the vibration direction Dv as the axial direction. The periphery of the acoustic radiator 11 is held by the first ring portion 37E. The second ring portion 38E is located away from the first ring portion 37E on the second surface 11b side of the acoustic radiator 11. The magnetic circuit forming portion 15E is held by the second ring portion 38E. The plurality of connection portions 39E each extend from the first ring portion 37E to the second ring portion 38E and connect the first ring portion 37E and the second ring portion 38E. The plurality of connection portions 39E are arranged at intervals in the circumferential direction of the first and second ring portions 37E and 38E.

[0053] The magnetic path forming section 15E is provided on the second surface 11b side of the acoustic radiator 11, similar to the first embodiment, and forms a magnetic field on the inside and outside of the voice coil 14. However, the magnetic path forming section 15E of the third embodiment does not have a second ventilation hole 51 (see Figures 1 and 2).

[0054] The damper 19E connects the frame 13E to the bobbin 25 and / or the acoustic radiator 11 on the second surface 11b side of the acoustic radiator 11. The damper 19E holds the bobbin 25 so that the bobbin 25 and the voice coil 14 do not come into contact with the magnetic path forming section 15E, while allowing vibration of the bobbin 25 and the acoustic radiator 11 in the vibration direction Dv. The specific shape and configuration of the damper 19E may be arbitrary.

[0055] The connecting ring 18E is an annular member held by the first ring portion 37E of the frame 13E together with the periphery of the sound radiator 11. The connecting ring 18E is a member for connecting the sound unit 10E to the wall portion 83 that defines the cavity 82 of the housing 81. In the third embodiment, the connecting ring 18E includes a shielding side wall 34 and a shielding top wall 32 similar to those in the first embodiment. That is, the shielding side wall 34 is positioned adjacent to the sound radiator 11 such that its second portion 22 is located between it and its first portion 21, and extends toward the first surface 11a of the sound radiator 11. The shielding top wall 32 is provided at the end of the shielding top wall 32 in the direction of extension and faces the second portion 22 of the sound radiator 11 toward the first surface 11a.

[0056] As shown in Figure 10, the housing 81 has a cavity 82 that houses the acoustic unit 10E. The connecting ring 18E of the acoustic unit 10E is attached to a first opening 84 formed in the wall portion 83 of the housing 81 that defines the cavity 82. When the connecting ring 18E is attached to the first opening 84 of the housing 81, the first surface 11a of the acoustic radiator 11 is exposed to the outside of the housing 81, and the second surface 11b of the acoustic radiator 11 faces inward (towards the cavity 82) of the housing 81. The housing 81 also has a second opening 85 that penetrates its wall portion 83. The cavity 82 of the housing 81 is provided with a cylindrical duct 86 that extends from the second opening 85 to the inside of the housing 81. For this reason, the speaker 2 of the third embodiment is a bass reflex type speaker.

[0057] The speaker 2 of the third embodiment provides the same effects as the first embodiment. This makes it possible to provide a speaker 2 that includes an acoustic unit 10E that can appropriately control the frequency characteristics of the output sound.

[0058] In the third embodiment, the connecting ring 18E may be formed integrally with, for example, the frame 13E. In this case, the shielding side wall 34 and the shielding top wall 32 may be components of the frame 13E.

[0059] Although the present invention has been described in detail above, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0060] In the present invention, the acoustic radiator 11 may be formed in an annular shape, for example, with the first portion 21 surrounding the second portion 22.

[0061] Furthermore, in the present invention, the nodal portion 23 located between the first portion 21 and the second portion 22 is not limited to being formed in an annular shape. For example, both ends of the nodal portion 23 may reach the edge of the acoustic radiator 11 when viewed from the vibration direction Dv. In this case, the nodal portion 23 may extend in a straight line or in a curved shape.

[0062] In the present invention, the acoustic metamaterial 16 may be formed separately from, for example, the shielding ceiling wall 32.

[0063] In the present invention, the acoustic units 10, 10D, and 10E do not necessarily have, for example, shielding side walls 34 and shielding top walls 32. In this case, the acoustic metamaterial 16 may be arranged on the first surface 11a side of the acoustic radiator 11 by being connected to the acoustic radiator 11, for example, via a connecting member.

[0064] 1...Headphones, 2...Speaker, 10, 10D, 10E...Acoustic unit, 11...Acoustic radiator, 11a...First surface, 11b...Second surface, 15, 15E...Magnetic path forming part, 16...Acoustic metamaterial, 21...First part, 21A...First adjacent part, 22...Second part, 22A...Second adjacent part, 23...Nodal part, 32...Shielding top wall, 34...Shielding side wall, 60...Resonator, 61...Opening, Dv...Vibration direction (crossing direction), S1...First space, S2...Second space

Claims

1. An acoustic unit comprising: an acoustic radiator formed in the shape of a plate having a first surface and a second surface facing the opposite side of the first surface, which vibrates in an intersecting direction that intersects the first surface and the second surface, thereby radiating sound at least toward the first surface, and including a first part and a second part that vibrate in the intersecting direction in opposite phases to each other; and an acoustic metamaterial disposed toward the first surface, which suppresses the transmission of a second sound generated by the vibration of the second part of the sound into the space toward the first surface of the first part of the sound, from which a first sound generated by the vibration of the first part of the sound is radiated.

2. The acoustic unit according to claim 1, wherein the acoustic radiator has a nodal portion located between the first portion and the second portion, the acoustic metamaterial has a plurality of resonators each having an opening and arranged on the first surface side of the acoustic radiator, the openings of the plurality of resonators each facing the nodal portion or an adjacent portion adjacent to the nodal portion of the acoustic radiator, and arranged at intervals in the direction in which the nodal portion extends.

3. The acoustic unit according to claim 2, wherein the openings of the plurality of resonators are each directed toward the nodal portion of the acoustic radiator.

4. The acoustic unit according to claim 2 or 3, wherein the nodal portion is formed in an annular shape, and the openings of the plurality of resonators are arranged in an annular shape along the nodal portion.

5. The acoustic unit according to any one of claims 1 to 3, further comprising: a shielding side wall positioned adjacent to the acoustic radiator such that the second portion is located between it and the first portion, and extending toward the first surface side of the acoustic radiator; and a shielding top wall provided at the tip in the extension direction of the shielding side wall, positioned toward the first surface side, and facing the second portion, wherein the shielding top wall does not face at least a portion of the first portion that is far from the second portion.

6. Headphones comprising the acoustic unit according to any one of claims 1 to 3.

7. The headphones according to claim 6, wherein the acoustic metamaterial is integrally provided with the frame that holds the acoustic radiator.

8. A speaker comprising the acoustic unit described in any one of claims 1 to 3.

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