Acoustic signal output device

Abstract

To provide an acoustic signal output device that does not seal an ear canal that can suppress sound leakage to the surroundings.SOLUTION: A frequency band of a reproduced acoustic signal is divided into a high frequency band and a low frequency band, and there is provided a first driver unit that emits an acoustic signal on the high frequency band side of the reproduced acoustic signal, an enclosure that accommodates the first driver unit inside, and the second driver unit that is larger in size than the first driver unit and emits the acoustic signal on the low frequency band side of the reproduced acoustic signal. First and third acoustic signals are emitted from one side of the first and second driver units, and second and fourth acoustic signals are emitted from the other side. A wall of the enclosure is provided with a first sound hole to conduct the first acoustic signal to the outside and a second sound hole to conduct the second acoustic signal to the outside. The emitted third and fourth acoustic signals cancel out the sound leakage components of the first and third acoustic signals.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an acoustic signal output device, and more particularly to an acoustic signal output device that does not seal the ear canal. [Background technology]

[0002] In recent years, the increased strain on the ears caused by wearing earphones and headphones has become a problem. Open-ear earphones and headphones, which do not block the ear canal, are known as devices that reduce strain on the ears. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] “WHAT ARE OPEN-EAR HEADPHONES?”, [online], Bose Corporation, [Retrieved September 13, 2021], Internet<https: / / www.bose.com / en_us / better_with_bose / open-ear-headphones.html> Summary of the Invention [Problem to be solved by the invention]

[0004] However, open-ear earphones and headphones have the problem of significant sound leakage into the surroundings. This problem is not limited to open-ear earphones and headphones, but is a common problem with any acoustic signal output device that does not seal the ear canal.

[0005] The present invention has been made in view of the above points, and has an object to provide an acoustic signal output device that does not seal the ear canal and is capable of suppressing sound leakage to the surroundings. [Means for solving the problem]

[0006] An acoustic signal output device is provided, in which the frequency band of a reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and which includes: a first driver unit that emits acoustic signals in the high-frequency band of the reproduced acoustic signals; a housing that houses the first driver unit; and a second driver unit that is larger in size than the first driver unit and emits acoustic signals in the low-frequency band of the reproduced acoustic signals. The acoustic signal emitted from the first driver unit to one side is referred to as the first acoustic signal, the acoustic signal emitted from the first driver unit to the other side is referred to as the second acoustic signal, the acoustic signal emitted from the second driver unit to one side is referred to as the third acoustic signal, and the acoustic signal emitted from the second driver unit to the other side is referred to as the fourth acoustic signal. The wall of the housing is provided with one or more first sound holes that guide the first acoustic signal to the outside, and one or more second sound holes that guide the second acoustic signal to the outside. Here, when a first acoustic signal is emitted from the first sound hole, a second acoustic signal is emitted from the second sound hole, and a third acoustic signal and a fourth acoustic signal are emitted from the second driver unit, the attenuation rates of the first acoustic signal and the third acoustic signal at a second point farther from the acoustic signal output device than a predetermined first point where the first acoustic signal and the third acoustic signal arrive are designed to be equal to or less than a predetermined value that is smaller than the attenuation rate of the acoustic signal due to propagation through the air at the second point relative to the first point, or the attenuation amounts of the first acoustic signal and the third acoustic signal at the second point relative to the first point are designed to be equal to or greater than a predetermined value that is greater than the attenuation amount of the acoustic signal due to propagation through the air at the second point relative to the first point. [Effects of the Invention]

[0007] This structure helps prevent sound from leaking into the surrounding area. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a see-through perspective view illustrating the configuration of an acoustic signal output device that serves as the basis for each embodiment. [Figure 2]Fig. 2A is a transparent plan view illustrating the configuration of an acoustic signal output device that serves as the base of each embodiment, Fig. 2B is a transparent front view illustrating the configuration of an acoustic signal output device that serves as the base of each embodiment, and Fig. 2C is a bottom view illustrating the configuration of an acoustic signal output device that serves as the base of each embodiment. [Figure 3] Figure 3A is an end view taken along line 2BA-2BA of Figure 2B, Figure 3B is an end view taken along line 2A-2A of Figure 2A, and Figure 3C is an end view taken along line 2BC-2BC of Figure 2B. [Figure 4] FIG. 4 is a conceptual diagram illustrating the arrangement of the sound holes. [Figure 5] Fig. 5A is a diagram illustrating a usage state of an acoustic signal output device that serves as the basis for each embodiment, and Fig. 5B is a diagram illustrating observation conditions for an acoustic signal emitted from the acoustic signal output device that serves as the basis for each embodiment. [Figure 6] FIG. 6 is a graph illustrating the frequency characteristics of the acoustic signal observed at position P1 in FIG. 5B. [Figure 7] FIG. 7 is a graph illustrating the frequency characteristics of the acoustic signal observed at position P2 in FIG. 5B. [Figure 8] FIG. 8 is a graph illustrating an example of the difference between the acoustic signal observed at position P1 and the acoustic signal observed at position P2. [Figure 9] 9A and 9B are graphs illustrating the relationship between the area ratio of the sound holes and sound leakage. [Figure 10] FIG. 10 is a see-through perspective view illustrating the configuration of the acoustic signal output device of the first embodiment. [Figure 11] FIG. 11 is a transparent plan view illustrating the configuration of the acoustic signal output device of the first embodiment. [Figure 12] FIG. 12 is a see-through front view illustrating the configuration of the acoustic signal output device of the first embodiment. [Figure 13] FIG. 13 is a conceptual diagram illustrating the arrangement of sound holes and driver units. [Figure 14]Fig. 14A is a diagram illustrating a usage state of the acoustic signal output device of the first embodiment, and Fig. 14B is a diagram illustrating a functional configuration of a signal separating device that separates an input signal into a high-frequency band signal and a low-frequency band signal. [Figure 15] FIG. 15 is a diagram illustrating observation conditions for the acoustic signal emitted from the acoustic signal output device of the first embodiment. [Figure 16] Fig. 16A illustrates the frequency characteristics of an acoustic signal observed at position P1 in Fig. 15, and Fig. 16B illustrates the frequency characteristics of an acoustic signal observed at position P2 in Fig. 15. "2way" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and the acoustic signal on the high-frequency band side is emitted from the small-sized driver unit, and the acoustic signal on the low-frequency band side is emitted from the large-sized driver unit. "WF Th." illustrates the frequency characteristics when the acoustic signal is emitted only from the large-sized driver unit, without dividing the frequency band. "TW Th." illustrates the frequency characteristics when the acoustic signal is emitted only from the small-sized driver unit, without dividing the frequency band. [Figure 17] FIG. 17A illustrates the frequency characteristics of an acoustic signal observed at position P1 in FIG. 15, and FIG. 17B illustrates the frequency characteristics of an acoustic signal observed at position P2 in FIG. 15. "2way" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and acoustic signals on the high-frequency band side are emitted from a small-sized driver unit, and acoustic signals on the low-frequency band side are emitted from a large-sized driver unit. "WF NW" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and acoustic signals on the low-frequency band side are emitted only from a large-sized driver unit. "TW NW" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and acoustic signals on the high-frequency band side are emitted only from a small-sized driver unit. [Figure 18]FIG. 18 is a transparent plan view illustrating the configuration of an acoustic signal output device having a shielding plate. [Figure 19] FIG. 19 is a transparent front view illustrating the configuration of an acoustic signal output device having a shielding plate. [Figure 20] FIG. 20 is a conceptual diagram illustrating a modified example of the arrangement of the sound holes and the driver unit. [Figure 21] FIG. 21 is a conceptual diagram illustrating a modified example of the arrangement of the sound holes and the driver unit. [Figure 22] FIG. 22 is a conceptual diagram illustrating a modified example of the arrangement of the sound holes and the driver unit. [Figure 23] FIG. 23 is a conceptual diagram illustrating a modified example of the arrangement of the sound holes and the driver unit. [Figure 24] FIG. 24 is a see-through perspective view illustrating the configuration of an acoustic signal output device according to the fourth embodiment. [Figure 25] FIG. 25 is a transparent plan view illustrating the configuration of an acoustic signal output device according to the fourth embodiment. [Figure 26] FIG. 26 is a see-through front view illustrating the configuration of an acoustic signal output device according to the fourth embodiment. [Figure 27] FIG. 27 is an end view taken along line 25-25 of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Base configuration] First, an acoustic signal output device that serves as the basis for each embodiment will be described. <Configuration> The acoustic signal output device 1 that forms the basis of each embodiment is a device for listening to sound that is worn without sealing the user's ear canal (for example, open-ear earphones, headphones, installed speakers, embedded speakers, etc.). As illustrated in Figures 1, 2A to 2C, and 3A to 3C, the acoustic signal output device 1 has a driver unit 11 that converts an output signal (an electrical signal representing an acoustic signal) output from a playback device into an acoustic signal and outputs it, and a housing 12 that houses the driver unit 11 inside.

[0010] <Driver unit 11> Driver unit (speaker driver unit, driver) 11 is a device (device with speaker functionality) that emits (sounds) an acoustic signal AC1 (first acoustic signal) based on an input output signal to one side (D1 direction), and emits an acoustic signal AC2 (second acoustic signal) that is an inverse phase signal (phase-inverted signal) of acoustic signal AC1 or a signal approximating the inverse phase signal to the other side (D2 direction). That is, the acoustic signal emitted from driver unit 11 to one side (D1 direction) will be referred to as acoustic signal AC1 (first acoustic signal), and the acoustic signal emitted from driver unit 11 to the other side (D2 direction) will be referred to as acoustic signal AC2 (second acoustic signal). For example, driver unit 11 includes diaphragm 113 that vibrates to emit acoustic signal AC1 in the D1 direction from one surface 113a and emits acoustic signal AC2 in the D2 direction from the other surface 113b (FIG. 2B). In this example, driver unit 11 emits acoustic signal AC1 from one surface 111 in the direction D1 by vibrating diaphragm 113 based on the input output signal, and emits acoustic signal AC2, which is an inverse phase signal of acoustic signal AC1 or a signal approximating the inverse phase signal, from the other surface 112 in the direction D2. In other words, acoustic signal AC2 is emitted secondarily in conjunction with the emission of acoustic signal AC1. Note that the D2 direction (other side) is, for example, the opposite direction to the D1 direction (one side), but the D2 direction does not need to be strictly the opposite direction of the D1 direction as long as the D2 direction is different from the D1 direction. The relationship between one side (D1 direction) and the other side (D2 direction) depends on the type and shape of driver unit 11. Also, depending on the type and shape of driver unit 11, acoustic signal AC2 may be strictly an inverse phase signal of acoustic signal AC1, or acoustic signal AC2 may be a signal approximating the inverse phase signal of acoustic signal AC1. For example, the approximation signal of the opposite phase signal of acoustic signal AC1 may be (1) a signal obtained by shifting the phase of the opposite phase signal of acoustic signal AC1, (2) a signal obtained by changing (amplifying or attenuating) the amplitude of the opposite phase signal of acoustic signal AC1, or (3) a signal obtained by shifting the phase of the opposite phase signal of acoustic signal AC1 and further changing the amplitude.The phase difference between the antiphase signal of acoustic signal AC1 and its approximation signal is preferably δ1% or less of one period of the antiphase signal of acoustic signal AC1. Examples of δ1% include 1%, 3%, 5%, 10%, and 20%. The difference between the amplitude of the antiphase signal of acoustic signal AC1 and the amplitude of its approximation signal is preferably δ2% or less of the amplitude of the antiphase signal of acoustic signal AC1. Examples of δ2% include 1%, 3%, 5%, 10%, and 20%. Examples of the type of driver unit 11 include a dynamic type, a balanced armature type, a hybrid type of a dynamic type and a balanced armature type, and an electrostatic type. The shapes of driver unit 11 and diaphragm 113 are not limited. For simplicity of explanation, an example is shown in which the outer shape of driver unit 11 is a substantially cylindrical shape with both end faces and diaphragm 113 is a substantially disc shape, but this does not limit the present invention. For example, the outer shape of driver unit 11 may be a rectangular parallelepiped shape, and diaphragm 113 may be a dome shape. Examples of audio signals include music, voice, sound effects, and environmental sounds.

[0011] <Case 12> Housing 12 is a hollow member having walls on the outside, with sound holes 121a and 123a provided in the walls, and driver unit 11 housed inside. For example, driver unit 11 is fixed to the end of housing 12 on the D1 direction side. However, this does not limit the present invention. There are no limitations on the shape of housing 12, but it is desirable that the shape of housing 12 be rotationally symmetric (line symmetric) or approximately rotationally symmetric about axis A1 extending along the D1 direction. This makes it easy to provide sound hole 123a (described in detail below) so as to reduce the variation in the energy of the sound emitted from housing 12 between directions. As a result, it becomes easy to reduce sound leakage uniformly in all directions. For example, housing 12 has a first end face that is wall portion 121 arranged on one side (D1 direction side) of driver unit 11, a second end face that is wall portion 122 arranged on the other side (D2 direction side) of driver unit 11, and a side face that is wall portion 123 that surrounds the space between the first end face and the second end face, with axis A1 passing through the first end face and the second end face as the center (FIGS. 2B and 3B). For simplicity of explanation, an example is shown here in which housing 12 has a substantially cylindrical shape with both end faces. For example, the distance between wall portion 121 and wall portion 122 is 10 mm, and wall portions 121 and 122 are circular with a radius of 10 mm. However, these are merely examples and do not limit the present invention. For example, housing 12 may have a substantially dome shape with walls at the ends, a hollow substantially cubic shape, or any other three-dimensional shape. Furthermore, there are no limitations on the material that constitutes housing 12. Housing 12 may be made of a rigid body such as synthetic resin or metal, or may be made of an elastic body such as rubber. Housing 12 that houses driver unit 11 as described above functions as, for example, an enclosure-type tweeter speaker.

[0012] <Sound holes 121a, 123a> As described above, the wall of housing 12 is provided with sound hole 121a (first sound hole) that guides acoustic signal AC1 (first acoustic signal) emitted from driver unit 11 to the outside, and sound hole 123a (second sound hole) that guides acoustic signal AC2 (second acoustic signal) emitted from driver unit 11 to the outside. Sound hole 121a and sound hole 123a are, for example, through holes that penetrate the wall of housing 12, but this does not limit the present invention. Sound hole 121a and sound hole 123a do not have to be through holes as long as they can guide acoustic signal AC1 and acoustic signal AC2 to the outside, respectively.

[0013] The acoustic signal AC1 emitted from the sound hole 121a reaches the ear canal of the user and is heard by the user. On the other hand, an acoustic signal AC2, which is an inverse phase signal of the acoustic signal AC1 or an approximation of the inverse phase signal, is emitted from the sound hole 123a. A part of this acoustic signal AC2 cancels out a part (sound leakage component) of the acoustic signal AC1 emitted from the sound hole 121a. That is, by emitting the acoustic signal AC1 (first acoustic signal) from the sound hole 121a (first sound hole) and emitting the acoustic signal AC2 (second acoustic signal) from the sound hole 123a (second sound hole), the attenuation rate η of the acoustic signal AC1 (first acoustic signal) at the position P2 (second position) relative to the position P1 (first position) becomes 11 Set a predetermined value η th The attenuation amount η of the acoustic signal AC1 (first acoustic signal) at the position P2 (second position) based on the position P1 (first position) can be expressed as follows: 12 a predetermined value ω th Here, the position P1 (first point) is a predetermined point where the acoustic signal AC1 (first acoustic signal) emitted from the sound hole 121a (first sound hole) arrives. On the other hand, the position P2 (second point) is a predetermined point that is farther away from the acoustic signal output device 1 than the position P1 (first point). The predetermined value η th is the attenuation rate η of any or specific acoustic signal (sound) due to air propagation at position P2 (second position) relative to position P1 (first position). 21 In addition, the predetermined value ω this the attenuation of any or specific acoustic signal (sound) due to air propagation at position P2 (second point) relative to position P1 (first point), η 22 That is, the acoustic signal output device 1 has an attenuation rate η 11 is the decay rate η 21 A predetermined value η smaller than th It is designed to be equal to or less than the attenuation η 12 is the attenuation η 22 a predetermined value ω greater than th The acoustic signal AC1 is propagated through the air from position P1 to position P2, and is attenuated due to this air propagation and the acoustic signal AC2. The attenuation rate η 11 is the ratio (AMP2(AC1) / AMP1(AC1)) of the magnitude AMP2(AC1) of the acoustic signal AC1 at the position P2 attenuated due to air propagation and the acoustic signal AC2 to the magnitude AMP1(AC1) of the acoustic signal AC1 at the position P1. Also, the attenuation amount η 12 is the difference between the magnitude AMP1(AC1) and the magnitude AMP2(AC1) (|AMP1(AC1)-AMP2(AC1)|). On the other hand, if the acoustic signal AC2 is not assumed, an arbitrary or specific acoustic signal AC propagating through the air from the position P1 to the position P2 ar is attenuated due to air propagation, not due to the acoustic signal AC2. 21 is the acoustic signal AC at position P1 ar The size of AMP1 (AC ar ) at position P2, which is attenuated due to air propagation (attenuation without being attributable to acoustic signal AC2) ar Size of AMP2 (AC ar ) ratio (AMP2(AC ar ) / AMP1(AC ar )) Also, the attenuation η 22 is the magnitude AMP1(AC ar ) and size AMP2(AC ar ) and the difference (|AMP1(AC ar )-AMP2(AC ar)|). Examples of the magnitude of an acoustic signal include the sound pressure of the acoustic signal or the energy of the acoustic signal. Furthermore, the "sound leakage component" refers to, for example, a component of the acoustic signal AC1 emitted from the sound hole 121a that is likely to reach an area other than that of the user wearing the acoustic signal output device 1 (for example, a person other than the user wearing the acoustic signal output device 1). For example, the "sound leakage component" refers to a component of the acoustic signal AC1 that propagates in a direction other than direction D1. For example, the direct wave of the acoustic signal AC1 is mainly emitted from the sound hole 121a, and the direct wave of the second acoustic signal is mainly emitted from the second sound hole. A portion of the direct wave of the acoustic signal AC1 emitted from the sound hole 121a (the sound leakage component) is canceled out by interference with at least a portion of the direct wave of the acoustic signal AC2 emitted from the sound hole 123a. However, this does not limit the present invention, and this cancellation can occur with waves other than direct waves. That is, the sound leakage component, which is at least one of the direct wave and the reflected wave of the acoustic signal AC1 emitted from the sound hole 121a, may be canceled out by at least one of the direct wave and the reflected wave of the acoustic signal AC2 emitted from the sound hole 123a, thereby suppressing sound leakage.

[0014] The arrangement of the sound holes 121a and 123a is shown below. Sound hole 121a (first sound hole) exemplified here is provided in area AR1 (first area) of wall portion 121 arranged on one side of driver unit 11 (the D1 direction side, which is the side from which acoustic signal AC1 is emitted) (FIGS. 1, 2A, 2B, 3B). That is, sound hole 121a opens facing in direction D1 (first direction) along axis A1. Furthermore, sound hole 123a (second sound hole) exemplified here is provided in area AR3 of wall portion 123 that contacts area AR between area AR1 (first area) of wall portion 121 of housing 12 and area AR2 (second area) of wall portion 122 arranged on the D2 direction side of driver unit 11 (the other side, which is the side from which acoustic signal AC2 is emitted). That is, if the center of the housing 12 is used as a reference and the direction between the D1 direction (first direction) and the direction opposite to the D1 direction is defined as the D12 direction (second direction) (Figure 3B), the sound hole 121a (first sound hole) is provided on the D1 direction side (first direction side) of the housing 12, and the sound hole 123a (second sound hole) is provided on the D12 direction side (second direction side) of the housing 12. For example, when housing 12 has a first end face that is wall portion 121 arranged on one side (D1 direction side) of driver unit 11, a second end face that is wall portion 122 arranged on the other side (D2 direction side) of driver unit 11, and a side face that is wall portion 123 that surrounds the space between the first end face and the second end face, centered on axis A1 that runs along the emission direction (D1 direction) of acoustic signal AC1 that passes through the first end face and the second end face (FIGS. 2B and 3B), sound hole 121a (first sound hole) is provided in the first end face, and sound hole 123a (second sound hole) is provided in the side face. Also, in this example, no sound hole is provided on the wall portion 122 side of housing 12. If a sound hole were provided on the wall portion 122 side of housing 12, the sound pressure level of acoustic signal AC2 emitted from housing 12 would exceed the level necessary to offset the sound leakage component of acoustic signal AC1, and this excess would be perceived as sound leakage.

[0015] As illustrated in FIG. 2A and other figures, sound hole 121a illustrated here is disposed on or near axis A1 along the emission direction (D1 direction) of acoustic signal AC1. In this example, axis A1 passes through the center of area AR1 (first area) of wall 121 disposed on one side (D1 direction side) of driver unit 11 of housing 12 or near the center. For example, axis A1 is an axis extending in the D1 direction through the central area of ​​housing 12. That is, sound hole 121a in this example is provided at the center position of area AR1 of wall 121 of housing 12. In this example, for simplicity of explanation, an example is shown in which the edge shape of the open end of sound hole 121a is circular (the open end is circular). The radius of such sound hole 121a is, for example, 3.5 mm. However, this does not limit the present invention. For example, the edge shape of the open end of sound hole 121a may be other shapes such as an ellipse, a rectangle, or a triangle. Furthermore, the open end of sound hole 121a may be mesh-like. In other words, the open end of sound hole 121a may be composed of a plurality of holes. In this example, for the sake of simplicity, one sound hole 121a is provided in area AR1 (first area) of wall 121 of housing 12. However, this does not limit the present invention. For example, two or more sound holes 121a may be provided in area AR1 (first area) of wall 121 of housing 12.

[0016] It is desirable that the sound hole 123a (second sound hole) be arranged in consideration of the following points, for example. (1) Positional viewpoint: The sound hole 123a is positioned so that the propagation path of the sound leakage component of the sound signal AC1 to be cancelled overlaps with the propagation path of the sound signal AC2 emitted from the sound hole 123a. (2) Area perspective: The propagation area of ​​acoustic signal AC2 emitted from sound hole 123a and the frequency characteristics of housing 12 vary depending on the opening area of ​​sound hole 123a. Furthermore, the frequency characteristics of housing 12 affect the frequency characteristics of acoustic signal AC2 emitted from sound hole 123a, i.e., the amplitude at each frequency. Taking into consideration the propagation area and frequency characteristics of acoustic signal AC2 emitted from sound hole 123a, the opening area of ​​sound hole 123a is determined so that the sound leakage components are canceled out by acoustic signal AC2 emitted from sound hole 123a in the area where they are to be canceled out. From the above viewpoint, it is desirable that the sound hole 123a (second sound hole) be configured as follows, for example. For example, as illustrated in FIGS. 2B, 3A, and 3C, it is desirable that a plurality of sound holes 123a (second sound holes) are provided along a circumference (circle) C1 centered on an axis A1 along the emission direction of an acoustic signal AC1 (first acoustic signal). When a plurality of sound holes 123a are provided along the circumference C1, the acoustic signal AC2 is emitted radially to the outside from the sound holes 123a (radially around the axis A1). Here, the sound leakage component of the acoustic signal AC1 is also emitted radially to the outside from the sound holes 123a (radially around the axis A1). Therefore, by providing a plurality of sound holes 123a along the circumference C1, the sound leakage component of the acoustic signal AC1 can be appropriately canceled out by the acoustic signal AC2. Here, for simplicity of explanation, an example is shown in which a plurality of sound holes 123a are provided on the circumference C1. However, it is sufficient that the plurality of sound holes 123a are provided along the circumference C1, and it is not necessary that all of the sound holes 123a are arranged strictly on the circumference C1.

[0017] Preferably, when the circumference C1 is equally divided into a plurality of unit arc regions, the sum of the opening areas of the sound holes 123a (second sound holes) provided along a first arc region, which is one of the unit arc regions, is the same as or approximately the same as the sum of the opening areas of the sound holes 123a (second sound holes) provided along a second arc region, which is one of the unit arc regions excluding the first arc region. For example, as illustrated in FIG. 4, when the circumference C1 is divided into four unit arc regions C1-1, ..., C1-4, the sum of the opening areas of the sound holes 123a (second sound holes) provided along a first arc region (e.g., unit arc region C1-1) that is one of the unit arc regions C1-1, ..., C1-4 is the same or substantially the same as the sum of the opening areas of the sound holes 123a (second sound holes) provided along a second arc region (e.g., unit arc region C1-2) that is one of the unit arc regions excluding the first arc region. Note that, for simplicity of explanation, an example in which the circumference C1 is divided into four unit arc regions C1-1, ..., C1-4 is shown, but this does not limit the present invention. Furthermore, "α1 and α2 are substantially the same" means that the difference between α1 and α2 is β% or less of α1. Examples of β% include 3%, 5%, and 10%. As a result, the sound pressure distribution of the acoustic signal AC2 emitted from the sound holes 123a provided along the first arc-shaped region and the sound pressure distribution of the acoustic signal AC2 emitted from the sound holes 123a provided along the second arc-shaped region are point-symmetric or approximately point-symmetric with respect to the axis A1. Preferably, the sums of the opening areas of the sound holes 123a (second sound holes) provided along each unit arc-shaped region for each unit arc-shaped region are all the same or approximately the same. As a result, the sound pressure distribution of the acoustic signal AC2 emitted from the sound holes 123a is point-symmetric or approximately point-symmetric with respect to the axis A1. This allows the acoustic signal AC2 to more appropriately cancel out the sound leakage component of the acoustic signal AC1.

[0018] More preferably, the multiple sound holes 123a are desirably arranged along the circumference C1 with the same shape, size, and spacing. For example, multiple sound holes 123a with a width of 4 mm and a height of 3.5 mm are arranged along the circumference C1 with the same shape, size, and spacing. When multiple sound holes 123a are arranged along the circumference C1 with the same shape, size, and spacing, the sound leakage component of the acoustic signal AC1 can be more appropriately canceled out by the acoustic signal AC2. However, this does not limit the present invention.

[0019] Preferably, sound hole 123a (second sound hole) is provided in a wall portion that contacts area AR located on the other side (D2 direction side) of driver unit 11 (FIG. 3B). This allows the direct wave of acoustic signal AC2 emitted from the other side of driver unit 11 to be efficiently guided to the outside from sound hole 123a. As a result, the sound leakage component of acoustic signal AC1 can be more appropriately canceled out by acoustic signal AC2.

[0020] Here, for simplicity of explanation, an example is shown in which the edge of the open end of sound hole 123a is quadrangular (the open end is square), but this does not limit the present invention. For example, the edge of the open end of sound hole 123a may be circular, elliptical, triangular, or other shapes. The open end of sound hole 123a may also be mesh-like. In other words, the open end of sound hole 123a may be composed of multiple holes. There is also no limit to the number of sound holes 123a; either a single sound hole 123a or multiple sound holes 123a may be provided in area AR3 of wall 123 of housing 12.

[0021] It is desirable that the ratio S2 / S1 of the sum S2 of the opening areas of the sound holes 123a (second sound holes) to the sum S1 of the opening areas of the sound holes 121a (first sound holes) satisfies 2 / 3≦S2 / S1≦4 (details will be described later). This allows the sound leakage component of the acoustic signal AC1 to be appropriately canceled out by the acoustic signal AC2.

[0022] Sound leakage suppression performance may also depend on the ratio between the area of ​​wall portion 123 in which sound hole 123a is provided and the opening area of ​​sound hole 123a. For example, consider a case in which housing 12 has a first end face which is wall portion 121 arranged on one side (D1 direction side) of driver unit 11, a second end face which is wall portion 122 arranged on the other side (D2 direction side) of driver unit 11, and a side face which is wall portion 123 that surrounds the space sandwiched between the first end face and the second end face, with axis A1 along the emission direction (D1 direction) of acoustic signal AC1 that passes through the first end face and the second end face as the center, and sound hole 121a (first sound hole) is provided in the first end face and sound hole 123a (second sound hole) is provided in the side face (FIGS. 2B and 3B). In such a case, it is desirable that the ratio S2 / S3 of the total opening area S2 of the sound holes 123a to the total area S3 of the side surfaces be 1 / 20≦S2 / S3≦1 / 5 (details will be described later). This allows the sound leakage component of the acoustic signal AC1 to be appropriately canceled out by the acoustic signal AC2. However, this does not limit the present invention.

[0023] <Usage status> FIG. 5A illustrates an example of how the acoustic signal output device 1 is used. In the example of FIG. 5A, one acoustic signal output device 1 is worn by a user 1000 on each of their right ear 1010 and left ear 1020. Any suitable wearing mechanism is used to wear the acoustic signal output devices 1 on the ears. The D1 direction of each acoustic signal output device 1 faces the user 1000. The output signal output from the playback device 100 is input to the driver unit 11 of each acoustic signal output device 1, and the driver unit 11 emits an acoustic signal AC1 toward the D1 direction and an acoustic signal AC2 toward the other side. The acoustic signal AC1 is emitted from the sound hole 121a, and the emitted acoustic signal AC1 enters the right ear 1010 and left ear 1020 and is heard by the user 1000. Meanwhile, an acoustic signal AC2, which is an inverse phase signal of the acoustic signal AC1 or a signal approximating the inverse phase signal, is emitted from the sound hole 123a. This part of the acoustic signal AC2 cancels out the part (sound leakage component) of the acoustic signal AC1 emitted from the sound hole 121a.

[0024] <Experimental Results> The following shows the results of an experiment demonstrating the sound leakage suppression effect of the acoustic signal output device 1. In this experiment, as shown in Fig. 5B, the acoustic signal output device 1 was attached to both ears of a dummy head 1100 simulating a human head, and acoustic signals were observed at positions P1 and P2. In this example, position P1 is located near the left ear 1120 of the dummy head 1100 (near the acoustic signal output device 1), and position P2 is located 15 cm outward from position P1.

[0025] FIG. 6 illustrates the frequency characteristics of the acoustic signal observed at position P1 in FIG. 5B , FIG. 7 illustrates the frequency characteristics of the acoustic signal observed at position P2 in FIG. 5B , and FIG. 8 illustrates the difference (difference in sound pressure level at each frequency) between the frequency characteristics of the acoustic signal observed at position P1 and the frequency characteristics of the acoustic signal observed at position P2. The horizontal axis represents frequency (Hz), and the vertical axis represents sound pressure level (SPL) (dB). The solid line graph illustrates the frequency characteristics when using the acoustic signal output device 1, and the dashed line graph illustrates the frequency characteristics when using a conventional acoustic signal output device (open-ear earphones). As illustrated in FIG. 8 , when using the acoustic signal output device 1 of this example, the difference in sound pressure between the acoustic signal observed at position P1 and the acoustic signal observed at position P2 is larger than when using the conventional acoustic signal output device. This indicates that the acoustic signal output device 1 is able to suppress sound leakage at position P2 compared to the conventional acoustic signal output device.

[0026] 9A illustrates the relationship between the ratio S2 / S1 of the total opening area S2 of the sound holes 123a (second sound holes) to the total opening area S1 of the sound holes 121a (first sound holes), and the difference between the frequency characteristics of the sound signal observed at position P1 and the frequency characteristics of the sound signal observed at position P2. The horizontal axis represents the ratio S2 / S1, and the vertical axis represents the sound pressure level (SPL) [dB] representing the difference. r12h6 illustrates the results when there are six sound holes 121a and four sound holes 123a, r12h12 illustrates the results when there are twelve sound holes 21a and four sound holes 123a, and r45h35 illustrates the results when there is one sound hole 121a and four sound holes 123a. 9A, it can be seen that the difference in sound pressure between the acoustic signal observed at position P1 and the acoustic signal observed at position P2 is particularly large when the ratio S2 / S1 of the sum S2 of the opening areas of sound holes 123a to the sum S1 of the opening areas of sound holes 121a is in the range of 2 / 3≦S2 / S1≦4. This indicates that the sound leakage suppression effect is large in this range.

[0027] FIG. 9B illustrates the relationship between the ratio S2 / S3 of the sum S2 of the opening areas of the sound holes 123a (second sound holes) to the total area S3 of the side surfaces and the difference between the frequency characteristics of the acoustic signal observed at position P1 and the frequency characteristics of the acoustic signal observed at position P2. The horizontal axis represents the ratio S2 / S3, and the vertical axis represents the sound pressure level (SPL) [dB] representing the difference. The meanings of r12h6, r12h12, and r45h35 are the same as in FIG. 9A. As illustrated in FIG. 9B, when the ratio S2 / S3 of the sum S2 of the opening areas of the sound holes 123a (second sound holes) to the total area S3 of the side surfaces is in the range of 1 / 20≦S2 / S3≦1 / 5, it can be seen that the difference in sound pressure between the acoustic signal observed at position P1 and the acoustic signal observed at position P2 is particularly large. This indicates that the sound leakage suppression effect is significant in this range.

[0028] [First embodiment] Next, a first embodiment of the present invention will be described. When using acoustic signal AC2 to cancel out the sound leakage component of acoustic signal AC1, it is ideal for the propagation distances of acoustic signal AC1 and acoustic signal AC2 to be the same. However, in reality, acoustic signal AC1 and acoustic signal AC2 are emitted from different positions, and their propagation distances are different. The greater the difference in this propagation distance, the greater the phase shift between acoustic signal AC1 and acoustic signal AC2 at the position where sound leakage is to be canceled, reducing the sound leakage prevention effect. Generally, the difference in these propagation distances becomes greater the larger the size of housing 12 and driver unit 11, and the larger the size of housing 12 and driver unit 11, the less effective the sound leakage prevention effect becomes. Therefore, to prevent sound leakage, it is desirable for the size of housing 12 and driver unit 11 to be small. However, if the size of housing 12 and driver unit 11 is reduced, it becomes difficult to increase the sound pressure in the low frequency range.

[0029] Furthermore, the lower the frequency, the less the effect of the difference in propagation distance is affected, and so the lower the frequency, the greater the sound leakage prevention effect. On the other hand, in the low-frequency range, not only the sound leakage component of the acoustic signal AC1 but also the reproduced sound that should be heard may be significantly attenuated by the acoustic signal AC2.

[0030] For these reasons, it may be difficult for the above-mentioned base acoustic signal output device to obtain sufficient low-frequency sound pressure while suppressing sound leakage.

[0031] In the following, we will explain an acoustic signal output device that can obtain sufficient low-frequency sound pressure while suppressing sound leakage. Note that the following explanation will focus on differences from the matters explained so far, and explanations of matters that have already been explained may be simplified.

[0032] <Configuration> The acoustic signal output device 10 of this embodiment is a device for listening to sound that is worn without sealing the user's ear canal (for example, open-ear earphones, headphones, installed speakers, built-in speakers, etc.). As illustrated in FIGS. 10 to 12, the acoustic signal output device 10 of this embodiment has a small driver unit 11 (speaker driver unit, driver) that converts an output signal (an electrical signal representing a reproduced acoustic signal) output from a playback device into an acoustic signal and outputs it, a large driver unit 15 (speaker driver unit, driver) that converts the output signal into an acoustic signal and outputs it, and a housing 12 that houses the driver unit 11 inside. The driver unit 11 and housing 12 are the same as those of the acoustic signal output device 1 described above.

[0033] <Driver unit 11 (first driver unit)> In this embodiment, the frequency band of the reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and the driver unit 11 emits the acoustic signal on the high-frequency band side of the reproduced acoustic signal. In other words, the driver unit 11 mainly handles the high-frequency band of the reproduced acoustic signal. The output signal output from the playback device is separated into a high-frequency band signal on the high-frequency side and a low-frequency band signal on the lower-frequency side, and the separated high-frequency band signal is input to the driver unit 11. Note that the frequency bands in which the levels of the high-frequency band signal and the low-frequency band signal are equal to or higher than a predetermined value may or may not overlap with each other. The driver unit 11 is a device (device with a speaker function) that emits (emits sound from) an acoustic signal AC1 (first acoustic signal) based on the input high-frequency band signal to one side (the D1 direction side), and emits an acoustic signal AC2 (second acoustic signal) that is an inverse phase signal (phase-inverted signal) of the acoustic signal AC1 or a signal approximating the inverse phase signal to the other side (the D2 direction side). That is, an acoustic signal emitted from driver unit 11 to one side (D1 direction side) will be called acoustic signal AC1 (first acoustic signal), and an acoustic signal emitted from driver unit 11 to the other side (D2 direction side) will be called acoustic signal AC2 (second acoustic signal). For example, driver unit 11 includes diaphragm 113 (first diaphragm) that vibrates to emit acoustic signal AC1 (first acoustic signal) from one surface 113a to the D1 direction side (one side), and emits acoustic signal AC2 (second acoustic signal) from the other surface 113b to the D2 direction side (other side) due to this vibration (FIG. 12). In this example, driver unit 11 emits acoustic signal AC1 from one surface 111 to the D1 direction side, and emits acoustic signal AC2, which is an inverse phase signal of acoustic signal AC1 or a signal approximating the inverse phase signal, from the other side 112 to the D2 direction side by vibrating diaphragm 113 based on the input high-frequency band signal. The rest is as described above.

[0034] <Driver unit 15 (second driver unit)> The driver unit 15 is larger than the driver unit 11 and emits acoustic signals on the low-frequency band side of the above-mentioned reproduced acoustic signals. In other words, the driver unit 15 mainly handles low-frequency acoustic signals among the reproduced acoustic signals. This makes it possible to obtain lower-frequency sound pressure compared to when only the driver unit 11 is used. The low-frequency band signal separated from the output signal as described above is input to the driver unit 15, which is a device (device with speaker functionality) that emits (emits sound) an acoustic signal AC3 (third acoustic signal) based on the input low-frequency band signal to one side (the D1 direction side) and emits an acoustic signal AC4 (fourth acoustic signal) that is an inverse phase signal (phase-inverted signal) of the acoustic signal AC3 or a signal approximating the inverse phase signal to the other side (the D2 direction side). In other words, the acoustic signal emitted from the driver unit 15 to one side (the D1 direction side) will be called the acoustic signal AC3 (third acoustic signal), and the acoustic signal emitted from the driver unit 15 to the other side (the D2 direction side) will be called the acoustic signal AC4 (fourth acoustic signal). For example, driver unit 15 includes diaphragm 153 (second diaphragm) that vibrates to emit acoustic signal AC3 (third acoustic signal) from one surface 153a in the D1 direction (one side), and emits acoustic signal AC4 (fourth acoustic signal) from the other surface 153b in the D2 direction (the other side) (FIG. 12). In this example, driver unit 15 emits acoustic signal AC3 from one surface 151 in the D1 direction, and emits acoustic signal AC4, which is an in-phase signal of acoustic signal AC3 or an approximation of the in-phase signal, from the other surface 152 in the D2 direction, by vibrating diaphragm 153 based on an input low-frequency band signal. In other words, acoustic signal AC4 is emitted secondarily in conjunction with the emission of acoustic signal AC3. Acoustic signal AC3 is an in-phase signal of acoustic signal AC1 or an approximation of the in-phase signal, and acoustic signal AC4 is an in-phase signal of acoustic signal AC2 or an approximation of the in-phase signal. Depending on the type and shape of driver unit 15, acoustic signal AC4 may be strictly an opposite-phase signal to acoustic signal AC3, or acoustic signal AC4 may be an approximate signal to an opposite-phase signal to acoustic signal AC3.For example, the approximation signal of the opposite-phase signal of acoustic signal AC3 may be (1) a signal obtained by shifting the phase of the opposite-phase signal of acoustic signal AC3, (2) a signal obtained by changing (amplifying or attenuating) the amplitude of the opposite-phase signal of acoustic signal AC3, or (3) a signal obtained by shifting the phase of the opposite-phase signal of acoustic signal AC3 and then changing the amplitude. The phase difference between the opposite-phase signal of acoustic signal AC3 and its approximation signal is preferably δ3% or less of one period of the opposite-phase signal of acoustic signal AC3. Examples of δ3% include 1%, 3%, 5%, 10%, and 20%. Furthermore, the difference in amplitude between the opposite-phase signal of acoustic signal AC3 and its approximation signal is preferably δ4% or less of the amplitude of the opposite-phase signal of acoustic signal AC3. Examples of δ4% include 1%, 3%, 5%, 10%, and 20%. Examples of the type of driver unit 15 include a dynamic type, a balanced armature type, a hybrid type of a dynamic type and a balanced armature type, and an electrostatic type. Furthermore, there are no limitations on the shapes of driver unit 15 or diaphragm 153. In this embodiment, for the sake of simplicity of explanation, an example is shown in which driver unit 15 has an outer shape that is generally cylindrical with both end faces, and diaphragm 153 has an approximately disk shape, but this does not limit the present invention. For example, driver unit 15 may have an outer shape that is a rectangular parallelepiped, and diaphragm 153 may have a dome shape.

[0035] As described above, driver unit 15 is larger in size than driver unit 11. For example, if the diameter of driver unit 11 (diameter in the direction perpendicular to the D1 direction and / or the D2 direction) is S11 and the diameter of driver unit 15 (diameter in the direction perpendicular to the D1 direction and / or the D2 direction) is S21, then S21 > S11 (FIG. 11). For example, S21 is more than twice as large as S11, S11 is 12 mm, and S21 is 35 mm. Also, if the diameter of diaphragm 113 (diameter in the direction perpendicular to the D1 direction and / or the D2 direction) is S12 and the diameter of diaphragm 153 (diameter in the direction perpendicular to the D1 direction and / or the D2 direction) is S22, then S22 > S12 (FIG. 12). For example, S22 is more than twice as large as S12, S12 is 10 mm, and S22 is 30 mm. That is, the diameter of diaphragm 153 (second diaphragm) is larger than the diameter of diaphragm 113 (first diaphragm).

[0036] <Case 12> Housing 12 is a hollow member with walls on the outside, with sound holes 121a and 123a provided in the walls, and driver unit 11 housed inside. For example, driver unit 11 is fixed to the end of housing 12 on the D1 direction side. However, this does not limit the present invention. The size of housing 12 is smaller than the size of driver unit 15. For example, if the diameter of housing 12 (the diameter in the direction perpendicular to the D1 direction and / or the D2 direction) is S13 and the diameter of driver unit 15 (the diameter in the direction perpendicular to the D1 direction and / or the D2 direction) is S21, then S21 > S13 is satisfied (FIG. 11). The rest is as described above.

[0037] Note that driver unit 15 of the present embodiment is disposed in the external space of housing 12 and is not housed in any other housing. That is, driver unit 15 (second driver unit) is open to the external space of housing 12, and acoustic signal AC3 (third acoustic signal) and acoustic signal AC4 (fourth acoustic signal) are emitted directly from driver unit 15 (second driver unit) into the external space of housing 12. As such, because driver unit 15 of the present embodiment is not housed in a housing, it is possible to reproduce sound with a more natural sound quality than when driver unit 15 is housed in a housing. Furthermore, when driver unit 15 is housed in a housing, the sound heard changes depending on the positional relationship between the housing and the ear canal, and if the headphones are not worn correctly due to glasses or the like, sufficient sound quality may not be ensured. However, this problem does not occur with driver unit 15 that is not housed in a housing. Furthermore, when driver unit 15 is housed in a housing, it is necessary to firmly secure the housing to the ear with a headband or the like to ensure sufficient sound quality. However, with driver unit 15 that is not housed in a housing, the position of driver unit 15 only needs to be fixed to a certain extent, and the user is freed from pain and tightness caused by a headband or the like.

[0038] Acoustic signal AC1 emitted from sound hole 121a and acoustic signal AC3 emitted from one surface 151 of driver unit 15 (one surface 153a side of diaphragm 153) reach the user's ear canal and are heard by the user. Meanwhile, acoustic signal AC2, which is an inverse phase signal of acoustic signal AC1 or a signal approximating the inverse phase signal, is emitted from sound hole 123a. Furthermore, acoustic signal AC4, which is an inverse phase signal of acoustic signal AC3 or a signal approximating the inverse phase signal, is emitted from the other surface 152 of driver unit 15 (the other surface 153b side of diaphragm 153). Portions of the emitted acoustic signals AC2 and AC4 cancel out portions of the emitted acoustic signals AC1 and AC3 (sound leakage components). For example, a portion of the emitted acoustic signal AC2 cancels out a portion of the emitted acoustic signal AC1, and a portion of the emitted acoustic signal AC4 cancels out a portion of the emitted acoustic signal AC3. That is, an acoustic signal AC1 (first acoustic signal) is emitted from sound hole 121a (first sound hole), an acoustic signal AC2 (second acoustic signal) is emitted from sound hole 123a (second sound hole), and an acoustic signal AC3 (third acoustic signal) and an acoustic signal AC4 (fourth acoustic signal) are emitted from driver unit 15 (second driver unit), whereby an attenuation rate η of the acoustic signal AC1 (first acoustic signal) and the acoustic signal AC3 (third acoustic signal) at position P2 (second position) relative to position P1 (first position) is 11 Set a predetermined value η th The attenuation amount η of the acoustic signal AC1 (first acoustic signal) and the acoustic signal AC3 (third acoustic signal) at the position P2 (second position) relative to the position P1 (first position) can be expressed as follows: 12 a predetermined value ω th Here, position P1 (first point) is a predetermined point where acoustic signal AC1 (first acoustic signal) emitted from sound hole 121a (first sound hole) and acoustic signal AC3 (third acoustic signal) emitted from one surface 151 of driver unit 15 arrive. On the other hand, position P2 (second point) is a predetermined point that is farther from acoustic signal output device 10 than position P1 (first point). The predetermined value η th is the attenuation rate η of any or specific acoustic signal (sound) due to air propagation at position P2 (second position) relative to position P1 (first position).21 In addition, the predetermined value ω th is the attenuation of any or specific acoustic signal (sound) due to air propagation at position P2 (second point) relative to position P1 (first point), η 22 That is, the acoustic signal output device 10 of this embodiment has an attenuation rate η 11 is the decay rate η 21 A predetermined value η smaller than th It is designed to be equal to or less than the attenuation η 12 is the attenuation η 22 a predetermined value ω greater than th The acoustic signals AC1 and AC3 are propagated through the air from position P1 to position P2, and are attenuated due to this air propagation and the acoustic signals AC2 and AC4. The attenuation rate η 11 is the ratio (AMP2(AC1) / AMP1(AC1)) of the magnitude AMP2(AC1) of the acoustic signal AC1 at position P2 attenuated due to air propagation and acoustic signals AC2 and AC4 to the magnitude AMP1(AC1) of the acoustic signal AC1 at position P1, or the ratio (AMP2(AC3) / AMP1(AC13)) of the magnitude AMP2(AC3) of the acoustic signal AC3 at position P2 attenuated due to air propagation and acoustic signals AC2 and AC4 to the magnitude AMP1(AC3) of the acoustic signal AC3 at position P1. Also, the attenuation amount η 12 is the difference between the magnitude AMP1(AC1) and the magnitude AMP2(AC1) (|AMP1(AC1)-AMP2(AC1)|), or the difference between the magnitude AMP1(AC3) and the magnitude AMP2(AC3) (|AMP1(AC3)-AMP2(AC3)|). On the other hand, if the acoustic signals AC2 and AC4 are not assumed, any or specific acoustic signal AC propagating through the air from position P1 to position P2 ar is attenuated due to air propagation, not due to the acoustic signals AC2 and AC4. 21 is the acoustic signal AC at position P1 ar The size of AMP1 (AC ar) at position P2, which is attenuated due to air propagation (attenuation without being attributable to acoustic signal AC2) ar Size of AMP2 (AC ar ) ratio (AMP2(AC ar ) / AMP1(AC ar )) Also, the attenuation η 22 is the magnitude AMP1(AC ar ) and size AMP2(AC ar ) and the difference (|AMP1(AC ar )-AMP2(AC ar)|). Examples of the magnitude of an acoustic signal include the sound pressure of the acoustic signal or the energy of the acoustic signal. Furthermore, the "sound leakage component" refers to, for example, the component of the acoustic signal AC1 emitted from the sound hole 121a and the acoustic signal AC3 emitted from one surface 151 of the driver unit 15 that is likely to reach an area other than that of the user wearing the acoustic signal output device 10 (for example, a person other than the user wearing the acoustic signal output device 10). For example, the "sound leakage component" refers to the component of the acoustic signal AC1 and the acoustic signal AC3 that propagates in a direction other than direction D1. For example, the direct wave of the acoustic signal AC1 is mainly emitted from the sound hole 121a, the direct wave of the second acoustic signal is mainly emitted from the second sound hole, the direct wave of the acoustic signal AC3 is emitted from one surface 151 of the driver unit 15, and the direct wave of the acoustic signal AC4 is emitted from the other surface 152 of the driver unit 15. A portion of the direct wave of acoustic signal AC1 emitted from sound hole 121a and a portion of the direct wave of acoustic signal AC3 from one surface 151 of driver unit 15 (sound leakage component) are cancelled out by interference with at least a portion of the direct wave of acoustic signal AC2 emitted from sound hole 123a and at least a portion of the direct wave of acoustic signal AC4 from the other surface 152 of driver unit 15. However, this does not limit the present invention, and this cancellation can occur with waves other than direct waves. In other words, the sound leakage component, which is at least one of the direct wave and reflected wave of acoustic signal AC1 emitted from sound hole 121a and the direct wave and reflected wave of acoustic signal AC3 from one surface 151 of driver unit 15, may be cancelled out by at least one of the direct wave and reflected wave of acoustic signal AC2 emitted from sound hole 123a and the acoustic signal AC4 from the other surface 152 of driver unit 15.

[0039] The above configuration makes it possible to suppress sound leakage. In particular, the size of driver unit 11 (first driver unit) is smaller than the size of driver unit 15 (second driver unit). Furthermore, the size of housing 12 that houses driver unit 11 is smaller than the size of driver unit 15. Therefore, the difference between the propagation distance until acoustic signal AC1 (first acoustic signal) emitted from the D1 direction side (one side) of diaphragm 113 (first diaphragm) of driver unit 11 reaches position P2 (second point) and the propagation distance until acoustic signal AC2 (second acoustic signal) emitted from the D2 direction side (other side) of diaphragm 113 (first diaphragm) reaches position P2 (second point) is smaller than the difference between the propagation distance until acoustic signal AC3 (third acoustic signal) emitted from the D1 direction side (one side) of diaphragm 153 (second diaphragm) of driver unit 15 reaches position P2 (second point) and the propagation distance until acoustic signal AC4 (fourth acoustic signal) emitted from the D2 direction side (other side) of diaphragm 153 (second diaphragm) reaches position P2 (second point). Here, the smaller the difference in propagation distance, the smaller the phase shift between the anti-phase waves (acoustic signals AC2 and AC4) and the reproduced sound (acoustic signals AC1 and AC3) at position P2, improving the sound leakage prevention effect. Therefore, in terms of size, the sound leakage prevention effect is greater on the housing 12 side that houses driver unit 11 than on the driver unit 15 side. On the other hand, the higher the frequency, the more susceptible to the difference in propagation distance, so the sound leakage prevention effect tends to decrease as the frequency increases. Here, driver unit 11 is responsible for mainly high-frequency acoustic signals among the reproduced acoustic signals, and driver unit 15 is responsible for mainly low-frequency acoustic signals among the reproduced acoustic signals. Therefore, in terms of frequency, the sound leakage prevention effect is greater on the driver unit 15 side than on the housing 12 side that houses driver unit 11. These characteristics of the sound leakage prevention effect in terms of size and frequency make it possible to obtain a sufficient sound leakage prevention effect over a wide frequency band. Furthermore, by making the driver unit 15 an enclosure-less type that is not housed in a housing, the amplitude of the emitted acoustic signal can be used to the maximum extent, and the effect of preventing sound leakage in the mid-low range can be maximized.In an enclosure-less driver unit 15, when the user is far away from the driver unit 15, not only the sound leakage components but also the reproduced sound to be heard may be significantly attenuated by antiphase waves at low frequencies. However, the acoustic signal output device 10 of this embodiment is an audio listening device (e.g., open-ear earphones, headphones, etc.) that is worn without sealing the ear canal, and the distance from the driver unit 15 to the ear canal is short. Therefore, such problems are unlikely to occur. Furthermore, because the diameter of the diaphragm 153 (second diaphragm) of the driver unit 15 is larger than the diameter of the diaphragm (first diaphragm) of the driver unit 11, the sound pressure of low frequencies can be increased on the driver unit 15 side compared to the driver unit 11. As a result, sufficient low-frequency sound pressure can be obtained while suppressing sound leakage.

[0040] <Arrangement configuration of sound holes 121a and 123a> The arrangement of sound holes 121a and 123a is as described above. Note that, in this embodiment as well, it is desirable not to provide a sound hole on the wall 122 side of housing 12. This is because if a sound hole were provided on the wall 122 side of housing 12, the sound pressure level of acoustic signal AC2 emitted from housing 12 would exceed the level necessary to cancel out the sound leakage component of acoustic signal AC1, and this excess may be perceived as sound leakage. However, even if sound hole 123a is provided on the wall 122 side of housing 12, sound hole 123a may be provided on the wall 122 side of housing 12 if acoustic signal AC2 emitted from sound hole 123a is blocked by driver unit 15 and the sound pressure level does not exceed the level necessary to cancel out the sound leakage component of acoustic signal AC1.

[0041] 10 and other examples, sound hole 121a in this embodiment is disposed on or near axis A1 along the emission direction (D1 direction) of acoustic signal AC1. Axis A1 in this embodiment passes through or near the center of area AR1 (first area) of wall 121 disposed on one side (D1 direction side) of driver unit 11 of housing 12. For example, axis A1 is an axis that passes through the central area of ​​housing 12 and driver unit 15 and extends in the D1 direction.

[0042] It is desirable that the sound hole 123a (second sound hole) of this embodiment be arranged in consideration of the following points, for example. (1) Positional viewpoint: The sound hole 123a is positioned so that the propagation path of the sound leakage components of the sound signals AC1 and AC3 to be cancelled out overlaps with the propagation path of the sound signal AC2 emitted from the sound hole 123a. (2) Area perspective: The propagation area of ​​acoustic signal AC2 emitted from sound hole 123a and the frequency characteristics of housing 12 vary depending on the opening area of ​​sound hole 123a. Furthermore, the frequency characteristics of housing 12 affect the frequency characteristics of acoustic signal AC2 emitted from sound hole 123a, i.e., the amplitude at each frequency. Taking into consideration the propagation area and frequency characteristics of acoustic signal AC2 emitted from sound hole 123a, the opening area of ​​sound hole 123a is determined so that the sound leakage components are canceled out by acoustic signal AC2 emitted from sound hole 123a in the area where they are to be canceled out.

[0043] From the above viewpoint, it is desirable that the sound hole 123a (second sound hole) be configured as follows, for example. For example, as illustrated in FIG. 12 , it is desirable that a plurality of sound holes 123a (second sound holes) in this embodiment are provided along a circumference (circle) C1 centered on an axis A1 along the emission direction of an acoustic signal AC1 (first acoustic signal). When a plurality of sound holes 123a are provided along the circumference C1, the acoustic signal AC2 is emitted radially from the sound holes 123a to the outside (radially from the axis A1). Here, the sound leakage component of the acoustic signal AC1 is also emitted radially from the sound holes 121a to the outside (radially from the axis A1). Therefore, by providing a plurality of sound holes 123a along the circumference C1, the sound leakage component of the acoustic signal AC1 can be appropriately canceled out by the acoustic signal AC2. In this embodiment, for simplicity of explanation, an example is shown in which a plurality of sound holes 123a are provided on the circumference C1. However, it is sufficient that the plurality of sound holes 123a are provided along the circumference C1, and it is not necessary that all of the sound holes 123a are positioned strictly on the circumference C1.

[0044] Preferably, when the circumference C1 is equally divided into a plurality of unit arc regions, the sum of the opening areas of the sound holes 123a (second sound holes) provided along a first arc region, which is one of the unit arc regions, is the same as or approximately the same as the sum of the opening areas of the sound holes 123a (second sound holes) provided along a second arc region, which is one of the unit arc regions excluding the first arc region. For example, as illustrated in FIG. 13 , when a circumference C1 is equally divided into four unit arc regions C1-1, ..., C1-4, the sum of the opening areas of the sound holes 123a (second sound holes) provided along a first arc region (e.g., unit arc region C1-1) that is one of the unit arc regions C1-1, ..., C1-4 is the same or substantially the same as the sum of the opening areas of the sound holes 123a (second sound holes) provided along a second arc region (e.g., unit arc region C1-2) that is one of the unit arc regions excluding the first arc region. Note that, for simplicity of explanation, an example in which the circumference C1 is equally divided into four unit arc regions C1-1, ..., C1-4 is shown, but this does not limit the present invention. Furthermore, "α1 and α2 are substantially the same" means that the difference between α1 and α2 is β% or less of α1. Examples of β% include 3%, 5%, and 10%. As a result, the sound pressure distribution of the acoustic signal AC2 emitted from the sound holes 123a provided along the first arc-shaped region and the sound pressure distribution of the acoustic signal AC2 emitted from the sound holes 123a provided along the second arc-shaped region are point-symmetric or approximately point-symmetric with respect to the axis A1. Preferably, the sums of the opening areas of the sound holes 123a (second sound holes) provided along each unit arc-shaped region for each unit arc-shaped region are all the same or approximately the same. As a result, the sound pressure distribution of the acoustic signal AC2 emitted from the sound holes 123a is point-symmetric or approximately point-symmetric with respect to the axis A1. This allows the acoustic signal AC2 to more appropriately cancel out the sound leakage components of the acoustic signals AC1 and AC3.

[0045] More preferably, the multiple sound holes 123a are desirably arranged along the circumference C1 with the same shape, size, and spacing. For example, multiple sound holes 123a with a width of 4 mm and a height of 3.5 mm are arranged along the circumference C1 with the same shape, size, and spacing. When multiple sound holes 123a are arranged along the circumference C1 with the same shape, size, and spacing, the sound leakage components of the acoustic signals AC1 and AC3 can be more appropriately canceled out by the acoustic signal AC2. However, this does not limit the present invention.

[0046] Preferably, sound hole 123a (second sound hole) is provided in a wall portion adjacent to area AR located on the other side (D2 direction side) of driver unit 11 (FIG. 3B). This allows the direct wave of acoustic signal AC2 emitted from the other side of driver unit 11 to be efficiently guided to the outside from sound hole 123a. As a result, the sound leakage components of acoustic signals AC1 and AC3 can be more appropriately canceled out by acoustic signal AC2. The rest is as described above.

[0047] <Arrangement of housing 12 and driver units 11, 15> In this embodiment, driver unit 15 is disposed on the D2 direction side of housing 12 that houses driver unit 11 (FIGS. 10 and 12). That is, sound hole 121a of housing 12 that emits acoustic signal AC1 is disposed on the D1 direction side (first direction side) of driver unit 11, and driver unit 15 (second driver unit) is disposed in the external space of housing 12, on the D2 direction side (second direction side) of driver unit 11. Here, the D2 direction (second direction) is the opposite direction or approximately the opposite direction of the D1 direction (first direction). This allows driver unit 15 to block sound leakage components that leak from housing 12 toward the D2 direction. In particular, in the high frequency range (e.g., 4 kHz or higher) handled by driver unit 11, there are cases where sound leakage components of acoustic signal AC1 that leak from housing 12 cannot be sufficiently canceled out by acoustic signal AC2. By disposing a large-sized driver unit 15 on the D2 direction side of housing 12, sound leakage in such high frequencies can also be suppressed. The relative position of housing 12 with respect to driver unit 15 (second driver unit) may or may not be fixed. For example, housing 12 may be fixed to driver unit 15 by a member not shown. For example, housing 12 may be attached to driver unit 15 by a member not shown so that the relative position with respect to driver unit 15 is adjustable (so that housing 12 can be fixed at a desired relative position with respect to driver unit 15).

[0048] Furthermore, the sound pressure of an acoustic signal emitted from driver unit 15, which is not housed in a housing, drops sharply when it deviates from the central axis of diaphragm 153. Similarly, the sound pressure of acoustic signal AC1 emitted from sound hole 121a of housing 12 housing driver unit 11 also drops when it deviates from the axis passing through sound hole 121a and diaphragm 113 (for example, on the central axis of diaphragm 113). For this reason, it is desirable that housing 12 housing driver unit 11 and driver unit 15 be arranged coaxially. For example, sound hole 121a (first sound hole) or the center of multiple sound holes 121a (first sound holes) is arranged on axis A1 (on a specific axis) or in the vicinity of axis A1 (axis), and driver unit 11 (first driver unit) emits acoustic signal AC1 (first acoustic signal) in a D1 direction (one side) along axis A1 (axis) and emits acoustic signal AC2 (second acoustic signal) in a D2 direction (other side) along axis A1 (axis). It is desirable that the driver unit 15 (second driver unit) has a diaphragm 153 (second diaphragm) that emits an acoustic signal AC3 (third acoustic signal) in the D1 direction (one side) along the axis A1 (axis) and emits an acoustic signal AC4 (fourth acoustic signal) in the D2 direction (the other side) along the axis A1 (axis), and that the diaphragm 153 (second diaphragm) be disposed on or near the axis A1 (axis). This makes it possible to position the ear canal at a position where the sound pressure of the driver units 11 and 15 is maximized, allowing the user to be presented with an acoustic signal of sufficient sound pressure over a wide frequency band. Furthermore, by arranging the housing 12 that houses the driver unit 11 and the driver unit 15 coaxially, it is possible to change the distance between the driver units 11 and 15 coaxially, making it easy to adjust the sound pressure of the acoustic signal to be heard and the amount of sound leakage.

[0049] <Usage status> 14A and 14B illustrate examples of how the acoustic signal output device 10 is used. In the example of FIG. 14A, one acoustic signal output device 10 is worn on each of the right ear 1010 and left ear 1020 of a user 1000. Any suitable wearing mechanism can be used to wear the acoustic signal output devices 10 on the ears. The D1 direction of each acoustic signal output device 10 faces the user 1000. An output signal output from the playback device 100 is input to the signal separating device 101. As illustrated in FIG. 14B, the signal separating device 101 separates the input output signal into a high-frequency band signal on the high-frequency side and a low-frequency band signal on the low-frequency side. In the example of FIG. 14B, the output signal is branched into two, and the branched output signals are input to a high-pass filter 101a and a low-pass filter 101b, respectively. The high-pass filter 101a attenuates the low-frequency side of the input output signal to obtain and output a high-frequency band signal. The low-pass filter 101b attenuates the high-frequency side of the input output signal to obtain and output a low-frequency band signal. The high-frequency band signal is input to the driver unit 11 of the acoustic signal output device 10, which emits an acoustic signal AC1 in the direction D1 and an acoustic signal AC2 to the other side. The low-frequency band signal is input to the driver unit 15 of the acoustic signal output device 10, which emits an acoustic signal AC3 in the direction D1 and an acoustic signal AC4 to the other side. The acoustic signal AC1 is emitted from the sound hole 121a, and a portion of the emitted acoustic signal AC1 enters the right ear 1010 and the left ear 1020 and is heard by the user 1000. In addition, a portion of the acoustic signal AC3 emitted from the driver unit 15 also enters the right ear 1010 and the left ear 1020 and is heard by the user 1000. On the other hand, acoustic signal AC2, which is an opposite phase signal of acoustic signal AC1 or a signal approximating the opposite phase signal, is emitted from sound hole 123a. Furthermore, acoustic signal AC4, which is an opposite phase signal of acoustic signal AC3 or a signal approximating the opposite phase signal, is emitted from driver unit 15. Parts of acoustic signal AC2 and acoustic signal AC4 cancel out part of acoustic signal AC1 emitted from sound hole 121a in direction D2 and part of acoustic signal AC3 emitted from driver unit 15 in direction D2 (sound leakage component).For example, part of the acoustic signal AC2 cancels out part of the acoustic signal AC1 emitted from the sound hole 121a in the direction D2, and part of the acoustic signal AC4 cancels out part of the acoustic signal AC3 emitted from the driver unit 15 in the direction D2.

[0050] <Experimental Results> The following shows the results of an experiment demonstrating the sound leakage suppression effect of the acoustic signal output device 10 of this embodiment. In this experiment, the acoustic signal output device 10 was attached to both ears of a dummy head 1100 simulating a human head, and acoustic signals were observed at positions P1 and P2, as shown in Fig. 15. In this example, position P1 is located near the left ear 1120 of the dummy head 1100 (near the acoustic signal output device 10), and position P2 is located 15 cm outward from position P1.

[0051] In this experiment, the output signal from the playback device 100 is input to the signal separation device 101, where it is separated into a high-frequency band signal on the high-frequency side and a low-frequency band signal on the low-frequency side by a high-pass filter 101a and a low-pass filter 101b. In the experiment, a high-pass filter 101a with a frequency of -24 dB / oct at 1500 Hz and a low-pass filter 101b with a frequency of -24 dB / oct at 1000 Hz were used. The high-frequency band signal is input to the driver unit 11 of the acoustic signal output device 10, which emits an acoustic signal AC1 in the direction D1 and an acoustic signal AC2 to the other side. The low-frequency band signal is input to the driver unit 15 of the acoustic signal output device 10, which emits an acoustic signal AC3 in the direction D1 and an acoustic signal AC4 to the other side.

[0052] FIG. 16A illustrates the frequency characteristics of an acoustic signal observed at position P1 in FIG. 15, and FIG. 16B illustrates the frequency characteristics of an acoustic signal observed at position P2 in FIG. 15. "2way" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high-frequency band and a low-frequency band, and the acoustic signal on the high-frequency band side is emitted from the small-sized driver unit 11, and the acoustic signal on the low-frequency band side is emitted from the large-sized driver unit 15. "WF Th." illustrates the frequency characteristics when the acoustic signal is emitted only from the large-sized driver unit 15 without dividing the frequency band. "TW Th." illustrates the frequency characteristics when the acoustic signal is emitted only from the small-sized driver unit 11 without dividing the frequency band. As shown in FIG. 16A, even though the frequency band is not divided, sufficient sound pressure cannot be obtained in the low range with only the small-sized driver unit 11. Note that in TW Th., the low range is significantly boosted by an equalizer, but despite this, sufficient sound pressure cannot be obtained in the low range. 16B, using only a large-sized driver unit 15 results in significant sound leakage in the high range. For example, in the 1000-6000 Hz band, the sound pressure is up to 30 dB higher with WF Th. compared to 2-way. In contrast, when acoustic signals on the high-frequency band side are emitted from a small-sized driver unit 11 and acoustic signals on the low-frequency band side are emitted from a large-sized driver unit 15, it is clear that sufficient sound pressure can be obtained in the low range and sound leakage can be suppressed over a wide frequency band, including the high range.

[0053] Figure 17A also illustrates the frequency characteristics of an acoustic signal observed at position P1 in Figure 15, and Figure 17B illustrates the frequency characteristics of an acoustic signal observed at position P2 in Figure 15. "2way" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high frequency band and a low frequency band, and acoustic signals on the high frequency band side are emitted from small-sized driver unit 11, and acoustic signals on the low frequency band side are emitted from large-sized driver unit 15. "WF NW" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high frequency band and a low frequency band, and acoustic signals on the low frequency band side are emitted only from large-sized driver unit 15. "TW NW" illustrates the frequency characteristics when the frequency band of the reproduced acoustic signal is divided into a high frequency band and a low frequency band, and acoustic signals on the high frequency band side are emitted only from small-sized driver unit 11. As shown in Fig. 17A, small-sized driver unit 11 alone cannot obtain sufficient sound pressure in the low range, and large-sized driver unit 15 alone cannot obtain sufficient sound pressure in the high range, but by using them together, sufficient sound pressure can be obtained over a wide frequency range including low and high frequencies. Also, as shown in the example of Fig. 17B, by dividing the frequency band of the reproduced sound signal into a high-frequency band and a low-frequency band and emitting them from driver unit 11 and driver unit 15 respectively, sound leakage can be suppressed over a wide frequency range including high frequencies.

[0054] [Second embodiment] The second embodiment is a modification of the first embodiment, in which a shielding plate 16 is further provided on the housing 12 side. As illustrated in FIGS. 18 and 19, the acoustic signal output device 10 of the second embodiment further includes a shielding plate 16 having a through-hole 16a in addition to the components described in the first embodiment. Here, an annular (donut-shaped) shielding plate 16 is illustrated as an example, but the shielding plate 16 may have any other plate shape having a through-hole 16a. The shielding plate 16 is disposed on the D1 direction side (first direction side) of the sound hole 123a (second sound hole) in the external space of the housing 12. The sound hole 121a (first sound hole) or the center of the multiple sound holes 121a (first sound holes) is disposed on or near the axis A1 (specific axis). The through-hole 16a is disposed on or near the axis A1 (specific axis). This prevents the acoustic signal AC2 emitted from the sound hole 123a from reaching the user's ear canal, thereby preventing the acoustic signal AC1 reaching the ear canal from being canceled out by the acoustic signal AC2. Note that FIGS. 18 and 19 show an example in which the plate surface 161 on the D1 direction side of the shielding plate 16 is disposed flush or substantially flush with the outer surface of the wall 121 of the housing 12. However, the shielding plate 16 may be disposed in another position as long as it is disposed closer to the D1 direction than the sound hole 123a. However, it is preferable that the plate surface 162 on the D2 direction side of the shielding plate 16 is disposed closer to the D2 direction than the outer surface of the wall 121 of the housing 12. This prevents the acoustic signal AC1 emitted from the sound hole 121a from being reflected by the plate surface 162 of the shielding plate 16 and being emitted in the D2 direction as a sound leakage component.

[0055] The sizes of the shielding plate 16 and the through-hole 16a may be determined appropriately so that the frequency characteristics and sound pressure of the acoustic signal reaching the ear canal and the sound pressure of the sound leakage component radiated to the surroundings are appropriate. The through-hole 16a is preferably positioned on the axis A1, and more preferably the center of the through-hole 16a is preferably positioned on the axis A1. This allows the acoustic signal reaching the ear canal to be line-symmetric or approximately line-symmetric with respect to the axis A1, thereby reducing changes in the audible sound due to the direction of misalignment of the acoustic signal output device 10 with respect to the ear canal.

[0056] [Third embodiment] In the first embodiment, an example was shown in which multiple sound holes 123a (second sound holes) of the same shape, size, and spacing are provided along the circumference C1. However, this does not limit the present invention. Multiple sound holes 123a of different shapes, sizes, and / or spacing may be provided along the circumference C1.

[0057] Even in such a case, when the circumference C1 is equally divided into a plurality of unit arc regions, it is preferable that the sum of the opening areas of the sound holes 123a (second sound holes) provided along a first arc region, which is one of the unit arc regions, is the same or approximately the same as the sum of the opening areas of the sound holes 123a provided along a second arc region, which is one of the unit arc regions excluding the first arc region.It is more preferable that the sums of the opening areas of the sound holes 123a provided along each unit arc region for each unit arc region are all the same or approximately the same.

[0058] It is sufficient that the plurality of sound holes 123a are arranged along the circumference C1, and it is not necessary that all of the sound holes 123a are arranged strictly on the circumference C1. Furthermore, the position of the circumference C1 is not limited to that exemplified in the first embodiment, and it is sufficient that the position is on a circumference centered on the axis A1.

[0059] Furthermore, as long as a sufficient sound leakage suppression effect can be obtained, all sound holes 123a do not have to be arranged along circumference C1. In other words, some sound holes 123a may be arranged at positions that are off circumference C1. Also, as long as a sufficient sound leakage suppression effect can be obtained, there is no limit to the number of sound holes 123a, and only one sound hole 123a may be provided.

[0060] [Modification of the third embodiment] As described above, a plurality of sound holes 121a may be provided in the region AR1 of the wall portion 121 of the housing 12, or the sound holes 121a may be offset to an eccentric position displaced from the center (central position) of the region AR1 of the wall portion 121 of the housing 12. For example, as illustrated in FIG. 20, a single sound hole 121a may be provided in an eccentric position in the region AR1 (a position on the axis A12 that is offset from the axis A1 and parallel to the axis A1) (hereinafter simply referred to as an "eccentric position"). In other words, the position of a single sound hole 121a provided in the region AR1 may be offset to an eccentric position. Alternatively, as illustrated in FIG. 21, a plurality of sound holes 121a may be provided in the region AR1, and the plurality of sound holes 121a may be offset to an eccentric position on the axis A12 that is offset from the axis A1 and parallel to the axis A1. In other words, the positions of the plurality of sound holes 121a provided in the region AR1 may be offset to an eccentric position. In such a case, it is desirable that driver unit 15 (second driver unit) is also disposed biased to this eccentric position. For example, sound hole 121a (first sound hole) or the center of multiple sound holes 121a (first sound holes) is disposed on axis A12 (on a specific axis) or in the vicinity of axis A12 (axis), and driver unit 11 (first driver unit) emits acoustic signal AC1 (first acoustic signal) in the D1 direction (one side) along axis A12 (axis) and emits acoustic signal AC2 (second acoustic signal) in the D2 direction (other side) along axis A12 (axis). The driver unit 15 (second driver unit) may have a diaphragm 113 (first diaphragm) that emits an acoustic signal AC3 (third acoustic signal) in the direction D1 (one side) along the axis A12 (axis) and a diaphragm 153 (second diaphragm) that emits an acoustic signal AC4 (fourth acoustic signal) in the direction D2 (the other side) along the axis A12 (axis), and the diaphragm 153 (second diaphragm) may be disposed on or near the axis A12 (axis). This makes it possible to position the ear canal at a position where the sound pressure of the driver units 11, 15 is maximized, and acoustic signals with sufficient sound pressure can be presented to the user over a wide frequency band.

[0061] If the position of one or more sound holes 121a or the position of the driver unit 15 is biased to an eccentric position, the distribution and opening area of ​​the sound holes 123a may be biased accordingly. For example, as shown in Fig. 20 or 21, the position of one or more sound holes 121a provided in area AR1 may be biased to an eccentric position on axis A12 that is shifted from axis A1, and the opening area of ​​the sound holes 121a provided in area AR3 may also be biased toward the eccentric position on axis A12, as exemplified in Fig. 22 and Fig. 23. In the example of Fig. 22, the number of sound holes 123a provided along unit arc area C1-3, which is far from the eccentric position on axis A12, is smaller than the number of sound holes 123a provided along unit arc area C1-1, which is closer to the eccentric position. 23, the opening area of ​​each of the sound holes 123a provided along unit arc area C1-3 that is farther from the eccentric position on axis A12 is smaller than the opening area of ​​each of the sound holes 123a provided along unit arc area C1-1 that is closer to the eccentric position. In other words, when circumference C1 is equally divided into multiple unit arc areas, the sum of the opening areas of the sound holes 123a (second sound holes) provided along a first arc area (for example, C1-3) that is one of the unit arc areas is smaller than the sum of the opening areas of the sound holes 123a provided along a second arc area (for example, C1-1) that is one of the unit arc areas that is closer to the eccentric position than the first arc area. When the position of the sound holes 121a is biased toward the eccentric position, the distribution of the acoustic signal AC1 emitted to the outside from the sound holes 121a is also biased toward the eccentric position. Here, by biasing the distribution and opening area of ​​sound hole 123a to the eccentric position, the distribution of acoustic signal AC2 emitted to the outside from sound hole 123a can also be biased to the eccentric position. This allows the emitted acoustic signal AC2 to sufficiently cancel out the sound leakage component of acoustic signal AC1. Also, as mentioned above, it is desirable to position driver unit 15 (second driver unit) biased to this eccentric position. This makes it possible to position the ear canal at a position where the sound pressure of driver units 11 and 15 is at its maximum, and acoustic signals with sufficient sound pressure can be presented to the user over a wide frequency band.

[0062] Furthermore, in the third embodiment, the shielding plate 16 described in the second embodiment may be further provided. This prevents the acoustic signal AC2 emitted from the sound hole 123a from reaching the user's ear canal, thereby preventing the acoustic signal AC1 reaching the ear canal from being canceled out by the acoustic signal AC2. In this case, it is desirable that the shielding plate 16 is also disposed at this eccentric position. For example, it is desirable that the shielding plate 16 is disposed on the D1 direction side (first direction side) of the sound hole 123a (second sound hole) in the external space of the housing 12, that the sound hole 121a (first sound hole) or the center of the multiple sound holes 121a (first sound holes) is disposed on or near the axis A12 (specific axis), and that the through-hole 16a is disposed on or near the axis A12 (specific axis). Furthermore, it is desirable that the through-hole 16a be positioned on the axis A12, and more preferably that the center of the through-hole 16a be positioned on the axis A12. This allows the acoustic signal reaching the ear canal to be line-symmetric or approximately line-symmetric with respect to the axis A12, thereby reducing changes in the audible sound due to the direction of misalignment of the acoustic signal output device 10 with respect to the ear canal. The rest is as described in the second embodiment.

[0063] [Fourth embodiment] In the first to third embodiments and their modified examples, driver unit 15 (second driver unit) may be housed in a housing.

[0064] <Configuration> Acoustic signal output device 40 of the present embodiment is also a device for listening to sound that is worn without sealing the user's ear canal (for example, open-ear earphones, headphones, installed speakers, built-in speakers, etc.). As illustrated in Figures 24 to 27, acoustic signal output device 40 of the present embodiment has a small-sized driver unit 11 that converts an output signal (an electrical signal representing a reproduced acoustic signal) output from a playback device into an acoustic signal and outputs it, a large-sized driver unit 15 that converts the output signal into an acoustic signal and outputs it, a housing 12 that houses driver unit 11 inside, and a housing 42 (second housing) that houses driver unit 15 inside.

[0065] <Case 42> Housing 42 (second housing) is a hollow member with walls on the outside, and sound holes 421a and 423a are provided in the walls, and driver unit 15 is housed inside. Housing 42 in this embodiment is disposed in the external space of housing 12. Driver unit 15 is fixed, for example, to the end of housing 42 on the D1 direction side. However, this does not limit the present invention. Housing 42 housing driver unit 15 is disposed on the D2 direction side of housing 12 housing driver unit 11 (FIGS. 26 and 27). That is, in this embodiment as well, sound hole 121a of housing 12 that emits acoustic signal AC1 is disposed on the D1 direction side (first direction side) of driver unit 11, and driver unit 15 (second driver unit) is disposed in the external space of housing 12, and is disposed on the D2 direction side (second direction side) of driver unit 11. The shape of the housing 42 is not limited, but it is desirable that the shape of the housing 42 be rotationally symmetric (line symmetric) or approximately rotationally symmetric about the axis A1 extending along the D1 direction. This makes it easy to provide sound holes 423a so that the variation in the energy of the sound emitted from the housing 42 between directions is reduced. As a result, it is easy to reduce sound leakage uniformly in each direction. For example, the housing 42 has a first end face that is a wall portion 421 arranged on one side (the D1 direction side) of the driver unit 15, a second end face that is a wall portion 422 arranged on the other side (the D2 direction side) of the driver unit 15, and a side face that is a wall portion 423 that surrounds the space between the first end face and the second end face, centered on the axis A1 that passes through the first end face and the second end face. In this embodiment, for simplicity of explanation, an example is shown in which the housing 42 has an approximately cylindrical shape with both end faces. However, this is merely an example and does not limit the present invention. For example, the housing 42 may be substantially dome-shaped with walls at its ends, may be hollow and substantially cubic, or may have any other three-dimensional shape. Furthermore, there are no limitations on the material from which the housing 42 is made. The housing 42 may be made of a rigid body such as synthetic resin or metal, or may be made of an elastic body such as rubber.The wall of housing 42 is provided with one or more sound holes 321a (third sound holes) that guide acoustic signal AC3 (third acoustic signal) emitted from driver unit 15 to the outside, and one or more sound holes 423a (fourth sound holes) that guide acoustic signal AC4 (fourth acoustic signal) emitted from driver unit 15 to the outside. Sound holes 421a and 423a are, for example, through holes that penetrate the wall of housing 42, but this does not limit the present invention. Sound holes 421a and 423a do not have to be through holes as long as they can guide acoustic signal AC3 and acoustic signal AC4 to the outside, respectively.

[0066] Sound hole 421a (third sound hole) in this embodiment is provided in area AR41 of wall portion 421 arranged on one side of driver unit 15 (the D1 direction side, which is the side from which acoustic signal AC3 is emitted) (FIGS. 24 to 27). That is, sound hole 421a opens facing direction D1 (first direction) along axis A1. In other words, sound hole 421a opens facing the housing 12 and driver unit 11 side. Furthermore, sound hole 423a (fourth sound hole) in this embodiment is provided in area AR43 of wall portion 423 that contacts area AR40 between area AR41 of wall portion 421 of housing 42 and area AR42 of wall portion 422 arranged on the D2 direction side of driver unit 15 (the other side, which is the side from which acoustic signal AC4 is emitted) (FIG. 27). In other words, if the center of the housing 42 is used as a reference and the direction between the D1 direction (first direction) and the opposite direction of the D1 direction is defined as the D42 direction (second direction), sound hole 421a (third sound hole) is provided on the D1 direction side (first direction side) of the housing 42, and sound hole 423a (fourth sound hole) is provided on the D42 direction side (second direction side) of the housing 42. For example, if housing 42 has a third end face that is wall portion 421 arranged on one side (D1 direction side) of driver unit 15, a fourth end face that is wall portion 422 arranged on the other side (D2 direction side) of driver unit 15, and a side face that is wall portion 423 that surrounds the space between the third and fourth end faces, centered on axis A1 that passes through the third and fourth end faces and is along the emission direction (D1 direction) of acoustic signal AC3, sound hole 421a (third sound hole) is provided in the third end face, and sound hole 423a (fourth sound hole) is provided in the side face. In this embodiment, it is desirable not to provide a sound hole on the wall portion 422 side of housing 42. This is because if a sound hole were provided on the wall portion 422 side of housing 42, the sound pressure level of acoustic signal AC4 emitted from housing 42 would exceed the level necessary to cancel out the sound leakage component of acoustic signal AC3, and this excess may be perceived as sound leakage.

[0067] As described above, the acoustic signals AC3 and AC4 emitted from the sound holes 421a and 423a of the housing 42 are acoustic signals on the low-frequency side of the reproduced acoustic signals. On the other hand, the acoustic signals AC1 and AC2 emitted from the sound holes 121a and 123a of the housing 12 are acoustic signals on the high-frequency side of the reproduced acoustic signals. As described above, the lower the frequency, the greater the sound leakage prevention effect. Therefore, the sound leakage prevention effect of the acoustic signal AC4 of the acoustic signal AC3 emitted from the sound hole 421a is greater than the sound leakage prevention effect of the acoustic signal AC1 of the acoustic signal AC2 emitted from the sound hole 121a. Therefore, even if the total opening area of ​​the sound holes 421a of the housing 42 is made larger than the total opening area of ​​the sound holes 121a of the housing 12, the impact of sound leakage of the acoustic signal AC3 emitted from the sound hole 421a is small. On the other hand, by increasing the total opening area of ​​the sound holes 421a of the housing 42, the low-frequency sound pressure heard by the user can be increased. Therefore, it is preferable that the sum of the opening areas of the sound holes 421a of the housing 42 (opening area of ​​the third sound holes) is larger than the sum of the opening areas of the sound holes 121a of the housing 12 (opening area of ​​the first sound holes). For the same reason, the sum of the opening areas of the sound holes 423a of the housing 42, S 44 The total opening area of ​​the sound holes 421a for 43 The ratio (the ratio of the opening area of ​​the third sound hole to the opening area of ​​the fourth sound hole) is calculated by multiplying the total opening area S of the sound holes 123a of the housing 12 by the ratio S 42 The total opening area S of the sound holes 121a 41 (the ratio of the opening area of ​​the first tone hole to the opening area of ​​the second tone hole) (i.e., S 43 / S 44 >S 41 / S 42 ) is desirable. In this embodiment, driver unit 15 is housed in housing 42, and because the opening area of ​​sound hole 421a can be made large, sound with a natural sound quality can be reproduced. Furthermore, because the opening area of ​​sound hole 421a can be made large, the sound heard does not change much even if the positional relationship between housing 42 and the ear canal changes, and sufficient sound quality can be ensured even if there is some misalignment in the wearing state.

[0068] The relative position of the housing 12 with respect to the housing 42 may or may not be fixed. For example, the housing 12 may be fixed to the housing 42 by a member not shown. For example, the housing 12 may be attached to the housing 42 by a member not shown so that the relative position with respect to the housing 42 is adjustable (so that the housing 12 can be fixed to a desired relative position with respect to the housing 42). The housing 12 and the housing 42 may not be separate bodies, but may be integrated. The arrangement of the sound holes 421a, 423a of the other parts of the housing 42 is the same as the arrangement of the sound holes 121a, 123a of the housing 12 described in the first to third embodiments and their modified examples.

[0069] Acoustic signal AC1 emitted from sound hole 121a and acoustic signal AC3 emitted from sound hole 421a reach the user's ear canal and are heard by the user. Meanwhile, acoustic signal AC2, which is an inverse phase signal of acoustic signal AC1 or a signal approximating the inverse phase signal, is emitted from sound hole 123a. Acoustic signal AC4, which is an inverse phase signal of acoustic signal AC3 or a signal approximating the inverse phase signal, is emitted from sound hole 423a. Portions of the emitted acoustic signals AC2 and AC4 cancel out portions of the emitted acoustic signals AC1 and AC3 (sound leakage components). This makes it possible to suppress sound leakage. Furthermore, acoustic signal AC3 makes it possible to obtain sufficient low-frequency sound pressure. Other matters are as described in the first to third embodiments and their modifications.

[0070] [Modification of the fourth embodiment] For example, the center of sound hole 121a (first sound hole) or multiple sound holes 121a (first sound holes) in housing 12 and the center of sound hole 421a (third sound hole) or multiple sound holes 421a (third sound holes) in housing 42 may be located on axis A1 (on a specific axis) or near axis A1 (axis). This makes it possible to position the ear canal at a position where the sound pressure of acoustic signal AC1 emitted from sound hole 121a and acoustic signal AC3 emitted from sound hole 421a is at its maximum, allowing the user to be presented with acoustic signals of sufficient sound pressure over a wide frequency band. Furthermore, by arranging driver unit 11 and driver unit 15 coaxially, the distance between driver units 11 and 15 can be changed coaxially, making it easy to adjust the sound pressure of the acoustic signal to be heard and the amount of sound leakage.

[0071] [Other variations] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the invention as defined in the claims. [Explanation of symbols]

[0072] 1,10,40 Acoustic signal output device 11,15 driver unit 12,42 Case 16 Shielding plate 113,153 Vibration plate

Claims

1. An acoustic signal output device, A frequency band of a reproduced sound signal is divided into a high frequency band and a low frequency band, and a first driver unit that emits a sound signal on the high frequency band side of the reproduced sound signal; A housing that houses the first driver unit therein; a second driver unit that is larger in size than the first driver unit and emits acoustic signals on the low frequency band side of the reproduced acoustic signals, an acoustic signal emitted from the first driver unit to one side is defined as a first acoustic signal, and an acoustic signal emitted from the first driver unit to the other side is defined as a second acoustic signal; an acoustic signal emitted from the second driver unit to one side is a third acoustic signal, and an acoustic signal emitted from the second driver unit to the other side is a fourth acoustic signal; a wall portion of the housing is provided with one or more first sound holes through which the first acoustic signal is guided to the outside, and one or more second sound holes through which the second acoustic signal is guided to the outside, When the first acoustic signal is emitted from the first sound hole, the second acoustic signal is emitted from the second sound hole, and the third acoustic signal and the fourth acoustic signal are emitted from the second driver unit, the attenuation rates of the first acoustic signal and the third acoustic signal at a second point that is farther from the acoustic signal output device than a predetermined first point at which the first acoustic signal and the third acoustic signal arrive are: a predetermined value smaller than the attenuation rate of the acoustic signal at the second point relative to the first point due to air propagation; Is designed to be: attenuation amounts of the first acoustic signal and the third acoustic signal at the second point relative to the first point, a predetermined value greater than the attenuation of the acoustic signal due to air propagation at the second point relative to the first point; It is designed to be more than the first sound hole or a center of the plurality of first sound holes is disposed on a specific axis or in the vicinity of the axis, the first driver unit has a first diaphragm that emits the first acoustic signal to one side along the axis and emits the second acoustic signal to the other side along the axis, the second driver unit has a second diaphragm that emits the third acoustic signal to one side along the axis and emits the fourth acoustic signal to the other side along the axis, the second diaphragm is disposed on or near the axis; Acoustic signal output device.

2. An acoustic signal output device, A frequency band of a reproduced sound signal is divided into a high frequency band and a low frequency band, and a first driver unit that emits a sound signal on the high frequency band side of the reproduced sound signal; A housing that houses the first driver unit therein; a second driver unit that is larger in size than the first driver unit and emits acoustic signals on the low frequency band side of the reproduced acoustic signals, an acoustic signal emitted from the first driver unit to one side is defined as a first acoustic signal, and an acoustic signal emitted from the first driver unit to the other side is defined as a second acoustic signal; an acoustic signal emitted from the second driver unit to one side is a third acoustic signal, and an acoustic signal emitted from the second driver unit to the other side is a fourth acoustic signal; a wall portion of the housing is provided with one or more first sound holes through which the first acoustic signal is guided to the outside, and one or more second sound holes through which the second acoustic signal is guided to the outside, When the first acoustic signal is emitted from the first sound hole, the second acoustic signal is emitted from the second sound hole, and the third acoustic signal and the fourth acoustic signal are emitted from the second driver unit, the attenuation rates of the first acoustic signal and the third acoustic signal at a second point that is farther from the acoustic signal output device than a predetermined first point at which the first acoustic signal and the third acoustic signal arrive are: a predetermined value smaller than the attenuation rate of the acoustic signal at the second point relative to the first point due to air propagation; Is designed to be: attenuation amounts of the first acoustic signal and the third acoustic signal at the second point relative to the first point, a predetermined value greater than the attenuation of the acoustic signal due to air propagation at the second point relative to the first point; It is designed to be more than the first sound hole is disposed on a first direction side of the first driver unit, the second driver unit is disposed in the external space of the housing and on the second direction side of the first driver unit, The second direction is opposite or substantially opposite to the first direction. Acoustic signal output device.

3. 3. The acoustic signal output device of claim 2, Further, a shielding plate having a through hole is provided, the shielding plate is disposed on the first direction side of the second sound hole in the external space of the housing, the first sound hole or a center of the plurality of first sound holes is disposed on a specific axis or in the vicinity of the axis, The through hole is disposed on or near the axis. Acoustic signal output device.

4. 4. The acoustic signal output device according to claim 1, Further comprising a second housing that houses the second driver unit therein, a wall portion of the second housing is provided with one or more third sound holes through which the third acoustic signal is guided to the outside, and one or more fourth sound holes through which the fourth acoustic signal is guided to the outside, an opening area of ​​the third sound hole is larger than an opening area of ​​the first sound hole;

5. 4. The acoustic signal output device according to claim 1, Further comprising a second housing that houses the second driver unit therein, a wall portion of the second housing is provided with one or more third sound holes through which the third acoustic signal is guided to the outside, and one or more fourth sound holes through which the fourth acoustic signal is guided to the outside, an acoustic signal output device, wherein a ratio of an opening area of ​​the third sound hole to an opening area of ​​the fourth sound hole is greater than a ratio of an opening area of ​​the first sound hole to an opening area of ​​the second sound hole.

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