Acoustic output device

Abstract

An embodiment of the present specification provides an acoustic output device, comprising: a housing; the first loudspeaker is arranged in the shell, the first loudspeaker is acoustically coupled with the first hole part and the second hole part on the shell, and the first loudspeaker outputs a first sound wave and a second sound wave with phase difference through the first hole part and the second hole part under the driving of the first electric signal; the first loudspeaker is arranged in the shell, the second loudspeaker is arranged in the shell, the second loudspeaker is driven by the second electric signal to output third sound waves, and in the target frequency range, the first sound waves, the second sound waves and the third sound waves are overlapped with one another, so that far-field radiation of the acoustic output device is directional.

Description

[0001] Cross-references

[0002] This application is a divisional application of a Chinese utility model patent application filed on August 24, 2023, with application number 202322298024.7, and the invention name is "An acoustic output device". This application claims priority to the Chinese application number 202211455122.0 filed on November 21, 2022, and all of the contents are incorporated herein by reference. Technical Field

[0003] The present invention relates to the field of acoustics, and in particular to an acoustic output device. Background Art

[0004] In order to solve the sound leakage problem of the acoustic output device, two or more sound sources are usually used to emit two sound signals with opposite phases. Under far-field conditions, the difference in the sound path between two sound sources with opposite phases to a certain point in the far field is basically negligible, so the two sound signals can cancel each other out to reduce far-field sound leakage. Although this method can achieve the effect of reducing sound leakage to a certain extent, it still has certain limitations. For example, since the wavelength of high-frequency sound leakage is shorter, the distance between the two sound sources under far-field conditions cannot be ignored compared to the wavelength, resulting in the inability to cancel out the sound signals emitted by the two sound sources. For another example, when the acoustic transmission structure of the acoustic output device resonates, there is a certain phase difference between the phase of the sound signal actually radiated by the sound outlet of the acoustic output device and the original phase of the sound wave generation position, and an additional resonance peak is added to the transmitted sound wave, resulting in a chaotic sound field distribution and it is difficult to ensure the sound leakage reduction effect of the far field at high frequencies, and may even increase the sound leakage.

[0005] Therefore, it is desirable to provide an acoustic output device with a better directional sound field. Utility Model Content

[0006] On one hand, the present application provides an acoustic output device, comprising: a housing; a first speaker, arranged in the housing, the first speaker comprising a first diaphragm, the front and rear sides of the first diaphragm are respectively provided with a first front cavity and a first rear cavity, the first front cavity and the first rear cavity are respectively acoustically coupled with a first hole and a second hole, the first speaker, driven by a first electrical signal, outputs a first sound wave and a second sound wave with a phase difference through the first hole and the second hole, respectively; and a second speaker, arranged in the housing, the second speaker, driven by a second electrical signal, outputs a third sound wave; wherein, within a first frequency range, the first sound wave, the second sound wave, and the third sound wave are superimposed on each other, so that the far-field radiation of the acoustic output device presents a cardioid directivity, and within a second frequency range, the sound pressure level of the third sound wave is much lower than the sound pressure level of the second sound wave, so that the far-field radiation of the acoustic output device presents a dual sound source directivity. The first speaker forms a dual sound source, and the second speaker forms a single sound source. By combining the single sound source with the dual sound source, the sound field of the acoustic output device is adjusted, so that the acoustic output device obtains a good directional sound field, thereby improving the far-field sound leakage problem of the acoustic output device.

[0007] In some embodiments, the second speaker outputs a third sound wave through a second hole portion acoustically coupled to the first rear cavity, and the sound pressure level of the third sound wave is much smaller than the sound pressure level of the second sound wave, which means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole portion and the sound pressure level of the third sound wave output by the second speaker at the second hole portion is not less than 6dB, or the ratio of the sound pressure radiated by the first speaker in the first rear cavity to the sound pressure radiated by the second speaker in the first rear cavity is greater than or equal to 2.

[0008] In some embodiments, the second speaker outputs a third sound wave through a third hole on the shell, the third hole and the second hole are different holes, and the sound pressure level of the third sound wave is much smaller than the sound pressure level of the second sound wave, which means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole and the sound pressure level of the third sound wave output by the second speaker at the third hole is not less than 6dB.

[0009] In some embodiments, a lower frequency limit of the first frequency range is greater than an upper frequency limit of the second frequency range.

[0010] In some embodiments, the first frequency range includes 1 kHz, 1.5 kHz, or 4 kHz, and the second frequency range includes 100 Hz or 800 Hz.

[0011] In some embodiments, the first frequency range includes a frequency band of 1 kHz-4 kHz, and the second frequency range includes a frequency band of 100 Hz-800 Hz.

[0012] In some embodiments, when dual sound source directivity is presented, the far-field radiation of the acoustic output device is arranged in an 8-shape; when cardioid directivity is presented, the absolute value of the sound pressure level difference of the far-field radiation of the acoustic output device at two far-field positions at the same distance from the acoustic output device in at least one pair of opposite directions is not less than 6dB.

[0013] The present application also provides another acoustic output device, comprising: a shell; a first speaker, arranged in the shell, the first speaker comprising a first diaphragm, a first front cavity and a first rear cavity are respectively provided on the front and rear sides of the first diaphragm, the first front cavity and the first rear cavity are respectively acoustically coupled with the first hole portion and the second hole portion, and the first speaker, driven by a first electrical signal, outputs a first sound wave and a second sound wave with a phase difference through the first hole portion and the second hole portion respectively to form a dual sound source; and a second speaker, arranged in the shell, the second speaker comprising a second diaphragm, a second front cavity and a second rear cavity are respectively provided on the front and rear sides of the second diaphragm, only one of the second front cavity and the second rear cavity is acoustically coupled with the hole portion on the shell, and outputs a third sound wave to form a single sound source; wherein, within the first frequency range, the single sound source and the dual sound sources work together, and within the second frequency range, the dual sound sources work approximately alone. The first speaker forms a dual sound source, and the second speaker forms a single sound source. Through the combination of the single sound source and the dual sound source, the sound field of the acoustic output device is adjusted so that the acoustic output device obtains a good directional sound field, thereby improving the far-field sound leakage problem of the acoustic output device.

[0014] In some embodiments, the second speaker outputs the third sound wave through the second hole portion acoustically coupled with the first rear cavity, and the dual sound sources are approximately working alone means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole portion and the sound pressure level of the third sound wave output by the second speaker at the second hole portion is not less than 6dB, or the ratio of the sound pressure radiated by the first speaker in the first rear cavity to the sound pressure radiated by the second speaker in the first rear cavity is greater than or equal to 2, or the second speaker outputs the third sound wave through the third hole portion on the shell, and the third hole portion and the second hole portion are different hole portions, and the dual sound sources are approximately working alone means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole portion and the sound pressure level of the third sound wave output by the second speaker at the third hole portion is not less than 6dB.

[0015] In some embodiments, a lower frequency limit of the first frequency range is greater than an upper frequency limit of the second frequency range. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] This specification will be further described in the form of exemplary embodiments, which will be described in detail by the accompanying drawings. These embodiments are not restrictive, and in these embodiments, the same number represents the same structure, wherein:

[0017] Figure 1is a schematic diagram of the relative position of an acoustic output device and a user's ear according to some embodiments of this specification;

[0018] Figure 2A yes Figure 1 Schematic diagram of the sound pressure level sound field distribution of the acoustic output device shown in FIG.

[0019] Figure 2B yes Figure 1 Schematic diagram of the sound pressure level sound field distribution of the acoustic output device shown in at high frequency;

[0020] Figure 3 yes Figure 1 A frequency response graph of the acoustic output device shown in ;

[0021] Figure 4 is a schematic diagram of directivity shown in some embodiments of this specification;

[0022] Figure 5A-5D is a schematic diagram of the structure of an acoustic output device including first speakers and second speakers in different arrangements according to some embodiments of this specification;

[0023] Figure 6 is a schematic diagram of the relationship between the resonant frequency and volume of the same cavity according to some embodiments of this specification;

[0024] Figure 7 is a schematic diagram of the relationship between the resonant frequency of the same cavity and the area of ​​the hole portion of the acoustic coupling thereof according to some embodiments of the present specification;

[0025] Figure 8 is a schematic diagram of the relationship between the resonant frequency and volume of a closed cavity according to some embodiments of this specification;

[0026] Fig. 9 is a schematic diagram of the structure of an acoustic output device according to other embodiments of this specification;

[0027] Figures 10A-10D is a schematic diagram of an acoustic output device with different sound outlet hole arrangement modes according to some embodiments of the present application specification;

[0028] Figures 11A-11D They are Figures 10A-10D A schematic diagram of the directivity of far-field radiation of the acoustic output device shown;

[0029] Fig. 12A and Fig. 12B is a schematic diagram of the directivity of far-field radiation of an acoustic output device with exemplary hole arrangement positions according to some embodiments of this specification;

[0030] Fig.13 is a schematic diagram of another acoustic output device according to some embodiments of the present specification;

[0031] Fig.14 is a schematic diagram of acoustic transmission of an acoustic output device provided with a second speaker according to some embodiments of this specification;

[0032] Fig.15 is a schematic diagram of an exemplary flow chart of a method for adjusting a second electrical signal according to some embodiments of this specification;

[0033] Fig.16 It is a schematic diagram of frequency response curves when a single sound source and a dual sound source are excited separately according to some embodiments of this specification;

[0034] Fig.17 is a schematic diagram of the directivity of far-field radiation of an acoustic output device after adjusting the second electrical signal according to some embodiments of this specification;

[0035] Fig.18A and Fig.18B is a directivity test curve diagram of an acoustic output device according to some embodiments of this specification;

[0036] Fig.19 is a schematic diagram of an equivalent model in which an acoustic output device shown in some embodiments of this specification is adjusted according to a preset algorithm;

[0037] Fig. 20 is a schematic diagram of an equivalent model of an acoustic output device adjusted according to an active algorithm according to some embodiments of this specification;

[0038] Fig.21 It is a schematic block diagram of an amplitude and phase adjustment algorithm according to some embodiments of this specification. DETAILED DESCRIPTION

[0039] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of this specification. For ordinary technicians in this field, this specification can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0040] It should be understood that the "system", "device", "unit" and / or "module" used herein are a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, if other words can achieve the same purpose, the words can be replaced by other expressions.

[0041] As shown in this specification and claims, unless the context clearly indicates an exception, the words "a", "an", "an" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "comprises" and "includes" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0042] Flowcharts are used in this specification to illustrate the operations performed by the system according to the embodiments of this specification. It should be understood that the preceding or following operations are not necessarily performed precisely in order. Instead, the steps may be processed in reverse order or simultaneously. At the same time, other operations may also be added to these processes, or one or more operations may be removed from these processes.

[0043] In some embodiments, in order to solve the sound leakage problem of the acoustic output device, two sound sources with opposite phases can be used to emit two sets of sounds with opposite phases. Under far-field conditions, the difference in sound path from two sound sources with opposite phases to a certain point in the far field is basically negligible, so the two sets of sounds can cancel each other out to reduce far-field sound leakage.

[0044] Figure 1 Schematic diagram of the relative position of the acoustic output device and the user's ear according to some embodiments of this specification. Figure 1 As shown, the acoustic output device 100 may include a housing 110 and a speaker 120. The speaker 120 may be disposed in a cavity formed by the housing 110. The speaker 120 includes a diaphragm (not shown in the figure). In the cavity of the housing 110, a front cavity 130 and a rear cavity 140 for radiating sound are respectively disposed on the front and rear sides of the diaphragm. The housing 110 is provided with a first hole portion 111 and a second hole portion 112. The front cavity 130 may be acoustically coupled with the first hole portion 111, and the rear cavity 140 may be acoustically coupled with the second hole portion 112. When the speaker 120 outputs sound waves, the sound waves on the front side of the diaphragm (or referred to as the first sound waves) may be emitted from the first hole portion 111 through the front cavity 130, and the sound waves on the rear side of the diaphragm (or referred to as the second sound waves) may be emitted from the second hole portion 112 through the rear cavity 140. At this time, the first hole portion 111 and the second hole portion 112 may be regarded as a set of dual sound sources, which can emit two sets of sounds with the same amplitude but opposite phases. For ease of understanding, in some embodiments of this specification, the front side of the diaphragm refers to the side of the diaphragm that is away from the magnetic circuit assembly (not shown in the figure); the rear side of the diaphragm refers to the side of the diaphragm that is facing the magnetic circuit assembly. Of course, in some scenarios, the front side and the rear side of the diaphragm can be interchangeable, that is, the side of the diaphragm that is away from the magnetic circuit assembly can be regarded as the rear side, and the side of the magnetic circuit assembly that is away from the diaphragm can be regarded as the front side.

[0045] In some embodiments, Figure 1 As shown, when the user wears or uses the acoustic output device 100, the acoustic output device 100 can be located near the user's auricle, and the first hole portion 111 can face the user's ear canal opening 201, so that the sound transmitted from the first hole portion 111 can be transmitted toward the user's ear canal. The second hole portion 112 can be away from the ear canal opening 201 relative to the first hole portion 111, and the distance between the first hole portion 111 and the ear canal opening is smaller than the distance between the second hole portion 112 and the ear canal opening.

[0046] In some embodiments, when the speaker 120 vibrates, the front and rear sides of the speaker 120 can respectively serve as a sound wave generating structure to generate sound waves with equal amplitude and opposite phases. In some embodiments, the sound waves with equal amplitude and opposite phases can be radiated outward through the first hole portion 111 and the second hole portion 112 respectively to form dual sound sources, which can interfere and destructively interfere at a spatial point (e.g., the far field), thereby effectively improving the sound leakage problem in the far field of the earphone 100.

[0047] Figure 2A yes Figure 1 The acoustic output device shown in the figure is a schematic diagram of the sound pressure level sound field distribution at medium and low frequencies. Figure 2A As shown, in the mid-low frequency range (for example, 50Hz-1kHz), the sound field distribution of the acoustic output device 100 shows good dual sound source directivity, and the sound leakage reduction effect is significant. That is to say, in the mid-low frequency range, the dual sound sources formed by the first hole portion 111 and the second hole portion 112 of the acoustic output device 100 output sound waves (i.e., the first sound wave and the second sound wave) with opposite phases, and the sound field forms a distribution mode of two lobe structures in space. In the two opposite directions of the dual sound source connection line, the sound pressure level is large, and in the direction perpendicular to the dual sound source connection line, the sound pressure level is small. However, for the two lobe structures formed in the sound field, one of the lobe structures will be far away from the user's ear, resulting in large sound leakage, which affects the sound leakage reduction effect of the acoustic output device.

[0048] In some embodiments, in a higher frequency range, the wavelengths of the first sound wave and the second sound wave are shorter, and the distance between the dual sound sources formed by the first hole portion 111 and the second hole portion 112 cannot be ignored compared to the wavelength. For example, the distance between the first hole portion 111 and the second hole portion 112 can make the acoustic path of the first sound wave and the second sound wave from the spatial point (e.g., the far field) different, so that the phase difference between the first sound wave and the second sound wave at the spatial point is small (e.g., the phase is the same or close), and the first sound wave and the second sound wave cannot interfere with each other at the spatial point, and may also be superimposed at the spatial point to increase the amplitude of the sound wave at the spatial point. In some embodiments, due to the shielding of high-frequency sound waves by structures such as the auricle 210 and / or the influence of reflected sound waves, the sound field distribution of the acoustic output device 100 may also be chaotic.

[0049] In some embodiments, the structures and parameters (such as volume, etc.) of the front cavity 130 and the rear cavity 140 are different, which may cause the front cavity 130 and the rear cavity 140 to have different resonant frequencies. In some embodiments, the front cavity 130 and / or the rear cavity 140 may be additionally provided with a special acoustic structure (such as a sound guide tube, etc.) to adjust the resonant frequency. When the sound waves in the front cavity 130 and / or the rear cavity 140 resonate, the frequency components of the sound waves transmitted in the front cavity 130 and / or the rear cavity 140 may be changed (for example, an additional resonance peak is added to the transmitted sound waves), or the phase of the transmitted sound waves may be changed. Compared with when no resonance occurs, the phase and / or amplitude of the sound waves radiated from the first hole portion 111 and / or the second hole portion 112 are changed, and the change in the phase and / or amplitude may cause the sound field of the dual sound sources to be chaotic in the high-frequency range, affecting the effect of the sound waves radiated from the first hole portion 111 and the second hole portion 112 interfering and destructing at a spatial point. For example, when resonance occurs, the phase difference of the sound waves radiated by the first hole portion 111 and the second hole portion 112 changes. For example, when the phase difference of the sound waves radiated by the first hole portion 111 and the second hole portion 112 is small (for example, less than 120°, less than 90° or 0, etc.), the effect of the sound waves interfering and destructing at the spatial point is weakened, and it is difficult to achieve the effect of reducing sound leakage; or, the sound waves with a small phase difference may also be superimposed on each other at the spatial point, increasing the amplitude of the sound waves at the spatial point (for example, the far field) near the resonant frequency, thereby increasing the far-field sound leakage of the acoustic output device 100. For another example, the resonance may increase the amplitude of the transmitted sound waves near the resonant frequency of the acoustic transmission structure (for example, manifested as a resonance peak near the resonant frequency), resulting in a chaotic sound field of the dual sound sources near the resonant frequency. At this time, the amplitude of the sound waves radiated from the first hole portion 111 and the second hole portion 112 differs greatly, and the effect of the sound waves interfering and destructing at the spatial point is weakened, and it is difficult to achieve the effect of reducing sound leakage.

[0050] Figure 2B yes Figure 1 The schematic diagram of the sound pressure level sound field distribution of the acoustic output device at high frequency is shown in, Figure 3 yes Figure 1 The frequency response curve of the acoustic output device shown in FIG. Figure 2B As shown, in a higher frequency range, the acoustic signal radiated outward by the second hole portion 112 of the acoustic output device 100 plays a dominant role in the entire sound field distribution, and the sound field distribution is relatively chaotic. There is a certain difference between the amplitude / phase of the sound wave actually radiated by the second hole portion 112 of the acoustic output device 100 and the original amplitude / phase of the sound wave emitted by the speaker 120, resulting in that the two sound waves radiated from the first hole portion 111 and the second hole portion 112 not only fail to reduce the sound leakage at a specific position in the far field, but also increase the sound leakage at that position.

[0051] like Figure 3 As shown, curve L 3 The frequency response curve of the front cavity 130 (eg, at the first hole portion 111) of the acoustic output device 100 is shown in FIG. 3 ' represents a frequency response curve of the rear cavity 140 (eg, at the second hole portion 112) of the acoustic output device 100. Figure 3 It can be seen that in the high frequency range, the front cavity 130 (having a resonance peak at a frequency of about 6 kHz) and the rear cavity 140 (having a resonance peak at a frequency of about 4 kHz) of the acoustic output device 100 have significantly different resonance peaks. 3 and curve L 3 It can be seen that the sound output of the front and rear cavities of the acoustic output device 100 in the mid-low frequency range (for example, 50Hz-1500Hz) is roughly equal, showing a good sound leakage reduction effect, but in the high frequency range (for example, 1500Hz-20kHz), the sound output of the front and rear cavities differs greatly, and the sound leakage reduction effect is significantly weakened. Figure 2B and Figure 3 It can be seen that in the high frequency range, the sound field distribution of the dual sound sources is relatively chaotic, and it may not be possible to reduce the sound leakage in the far field, and may even increase the sound leakage in the far field. In some embodiments, the sound field distribution of the dual sound sources can be adjusted by adjusting the structure of the acoustic output device 100 to obtain a good directional sound field, thereby improving the problem of increased sound leakage in the far field of the acoustic output device 100.

[0052] In some embodiments, a second speaker may be provided in the acoustic output device so that the sound waves of the second speaker and the sound waves generated by the speaker 120 (or referred to as the first speaker) cancel each other out, thereby suppressing the confusion of the sound field of the dual sound source structure (for example, in the high frequency range), and reducing or eliminating the sound leakage of the acoustic output device in the far field. In some embodiments, the acoustic output device may include a housing, a first speaker, and a second speaker. Among them, the first speaker is provided in the housing, and the first speaker is acoustically coupled with two holes (for example, the first hole and the second hole) on the housing to output the first sound wave and the second sound wave with a phase difference, respectively. In some embodiments, the first speaker includes a first diaphragm, and in the housing, the first diaphragm is provided with a first front cavity and a first rear cavity on the front and rear sides respectively, and the first front cavity and the first rear cavity are acoustically coupled with the above-mentioned two holes (for example, the first hole and the second hole) respectively, to output the first sound wave and the second sound wave with a phase difference, respectively. In some embodiments, the first speaker can be driven by a first electrical signal to output the first sound wave and the second sound wave with a phase difference through the above-mentioned two holes (for example, the first hole and the second hole). The second speaker is disposed in the shell, and the second speaker is acoustically coupled with a hole portion (e.g., a third hole portion, the third hole portion may be one of the first hole portion and the second hole portion, or may be another hole portion different from the first hole portion and the second hole portion) disposed on the shell. In some embodiments, the second speaker includes a second diaphragm, and in the shell, a second front cavity and a second rear cavity are respectively disposed on the front and rear sides of the second diaphragm, and only one of the second front cavity and the second rear cavity is acoustically coupled with the above-mentioned one hole portion (e.g., the third hole portion) to output a third sound wave. In some embodiments, the second speaker can output the third sound wave through the above-mentioned one hole portion (e.g., the third hole portion) under the drive of the second electrical signal. At this time, the first sound wave and the second sound wave of the first speaker are respectively output through two holes (e.g., the first hole portion and the second hole portion) to form a dual sound source; the second speaker only outputs the third sound wave through one hole portion (e.g., the third hole portion) to form a single sound source. In some embodiments, within the target frequency range, the third sound wave output by the second speaker can be superimposed and cancelled with the first sound wave and the second sound wave output by the first speaker at a far-field position in a specific direction of the acoustic output device, and the sound pressure after superposition and cancellation at the position is small (e.g., close to zero), and the sound pressure at the corresponding far-field position in the opposite direction of the specific direction is large, so that the absolute value of the sound pressure level difference at the above two positions is not less than a preset sound pressure level threshold, so that the far-field radiation of the acoustic output device is directional. The distances between the two corresponding far-field positions in the specific direction and the opposite direction mentioned here and the acoustic output device are equal.In some embodiments, the sound pressure levels at the specific direction and the two far-field positions in the corresponding opposite directions can be measured by using test microphones set at the two far-field positions to measure the sound pressure at the corresponding far-field positions, and then the corresponding sound pressure levels can be obtained by the sound pressure, and finally the sound pressure level difference between the specific direction and the two far-field positions in the corresponding opposite directions can be obtained.

[0053] In order to ensure that the sound waves output by the first speaker (for example, the sound waves after the superposition of the first sound wave and the second sound wave) and the sound waves output by the second speaker (for example, the third sound wave) can effectively cancel each other at the far field position, the sound waves output by the first speaker and the sound waves output by the second speaker should be equal or similar in amplitude and opposite or approximately opposite in phase at the far field position. Considering that the frequency responses of the first speaker and the second speaker at the far field position may differ due to their different structures under the drive of the same electrical signal, electrical signals of different strengths can be provided to the first speaker and the second speaker to compensate for the difference in frequency response, so that the sound waves output by the first speaker and the sound waves output by the second speaker have the same or similar amplitude at the far field position. For example, the processing circuit can provide different degrees of gain for the two electrical signals driving the first speaker and the second speaker to compensate for the difference in frequency response. In order to reduce the difficulty of adjusting the electrical signal and improve the stability of the electrical signal, the difference in frequency response of the first speaker and the second speaker at the far field position can be reduced. For example, the difference in frequency response of the first speaker and the second speaker at the far field position can be reduced by adjusting the structure of the first speaker and the second speaker, such as the volume of the cavity, the size and position of the hole, etc. Regarding the adjustment of the parameters related to the structure of the first speaker and the second speaker, reference may be made to the description elsewhere in this specification. The "reducing the difference in frequency response of the first speaker and the second speaker at the far-field position" described here can be understood as: within the target frequency range, under the drive of the same electrical signal (i.e., the first electrical signal is the same as the second electrical signal), at the far-field position in a specific direction of the acoustic output device, the sound pressure level difference between the superposition of the first sound wave and the second sound wave output by the first speaker and the third sound wave output by the second speaker is less than 14 dB, so that after the first electrical signal or the second electrical signal undergoes appropriate amplitude-frequency adjustment, the first sound wave and the second sound wave output by the first speaker and the third sound wave output by the second speaker can be superimposed and canceled at the far-field position in the specific direction of the acoustic output device, so that the sound pressure at the far-field position is low, for example, close to zero. In some embodiments, in order to reduce the sound pressure at the far-field position in a specific direction of the acoustic output device and improve the sound leakage reduction effect of the acoustic output device, within the target frequency range, driven by the same electrical signal (that is, the first electrical signal is the same as the second electrical signal), at the far-field position in a specific direction of the acoustic output device, the sound pressure level difference between the superposition of the first sound wave and the second sound wave output by the first speaker and the third sound wave output by the second speaker is less than 10dB.In some embodiments, in order to further reduce the sound pressure at the far-field position in a specific direction of the acoustic output device and enhance the sound leakage reduction effect of the acoustic output device, within the target frequency range, under the same electrical signal (i.e., the first electrical signal is the same as the second electrical signal), at the far-field position in the specific direction of the acoustic output device, the sound pressure level difference between the first sound wave output by the first speaker and the second sound wave after superposition and the third sound wave output by the second speaker is less than 6dB. In some embodiments, the target frequency range may include a first frequency range, within the first frequency range, the first sound wave, the second sound wave, and the third sound wave are superimposed on each other, so that the far-field radiation of the acoustic output device presents a cardioid directivity. In some embodiments, the target frequency range may include a second frequency range, within the second frequency range, the sound pressure level of the third sound wave is much lower than the sound pressure level of the second sound wave, and when the first sound wave, the second sound wave, and the third sound wave are superimposed on each other, the influence of the third sound wave can be ignored, and the first sound wave and the second sound wave can be regarded as two sound sources superimposed on each other, so that the far-field radiation of the acoustic output device presents a double sound source directivity. In some embodiments, the first frequency range may include a mid-high frequency band (eg, 800 Hz-10 kHz, etc.), and the second frequency range may include a mid-low frequency band (eg, 100 Hz-800 Hz, etc.). For more information on the directivity and cardioid directivity of the acoustic output device, please refer to . Figure 4 and its related description; for more information about dual sound source directivity, please refer to the previous article Figure 2A and its related description.

[0054] In some embodiments, the acoustic output device may include at least one of a back-hook earphone, an ear-hook earphone, an in-ear earphone, and glasses. In the wearing state, the opposite direction of the specific direction may point to the user's ear canal opening. Figure 4 is a schematic diagram of the directivity shown in some embodiments of this specification. Figure 4 , Figure 4 The acoustic output device is shown in a wearing state, wherein the AS 1 Indicates the front cavity sound outlet of the acoustic output device, AS 2 In some embodiments, the far-field radiation of the acoustic output device is directional, which means that the output sound direction of the acoustic output device is within a specified direction range, that is, the far-field radiation of the acoustic output device within the specified direction range is significantly greater than the far-field radiation outside the specified direction range. In some embodiments, when the acoustic output device is worn, the hole AS corresponding to the back cavity of the acoustic output device for sound output 2 Pointing to the hole AS corresponding to the front cavity for sound emission 1 Direction X 1 (i.e. from the sound hole AS in the back cavity 2 Pointing to the front cavity sound outlet AS 1Direction X 1 ) and its surrounding directions (such as direction X 2 , Direction X 3 ), is directed toward the user's ear canal opening. That is, in the wearing state, the sound output hole AS corresponding to the front cavity of the acoustic output device 1 The sound outlet AS of the front cavity is closer to the ear canal opening of the user's ear. 1 The sound outlet AS pointing to the rear cavity 2 Direction X 1 ' and its surrounding directions (such as direction X 2 ', Direction X 3 '), is the direction in which the acoustic output device is away from the user's ear canal opening. In some embodiments, in the wearing state and / or the non-wearing state, the sound outlet portion AS of the rear cavity of the acoustic output device 2 The sound outlet AS points to the front cavity 1 Direction X 1 and its surrounding directions can constitute the above-mentioned specified direction range. 1 The far-field radiation in the direction near it is significantly greater than that in other directions (such as 1 and the direction perpendicular to the direction near it, and the direction perpendicular to X 1 In some embodiments, the directivity of the acoustic output device can be expressed as follows: the absolute value of the difference in sound pressure level between the specific direction of the acoustic output device and the two corresponding far-field positions in the opposite direction is not less than a preset sound pressure level threshold. In the wearing state, the specific direction can refer to the direction in which the acoustic output device is away from the user's ear canal opening, and the opposite direction can refer to the direction in which the acoustic output device is pointing to the user's ear canal. In some embodiments, the specific direction can refer to the direction from the sound outlet portion AS of the front cavity to the ear canal. 1 The sound outlet AS pointing to the rear cavity 2 Direction X 1 'And its vicinity; the opposite direction of a specific direction may refer to the sound outlet portion AS of the rear cavity 2 The sound outlet AS points to the front cavity 1 Direction X 1 In some embodiments, direction X 1 ' can be understood as the direction near the direction X 1 ' is less than 60°. It should be noted that for the purpose of understanding directivity, only AS is used here. 1 and AS 2 These two holes are used as an example. When the acoustic output device has more different holes, AS 1 It is understood as the equivalent hole part formed by some of the holes, AS 2It is understood that the equivalent hole portion is formed by another part of the hole portion, and the direction of directivity at this time can be determined by the position of the equivalent hole portion. In some embodiments, the position of the equivalent hole portion formed by multiple hole portions can be determined by connecting the center points of adjacent hole portions in sequence to form a polygon or a polyhedron, and the centroid of the polygon or the polyhedron is the center point of the equivalent hole portion, which can be used to indicate the position of the equivalent hole portion.

[0055] In some embodiments, the far-field radiation of the acoustic output device may present a cardioid directivity, which is manifested as: within a specified direction range, the absolute value of the sound pressure level difference of the far-field radiation sound of the acoustic output device in at least one pair of opposite directions is not less than a preset sound pressure level threshold. Wherein, the at least one pair of opposite directions may fall within the above-mentioned specified direction range and the opposite direction range thereof, respectively. In some embodiments, at least one pair of opposite directions may include the aforementioned specific direction and its opposite direction. That is, the aforementioned specific direction and its opposite direction may be included in the above-mentioned specified direction range and its opposite direction range, respectively. In some embodiments, the above-mentioned at least one pair of opposite directions includes the sound outlet portion AS of the front cavity. 1 (e.g. the first hole) and the sound outlet AS of the rear cavity 2 The cardioid directivity of the acoustic output device can be expressed as a pair of opposite directions corresponding to the line connecting the front cavity sound outlet portion and the rear cavity sound outlet portion. The sound field intensity of a pair of opposite or nearly opposite directions in the above-mentioned specified direction range and its opposite direction range has a large difference. Exemplarily, the above-mentioned pair of opposite or nearly opposite directions can refer to a direction X from the front cavity sound outlet portion to the rear cavity sound outlet portion. 1 ', and the other direction is located in the direction X from the rear cavity sound hole to the front cavity sound hole 1 For example, direction X 1 'Can be with direction X 1 , Direction X 2 , Direction X 3 Opposite or nearly opposite.

[0056] Through the cardioid directivity setting of the far-field radiation of the acoustic output device, the sound output by the acoustic output device can be transmitted more concentratedly in the direction of the user's ear canal opening, reducing the transmission of sound in other directions, improving the sound leakage problem of the acoustic output device, and enhancing the user's listening effect.

[0057] In some embodiments, the preset sound pressure level threshold may be 6 dB. For example, the far-field radiation of the acoustic output device has a cardioid directivity, which may be expressed as follows: the far-field radiation sound of the acoustic output device is in at least one pair of opposite directions (for example, direction X 1 With direction X 1') The absolute value of the sound pressure level difference is not less than 6dB, so that the user's ear canal opening can receive a larger volume, allowing the user to get a clear listening effect.

[0058] In some embodiments, the first electrical signal driving the first speaker and the second electrical signal driving the second speaker have amplitude and / or phase differences within the target frequency range, and within the target frequency range, the first sound wave, the second sound wave, and the third sound wave superimpose and cancel each other at the far-field position in a specific direction of the acoustic output device, so that the sound pressure after superposition and cancellation is small, for example, close to zero, so that the far-field radiation of the acoustic output device is directional, improving the problem of sound leakage in the far field of the acoustic output device. In some embodiments, the first electrical signal can be measured by a measuring instrument (for example, an oscilloscope, etc.) disposed between the first speaker and the corresponding signal generator; the second acoustic signal can be measured by a measuring instrument (for example, an oscilloscope) disposed between the second speaker and the corresponding signal generator. In some embodiments, the adjusted first electrical signal and / or second electrical signal can be measured by a measuring instrument disposed between the corresponding speaker and the corresponding signal modulator.

[0059] In order to achieve the directivity of the far-field radiation of the acoustic output device, the first loudspeaker and the second loudspeaker may be arranged in a variety of ways. Figure 5A-5D 1 is a schematic diagram of a structure of an acoustic output device including first speakers and second speakers arranged in different ways according to some embodiments of this specification. Figure 5A-5D As shown, in some embodiments, the first diaphragm 521 and the second diaphragm 551 have the same vibration direction (eg Figure 5A-5D The first diaphragm 521 and the second diaphragm 551 are arranged at intervals along the vibration direction, that is, the first speaker 520 and the second speaker 550 are arranged at intervals along the vibration direction (such as Figure 5A and Figure 5B In some embodiments, the first diaphragm 521 and the second diaphragm 551 are arranged at intervals in a direction perpendicular to the vibration direction, that is, the first speaker 520 and the second speaker 550 are arranged at intervals in a direction perpendicular to the vibration direction (as shown in FIG. Figure 5C and Figure 5DAs shown). It should be noted that it is an ideal situation that the vibration directions of the first diaphragm 521 and the second diaphragm 551 are the same. In actual products, due to factors such as structural design and installation errors, the vibration directions of the first diaphragm 521 and the second diaphragm 551 may not be exactly the same, but slightly different (for example, the angle between the vibration directions of the first diaphragm 521 and the second diaphragm 551 may be less than 10°, etc.). At this time, the arrangement direction of the first speaker 520 and the second speaker 550 or the perpendicular direction of their emission direction may be the vibration direction of the first diaphragm 521 or the vibration direction of the second diaphragm 551 or the direction between the angles formed by the vibration directions of the two diaphragms. In some embodiments, the orientation of the first diaphragm 521 in the first speaker 520 may be the same as or opposite to the orientation of the second diaphragm 551 in the second speaker 550. In some embodiments, the first rear cavity 540 of the first speaker 520 may be adjacent to or communicate with the second rear cavity 570 of the second speaker 550. At this time, the second front cavity 560 of the second speaker 550 is closed, such as Figure 5A and Figure 5C In some embodiments, the first rear cavity 540 of the first speaker 520 may be adjacent to or communicate with the second front cavity 560 of the second speaker 550. In this case, the second rear cavity 570 of the second speaker 550 is closed. Figure 5B and Figure 5D In some embodiments, when the volumes of the cavities (e.g., the first front cavity 530, the first rear cavity 540, the second front cavity 560, the second rear cavity 570, etc.) are the same, Figure 5A The acoustic output device 500 shown can be used with Figure 5C The acoustic output device 500 shown is equivalent to, Figure 5B The acoustic output device 500 shown can be used with Figure 5D The acoustic output device 500 shown is equivalent.

[0060] The acoustic output device is exemplarily described below by taking the first speaker and the second speaker arranged at intervals along the vibration direction as an example.

[0061] like Figure 5A and Figure 5BAs shown, in some embodiments, an acoustic output device 500 includes a housing 510, a first speaker 520, and a second speaker 550. The first speaker 520 is disposed in the housing 510, and includes a first diaphragm 521. The first diaphragm 521 has a first front cavity 530 and a first rear cavity 540 disposed on the front and rear sides thereof, respectively. The first front cavity 530 and the first rear cavity 540 are acoustically coupled to a first hole 511 and a second hole 512 on the housing 510, respectively. The first speaker 520, driven by a first electrical signal, outputs a first sound wave and a second sound wave with a phase difference through the first hole 511 and the second hole 512, respectively. The second speaker 550 is disposed in the housing 510. The second speaker 550 includes a second diaphragm 551. A second front cavity 560 and a second rear cavity 570 are respectively disposed on the front and rear sides of the second diaphragm 551. One of the second front cavity 560 and the second rear cavity 570 is the same cavity as the first rear cavity 540. That is, the second front cavity 560 or the second rear cavity 570 constituting the same cavity is acoustically coupled with the second hole 512 on the housing 510. Driven by the second electrical signal, the second speaker 550 outputs the third sound wave through the second hole 512. In some embodiments, the second front cavity 560 and the first rear cavity 540 may constitute the same cavity. In this case, the first diaphragm 521 and the second diaphragm 551 have the same orientation, such as Figure 5B In some embodiments, the second rear cavity 570 and the first rear cavity 540 may form the same cavity, and in this case, the first diaphragm 521 and the second diaphragm 551 face opposite directions, as shown in FIG. Figure 5A As shown. Figure 5A The acoustic output device 500 shown is Figure 5B In the acoustic output device 500 shown in the figure, the first diaphragm 521 and the second diaphragm 551 are arranged in different directions. Figure 5A The acoustic output device 500 shown is Figure 5B The frequency response curves of the acoustic output device 500 shown in FIG. 5 are somewhat different, but the far-field radiated sound of both devices can achieve directivity. Figure 5A The acoustic output device 500 is described by taking the example that the first speaker 520 and the second speaker 550 are arranged at intervals along the vibration direction, and the first diaphragm 521 and the second diaphragm 551 are facing opposite directions (that is, the second rear cavity 570 and the first rear cavity 540 constitute the same cavity).

[0062] For corresponding Figure 4 , Figure 5A and Figure 5B , the first front cavity 530 can be used as the front cavity of the acoustic output device 500, and the same cavity can be used as the rear cavity of the acoustic output device 500. At this time, the first hole portion 511 serves as the front cavity sound outlet hole portion AS of the acoustic output device 500. 1The second hole portion 512 serves as the rear cavity sound outlet hole AS of the acoustic output device 500. 2 At this time, the direction of the extension line of the connection line between the first hole portion 511 and the second hole portion 512 is the specific direction.

[0063] In some embodiments, by setting the first electrical signal and the second electrical signal to have an amplitude and / or phase difference within the target frequency range, the first sound wave generated by the first speaker 520 in the first front cavity 530, the second sound wave generated by the first speaker 520 in the first rear cavity 540, and the third sound wave generated by the second speaker 550 in the second rear cavity 570 meet certain phase and amplitude conditions at the far-field position in a specific direction of the acoustic output device 500. For example, the superimposed sound wave formed by the first sound wave and the second sound wave at the far-field position in a specific direction has a phase difference with the third sound wave, and after the superimposed phase cancellation, the sound pressure at the far-field position is small, for example, close to zero, so that the absolute value of the sound pressure level difference between the far-field position in the specific direction and the corresponding far-field position in the opposite direction of the specific direction is not less than the preset sound pressure level threshold, thereby realizing the directivity of the acoustic output device 500. At the same time, such a setting can suppress the sound field confusion of the dual sound sources in the high-frequency range, thereby reducing or eliminating the sound wave radiation of the acoustic output device 500 in the far field.

[0064] In order to prevent the resonant frequency of each cavity from interfering with the cardioid directivity of the acoustic output device and improve the user's listening experience, the structural parameters of each cavity can be adjusted so that the resonant frequency of each cavity falls outside the frequency range for achieving cardioid directivity. In some embodiments, the target frequency range for the acoustic output device to achieve cardioid directivity can be within the range of the relatively stable frequency response of the first speaker 520 and the second speaker 550. That is, the same cavity between the first speaker 520 and the second speaker 550 (such as Figure 5A The first rear cavity 540 and the second rear cavity 570 constitute the same cavity, Figure 5BThe resonant frequency of the same cavity (the same cavity formed by the first rear cavity 540 and the second front cavity 560 in the middle) determines the upper frequency limit at which the cardioid directivity can be easily achieved. In some embodiments, in order to improve the user's sound reception effect, the acoustic output device can have a cardioid directivity within the frequency range that the human ear is sensitive to, such as around 3kHz or around 3.5kHz. At this time, the upper limit of the frequency range in which the far-field radiation of the acoustic output device achieves cardioid directivity may not be less than 4kHz (for example, the frequency range in which the cardioid directivity is achieved may be 1kHz-4kHz). At this time, the resonant frequency of the same cavity is not less than 4kHz. In some embodiments, due to different application scenarios of the acoustic output device, the frequency range in which the cardioid directivity needs to be achieved may also be different accordingly. For example, for an acoustic output device that mainly works under medium and low frequency conditions, the frequency range in which the cardioid directivity is achieved may be 800Hz-2kHz; at this time, the resonant frequency of the same cavity may not be less than 2kHz. For an acoustic output device that mainly works under medium and high frequency conditions, the upper limit of the frequency range in which the cardioid directivity is achieved may be larger, and the corresponding resonant frequency of the same cavity is also larger. In order to improve the output quality of the acoustic output device within the frequency range sensitive to the human ear, the resonant frequency of the same cavity may be outside the frequency range sensitive to the human ear, for example, greater than 4kHz, greater than 4.5kHz, greater than 5kHz, etc. At this time, the upper limit of the frequency range for achieving cardioid directivity may be 4kHz, 4.5kHz, 5kHz, etc.

[0065] Figure 6 is a schematic diagram of the relationship between the resonant frequency and volume of the same cavity shown in some embodiments of this specification, Figure 7 Schematic diagram of the relationship between the resonant frequency of the same cavity and the area of ​​the hole portion of its acoustic coupling according to some embodiments of this specification. Figure 6 and Figure 7 As shown, in some embodiments, when the resonant frequency of the same cavity is adjusted to be not less than 3.8 kHz, the volume of the same cavity is not greater than 0.38 cm 3 The area of ​​the second hole 512 acoustically coupled to the same cavity is not less than 17 mm 2 In some embodiments, when the resonant frequency of the same cavity is adjusted to be not less than 4 kHz, the volume of the same cavity is not greater than 0.28 cm 3 The area of ​​the second hole 512 acoustically coupled to the same cavity is not less than 20 mm 2 In some embodiments, when the resonant frequency of the same cavity is adjusted to be no less than 4.2 kHz, the volume of the same cavity is no greater than 0.2 cm 3 The area of ​​the second hole 512 acoustically coupled to the same cavity is not less than 22 mm 2In some embodiments, when the resonant frequency of the same cavity is adjusted to be no less than 4.3 kHz, the volume of the corresponding same cavity is no greater than 0.18 cm 3 The area of ​​the second hole 512 acoustically coupled to the same cavity is not less than 23 mm 2 By adjusting the volume of the same cavity and the area of ​​the hole portion acoustically coupled to the same cavity, the resonant frequency of the same cavity can be further regulated to fall outside the frequency range of the acoustic output device to achieve cardioid directivity, thereby avoiding interference with the acoustic output device to achieve cardioid directivity, thereby improving the user's listening experience.

[0066] In some embodiments, one of the second front cavity 560 and the second rear cavity 570 of the second speaker 550 that does not constitute the same cavity is a closed cavity that is not acoustically coupled to the second hole portion 512. For example, Figure 5A The second front cavity 560 in the embodiment is a closed cavity and is not acoustically coupled with the second hole portion 512. For another example, Figure 5B The second rear cavity 570 in the embodiment is a closed cavity and is not acoustically coupled with the second hole portion 512. In some embodiments, the resonant frequency of the closed cavity can be adjusted so that it is not higher than the lower frequency limit of the target frequency range for achieving the cardioid directivity, so that it does not fall within the frequency band in which the acoustic output device achieves the cardioid directivity. In some embodiments, the resonant frequency of the closed cavity may be no higher than 1kHz, so that the lower frequency limit of the acoustic output device to achieve the cardioid directivity may be no lower than 1kHz (for example, the frequency range for achieving the cardioid directivity may include 1kHz-4kHz), so as to improve the output performance of the acoustic output device within the frequency range sensitive to the human ear. In some embodiments, the resonant frequency of the closed cavity may be lower than the lower frequency limit of the frequency range in which the acoustic output device achieves the cardioid directivity. For example, the resonant frequency of the closed cavity may be no higher than 800Hz. In some embodiments, considering factors such as structural design and difficulty in processing and installation, the resonant frequency of the closed cavity may be no higher than 600Hz.

[0067] Figure 8 Schematic diagram of the relationship between the resonant frequency and volume of a closed cavity according to some embodiments of this specification. Figure 8 As shown, in some embodiments, when the resonance frequency of the closed cavity of the second speaker 550 is not higher than 1 kHz, the volume of the corresponding closed cavity is not less than 0.8 cm 3 In some embodiments, when the resonance frequency of the closed cavity of the second speaker 550 is not higher than 1.2 kHz, the volume of the corresponding closed cavity is not less than 0.6 cm 3 In some embodiments, when the resonance frequency of the closed cavity of the second speaker 550 is not higher than 1.4 kHz, the volume of the corresponding closed cavity is not less than 0.5 cm 3In some embodiments, when the resonance frequency of the closed cavity of the second speaker 550 is not higher than 1.6 kHz, the volume of the corresponding closed cavity is not less than 0.45 cm 3 In some embodiments, when the resonance frequency of the closed cavity of the second speaker 550 is not higher than 0.8 kHz, the volume of the corresponding closed cavity is not less than 1.1 cm 3 By adjusting the volume of the closed cavity, the resonant frequency of the closed cavity can be further adjusted so that it is not higher than the lower limit of the target frequency range for the acoustic output device to achieve cardioid directivity, thereby avoiding interference, improving the user's listening quality and the sound leakage reduction effect of the acoustic output device.

[0068] In some embodiments, due to the closed cavity setting of the second speaker, the second speaker is not easy to output low-frequency sound waves at its acoustically coupled hole (e.g., the second hole 512). Therefore, in the low-frequency range, the sound pressure of the sound wave output by the second speaker is much smaller than the sound pressure of the sound wave output by the first speaker. At this time, the sound wave output by the second speaker can be ignored, and the first speaker mainly outputs the sound wave for the acoustic output device, and the acoustic output device can achieve dual sound source directivity. In the mid-to-high frequency range, the first speaker and the second speaker cooperate to output sound waves for the acoustic output device, and the acoustic output device can achieve cardioid directivity. In some embodiments, the acoustic output device can achieve dual sound source directivity in the frequency range of 100Hz-800Hz, and achieve cardioid directivity in the frequency range of 1kHz-4kHz. In some embodiments, the frequency range in which the acoustic output device achieves dual sound source directivity can be designed and adjusted according to actual conditions. For example, the target frequency range for the acoustic output device to achieve dual sound source directivity can be 100Hz-1.2kHz, 100Hz-1.5kHz, 200Hz-2kHz, etc. In some embodiments, in order to achieve dual sound source directivity within the target frequency range, the amplitude of the second electrical signal driving the second speaker can be reduced within the target frequency range, for example, the amplitude of the second electrical signal is adjusted to 0 within the target frequency range, that is, the second electrical signal is not provided within the target frequency range. In some embodiments, the lower frequency limit of the frequency range in which the acoustic output device achieves cardioid directivity can be greater than the upper frequency limit of the frequency range in which the dual sound source directivity is achieved, so as to avoid confusion in the sound field of the acoustic output device. When the target frequency range in which the acoustic output device achieves dual sound source directivity is different, the mid- and high-frequency range in which the acoustic output device achieves cardioid directivity may also change accordingly, and since the resonant frequency of the closed cavity of the second speaker affects the lower frequency limit of the frequency range in which the cardioid directivity is achieved, the resonant frequency of the closed cavity of the second speaker also needs to change accordingly. For example, when the acoustic output device achieves dual sound source directivity at 100Hz-800Hz and cardioid directivity at 1kHz-4kHz, the resonant frequency of the closed cavity of the second speaker may not be higher than 1kHz. For another example, when the acoustic output device realizes dual sound source directivity at 100 Hz-1.2 kHz and realizes cardioid directivity at 1.5 kHz-4 kHz, the resonance frequency of the closed cavity of the second speaker may be no higher than 1.5 kHz. In some embodiments, in the wearing state, the hole portion of the first speaker acoustically coupled with the first front cavity may be arranged close to the user's ear, while the hole portion acoustically coupled with the first rear cavity is arranged away from the user's ear, and the direction from the hole portion acoustically coupled with the first rear cavity to the hole portion acoustically coupled with the first front cavity points to the user's ear, that is, the dual sound source directivity formed in the low-frequency range can point to the user's ear.In some embodiments, in the wearing state, the hole portion of the first speaker acoustically coupled to the first front cavity can be arranged close to the user's ear, the hole portion acoustically coupled to the first rear cavity and the hole portion through which the second speaker outputs the third sound wave are arranged away from the user's ear, the hole portion acoustically coupled to the first rear cavity and the hole portion through which the second speaker outputs the third sound wave have an equivalent hole portion, and the direction pointed by the equivalent hole portion to the hole portion acoustically coupled to the first front cavity points to the user's ear, that is, the directivity formed in the mid- and high-frequency range can point to the user's ear.

[0069] Fig. 9 is a schematic diagram of the structure of the acoustic output device according to other embodiments of this specification. In order to prevent the sound waves radiated by the first speaker and the second speaker from interfering with each other and reduce the mutual radiation impedance, the acoustic output device may also include: Fig. 9 The first speaker 620 and the second speaker 650 shown do not have the same cavity. For example, the acoustic output device housing may be provided with two accommodation spaces, and the first speaker 620 and the second speaker 650 may be respectively provided in the two accommodation spaces; for another example, the first speaker 620 and the second speaker 650 are provided in the same accommodation space of the housing, but a partition is provided between the two, so that the two cavities opposite to each other of the two speakers are not intercommunication. The acoustic output device 600 shown in other embodiments is described below by taking the first speaker and the second speaker arranged at intervals along the vibration direction, and the first diaphragm and the second diaphragm facing opposite directions as an example.

[0070] like Fig. 9 As shown, the acoustic output device 600 may include a housing 610, a first speaker 620, and a second speaker 650. The first speaker 620 includes a first diaphragm 621, and a first front cavity 630 and a first rear cavity 640 are respectively provided on the front and rear sides of the first diaphragm 621. The housing 610 is provided with a first hole portion 611 acoustically coupled with the first front cavity 630 and a second hole portion 612 acoustically coupled with the first rear cavity 640. The first hole portion 611 and the second hole portion 612 serve as sound outlet holes of the first speaker 620 to form a dual sound source. The second speaker 650 includes a second diaphragm 651, and a second front cavity 660 and a second rear cavity 670 are respectively provided on the front and rear sides of the second diaphragm 651. One of the second front cavity 660 and the second rear cavity 670 is acoustically coupled with the third hole portion 613 on the housing 610, and the other serves as a closed cavity. Among them, the third hole portion 613 is a hole portion different from the first hole portion 611 and the second hole portion 612. In some embodiments, a partition 614 is disposed in the housing 610, and a cavity (eg, Fig. 9The second rear cavity 570 in the first rear cavity 640 is separated from the first rear cavity 640 by a partition 614, and the second hole portion 612 and the third hole portion 613 are respectively located on both sides of the partition 614. In some embodiments, the distance between the third hole portion 613 and the second hole portion 612 may be greater than 0 mm but not greater than 10 mm, so as to avoid the distance between the second hole portion 612 and the third hole portion 613 being too large, thereby avoiding the volume of the corresponding cavity being too large, and making the positions of the equivalent hole portions of the second hole portion 612 and the third hole portion 613 appropriate, so as to avoid causing significant interference to the directivity of the acoustic output device 600.

[0071] In some embodiments, within the target frequency range, at a far-field position in a specific direction of the acoustic output device 600, the sound pressure after the superposition of the first sound wave, the second sound wave output by the first speaker 620 and the third sound wave output by the second speaker 650 is small, for example, close to zero, so that the far-field radiation of the acoustic output device 600 is directional, thereby improving the problem of sound leakage in the far field of the acoustic output device 600. In some embodiments, the target frequency range may include 1kHz-4kHz, so that the acoustic output device 600 can have a flatter frequency response curve in a wider frequency range while having better cardioid directivity.

[0072] It should be noted that, for the acoustic output device 600, when expressing its directivity, the second hole portion 612 acoustically coupled to the first rear cavity 640 of the first speaker 620 and the third hole portion 613 acoustically coupled to the second rear cavity 670 of the second speaker 650 can be equivalent to one hole portion. Specifically, the center position point M between the second hole portion 612 and the third hole portion 613 is determined, and the center position point M can represent the position of the equivalent hole portion. At this time, the first front cavity 630 can be used as the front cavity of the acoustic output device 600, and the first rear cavity 640 and the cavity acoustically coupled to the third hole portion 613 (for example Fig. 9 The second rear cavity 670 shown in the figure can be used as the rear cavity of the acoustic output device 600. The first hole portion 611 is used as the front cavity sound outlet hole portion AS of the acoustic output device 600. 1 The equivalent hole portion of the second hole portion 612 and the third hole portion 613 can be used as the rear cavity sound outlet hole portion AS of the acoustic output device 600. 2 Then, the direction of the extension line of the line connecting the first hole portion 611 and the equivalent hole portion (point M) is the specific direction.

[0073] In some embodiments, the resonant frequency of the cavity (the second front cavity 660 or the second rear cavity 670) acoustically coupled to the third hole portion 613 and the resonant frequency of the first rear cavity 640 determine the upper frequency limit of the acoustic output device 600 to achieve cardioid directivity. If the difference between the above two resonant frequencies is too large, one of the resonant frequencies will be too small, which will cause the upper frequency limit of the acoustic output device 600 to achieve cardioid directivity to be too small, resulting in the frequency band range of the acoustic output device 600 to achieve cardioid directivity to be too small, which will ultimately affect the output performance of the acoustic output device 600. In some embodiments, the difference between the above two resonant frequencies is not greater than 3000Hz. In order to further make the cardioid directivity have a higher upper frequency limit, in some embodiments, the difference between the above two resonant frequencies is not greater than 2500Hz. Further, in order to make the cardioid directivity have a higher upper frequency limit, in some embodiments, the difference between the above two resonant frequencies is not greater than 2000Hz. Preferably, the difference between the above two resonant frequencies is not greater than 1500Hz. More preferably, the difference between the above two resonant frequencies is not greater than 1000Hz.

[0074] In some embodiments, in order to enable the acoustic output device to achieve cardioid directivity within the sound frequency range that the human ear is sensitive to, the upper frequency limit of the cardioid directivity may be no less than 4kHz. In some embodiments, in order to prevent the resonance frequency of the cavity from interfering with the cardioid directivity, the resonance frequency of the cavity (the second front cavity 660 or the second rear cavity 670) acoustically coupled to the third hole portion 613 may fall outside the frequency range for achieving the cardioid directivity, for example, the resonance frequency of the cavity (the second front cavity 660 or the second rear cavity 670) acoustically coupled to the third hole portion 613 may be no less than 4kHz. In some embodiments, in order to make the upper frequency limit of the cardioid directivity larger, the resonance frequency of the cavity (the second front cavity 660 or the second rear cavity 670) acoustically coupled to the third hole portion 613 may be no less than 5kHz.

[0075] In some embodiments, the structures of the first rear cavity 640 and the second hole portion 612, the cavity (the second front cavity 660 or the second rear cavity 670) acoustically coupled to the third hole portion 613, and the third hole portion 613 are the same or similar, and the resonant frequencies of the two are close (for example, the difference between the resonant frequencies of the two is less than 3000 Hz). When the resonant frequency of the cavity (the second front cavity 660 or the second rear cavity 670) acoustically coupled to the third hole portion 613 is not less than 4 kHz, the cavity (for example Fig. 9 The volume of the second rear cavity 570 shown is no greater than 0.3 cm 3 , the area corresponding to the third hole portion 613 is not less than 12mm 2 At this time, the volume of the first rear cavity 640 may also be no greater than 0.3 cm 3The area corresponding to the second hole 612 may also be not less than 12 mm 2 .

[0076] In some embodiments, the cavities in the second front cavity 660 and the second rear cavity 670 of the second speaker 650 that are not acoustically coupled with the second hole portion 612 are closed cavities, for example, Fig. 9 The second front cavity 660 in the embodiment is a closed cavity. The resonant frequency of the closed cavity can determine the lower limit of the frequency range for achieving the cardioid directivity. In some embodiments, in order to prevent the resonant frequency of the closed cavity from interfering with the cardioid directivity, the resonant frequency of the closed cavity can be made to fall outside the frequency range for achieving the cardioid directivity. For example, the closed cavity (e.g. Fig. 9 The resonant frequency of the second front cavity 660 in the closed cavity is not higher than 1kHz. In some embodiments, the resonant frequency of the closed cavity can be lower than the lower limit of the frequency range of the acoustic output device to achieve cardioid directivity. For example, the resonant frequency of the closed cavity can be no higher than 900Hz. In some embodiments, considering factors such as structural design and difficulty in processing and installation, the resonant frequency of the closed cavity can be no higher than 1.1kHz. At this time, the frequency range of the acoustic output device to achieve cardioid directivity may be correspondingly reduced, and the lower limit of the frequency to achieve cardioid directivity may be 1.1kHz.

[0077] In some embodiments, when the first hole portion 611 acoustically coupled to the first front cavity 630 is arranged in the corresponding area on the housing 610 along the vibration direction of the first speaker 620 (that is, the direction of the line connecting the geometric center of the first hole portion 611 and the geometric centroid of the first diaphragm 621 of the first speaker 620 is parallel to the vibration direction), the hole portion corresponding to the first rear cavity 640 and the cavity adjacent thereto (the second front cavity 660 or the second rear cavity 670) can have a variety of settings. The following describes different hole portion settings of the acoustic output device 600, taking the example that the first speaker and the second speaker do not have the same cavity, are arranged at intervals along the vibration direction, and the first diaphragm and the second diaphragm face opposite directions.

[0078] Figures 10A-10D is a schematic diagram of an acoustic output device with different sound outlet hole arrangement modes according to some embodiments of the present application specification, Figures 11A-11D They are Figures 10A-10D The directivity diagram of the far-field radiation of the acoustic output device is shown in FIG. Fig. 10A and Fig.11AAs shown, when the first hole portion 611 is arranged directly above the first speaker 620 along the vibration direction (that is, the first hole portion 611 is located on the side wall of the shell directly opposite to the first diaphragm 621, and the line connecting the geometric center of the first hole portion 611 and the geometric centroid of the first diaphragm 621 is parallel to the vibration direction of the first speaker 620), and the second hole portion 612 and the third hole portion 613 are arranged on the same side wall of the shell in the vertical vibration direction relative to the first hole portion 611, the maximum and minimum directions of the sound pressure output by the acoustic output device are the directivity directions of the acoustic output device, and the maximum direction is opposite to the minimum direction. The minimum direction is the aforementioned specific direction, and the sound pressure of the acoustic output device at the far-field position in the specific direction (minimum direction) is small (for example, close to zero). The specific direction is determined by the front cavity sound outlet hole of the acoustic output device 600 (for example, Fig. 10A The first hole portion 611 of the embodiment of the present invention is directed to the rear cavity sound outlet hole (for example, Fig. 10A The direction of the equivalent hole portion M) of the second hole portion 612 and the third hole portion 613.

[0079] like Fig. 10B and Fig. 11B As shown, the first hole portion 611 is arranged directly above the first speaker 620 along the vibration direction, that is, the first hole portion 611 is located on the side wall of the shell directly opposite to the first diaphragm; the first rear cavity 640 is acoustically coupled with two acoustic hole portions (the second hole portion 612 and the other second hole portion 612') at the same time, and the second hole portion 612 and the other second hole portion 612' are respectively arranged on the two side walls of the shell in the vertical vibration direction relative to the first hole portion 611; the second rear cavity 670 is adjacent to the first rear cavity 640, and the second rear cavity 670 is acoustically coupled with the third hole portion 613 and the other third hole portion 613' at the same time, and the third hole portion 613 and the other third hole portion 613' are respectively arranged on the two side walls of the shell in the vertical vibration direction relative to the first hole portion 611. At this time, along the vibration direction, the second hole portion 612 and the other second hole portion 612' are symmetrical with respect to the first hole portion 611, and the third hole portion 613 and the other third hole portion 613' are symmetrical with respect to the first hole portion 611. At this time, the direction of the line connecting the equivalent hole portions of the second hole portion 612, the other second hole portion 612', the third hole portion 613, the other third hole portion 613' and the first hole portion 611 is basically consistent with the vibration direction. Fig. 10BAs shown, point M shows the position of the equivalent hole portion. At this time, the line connecting point M and the geometric center of the first hole portion 611 is parallel to the vibration direction of the first speaker 620, and point M is located on the midline of the line connecting the geometric center of the second hole portion 612 and the geometric center of the third hole portion 613. For example, when the second hole portion 612 and the third hole portion 613 are symmetrically arranged relative to the partition 614, point M can be located at the position of the geometric center of the partition 614. The direction of the maximum sound pressure and the minimum sound pressure of the far-field radiation of the acoustic output device 600 is the directivity direction of the acoustic output device, and the maximum direction is opposite to the minimum direction. Among them, the minimum direction is a specific direction, that is, the sound outlet hole of the front cavity of the acoustic output device 600 (for example, Fig. 10B The first hole portion 611 in the middle is directed to the rear cavity sound outlet hole (for example, Fig. 10B The direction of the equivalent hole portion M of the second hole portion 612, another second hole portion 612', the third hole portion 613, and another third hole portion 613'.

[0080] like Fig. 10C and Fig. 11C As shown, the first hole portion 611 is arranged directly above the first speaker 620 along the vibration direction, that is, the first hole portion 611 is located on the side wall of the shell directly opposite to the first diaphragm; the first rear cavity 640 is acoustically coupled with the second hole portion 612 and the other second hole portion 612' at the same time, and the second hole portion 612 and the other second hole portion 612' are respectively arranged on the two side walls of the shell in the vertical vibration direction relative to the first hole portion 611; the second rear cavity 670 is adjacent to the first rear cavity 640, and the second rear cavity 670 is a closed cavity at this time; the second front cavity 660 is acoustically coupled with the third hole portion 613, and along the vibration direction, the third hole portion 613 is arranged on the shell opposite to the first hole portion 611, that is, directly below the geometric centroid of the second diaphragm 651 of the second speaker 650, that is, the third hole portion 613 is located on the side wall of the shell directly opposite to the geometric centroid of the second diaphragm 651. At this time, the direction of the line connecting the second hole portion 612, the equivalent hole portion of the other second hole portion 612' and the first hole portion 611 is substantially consistent with the vibration direction. Fig. 10C As shown, point M shows the position of the equivalent hole portion. At this time, the far-field radiation of the acoustic output device 600 has a main lobe (corresponding to the direction of the maximum sound pressure) and a side lobe. The direction of the main lobe (i.e., the direction of the maximum value) is from the second hole portion 612 and the equivalent hole portion M of the other second hole portion 612' to the first hole portion 611. The direction of the side lobe is from the second hole portion 612 and the equivalent hole portion M of the other second hole portion 612' to the third hole portion 613. And combined Fig. 10C and Fig. 11C It can be seen that the minimum direction is in the direction from the second hole portion 612 to the third hole portion 613 and in the direction from the other second hole portion 612 ′ to the third hole portion 613 .

[0081] like Fig. 10D and Fig.11D As shown, the first hole portion 611 is arranged directly above the first speaker 620 along the vibration direction, that is, the first hole portion 611 is located on the side wall of the shell body directly opposite to the first diaphragm; the first rear cavity 640 is acoustically coupled with the second hole portion 612 and the other second hole portion 612' at the same time, and the second hole portion 612 and the other second hole portion 612' are respectively arranged on the two side walls of the shell body in the vertical vibration direction relative to the first hole portion 611; the second rear cavity 670 is adjacent to the first rear cavity 640, and the second rear cavity 670 At the same time, it is acoustically coupled with the third hole portion 613 and another third hole portion 613', and the third hole portion 613 and another third hole portion 613' are respectively arranged on the two side walls of the shell in the vertical vibration direction relative to the first hole portion 611; the second front cavity 660 is acoustically coupled with the fourth hole portion 615, and along the vibration direction, the fourth hole portion 615 is arranged directly below the shell position corresponding to the first hole portion 611, that is, the fourth hole portion 615 is located on the shell side wall directly opposite to the geometric centroid of the second diaphragm. At this time, the first hole portion 611 of the first speaker 620, the second hole portion 612 and the equivalent hole portion of the other second hole portion 612' are used as a group of dual sound sources, and the third hole portion 613 of the second speaker 650 and the equivalent hole portion of the other third hole portion 613' and the fourth hole portion 615 are used as dual sound sources. At this time, the second hole portion 612 and the third hole portion 613 have an equivalent hole portion M. 1 The other second hole portion 612' and the other third hole portion 613' have an equivalent hole portion M 2 The second hole portion 612, another second hole portion 612', the third hole portion 613, and another third hole portion 613' have an equivalent hole portion M. 3 , click M 3 The location can be referred to Fig. 10B The position of point M in the figure is not described here. 3 The direction of the line connecting the first hole 611 is basically consistent with the vibration direction. The far-field radiation of the acoustic output device 600 has a main lobe (corresponding to the direction of the maximum sound pressure) and a side lobe. The direction of the main lobe (i.e., the direction of the maximum sound pressure) is determined by the equivalent hole M. 3 Pointing to the direction of the first aperture portion 611. The direction of the side lobe is determined by the equivalent aperture portion M 3 Pointing to the direction of the fourth hole portion 615. And combined Fig. 10D and Fig.11D It can be seen that the minimum direction is in the equivalent hole part M 1 The direction of the fourth hole portion 615 and the direction of the equivalent hole portion M 2 Pointing to the direction of the fourth hole portion 615. At this time, the far-field radiation of the acoustic output device 600 can also achieve weak cardioid directivity, such as Fig.11D As shown. Fig.11A and Fig. 11B The cardioid polar pattern shown, Fig.11DThe far-field radiation of the acoustic output device 600 shown in the figure has a narrow minimum region, a large sound pressure level in the minimum direction and in the directions on both sides of the minimum direction, and a relatively uniform sound pressure level in the direction near the maximum direction (0°-180° direction). In some embodiments, Fig. 10D The acoustic output device 600 shown is suitable for use in scenarios where uniform radiation in half space is required.

[0082] In some embodiments, the arrangement of the sound outlet portion of the acoustic output device is not limited to the above-mentioned methods, and the sound outlet portion can be arranged according to actual needs. In some embodiments, the first hole portion corresponding to the first front cavity of the first speaker can be arranged to correspond to the listening position of the user's ear in the wearing state (for example, arranged toward the external auditory canal of the user's ear or arranged close to the external auditory canal of the user), and the sound outlet portion corresponding to the first rear cavity of the first speaker and the sound outlet portion of the second speaker should be as far away from the first hole portion as possible to reduce the interference of other sound outlet portions on the first sound wave radiated by the first hole portion. In some embodiments, the area where the acoustic output device needs to reduce sound leakage (for example, a 30° fan-shaped area 10 cm away from the user's ear) can be determined according to the actual application scenario, the listening quality of the acoustic output device, or the need to reduce sound leakage, so as to determine the direction of the maximum sound pressure and the minimum sound pressure of the far-field radiation of the acoustic output device, and then determine the setting position of the corresponding sound outlet portion.

[0083] In order to reduce the overall size of the acoustic output device, the size of the speaker as a single sound source should not be too large, otherwise the fundamental resonance frequency of the speaker of the single sound source (that is, the resonance frequency of the closed cavity of the speaker of the single sound source) will be higher, and the lower limit of the frequency range of the acoustic output device to achieve cardioid directivity will be difficult to dive into the human voice frequency band. Fig. 12A and Fig. 12B 1 is a schematic diagram of the directivity of far-field radiation of an acoustic output device with exemplary hole arrangement positions according to some embodiments of this specification. Fig. 12A and Fig. 12B As shown, the acoustic output device 700 has a first speaker 710 and a second speaker 720. The front cavity and the rear cavity of the first speaker 710 are acoustically coupled with the first hole 711 and the second hole 712, respectively, as a dual sound source; one cavity of the second speaker 720 is closed, and the other cavity is acoustically coupled with the third hole 713, as a single sound source. In order to make the sound leakage of the acoustic output device 700 at the side of the user's head always small in the whole frequency band, as shown in FIG. Fig. 12A and Fig. 12BAs shown, compared with the first speaker 710 as a dual sound source, the second speaker 720 as a single sound source is smaller in size, and the length of the second speaker 720 is close to the thickness of the first speaker 710. The first hole portion 711 is arranged toward the user's ear canal opening, and the second hole portion 712 and the third hole portion 713 are both arranged away from the first hole portion 711. At this time, in the frequency range of the middle and low frequency bands (for example, below 1kHz), since the output sound pressure level of the single sound source is smaller than that of the dual sound sources, the output of the single sound source can be ignored at this time, and the acoustic output device 700 can be similar to the dual sound sources working alone, realizing the "8"-shaped dual sound source directivity to reduce leakage sound, such as Fig. 12A In the mid-high frequency band (e.g. 1kHz-4kHz), the single sound source and the dual sound source work together to achieve a cardioid directivity, as shown in Figure 1. Fig. 12B shown.

[0084] In some embodiments, the second speaker of the acoustic output device is not acoustically coupled to the closed cavity (eg, Figure 5A The second front cavity 560 shown, Figure 5B The second rear cavity 570 shown in the figure can be filled with acoustic granular material to increase the virtual volume of the closed cavity, reduce the resonant frequency of the closed cavity, thereby reducing the lower frequency limit of the cardioid directivity of the acoustic output device and increasing the frequency range of the cardioid directivity.

[0085] Fig.13 is a schematic diagram of another acoustic output device according to some embodiments of this specification. Fig.13 As shown, in some embodiments, the acoustic output device 800 may include a first speaker 810, a second speaker 820, and a third speaker 830 that are separately arranged. The first speaker 810 may radiate a first sound wave, the second speaker 820 may radiate a second sound wave, and the first sound wave and the second sound wave radiated by both may meet certain phase and amplitude conditions (for example, the same amplitude and opposite phase), thereby forming a dual sound source structure; the third speaker 830 may radiate a third sound wave, and the third sound wave radiated by the third speaker 830 may meet certain phase and amplitude conditions with the second sound wave radiated by the second speaker 820 and the first sound wave radiated by the first speaker 810 at a far-field position in a specific direction of the acoustic output device 800, so that the third sound wave superimposes and cancels the first sound wave and the second sound wave at the far-field position, thereby realizing the far-field directivity of the acoustic output device 800. In some embodiments, the first speaker 810, the second speaker 820, and the third speaker 830 may be speakers that close the front cavity or the rear cavity and only derive sound from the unclosed cavity. In some embodiments, the acoustic output device 800 may include a speaker.

[0086] In some embodiments, a test microphone may be used to measure the output of the acoustic output device. In some embodiments, a test microphone may be provided at a far-field position in a specific direction of the acoustic output device and a corresponding far-field position in the opposite direction, respectively, to measure the sound pressure levels at the two far-field positions, and obtain the sound pressure level difference at the two corresponding far-field positions. By comparing the absolute value of the sound pressure level difference with the preset sound pressure level threshold, it can be determined whether the acoustic output device has directivity in the specific direction and the opposite direction.

[0087] Fig.14 Schematic diagram of acoustic transmission of an acoustic output device provided with a second speaker according to some embodiments of this specification. Fig.14 In some embodiments, one of the test microphones may be set at a far-field position in a specific direction of the acoustic output device. In some embodiments, the far-field position of the acoustic output device may refer to a position at a distance from the acoustic output device greater than a preset distance threshold, such as a position greater than 25 cm. In some embodiments, when the frequency range is 1 kHz-4 kHz, the far-field position of the acoustic output device may refer to a position at a distance from the acoustic output device greater than 5.5 cm. In some embodiments, the test microphone may be set at a position 30 cm away from the acoustic output device in a specific direction. The specific direction is the direction in which the front cavity sound outlet hole (e.g., the first hole) of the acoustic output device points to the rear cavity sound outlet hole (e.g., the second hole) and its vicinity. In some embodiments, the front cavity of the acoustic output device may refer to the first front cavity of the first speaker, and the rear cavity of the acoustic output device may refer to the first rear cavity of the first speaker and the equivalent cavity or the same cavity of the output cavity of the second speaker. When the acoustic output device is in a wearing state, the specific direction may also be the direction in which the acoustic output device is away from the user's ear. In some embodiments, in order to achieve directivity, the absolute value of the difference between the sound pressure levels measured by the test microphones at the corresponding two far-field positions in a specific direction and the opposite direction of the acoustic output device is not less than a preset sound pressure level threshold. The sound pressure measured by the test microphone at the far-field position in the specific direction may be small, for example, close to zero.

[0088] In some embodiments, the sound pressure received by the test microphone includes two groups of sound waves, one of which is the sound wave radiated by the hole portion acoustically coupled with the front cavity (e.g., the first sound wave), whose transfer function is z(1); the other is the sound wave radiated by the hole portion acoustically coupled with the rear cavity (e.g., the second sound wave and the third sound wave), whose transfer function is z(2). In order to make the far-field radiation of the acoustic output device directional, it is necessary to make the two groups of sound waves received by the test microphone cancel each other out, that is, the sound pressure amplitudes of the two groups of sound waves at the position of the test microphone are equal and the phases are opposite, and the received signal p of the test microphone is equal to the sound pressure amplitudes of the two groups of sound waves at the position of the test microphone. mic for:

[0089] p mic =p(1)*z(1)+[p(2)+p(3)]*z(2)=0 (1)

[0090] Where p(1) is the dual sound source (i.e. the first loudspeaker, such as Fig.14 SPK1 in the front cavity radiates the sound pressure, p(2) is the double sound source (i.e. the first loudspeaker, such as Fig.14 The sound pressure radiated by SPK1 in the back cavity, p(3) is the sound pressure of a single sound source (i.e., the second loudspeaker, such as Fig.14 The sound pressure radiated by SPK2 in the back cavity.

[0091] In some embodiments, when measuring p(1), p(2), and p(3), it is necessary to avoid mutual interference. Therefore, when measuring p(1), the first speaker can be operated and the second speaker can be turned off. At the same time, cotton, rubber, etc. can be used to temporarily block the hole portion (e.g., the second hole portion) connected to the back cavity, and the measurement is performed by another test microphone set in or near (e.g., within a distance interval of 2mm-3mm) the hole portion (e.g., the first hole portion) connected to the front cavity. When measuring p(2), the first speaker can be operated and the second speaker can be turned off. At the same time, cotton, rubber, etc. can be used to temporarily block the hole portion (e.g., the first hole portion) connected to the front cavity, and the measurement is performed by another test microphone set in or near the hole portion (e.g., the second hole portion) connected to the back cavity of the first speaker. When measuring p(3), the second speaker can be operated and the first speaker can be turned off. The measurement is performed by another test microphone set in or near the hole portion (e.g., the second hole portion or the third hole portion described later, etc.) connected to the back cavity of the second speaker.

[0092] In some embodiments, a baffle with a larger size (for example, a diameter of 1m) can also be set around the acoustic output device. The baffle is set around the acoustic output device, and the baffle is tightly connected to the acoustic output device. The sound outlet hole of the front cavity (that is, the hole connected to the front cavity) and the sound outlet hole of the rear cavity (that is, the hole connected to the rear cavity) are respectively located on both sides of the baffle. By setting the baffle, the mutual interference between the first sound wave emitted by the sound outlet hole of the front cavity and the second sound wave and the third sound wave emitted by the sound outlet hole of the rear cavity is greatly weakened or even isolated, thereby improving the test accuracy of p(1), p(2) and p(3). In some embodiments, when a baffle is set, the first speaker can be operated and the second speaker can be turned off. At the same time, a test microphone is set at the hole connected to the front cavity and the hole connected to the rear cavity, and p(1) and p(2) are measured at the same time.

[0093] According to the distribution rate of convolution, formula (1) can be expressed as:

[0094] p mic=[p(1)*z(1)+p(2)*z(2)]+p(3)*z(2)=0 (2)

[0095] Where [p(1)*z(1)+p(2)*z(2)] represents the dual sound source (i.e., the first loudspeaker, such as Fig.14 The sound pressure of the sound waves (e.g., the first sound wave and the second sound wave) radiated by the SPK1 in the figure at the test microphone, p(3)*z(2) represents the sound pressure of a single sound source (i.e., the second loudspeaker, such as Fig.14 Therefore, by adjusting the first electrical signal and the second electrical signal, the dual sound source (i.e., the first speaker) and the single sound source (i.e., the second speaker) can be excited respectively, and the sound pressure amplitude and phase of the sound waves radiated by the two sound sources reaching the test microphone can be recorded. By adjusting the amplitude and phase of the second electrical signal driving the single sound source (i.e., the second speaker, SPK2) and / or the amplitude and phase of the first electrical signal driving the dual sound sources (i.e., the first speaker, SPK1), the sound pressure amplitudes of the sound wave radiated by the single sound source (i.e., the second speaker) (i.e., the third sound wave) and the sound wave radiated by the dual sound sources (i.e., the first speaker) (i.e., the superimposed sound wave of the first sound wave and the second sound wave) at the test microphone are equal (i.e., the sound pressure level amplitudes are equal) and the phases are opposite, so that the sound pressure of the acoustic output device at the far-field position in a specific direction is zero, thereby making the sound pressure level of the acoustic output device at the far-field position in a specific direction zero, so that the absolute value of the sound pressure level difference of the acoustic output device at the far-field position in at least one pair of opposite directions is not less than the preset sound pressure level threshold, thereby achieving the directionality of the far-field radiation of the acoustic output device.

[0096] Fig.15 FIG. 1 is a schematic diagram of an exemplary flow chart of a method for adjusting a second electrical signal according to some embodiments of this specification. Fig.15 As shown, process 900 may include the following steps:

[0097] Step 910: Excite the dual sound sources separately and record the first sound pressure level amplitude and the first phase of the test microphone.

[0098] In some embodiments, the dual sound source may be a first speaker. The test microphone may be set at a far-field position in a specific direction of the acoustic output device. In some embodiments, the specific direction may refer to a direction from the sound outlet portion of the front cavity to the sound outlet portion of the rear cavity and a direction nearby within a specified direction range. At this time, the first sound pressure level amplitude and the first phase measured by the test microphone may be the first sound pressure level amplitude and the first phase after the first sound wave and the second sound wave generated by the first speaker are superimposed at the test microphone.

[0099] In some embodiments, the first speaker can be operated while the second speaker cannot be operated by providing the first electrical signal only to the first speaker and not providing the second electrical signal to the second speaker, thereby achieving separate excitation of dual sound sources.

[0100] Step 920: Excite the single sound source alone and record the second sound pressure level amplitude and the second phase of the test microphone.

[0101] In some embodiments, the single sound source may be a second speaker. The test microphone may be set at a far-field position in a specific direction of the acoustic output device, which is the same as the position of the test microphone in step 910. At this time, the sound pressure level amplitude and phase measured by the test microphone may be the second sound pressure level amplitude and second phase of the third sound wave generated by the second speaker at the test microphone.

[0102] In some embodiments, the second speaker can be operated while the first speaker cannot be operated by providing the second electrical signal only to the second speaker and not providing the first electrical signal to the first speaker, thereby achieving independent excitation of a single sound source.

[0103] Step 930: Calculate the sound pressure amplitude difference and phase difference between the single sound source and the dual sound sources.

[0104] The second sound pressure level amplitude of the single sound source measured by the test microphone is compared with the first sound pressure level amplitude of the dual sound sources to obtain the difference in sound pressure level amplitude between the two. The second phase of the single sound source measured by the test microphone is compared with the first phase of the dual sound sources to obtain the phase difference between the two.

[0105] Step 940: Adjust the second electrical signal so that the sound pressure level amplitude of the sound wave radiated by the single sound source at the test microphone is the same as that of the dual sound sources, and the phase is opposite to that of the dual sound sources.

[0106] According to the sound pressure amplitude difference and phase difference between the single sound source and the dual sound source obtained in step 930, the second electrical signal driving the single sound source is adjusted so that the sound pressure level amplitude of the sound wave radiated by the single sound source at the test microphone is the same as that of the dual sound source, and the phase is opposite to that of the dual sound source, so that the third sound wave radiated by the single sound source can be superimposed and canceled with the first sound wave and the second sound wave radiated by the dual sound source at the position of the test microphone, so that the far-field radiation of the acoustic output device is directional (for example, cardioid directivity), thereby reducing the far-field sound leakage of the acoustic output device.

[0107] In some embodiments, the sound pressure amplitude difference and phase difference between the single sound source and the dual sound source are obtained according to step 930, and the first electrical signal driving the dual sound source can also be adjusted so that the sound pressure level amplitudes of the sound waves radiated by the single sound source and the dual sound source at the test microphone are the same and the phases are opposite, thereby making the far-field radiation of the acoustic output device directional (for example, cardioid directivity) and reducing the far-field sound leakage of the acoustic output device.

[0108] Fig.16 1 is a schematic diagram of frequency response curves when a single sound source and a dual sound source are excited separately according to some embodiments of this specification. As an example only, a single sound source (i.e., the second speaker) and a dual sound source (i.e., the first speaker) share the back cavity of the acoustic output device (e.g., Figure 5A The structure shown in FIG. 1 is a structure in which the volume of the rear cavity of the acoustic output device is equal to the volume of the front cavity. In this case, the hole portion connected to the front cavity is the first hole portion, and the hole portion connected to the rear cavity is the second hole portion (for example, Figure 5A The area of ​​the first hole portion is equal to that of the second hole portion. The amplitude of the second electrical signal that excites the single sound source and the first electrical signal that excites the dual sound sources are both 1V and 0° in phase. Fig.16 As shown, under the above conditions, the curve L 101 It represents the frequency response curve measured by the test microphone when the dual sound sources are excited separately. Curve L 102 It represents the frequency response curve measured by the test microphone when a single sound source is excited.

[0109] Under the above conditions, the sound pressure level amplitude difference and phase difference between the single sound source and the dual sound source at different frequencies at the test microphone position (i.e., the far field of the acoustic output device) can be measured by process 900. Fig.16 Middle curve L 101 With curve L 102 By comparing the sound pressure levels of the single sound source and the dual sound source at different frequencies at the test microphone position (i.e., the far field of the acoustic output device), the difference in sound pressure level can also be determined.

[0110] In some embodiments, by adjusting the amplitude and phase of the first electrical signal and the second electrical signal, the first electrical signal and the second electrical signal have a certain amplitude and / or phase difference within the target frequency range, so that the sound wave (third sound wave) generated by the single sound source (second speaker) and the sound wave (first sound wave, second sound wave) generated by the dual sound source (first speaker) are superimposed on each other, so that the far-field radiation of the acoustic output device is directional. In some embodiments, the target frequency range may include 100Hz-10kHz. In some embodiments, the acoustic output device composed of a single sound source and a dual sound source can achieve a wide band of 100Hz-10kHz leakage sound reduction. Among them, the target frequency range may include a first frequency range, and the first frequency range may include some mid-high frequency bands, for example, 800Hz-10000Hz. In the first frequency range, the acoustic output device can use the cardioid directivity principle to reduce leakage sound, that is, the far-field radiation of the acoustic output device is cardioid directivity. The target frequency range may include a second frequency range, and the second frequency range may include some mid-low frequency bands. In the second frequency range, for example, 100Hz-800Hz, the acoustic output device may use the dual sound source directivity principle to reduce sound leakage. For details, please refer to Figure 1 and its related description.

[0111] In some embodiments, the acoustic output device can have dual sound source directivity within the range of 100 Hz-800 Hz. That is, within the range of 100 Hz-800 Hz, the difference between the sound pressure level of the sound wave (e.g., the superimposed sound wave of the first sound wave and the second sound wave) output by the first speaker at the hole portion (e.g., the second hole portion) acoustically coupled to the first rear cavity and the sound pressure level of the third sound wave output by the second speaker at the hole portion (e.g., the third hole portion) coupled thereto is not less than 6 dB. In some embodiments, when the sound pressure radiated by a single sound source in the rear cavity is much smaller than the sound pressure radiated by dual sound sources in the rear cavity, that is, when p(3)<<p(2), the sound pressure level radiated by a single sound source is extremely small compared to the sound pressure level radiated by dual sound sources, and the acoustic output device can achieve dual sound source directivity. For example, when p(2) / p(3)≥2, it can be considered that p(3)<<p(2). At this time, the difference in sound pressure levels radiated by the dual sound sources and the single sound source in the rear cavity is greater than or equal to 6dB, that is, the difference between the sound pressure level corresponding to p(2) and the sound pressure level corresponding to p(3) is greater than or equal to 6dB, and the acoustic output device can achieve dual sound source directivity.

[0112] In summary, in the frequency band of 100Hz-800Hz, when the same electrical signal is provided to the single sound source and the dual sound source (that is, the amplitude and phase of the first electrical signal and the second electrical signal are the same), since the front cavity of the single sound source (the second speaker) is closed, only the rear cavity is connected to the outside air, and the air cannot flow freely, it is difficult for the single sound source to output low-frequency sound waves at the hole portion acoustically coupled with the rear cavity. Therefore, in this frequency band, the difference between the sound pressure level of the sound wave output by the dual sound source (the first speaker) at the hole portion acoustically coupled with the rear cavity and the sound pressure level of the sound wave output by the single sound source (the second speaker) at the hole portion acoustically coupled with the rear cavity can be greater than or equal to 6dB. At this time, the acoustic output device can have better dual sound source directivity, thereby realizing a mid- and low-frequency leakage reduction design. In some embodiments, in order to achieve that the difference between the sound pressure level of the sound wave output by the dual sound source (first speaker) at the hole portion acoustically coupled with the rear cavity and the sound pressure level of the sound wave output by the single sound source (second speaker) at the hole portion acoustically coupled with the rear cavity in the range of 100Hz-800Hz can be greater than or equal to 6dB, a method of reducing the amplitude of the second electrical signal driving the single sound source (second speaker) in the range of 100Hz-800Hz can also be adopted. For example, in the range of 100Hz-800Hz, the amplitude of the second electrical signal can be 0, that is, the second electrical signal is not provided to the single sound source in the range of 100Hz-800Hz. In some embodiments, in the wearing state, the hole portion of the first front cavity acoustically coupled of the first speaker is arranged close to the user's ear, and the hole portion of the first rear cavity acoustically coupled is arranged away from the user's ear, and the direction from the hole portion of the first rear cavity acoustically coupled to the hole portion of the first front cavity acoustically coupled points to the user's ear, that is, the dual sound source directivity formed in the low-frequency range can point to the user's ear.

[0113] In some embodiments, within the frequency range of 1kHz-10kHz, in order to make the first sound wave, the second sound wave, and the third sound wave superimposed on each other at the far-field position in a specific direction of the acoustic output device, so that the sound pressure level at the far-field position is zero, so that the absolute value of the sound pressure level difference of the acoustic output device at at least one pair of far-field positions in opposite directions is not less than a preset sound pressure level threshold, so that the far-field radiation of the acoustic output device is directional, the amplitude and phase of the first electrical signal and the second electrical signal can be adjusted. In some embodiments, please refer to Fig.16 , since the resonance peak E of the dual sound source is close to the resonance peak D of the single sound source, the dual sound source and the single sound source have a first resonance frequency (i.e., the frequency corresponding to the resonance peak D). The back cavity shared by the single sound source and the dual sound source has a second resonance frequency (i.e., the frequency corresponding to the resonance peak F). Fig.16 It can be seen that the frequency response curves of the single sound source and the dual sound source have a flat area between the first resonant frequency and the second resonant frequency. In some embodiments, the frequency band between the first resonant frequency and the second resonant frequency may include a range of 1kHz-4kHz. In some embodiments, the first resonant frequency may be located near 1kHz, and the second resonant frequency may be located near 4kHz, so that the frequency response curves of the single sound source and the dual sound source may have a wider flat area, thereby improving the acoustic output performance of the acoustic output device. In some embodiments, by adjusting the second electrical signal and / or the first electrical signal, the far-field radiation of the acoustic output device may have a cardioid directivity between the first resonant frequency and the second resonant frequency (for example, 1kHz-4kHz). In some embodiments, in a frequency band greater than the second resonant frequency (for example, 4kHz-10kHz), by adjusting the second electrical signal and / or the first electrical signal, the far-field radiation of the acoustic output device may also have a cardioid directivity. In some embodiments, in the wearing state, the hole portion of the first front cavity acoustically coupled of the first speaker is arranged close to the user's ear, the hole portion of the first rear cavity acoustically coupled and the hole portion of the second speaker outputting the third sound wave are arranged away from the user's ear, the hole portion of the first rear cavity acoustically coupled and the hole portion of the second speaker outputting the third sound wave have an equivalent hole portion, and the direction from the equivalent hole portion to the hole portion of the first front cavity acoustically coupled points to the user's ear, that is, the directivity formed in the mid- and high-frequency range can point to the user's ear.

[0114] In some embodiments, between the first resonant frequency and the second resonant frequency, the phase difference between the second electrical signal and the first electrical signal is not less than 150°. In some embodiments, within the range of 1kHz-4kHz, the phase difference between the second electrical signal and the first electrical signal is not less than 150°. In some embodiments, at a frequency of 1kHz, the phase difference between the second electrical signal and the first electrical signal is not less than 200°; at a frequency of 4kHz, the phase difference between the second electrical signal and the first electrical signal is not less than 150°. Exemplarily, for Fig.16 In the case shown, when the amplitude of the first electric signal remains unchanged at 1V (i.e., 1000mV) and the phase remains unchanged at 0°, in order to make the sound pressure level at the far-field position in a specific direction of the acoustic output device zero, so that the absolute value of the sound pressure level difference at the far-field position of the acoustic output device in at least one pair of opposite directions is not less than the preset sound pressure level threshold, the second electric signal can be modulated. Within the range of 1kHz-4kHz, the phase and amplitude of the modulated second electric signal at each frequency point are as follows: at 1kHz, the amplitude of the second electric signal is 27.5mV and the phase is 250°; at 1.5kHz, the amplitude of the second electric signal is 344.3mV and the phase is 225°; at 2kHz, the amplitude of the second electric signal is 472mV and the phase is 229°; at 3kHz, the amplitude of the second electric signal is 738.7mV and the phase is 202°; at 4kHz, the amplitude of the second electric signal is 708.76mV and the phase is 179°. It should be noted that, in some embodiments, the sound pressure at the far-field position in a specific direction of the acoustic output device may be small but not zero. Therefore, the amplitude and phase of the corresponding second electrical signal may have a deviation of 10%. Exemplarily, at 1kHz, the amplitude of the second electrical signal may be 27.5*(1±0.1)mV, and the phase may be 250*(1±0.1)°, that is, the amplitude of the second electrical signal may be 24.75mV-30.25mV, and the phase may be 225°-247.5°.

[0115] Depend on Fig.16It can be seen that the single sound source (the second speaker) has a first resonant frequency, that is, the frequency corresponding to the resonance peak D. When passing through the first resonant frequency, the phase of the sound wave radiated by the single sound source will be reversed. Correspondingly, the resonance peak E of the dual sound source near the first resonant frequency is caused by the diaphragm of the single sound source that is not working when the dual sound source is working as a passive diaphragm. Therefore, at the resonant frequency of the resonance peak E, the sound wave radiated by the dual sound source does not reverse. Therefore, before and after the first resonant frequency, in order to ensure that the sound wave radiated by the single sound source and the sound wave radiated by the dual sound source maintain opposite phases in the far field, it is necessary to compensate the phase of the sound wave radiated by the single sound source. In some embodiments, at the two frequency points before and after the first resonant frequency, the phase difference of the second electrical signal is not less than 100°. Among them, the phase of the second electrical signal at the frequency point before the first resonant frequency is the phase before compensation; the phase of the second electrical signal at the frequency point after the first resonant frequency is the phase after compensation. In some embodiments, at the two frequency points before and after the first resonant frequency, the phase difference of the second electrical signal can be 100°-240°. In some embodiments, at two frequency points before and after the first resonant frequency, the phase difference of the second electrical signal may be 120°-220°. In some embodiments, at two frequency points before and after the first resonant frequency, the phase difference of the second electrical signal may be 140°-180°. In some embodiments, at two frequency points before and after the first resonant frequency, the phase difference of the second electrical signal may be 150°-160°.

[0116] It should be noted that if the phase of the sound waves radiated by only one of the dual sound sources and the single sound source changes by 180° near a certain resonant frequency, in order to avoid the far-field sound waves from no longer canceling each other due to this change, the electrical signal of one of the dual sound sources or the single sound source needs to be changed before and after the resonant frequency (for example, reversed by 180° or close to 180°). However, since the phase difference between the first electrical signal and the second electrical signal at each frequency point may be different, after compensating the phase of one of the electrical signals on this basis, the final phase difference between the two may not be strictly 180°, but close to 180° or approximately 180°.

[0117] In some embodiments, in actual products, the specifications of the speakers of the acoustic output device may be different, the sizes of the front and rear cavities may be different, the area and depth of the corresponding sound outlet portions may be different, and the structural shapes of the front and rear cavities may be different, resulting in the position of the resonance peak (e.g., the resonance peak D and resonance peak F of a single sound source, the resonance peak G of a dual sound source, etc.) may shift. Therefore, at two frequency points in different frequency ranges before and after the resonance peak, the value range of the phase difference of the second electrical signal may be different.

[0118] In some embodiments, at two frequency points of 100 Hz before and after the first resonant frequency, the phase difference of the second electrical signal may be 100°-240°. In some embodiments, since the size of a single sound source may be different, at two frequency points of 500 Hz before and after the first resonant frequency, the phase difference of the second electrical signal may be 120°-220°. In some embodiments, since the structure of a single sound source may be different, at two frequency points of 1000 Hz before and after the first resonant frequency, the phase difference of the second electrical signal may be 140°-180°.

[0119] In some embodiments, Fig.16 It can be seen that the first resonant frequency (the frequency corresponding to the resonance peak D) is between 800 Hz and 1.2 kHz, and is located near 1 kHz. In some embodiments, at 800 Hz and 1.2 kHz, the phase difference of the second electrical signal is in the range of 100°-220°, for example, 130°-180°. In some embodiments, since the size of a single sound source may be different, at 900 kHz and 1.1 kHz, the phase difference of the second electrical signal may be in the range of 120°-150°, for example, 130°-150°. In some embodiments, since the size of a single sound source may be different, at 950 Hz and 1 kHz, the phase difference of the second electrical signal may be in the range of 140°-170°, for example, 145°-155°.

[0120] Depend on Fig.16 It can be seen that in some embodiments, the back cavity shared by the single sound source and the dual sound source has a second resonant frequency (i.e., the frequency corresponding to the resonance peak F). Before and after the second resonant frequency, the phases of the sound waves radiated by the single sound source and the sound waves radiated by the dual sound sources are not all reversed by 180°. Observation of the vibration mode reveals that the two change from moving toward each other to relative motion. Therefore, before and after the second resonant frequency, it is still necessary to compensate for the phase of the sound waves radiated by the single sound source or one of the dual sound sources. In some embodiments, in the frequency band between the two frequency points before and after the second resonant frequency, the phase difference of the second electrical signal is not less than 100°. In some embodiments, at the two frequency points before and after the second resonant frequency, the phase difference of the second electrical signal may be 100°-260°. In some embodiments, at the two frequency points before and after the second resonant frequency, the phase difference of the second electrical signal may be 120°-170°. In some embodiments, at the two frequency points before and after the second resonant frequency, the phase difference of the second electrical signal may be 140°-160°.

[0121] In some embodiments, at two frequency points of 100 Hz before and after the second resonant frequency, the phase difference of the second electrical signal may be 100°-260°. In some embodiments, since the size of the rear cavity may be different, at two frequency points of 300 Hz before and after the second resonant frequency, the phase difference of the second electrical signal may be 130°-180°. In some embodiments, since the area of ​​the sound outlet portion of the rear cavity may be different, at two frequency points of 500 Hz before and after the second resonant frequency, the phase difference of the second electrical signal may be 160°-170°. In some embodiments, since the depth of the sound outlet portion of the rear cavity may be different, at two frequency points of 700 Hz before and after the second resonant frequency, the phase difference of the second electrical signal may be 140°-180°. In some embodiments, since the structure of the rear cavity may be different, resulting in different volumes, at two frequency points of 700 Hz before and after the second resonant frequency, the phase difference of the second electrical signal may be 170°-240°.

[0122] In some embodiments, Fig.16 It can be seen that the second resonant frequency (the frequency corresponding to the resonance peak F) is between 3kHz and 5kHz, and is located near 4kHz. In some embodiments, at 3kHz and 5kHz, the phase difference of the second electrical signal can be in the range of 100°-240°, for example, 138°-160°. In some embodiments, since the volume of the back cavity may be different, at 3.1kHz and 4.8kHz, the phase difference of the second electrical signal can be in the range of 120°-140°, for example, 130°-140°. In some embodiments, since the area of ​​the sound outlet portion of the back cavity may be different, at 3.5kHz and 4.5kHz, the phase difference of the second electrical signal can be in the range of 160°-170°, for example, 162°-168°. In some embodiments, since the depth of the sound outlet portion of the back cavity may be different, at 3.8kHz and 4.2kHz, the phase difference of the second electrical signal can be in the range of 155°-180°, for example, 160°-170°.

[0123] Depend on Fig.16It can be seen that in some embodiments, the front cavity of the dual sound source (the first speaker) has a third resonant frequency (i.e., the frequency corresponding to the resonance peak G). When passing through the third resonant frequency, the phase of the sound wave radiated by the dual sound source will be reversed. Correspondingly, when a single sound source is excited alone, the resonance peak of the single sound source near the third resonant frequency (not shown in the figure) is generated by the diaphragm of the non-working dual sound source as a passive diaphragm, but the phase of the sound wave radiated by the single sound source near the third resonant frequency does not reverse. Therefore, in order to ensure that the sound waves radiated by the single sound source and the sound waves radiated by the dual sound sources maintain opposite phases in the far field, it is necessary to compensate for the phase of the sound wave radiated by the single sound source. In the frequency band between the two frequency points before and after the third resonant frequency, the second electrical signal needs to be compensated. In some embodiments, at the two frequency points before and after the third resonant frequency, the phase difference of the second electrical signal is not greater than 100°. In some embodiments, at the two frequency points before and after the third resonant frequency, the phase difference of the second electrical signal can be 100°-240°. In some embodiments, at two frequency points before and after the third resonant frequency, the phase difference of the second electrical signal may be 170°-200°.

[0124] In some embodiments, at two frequency points of 100 Hz before and after the third resonant frequency, the phase difference of the second electrical signal may be 175°-185°. In some embodiments, since the size of the front cavity may be different, at two frequency points of 200 Hz before and after the third resonant frequency, the phase difference of the second electrical signal may be 170°-200°. In some embodiments, since the volume of the front cavity may be different, at two frequency points of 600 Hz before and after the third resonant frequency, the phase difference of the second electrical signal may be 150°-180°. In some embodiments, since the area and / or depth of the sound outlet portion of the front cavity may be different, at two frequency points of 1000 Hz before and after the third resonant frequency, the phase difference of the second electrical signal may be 120°-200°.

[0125] In some embodiments, Fig.16It can be seen that the third resonant frequency (the frequency corresponding to the resonance peak G) is between 5kHz and 8kHz. In some embodiments, at 5kHz and 8kHz, the phase difference of the second electrical signal may be in the range of 100°-200°, for example, 115°-160°. In some embodiments, since the volume of the front cavity may be different, at 5.1kHz and 7.5kHz, the phase difference of the second electrical signal may be in the range of 110°-150°, for example, 130°-140°. In some embodiments, since the area of ​​the sound outlet portion of the front cavity may be different, at 5.4kHz and 7kHz, the phase difference of the second electrical signal may be in the range of 140°-170°, for example, 150°-159°. In some embodiments, since the depth of the sound outlet portion of the front cavity may be different, at 5.8kHz and 6kHz, the phase difference of the second electrical signal may be in the range of 170°-180°, for example, 170°-176°.

[0126] By adjusting the amplitude and phase of the second electrical signal driving the single sound source and / or the first electrical signal driving the dual sound sources at multiple frequency points through the single sound source and dual sound sources, the second electrical signal and the first electrical signal have corresponding amplitude difference and phase difference, so that the sound pressure of the sound waves radiated by the single sound source and the dual sound source at the test microphone is small, for example, close to zero, so that formula (1) holds true.

[0127] Fig.17 FIG. 1 is a schematic diagram of the directivity of the far-field radiation of the acoustic output device after adjusting the second electrical signal according to some embodiments of this specification. Fig.17 As shown, at the frequency points of 1kHz, 2kHz, 3kHz, 5kHz, 8kHz, and 10kHz, by setting the second electrical signal, the output (e.g., the phase and / or amplitude of the output) of the single sound source (the second speaker) can be adjusted so that there is almost no output at the far-field position in a specific direction of the acoustic output device. At this time, the far-field radiation of the acoustic output device presents directivity. The 0° direction indicates the direction in which the acoustic output device points to the ear canal opening of the user's ear, for example, the sound outlet AS of the rear cavity of the acoustic output device 2 (e.g., the second hole portion) points to the sound outlet portion AS of the front cavity 1 (e.g. the direction of the first hole portion) Figure 4 Direction X 1 ); 180° direction indicates the direction in which the acoustic output device is away from the ear canal opening of the user's ear, for example, the sound outlet portion AS of the front cavity of the acoustic output device 1 (For example, the first hole portion) points to the sound outlet portion AS of the rear cavity 2 (e.g. the direction of the second hole portion) Figure 4 Direction X 1'). At the frequency point of 1kHz, the far-field radiation of the acoustic output device presents a cardioid directivity, the maximum point of the sound field is near 15°, the minimum point is near 180°, and the absolute value of the sound pressure level difference in the two directions is about 22.5dB. At the frequency point of 2kHz, the far-field radiation of the acoustic output device presents a cardioid directivity, the maximum point of the sound field is near 15°, the minimum point is near 200°, and the absolute value of the sound pressure level difference in the two directions is about 20.8dB. At the frequency point of 3kHz, the far-field radiation of the acoustic output device presents a cardioid directivity, the maximum point of the sound field is near 15°, the minimum point is near 190°, and the absolute value of the sound pressure level difference in the two directions is about 19.9dB. At a frequency of 5kHz, the far-field radiation of the acoustic output device is cardioid, with the maximum point of the sound field near 30°, the minimum point near 200°, and the absolute value of the sound pressure level difference in the two directions is about 19.6dB. At a frequency of 8kHz, the far-field radiation of the acoustic output device is cardioid and includes a main lobe and a side lobe. The direction of the main lobe (i.e., the maximum direction of the sound field) is near 40°, and the direction of the side lobe is near 200°. There is a minimum between the side lobe and the main lobe, and the minimum directions are near 150° and 250°, respectively. The absolute values ​​of the sound pressure level difference between the two minimum and maximum values ​​are approximately 16.6dB and 12.9dB, respectively. At the frequency point of 10kHz, the far-field radiation of the acoustic output device has a cardioid directivity and includes a main lobe and a side lobe. The direction of the main lobe (i.e., the direction of the maximum value of the sound field) is near 10°, and the direction of the side lobe is near 200°. There are minimum values ​​between the side lobe and the main lobe. The minimum values ​​are near 160° and 240° respectively. The absolute values ​​of the sound pressure level difference between the two minimum values ​​and the maximum value are approximately 32.4dB and 19.93dB respectively. Therefore, at the frequency points of 1kHz, 2kHz, 3kHz, 5kHz, 8kHz, and 10kHz, the directivity direction of the far-field radiation of the acoustic output device is from 180° and its vicinity to the direction of 0° and its vicinity, that is, the sound outlet AS of the rear cavity of the acoustic output device. 2 (e.g., the second hole portion) points to the sound outlet portion AS of the front cavity 1 (e.g. the direction of the first hole portion) Figure 4 Direction X 1 ) and its vicinity.

[0128] Fig.18A and Fig.18B is a directivity test curve diagram of an acoustic output device according to some embodiments of this specification. Fig.18A The test signal used is a white noise signal. Fig.18BThe test signal used is a frequency sweep signal, and the frequency range of the white noise signal and the frequency sweep signal is 1kHz-4kHz, so as to test the directivity of the acoustic output device within the frequency range of 1kHz-4kHz. In some embodiments, the white noise signal may refer to a signal that includes all frequencies in the frequency range of 1kHz-4kHz at any time, and the white noise signal can simulate complex signal output; the frequency sweep signal may refer to a signal that gradually changes from 1kHz to 4kHz, and the frequency sweep signal only includes a single frequency signal at any time, and the frequency sweep signal can simulate simple signal input. Fig.18A and Fig.18B As shown, the dotted line represents the frequency response curve of the acoustic output device in the 0° direction, and the solid line represents the frequency response curve of the acoustic output device in the 180° direction. In some embodiments, the output sound pressure level of the acoustic output device in the 0° direction can be measured by a test microphone disposed near the sound outlet portion (e.g., the first hole portion) of the front cavity (e.g., 10 cm away from the sound outlet portion of the front cavity); the output sound pressure level of the acoustic output device in the 180° direction can be measured by a test microphone disposed near the sound outlet portion (e.g., the second hole portion and / or the third hole portion) of the rear cavity (e.g., 10 cm away from the sound outlet portion of the rear cavity). In some embodiments, the test microphone, the sound outlet portion of the front cavity, and the sound outlet portion of the rear cavity are on a straight line, and the straight line is a straight line where the 0° direction and the 180° direction are located. As shown in FIG. Fig.18A As shown in FIG. 1 , when the test signal is a white noise signal, the absolute value of the sound pressure level difference between the acoustic output device in the 0° direction and the 180° direction is 8dB-18dB, and the acoustic output device has a good cardioid directivity; Fig.18B As shown, when the test signal is a swept frequency signal, the absolute value of the sound pressure level difference between the acoustic output device in the 0° direction and the 180° direction is 15dB-25dB, and the acoustic output device has a better cardioid directivity.

[0129] It should be noted that the above content is only for the adjustment of the second electrical signal. In some embodiments, corresponding adjustments can also be made only for the first electrical signal. In some embodiments, corresponding adjustments can also be made for both the first electrical signal and the second electrical signal. The specific adjustment method of the electrical signal is described below by taking the adjustment of the second electrical signal as an example.

[0130] Fig.19 Schematic diagram of an equivalent model of an acoustic output device adjusted according to a preset algorithm according to some embodiments of this specification. Fig.19As shown, in some embodiments, the acoustic output device may further include a modulator, which may modulate the second electrical signal driving the second speaker according to a preset algorithm, so that within the target frequency range, the third sound wave output by the second speaker and the first sound wave and the second sound wave output by the first speaker are superimposed and canceled at a remote position in a specific direction of the acoustic output device, so that the absolute value of the sound pressure level difference of the acoustic output device at at least one pair of far-field positions in opposite directions is not less than a preset sound pressure level threshold (for example, the sound pressure of the acoustic output device at the far-field position in a specific direction is small, for example, close to zero). In some embodiments, the preset algorithm may include a preset amplitude-frequency adjustment method, such as a preset amplitude modulation scheme, a preset frequency (phase) modulation scheme, etc. For more information about amplitude modulation and phase modulation, please refer to Fig.21 The relevant description will not be repeated here.

[0131] In some embodiments, Fig.19 The principle and Fig.14 The principle is similar to that shown in FIG. 1 , and a preset algorithm (such as a modulation function H of a modulator) for modulating the second electrical signal is determined by measuring the sound pressure of a test microphone arranged at a far-field position of the acoustic output device in a specific direction. 0 ). When the acoustic output device is working, the modulator can modulate the second electrical signal according to a preset algorithm.

[0132] In some embodiments, the signal Music may include a first electrical signal to drive the first speaker and a second electrical signal to drive the second speaker. The first speaker and the second speaker may respectively receive the first electrical signal and the second electrical signal in the signal Music and output sound to the space. The test microphone is set at the far-field position of the acoustic output device in a specific direction and measures the sound pressure of the sound at that position. When the sound pressure signal received by the test microphone is zero, it means that the sound pressure of the sound radiated by the first speaker and the second speaker to the target position (that is, the far-field position of the above-mentioned acoustic output device in a specific direction) (that is, the sound after the superposition of the first sound wave, the second sound wave and the third sound wave) is zero, that is:

[0133] Music·H 1 +Music·H 0 ·H 2 =0 (3)

[0134] Among them, H 1 With H 2 H represent the transfer functions of the sound waves (first sound wave, second sound wave) generated by the first loudspeaker transmitted to the test microphone and the third sound wave generated by the second loudspeaker transmitted to the test microphone respectively; 0 Represents a transfer function of a modulator for modulating a second electrical signal driving a second speaker.

[0135] Turning off the second speaker can test the transfer function H of the first speaker. 1 (First transfer function):

[0136] H 1 =Mic′ / Music′ (4)

[0137] Here, Music′ represents the signal (first electrical signal) input when the second speaker is turned off, and Mic′ represents the sound pressure signal received at the test microphone when the second speaker is turned off.

[0138] Similarly, turning off the first speaker can test the transfer function H of the second speaker. 2 (Second transfer function):

[0139] H 2 =Mic" / Music" (5)

[0140] Wherein, "Music" represents the signal (second electrical signal) input when the first speaker is turned off, and "Mic" represents the sound pressure signal received at the test microphone when the first speaker is turned off.

[0141] According to formulas (3)-(5), the modulator transfer function H can be obtained 0 :

[0142]

[0143] Therefore, for different frequencies, the modulator transfer function H can be determined according to the above formula (6): 0 , and the set modulator is applied to the acoustic output device, so that the acoustic output device can achieve leakage reduction effects at different frequencies. In some alternative embodiments, when there are multiple test microphones, the sound output by the first speaker and the second speaker at any position in the space can be measured or simulated. Therefore, by setting up at least one pair of test microphones in opposite directions, the sound pressure level difference of the far-field radiated sound of the acoustic output device in at least one pair of opposite directions can be measured. Corresponding to different frequencies, the transfer function of the modulator can be adjusted by formulas (3)-(6) so that the sound pressure level difference of the far-field radiated sound of the acoustic output device in at least one pair of opposite directions is not less than the preset sound pressure level threshold.

[0144] In some embodiments, the test microphone may include a microphone array. By measuring the sound at a far-field position in a specific direction of the acoustic output device through the microphone array, the accuracy of the measurement data may be improved.

[0145] Fig. 20 is a schematic diagram of an equivalent model of an acoustic output device adjusted according to an active algorithm according to some embodiments of this specification. Fig. 20 As shown, in some embodiments, the acoustic output device may further include a controller, a modulator, and a microphone array. The microphone array may be arranged on the housing of the acoustic output device. The microphone array may be used to estimate the sound signal at a preset position. The preset position may include a far-field position of a specific direction of the acoustic output device. In some embodiments, the preset position may also include at least one pair of far-field positions of the acoustic output device in opposite directions. In some embodiments, the controller may determine an active algorithm (e.g., an active amplitude-frequency adjustment method) based on the sound signal collected by the microphone array, and the modulator may dynamically modulate the second electrical signal driving the second speaker according to the active algorithm (e.g., an active amplitude-frequency adjustment method) determined by the controller, so that within the target frequency range, the third sound wave output by the second speaker and the first sound wave and the second sound wave output by the first speaker are superimposed and cancelled at the far-field position of the specific direction of the acoustic output device, so that the absolute value of the sound pressure level difference of the acoustic output device at at least one pair of far-field positions in opposite directions is not less than the preset sound pressure level threshold, so as to achieve the directivity of the far-field radiation of the acoustic output device.

[0146] In some embodiments, when the acoustic output device is worn by the user, the transfer function corresponding to the first speaker changes from the initial value H 1 Change to H′ 1 , the transfer function corresponding to the second speaker is changed from the initial value H 2 Change to H′ 2 , and different users correspond to H′ 1 and H′ 2 Can be different. Accordingly, the above formula (3) can be expressed as:

[0147] Music·H′ 1 +Music·H 0 ·H′ 2 =0 (7)

[0148] In some embodiments, for a variable H′ 1 and H′ 2 , the controller can adjust H according to the sound waves collected by the microphone array 0 , so that formula (7) holds true, thereby achieving the effect of reducing sound leakage in a specific direction. According to formula (6), the adjusted H 0 :

[0149]

[0150] according to Fig. 20 The method described can adjust H in real time based on the collected sound waves. 0, achieving the effect of real-time leakage sound reduction, so that the absolute value of the sound pressure level difference of the acoustic output device at at least one pair of far-field positions in opposite directions is not less than the preset sound pressure level threshold, so as to achieve the directionality of the far-field radiation of the acoustic output device.

[0151] In some embodiments, for acoustic output devices of different structures, the transfer function of the corresponding first speaker is represented by H 1 and the transfer function of the second speaker H 2 is also different, so the corresponding modulator transfer function H 0 The adjustment method may also be different. For example, the corresponding adjustment method may be different when the first speaker and the second speaker are arranged in the same cavity. For another example, the corresponding adjustment method may be different when there are different distances between the rear cavity sound outlet hole of the first speaker (for example, the second hole portion 912) and the second speaker sound outlet hole (for example, the third hole portion 913). For another example, the corresponding adjustment method may be different when the acoustic resistance at the sound outlet hole (for example, the first hole portion 911, the second hole portion 912, the third hole portion 913, etc.) is different.

[0152] Fig.21 is a schematic block diagram of an amplitude and phase adjustment algorithm according to some embodiments of this specification. Fig.21 Taking the adjustment of the second electrical signal driving the second speaker as an example, the input signal includes an initial first electrical signal and an initial second electrical signal, which are respectively input into the first speaker and the second speaker, and the first speaker and the second speaker vibrate respectively to generate sound waves which are superimposed on each other. Fig.19 and / or Fig. 20 The principle shown determines the modulator transfer function H 0 , through the transfer function H 0The amplitude adjustment value and the phase adjustment value for the initial second electrical signal can be determined. In some embodiments, the amplitude of the initial second electrical signal can be adjusted by a filter. In some embodiments, the filter can select an infinite impulse response (IIR) filter. The IIR filter has a small amount of calculation and good real-time performance. In some embodiments, the filter can also select a finite impulse response (FIR) filter. The FIR filter has good stability and controllable phase. While performing amplitude selection, the synchronous input signal can be output synchronously to avoid signal distortion. In some embodiments, the phase of the initial second electrical signal can be adjusted by a phase shifter. In some embodiments, the adjustment of the initial second electrical signal by the filter and the phase shifter can be performed synchronously; or one of them can be adjusted first and the other can be adjusted later. The adjusted second electrical signal is combined with the initial first electrical signal and output as an output signal. The sound waves generated by the second speaker driven by the adjusted second electrical signal can be superimposed and canceled with the sound waves generated by the first speaker driven by the initial first electrical signal at the target position (for example, the far-field position in a specific direction of the acoustic output device), so that the absolute value of the sound pressure level difference of the acoustic output device at at least one pair of far-field positions in opposite directions is not less than a preset sound pressure level threshold (for example, not less than 6 dB), thereby realizing the directionality of the acoustic output device.

[0153] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only for example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the present application.

[0154] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0155] Similarly, it should be noted that in order to simplify the description of the disclosure of this application and thus help understand one or more embodiments of the invention, in the above description of the embodiments of this application, multiple features are sometimes combined into one embodiment, figure or description thereof. However, this disclosure method does not mean that the features required by the object of this application are more than the features mentioned in the claims. In fact, the features of the embodiments are less than all the features of the single embodiment disclosed above.

[0156] In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may change according to the required features of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining digits. Although the numerical domains and parameters used to confirm the breadth of their range in some embodiments of the present application are approximate values, in specific embodiments, the setting of such numerical values ​​is as accurate as possible within the feasible range.

[0157] Each patent, patent application, patent application disclosure, and other materials, such as articles, books, instructions, publications, documents, etc., cited in this application are hereby incorporated by reference in their entirety. Except for application history documents that are inconsistent with or conflicting with the content of this application, documents that limit the broadest scope of the claims of this application (currently or later attached to this application) are also excluded. It should be noted that if the descriptions, definitions, and / or use of terms in the attached materials of this application are inconsistent or conflicting with the content described in this application, the descriptions, definitions, and / or use of terms in this application shall prevail.

[0158] Finally, it should be understood that the embodiments described in this application are only used to illustrate the principles of the embodiments of the present application. Other variations may also fall within the scope of the present application. Therefore, as an example and not a limitation, the alternative configurations of the embodiments of the present application may be considered to be consistent with the teachings of the present application. Accordingly, the embodiments of the present application are not limited to the embodiments explicitly introduced and described in the present application.

Claims

1. An acoustic output device, characterized in that: include: A housing, wherein the housing is provided with a first hole portion and a second hole portion; a first speaker, arranged in the housing, comprising a first diaphragm, a first front cavity and a first rear cavity being respectively arranged at the front and rear sides of the first diaphragm, the first front cavity and the first rear cavity being respectively acoustically coupled with the first hole portion and the second hole portion, and the first speaker being driven by a first electrical signal to output a first sound wave and a second sound wave having a phase difference through the first hole portion and the second hole portion; as well as A second speaker is disposed in the housing, and the second speaker outputs a third sound wave under the drive of a second electrical signal; Among them, within the first frequency range, the first sound wave, the second sound wave, and the third sound wave are superimposed on each other, so that the far-field radiation of the acoustic output device presents a cardioid directivity, and within the second frequency range, the sound pressure level of the third sound wave is much smaller than the sound pressure level of the second sound wave, so that the far-field radiation of the acoustic output device presents a dual sound source directivity.

2. The acoustic output device according to claim 1, characterized in that: The second speaker outputs the third sound wave through the second hole portion acoustically coupled with the first rear cavity, and the sound pressure level of the third sound wave is much smaller than the sound pressure level of the second sound wave, which means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole portion and the sound pressure level of the third sound wave output by the second speaker at the second hole portion is not less than 6dB, or the ratio of the sound pressure radiated by the first speaker in the first rear cavity to the sound pressure radiated by the second speaker in the first rear cavity is greater than or equal to 2.

3. The acoustic output device according to claim 1, characterized in that: The second speaker outputs the third sound wave through the third hole portion on the shell, the third hole portion and the second hole portion are different holes, and the sound pressure level of the third sound wave is much smaller than the sound pressure level of the second sound wave, which means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole portion and the sound pressure level of the third sound wave output by the second speaker at the third hole portion is not less than 6dB.

4. The acoustic output device according to claim 1, characterized in that: A lower frequency limit of the first frequency range is greater than an upper frequency limit of the second frequency range.

5. The acoustic output device according to claim 4, characterized in that: The first frequency range includes 1 kHz, 1.5 kHz or 4 kHz, and the second frequency range includes 100 Hz or 800 Hz.

6. The acoustic output device according to claim 5, characterized in that: The first frequency range includes a frequency band of 1 kHz-4 kHz, and the second frequency range includes a frequency band of 100 Hz-800 Hz.

7. The acoustic output device according to claim 1, characterized in that: When presenting the dual sound source directivity, the far-field radiation of the acoustic output device is arranged in an 8-shape; when presenting the cardioid directivity, the absolute value of the sound pressure level difference of the far-field radiation of the acoustic output device at two same far-field positions of the acoustic output device in at least one pair of opposite directions is not less than 6dB.

8. An acoustic output device, characterized in that: include: A housing, wherein the housing is provided with a first hole portion and a second hole portion; A first speaker is arranged in the housing, the first speaker comprises a first diaphragm, a first front cavity and a first rear cavity are respectively provided on the front and rear sides of the first diaphragm, the first front cavity and the first rear cavity are respectively acoustically coupled with the first hole portion and the second hole portion, and the first speaker is driven by a first electrical signal to output a first sound wave and a second sound wave with a phase difference through the first hole portion and the second hole portion, respectively, to form a dual sound source; as well as a second speaker, disposed in the housing, comprising a second diaphragm, wherein a second front cavity and a second rear cavity are respectively disposed on the front and rear sides of the second diaphragm, wherein only one of the second front cavity and the second rear cavity is acoustically coupled with the hole on the housing, and outputs a third sound wave to form a single sound source; Wherein, within the first frequency range, the single sound source and the dual sound sources work together and cooperate with each other, and within the second frequency range, the dual sound sources work approximately alone.

9. The acoustic output device according to claim 8, characterized in that: The second speaker outputs the third sound wave through the second hole portion acoustically coupled with the first rear cavity, and the dual sound sources approximately work alone means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole portion and the sound pressure level of the third sound wave output by the second speaker at the second hole portion is not less than 6 dB, or the ratio of the sound pressure radiated by the first speaker in the first rear cavity to the sound pressure radiated by the second speaker in the first rear cavity is greater than or equal to 2, or The second speaker outputs the third sound wave through the third hole on the shell, the third hole and the second hole are different holes, and the dual sound sources approximately work independently means that the difference between the sound pressure level of the second sound wave output by the first speaker at the second hole and the sound pressure level of the third sound wave output by the second speaker at the third hole is not less than 6dB.

10. The acoustic output device according to claim 8, characterized in that: A lower frequency limit of the first frequency range is greater than an upper frequency limit of the second frequency range.

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