An acoustic device

Abstract

Embodiments of the present specification provide an acoustic device, comprising: a diaphragm; a housing for accommodating the diaphragm and forming a first acoustic cavity and a second acoustic cavity corresponding to front and back sides of the diaphragm respectively, wherein the diaphragm radiates sound to the first acoustic cavity and the second acoustic cavity respectively, and conducts sound out through a first acoustic hole coupled with the first acoustic cavity and a second acoustic hole coupled with the second acoustic cavity respectively; and an acoustic absorption structure coupled with the second acoustic cavity, for absorbing sound in a target frequency range transmitted to the second acoustic hole via the second acoustic cavity, wherein the target frequency range includes a resonance frequency of the second acoustic cavity.

Description

[0001] Cross-referencing

[0002] This application claims priority to international application No. PCT / CN2022 / 101273, filed on June 24, 2022, and Chinese application No. 202211455122.0, filed on November 21, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This specification relates to the field of acoustic devices, and in particular to an acoustic device. Background Technology

[0004] To address sound leakage in acoustic devices, two or more sound sources are typically used to emit two sound signals with opposite phases. Under far-field conditions, the path difference between the two out-of-phase sound sources reaching a point in the far field is negligible, thus the two sound signals can cancel each other out, reducing far-field sound leakage. While this method can reduce sound leakage to some extent, it still has limitations. For example, because high-frequency sound leakage has a shorter wavelength, the distance between the two sound sources is not negligible compared to the wavelength under far-field conditions, preventing the sound signals from canceling out. Furthermore, when the acoustic transmission structure of the acoustic device resonates, the phase of the sound signal actually radiated from the outlet of the device differs from the original phase at the sound wave generation location, adding additional resonance peaks to the transmitted sound wave. This results in a chaotic sound field distribution and makes it difficult to guarantee the sound leakage reduction effect in the far field at high frequencies; it may even increase sound leakage.

[0005] Therefore, it is desirable to provide an acoustic device with a better directional sound field. Summary of the Invention

[0006] One embodiment of this specification provides an acoustic device, comprising: a diaphragm; a housing for accommodating the diaphragm and forming a first acoustic cavity and a second acoustic cavity corresponding to the front and rear sides of the diaphragm, respectively, wherein the diaphragm radiates sound to the first acoustic cavity and the second acoustic cavity, and outputs sound through a first acoustic aperture coupled to the first acoustic cavity and a second acoustic aperture coupled to the second acoustic cavity, respectively; and a sound-absorbing structure coupled to the second acoustic cavity for absorbing sound transmitted from the second acoustic cavity to the second acoustic aperture within a target frequency range, wherein the target frequency range includes the resonant frequency of the second acoustic cavity. The sound-absorbing structure can absorb sound waves within the target frequency range of the second acoustic cavity to reduce or avoid the superposition of the first sound wave output from the first acoustic aperture and the second sound wave output from the second acoustic aperture at a certain spatial point (e.g., far field) outside the acoustic device, thereby reducing the amplitude of the sound waves within the target frequency range at that spatial point, adjusting the directivity of the acoustic output device, and achieving the effect of reducing far-field sound leakage.

[0007] In some embodiments, the target frequency range further includes the resonant frequency of the first acoustic cavity. Including the resonant frequency of the first acoustic cavity in the target frequency range avoids adding additional resonance peaks to the sound waves transmitted in the second acoustic cavity due to the resonance of the first acoustic cavity.

[0008] In some embodiments, the target frequency range includes 3kHz-6kHz. The human ear is relatively sensitive to sounds in the 3kHz-6kHz range, therefore, including a target frequency range of 3kHz-6kHz can achieve more targeted and effective sound leakage reduction.

[0009] In some embodiments, the sound-absorbing structure has a sound absorption effect of not less than 3dB on sound within the target frequency range. A sound absorption effect of not less than 3dB can improve sound leakage within the target frequency range of the acoustic device.

[0010] In some embodiments, the sound-absorbing structure has a sound absorption effect of not less than 14 dB on the sound at the resonant frequency. Thus, sound waves at or near the resonant frequency of the second acoustic cavity can be effectively absorbed by the sound-absorbing structure, reducing or avoiding resonance of sound waves near the resonant frequency under the action of the acoustic cavity. This reduces or avoids amplitude and phase differences (e.g., a phase difference not equal to 180 degrees) between the first and second sound waves near the resonant frequency, which could lead to a deterioration in the sound leakage reduction effect at the spatial point, or even a situation where the two sets of sounds not only do not cancel each other out but also interfere with each other, thereby reducing sound leakage of the acoustic device at the far-field spatial point.

[0011] In some embodiments, the sound-absorbing structure includes a micro-perforated plate and a cavity, the micro-perforated plate including through holes, wherein the second acoustic cavity coupled to the sound-absorbing structure is connected to the cavity through the through holes.

[0012] In some embodiments, the cavity is filled with N′Bass sound-absorbing particles. The N′Bass particles can be used to increase the effective height of the cavity in the micro-perforated plate sound-absorbing structure, thereby improving the sound absorption effect of the micro-perforated plate sound-absorbing structure while reducing the design size of the acoustic device.

[0013] In some embodiments, the diameter of the N′Bass sound-absorbing particles is in the range of 0.15mm-0.7mm, thereby ensuring sound absorption effect while taking cost into account.

[0014] In some embodiments, the N′Bass sound-absorbing particles are filled in the cavity at a rate of 70%-95%, which can ensure the sound absorption effect while avoiding the pressure of the micro-perforated plate sound-absorbing structure on the N′Bass sound-absorbing particles causing blockage of the gaps and thus reducing the sound absorption effect.

[0015] In some embodiments, the cavity is filled with a porous sound-absorbing material, the porosity of which is greater than 70%, thereby achieving better sound absorption.

[0016] In some embodiments, the ratio between the hole spacing and the hole diameter of the through holes is greater than 5, so that the characteristics of sound wave transmission between the holes do not affect each other.

[0017] In some embodiments, the ratio of the wavelength of the sound in the target frequency range to the hole spacing between the through holes on the micro-perforated plate is greater than 5, so that when the hole spacing is much smaller than the wavelength, the reflection of the sound wave by the perforated plate can be ignored, thereby avoiding the influence of the reflection of the perforated plate on the sound wave propagation process.

[0018] In some embodiments, the aperture of the through hole is in the range of 0.1mm-0.2mm, the perforation rate of the micro-perforated plate is in the range of 2%-5%, the thickness of the micro-perforated plate is in the range of 0.2mm-0.7mm, and the height of the cavity is in the range of 7mm-10mm. This allows for a balance between the sound absorption bandwidth and the sound absorption coefficient, enabling the sound absorption structure to effectively absorb sound waves within the target frequency range and improve the sound leakage reduction effect within the target frequency range.

[0019] In some embodiments, the aperture of the through hole is in the range of 0.2mm-0.4mm, the perforation rate of the micro-perforated plate is in the range of 1%-5%, the thickness of the micro-perforated plate is in the range of 0.2mm-0.7mm, and the height of the cavity is in the range of 4mm-9mm. This allows for a balance between the sound absorption bandwidth and the sound absorption coefficient, enabling the sound absorption structure to effectively absorb sound waves within the target frequency range and improve the sound leakage reduction effect within the target frequency range.

[0020] In some embodiments, the micro-perforated plate includes a racetrack-shaped micro-perforated plate or a circular micro-perforated plate. The thickness of the circular micro-perforated plate is in the range of 0.3mm-1mm, so that the natural frequency of the micro-perforated plate in its free state is in the range of 500Hz-3.6kHz, and thus its natural frequency in its fixed state is much greater than the upper limit frequency of sound absorption.

[0021] In some embodiments, the natural frequency of the micro-perforated plate is greater than 500Hz, thereby preventing the natural frequency of the micro-perforated plate in the fixed state from falling within the sound absorption bandwidth, so that its natural frequency in the fixed state is much greater than the upper limit frequency of sound absorption.

[0022] In some embodiments, the height of the cavity is in the range of 0.5mm-10mm, thereby balancing the sound absorption bandwidth and maximum sound absorption coefficient of the micro-perforated plate sound absorption structure.

[0023] In some embodiments, the microperforated plate has a waterproof and breathable structure on the side facing the diaphragm, which can be used for waterproofing and dustproofing.

[0024] In some embodiments, the acoustic device further includes a magnetic circuit assembly and a coil. The coil is connected to the diaphragm and is at least partially located in the magnetic gap formed by the magnetic circuit assembly. When the coil is energized, it drives the diaphragm to vibrate to generate sound. The micro-perforated plate satisfies at least one of the following conditions: the micro-perforated plate includes an annular structure surrounding the magnetic circuit assembly; the micro-perforated plate and the magnetic circuit assembly are spaced apart in the diaphragm vibration direction; or the micro-perforated plate includes a magnetically conductive element in the magnetic circuit assembly. In some embodiments, setting the micro-perforated plate as an annular structure surrounding the magnetic circuit assembly effectively utilizes the circumferential space of the magnetic circuit assembly without increasing the thickness of the acoustic device, which is beneficial for miniaturization design. In some embodiments, the spaced-apart arrangement of the micro-perforated plate and the magnetic circuit assembly in the diaphragm vibration direction allows for a larger area of ​​the micro-perforated plate in the panel structure, a relatively larger number of through holes, better sound absorption, and a simpler structure, facilitating assembly. In some embodiments, directly setting a portion of the magnetic circuit assembly as a sound-absorbing structure achieves sound absorption while saving costs and simplifying the process. Attached Figure Description

[0025] This application will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0026] Figure 1 These are schematic diagrams of acoustic devices according to some embodiments of this specification;

[0027] Figure 2A yes Figure 1 A schematic diagram of the sound pressure level and sound field distribution of the acoustic device at low and medium frequencies.

[0028] Figure 2B yes Figure 1 A schematic diagram of the sound pressure level and sound field distribution of the acoustic device at high frequencies;

[0029] Figure 3 This is a block diagram of an acoustic device according to some embodiments shown in this specification;

[0030] Figure 4 These are frequency response curves of acoustic devices with different sound-absorbing structures as shown in some embodiments of this specification;

[0031] Figure 5 These are frequency response curves of acoustic devices with different sound-absorbing structures as shown in some embodiments of this specification;

[0032] Figure 6 This is a schematic diagram of an acoustic device with a sound-absorbing structure according to some embodiments of this specification;

[0033] Figure 7 These are sound absorption diagrams of acoustic devices according to some embodiments of this specification, using metal microperforated plates and non-metal microperforated plates respectively.

[0034] Figure 8 These are frequency response curves of the acoustic devices shown in some embodiments of this specification, using metal microperforated plates and non-metal microperforated plates respectively.

[0035] Figure 9 This is a frequency response curve at the second acoustic hole measured with and without a 025HY type mesh on the side of the micro-perforated plate facing the speaker (or diaphragm) as shown in some embodiments of this specification.

[0036] Figure 10 This is a graph showing the sound absorption coefficient of the micro-perforated plate sound-absorbing structure with different cavity heights, as illustrated in some embodiments of this specification.

[0037] Figure 11This is a comparison chart showing the variation trend of the maximum sound absorption coefficient with 0.5 octave band sound absorption for different cavity heights according to some embodiments of this specification;

[0038] Figure 12 These are sound absorption effect diagrams of micro-perforated plates with through-hole diameters of 0.15 mm and 0.3 mm, as shown in some embodiments of this specification.

[0039] Figure 13 The frequency response curves of micro-perforated plates with 0.15 mm and 0.3 mm apertures, as shown in some embodiments of this specification, are shown.

[0040] Figure 14 These are sound absorption effect diagrams corresponding to micro-perforated plates with different cavity heights when the aperture is 0.15 mm, the perforation rate is 2.18%, and the plate thickness is 0.3 mm, according to some embodiments of this specification.

[0041] Figure 15 These are sound absorption effect diagrams for micro-perforated plates of different thicknesses with an aperture of 0.3 mm, a perforation rate of 2.18%, and a cavity height of 5 mm, as shown in some embodiments of this specification.

[0042] Figure 16 This is a schematic diagram of an acoustic device with a sound-absorbing structure according to some embodiments of this specification;

[0043] Figure 17 This is a frequency response curve of the second acoustic cavity of the acoustic device corresponding to different filling material filling rates according to some embodiments of this specification;

[0044] Figure 18 These are frequency response curves of some embodiments of this specification, showing the following: no microperforated plate, only microperforated plate, microperforated plate combined with N′Bass sound-absorbing particles, and microperforated plate combined with porous sound-absorbing material.

[0045] Figure 19 This is an internal structural diagram of the acoustic device shown in some embodiments of this specification;

[0046] Figure 20 This is an internal structural diagram of the acoustic device shown in some embodiments of this specification;

[0047] Figure 21 This is an internal structural diagram of the acoustic device shown in some embodiments of this specification;

[0048] Figure 22 yes Figures 19-20 The acoustic device shown and Figure 21 The frequency response curve of the acoustic device is shown. Detailed Implementation

[0049] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0050] Figure 1 These are schematic diagrams of acoustic devices according to some embodiments of this specification. Figure 1 As shown, the acoustic device 100 may include a housing 110 and a speaker 120. The speaker 120 may be disposed within the cavity formed by the housing 110, and a first acoustic cavity 130 and a second acoustic cavity 140 for radiating sound are respectively provided on the front and rear sides of the speaker 120. The housing 110 is provided with a first acoustic hole 111 and a second acoustic hole 112. The first acoustic cavity 130 may be acoustically coupled to the first acoustic hole 111, and the second acoustic cavity 140 may be acoustically coupled to the second acoustic hole 112. When a user uses the acoustic device 100, the acoustic device 100 may be located near the user's auricle, and the first acoustic hole 111 may face the user's ear canal opening, so that the sound emitted from the first acoustic hole 111 can propagate toward the user's ear canal. The second acoustic hole 112 may be located away from the ear canal opening relative to the first acoustic hole 111, and the distance between the first acoustic hole 111 and the ear canal opening may be less than the distance between the second acoustic hole 112 and the ear canal opening.

[0051] In some embodiments, the front and rear sides of the loudspeaker 120 can each serve as a sound wave generating structure, producing a set of sound waves (or sounds) with equal amplitude and opposite phase. In some embodiments, the set of sound waves with equal amplitude and opposite phase can be radiated outward through the first acoustic aperture 111 and the second acoustic aperture 112, respectively. When the loudspeaker 120 outputs sound waves, the sound wave (or first sound wave) on the front side of the loudspeaker 120 can be emitted from the first acoustic aperture 111 through the first acoustic cavity 130, and the sound wave (or second sound wave) on the rear side of the loudspeaker 120 can be emitted from the second acoustic aperture 112 through the second acoustic cavity 140, thereby forming a dipole sound source including the first acoustic aperture 111 and the second acoustic aperture 112. The dipole sound source can undergo destructive interference at a spatial point (e.g., the far field), thereby effectively improving the sound leakage problem in the far field of the acoustic device 100.

[0052] Figure 2A yes Figure 1 The diagram shows the sound pressure level and sound field distribution of the acoustic device 100 at low and mid frequencies. Figure 2AAs shown, in the mid-to-low frequency range (e.g., 50Hz-1kHz), the sound field distribution of the acoustic device 100 exhibits good dipole directivity, and the dipole reduces sound leakage significantly. That is, in the mid-to-low frequency range, the dipole sound source formed by the first acoustic aperture 111 and the second acoustic aperture 112 of the acoustic device 100 outputs sound waves with opposite or nearly opposite phases. According to the principle of sound wave phase cancellation, the two sound waves cancel each other out in the far field, thereby reducing far-field sound leakage.

[0053] Figure 2B yes Figure 1 A schematic diagram of the sound pressure level and sound field distribution of the acoustic device 100 at high frequencies. Figure 2B As shown, the sound field distribution of the acoustic device 100 is rather chaotic in the higher frequency range.

[0054] In some embodiments, in a higher frequency range (e.g., 1500Hz-20kHz), the wavelengths of the first and second sound waves are shorter than those in the mid-to-low frequency range. In this case, the distance between the dipole sound sources formed by the first acoustic aperture 111 and the second acoustic aperture 112 is not negligible compared to the wavelength, causing the sound waves emitted by the two sources to fail to cancel each other out. This makes it difficult to guarantee the sound leakage reduction effect of the acoustic device in the far field in a higher frequency range, and may even increase sound leakage, resulting in a more chaotic sound field distribution of the acoustic device. For illustrative purposes only, the distance between the first acoustic aperture 111 and the second acoustic aperture 112 can cause the first and second sound waves to have different path lengths from a certain spatial point (e.g., in the far field), resulting in a smaller phase difference (e.g., the same or close phase) between the first and second sound waves at that spatial point. This prevents the first and second sound waves from interfering and canceling each other out at that spatial point, and they may even superimpose at that point, increasing the amplitude of the sound wave at that point and thus increasing sound leakage.

[0055] In some embodiments, sound waves emitted from the front and rear sides of the speaker 120 may first pass through an acoustic transmission structure and then radiate outward from the first acoustic aperture 111 and / or the second acoustic aperture 112. The acoustic transmission structure refers to the acoustic path taken by the sound waves as they radiate from the speaker 120 to the external environment. In some embodiments, the acoustic transmission structure may include a housing 110 between the speaker 120 and the first acoustic aperture 111 and / or the second acoustic aperture 112. In some embodiments, the acoustic transmission structure may include an acoustic cavity. The acoustic cavity may be an amplitude space reserved for the diaphragm (not shown) of the speaker 120; for example, the acoustic cavity may include the cavity formed between the diaphragm of the speaker 120 and the housing 110. Alternatively, the acoustic cavity may also include the cavity formed between the diaphragm of the speaker 120 and the drive system (e.g., a magnetic circuit assembly). In some embodiments, the acoustic transmission structure may be acoustically connected to the first acoustic aperture 111 and / or the second acoustic aperture 112, and the first acoustic aperture 111 and / or the second acoustic aperture 112 may also be part of the acoustic transmission structure. In some embodiments, when the speaker 120 is far from the ear canal opening, or when the radiation direction of the sound waves generated by the speaker 120 is not as expected or far from the ear canal opening, the sound waves can be guided to the expected location through the sound guide tube, and then radiated to the external environment using the first acoustic aperture 111 and / or the second acoustic aperture 112. Thus, the acoustic transmission structure may also include a sound guide tube.

[0056] In some embodiments, the acoustic transmission structure may have a resonant frequency, and the acoustic transmission structure may resonate when the frequency of the sound waves generated by the loudspeaker 120 is near this resonant frequency. Under the action of the acoustic transmission structure, the sound waves located in the acoustic transmission structure also resonate, and the resonance may change the frequency components of the transmitted sound waves (e.g., adding additional resonant peaks to the transmitted sound waves) or change the phase of the sound waves transmitted in the acoustic transmission structure. Compared with the absence of resonance, the phase and / or amplitude of the sound waves radiated from the first acoustic aperture 111 and / or the second acoustic aperture 112 change, and the change in phase and / or amplitude may cause the sound field of the dipole structure to become chaotic near the resonant frequency, affecting the destructive interference effect of the sound waves radiated from the first acoustic aperture 111 and the second acoustic aperture 112 at spatial points. For example, when resonance occurs, the phase difference between the sound waves radiated from the first acoustic aperture 111 and the second acoustic aperture 112 changes. For instance, when the phase difference between the sound waves radiated from the first acoustic aperture 111 and the second acoustic aperture 112 is small (e.g., less than 120°, less than 90°, or 0), the destructive interference effect of the sound waves at the spatial point is weakened, making it difficult to reduce sound leakage. Alternatively, sound waves with a small phase difference may also superimpose at the spatial point, increasing the amplitude of the sound waves near the resonant frequency at the spatial point (e.g., in the far field), thereby increasing the far-field sound leakage of the acoustic device 100. As another example, the resonance may cause the amplitude of the transmitted sound waves near the resonant frequency of the acoustic transmission structure to increase (e.g., manifested as a resonant peak near the resonant frequency), leading to a chaotic sound field near the resonant frequency of the dipole structure. In this case, the amplitude difference between the sound waves radiated from the first acoustic aperture 111 and the second acoustic aperture 112 is large, weakening the destructive interference effect of the sound waves at the spatial point, making it difficult to reduce sound leakage. In some embodiments, differences in parameters such as the volume of the first acoustic cavity 130 and the second acoustic cavity 140, and the size and height of the first acoustic aperture 111 and the second acoustic aperture 112, can lead to inconsistent resonant frequencies of the first acoustic cavity and the second acoustic cavity (also referred to simply as acoustic cavities), resulting in different resonant frequencies of the acoustic transmission structures on the front and rear sides of the acoustic device. In some embodiments, the blocking and / or reflection of high-frequency sound waves by structures such as the auricle 210 may also lead to a chaotic sound field distribution of the acoustic device 100.

[0057] Since the first acoustic aperture 111 faces the user's ear canal opening, and the second acoustic aperture 112 is farther from the ear canal opening relative to the first acoustic aperture 111, the sound waves radiated outward by the acoustic device are mostly radiated through the second acoustic aperture 112. In other words, the sound waves radiated outward by the second acoustic aperture 112 of the acoustic device 100 dominate the chaotic sound field distribution. Therefore, by adjusting the structure of the acoustic device 100, the output within the target frequency range of the second acoustic cavity (e.g., including the resonant frequency of the acoustic transmission structure and the high-frequency range) can be reduced without affecting the low-frequency output of the second acoustic cavity, thereby reducing far-field sound leakage.

[0058] Figure 3 This is a block diagram of an acoustic device according to some embodiments of this specification. In some embodiments, such as Figure 3 As shown, the acoustic device 300 may include a housing 310, a diaphragm 321, and a sound-absorbing structure 330.

[0059] The housing 310 can be a regular or irregular three-dimensional structure with an internal accommodating cavity. For example, the housing 310 can be a hollow frame structure, including but not limited to regular shapes such as rectangular frames, circular frames, and regular polygonal frames, as well as any irregular shape, such as a racetrack shape. The housing 310 can be used to house the speaker and the sound-absorbing structure 330. In some embodiments, the housing 310 can be made of metal (e.g., stainless steel, copper, etc.), plastic (e.g., polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS), etc.), composite material (e.g., metal matrix composite material or non-metal matrix composite material), epoxy resin, phenolic resin, ceramic, polyimide, glass fiber (e.g., FR4-glass fiber), etc., or any combination thereof. The housing 310 can also be provided with a first acoustic hole 111 and a second acoustic hole 112 for outputting sound waves. The speaker 120 outputs sound waves with a phase difference through the first acoustic hole 111 and the second acoustic hole 112.

[0060] A loudspeaker is a component that receives electrical signals and converts them into sound signals for output. In some embodiments, loudspeakers can be categorized by frequency, including low-frequency (e.g., 30Hz–150Hz) loudspeakers, mid-low-frequency (e.g., 150Hz–500Hz) loudspeakers, mid-high-frequency (e.g., 500Hz–5kHz) loudspeakers, high-frequency (e.g., 5kHz–16kHz) loudspeakers, or full-range (e.g., 30Hz–16kHz) loudspeakers, or any combination thereof. The terms "low frequency," "high frequency," etc., refer only to approximate frequency ranges; different classification methods may be used in different applications. For example, a crossover point can be defined, with low frequency representing the frequency range below the crossover point and high frequency representing the frequency range above the crossover point. This crossover point can be any value within the audible range of the human ear, such as 500Hz, 700Hz, 1000Hz, etc.

[0061] In some embodiments, the loudspeaker may include a diaphragm 321, which, along with the diaphragm 321, divides the accommodating cavity of the housing 310 to form a first acoustic cavity and a second acoustic cavity. The diaphragm 321 may be a resilient thin-film structure. In some embodiments, the material of the diaphragm 321 may include, but is not limited to, one or more of polyimide (PI), polyethylene terephthalate (PET), polyethyleneimine (PEI), polyetheretherketone (PEEK), silicone, polycarbonate (PC), vinyl polymer (PVC), acrylonitrile-butadiene-styrene copolymer (ABS), polyethylene (PE), and parylene (PPX), or a multilayer composite material composed of the above materials. In some embodiments, the first acoustic cavity may be acoustically coupled to a first acoustic aperture, and the second acoustic cavity may be acoustically coupled to a second acoustic aperture. When the diaphragm 321 vibrates, sound waves can radiate to its front and rear sides, respectively. The front side of the diaphragm 321 can refer to the side away from the driving system (e.g., magnetic circuit assembly) of the diaphragm 321, and the rear side of the diaphragm 321 can refer to the side facing the driving system (e.g., magnetic circuit assembly) of the diaphragm 321. Sound waves from the front side of the diaphragm 321 can be emitted from the first acoustic aperture through the first acoustic cavity, and sound waves from the rear side of the diaphragm 321 can be emitted from the second acoustic aperture through the second acoustic cavity. It should be noted that when the diaphragm 321 vibrates, a set of sound waves with a phase difference can be generated simultaneously from both the front and rear sides of the diaphragm 321.

[0062] In some embodiments, the diaphragm 321 simultaneously generates a set of sound waves with a phase difference on its front and rear sides, which are emitted from the first acoustic aperture via the first acoustic cavity and from the second acoustic aperture via the second acoustic cavity. The two sound waves superimpose and cancel each other out at a certain spatial point outside the acoustic device (e.g., in the far field), which can reduce sound leakage in the far field of the acoustic device. The existence of such sound wave outputs in the first acoustic aperture 111 and the second acoustic aperture 112 forms a dipole sound source. When the position, phase difference, etc. between the dipole sound sources meet certain conditions, the acoustic device can exhibit different sound effects in the near field and far field. For example, when the phases of the point sound sources corresponding to the two acoustic apertures are opposite and the amplitudes are the same or similar, that is, when the absolute value of the phase difference between the two point sound sources is 180° or close to 180°, the reduction of far-field sound leakage can be achieved according to the principle of sound wave phase cancellation. As another example, when the phases of the point sound sources corresponding to the two acoustic apertures are approximately opposite, the reduction of far-field sound leakage can also be achieved. As an example only, the absolute value of the phase difference between two point sound sources that achieve far-field sound leakage reduction can be in the range of 120°-240°.

[0063] based on Figures 1-2B As described, dipoles exhibit chaotic sound fields in the high-frequency range, resulting in poor sound leakage reduction and, in some cases, even increased sound leakage. To improve the sound leakage reduction effect of acoustic devices in the high-frequency range, a sound-absorbing structure 330 can be installed in the second acoustic cavity of the acoustic device. The sound-absorbing structure 330 can absorb sound waves within the target frequency range of the second acoustic cavity, thereby reducing or avoiding the superposition of the first and second sound waves at a certain spatial point (e.g., the far field) outside the acoustic device, reducing the amplitude of the sound waves within the target frequency range at that spatial point, adjusting the directivity of the acoustic output device, and achieving the effect of reducing far-field sound leakage.

[0064] The sound-absorbing structure 330 refers to a structure that absorbs sound waves within a specific frequency band (e.g., within a target frequency range). The sound-absorbing structure 330 can be coupled to a second acoustic cavity to absorb sound radiated from the second acoustic cavity to the second acoustic aperture within the target frequency range. Accordingly, within the target frequency range, the sound pressure level at the second acoustic aperture can be higher when the sound-absorbing structure 330 is not present than when the sound pressure level is present.

[0065] In some embodiments, the target frequency range may include the frequency range near the resonant frequency of the second acoustic cavity. The sound-absorbing structure 330 can absorb sound waves near the resonant frequency of the second acoustic cavity to avoid changes in the phase and / or amplitude of the second sound wave caused by resonance of the second acoustic cavity near that resonant frequency, thereby reducing the amplitude of the sound wave near the resonant frequency and thus reducing sound leakage. In some embodiments, the resonant frequency may occur in the mid-high frequency band, for example, 2kHz-8kHz. Accordingly, the target frequency range may include frequencies in this mid-high frequency band. For example, the target frequency range may be in the range of 1kHz-10kHz. In some embodiments, in the higher frequency range, since the distance between the dipole sound sources formed by the first acoustic aperture and the second acoustic aperture is not negligible compared to the wavelength, the first sound wave and the second sound wave cannot interfere destructively at the spatial point and may even superimpose at the spatial point, increasing the amplitude of the sound wave at the spatial point. In some embodiments, in order to reduce the increase in the amplitude of the sound wave due to the superposition of the first sound wave and the second sound wave in the higher frequency range, the target frequency range may also include frequencies greater than the resonant frequency. Therefore, the sound-absorbing structure can absorb sound waves in a higher frequency range, thereby reducing or avoiding the superposition of the first and second sound waves at a spatial point and lowering the amplitude of the sound waves within the target frequency range at that spatial point. For example, the target frequency range can be 1kHz-20kHz. It should be noted that the resonant frequency of the second acoustic cavity can be obtained through various testing methods. Here is an example: when testing the frequency response curve of the second acoustic cavity without or without the sound-absorbing structure 330, the first acoustic aperture is kept open, and a microphone is used to test the frequency response curve at the location of the second acoustic aperture (e.g., placing the microphone 2-5mm in front of the second acoustic aperture), obtaining the resonant frequency corresponding to the resonant peak on the frequency response curve. Specific methods for testing the frequency response curve of the second acoustic cavity without or without the sound-absorbing structure 330 can be found in [reference needed]. Figure 18 And its description.

[0066] In some embodiments, the acoustic device can achieve different sound effects at a spatial point by setting sound-absorbing structures (e.g., the position of the sound-absorbing structure, the sound-absorbing frequency, etc.). In some embodiments, the resonance of the first acoustic cavity also affects the sound wave radiation of the second acoustic cavity, generating additional resonance peaks on the frequency response curve measured at the location of the second acoustic aperture. Therefore, to avoid adding additional resonance peaks to the sound waves transmitted in the second acoustic cavity due to the resonance of the first acoustic cavity, the target frequency range may also include the resonance frequency of the first acoustic cavity. In some embodiments, another sound-absorbing structure 330 can also be provided in the first acoustic cavity to absorb sound waves near the resonance frequency of the first acoustic cavity, avoiding interference enhancement between the sound waves near the resonance frequency of the first acoustic cavity and the sound waves of the same frequency range output by the second acoustic aperture at a spatial point (e.g., a spatial point), thereby reducing the amplitude of the sound waves near the resonance frequency of the first acoustic cavity received at the spatial point. In some embodiments, the sound-absorbing structure can also be provided simultaneously in the first acoustic cavity and the second acoustic cavity, thereby absorbing sound waves near the resonance frequencies of the first and second sound waves, thereby better reducing the amplitude of the sound waves at any spatial point. In some embodiments, the sound-absorbing structure can also absorb low-frequency sounds within a specific frequency range. For example, the sound-absorbing structure can be disposed in a second acoustic cavity to reduce low-frequency sounds within a specific frequency range output from the second acoustic aperture, preventing the low-frequency sounds within that specific frequency range from interfering destructively with the low-frequency sounds within the same frequency range output from the first acoustic aperture at a spatial point (e.g., in the near field), thereby increasing the volume of the acoustic device in the near field (i.e., transmitted to the user's ear) within that specific frequency range. In some embodiments, the sound-absorbing structure may also include sub-sound-absorbing structures that absorb different frequency ranges, for example, absorbing mid-high frequency bands and low frequency bands, for absorbing sounds within different frequency ranges.

[0067] In some embodiments, since the wavelength of high-frequency sound waves is shorter in the high-frequency range above the resonant frequency of the second acoustic cavity, the distance between the two acoustic holes (e.g., the distance between the geometric centers of the two acoustic holes) may affect the phase difference of the sound waves radiated by the two acoustic holes at spatial points, thereby weakening the sound leakage reduction effect of the dipole sound source formed by the two acoustic holes in the high-frequency range. Therefore, in order to reduce the high-frequency output of the second acoustic cavity, the target frequency range may include a high-frequency range above the resonant frequency of the second acoustic cavity, so that the sound-absorbing structure 330 can absorb high-frequency sound waves, thereby improving the problem of the unsatisfactory sound leakage reduction effect of the dipole sound source in the high-frequency range.

[0068] Because the human ear is relatively sensitive to sounds in the 3kHz-6kHz range near the resonant frequency and in the relatively high-frequency range, in some embodiments, the target frequency range may include the 3kHz-6kHz frequency range to achieve more targeted and effective sound leakage reduction. In some embodiments, the target frequency range may include 4kHz-6kHz. It should be noted that the resonant frequency here mainly refers to the resonant frequency of the second acoustic cavity. In some embodiments, it may also refer to the resonant frequency of the second acoustic cavity or the resonant frequency of the first acoustic cavity, hereinafter referred to as the resonant frequency.

[0069] According to the above embodiments, the sound-absorbing structure can absorb sound waves within the target frequency range of the first and / or second sound waves, thereby reducing the amplitude of the sound waves within the target frequency range at the spatial point. For the first and second sound waves outside the target frequency range (e.g., sound waves below the resonant frequency), the first and second sound waves can be transmitted to the spatial point through the acoustic transmission structure and interfere at that point. This interference can reduce the amplitude of the sound waves outside the target frequency range at that spatial point. In other words, the first and second sound waves outside the target frequency range (or the first frequency range) can interfere destructively at the spatial point, achieving the effect of dipole-based sound leakage reduction; the first and / or second sound waves within the target frequency range (or the second frequency range) can be absorbed by the sound-absorbing structure, thereby reducing or avoiding the enhanced interference of the first and / or second sound waves at the spatial point, or weakening or absorbing the additional resonant peaks generated by the first or second sound waves under the action of the acoustic transmission structure, thus reducing the amplitude of the sound waves within the target frequency range at the spatial point. Therefore, by setting a sound-absorbing structure, the embodiments of this specification can enable the acoustic device to output a first sound wave and a second sound wave in a first frequency range, and can reduce the sound wave output of the acoustic device (e.g., the second acoustic aperture) near or above the resonant frequency of the acoustic transmission structure. While ensuring that the acoustic device interferes and cancels each other in the first frequency range, it reduces or avoids the increase of sound wave amplitude in the second frequency range at a spatial point (e.g., the far field), thereby adjusting the directivity of the acoustic device and ensuring the sound leakage reduction effect across the entire frequency band.

[0070] The sound absorption effect of the sound-absorbing structure 330 refers to the amount of sound that the sound-absorbing structure 330 can absorb within the target frequency range, and can be expressed in terms of sound pressure level. For example, the sound absorption effect of the sound-absorbing structure 330 can be expressed as the difference between the sound pressure levels measured at the same frequency and at the same location corresponding to the second acoustic cavity, with and without the sound-absorbing structure 330, within the target frequency range. As an example only, the difference between the sound pressure levels at the second acoustic aperture with and without the sound-absorbing structure 330 can be used to represent the difference between the sound pressure levels of the second acoustic cavity with and without the sound-absorbing structure 330. As an example only, the sound pressure level at the second acoustic aperture with and without the sound-absorbing structure 330 can be measured as follows: A test microphone is placed directly in front of the second acoustic aperture at a distance of approximately 2mm-5mm, and the sound pressure level at the second acoustic aperture with and without the sound-absorbing structure 330 is measured. The test frequency is near the resonant frequency of the second acoustic cavity or near 1kHz. In some embodiments, with and without the sound-absorbing structure 330, the difference between the sound pressure levels measured at the same frequency and the same location within the second acoustic cavity can be no less than 3 dB. For example, with and without the sound-absorbing structure 330, the difference between the sound pressure levels measured at the second acoustic aperture at the same frequency can be no less than 3 dB. In some embodiments, the aforementioned target frequency range can be referred to as the sound absorption bandwidth of the sound-absorbing structure 330. When the sound absorption bandwidth is in the range of 3 kHz to 6 kHz, the sound-absorbing structure 330 can effectively absorb sound waves in the range of 3 kHz to 6 kHz, and the sound absorption effect is no less than 3 dB, thereby improving the sound leakage of the acoustic device in the range of 3 kHz to 6 kHz. In some embodiments, to further reduce the sound leakage of the acoustic device, the sound absorption effect of the sound-absorbing structure 330 in the target frequency range can be no less than 6 dB. In some embodiments, to further reduce the sound leakage of the acoustic device, the sound absorption effect of the sound-absorbing structure 330 in the target frequency range can be no less than 10 dB. In some embodiments, the sound absorption effect of the sound-absorbing structure 330 can be different in different frequency ranges. For example, in the 3kHz-6kHz range, the sound absorption effect of the sound-absorbing structure 330 is no less than 3dB. As another example, in the 4kHz-6kHz range, the sound absorption effect of the sound-absorbing structure 330 is no less than 6dB. Furthermore, in the 5kHz-6kHz range, the sound absorption effect of the sound-absorbing structure 330 is no less than 8dB, thus more effectively reducing sound leakage in higher frequency ranges.

[0071] Since the frequency response curve of the second acoustic cavity exhibits a resonance peak at a specific frequency (e.g., the resonant frequency), and the vibration amplitude at the resonant frequency is relatively large, the sound-absorbing structure 330 needs to absorb more sound at the resonant frequency to achieve a better sound leakage reduction effect at the resonant frequency of the second acoustic cavity. Therefore, in some embodiments, the sound-absorbing structure 330 has a sound absorption effect of not less than 14dB for sound at the resonant frequency or sound with a vibration frequency close to the resonant frequency. In this way, sound waves at or near the resonant frequency of the second acoustic cavity can be effectively absorbed by the sound-absorbing structure 330, reducing or avoiding resonance of sound waves near the resonant frequency under the action of the acoustic cavity. This reduces or avoids changes in amplitude and phase difference (e.g., phase difference not equal to 180 degrees) between the first and second sound waves near the resonant frequency, which would lead to a deterioration in the sound leakage reduction effect at the spatial point, or even a situation where the two sets of sounds not only do not cancel each other out but also interfere with each other, thus reducing sound leakage of the acoustic device at the far-field spatial point. In some embodiments, to further reduce sound leakage of the acoustic device, the sound-absorbing structure 330 has a sound absorption effect of not less than 18 dB on sound at the resonant frequency or sound with a vibration frequency close to the resonant frequency. In some embodiments, to further reduce sound leakage of the acoustic device, the sound-absorbing structure 330 has a sound absorption effect of not less than 22 dB on sound at the resonant frequency or sound with a vibration frequency close to the resonant frequency.

[0072] In some embodiments, the sound-absorbing structure 330 may include at least one of a resistive sound-absorbing structure or a reactive sound-absorbing structure. For example, the function of the sound-absorbing structure 330 can be achieved by a resistive sound-absorbing structure. As another example, the function of the sound-absorbing structure 330 can be achieved by a reactive sound-absorbing structure. Yet another example is that the function of the sound-absorbing structure 330 can also be achieved by a hybrid resistive and reactive sound-absorbing structure.

[0073] A resistive sound-absorbing structure can refer to a structure capable of providing acoustic resistance when sound waves pass through it. In some embodiments, the resistive sound-absorbing structure may include at least one of porous sound-absorbing material or acoustic mesh. In some embodiments, the resistive sound-absorbing structure may be disposed at any position on the transmission path of the first sound wave and / or the second sound wave. For example, the porous sound-absorbing material or acoustic mesh may be attached to the inner wall of the acoustic transmission structure. For another example, the porous sound-absorbing material or acoustic mesh may constitute at least a portion of the inner wall of the acoustic transmission structure. For yet another example, the porous sound-absorbing material or acoustic mesh may fill at least a portion of the interior of the acoustic transmission structure. A reactive sound-absorbing structure can refer to a structure that absorbs sound using resonance. In some embodiments, the reactive sound-absorbing structure may include, but is not limited to, a Helmholtz sound-absorbing cavity, a perforated plate sound-absorbing structure, a micro-perforated plate sound-absorbing structure, a thin plate, a thin film, a quarter-wavelength resonant tube, or any combination thereof. In some embodiments, a resistive sound-absorbing structure and a reactive sound-absorbing structure may be simultaneously disposed as a hybrid impedance sound-absorbing structure to achieve the function of the sound-absorbing structure 330. For example, an impedance-hybrid sound-absorbing structure may include a perforated plate sound-absorbing structure and a porous sound-absorbing material or acoustic mesh. The porous sound-absorbing material or acoustic mesh may be disposed within the cavity of the perforated plate sound-absorbing structure or within the acoustic transmission structure. As another example, an impedance-hybrid sound-absorbing structure may include a quarter-wavelength resonant tube structure and a porous sound-absorbing material or acoustic mesh. The quarter-wavelength resonant tube structure may be disposed inside or outside the acoustic transmission structure, and the porous sound-absorbing material or acoustic mesh may be disposed inside the acoustic transmission structure. As yet another example, an impedance-hybrid sound-absorbing structure may include a perforated plate sound-absorbing structure, a quarter-wavelength resonant tube structure, and a porous sound-absorbing material or acoustic mesh.

[0074] Figure 4 These are frequency response curves of acoustic devices with different sound-absorbing structures according to some embodiments of this specification. Curves 411 and 421 respectively represent the first acoustic cavity (e.g., without a sound-absorbing structure) in the acoustic device. Figure 1 The first acoustic cavity 130 shown) and the second acoustic cavity (e.g., Figure 1 The frequency response curves of the second acoustic cavity 140 shown are: curves 412 and 422, representing the frequency response curves of the first and second acoustic cavities respectively when a 1 / 4 wavelength resonant tube is installed in the second acoustic cavity of the acoustic device; and curves 413 and 423, representing the frequency response curves of the first and second acoustic cavities respectively when a micro-perforated plate sound-absorbing structure is installed in the second acoustic cavity of the acoustic device. Figure 4As shown, compared to an acoustic device without a sound-absorbing structure, the acoustic device with a sound-absorbing structure exhibits little change in the frequency response of the first acoustic cavity. The frequency response of the second acoustic cavity also shows little change in the low-frequency range (e.g., less than 2kHz), but it can form a trough in the high-frequency range (e.g., greater than 2kHz). In other words, the sound-absorbing structure can reduce the amplitude of the high-frequency sound waves output from the second acoustic cavity, thereby reducing high-frequency sound leakage. Furthermore, compared to a quarter-wavelength resonant tube, the acoustic device employing a micro-perforated plate sound-absorbing structure has a superior high-frequency sound leakage reduction effect.

[0075] In some embodiments, the acoustic transmission structure (e.g., a housing) of an acoustic device may include a perforated plate sound-absorbing structure and a resistive sound-absorbing structure. The resistive sound-absorbing structure may include porous sound-absorbing material and / or acoustic mesh. In some embodiments, the resistive sound-absorbing structure may be disposed around the openings of one or more holes in the perforated plate sound-absorbing structure. In some embodiments, by providing an impedance-hybrid sound-absorbing structure, not only can resonant sound absorption be achieved through the resistive sound-absorbing structure, but the frictional dissipation of sound waves can also be increased through the resistive sound-absorbing structure, thereby increasing the sound absorption bandwidth and further improving the sound leakage reduction effect within the target frequency range of the acoustic device. In some embodiments, the resistive sound-absorbing structure may be attached to the inner wall of the cavity of the perforated plate sound-absorbing structure. In some embodiments, the resistive sound-absorbing structure may fill at least a portion of the cavity. In some embodiments, the resistive sound-absorbing structure may also be disposed inside the housing or as part of the housing.

[0076] Figure 5 These are frequency response curves of acoustic devices with different sound-absorbing structures as shown in some embodiments of this specification. Figure 5 As shown, curve L 5-1 The frequency response curve of the acoustic device without sound-absorbing structure in the second acoustic cavity, curve L 5-2 The frequency response curve of the acoustic device with a micro-perforated plate sound-absorbing structure in the second acoustic cavity is represented by curve L. 5-3 The frequency response curve of the acoustic device, which incorporates a micro-perforated sound-absorbing structure and an acoustic mesh, within the second acoustic cavity is represented by curve L. 5-4 The frequency response curve of the acoustic device, which incorporates a micro-perforated sound-absorbing structure, acoustic mesh, and N′Bass material, within the second acoustic cavity. Figure 5 It can be seen that in the low-frequency range (e.g., 1kHz-2kHz), the four curves overlap significantly, indicating that the four acoustic devices have roughly the same low-frequency output. However, in the mid-to-high frequency range (e.g., above 2kHz), compared to L without a sound-absorbing structure... 5-1 L with sound-absorbing structure 5-2 L 5-3 With L 5-4This can create troughs. In other words, the sound-absorbing structure can reduce the high-frequency output of the second acoustic cavity of the acoustic device, thereby improving the high-frequency sound leakage reduction effect. Furthermore, within a relatively large range (e.g., 2kHz-5kHz), L-shaped structures with triple sound-absorbing features... 5-4 It is generally below the other three curves, exhibiting the best sound leakage reduction effect. Therefore, by setting up a sound-absorbing structure (e.g., an impedance-mixed sound-absorbing structure) to reduce the high-frequency output of the second acoustic cavity of the acoustic device, the sound field chaos of the acoustic device in the high-frequency range can be suppressed, thereby improving the high-frequency sound leakage reduction effect.

[0077] By coupling the sound-absorbing structure 330 with the second acoustic cavity, sound waves within the target frequency range are absorbed by the sound-absorbing structure 330. This reduces or avoids resonance of sound waves near a specific frequency (e.g., the resonant frequency) under the influence of the acoustic cavity. Consequently, it reduces or avoids amplitude and phase differences (e.g., a phase difference not equal to 180 degrees) between the first and second sound waves near the specific frequency of the cavity, which could lead to a deterioration in sound leakage reduction at the spatial point, or even a situation where the two sets of sounds not only fail to cancel each other out but instead enhance interference, thus reducing sound leakage within the target frequency range. The target frequency range can include the high-frequency range; the first and second sound waves outside the target frequency range can achieve dipole cancellation, reducing sound leakage at the spatial point.

[0078] Figure 6 This is a schematic diagram of an acoustic device with a sound-absorbing structure according to some embodiments of this specification.

[0079] like Figure 6 As shown, in some embodiments, the acoustic device 600 may include a housing 610 and a speaker 620. The speaker 620 is disposed within the accommodating cavity formed by the housing 610, and a first acoustic cavity 630 and a second acoustic cavity 640 are respectively provided on the front and rear sides of the speaker 620 (or diaphragm). The housing 610 is provided with a first acoustic hole 611 and a second acoustic hole 612. The first acoustic cavity 630 can be acoustically coupled to the first acoustic hole 611, and the second acoustic cavity 640 can be acoustically coupled to the second acoustic hole 612.

[0080] In some embodiments, such as Figure 6 As shown, the acoustic device 600 may further include a sound-absorbing structure 650, which can be coupled to the second acoustic cavity 640. In some embodiments, the sound-absorbing structure 650 may include a micro-perforated plate sound-absorbing structure. The micro-perforated plate sound-absorbing structure includes a micro-perforated plate 651 and a cavity 652. The micro-perforated plate 651 includes through holes, and the second acoustic cavity 640 coupled to the micro-perforated plate structure communicates with the cavity 652 through the through holes in the micro-perforated plate. It should be noted that, as... Figure 6The acoustic device 600 shown is merely an example; the specific arrangement of the sound-absorbing structure 650 can have various variations or modifications.

[0081] Sound waves from the second acoustic cavity 640 can enter the cavity 652 of the micro-perforated plate sound-absorbing structure through one or more through holes, and under certain conditions, cause the micro-perforated plate sound-absorbing structure to resonate. For example, when the vibration frequency of the sound waves entering the cavity 652 is close to the resonant frequency of the micro-perforated plate sound-absorbing structure, the sound waves entering the cavity 652 cause the micro-perforated plate sound-absorbing structure to resonate. The air inside the cavity 652 will dissipate energy along with the micro-perforated plate sound-absorbing structure through resonance, thus achieving a sound absorption effect. The frequency of the sound waves absorbed by the micro-perforated plate sound-absorbing structure is the same as or close to its resonant frequency.

[0082] In some embodiments, the material of the micro-perforated plate 651 can be a metal (e.g., aluminum) or a non-metal (e.g., acrylic, polycarbonate (PC), etc.). When the micro-perforated plate 651 is a non-metallic plate, the thermal conductivity of the non-metallic plate is relatively low, and the process of sound waves passing through the perforations can be considered an adiabatic process. When the micro-perforated plate 651 is a metallic plate, the thermal conductivity of the metallic plate is relatively high, and when the aperture of the perforations is small, the process of sound waves passing through the perforations can be considered an isothermal process. Heat conduction represents an increase in energy dissipation; therefore, the equivalent damping of the metallic plate is greater than that of the non-metallic plate.

[0083] Figure 7 These are sound absorption diagrams illustrating the acoustic devices shown in some embodiments of this specification, employing metal micro-perforated plates and non-metal micro-perforated plates respectively. Figure 7 The horizontal axis represents the sound absorption frequency, and the vertical axis represents the sound absorption coefficient. Curve 71 represents the sound absorption effect of the non-metallic micro-perforated plate, and curve 72 represents the sound absorption effect of the metallic micro-perforated plate. For example... Figure 7 As shown, the maximum sound absorption coefficient of the metal micro-perforated plate is slightly lower than that of the non-metal micro-perforated plate, but the sound absorption bandwidth of the metal micro-perforated plate is wider than that of the non-metal micro-perforated plate. This is because the metal micro-perforated plate has better thermal conductivity and greater equivalent damping for sound waves to pass through.

[0084] Figure 8 The frequency response curves of the acoustic devices shown in some embodiments of this specification, using metal microperforated plates and non-metal microperforated plates respectively, are based on these curves. Figure 8 The horizontal axis represents frequency, and the vertical axis represents sound pressure level. Curve 81 represents the frequency response using a metal micro-perforated plate, and curve 82 represents the frequency response using a non-metallic micro-perforated plate. Here, the frequency response refers to the frequency response at the second acoustic aperture (e.g., 10mm directly in front of the second acoustic aperture). Figure 8As shown, metal microperforated plates exhibit better sound absorption than non-metallic microperforated plates in the mid-to-low frequency range (e.g., below 4kHz), reducing sound leakage of the acoustic device by approximately 2-3dB. In this case, the metal microperforated plate is made of aluminum. Although the sound absorption of non-metallic microperforated plates is slightly inferior, using them reduces the weight of the acoustic device, improving its portability and lowering its cost. In some embodiments, since both metal and non-metal plates have their advantages, either metal or non-metallic microperforated plates can be flexibly selected based on factors such as weight, cost, and corrosion resistance.

[0085] If the natural frequency of the micro-perforated plate 651 installed in the acoustic device (or in a fixed state) falls within the target frequency range, the micro-perforated plate 651 may resonate within the target frequency range, affecting the sound absorption effect. Therefore, the natural frequency of the micro-perforated plate 651 in the fixed state should be much greater than the target frequency. In some embodiments, the natural frequency of the micro-perforated plate 651 in the fixed state is not easy to measure, and its natural frequency in the free state can be used to characterize its natural frequency in the fixed state. The free state can refer to the state when the micro-perforated plate 651 is not installed in the acoustic device, and the natural frequency of the micro-perforated plate 651 in the fixed state is much greater than its natural frequency in the free state. The method for measuring the natural frequency in the free state can be as follows: Keep the micro-perforated plate 651 in a free state, apply a constant amplitude excitation force with a frequency varying from low to high to the micro-perforated plate 651 using a vibrator, and use a laser vibrometer to measure the velocity amplitude of the micro-perforated plate 651. Record the frequency at which the velocity amplitude of the micro-perforated plate 651 first reaches its maximum value; this is the natural frequency of the micro-perforated plate 651 in the free state. In some embodiments, the sound absorption bandwidth is in the range of 3kHz-6kHz. To avoid the natural frequency of the micro-perforated plate in the fixed state falling within the sound absorption bandwidth, the theoretical value of the natural frequency of the micro-perforated plate 651 in the free state can be greater than 500Hz (e.g., 500Hz-3.6kHz), making its natural frequency in the fixed state much greater than the upper limit frequency of sound absorption (i.e., the maximum frequency in the sound absorption bandwidth, for example, 6kHz). The natural frequency is related to the stiffness and mass of the micro-perforated plate 651. Therefore, its natural frequency can be determined by setting the stiffness and / or mass of the micro-perforated plate 651, thereby enabling it to absorb sound waves within a target frequency range. In some embodiments, micro-perforated plates 651 of different shapes, materials, etc., have different stiffness and / or mass, resulting in different natural frequencies. In some embodiments, the micro-perforated plate 651 can be a regular shape or an irregular shape, such as a circle, fan, rectangle, or rhombus. In some embodiments, the material of the micro-perforated plate 651 can be a non-metallic or metallic material.

[0086] In some embodiments, the micro-perforated plate 651 can be a racetrack-shaped micro-perforated plate. In some embodiments, when the micro-perforated plate 651 is a racetrack-shaped micro-perforated plate, in order to ensure that the natural frequency of the micro-perforated plate 651 in its free state is in the range of 500Hz-3.6kHz, the Young's modulus of its material is in the range of 5Gpa-200Gpa. For example, the Young's modulus of the material is in the range of 10Gpa-180Gpa. Another example is that the Young's modulus of the material is in the range of 50Gpa-100Gpa. In some embodiments, the thickness of the micro-perforated plate 651 can affect its natural frequency. When the micro-perforated plate 651 is a racetrack-shaped micro-perforated plate, in order to ensure that the natural frequency of the micro-perforated plate 651 in its free state is in the range of 500Hz-3.6kHz, the thickness of the racetrack-shaped micro-perforated plate can be in the range of 0.1mm-0.8mm. For example, the thickness of the racetrack-shaped micro-perforated plate can be in the range of 0.2mm-0.7mm.

[0087] In some embodiments, the microperforated plate 651 can be a circular microperforated plate. With the same parameters (e.g., pore size, plate thickness, perforation rate, cavity height (e.g., cavity 652)), the natural frequency of the circular microperforated plate 651 is lower than that of the racetrack-shaped microperforated plate 651. Therefore, the circular microperforated plate requires a material with greater stiffness and / or a thicker plate than the racetrack-shaped microperforated plate to ensure that its natural frequency is much higher than the upper limit of sound absorption frequency. In some embodiments, when the microperforated plate 651 is a circular microperforated plate, in order to ensure that the natural frequency of the microperforated plate 651 in its free state is in the range of 500Hz-3.6kHz, the Young's modulus of the material of the microperforated plate 651 is in the range of 50Gpa-200 Gpa. For example, the Young's modulus of the circular microperforated plate material is in the range of 60Gpa-180 Gpa. As another example, the Young's modulus of the circular microperforated plate material is in the range of 80Gpa-150 Gpa. In some embodiments, when the microperforated plate 651 is a circular perforated plate, in order to ensure that the natural frequency of the microperforated plate 651 in its free state is in the range of 500Hz-3.6kHz, the thickness of the circular microperforated plate needs to be in the range of 0.3mm-1mm. For example, the thickness of the circular microperforated plate needs to be in the range of 0.4mm-0.9mm. As another example, the thickness of the circular microperforated plate needs to be in the range of 0.6mm-0.7mm.

[0088] By adjusting the Young's modulus and / or thickness of the micro-perforated plate 651, its natural frequency can be avoided from falling within the sound absorption bandwidth in a fixed state, thus affecting its sound absorption effect.

[0089] In some embodiments, a waterproof and breathable structure may be provided on the side of the micro-perforated plate 651 facing the speaker 420 (or diaphragm), which can be used for waterproofing and dustproofing. Specifically, since the aperture of the through holes in the micro-perforated plate 651 is relatively small, capillary action is prone to occur, making it difficult for water to drain after entering, which will affect the sound leakage reduction effect of the sound absorption structure. Therefore, a waterproof and breathable structure needs to be provided at the interface between the micro-perforated plate 651 and the second acoustic cavity 440. In some embodiments, the waterproof and breathable structure can cover the entire side of the micro-perforated plate 651 that contacts the second acoustic cavity 440. In some embodiments, the waterproof and breathable structure can cover all the through holes on the micro-perforated plate 651, so that the through holes are connected to the second acoustic cavity 440 through the waterproof and breathable structure.

[0090] In some embodiments, the waterproof and breathable structure may be a mesh. Figure 9 This is a frequency response curve at the second acoustic hole 612 measured according to some embodiments of this specification, with and without a 025HY type mesh on the side of the micro-perforated plate 651 facing the speaker 120 (or diaphragm). Figure 9 In the diagram, the horizontal axis represents frequency, and the vertical axis represents sound pressure level. Curve 91 represents the frequency response curve measured at the second acoustic aperture 612 (e.g., 10mm directly in front of the second acoustic aperture 612) when a 025HY type mesh is installed, and curve 92 represents the frequency response curve measured at the second acoustic aperture 612 (e.g., 10mm directly in front of the second acoustic aperture 612) when no mesh is installed. Figure 9 As shown, curve 91 is slightly higher than curve 92, but the difference in sound pressure level between the two is not significant. It can be seen that the sound absorption effect of the micro-perforated plate 651 with 025HY mesh is slightly lower than that without mesh, but the impact is minimal. However, it can provide some degree of waterproofing and dustproofing (for example, acoustic devices using 025HY mesh can pass the IPX7 waterproof test). Therefore, in some embodiments, 025HY mesh can be provided on the side of the micro-perforated plate 651 facing the diaphragm to achieve waterproofing and dustproofing of the micro-perforated plate sound-absorbing structure. In some embodiments, the acoustic impedance of the 025HY mesh is lower than 50 MKS Rayls. Thus, the side of the micro-perforated plate 651 facing the diaphragm can be provided with mesh, and the acoustic impedance of the mesh can be lower than 50 MKS Rayls, thereby achieving waterproofing and dustproofing while having almost no impact on the output effect of the acoustic device (e.g., the second acoustic aperture).

[0091] Cavity 652 is a cavity located away from the second acoustic cavity 440, and it communicates with the outside only through a through-hole on the micro-perforated plate 651. In some embodiments, the shape of cavity 652 includes, but is not limited to, those of other than, the shape of cavity 652. Figure 6 The cuboid shown may also include regular shapes such as spheres and cylinders, or irregular shapes such as racetracks. In some embodiments, the cavity 652 has a certain height D (see...). Figure 6 The larger the cavity height D, the wider its sound absorption bandwidth. Therefore, in some embodiments, the sound absorption effect of the micro-perforated plate sound absorption structure can be improved by setting a larger cavity height D.

[0092] Figure 10 This is a graph showing the sound absorption coefficient of a micro-perforated plate sound-absorbing structure with different cavity heights, as illustrated in some embodiments of this specification. Figure 10 As shown, as the height D of cavity 652 increases, the horizontal axis of the corresponding peak value gradually shifts to the left, the peak value of the corresponding curve gradually decreases, but the coverage width of the corresponding curve gradually increases. Therefore, the larger the cavity height D, the lower the corresponding sound absorption frequency, the smaller the maximum sound absorption coefficient, but the wider the sound absorption bandwidth.

[0093] Figure 11 This is a comparison chart showing the variation trend of the maximum sound absorption coefficient with 0.5 octave bands for different cavity heights according to some embodiments of this specification. The 0.5 octave band refers to the octave range spanned by the sound absorption curve when the sound absorption coefficient is 0.5. A larger octave band indicates a wider sound absorption bandwidth. Figure 11 As shown, as the cavity height D increases, the corresponding maximum sound absorption coefficient gradually decreases, but the 0.5 octave band of sound absorption gradually increases, that is, the sound absorption bandwidth gradually widens.

[0094] In summary, a larger cavity height D results in a wider sound absorption bandwidth near the desired resonant absorption frequency. However, a larger cavity height also reduces the maximum absorption coefficient at the resonant absorption frequency. Therefore, in some embodiments, to balance the sound absorption bandwidth and maximum absorption coefficient of the micro-perforated plate sound absorption structure, the cavity height D can range from 0.5mm to 10mm. For example, the cavity height D can range from 2mm to 9mm. Another example is a range of 7mm to 10mm.

[0095] In some embodiments, a plurality of through holes may be provided on the micro-perforated plate 651, with the through holes spaced apart. In some embodiments, the plurality of through holes may be distributed in any manner. For example, the plurality of through holes may be distributed in an array. Another example is that the plurality of through holes may be distributed in a ring around a center point. In some embodiments, the spacing between the through holes (referred to as hole spacing) may be uniform or non-uniform. The spacing between through holes described in the specification refers to the minimum distance between the edge of one through hole and the edge of an adjacent through hole.

[0096] In some embodiments, the spacing between through holes can be much larger than the diameter of the through hole (where the diameter refers to the diameter of the through hole), and the ratio between the spacing and the diameter of the through hole can be greater than 5. In some embodiments, the spacing between holes can be much larger than the diameter of the through hole, and the ratio between the spacing and the diameter of the through hole can be greater than 10. When the spacing between holes is greater than the diameter, the characteristics of sound wave transmission between the holes can be independent of each other.

[0097] In some embodiments, the hole spacing of the through holes on the micro-perforated plate can be much smaller than the wavelength of sound within the target frequency range. In some embodiments, the ratio of the wavelength of sound within the target frequency range to the hole spacing can be greater than 5. In some embodiments, the ratio of the wavelength of sound within the target frequency range to the hole spacing can be greater than 10. As an example only, the target frequency range can be 3kHz-6kHz, and the wavelength of sound within the target frequency range can be in the range of 56mm-110mm. The ratio of the wavelength of sound within the target frequency range to the hole spacing can be greater than 5; for example, the hole spacing can be in the range of 10mm-22mm. When the hole spacing is much smaller than the wavelength, the reflection of sound waves by the inter-hole plate (the micro-perforated plate 651 region between the edge of the through hole and the edge of the adjacent through hole) can be ignored, thereby avoiding the influence of the reflection of the inter-hole plate on the sound wave propagation process.

[0098] In some embodiments, within the effective aperture range, the smaller the aperture of the through hole, the greater the acoustic resistance when sound waves pass through the through hole, the more energy is dissipated, and the wider the sound absorption bandwidth. Therefore, the sound absorption effect of the micro-perforated plate sound absorption structure can be improved by setting a smaller through hole diameter. The effective aperture range refers to the range within which the sound absorption bandwidth of the micro-perforated plate sound absorption structure can meet the requirements for reducing sound leakage. When the aperture is within the effective aperture range, the smaller the aperture, the better the sound absorption effect. When the aperture is smaller than the effective aperture range, the sound absorption bandwidth will be significantly reduced. In some embodiments, the effective aperture range can be in the range of 0.1mm-1mm. Considering the processing requirements, in some embodiments, the effective aperture range can be in the range of 0.2mm-0.4mm; for example, the effective aperture range can be in the range of 0.2mm-0.3mm. In some embodiments, the effective aperture range can be in the range of 0.1mm-0.4mm; for example, the effective aperture range can be in the range of 0.1mm-0.2mm.

[0099] Figure 12 The diagram shows the sound absorption effect of a micro-perforated plate 651 with through-hole diameters of 0.15 mm and 0.3 mm, as illustrated in some embodiments of this specification. Figure 12 The horizontal axis represents the sound absorption frequency, and the vertical axis represents the sound absorption coefficient. Curve 121 represents the sound absorption effect of the micro-perforated plate 651 with a pore size of 0.15 mm, and curve 122 represents the sound absorption effect of the micro-perforated plate 651 with a pore size of 0.3 mm. For example... Figure 12As shown, curve 121 has a wider width than curve 122, but their heights are similar. Therefore, it is evident that the sound absorption bandwidth and sound absorption effect of the micro-perforated plate 651 with a pore size of 0.15 mm are significantly better than those of the micro-perforated plate 651 with a pore size of 0.3 mm.

[0100] Figure 13 This is a frequency response curve of a micro-perforated plate 651 with apertures of 0.15 mm and 0.3 mm, as shown in some embodiments of this specification. Figure 13 In the diagram, the horizontal axis represents frequency, and the vertical axis represents sound pressure level. Curve 131 represents the frequency response of the micro-perforated plate 651 with a 0.15mm aperture, and curve 132 represents the frequency response of the micro-perforated plate 651 with a 0.3mm aperture. Here, frequency response refers to the frequency response of the sound emitted from the second acoustic hole. Figure 13 As shown, curve 131 exhibits approximately 6 dB lower sound leakage in the 2kHz-4kHz frequency band compared to curve 132. This demonstrates that the micro-perforated plate 651 with a 0.15mm aperture exhibits significantly better sound absorption in the mid-to-high frequency range than the micro-perforated plate 651 with a 0.3mm aperture. Therefore, in some embodiments, to achieve better sound absorption, a micro-perforated plate 651 with an aperture of 0.15mm or close to 0.15mm can be used. For example, a micro-perforated plate 651 with an aperture in the range of 0.1mm-0.2mm can be used. In some embodiments, considering the requirements for dustproofing and drainage, a micro-perforated plate 651 with an aperture of 0.3mm or close to 0.3mm (e.g., 0.28mm-0.35mm) can be used.

[0101] In some embodiments, to avoid an excessive number of through holes leading to too small a hole spacing and affecting the characteristics of sound wave transmission between through holes, the perforation rate of the micro-perforated plate 651 can be less than 5%. The perforation rate refers to the ratio of the total area of ​​the through holes to the side area of ​​the micro-perforated plate 651 near the second acoustic cavity 440.

[0102] As can be seen from the above, the cavity height D, the thickness of the micro-perforated plate 651, the diameter of the through hole, and the perforation rate all affect the sound absorption bandwidth and sound absorption coefficient of the micro-perforated plate 651. The comprehensive values ​​of these parameters can be found in the following description.

[0103] Typically, the acoustic impedance of a single through-hole on the micro-perforated plate 651 is:

[0104]

[0105] (1) In the formula, ρ is the air density, μ is the air viscosity coefficient, t is the plate thickness, and d is the aperture. When the plate thickness of the through hole is comparable to the aperture, the end correction of the through hole needs to be considered, that is, the effective plate thickness is increased by 0.85d. The micro-perforated plate 651 is provided with multiple through holes, and its acoustic impedance can be equivalent to the parallel connection of the acoustic impedances of multiple through holes, that is, the acoustic impedance ratio of the micro-perforated plate 651 can be obtained by dividing the acoustic impedance ratio of a single through hole by the perforation ratio:

[0106]

[0107] (2) In the formula, σ is the perforation rate and k is the wave number, and the expression is: Where ω is the angular frequency and c is the speed of sound. The cavity 652 of the micro-perforated plate sound-absorbing structure is equivalent to an acoustic volume, and its acoustic impedance is:

[0108]

[0109] (3) In the formula, D is the height of the cavity. Then the acoustic impedance of the micro-perforated plate sound-absorbing structure can be expressed as:

[0110] Z total =Z MPP +Z D (4)

[0111] After normalization:

[0112]

[0113] (5) In the formula, r is the relative acoustic impedance and m is the relative acoustic mass, specifically:

[0114]

[0115]

[0116] When the sound wave is incident perpendicularly, the sound absorption coefficient α of the micro-perforated plate sound-absorbing structure can be obtained by solving:

[0117]

[0118] The resonant frequency of the sound-absorbing structure 650 is:

[0119]

[0120] According to equations (1) to (9), the sound absorption bandwidth and sound absorption coefficient of the sound absorption structure 650 can be controlled by adjusting the pore size, perforation rate, plate thickness, and cavity height of the micro-perforated plate 651.

[0121] Furthermore, the values ​​of parameters such as aperture, perforation rate, plate thickness, and cavity height can be combined with considerations of sound absorption coefficient, sound absorption frequency range, and structural dimensions to comprehensively determine the parameter combination. For example, the sound absorption bandwidth and maximum sound absorption coefficient of the sound absorption structure 650 are mutually restrictive and can be balanced according to actual needs. For instance, the smaller the aperture of the micro-perforated plate 651, the wider the sound absorption bandwidth. A wider sound absorption bandwidth corresponds to an effective aperture range. When the aperture is within the effective aperture range, the smaller the aperture, the better the sound absorption effect. When the aperture is smaller than the effective aperture range, the sound absorption bandwidth will decrease significantly. As another example, small aperture, large perforation rate, small plate thickness, and cavity height are suitable for the high-frequency sound absorption range, while the opposite is true for the low-frequency sound absorption range.

[0122] In some embodiments, the aperture can be in the range of 0.1mm-0.2mm, the perforation rate can be in the range of 2%-5%, the plate thickness can be in the range of 0.2mm-0.7mm, and the cavity height can be in the range of 7mm-10mm. As an example only, the aperture of the micro-perforated plate 651 can be in the range of 0.1mm-0.2mm, the perforation rate can be in the range of 2.18%-4.91%, the plate thickness can be in the range of 0.3mm-0.6mm, and the cavity height can be in the range of 7.5mm-9.5mm. For example, the aperture of the micro-perforated plate 651 can be 0.15mm, the perforation rate can be 2.18%, the plate thickness can be 0.3mm, and the cavity height can be 9mm; as another example, the aperture of the micro-perforated plate 651 can be 0.15mm, the perforation rate can be 2.76%, the plate thickness can be 0.4mm, and the cavity height can be 7.5mm.

[0123] Figure 14 The diagram shows the sound absorption effect of a micro-perforated plate 651 with different cavity heights when the aperture is 0.15 mm, the perforation rate is 2.18%, and the plate thickness is 0.3 mm, according to some embodiments of this specification. Figure 14 In the diagram, the horizontal axis represents frequency, and the vertical axis represents the sound absorption coefficient. Curve 141 represents the sound absorption effect of the micro-perforated plate 651 with a cavity height of 9mm, curve 142 represents the sound absorption effect of the micro-perforated plate 651 with a cavity height of 7.5mm, and curve 143 represents the sound absorption effect of the micro-perforated plate 651 with a cavity height of 5mm. For example... Figure 14 As shown, the sound absorption effect is not significantly different when the cavity height is 7.5mm and 9mm. However, if the cavity height is reduced to 5mm, the sound absorption center frequency (the frequency corresponding to the highest sound absorption coefficient) of the micro-perforated plate 651 shifts from 4kHz to 4.9kHz, and the sound absorption coefficient decreases significantly in the frequency range below the sound absorption center frequency (e.g., 2kHz-4.9kHz). Therefore, the sound absorption effect of cavity heights of 9mm, 7.5mm, and 5mm can all meet the requirements for reducing sound leakage, but the sound absorption effect of cavity height 5mm is worse than that of cavity heights of 9mm and 7.5mm.

[0124] In some embodiments, the aperture can be in the range of 0.2mm-0.4mm, the perforation rate can be in the range of 1%-5%, the thickness of the micro-perforated plate 651 can be in the range of 0.2mm-0.7mm, and the cavity height can be in the range of 4mm-9mm. As an example only, the aperture of the micro-perforated plate 651 can be in the range of 0.25mm-0.3mm, the perforation rate can be in the range of 1.11%-4.06%, the thickness of the micro-perforated plate 651 can be in the range of 0.3mm-0.6mm, and the cavity height can be in the range of 4mm-8.5mm. For example, the aperture of the micro-perforated plate 651 can be 0.3mm, the perforation rate can be 2.18%, the thickness can be 0.5mm, and the cavity height can be 5mm; as another example, the aperture of the micro-perforated plate 651 can be 0.25mm, the perforation rate can be 3.41%, the thickness can be 0.6mm, and the cavity height can be 8.5mm.

[0125] Figure 15 These are sound absorption effect diagrams of micro-perforated plates 651 with different thicknesses, based on some embodiments of this specification, when the aperture is 0.3 mm, the perforation rate is 2.18%, and the cavity height is 5 mm. Figure 15 In the diagram, the horizontal axis represents frequency, and the vertical axis represents the sound absorption coefficient. Curve 151 represents the sound absorption effect of a micro-perforated plate 651 with a thickness of 0.6 mm, curve 152 represents the sound absorption effect of a micro-perforated plate 651 with a cavity height of 0.5 mm, and curve 153 represents the sound absorption effect of a micro-perforated plate 651 with a cavity height of 0.4 mm. Figure 15 As shown, the sound absorption center frequencies of curves 151, 152, and 153 gradually increase, while their maximum sound absorption coefficients gradually decrease. The sound absorption effects of plate thicknesses of 0.4mm, 0.5mm, and 0.6mm all meet the requirements for reducing sound leakage, but the sound absorption effect at a thickness of 0.4mm is worse than that at 0.5mm and 0.6mm. In some embodiments, using a micro-perforated plate 651 with a thickness of 0.4mm can reduce the mass of the acoustic device. Therefore, considering the user's wearing experience, a micro-perforated plate with a thickness of 0.4mm can also be used.

[0126] By setting the above parameter combinations, both sound absorption bandwidth and sound absorption coefficient can be considered, enabling the sound absorption structure to effectively absorb sound waves within the target frequency range and improve the sound leakage reduction effect within that range. Furthermore, different parameter combinations can be adapted to the needs of different application scenarios.

[0127] In some embodiments, excessively small micropore size may increase the difficulty of the process, and a deeper cavity depth D may increase the size of the acoustic device. Therefore, the sound absorption effect of the micro-perforated plate sound absorption structure can be improved by a resistive sound absorption structure. Figure 16This is a schematic diagram of an acoustic device with a sound-absorbing structure, as shown in some embodiments of this specification. Figure 16 As shown, a resistive sound-absorbing structure can be disposed in the cavity 652 of the micro-perforated plate sound-absorbing structure. In some embodiments, the resistive sound-absorbing structure may further include a filling material 654 (e.g., N′Bass particles or porous sound-absorbing material). The filling material 654 can be used to increase the equivalent height of the cavity 652 of the micro-perforated plate sound-absorbing structure, thereby improving the sound absorption effect of the micro-perforated plate sound-absorbing structure while reducing the design size of the acoustic device 1600. Specifically, the filling material 654 has a "sponge" effect; when sound waves propagate, air molecules are adsorbed and desorbed in the pores of the filling material 654, which can be regarded as a reduction in the sound velocity in the filling material 654, which is equivalent to increasing the volume of the cavity 652. This achieves the purpose of widening the sound absorption bandwidth of the micro-perforated plate 651 and increasing the sound absorption coefficient (without affecting the center frequency of sound absorption), thereby improving the sound absorption effect of the micro-perforated plate sound-absorbing structure while reducing the design size of the acoustic device.

[0128] In some embodiments, the cavity 652 may be filled with N′Bass (aluminosilicate) sound-absorbing particles. In some embodiments, the N′Bass sound-absorbing particles may be filled into the cavity 652 in a variety of ways. By way of example only, the N′Bass sound-absorbing particles may be directly filled into the cavity 652, or the N′Bass sound-absorbing particles may be filled into a powder package disposed within the cavity 652, or the N′Bass sound-absorbing particles may be encapsulated in a mesh of a specific shape with the powder package disposed within the cavity 652, or the N′Bass sound-absorbing particles may be filled into the cavity 652 using at least two of the above filling methods.

[0129] In some embodiments, the smaller the N′Bass sound-absorbing particles and the smaller the spacing between them, the stronger their adsorption of air molecules. Correspondingly, smaller particles require more N′Bass sound-absorbing particles, increasing cost. Therefore, the diameter of the N′Bass sound-absorbing particles can be in the range of 0.15mm-0.7mm to balance sound absorption performance with cost. For example, the diameter of the N′Bass sound-absorbing particles can be in the range of 0.15-0.6mm. As another example, the diameter of the N′Bass sound-absorbing particles can be in the range of 0.3-0.5mm.

[0130] In some embodiments, as the filling rate of N′Bass sound-absorbing particles in cavity 652 gradually increases, the more N′Bass sound-absorbing particles are present in cavity 652, and the sound absorption effect gradually enhances. Here, the filling rate refers to the ratio of the volume of the filled N′Bass sound-absorbing particles to the volume of cavity 652. However, when the cavity 652 is completely filled with N′Bass sound-absorbing particles, the pressure of the micro-perforated plate sound-absorbing structure on the N′Bass sound-absorbing particles may cause the N′Bass sound-absorbing particles to break, thereby blocking the gaps between the N′Bass sound-absorbing particles and actually reducing the sound absorption effect.

[0131] Figure 17 This is a frequency response curve of the second acoustic cavity of the acoustic device corresponding to different filling material filling rates according to some embodiments of this specification. For example... Figure 17 As shown, when the filling material (e.g., N′Bass sound-absorbing particles) has a filling rate of 0%, that is, when there is no filling material in the cavity of the micro-perforated plate sound-absorbing structure, the frequency response curve corresponding to the second acoustic cavity of the acoustic device forms a peak near 2kHz (e.g., Figure 17 (As shown by the dashed circle in the middle), this indicates that the second acoustic cavity has a relatively large output at 2kHz. When the filling material content is 25%, meaning 25% of the cavity of the micro-perforated plate sound-absorbing structure is filled with filling material, the wave peak near 2kHz is largely absorbed, but small wave peaks still exist. When the filling material content is 50%, meaning 50% of the cavity of the micro-perforated plate sound-absorbing structure is filled with filling material, the wave peak near 2kHz is further absorbed, and the corresponding frequency response curve becomes flatter. When the filling material content is 75%, meaning 75% of the cavity of the micro-perforated plate sound-absorbing structure is filled with filling material, the wave peak near 2kHz is further absorbed, but another wave peak forms near 3kHz, and the output of the second acoustic cavity near 3kHz increases slightly. When the filling material content is 100%, meaning the cavity of the micro-perforated plate sound-absorbing structure is completely filled with filling material, the wave peak near 2kHz is further absorbed, but the wave peak near 3kHz further increases, with a significant peak value, and the output of the second acoustic cavity near 3kHz further increases. To ensure a smoother frequency response curve for the second acoustic cavity, avoiding peaks within a preset range (e.g., 2kHz-3kHz), the filler material's fill rate can range from 60% to 100% in some embodiments. In some embodiments, the filler rate can be in the range of 70% to 95%. In some embodiments, considering the cost of N′Bass sound-absorbing particles, the filler rate can be in the range of 75% to 85%. For example, the filler rate can be 80%.

[0132] Setting the filling rate of N′Bass sound-absorbing particles in the range of 70%-95% can ensure the sound absorption effect while avoiding the pressure of the micro-perforated plate sound-absorbing structure on the N′Bass sound-absorbing particles causing blockage of the gaps, thereby reducing the sound absorption effect.

[0133] In some embodiments, since the diameter of the N′Bass sound-absorbing particles is close to or smaller than the diameter of the through-hole, to prevent the N′Bass sound-absorbing particles from clogging the through-hole, such as... Figure 16 As shown, a mesh 653 may be disposed between the N′Bass sound-absorbing particles and the micro-perforated plate 651. In some embodiments, the mesh 653 may cover the side of the micro-perforated plate 651 away from the second acoustic cavity 640 (or diaphragm), and the mesh 653 covers all the through holes on the micro-perforated plate 651. In some embodiments, the mesh 653 may be disposed in the cavity 652 between the N′Bass sound-absorbing particles and the micro-perforated plate 651. Specifically, the mesh 653 may be connected to the inner wall of the cavity 652 between the N′Bass sound-absorbing particles and the micro-perforated plate 651.

[0134] In some embodiments, the cavity 652 may include a porous sound-absorbing material. In some embodiments, the porous sound-absorbing material may include, but is not limited to, polyurethane, polypropylene, melamine foam, wood fiberboard, wool felt, etc. In some embodiments, the filling method of the porous sound-absorbing material may be similar to that of N′Bass sound-absorbing particles. In some embodiments, to achieve better sound absorption, the porous sound-absorbing material may uniformly fill the cavity 652. In some embodiments, to achieve better sound absorption, the porosity of the porous sound-absorbing material may be greater than 70%. Here, porosity refers to the percentage of pore volume in the porous sound-absorbing material to the total volume of the porous sound-absorbing material.

[0135] In some embodiments, the micro-perforated plate sound-absorbing structure can effectively reduce the sound pressure level by 4dB-20dB in the 4kHz-6kHz frequency band. After filling the cavity 652 of the micro-perforated plate sound-absorbing structure with porous sound-absorbing material or N′Bass sound-absorbing particles, the sound absorption frequency band can be further extended to lower frequencies. Both the porous sound-absorbing material and the N′Bass sound-absorbing particle sound absorption scheme have good sound absorption effects. For a description of the sound absorption effects of porous sound-absorbing materials and N′Bass sound-absorbing particles, please refer to [link to relevant documentation]. Figure 18 .

[0136] Figure 18 These are frequency response curves of some embodiments of this specification, showing the absence of microperforated plate 651, microperforated plate 651 only, microperforated plate 651 combined with N′Bass sound-absorbing particles, and microperforated plate 651 combined with porous sound-absorbing material. Figure 18In the diagram, the horizontal axis represents frequency, and the vertical axis represents sound pressure level. Curve 181 represents the frequency response without the micro-perforated plate 651, curve 182 represents the frequency response with the micro-perforated plate 651, curve 183 represents the frequency response with the micro-perforated plate 651 and porous sound-absorbing material filling the cavity 452, and curve 184 represents the frequency response with the micro-perforated plate 651 and N′Bass sound-absorbing particles filling the cavity 652. Here, the frequency response refers to the frequency response of the sound emitted from the second acoustic hole. Figure 18 As shown, without the micro-perforated plate 651 (curve 181), there is an extremely high resonance peak near 3.9kHz, and 4.2kHz corresponds to the resonant frequency of the second acoustic cavity 440. However, after adding the micro-perforated plate sound-absorbing structure (curve 182), the sound pressure level in the 3kHz-6kHz frequency band is effectively reduced by 4dB-20dB. This demonstrates that the micro-perforated plate sound-absorbing structure can effectively absorb sound waves in the 3kHz-6kHz range, and its absorption at the resonant frequency is approximately 20dB. This reduces or avoids resonance of sound waves near the resonant frequency under the influence of the second acoustic cavity 440, thereby reducing sound leakage at the resonant frequency. Furthermore, filling the cavity 652 of the micro-perforated plate sound-absorbing structure with porous sound-absorbing material (curve 183) or N′Bass sound-absorbing particles (curve 184) further extends the sound absorption frequency band to lower frequencies. Both combined sound absorption schemes exhibit good sound absorption effects.

[0137] It should be noted that when testing the frequency response curve of the acoustic device without the micro-perforated plate sound-absorbing structure, the through holes on the micro-perforated plate 651 can be blocked to simulate the frequency response of the sound emitted by the second acoustic hole without the micro-perforated plate sound-absorbing structure. For example, opening the back plate on the side of the cavity 652 away from the second acoustic cavity 640 changes the cavity 652 from a closed state to an open state, which is equivalent to removing the cavity 652 in the micro-perforated plate sound-absorbing structure. Furthermore, the through holes of the micro-perforated plate 651 can be blocked with materials such as clay or glue, which is equivalent to removing the micro-perforated plate 651 in the micro-perforated plate sound-absorbing structure. In the above way, the micro-perforated plate sound-absorbing structure can be equivalently removed without affecting the volume of the second acoustic cavity 640, thereby avoiding affecting the frequency response of the second acoustic cavity 640. Furthermore, the frequency response of the sound emitted by the second acoustic hole can be tested. For example, the test microphone can be pointed directly at the second acoustic hole at a distance of about 2mm-5mm. The method for testing the frequency response of the first acoustic hole is similar to that for testing the frequency response of the second acoustic hole.

[0138] Figure 19 This is an internal structural diagram of an acoustic device according to some embodiments of this specification. Figure 20 This is an internal structural diagram of an acoustic device according to some embodiments of this specification.

[0139] like Figure 19 and Figure 20 As shown, the loudspeaker divides the accommodating cavity of the housing 1910 into a first acoustic cavity 1930 and a second acoustic cavity 1940. The loudspeaker includes a diaphragm 1921, a coil 1922, a frame 1923, and a magnetic circuit assembly 1924. The frame 1923 surrounds the diaphragm 1921, the coil 1922, and the magnetic circuit assembly 1924, providing a mounting platform. The loudspeaker can be connected to the housing 1910 via the frame 1923. The diaphragm 1921 covers the coil 1922 and the magnetic circuit assembly 1924 in the Z direction. At least a portion of the coil 1922 extends into the magnetic gap formed by the magnetic circuit assembly 1924 and is connected to the diaphragm 1921. The magnetic field generated by the coil 1922 after being energized interacts with the magnetic field formed by the magnetic circuit assembly 1924, thereby driving the diaphragm 1921 to produce mechanical vibration, which then generates sound through the propagation of a medium such as air. The sound is output through the holes on the housing 1910. The micro-perforated plate sound-absorbing structure can be disposed within the second acoustic cavity 1940. For example, the micro-perforated plate sound-absorbing structure can be disposed around the magnetic circuit assembly 1924. The micro-perforated plate sound-absorbing structure includes a micro-perforated plate 1651 and a filling layer 1953. The side of the micro-perforated plate 1951 away from the diaphragm 1921 along the Z direction is connected to the filling layer 1953. The micro-perforated plate 1951 has a ring-shaped structure and is disposed around the magnetic circuit assembly 1924. The filling layer 1953 is filled with N′Bass sound-absorbing particles or porous sound-absorbing material. In some embodiments, the housing 1910 (e.g., the back plate 1952) can together with the magnetic circuit assembly 1924 form a sealed cavity, i.e., the cavity of the micro-perforated plate sound-absorbing structure, and the filling layer 1953 can be filled in the cavity.

[0140] In some embodiments, the magnetic circuit assembly 1924 includes a magnetic guide plate 19241, a magnet 19242, and a magnetic guide cover 19243. The magnetic guide plate 19241 and the magnet 19242 are interconnected. The side of the magnet 19242 away from the magnetic guide plate 19241 is mounted on the bottom wall of the magnetic guide cover 19243, and a magnetic gap is formed between the periphery of the magnet 19242 and the inner periphery of the magnetic guide cover 19243. In some embodiments, the outer periphery of the magnetic guide cover 19243 is connected and fixed to the frame 1923. In some embodiments, both the magnetic guide cover 19243 and the magnetic guide plate 19241 can be made of a magnetically conductive material (e.g., iron).

[0141] In some embodiments, a plurality of through holes may be provided on the micro-perforated plate 1951, and the plurality of through holes are arranged around the magnet assembly, which helps to ensure appropriate hole spacing and perforation rate.

[0142] In some embodiments, since a sealed cavity of a certain height is required on the side of the micro-perforated plate 1951 away from the diaphragm, if the micro-perforated plate 1951 is completely placed on the side of the magnetic circuit assembly away from the diaphragm, the micro-perforated plate 1951 and the filling layer 1953 may occupy too much space in the housing 1910, making it difficult to meet the small size design requirements of the acoustic device. However, in this embodiment, the acoustic device 1900 sets the micro-perforated plate 1951 as a ring structure surrounding the magnetic circuit assembly, which can effectively utilize the circumferential space of the magnetic circuit assembly without increasing the thickness of the acoustic device (i.e., the dimension along the Z direction), which is beneficial to the miniaturization design of the acoustic device.

[0143] In some embodiments, the micro-perforated plate can also be disposed on the side of the magnetic circuit assembly 1924 opposite to the diaphragm 1921, that is, the micro-perforated plate 1651 and the magnetic circuit assembly are spaced apart in the Z direction (diaphragm vibration direction). For specific arrangements, please refer to [reference needed]. Figure 4 In some embodiments, the micro-perforated plate can be a panel (e.g., racetrack-shaped, circular, etc.) adapted to the shape of the second acoustic cavity 1940 or the housing 1910. The pore diameter, perforation rate, and pore spacing of the micro-perforated plate can be consistent with the relevant parameters of the micro-perforated plate 1951. This results in a larger area, a relatively greater number of through holes, better sound absorption, and a simpler structure that is easier to assemble.

[0144] Figure 21 This is an internal structural diagram of an acoustic device according to some embodiments of this specification. Figure 21 The acoustic device 2100 and its loudspeaker shown are, with Figure 19 and Figure 20 The acoustic device 1900 shown is similar to its loudspeaker, except that it does not have a separately installed micro-perforated plate.

[0145] At least a portion of the magnetically conductive element of the acoustic device 2100 can be configured as a micro-perforated plate. For example, such as Figure 21 As shown, the magnetic shield 21243 has multiple through holes at its bottom, away from the diaphragm, which can serve as a micro-perforated plate. The side of the magnetic shield 21243 away from the diaphragm along the Z-direction is connected to the cavity. In some embodiments, a filling layer may be provided inside the cavity. This embodiment directly sets a part of the magnetic circuit assembly as a sound-absorbing structure, achieving sound absorption while saving costs and simplifying the process.

[0146] Figure 22 yes Figures 19-20 The acoustic device 1900 shown and Figure 21 The frequency response curve of the acoustic device 2100 is shown. Figure 22In the diagram, the horizontal axis represents frequency, and the vertical axis represents sound pressure level. Curve a1 represents the frequency response of acoustic device 2100 at the first acoustic aperture, curve a2 represents the frequency response of acoustic device 1900 at the first acoustic aperture, curve b1 represents the frequency response of acoustic device 2100 at the first pressure relief aperture, curve b2 represents the frequency response of acoustic device 1900 at the first pressure relief aperture, curve c1 represents the frequency response of acoustic device 2100 at the second pressure relief aperture, curve c2 represents the frequency response of acoustic device 1900 at the second pressure relief aperture, curve d1 represents the frequency response of sound emitted by acoustic device 2100 at the third pressure relief aperture, and curve d2 represents the frequency response of sound emitted by acoustic device 1900 at the third pressure relief aperture. The first, second, and third pressure relief apertures are acoustic apertures (i.e., second acoustic apertures) located at different positions on the housing corresponding to the second acoustic cavity. The acoustic device is as follows... Figure 22 As shown, curves a1, a2, b1, b2, c1, c2, d1, and d2 all reach their lowest points near 3.9kHz, and within the frequency band near 3.9kHz, curves a2, b2, c2, and d2 are all lower than curves a1, b1, c1, and d1. It is evident that the sound absorption center frequency for both micro-perforated plate configurations corresponding to acoustic devices 1900 and 2100 is 3.9kHz, but the sound absorption effect of the micro-perforated plate corresponding to acoustic device 1900 is superior to that of the micro-perforated plate corresponding to acoustic device 2100. The reason is that when the magnetic shield 21243 is used as a micro-perforated plate, the cavity in which its corresponding micro-perforated plate sound-absorbing structure acts is the magnetic gap cavity between the magnetic shield 21243 and its corresponding magnet (not shown), rather than the second acoustic cavity (not shown) in the acoustic device 2100. Therefore, the absorption effect of this micro-perforated plate sound-absorbing structure on sound waves in the second acoustic cavity is limited. In some embodiments, it is possible to simultaneously set... Figure 19 and Figure 20 The microperforated plate 1951 shown Figure 21 The magnetic shield 21243 shown serves as the sound-absorbing structure of the acoustic device. This design allows for a relatively larger number of through holes in the sound-absorbing structure, resulting in better sound absorption.

[0147] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0148] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. An acoustic device, characterized in that, include: Diaphragm; A housing for accommodating the diaphragm and forming a first acoustic cavity and a second acoustic cavity corresponding to the front and rear sides of the diaphragm, respectively, wherein the diaphragm radiates sound into the first acoustic cavity and the second acoustic cavity, the diaphragm outputs a first sound wave through a first acoustic aperture coupled to the first acoustic cavity, and the diaphragm outputs a second sound wave through a second acoustic aperture coupled to the second acoustic cavity, the first sound wave and the second sound wave cancelingly interfere at a far-field position; and A sound-absorbing structure coupled to the second acoustic cavity is used to absorb sound transmitted through the second acoustic cavity to the second acoustic aperture within a target frequency range, thereby reducing the amplitude of sound waves within the target frequency range at the far-field location, wherein the target frequency range includes the resonant frequency of the second acoustic cavity.

2. The acoustic device according to claim 1, characterized in that, The target frequency range also includes the resonant frequency of the first acoustic cavity.

3. The acoustic device according to claim 1, characterized in that, The target frequency range includes 3 kHz to 6 kHz.

4. The acoustic device according to claim 3, characterized in that, The sound-absorbing structure has a sound absorption effect of not less than 3 dB on sound within the target frequency range.

5. The acoustic device according to claim 3, characterized in that, The sound-absorbing structure has a sound absorption effect of not less than 14 dB on the sound at the resonant frequency.

6. The acoustic device according to claim 1, characterized in that, The sound-absorbing structure includes a micro-perforated plate and a cavity. The micro-perforated plate includes through holes, wherein the second acoustic cavity coupled to the sound-absorbing structure is connected to the cavity through the through holes.

7. The acoustic device according to claim 6, characterized in that, The cavity is filled with a filling material.

8. The acoustic device according to claim 7, characterized in that, The filling material includes N′Bass sound-absorbing particles with a diameter in the range of 0.15 mm to 0.7 mm.

9. The acoustic device according to claim 7, characterized in that, The filling material has a filling rate in the cavity ranging from 70% to 95%.

10. The acoustic device according to claim 6, characterized in that, The cavity is filled with a porous sound-absorbing material, and the porosity of the porous sound-absorbing material is greater than 70%.

11. The acoustic device according to claim 6, characterized in that, The ratio between the hole spacing and the hole diameter of the through holes is greater than 5.

12. The acoustic device according to claim 11, characterized in that, The ratio of the wavelength of the sound within the target frequency range to the spacing between the holes on the micro-perforated plate is greater than 5.

13. The acoustic device according to claim 6 or 12, characterized in that, The diameter of the through hole is in the range of 0.1 mm to 0.2 mm, the perforation rate of the micro-perforated plate is in the range of 2% to 5%, the thickness of the micro-perforated plate is in the range of 0.2 mm to 0.7 mm, and the height of the cavity is in the range of 7 mm to 10 mm.

14. The acoustic device according to claim 6 or 12, characterized in that, The diameter of the through hole is in the range of 0.2 mm to 0.4 mm, the perforation rate of the micro-perforated plate is in the range of 1% to 5%, the thickness of the micro-perforated plate is in the range of 0.2 mm to 0.7 mm, and the height of the cavity is in the range of 4 mm to 9 mm.

15. The acoustic device according to claim 6, characterized in that, The micro-perforated plate includes a racetrack-shaped micro-perforated plate or a circular micro-perforated plate, wherein the thickness of the circular micro-perforated plate is in the range of 0.3 mm to 1 mm.

16. The acoustic device according to claim 6, characterized in that, The natural frequency of the micro-perforated plate is greater than 500Hz.

17. The acoustic device according to claim 6, characterized in that, The height of the cavity is in the range of 0.5 mm to 10 mm.

18. The acoustic device according to claim 6, characterized in that, The micro-perforated plate has a waterproof and breathable structure on the side facing the diaphragm.

19. The acoustic device according to claim 6, characterized in that, Also includes: Magnetic circuit components; as well as A coil, which is connected to the diaphragm and is at least partially located in the magnetic gap formed by the magnetic circuit assembly, wherein the coil, when energized, drives the diaphragm to vibrate to generate sound, wherein the micro-perforated plate includes an annular structure disposed around the magnetic circuit assembly.

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