WO2024252549A1 - Headphone device and acoustic signal output method - Google Patents

Abstract

The purpose of the present invention is to provide a headphone device that positions a virtual sound source at an arbitrary location while suppressing an operation amount, and that uses a plurality of acoustic signal output devices. This headphone device includes an acoustic signal output device array including a plurality of acoustic signal output devices for achieving local reproduction based on a dipole sound source, the acoustic signal output devices being arranged so as to surround the auricle. An input signal of an acoustic signal output device included in the acoustic signal output device array is obtained by signal-processing an electric signal representing an acoustic signal on the basis of a physical quantity determined by a positional relationship between the virtual sound source and the acoustic signal output device in order to position the virtual sound source.

Description

Headphone device and audio signal output method

The present invention relates to a headphone device that is configured using multiple audio signal output devices.

Technologies for localizing a virtual sound source at any position using multiple speakers include those described in Non-Patent Document 1 and Non-Patent Document 2. In Non-Patent Document 1, the virtual sound source is localized using the Head Related Transfer Function (HRTF). In Non-Patent Document 2, the virtual sound source is localized by simulating the incoming wavefront around the ear using wave field synthesis.

Jens Blauert, Masayuki Morimoto, Toshiyuki Goto, "Spatial Acoustics," Kashima Publishing Co., pp.204-206, 1986. Shoichi Koyama, "Mathematical problems in sound field reproduction technology: Mathematics of wave field synthesis and higher-order Ambisonics," Journal of the Acoustical Society of Japan, Vol. 68, No. 11, pp. 584-589, 2012.

Instead of using multiple speakers, it is also possible to localize a virtual sound source by using headphones equipped with multiple audio signal output devices equivalent to speakers. However, when using the techniques described in Non-Patent Document 1 and Non-Patent Document 2, the amount of calculation required to localize the virtual sound source becomes large.

The present invention aims to provide a headphone device that uses multiple audio signal output devices and localizes a virtual sound source at any position while minimizing the amount of calculations.

One aspect of the present invention is a headphone device including an acoustic signal output device array including acoustic signal output devices that realize localized reproduction based on a dipole sound source arranged to surround the auricle, and the input signal of the acoustic signal output device included in the acoustic signal output device array is a signal obtained by signal processing an electrical signal representing an acoustic signal based on a physical quantity determined by the positional relationship between the virtual sound source and the acoustic signal output device in order to localize the virtual sound source.

The present invention makes it possible to localize a virtual sound source at any position while minimizing the amount of calculation required.

FIG. 1 is a see-through perspective view illustrating the configuration of an acoustic signal output device 10. As shown in FIG. Fig. 2A is a transparent plan view illustrating the configuration of the acoustic signal output device 10. Fig. 2B is a transparent front view illustrating the configuration of the acoustic signal output device 10. Fig. 2C is a bottom view illustrating the configuration of the acoustic signal output device 10. Figure 3A is an end view of 2BA-2BA of Figure 2B, Figure 3B is an end view of 2A-2A of Figure 2A, and Figure 3C is an end view of 2BC-2BC of Figure 2B. FIG. 4 is a conceptual diagram illustrating the arrangement of sound holes. FIG. 5 is a front view illustrating the configuration of the headphone device 20. As shown in FIG. FIG. 6 is a side view illustrating the configuration of the headphone device 20. As shown in FIG. FIG. 7 is a top view illustrating the configuration of the headphone device 20. As shown in FIG. FIG. 8 is a diagram illustrating a frame of the acoustic signal output device array 211. As shown in FIG. FIG. 9 is a diagram illustrating an acoustic signal output device array 211 including four acoustic signal output devices 212 .

Below, an embodiment of the present invention will be described in detail. Components having the same functions will be given the same numbers, and duplicate explanations will be omitted.

<Technical Background>
In an embodiment of the present invention, a headphone device including an audio signal output device array including a plurality of audio signal output devices that realize local reproduction based on a dipole sound source is used. Here, local reproduction based on a dipole sound source refers to reproduction utilizing the characteristic of a dipole sound source, in which the sound pressure is high only in the vicinity of the sound source and the sound pressure drops rapidly when moving away from the sound source. The reproduction method using a plurality of such audio signal output devices is theoretically equivalent to reproduction of a sound field based on the second kind of Rayleigh integral derived from the Kirchhoff-Helmholtz integral equation (see Reference Non-Patent Document 1). In addition, in this reproduction method, since the sound pressure is high only in the vicinity of each audio signal output device, sounds leaking from each audio signal output device do not interfere with each other, and it is possible to prevent amplification of sound leakage due to interference. Therefore, this reproduction method has the characteristic of less sound leakage to the surroundings.

(Reference non-patent document 1: Akio Ando, "Research trends in acoustic systems based on physical acoustic models," NHK STRL R&D, March 2011 issue, Commentary 02, 2011.)
In the following, it will be explained that local reproduction based on a dipole sound source and a reproduction method using multiple acoustic signal output devices to realize local reproduction based on a dipole sound source correspond to reproduction of a sound field based on the Rayleigh integral of the second kind.

First, local reproduction based on a dipole sound source will be described. A dipole sound source is a sound source in which a positive phase sound source and a negative phase sound source are arranged adjacent to each other. When a dipole sound source is described as an infinitesimal positive and negative dual sound source, the sound from the positive phase sound source and the sound from the negative phase sound source cancel each other out regardless of frequency, resulting in a directional characteristic of a figure of eight (see Reference Non-Patent Document 2). However, since the size of the sound source is actually finite, the cancellation area becomes wider as the frequency of the sound that is easily diffracted (i.e., the wavelength is long). However, in the vicinity of the positive phase sound source, the sound from the positive phase sound source and the sound from the negative phase sound source do not cancel out completely due to the distance attenuation and phase difference that occur in the process of diffraction of the sound from the negative phase sound source. For this reason, local reproduction is possible when a dipole sound source is used. Note that a single speaker driver unit can also be considered as a positive and negative dual sound source, so an acoustic signal output device that realizes local reproduction based on a dipole sound source can be configured using one speaker driver unit. An example of such a configuration will be described later.

(Reference non-patent document 2: Masao Nishimaki, "Revised Edition of Electroacoustic Vibration Science," Corona Publishing, pp. 58-59, 1980.)
Next, it will be explained that the reproduction method using a plurality of sound signal output devices that realizes local reproduction based on a dipole sound source corresponds to reproduction of a sound field based on the Rayleigh integral of the second kind. According to the reference non-patent document 1, the Kirchhoff-Helmholtz integral equation can be transformed into the Rayleigh integral of the first kind and the Rayleigh integral of the second kind (see formulas (4) and (5) in the reference non-patent document 1). If sound pressure is treated as a velocity potential, the spatial derivative of sound pressure corresponds to particle velocity. If the boundary plane S1 is a rigid body, the particle velocity on the plane S1 becomes zero, so the Rayleigh integral of the first kind disappears. In addition, as can be seen from formula (5) in the reference non-patent document 1, the Rayleigh integral of the second kind is an integral of the product of sound pressure and a dipole function on the plane S1, but in practice, the Rayleigh integral of the second kind can be regarded as the sum of the products of sound pressure and dipole function when dipole sound sources are discretely arranged. Therefore, a reproduction method using a plurality of sound signal output devices that realizes local reproduction based on a dipole sound source can be said to correspond to reproduction of a sound field based on the Rayleigh integral of the second kind.

<<Example of configuration of an acoustic signal output device that realizes local reproduction based on a dipole sound source>>
[composition]
The acoustic signal output device 10 is an acoustic signal output device that outputs an acoustic signal from a dipole sound source, and can be used, for example, in open-ear headphones, which are acoustic listening devices worn without sealing the ear canal of a listener. As illustrated in Fig. 1, Fig. 2A, Fig. 2B, Fig. 2C, Fig. 3A, Fig. 3B, and Fig. 3C, the acoustic signal output device 10 has a driver unit 11 that converts an output signal (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.

[Driver unit 11]
The driver unit (speaker driver unit) 11 is a device (device having a speaker function) that emits (emits sound) an acoustic signal AC1 (first acoustic signal) based on an input output signal to one side (D1 direction side) and emits an acoustic signal AC2 (second acoustic signal) that is an inverse phase signal (phase inversion signal) of the acoustic signal AC1 or an approximation signal of the inverse phase signal to the other side (D2 direction side). That is, the acoustic signal emitted from the driver unit 11 to one side (D1 direction side) is called the acoustic signal AC1 (first acoustic signal), and the acoustic signal emitted from the driver unit 11 to the other side (D2 direction side) is called the acoustic signal AC2 (second acoustic signal). For example, the driver unit 11 includes a diaphragm 113 that emits the acoustic signal AC1 from one surface 113a in the D1 direction by vibration and emits the acoustic signal AC2 from the other surface 113b in the D2 direction by this vibration (see FIG. 2B). In this example, the driver unit 11 emits the acoustic signal AC1 from the surface 111 on one side in the D1 direction by vibrating the diaphragm 113 based on the input output signal, and emits the acoustic signal AC2, which is an inverse phase signal of the acoustic signal AC1 or an approximation of the inverse phase signal, from the other side 112 in the D2 direction. That is, the acoustic signal AC2 is emitted secondarily with the emission of the acoustic signal AC1. Note that the D2 direction (the 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 to the D1 direction, as long as the D2 direction is different from the D1 direction. The relationship between the one side (D1 direction) and the other side (D2 direction) depends on the type and shape of the driver unit 11. Also, depending on the type and shape of the driver unit 11, the acoustic signal AC2 may be strictly an inverse phase signal of the acoustic signal AC1, or the acoustic signal AC2 may be an approximation of the inverse phase signal of the acoustic signal AC1. For example, the approximation signal of the opposite phase signal of the acoustic signal AC1 may be (1) a signal obtained by shifting the phase of the opposite phase signal of the acoustic signal AC1, (2) a signal obtained by changing (amplifying or attenuating) the amplitude of the opposite phase signal of the acoustic signal AC1, or (3) a signal obtained by shifting the phase of the opposite phase signal of the acoustic signal AC1 and further changing the amplitude. The phase difference between the opposite phase signal of the acoustic signal AC1 and its approximation signal is desirably δ ₁ % or less of one period of the opposite phase signal of the acoustic signal AC1. Examples of δ ₁ % are 1%, 3%, 5%, 10%, 20%, etc. Moreover, the difference between the amplitude of the opposite phase signal of the acoustic signal AC1 and the amplitude of its approximation signal is desirably δ ₂ % or less of the amplitude of the opposite phase signal of the acoustic signal AC1. Examples of _{δ 2} % are 1%, 3%, 5%, 10%, 20%, etc. In addition, examples of the type of the driver unit 11 include a dynamic type, a balanced armature chair type, a hybrid type of a dynamic type and a balanced armature type, and a condenser type. In addition, there is no limitation on the shape of the driver unit 11 and the diaphragm 113. Here, for the sake of simplicity of explanation, an example is shown in which the outer shape of the driver unit 11 is a substantially cylindrical shape with both end faces, and the diaphragm 113 is a substantially disc shape, but this does not limit the acoustic signal output device 10. For example, the outer shape of the driver unit 11 may be a rectangular parallelepiped shape, and the diaphragm 113 may be a dome shape. In addition, examples of the acoustic signal are sounds such as music, voice, sound effects, and environmental sounds.

Note that acoustic signal AC1 and acoustic signal AC2 are acoustic signals from a positive-phase sound source and a negative-phase sound source, respectively.

[Housing 12]
The housing 12 is a hollow member having a wall on the outside, and houses the driver unit 11 inside. For example, the driver unit 11 is fixed to the end of the housing 12 on the D1 direction side. However, this does not limit the acoustic signal output device 10. There is no limitation on the shape of the housing 12, but for example, it is desirable that the shape of the housing 12 is rotationally symmetric (line symmetric) or approximately rotationally symmetric about the axis A1 extending along the D1 direction. This makes it easy to provide a sound hole 123a (described in detail later) so that the variation in the energy of the sound emitted from the housing 12 for each direction is reduced. As a result, it becomes easy to reduce sound leakage uniformly in each direction. For example, the housing 12 has a first end face which is a wall portion 121 arranged on one side (D1 direction side) of the driver unit 11, a second end face which is a wall portion 122 arranged on the other side (D2 direction side) of the driver unit 11, and a side face which is a wall portion 123 which surrounds the space between the first end face and the second end face and is centered on an axis line A1 passing through the first end face and the second end face (see FIG. 2B and FIG. 3B). Here, for the sake of simplicity of explanation, an example is shown in which the housing 12 has a substantially cylindrical shape with both end faces. For example, the distance between the wall portion 121 and the wall portion 122 is 10 mm, and the walls 121 and 122 are circular with a radius of 10 mm. However, these are only examples and do not limit the acoustic signal output device 10. For example, the housing 12 may be a substantially dome-shaped shape with walls at the ends, a hollow substantially cubic shape, or any other three-dimensional shape. There is also no limitation on the material that constitutes the housing 12. The 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.

[Sound holes 121a, 123a]
The wall of the housing 12 is provided with a sound hole 121a (first sound hole) for guiding the acoustic signal AC1 (first acoustic signal) emitted from the driver unit 11 to the outside, and a sound hole 121b (second sound hole) for guiding the acoustic signal AC2 (first acoustic signal) emitted from the driver unit 11 to the outside. The sound hole 121a and the sound hole 123a are, for example, through holes that penetrate the wall of the housing 12. However, this does not limit the acoustic signal output device 10. As long as the acoustic signals AC1 and AC2 can be output to the outside, the sound holes 121a and 123a do not have to be through holes. .

The acoustic signal AC1 emitted from the sound hole 121a reaches the ear canal of the listener and is heard by the listener. 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 of the acoustic signal AC1 emitted from the sound hole 121a (sound leakage component). 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 ₁₁ of the acoustic signal AC1 (first acoustic signal) at the position P2 (second point) based on the position P1 (first point) can be set to a predetermined value η _th or less, and the attenuation amount η ₁₂ of the acoustic signal AC1 (first acoustic signal) at the position P2 (second point) based on the position P1 (first point) can be set to a predetermined value ω _{th or} more. 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 10 than the position P1 (first point). The predetermined value η _th is a value smaller (lower) than the attenuation rate η ₂₁ of an arbitrary or specific acoustic signal (sound) due to air propagation at a position P2 (second position) based on the position P1 (first position). The predetermined value ω _th is a value larger than the attenuation amount η ₂₂ of an arbitrary or specific acoustic signal (sound) due to air propagation at a position P2 (second position) based on the position P1 (first position). That is, the acoustic signal output device 10 is designed so that the attenuation rate η ₁₁ is equal to or smaller than a predetermined value η _th smaller than the attenuation rate η ₂₁ , or the attenuation amount η ₁₂ is equal to or larger than a predetermined value ω _th larger than the attenuation amount η _22. The acoustic signal AC1 is propagated through the air from the position P1 to the position P2, and is attenuated due to this air propagation and the acoustic signal AC2. The attenuation rate _η11 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 signal AC2 to the magnitude _AMP1 (AC1) of the acoustic signal AC1 at position P1. Moreover, the attenuation amount _η12 is the difference (| _AMP1 (AC1) _-AMP2 (AC1)|) between the magnitude _AMP1 (AC1) and the magnitude _AMP2 ( _AC1 ). On the other hand, if the acoustic signal AC2 is not assumed, any or a specific acoustic signal _ACar propagated through the air from position P1 to position P2 is attenuated due to air propagation, not due to the acoustic signal AC2. The attenuation rate _η21 is the ratio ( _{AMP2(ACar)/AMP1} ( _ACar )) of the magnitude _AMP2 ( _ACar ) of the acoustic signal _ACar at position P2 attenuated due to air propagation (attenuation without being due to the acoustic signal AC2) to the magnitude AMP1( _ACar ) of the acoustic signal _ACar at position P1. The attenuation amount _η22 is the difference (| _AMP1 ( _{ACar ) -AMP2} ( _ACar )|) between the magnitude _AMP1 ( _ACar ) and _the magnitude _AMP2 ( _ACar ). Examples of the magnitude of the acoustic _signal include the sound pressure of the acoustic signal or the energy of the acoustic signal. Further, the "sound leakage component" means, 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 listener wearing the acoustic signal output device 10 (for example, a person other than the listener wearing the acoustic signal output device 10). For example, the "sound leakage component" means a component of the acoustic signal AC1 that propagates in a direction other than the D1 direction. 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 part of the direct wave of the acoustic signal AC1 emitted from the sound hole 121a (sound leakage component) is offset by interference with at least a part of the direct wave of the acoustic signal AC2 emitted from the sound hole 123a. However, this does not limit the acoustic signal output device 10, and this offsetting can occur with 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 cancelled out by at least one of the direct wave and the reflected wave of the acoustic signal AC2 emitted from the sound hole 123a. This makes it possible to suppress sound leakage.

The following shows an example of the arrangement of sound holes 121a and 123a.

Sound hole 121a (first sound hole) is provided in area AR1 (first area) of wall 121 arranged on one side of driver unit 11 (the D1 direction side where acoustic signal AC1 is emitted) (see Figures 1, 2A, 2B, and 3B). That is, sound hole 121a opens facing the D1 direction (first direction) along axis A1. Also, sound hole 123a (second sound hole) is provided in area AR3 of wall 123 adjacent to area AR between area AR1 (first area) of wall 121 of housing 12 and area AR2 (second area) of wall 122 arranged on the D2 direction side of driver unit 11 (the other side where acoustic signal AC2 is emitted). In other words, if the center of the housing 12 is used as a reference and the direction between the D1 direction (first direction) and the opposite direction to the D1 direction is the D12 direction (second direction) (see 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 the housing 12 has a first end face which is a wall portion 121 arranged on one side (D1 direction side) of the driver unit 11, a second end face which is a wall portion 122 arranged on the other side (D2 direction side) of the driver unit 11, and a side face which is a wall portion 123 which surrounds the space between the first end face and the second end face and is centered on an axis A1 along the emission direction (D1 direction) of the acoustic signal AC1 passing through the first end face and the second end face (see FIG. 2B and FIG. 3B), the sound hole 121a (first sound hole) is provided on the first end face, and the sound hole 123a (second sound hole) is provided on the side face. In addition, no sound hole is provided on the wall portion 122 side of the housing 12. If a sound hole is provided on the wall portion 122 side of the housing 12, the sound pressure level of the acoustic signal AC2 emitted from the housing 12 exceeds the level necessary to offset the sound leakage component of the acoustic signal AC1, and the excess is perceived as sound leakage.

As illustrated in FIG. 2A etc., the sound hole 121a is disposed on or near the axis A1 along the emission direction (D1 direction) of the acoustic signal AC1. The axis A1 passes through the center or near the center of the area AR1 (first area) of the wall 121 disposed on one side (D1 direction side) of the driver unit 11 of the housing 12. For example, the axis A1 is an axis extending in the D1 direction through the central area of the housing 12. That is, the sound hole 121a is provided at the central position of the area AR1 of the wall 121 of the housing 12. Here, for the sake of simplicity of explanation, an example is shown in which the edge shape of the open end of the sound hole 121a is a circle (the open end is circular). The radius of such a sound hole 121a is, for example, 3.5 mm. However, this does not limit the acoustic signal output device 10. For example, the edge shape of the open end of the sound hole 121a may be other shapes such as an ellipse, a rectangle, a triangle, etc. Also, the open end of the sound hole 121a may be in a mesh pattern. In other words, the open end of the sound hole 121a may be composed of multiple holes. Also, for the sake of simplicity, an example is shown in which one sound hole 121a is provided in the area AR1 (first area) of the wall 121 of the housing 12. However, this does not limit the acoustic signal output device 10. For example, two or more sound holes 121a may be provided in the area AR1 (first area) of the wall 121 of the housing 12.

It is desirable that the sound hole 123a (second sound hole) be positioned taking into consideration the following points, for example:

(1) Positioning: Sound hole 123a is positioned so that the propagation path of the sound leakage component of sound signal AC1 to be cancelled overlaps with the propagation path of sound signal AC2 emitted from sound hole 123a.

(2) From the perspective of area: The propagation area of the acoustic signal AC2 emitted from the sound hole 123a and the frequency characteristics of the housing 12 vary depending on the opening area of the sound hole 123a. Furthermore, the frequency characteristics of the housing 12 affect the frequency characteristics of the acoustic signal AC2 emitted from the sound hole 123a, i.e., the amplitude at each frequency. Taking into consideration the propagation area and frequency characteristics of the acoustic signal AC2 emitted from the sound hole 123a, the opening area of the sound hole 123a is determined so that in the area where the sound leakage components are to be cancelled out, the sound leakage components are cancelled out by the acoustic signal AC2 emitted from the sound hole 123a.

In view of the above, it is desirable that the sound hole 123a (second sound hole) be configured as follows, for example.

For example, as illustrated in Figures 2B, 3A, and 3C, it is desirable that the sound holes 123a (second sound holes) are provided along a circumference (circle) C1 centered on the axis A1 along the emission direction of the acoustic signal AC1 (first acoustic signal). When multiple sound holes 123a are provided along the circumference C1, the acoustic signal AC2 is emitted radially (radially centered on the axis A1) from the sound holes 123a to the outside. Here, the sound leakage component of the acoustic signal AC1 is also emitted radially (radially centered on the axis A1) from the sound hole 121a to the outside. Therefore, by providing multiple sound holes 123a along the circumference C1, the sound leakage component of the acoustic signal AC1 can be appropriately canceled by the acoustic signal AC2. Here, for the sake of simplicity, an example is shown in which multiple sound holes 123a are provided on the circumference C1. However, it is sufficient that the multiple 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.

Furthermore, 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 any of the unit arc regions, is the same 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 any of the unit arc regions excluding the first arc region. For example, as illustrated in FIG. 4, when the 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 (for example, unit arc region C1-1) that is one of the unit arc regions C1-1, ..., C1-4 is the same 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 (for example, unit arc region C1-2) that is one of the unit arc regions excluding the first arc region. Note that, for the sake of simplicity of explanation, an example in which the circumference C1 is equally divided into four unit arc regions C1-1, ..., C1-4 is shown here, but this does not limit the acoustic signal output device 10. In addition, "α1 and α2 are approximately the same" means that the difference between α1 and α2 is β% or less of α1. Examples of β% are 3%, 5%, 10%, etc. As a result, the sound pressure distribution of the acoustic signal AC2 emitted from the sound hole 123a provided along the first arc region and the sound pressure distribution of the acoustic signal AC2 emitted from the sound hole 123a provided along the second arc 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 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 hole 123a is point symmetric or approximately point symmetric with respect to the axis A1. As a result, the sound leakage component of the acoustic signal AC1 can be more appropriately canceled out by the acoustic signal AC2.

More preferably, the multiple sound holes 123a are 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 signal AC1 can be more appropriately cancelled out by the acoustic signal AC2. However, this is not a limitation of the acoustic signal output device 10.

More 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 (see 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 cancelled out by acoustic signal AC2.

Here, for the sake of simplicity, an example is shown in which the edge of the open end of the sound hole 123a is rectangular (the open end is square), but this does not limit the acoustic signal output device 10. For example, the edge of the open end of the sound hole 123a may be circular, elliptical, triangular, or other shapes. The open end of the sound hole 123a may also be mesh-like. In other words, the open end of the sound hole 123a may be composed of multiple holes. There is also no limit to the number of sound holes 123a, and a single sound hole 123a may be provided in the area AR3 of the wall 123 of the housing 12, or multiple sound holes 123a may be provided.

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. This allows the sound leakage component of the acoustic signal AC1 to be appropriately cancelled out by the acoustic signal AC2.

The sound leakage suppression performance may also depend on the ratio between the area of the wall 123 in which the sound hole 123a is provided and the opening area of the sound hole 123a. For example, assume that the housing 12 has a first end face which is the wall 121 arranged on one side (D1 direction side) of the driver unit 11, a second end face which is the wall 122 arranged on the other side (D2 direction side) of the driver unit 11, and a side face which is the wall 123 surrounding the space between the first end face and the second end face around the axis A1 along the emission direction (D1 direction) of the acoustic signal AC1 passing through the first end face and the second end face, and the sound hole 121a (first sound hole) is provided on the first end face, and the sound hole 123a (second sound hole) is provided on the side face (see FIG. 2B and FIG. 3B). In such a case, it is desirable that the ratio _S2 / _S3 of the sum _{S2 of the opening areas of the sound holes 123a to the total area S3 of} the side surfaces is 1/20≦ _S2 / _S3 ≦1/5. This allows the sound leakage component of the acoustic signal AC1 to be appropriately cancelled by the acoustic signal AC2. However, this does not limit the acoustic signal output device 10.

First Embodiment
The headphone device 20 will be described below with reference to Fig. 5 to Fig. 7. Fig. 5 to Fig. 7 are all diagrams showing the configuration of the headphone device 20, with Fig. 5 being a front view of the headphone device 20 seen from the front, Fig. 6 being a side view of the headphone device 20 seen from the left side, and Fig. 7 being a top view of the headphone device 20 seen from above. As shown in Fig. 5, the headphone device 20 includes a right headphone 21R, a left headphone 21L, and a headband 22. The headphone device 20 is configured such that the right headphone 21R and the left headphone 21L are connected to the left and right ends of the headband 22. Both the right headphone 21R and the left headphone 21L have an acoustic signal output device array 211. The acoustic signal output device array 211 includes a plurality of acoustic signal output devices 212 arranged to surround the pinna of the listener (see Fig. 6). The acoustic signal output device 212 is an acoustic signal output device that realizes local reproduction based on a dipole sound source, and is, for example, the acoustic signal output device 10 described in <Technical Background>. Therefore, the acoustic signal output device array 211 is configured to reproduce a sound field based on the Rayleigh integral of the second kind in the vicinity of the pinna.

The acoustic signal output device array 211 is configured as a frame-like structure surrounding the auricle, which serves as the framework of the headphone device 20, and multiple acoustic signal output devices 212 may be provided on the frame so as to surround the auricle (see FIG. 8). When configured in this way, the headphone device 20 becomes an open-type headphone, which allows the headphone device 20 to take in sounds around the listener without blocking them, and allows the listener to easily hear sounds that warn of danger, such as horns, warning sounds, and alarms, even when the headphone device 20 is used outdoors.

The input signals of the acoustic signal output devices 212 included in the acoustic signal output device array 211 are signals obtained by signal processing of electrical signals representing acoustic signals based on physical quantities determined by the positional relationship between the virtual sound source and the acoustic signal output device in order to localize the virtual sound source. Examples of physical quantities are described below. In this case, the acoustic signal output device array 211 included in the right headphone 21R includes four acoustic signal output devices 212-R1, acoustic signal output device 212-R2, acoustic signal output device 212-R3, and acoustic signal output device 212-R4, and the acoustic signal output device array 211 included in the left headphone 21L includes four acoustic signal output devices 212-L1, acoustic signal output device 212-L2, acoustic signal output device 212-L3, and acoustic signal output device 212-L4 (see FIG. 9).

(Example 1) Phase Difference of Acoustic Signals Consider a situation in which sound emitted from a virtual sound source reaches the acoustic signal output device array 211 included in the left headphone 21L. If the distances between the virtual sound source and the acoustic signal output device 212-L1, the distance between the virtual sound source and the acoustic signal output device 212-L2, the distance between the virtual sound source and the acoustic signal output device 212-L3, and the distance between the virtual sound source and the acoustic signal output device 212-L4 are r(L1), r(L2), r(L3), and r(L4), respectively, and the speed of sound is c, then the time Delay(L1) that it takes for the sound emitted from the virtual sound source to reach the acoustic signal output device 212-L1, the time Delay(L2) that it takes for the sound emitted from the virtual sound source to reach the acoustic signal output device 212-L2, the time Delay(L3) that it takes for the sound emitted from the virtual sound source to reach the acoustic signal output device 212-L3, and the time Delay(L4) that it takes for the sound emitted from the virtual sound source to reach the acoustic signal output device 212-L4 are respectively Delay(L1)=r(L1)/c, Delay(L2)=r(L2)/c, Delay(L3)=r(L3)/c, Delay(L4)=r(L4)/c. If the sampling frequency is fs, then the sample time Ts(L1) corresponding to the time Delay(L1), the sample time Ts(L2) corresponding to the time Delay(L2), the sample time Ts(L3) corresponding to the time Delay(L3), and the sample time Ts(L4) corresponding to the time Delay(L4) are Ts(L1)=fs×r(L1)/c, Ts(L2)=fs×r(L2)/c, Ts(L3)=fs×r(L3)/c, and Ts(L4)=fs×r(L4)/c, respectively. Thus, a signal obtained by performing signal processing to impart a phase difference to an electrical signal representing an acoustic signal based on a delay equivalent to sample time Ts(L1) (i.e., the phase difference between the acoustic signals) is set as the input signal for the acoustic signal output device 212-L1. Similarly, a signal obtained by performing signal processing to impart a phase difference to an electrical signal representing an acoustic signal based on a delay equivalent to sample time Ts(L2) is set as the input signal for the acoustic signal output device 212-L2, a signal obtained by performing signal processing to impart a phase difference to an electrical signal representing an acoustic signal based on a delay equivalent to sample time Ts(L3) is set as the input signal for the acoustic signal output device 212-L3, and a signal obtained by performing signal processing to impart a phase difference to an electrical signal representing an acoustic signal based on a delay equivalent to sample time Ts(L4) is set as the input signal for the acoustic signal output device 212-L4.

For example, the phase difference may be determined based on the time Delay(L1) that it takes for sound emitted from a virtual sound source to reach the audio signal output device 212-L1. In this case, signal processing is performed to determine the phase difference as Delay(L1)=0, Delay(L2)=(r(L2)-r(L1))/c, Delay(L3)=(r(L3)-r(L1))/c, and Delay(L4)=(r(L4)-r(L1))/c.

The same applies to the acoustic signal output device array 211 included in the right headphone 21R.

(Example 2) Amplitude difference of acoustic signals Instead of the phase difference of acoustic signals, the position of a virtual sound source may be localized using the amplitude difference of acoustic signals. As in Example 1, consider a situation in which a sound emitted from a virtual sound source reaches the acoustic signal output device array 211 included in the left headphone 21L. Also, assume that the sound from the virtual sound source is a spherical wave. In this case, distance attenuation 1/r(L1) occurs before the sound emitted from the virtual sound source reaches the acoustic signal output device 212-L1. Therefore, a signal obtained by performing signal processing to adjust the amplitude of an electrical signal representing an acoustic signal based on the amplitude difference of acoustic signals equivalent to the distance attenuation 1/r(L1) is used as the input signal to the acoustic signal output device 212-L1. Similarly, a signal obtained by performing signal processing to adjust the amplitude of an electrical signal representing an acoustic signal based on an amplitude difference between acoustic signals equivalent to distance attenuation 1/r(L2) is the input signal to acoustic signal output device 212-L2, a signal obtained by performing signal processing to adjust the amplitude of an electrical signal representing an acoustic signal based on an amplitude difference between acoustic signals equivalent to distance attenuation 1/r(L3) is the input signal to acoustic signal output device 212-L3, and a signal obtained by performing signal processing to adjust the amplitude of an electrical signal representing an acoustic signal based on an amplitude difference between acoustic signals equivalent to distance attenuation 1/r(L4) is the input signal to acoustic signal output device 212-L4. Here, signal processing to adjust the amplitude of an electrical signal representing an acoustic signal refers to signal processing in which the amplitude of the electrical signal is multiplied by distance attenuation.

The same applies to the acoustic signal output device array 211 included in the right headphone 21R.

(Example 3) Phase difference and amplitude difference of acoustic signals The position of a virtual sound source may be localized using the phase difference and amplitude difference of acoustic signals. As in Example 1, consider a situation in which a sound emitted from a virtual sound source reaches the acoustic signal output device array 211 included in the left headphone 21L. Also assume that the sound from the virtual sound source is a spherical wave. In this case, the phase difference and amplitude difference that occur when the sound emitted from the virtual sound source reaches the acoustic signal output device 212-L1 can be expressed as exp(-jkr(L1))/r(L1). Therefore, a signal obtained by performing signal processing to adjust the phase difference and amplitude of an electrical signal representing an acoustic signal based on the phase difference and amplitude difference of the acoustic signal equivalent to exp(-jkr(L1))/r(L1) is used as the input signal of the acoustic signal output device 212-L1. Similarly, a signal obtained by performing signal processing to adjust the phase difference and amplitude of an electrical signal representing an acoustic signal based on the phase difference and amplitude difference of an acoustic signal equivalent to exp(-jkr(L2))/r(L2) is set as an input signal for the acoustic signal output device 212-L2, a signal obtained by performing signal processing to adjust the phase difference and amplitude of an electrical signal representing an acoustic signal based on the phase difference and amplitude difference of an acoustic signal equivalent to exp(-jkr(L3))/r(L3) is set as an input signal for the acoustic signal output device 212-L3, and a signal obtained by performing signal processing to adjust the phase difference and amplitude of an electrical signal representing an acoustic signal based on the phase difference and amplitude difference of an acoustic signal equivalent to exp(-jkr(L4))/r(L4) is set as an input signal for the acoustic signal output device 212-L4. Here, j is an imaginary unit, k is a wave number, and the wave number k can be expressed as k=2πf/c using frequency f and sound speed c.

The same applies to the acoustic signal output device array 211 included in the right headphone 21R.

In both examples, taking into account the scattering of the sound field by the upper body, such as the head and chest, makes it possible to localize the virtual sound source more faithfully. In addition, for example, by using a sinc function for interpolation, it becomes possible to localize the virtual sound source more faithfully.

Note that while FIG. 6 illustrates an acoustic signal output device array 211 in which multiple acoustic signal output devices 212 are arranged in a circle, the arrangement shape does not necessarily have to be circular, and may be elliptical, rectangular, or even other shapes. In other words, it is sufficient that the multiple acoustic signal output devices 212 are arranged so as to surround the auricle.

According to an embodiment of the present invention, it is possible to localize a virtual sound source at any position while minimizing the amount of calculations. It is also possible to play back sound so that it cannot be heard by anyone other than the listener, thereby suppressing sound leakage.

<Additional Notes>
The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings. The embodiments have been chosen and depicted to provide a best illustration of the principles of the invention and to enable those skilled in the art to utilize the invention in various embodiments and with various modifications as may be suitable for the practical use contemplated. All such modifications and variations are within the scope of the invention as defined by the appended claims interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims (3)

A headphone device including an acoustic signal output device array including a plurality of acoustic signal output devices arranged to surround an auricle, the acoustic signal output devices realizing local reproduction based on a dipole sound source,
The input signals of the acoustic signal output devices included in the acoustic signal output device array are
A headphone device in which a signal is obtained by signal processing an electrical signal representing an acoustic signal based on a physical quantity determined by the positional relationship between a virtual sound source and the acoustic signal output device in order to localize the virtual sound source. 2. The headphone device according to claim 1,
A headphone device, wherein the physical quantity is any one of a phase difference of an acoustic signal, an amplitude difference of an acoustic signal, and a phase difference and an amplitude difference of an acoustic signal. 1. An audio signal output method in which a headphone device including an audio signal output device array outputs an audio signal, comprising:
the acoustic signal output device array includes a plurality of acoustic signal output devices arranged to surround the auricle, the acoustic signal output devices realizing local reproduction based on a dipole sound source,
An acoustic signal output method in which an input signal of an acoustic signal output device included in the acoustic signal output device array is a signal obtained by signal processing an electrical signal representing an acoustic signal based on a physical quantity determined by the positional relationship between a virtual sound source and the acoustic signal output device in order to localize the virtual sound source.

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