Sound emission method, sound emission device, and program

Abstract

To maintain volume heard by a user constant, even when the user of a spot-sound-reproduction chair moves his / her head. To this end, a sound emission device according to the disclosed technology emits sound such that only an area in the immediate vicinity of the user becomes an audible region, the sound emission device including a speaker sound-reproduction unit, a sensor signal acquisition unit, and an acoustic processing unit. The speaker sound-reproduction unit makes a first speaker and a second speaker emit acoustic signals that are approximately opposite in phase to each other. The sensor signal acquisition unit acquires movement of at least part of the head of the user. The acoustic processing unit determines a gain of acoustic signals emitted from the first speaker and the second speaker on the basis of the movement. Here, acoustic signals emitted from the first speaker and acoustic signals emitted from the second speaker make up one audible region for the user.

Description

Sound emission method, sound emission device, and program

[0001] The disclosed technology relates to a method / device for controlling the audible range according to the user's position in a sound emission method / device where the audible range is limited to the immediate vicinity.

[0002] Figure 1(a) schematically shows a typical speaker unit. 101 is the speaker cone, 102 is a coil fixed to the speaker cone, and 103 is a magnet. When an electric current based on an acoustic signal flows through the coil, it vibrates together with the speaker cone due to electromagnetic induction. Normally, as shown in Figure 1(b), the speaker unit 10 is housed in an enclosure 111, and only sound waves generated from the front surface 11 of the speaker cone are radiated into the air.

[0003] The speaker in Figure 1(b) is designed to deliver sound over a wide area, but the demand for delivering sound to a specific area (spot reproduction) has been increasing in recent years. Figure 2(a) utilizes an open enclosure structure to achieve spot reproduction by using in-phase sound waves generated from the front 11 of the speaker unit and out-of-phase sound waves generated from the back 12 (Patent Document 1). 201 is the opening, and in this case, sound waves generated by the vibration of the back 12 of the speaker cone are emitted from the opening 201 to the outside of the enclosure 111, diffract and interfere with the in-phase sound generated from the front 11 of the speaker cone, canceling each other out while leaving a predetermined region (audible region). Figure 2(b) shows two speaker units 10 housed in a container 121 that does not shield sound waves. Speaker unit 10-1 emits in-phase sound from the front, and 10-2 emits out-of-phase sound from the front, which allows for a more limited audible region than the structure in Figure 2(a) (Patent Document 1).

[0004] As shown in Figure 2, a speaker that can limit the audible range will be called a spot-playback speaker. If a spot-playback speaker is used, for example, in an airplane seat, the sound will be limited to the area around the seat user's ears, eliminating the need for the user to wear headphones or similar devices. Such a seat will be called a "spot-playback chair."

[0005] International release WO2021 / 192166

[0006] Spot playback chairs have the challenge of a small audible range. If the user's head is too far from the speaker, the user will have difficulty hearing the sound. Similarly, if the user's head does not reach the speaker, the user will have difficulty hearing the sound. In the case of a system using a pair of speaker units (Figure 2(b)), the audible range can be widened by installing a baffle, but the baffle is a physical structure and cannot adaptively change the audible range.

[0007] To solve the above problems, the sound emission device according to the disclosed technology is a device that emits sound such that only the immediate vicinity of the user is in the audible range, and comprises a speaker reproduction unit, a sensor signal acquisition unit, and an acoustic processing unit. The speaker reproduction unit emits acoustic signals that are substantially out of phase with respect to each other from a first speaker and a second speaker. The sensor signal acquisition unit acquires the movement of at least a part of the user's head. Based on the movement, the acoustic processing unit determines the gain of the acoustic signals emitted from the first speaker and the second speaker. Here, the acoustic signal emitted from the first speaker and the acoustic signal emitted from the second speaker constitute a single audible range for the user.

[0008] According to the disclosed technology, it is possible to reduce the difficulty in hearing sounds when the user of the spot playback chair moves their head.

[0009] A diagram illustrating a general speaker unit and speaker. A diagram illustrating an example of a spot playback speaker. A functional block diagram showing an example configuration of a spot playback system according to the first embodiment. A flowchart illustrating an example of the operation of a spot playback control device. A diagram illustrating crosstalk in transaural playback. A functional block diagram showing an example configuration of a spot playback system according to Modification 1. A flowchart illustrating an example of the operation of a spot playback control device according to Modification 1. A diagram illustrating CCRD. A diagram illustrating directional control by a CCRD array. A flowchart illustrating an example of the operation of a spot playback control device according to Modification 2. A diagram showing the coefficient dependence of an all-pass filter. A flowchart illustrating an example of the operation of a spot playback control device according to the second embodiment. A flowchart illustrating an example of the operation of a spot playback control device according to the third embodiment. A diagram illustrating inverse phase control of a CCRD. A diagram showing an example of the functional configuration of a computer.

[0010] As the user moves away from the spot playback speaker, distance attenuation (the inverse square law for sound intensity) occurs, causing the sound to become quieter. In the disclosed technology, to counteract this attenuation, the volume of the spot playback speaker is increased according to the distance between the ear and the spot playback speaker.

[0011] [Gain Adjustment] The principle of gain adjustment will be explained. If the distance between the speaker and the ear is r0 when the spot playback speaker is near the ear, and the amplitude A0 of the spot playback sound obtained at distance r0 is known, then the amplitude A(r) at any distance r can be expressed by the following formula. Therefore, the gain G(r) given to compensate for this damping is given by the following equation.

[0012] The embodiments of the disclosed technology will be described in detail below. Components with the same function will be numbered identically, and redundant explanations will be omitted.

[0013] [First Embodiment] Figure 3 is a functional block diagram showing an example of the configuration of a spot playback system 3 according to the first embodiment. The spot playback system 3 provides spot sound to a user 301 using a spot playback chair 302 using spot playback speakers 303R (right ear side) and 303L (left ear side), and includes a spot playback control device 310 and a sensor 320. The spot playback control device 310 includes a sensor signal acquisition unit 311, an information processing unit 312, an acoustic processing unit 313, and a speaker playback unit 314.

[0014] For the sensor 320, a commercially available motion capture device can be used. For example, Kinect® or Orbbec Femto Bolt® can be used. Alternatively, since it is sufficient to obtain the positional relationship between the head and the speaker, an ultrasonic sensor, an infrared sensor, or a device that reproduces high frequencies of 18kHz or higher outside the speaker's audible range and acquires the head position using a microphone for calls placed near the user's mouth or a noise-canceling microphone placed near the speaker.

[0015] Figure 4 is a flowchart illustrating an example of the operation of the spot regeneration control device 310. The following explanation will use Figures 3 and 4.

[0016] <Initialization> First, the user is seated to initialize the positional relationship between the speaker and the ears. The sensor signal acquisition unit 311 acquires the positions (absolute coordinates) of the user's left and right ears based on the sensor signals (step S401). Note that "absolute coordinates" refers to the coordinates defined by the sensor. The positions of the left and right ears are determined, for example, by estimating a skeletal model of the head based on the sensor signals, estimating the orientation of the head from the estimated skeletal model, and estimating the positions of the left and right ears from the estimated orientation of the head. The information processing unit 312 reads the recorded speaker positions (absolute coordinates) (step S401). At this time, if the positions of the left and right ears are different from the seated position due to a sensor malfunction or other reasons, the user moves the ear positions to the initial seated position. The information processing unit 312 determines the initial distance (r0) between the right ear and the spot playback speaker 303R. R , and the initial distance (r0) between the left ear and the spot playback speaker 303L LCalculate it (step S402).

[0017] <Volume Control> The sensor signal acquisition unit 311 acquires the position of the ear (absolute coordinates) based on the sensor signal (step S403). The re-acquisition of the ear position may be performed periodically or may be performed by detecting a change in the user's head position. The information processing unit 312 calculates the distance r R between the right ear and the spot playback speaker 303R, and the distance r L between the left ear and the spot playback speaker 303L (step S404).

[0018] The acoustic processing unit 313 calculates the gain G R (r) for adjusting the output of the spot playback speaker 303R and the gain G L (r) for adjusting the output of the spot playback speaker 303L (step S405). The gains G R (r) and G L (r) are given by the following equation from Equation (2).

[0019] The speaker playback unit 314 gives G R (r) to the right speaker and G L (r) to the left speaker as the gain. The spot playback control device 310 repeats steps S403 to S405 to suppress the attenuation of the volume perceived by the user following the position change of the head. In other words, control is performed such that the gain increases as the distance between the right ear and the spot playback speaker 303R for outputting to the right ear increases. Control is performed such that the gain increases as the distance between the left ear and the spot playback speaker 303L for outputting to the left ear increases. In the first embodiment, the above distance is calculated using motion capture. Also, in any of the embodiments / modifications, the spot playback speaker may have a configuration in which the sound wave generated by the vibration of the back surface 12 of the speaker cone is guided by a sound guide tube to interfere with the positive-phase sound generated from the front surface 11 of the speaker cone instead of a structure that wraps around the sound wave generated by the vibration of the back surface 12 of the speaker cone.

[0020] The above is the description of the first embodiment.

[0021] [Modification 1] In the first embodiment, the user's head position (ear position) was tracked and the volume perceived by the user was adjusted. In Modification 1, the user's ear position is tracked and transoral is performed.

[0022] <Transaural> Binaural playback is a technique that reproduces the sound signal arriving at the left and right eardrum positions of a listener from a given sound source, thereby allowing the listener to perceive the sound image. Headphones are the most common playback device used for binaural playback, but it is also possible to use multiple speakers as playback devices. Binaural playback using speakers is called transaural playback to distinguish it from playback using headphones. In binaural playback, the signal with the head-related transfer function (HRTF) applied is presented separately to the left and right ears using headphones (Figure 5(a) H R and H L ), if this is played back directly through a speaker, the signal that should only be presented to one ear will also reach the other ear (Figure 5(b) H R,l and H L,r Such signal components, which differ from the signals that should be presented to each ear, are called crosstalk, and their inclusion makes it difficult to present the desired sound image to the listener. Therefore, in implementing transaural playback, it is generally necessary to apply an HRTF to the sound source signal and design a controller that cancels out the crosstalk components at the same time.

[0023] When using a spot playback chair for transoral playback, H R,l and H L,r Because the influence of such components is minimal, crosstalk cancellation becomes unnecessary. However, as mentioned above, if the relative position of the head (ears) and the spot playback speaker changes, H R,r and H L,l This changes. Therefore, by performing head tracking using motion capture (e.g., Kinect), it is possible to achieve dynamic binaural playback that matches head movements, such as those used with headphones, by taking head rotation into consideration. Note that the head transfer function H R,r and H L,lSince it changes according to the positional relationship between the position of the head (ear position) and the position of the spot playback speaker, by pre-holding a plurality of transfer functions in accordance with the positional relationship and selecting the head transfer function according to the movement, it is possible to reproduce high-precision stereo sound without the need for headphones or the like.

[0024] FIG. 6 is a functional block diagram showing a configuration example of the spot playback system 6 according to the first modification. The difference from FIG. 1 is that the spot playback control device 310 includes a transfer function storage unit 601. FIG. 7 is a flowchart for explaining an example of the operation of the spot playback control device 310 according to the first modification. Hereinafter, the difference from the first embodiment will be mainly described with reference to FIGS. 6 and 7.

[0025] <Initialization> Steps S401 to S402 are the same as those in the first embodiment. The acoustic processing unit 313 selects an initial transfer function from the head transfer function storage unit based on the head posture and ear position, and the speaker playback unit uses the initial transfer function to play back spot sound (step S701).

[0026] <Transoral control> Steps S403 to S404 are the same as those in the first embodiment. The acoustic processing unit 313 selects the current transfer function from the head transfer function storage unit based on the head posture and ear position (step S702), and the speaker playback unit uses the selected transfer function to play back spot sound.

[0027] The above is the description of the first modification.

[0028] [Second modification] In the first embodiment, the position of the user's head (ear position) is tracked to adjust the volume perceived by the user. In the second modification, Kinect is used for motion capture to grasp the position of the user's head and the positions of other users around the speaker (for example, users in other spot playback chairs), and the directivity control of the spot playback speaker is performed according to each position. For example, if each of the left and right spot playback speakers is configured as a speaker array, by controlling the directivity and null by the delay sum array, it is possible to perform control such that it can be heard by the seat user but not by other users outside.

[0029] A CCRD (Coaxial Counter Ring Driver) can be used as a spot-reproducing speaker. A schematic representation of a CCRD is shown in Figure 8(a). A CCRD consists of a center speaker 801 and a ring-shaped subspeaker 802 arranged on the same axis and plane. For example, by radiating positive-phase sound waves from the center speaker 801 and negative-phase sound waves from the ring speaker 802, it functions as a spot-reproducing speaker using the same principle as in Figure 2.

[0030] Figure 8(b) shows how the spot playback speaker 303R / L is configured with two CCRD arrays. By driving each speaker in one of the left or right CCRD arrays in opposite phase and controlling the directivity with a delay of d / c (where d is the distance between sound sources and c is the speed of sound), an acoustic beam with the following directivity coefficients, depending on the wavenumber k of the sound wave, is obtained, with θ = 90° being the direction of the backrest of the spot playback chair (Figure 9). Furthermore, by directing the acoustic beam towards the backrest of the spot playback chair, sound leakage is reduced due to the chair's shielding.

[0031] The configuration of the spot regeneration system according to Modification 2 is the same as that of the first embodiment. Figure 10 is a flowchart illustrating an example of the operation of the spot regeneration control device 310 according to Modification 2. The following explanation will use Figures 3 and 10.

[0032] <Initialization> First, the user is seated and the initial position of the user's head and the initial positions of surrounding users are measured. The sensor signal acquisition unit 311 acquires the sensor signal (step S1001). The information processing unit 312 acquires the initial position of the user's head and the initial positions of surrounding users based on the sensor signal (step S1002). The sound processing unit 313 generates a speaker drive signal to control the directionality of the CCRD based on the initial head position and the initial positions of surrounding users (step S1003). The speaker playback unit 314 outputs the drive signal to the spot playback speaker 303R / L.

[0033] <Directional Control> The directivity of the spot playback speakers 303R / L is controlled in accordance with changes in the position of the user's head and surrounding users. The sensor signal acquisition unit 311 acquires the sensor signal (step S1004). The sensor signal may be reacquired periodically, or it may be done when a change in the user's head position or a change in the position of surrounding users is detected. The information processing unit 312 acquires the current position of the user's head and the current position of surrounding users based on the sensor signal (step S1005). The acoustic processing unit 313 generates a speaker drive signal to control the directivity of the CCRD based on the acquired head position and surrounding user position (step S1006). The speaker playback unit 314 outputs the drive signal to the spot playback speakers 303R / L. The spot playback control device 310 controls the directivity of the spot playback speakers in accordance with changes in the position of the user's head and surrounding users by repeating steps S1004 to S1006.

[0034] The above is an explanation of the second modified example.

[0035] [Second Embodiment] In the first embodiment, the user's perceived volume was adjusted by tracking the user's head position (ear position). In the second embodiment, the spot playback system is controlled using the user's head position. This will be explained using "adjustment of low-frequency attenuation" and "automatic mute when leaving the seat" as examples.

[0036] <Adjustment of Low-Frequency Attenuation> In the low-frequency range, the inverse phase causes nearby sounds to be lost too much. Therefore, in addition to volume control according to the head position, the phase component of the inverse-phase playback speaker (spot speaker 10-2 in Figure 2(b) or ring speaker 902 in Figure 8(a)) is controlled. Phase control is performed by an all-pass filter (Figure 11). The degree of phase inversion in the low-frequency range is controlled by using a phase characteristic that transitions to inverse phase as the frequency increases. The all-pass filter is controlled by adjusting the coefficient λ of the frequency domain filter function given by the following equation. The further the user's head is from the spot playback speaker, the greater the phase shift of the low frequencies from inverse phase (180°), which suppresses low-frequency cancellation without increasing the volume amplitude. The all-pass filter is lightweight in terms of processing and allows for continuous, real-time adjustment of the attenuation level.

[0037] <Automatic mute when leaving seat> The speaker stops playing when the user's head is more than a threshold away from their seating position. This prevents sound leakage to the surrounding area.

[0038] The configuration of the spot regeneration system according to the second embodiment is the same as that of the first embodiment. Figure 12 is a flowchart illustrating an example of the operation of the spot regeneration control device 310 according to the second embodiment. The following explanation will be given using Figures 3 and 12.

[0039] <Initialization> Steps S401 to S402 are the same as in the first embodiment.

[0040] <Perceived Volume Control> The volume of the spot playback speakers 303R / L perceived by the user is controlled by taking the user's head position change as input. Steps S403 to S404 are the same as in the first embodiment. Next, the sound processing unit 313 controls r R and r L Determine whether it is below a predetermined threshold.

[0041] <<Automatic mute when away from desk>> r R or r L If the value exceeds a predetermined threshold (No in step S1201), the speaker playback unit 314 stops speaker playback (step S1202). Next, the spot playback control device 310 returns to step S403. R and r L The speaker playback unit 314 stops playback until the value falls within a predetermined threshold.

[0042] <<Adjusting Gain and Low-Frequency Attenuation>> r R and r L If the gain is below a predetermined threshold (Yes in step S1201), the sound processing unit 313 adjusts the gain G R (r) and G L(r) is calculated (step S405). Then the acoustic processing unit 313 calculates r R and / or r L The filter coefficient λ is determined based on this (step S1203). The speaker playback unit 314 controls the phase of the signal that drives the inverted-phase speaker based on λ, G R (r) to the right, G L (r) is applied to the gain of the left spot playback speaker. The spot playback control device 310 repeats steps S403 to S1203, taking the user's head position change as input and controlling the volume of the spot playback speakers 303R / L as perceived by the user.

[0043] The above is a description of the second embodiment.

[0044] [Third Embodiment] In the second embodiment, the problem of nearby sounds being too silenced in the low frequencies was solved by controlling the degree of phase inversion in the inverted-phase playback speaker using an all-pass filter. In the third embodiment, instead of phase control, the low-frequency intensity of the inverted-phase playback speaker is adjusted.

[0045] The configuration of the spot regeneration system according to the third embodiment is the same as that of the first embodiment. Figure 13 is a flowchart illustrating an example of the operation of the spot regeneration control device 310 according to the third embodiment. The following explanation will be given using Figures 3 and 13.

[0046] <Initialization> Steps S401 to S402 are the same as in the first embodiment.

[0047] <Perceptual Volume Control> Steps S403 to S404 are the same as in the first embodiment. The acoustic processing unit 313 controls r R and / or r L Based on this, the drive signal (inverted phase drive signal) for the inverted phase playback speaker is adjusted according to the frequency (step S1301). For example, the amplitude of the low-frequency (approximately 700Hz or lower) of the inverted phase drive signal is adjusted to decrease as the distance between the head and the spot playback speaker increases. When the intensity of the inverted phase drive signal decreases, the effect of cancellation due to interference decreases. The acoustic processing unit 313 controls the gain G R (r) and G L(r) is calculated (step S405). When the speaker playback unit 314 drives the spot playback speaker using the adjusted inverse phase drive signal, G R (r) to the right, G L (r) is applied to the gain of the left spot playback speaker. The spot playback control device 310 repeats steps S403 to S405, taking the user's head position change as input and controlling the volume of the spot playback speakers 303R / L as perceived by the user.

[0048] The above is a description of the third embodiment.

[0049] [Modification 3] CCRD has the problem of suppressing too much of the low frequencies. We want to emphasize the low frequencies and primarily control the mid-range. Therefore, in Modification 3, instead of simply radiating in-phase sound from the center speaker and out-of-phase sound from the ring speaker, the radiated sound is divided into frequency bands, and different controls are applied to each band.

[0050] <Control Policy> (High Frequencies) Control is difficult, and the ring speaker's sound actually amplifies the overall sound, so only the center speaker is driven. (Mid Frequencies) The center speaker is driven in phase, and the ring speaker is driven in reverse phase to attenuate the sound. (Low Frequencies) The center speaker and ring speaker are driven in phase to increase the vibration surface area.

[0051] Figure 14 shows the acoustic signal control device 14 that implements the above control policy. The low-pass filter 1403 allows frequencies below approximately 700 Hz to pass through. The high-pass filter (HPF) 1401 allows frequencies above approximately 2.8 kHz to pass through. The band-pass filter (BPF) 1402 allows frequencies from approximately 700 Hz to 2.8 kHz to pass through. The phase inversion control unit 1404 inverts the phase of the acoustic signal. The mixer 1405 mixes the outputs of the HPF 1401, BPF 1402, and LPF 1403 and outputs it to the center speaker 901. The mixer 1406 mixes the output of the phase inversion control unit 1404 (with the phase of the BPF output inverted) and the output of the LPF 1403 and outputs it to the ring speaker 902.

[0052] The above is an explanation of the third variation.

[0053] [Programs, Recording Media] The functions realized by the components described herein may be implemented in a circuitry or processing circuitry, including a general-purpose processor, an application-specific processor, an integrated circuit, an ASIC (Application Specific Integrated Circuit), a CPU (a Central Processing Unit), conventional circuits, and / or a combination thereof, programmed to realize the functions described herein. A processor includes transistors and other circuits and is considered a circuitry or processing circuitry. A processor may be a programmed processor that executes a program stored in memory.

[0054] In this specification, circuitry, unit, and means are hardware programmed to perform or execute the functions described herein. Such hardware may be any hardware disclosed herein, or any hardware known to be programmed to perform or execute the functions described herein.

[0055] If the hardware is a processor that is considered to be a type of circuitry, then the circuitry, means, or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0056] The various processes described above can be carried out by loading a program that executes each step of the above method into the recording unit 2020 of the computer 2000 shown in Figure 15, and then causing the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc. to operate.

[0057] The program describing this process can be recorded on a computer-readable recording medium. Any computer-readable recording medium can be used, such as a magnetic recording device, optical disc, magneto-optical recording medium, or semiconductor memory.

[0058] Furthermore, this program may be distributed, for example, by selling, transferring, or lending portable recording media such as DVDs or CD-ROMs on which the program is recorded. Alternatively, the program may be stored in the storage device of a server computer and distributed by transferring the program from the server computer to other computers via a network.

[0059] A computer executing such a program may, for example, first store the program, either recorded on a portable storage medium or transferred from a server computer, in its own memory. Then, when processing is to be executed, the computer reads the program stored in its memory and executes the processing according to the read program. Alternatively, the computer may directly read the program from the portable storage medium and execute the processing according to that program, or it may sequentially execute the processing according to the received program each time a program is transferred to it from a server computer. Furthermore, the processing may be executed using a so-called ASP (Application Service Provider) type service, where the processing function is realized only by issuing execution instructions and obtaining results, without transferring the program from the server computer to this computer.In addition, the processing may be executed using a so-called SaaS (Software as a Service) type service, where a part of the server computer is made available to the user along with the program. Furthermore, the aforementioned programs include information used for processing by electronic computers that is equivalent to a program (data, etc., that is not a direct instruction to the computer but has the property of defining the computer's processing).

[0060] Furthermore, although the above explanation assumes that the device is configured by executing a predetermined program on a computer, at least a part of these processes may be implemented in hardware.

Claims

1. A sound emission method that emits sound such that only the immediate vicinity of a user is within the audible range, comprising: emitting an acoustic signal from a first speaker; emitting an acoustic signal from a second speaker that is substantially in opposite phase to the acoustic signal; acquiring the movement of at least a part of the user's head; determining the gain of the acoustic signals emitted from the first speaker and the second speaker based on the movement; and the acoustic signal emitted from the first speaker and the acoustic signal emitted from the second speaker constitute a single audible range for the user.

2. A sound emission method according to claim 1, wherein if the movement increases the distance between the first and second speakers and the user, the gain of the acoustic signals emitted from the first and second speakers is determined to increase.

3. A sound emission method according to claim 1, wherein if the movement increases the distance between the first and second speakers and the user to a predetermined size, the sound emission from the first and second speakers is stopped.

4. A sound emission method according to claim 2, comprising: calculating the coefficient λ of an all-pass filter based on the distance between the first and second speakers and the user; phase-controlling the signal that drives the second speaker based on the λ; and adjusting the drive signal after phase control with the gain to emit sound.

5. A sound emission method according to claim 2, comprising adjusting the low-frequency amplitude of a signal that drives the second speaker based on the distance between the first and second speakers and the user, and emitting sound by adjusting the adjusted drive signal with the gain.

6. A sound emission method according to claim 2, comprising: acquiring the current posture of the user's head and the current positions of the left and right ears; selecting a head transfer function based on the current posture of the head and the current positions of the ears; converting the signals that drive the first and second speakers using the head transfer function; and emitting sound by adjusting the converted drive signals with the gain.

7. A sound-emitting device that emits sound such that only the immediate vicinity of a user is within the audible range, comprising: a speaker reproduction unit that emits acoustic signals that are substantially out of phase with respect to each other from a first speaker and a second speaker; a sensor signal acquisition unit that acquires the movement of at least a part of the user's head; and an acoustic processing unit that determines the gain of the acoustic signals emitted from the first speaker and the second speaker based on the movement, wherein the acoustic signal emitted from the first speaker and the acoustic signal emitted from the second speaker constitute a single audible range for the user.

8. A program for causing a computer to perform the method according to any one of claims 1 to 6.

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