Sound system

Abstract

Provided is an audio system that, without the use of earphones or headphones, plays back sound that cannot be heard by users in one's surroundings. The audio system comprises at least two speaker unit pairs that each include a positive speaker which does not include a speaker box and a negative speaker which does not include a speaker box, said audio system including: a selection unit that selects one of the speaker unit pairs in accordance with the position of an auditory organ of a user and the position of the speaker unit pairs; and a control unit that performs control such that an audio signal (first audio signal) from a prescribed audio source is output only from the positive speaker of the selected speaker unit pair, and an audio signal (second audio signal) of the opposite phase to the first audio signal is output only from the negative speaker of the selected speaker unit pair.

Description

[Technical Field]

[0001] The present invention relates to a technology for localized sound reproduction. [Background technology]

[0002] Conventionally, users have used earphones or headphones to watch movies or listen to music on airplanes (see Non-Patent Document 1). This is because when speakers are used, the playback sound reaches the user's surroundings, causing a nuisance to other users. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] In-flight entertainment / JAL First Class, [online], [searched February 1, 2021], Internet<URL: https: / / www.jal.co.jp / jp / ja / inter / service / first / entertainment / index.html> Summary of the Invention [Problem to be solved by the invention]

[0004] However, wearing earphones or headphones can be a hassle for users. Some users dislike wearing them because they mess up their hair. Others dislike the pressure they put on their ears. For some people, such as children, it may be difficult to select headphones of the appropriate size, or for some people, such as babies, to wear earphones or headphones.

[0005] To eliminate the need to wear earphones or headphones, it is possible to synthesize a virtual sound field using wave field synthesis technology, but this would require the preparation of a large-scale speaker array, which is not realistic. Furthermore, when attempting to emit localized sound that is inaudible to other users, unless the speaker arrangement is changed depending on the implementation target, it is not possible to make the appropriate area an audible area.

[0006] Therefore, an object of the present invention is to provide an audio system that reproduces sounds that cannot be heard by surrounding users without using earphones or headphones. [Means for solving the problem]

[0007] In one aspect of the present invention, an acoustic system includes at least two speaker unit pairs each including a positive speaker that does not include a speaker box and a negative speaker that does not include a speaker box, a selection unit that selects one of the speaker unit pairs depending on the position of the user's auditory organs and the positions of the speaker unit pairs, and a control unit that controls the system so that an acoustic signal of a predetermined sound source (hereinafter referred to as a first acoustic signal) is emitted only from the positive speaker of the selected speaker unit pair, and so that an acoustic signal that is in phase opposite to the first acoustic signal (hereinafter referred to as a second acoustic signal) is emitted only from the negative speaker of the selected speaker unit pair.

[0008] In one aspect of the present invention, an audio system includes at least three speakers that do not include speaker boxes, a selection unit that selects any two speakers depending on the position of the user's auditory organs and the positions of the speakers, and a control unit that controls the system so that an audio signal of a predetermined sound source (hereinafter referred to as a first audio signal) is emitted only from one selected speaker, and an audio signal that is in phase opposite to the first audio signal (hereinafter referred to as a second audio signal) is emitted only from the other selected speaker.

[0009] In one aspect of the present invention, a vehicle is a vehicle in which a person rides and moves from one position to another by rotating wheels driven by human power or electricity. The vehicle includes a directivity control device including at least one directivity control unit that generates a first processed sound signal from an acoustic signal of a predetermined sound source (hereinafter referred to as a first acoustic signal) and generates a second processed sound signal from an acoustic signal of the opposite phase to the first acoustic signal (hereinafter referred to as a second acoustic signal) by performing predetermined signal processing to give directionality to the sound emitted by the speaker unit pair; a speaker system including at least one speaker unit pair that includes a speaker (hereinafter referred to as a positive speaker) that does not have a speaker box that emits sound based on the first processed acoustic signal, and a speaker (hereinafter referred to as a negative speaker) that does not have a speaker box that emits sound based on the second processed acoustic signal; and a position acquisition unit that acquires the position where the user's auditory organs are located or the position where the speaker unit pair is located, and selects a filter that directs the sound emitted by the speaker unit pair toward the acquired position where the user's auditory organs are located, and the directivity control device performs predetermined signal processing using the selected filter. [Effects of the Invention]

[0010] According to the present invention, it is possible to reproduce sounds that can only be heard in a very limited range. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram illustrating the directivity of sound emitted from a speaker. [Figure 2] 3A and 3B are diagrams for explaining the directionality of sound emitted from a speaker unit. [Figure 3] 10A and 10B are diagrams for explaining sounds emitted from a speaker unit pair. [Figure 4] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 5] FIG. 1 shows the experimental setup (the relative positions of the speaker and microphone). [Figure 6]FIG. 1 shows the experimental setup (the relative positions of the speaker unit and microphone). [Figure 7] FIG. 1 shows the experimental setup (the relative positions of the speaker unit pair and microphone). [Figure 8] FIG. 10 is a diagram showing the experimental conditions (other measurement positions). [Figure 9] FIG. 10 is a diagram showing experimental results (condition 1). [Figure 10] FIG. 10 is a diagram showing experimental results (condition 2). [Figure 11] FIG. 10 is a diagram showing experimental results (condition 3). [Figure 12] FIG. 10 is a diagram showing experimental results (condition 4). [Figure 13] FIG. 1 is a diagram showing an example of an audio system installed in an aircraft seat. [Figure 14] 1 is a block diagram showing an example of the configuration of an acoustic system 100. FIG. [Figure 15] 10A and 10B are diagrams illustrating sounds emitted from a pair of speaker units. [Figure 16] FIG. 2 is a block diagram showing an example of the configuration of an acoustic system 200. [Figure 17] FIG. 2 is a block diagram showing an example of the configuration of an acoustic system 202. [Figure 18] 12 is a diagram showing an example of the configuration of a speaker unit pair 122 to which a member 1224 is attached. [Figure 19] FIG. 1 is a diagram showing an example of an audio system installed in a car seat. [Figure 20] FIG. 1 is a diagram showing an example of an audio system installed in a car seat. [Figure 21] FIG. 10 is a diagram showing an example of an audio system installed on a partition. [Figure 22] FIG. 2 is a block diagram showing an example of the configuration of an acoustic system 300. [Figure 23] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 24] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 25] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 26] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 27] FIG. 10 is a diagram showing an example of an audio system installed on a partition. [Figure 28] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 29] FIG. 4 is a block diagram showing an example of the configuration of an acoustic system 400. [Figure 30] FIG. 10 is a diagram showing an example of an audio system installed on a partition. [Figure 31] FIG. 10 is a diagram showing an example of an audio system installed on a partition. [Figure 32] FIG. 5 is a block diagram showing an example of the configuration of an acoustic system 500. [Figure 33] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 34] 10A and 10B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Figure 35] FIG. 10 is a diagram showing an example of an audio system installed on a partition. [Figure 36] FIG. 6 is a block diagram showing an example of the configuration of an acoustic system 600. [Figure 37] FIG. 1 is a diagram illustrating an example of a sound system installed in a vehicle. [Figure 38] FIG. 1 is a diagram illustrating an example of a sound system installed in a vehicle. [Figure 39] FIG. 1 is a diagram illustrating an example of a sound system installed in a vehicle. [Figure 40] FIG. 1 is a diagram illustrating an example of a sound system installed in a vehicle. [Figure 41] FIG. 7 is a block diagram showing an example of the configuration of an acoustic system 700. [Figure 42] FIG. 1 is a diagram illustrating an example of a sound system installed in a vehicle. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail. Components having the same functions are given the same numbers, and duplicated explanations will be omitted.

[0013] <Technical background> First, the directivity of the sound emitted from the speaker will be described. Next, the directivity of the sound emitted from the speaker unit pair of the present invention will be described. Finally, the results of an experiment to confirm the effects of the speaker unit pair of the present invention will be described.

[0014] 1: Directionality of sound emitted from a speaker Typically, a speaker consists of a speaker unit and a speaker box. The speaker unit is a component that includes a diaphragm that converts electrical acoustic signals into vibrations in the air (i.e., generates sound waves). The speaker box is a component that houses the speaker unit.

[0015] When an acoustic signal is input to a speaker, the diaphragm of the speaker unit vibrates, and sound waves are emitted in both directions of the diaphragm's vibration. Here, sound waves emitted outside the speaker box (i.e., toward the front of the speaker unit) are called positive sound waves, and sound waves emitted inside the speaker box (i.e., toward the back of the speaker unit) are called negative sound waves. Negative sound waves are sound waves with the opposite phase to positive sound waves. Figure 1 is a diagram explaining the directionality of sound emitted from a speaker. As shown in Figure 1, positive sound waves are emitted from the speaker in all directions, while negative sound waves do not leave the speaker box. As a result, the sound emitted from the speaker can be heard over a wide range.

[0016] 2: Directivity of sound emitted from a speaker unit pair Here, we will first explain the directionality of sound emitted from a speaker unit, which is a bare speaker. Figure 2 is a diagram for explaining the directionality of sound emitted from a speaker unit. Unlike the case of a speaker unit alone, negative sound waves are emitted from the back of the speaker unit, which is hidden inside the speaker box. Therefore, as shown in Figure 2, the sound emitted from the speaker unit has a bidirectional characteristic.

[0017] The present invention utilizes this bidirectionality. A detailed explanation follows. First, as shown in FIG. 3, two speaker units are arranged to form a speaker unit pair. The two speaker units are arranged so that they emit sound in approximately the same direction. When acoustic signals of the same magnitude but in opposite phase are input to this speaker unit pair, the diaphragms of the two speaker units vibrate, emitting sounds based on these two acoustic signals. As a result, the sound emitted from the speaker unit pair is greatly suppressed in all directions except for the vicinity of the speaker unit pair, and the sound pressure approaches zero. For example, in FIG. 4, sound is not eliminated in the point area near the speaker unit, but is inaudible outside the point area. In other words, sound is eliminated only at positions sufficiently far from the speaker unit pair, and sound is not eliminated near the speaker unit pair. The reason why sounds are not cancelled near the speaker unit pair is that when the sound waves emitted from each of the speaker unit pair overlap at the observation point, the distance based on the arrival path from each speaker unit to the observation point has a large effect. At distances where the influence of path differences due to the spacing between the speaker unit pair and wraparound is small, the positive and negative phases overlap and cancel each other out, but near the speaker unit pair, the difference in the path taken by the sound waves emitted from the front of the speaker unit and the sound waves wraparound from the back is large, so the positive and negative phases are in a completely opposite relationship and do not overlap.

[0018] In other words, by taking advantage of the property that when a specified acoustic signal is input to one speaker unit that makes up a speaker unit pair and an acoustic signal of the opposite phase to the specified acoustic signal is input to the other speaker unit, the sound can only be heard in the vicinity of the speaker unit pair, it is possible to create a situation in which the sound can only be heard by users in the vicinity of the speaker unit pair, and cannot be heard by other users.

[0019] 3. Experimental Results Here we explain the results of an experiment to measure the frequency characteristics of a speaker, speaker unit, and speaker unit pair. The speakers, speaker units, and speaker unit pairs used in the experiment were a speaker with a 4.5 cm diameter diaphragm (see Figure 5), a speaker with the speaker box removed, leaving only the speaker unit (see Figure 6), and two of these speaker units lined up (see Figure 7). In addition, to measure the frequency characteristics near the speaker, speaker unit, and speaker unit pair, microphones were placed under the following four conditions.

[0020] (Condition 1) 5cm from the front of the speaker (Condition 2) 5cm from the front of the speaker unit (Condition 3) 2 cm from the front of the speaker unit (Condition 4) 2 cm from the front of the speaker unit pair In addition, for comparison purposes, microphones were placed 100 cm from the front, back, and side of the speaker, speaker unit, and speaker unit pair under all conditions (see Figure 8).

[0021] The experimental results are explained below. Figures 9, 10, 11, and 12 show the experimental results, illustrating the relationship between frequency and attenuation under Conditions 1, 2, 3, and 4, respectively. Each figure shows four curves. The curve indicated by the arrow represents sound picked up by a microphone positioned 5 cm or 2 cm from the front, while the other three curves represent sound picked up by microphones positioned 100 cm from the front, back, and side. Note that the curves positioned 5 cm or 2 cm from the front are located near the speaker, so the gain is very large. Therefore, for ease of viewing, the curve positioned 5 cm from the front is plotted at a -25 dB offset from the three curves positioned 100 cm from the front. Similarly, the curve positioned 2 cm from the front is plotted at a -32 dB offset. Comparing Figures 9 and 10, when a speaker is used, there is almost no difference between the four curves. However, when a speaker unit is used, there is a difference between the curve positioned 5 cm from the front and the other three curves. This difference is more pronounced in the low frequency range. Also, comparing Figure 11 and Figure 12, it can be seen that the difference between the curve 2 cm from the front and the other three curves is greater for the speaker unit pair than for the speaker unit itself.

[0022] As described above, it has been confirmed through experiments that the sound emitted from the speaker unit pair of the present invention can be heard only in the vicinity of the speaker unit pair.

[0023] First Embodiment A system that reproduces an acoustic signal obtained based on a reproduction object is called an acoustic system. An acoustic system includes a speaker system for emitting the acoustic signal as sound (hereinafter, this sound will be referred to as sound based on the acoustic signal). Here, a speaker system is a device that converts an analog acoustic signal into sound. Furthermore, a reproduction object refers to data or signals from which an acoustic signal can be obtained by predetermined processing, such as data recorded on a CD, DVD, or record, data received via the Internet, or signals received via radio or television broadcasts.

[0024] Here, we will describe an acoustic system that reproduces sound based on an acoustic signal obtained from a playback target so that only users near the speaker system can hear it. In other words, the sound reproduced by the acoustic system cannot be heard by users other than those near the speaker system. If such an acoustic system is used as an acoustic system for a user using a seat on an airplane, for example, a system can be provided in which the reproduced sound can only be heard by the user using that seat. FIG. 13 is a diagram showing an example of an acoustic system installed on an airplane seat. The acoustic system of FIG. 13 is installed on the seat so as to sandwich the head of a seated user, with two speaker unit pairs positioned near the left and right ears. Note that such an acoustic system can also be installed in vehicles other than airplanes, such as automobiles and trains, or in reclining chairs, and can also be installed in a wearable form, such as on the shoulder. Furthermore, a driver unit pair consisting of two driver units arranged side by side, corresponding to the above-mentioned speaker unit pair, may be installed in each of the left and right units of headphones or earphones. Headphones are generally divided into two main types: open-air and closed-air. Applying the above technology to open-air headphones, which are particularly susceptible to sound leakage, is expected to reduce sound leakage.

[0025] The acoustic system 100 will be described below with reference to FIG. 14. FIG. 14 is a block diagram showing the configuration of the acoustic system 100. As shown in FIG. 14, the acoustic system 100 includes a playback device 110 and a speaker system 120. The playback device 110 includes N (where N is an integer equal to or greater than 1) playback units 112 (i.e., first playback unit 112, ..., Nth playback unit 112). The speaker system 120 includes N speaker unit pairs 122 (i.e., first speaker unit pair 122, ..., Nth speaker unit pair 122). Each speaker unit pair 122 includes two speaker units (i.e., a positive speaker unit 1221 and a negative speaker unit 1221). An acoustic signal having an opposite phase to that input to the positive speaker unit 1221 is input to the negative speaker unit 1221. The speaker system 120 is installed near the head of a user using the seat.

[0026] The direction in which the nth speaker unit pair 122 faces the user is defined as the nth user direction (n=1, ..., N), and the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122 (n=1, ..., N) are arranged so that sound emitted from the positive speaker unit 1221 in the direction opposite to the nth user direction and sound emitted from the negative speaker unit 1221 in the direction opposite to the nth user direction are transmitted to the nth user direction by wraparound. Here, the nth user direction refers to the front direction of the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122. Furthermore, the direction opposite to the nth user direction refers to the rear direction of the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122.

[0027] In addition, the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122 (n=1, ..., N) are positioned in a positional relationship such that the sounds emitted from the positive speaker unit 1221 and the negative speaker unit 1221 cancel each other out so that they cannot be heard by users using other seats.

[0028] The operation of the acoustic system 100 will be described below with reference to FIG.

[0029] The playback device 110 receives as input a first acoustic signal, a third acoustic signal, ..., a 2N-1th acoustic signal, which are acoustic signals obtained based on a playback object, and outputs the first acoustic signal, the second acoustic signal, ..., the 2Nth acoustic signal. More specifically, the nth playback unit 112 (n = 1, ..., N) receives as input the 2n-1th acoustic signal, generates from the 2n-1th acoustic signal a 2nth acoustic signal that is an acoustic signal of opposite phase to the 2n-1th acoustic signal, and outputs the 2n-1th acoustic signal and the 2nth acoustic signal. The 2n-1th acoustic signal and the 2nth acoustic signal are input to the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122, respectively.

[0030] The speaker system 120 receives as input the first acoustic signal, the second acoustic signal, ..., the 2Nth acoustic signal output by the playback device 110, and emits a sound based on the first acoustic signal, a sound based on the second acoustic signal, ..., a sound based on the 2Nth acoustic signal. More specifically, the nth speaker unit pair 122 (n = 1, ..., N) receives as input the 2n-1th acoustic signal and the 2nth acoustic signal, and emits a sound based on the 2n-1th acoustic signal from the positive speaker unit 1221, and emits a sound based on the 2nth acoustic signal from the negative speaker unit 1221. Because the 2n-1th acoustic signal and the 2nth acoustic signal are in opposite phase to each other, as described in <Technical Background>, the sounds can be heard only in the vicinity of the seat where the speaker system 120 is installed. For example, when N=2, if the first acoustic signal and the third acoustic signal are the right channel acoustic signal and the left channel acoustic signal of a certain sound source, respectively, stereo sound can be heard only in the vicinity of the seat where the speaker system 120 is installed.

[0031] Note that the sound emitted from the positive speaker unit 1221 of the n-th speaker unit pair 122 in the n-th user direction and the sound emitted from the positive speaker unit 1221 of the n-th speaker unit pair 122 in the direction opposite to the n-th user direction have opposite phases to each other. Similarly, the sound emitted from the negative speaker unit 1221 of the n-th speaker unit pair 122 in the n-th user direction and the sound emitted from the negative speaker unit 1221 of the n-th speaker unit pair 122 in the direction opposite to the n-th user direction have opposite phases to each other.

[0032] According to an embodiment of the present invention, it is possible to reproduce a sound that can only be heard within a very narrow range, namely, the vicinity of the speaker system. The term "vicinity" refers to a distance defined based on the environment and experimental results, in accordance with the frequency and the degree of sound attenuation. For example, in <3: Experimental Results>, if the state of sound at a distance where the sound pressure at a position approximately the diameter of the speaker diaphragm from the center of the speaker diaphragm gradually decreases to a sound pressure equivalent to background noise, and this state is considered to be sound attenuation, then "vicinity" is defined as, for example, a distance of approximately twice the diameter of the speaker diaphragm from the center of the speaker diaphragm. In other words, assuming an environment with a certain level of background noise, such as the inside of a car, the vicinity range is set so that the speaker system 120 can be heard by a person sitting in the seat where it is installed, but cannot be heard by a person sitting in the seat next to it. For example, in (3: Experimental Results), if we consider the state in which sound emitted from a speaker unit is radiated into the surrounding area and reaches a sound pressure equivalent to that of background noise to be sound elimination, then "nearby" can be considered to be up to a distance of approximately twice the user's shoulder width from the center of the speaker diaphragm.

[0033] Second Embodiment FIG. 15 is a diagram showing the sound emitted from a speaker unit pair. In the diagram, SPU represents a speaker unit. In the case of a speaker unit pair installed near the right ear, the sounds from each speaker unit cancel each other out in the intermediate region between the two speaker units, creating an area where the sound emitted from the speaker unit pair cannot be heard, and the user cannot hear the sound. On the other hand, in the case of a speaker unit pair installed near the left ear, the area where the sound emitted from the speaker unit pair can be heard shifts from the position of the ears, causing the user to be unable to hear the sound. In other words, when (i) both / either of the left and right ears are located in the intermediate region, (ii) both / either of the left and right ears are located outside the audible region, or (iii) one of the left and right ears is located in the intermediate region and the other is located outside the audible region, the user cannot hear the sound or has difficulty hearing it. To solve these problems, the directivity of the sound emitted from the speaker unit pair is controlled. Here, an audio system that performs directivity control processing is described.

[0034] The acoustic system 200 will be described below with reference to Fig. 16. Fig. 16 is a block diagram showing the configuration of the acoustic system 200. As shown in Fig. 16, the acoustic system 200 includes a playback device 110, a directivity control device 210, and a speaker system 120. The directivity control device 210 includes N directivity control units 212 (i.e., a first directivity control unit 212, ..., an Nth directivity control unit 212). The acoustic system 200 differs from the acoustic system 100 in that it includes the directivity control device 210.

[0035] The operations of the directivity control device 210 and the speaker system 120 will be described below with reference to FIG.

[0036] The directivity control device 210 receives the first acoustic signal, the second acoustic signal, ..., the 2Nth acoustic signal output by the playback device 110 as input, and outputs a first-processed acoustic signal obtained by signal processing the first acoustic signal, a second-processed acoustic signal obtained by signal processing the second acoustic signal, ..., a 2Nth-processed acoustic signal obtained by signal processing the 2Nth acoustic signal. More specifically, the nth directivity control unit 212 (n = 1, ..., N) receives the 2n-1th acoustic signal and the 2nth acoustic signal as input, and performs predetermined signal processing to generate a 2n-1th-processed acoustic signal from the 2n-1th acoustic signal, generate a 2nth-processed acoustic signal from the 2nth acoustic signal, and output the 2n-1th-processed acoustic signal and the 2nth-processed acoustic signal. Here, the predetermined signal processing refers to processing for controlling directivity, and can be, for example, the method described in Reference 1 or other directivity control techniques. Needless to say, other directivity control techniques may also be used. In short, any technology may be used as long as it can control the directionality according to the positions of the user's ears and the positions of the speaker unit pair. (Reference 1) Futoshi Asano, "Sound Array Signal Processing - Sound Source Localization, Tracking and Separation", Corona Publishing, 2011, pp. 69-91 The predetermined signal processing is, for example, filtering using an FIR (Finite Impulse Response) filter. The FIR filter used here is designed by placing microphones in an audible range and an inaudible range, respectively, so that the filter coefficient value approaches 1 for the microphones placed in the audible range and the filter coefficient value approaches 0 for the microphones placed in the inaudible range. A specific explanation will be given below. The audible range and the inaudible range need to be designed depending on the case. For example, consider the case of placement in a car seat (hereinafter referred to as seat S). The position where the ear of a user using seat S would be when moving their head or turning their face should be included in the audible range, while the position where the ear of a user using a seat adjacent to seat S (e.g., the seat next to or in front of or behind seat S) would be included in the inaudible range. Therefore, for example, the filter coefficient value approaches 0 for microphones placed in an area that includes seats adjacent to seat S but does not include seat S. As described above, sounds cancel each other out in the intermediate region between the two speaker units, and as a result, sounds may not be heard even at the position where the ears are located when the head is moved or the direction of the face is changed. Taking this into consideration, the filter coefficient value of the microphone placed in the intermediate region is set to approach 1. In essence, the filter coefficient of the microphone placed in the region where the user's ears are assumed to be located can be controlled to approach 1, and / or the filter coefficient of the microphone placed in the region where the user's ears are assumed not to be located can be controlled to approach 0. In other words, the filter can be configured so that the sound arriving in the region where the user's ears are assumed to be located is as loud as possible, and so that the sound arriving in the region where the user's ears are assumed not to be located is reduced as much as possible.

[0037] As a result, the nth directivity control unit (n=1, ..., N) executes signal processing to make the sound emitted from the positive speaker unit of the nth speaker unit pair and the sound emitted from the negative speaker unit of the nth speaker unit pair audible in an area near the nth speaker unit pair that should be audible, but inaudible in an area that should not be audible. Note that the area that should be the audible area includes a point equidistant from the positive speaker unit of the nth speaker unit pair and the negative speaker unit of the nth speaker unit pair, where the sound emitted from the positive speaker unit of the nth speaker unit pair and the sound emitted from the negative speaker unit of the nth speaker unit pair cancel each other out.

[0038] The speaker system 120 receives as input the first processed acoustic signal, the second processed acoustic signal, ..., the 2Nth processed acoustic signal output by the directivity control device 210, and emits sound based on the first processed acoustic signal, the second processed acoustic signal, ..., the 2Nth processed acoustic signal. More specifically, the nth speaker unit pair 122 (n=1, ..., N) receives as input the 2n-1th processed acoustic signal and the 2nth processed acoustic signal, and emits sound based on the 2n-1th processed acoustic signal from the positive speaker unit 1221, and emits sound based on the 2nth processed acoustic signal from the negative speaker unit 1221.

[0039] (Variation) Here, we will explain an acoustic system that uses materials with sound-absorbing properties to prevent high-frequency sounds from leaking.

[0040] The acoustic system 202 will be described below with reference to Fig. 17. Fig. 17 is a block diagram showing the configuration of the acoustic system 202. As shown in Fig. 17, the acoustic system 202, like the acoustic system 200, includes a playback device 110, a directivity control device 210, and a speaker system 120. However, the acoustic system 202 differs from the acoustic system 200 in that a member 1224 is attached to the speaker unit pair 122.

[0041] The structure of the n-th speaker unit pair 122 (n=1, . . . , N) will be described below with reference to FIG.

[0042] The nth speaker unit pair 122 is fitted with a member 1224 for absorbing sounds emitted from the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122 in the direction opposite to the nth user direction (see FIG. 18). The member 1224 may be any member that can prevent high-frequency sounds from being radiated from the rear surface. Note that instead of installing the member 1224 only on the rear surface of the speaker unit pair 122, the member 1224 may be installed so as to surround the speaker unit pair 122 on all sides except the front surface.

[0043] (Example of a car seat-mounted sound system) 19 and 20 are diagrams showing examples of sound systems installed in automobile seats. In the example of FIG. 19, a speaker unit pair is installed in the headrest of the automobile seat. Specifically, N=2, and a first speaker unit pair and a second speaker unit pair are installed in the headrest of the automobile seat. On the other hand, in the example of FIG. 20, a speaker unit pair is installed on arms attached to the automobile seat. Specifically, N=2, and the speaker units are installed on two arms attached to the automobile seat so as to sandwich the head of a user using the automobile seat. The arms may be movable.

[0044] (Other examples) An example other than a car seat, specifically a seat for a gaming machine such as a pachinko or slot machine, will be described. Typically, a user sits in front of the gaming machine and enjoys playing games on the gaming machine. Therefore, the seats for gaming machines may also be provided with arms as described in the example of a car, so that the speaker unit pair is located near the position of the user's ears when seated in the seat. Note that since the seats for gaming machines may not have a backrest, the arms may be provided on the gaming machine instead of the seat. Furthermore, the arms may be movable so that the user can adjust them so that the speaker unit pair is located near the user's ears.

[0045] Third Embodiment Fig. 21 is a diagram showing an example of an audio system according to this embodiment installed behind a partition. The audio system in Fig. 21 is installed behind a partition, with two speaker unit pairs arranged side by side in the horizontal direction and the two speaker units included in each speaker unit pair arranged side by side in the vertical direction. In this example, the partition is installed behind the sofa on which the user sits.

[0046] The acoustic system 300 will be described below with reference to Fig. 22. Fig. 22 is a block diagram showing the configuration of the acoustic system 300. As shown in Fig. 22, the acoustic system 300 includes a playback device 110, a position acquisition unit 330, a directivity control device 210, and a speaker system 120. The acoustic system 300 differs from the acoustic system 200 in that the acoustic system 300 includes the position acquisition unit 330.

[0047] The operation of the position acquisition unit 330 will be described below with reference to FIG.

[0048] The position acquisition unit 330 changes the directivity of the directivity control process performed by the directivity control device 210 depending on the location of the user's auditory organs and the location of the speaker unit pair, so that the directionality of the sound emitted from the speaker unit pair is directed toward the location of the user's auditory organs. In this embodiment, the speakers are arranged vertically in order to control the viewing area with emphasis on the height at which the user's auditory organs are located. When the height at which the users' auditory organs are located is approximately the same, as in cases where the same user uses the speakers exclusively, the speakers may be arranged horizontally to control the horizontal directivity. Whether the speakers are arranged vertically or horizontally, it is desirable that the speaker closest to the ears be the positive speaker unit and the speaker farthest from the ears be the negative speaker unit. The roles of the positive and negative speakers are switched using a filter used in the directivity control device 210.

[0049] First, the position acquisition unit 330 acquires the position of the user's auditory organs. The position may be acquired by any method. Below, an example in which the position acquisition unit 330 estimates the position and an example in which the user selects the position will be described.

[0050] (Acquisition method 1 (location estimation)) For example, the position acquisition unit 330 estimates the position of the user's head and estimates the position of the auditory organs from the head position. Note that the head position may be estimated by any method.

[0051] For example, a camera or the like is used to capture an image of the user's head, feature amounts are extracted from the captured image, and the position of the user's head or auditory organs is estimated from the extracted feature amounts.

[0052] (Acquisition method 2 (user selection)) For example, the position acquisition unit 330 may have a selection unit such as a button (not shown), and the user may select the position of the head or auditory organs via the selection unit, and the position of the user's auditory organs may be acquired from the selection result. The position acquisition unit 330 may further have a communication function (not shown), and may be configured to allow selection from a terminal carried by the user. The terminal may be configured as an integrated part of the sound system, or may be a terminal carried by the user, such as a smartphone or tablet.

[0053] Next, the position acquisition unit 330 selects a filter that directs the directionality of the sound emitted by the speaker unit pair toward the position where the user's auditory organs are located, and sets the selected filter as the filter to be used in the directivity control device 210. In essence, the position acquisition unit 330 changes the filter to be used in the directivity control device 210 according to the positional relationship between the speaker unit pair and the position where the user's auditory organs are located, thereby changing the area that should be audible and the area that should not be audible, so that the position where the user's auditory organs are located (the position where they are assumed to exist) becomes the area that should be audible, and the position where the user's auditory organs are not located (the position where they are assumed not to exist) becomes the area that should not be audible. Note that the positional relationship may be determined based on the estimated or selected positions of the head and auditory organs and a reference point of the speaker unit pair (for example, the center position of the speaker unit pair, the center or bottom position of a speaker close to the ground, etc.).

[0054] The filters may be calculated in advance through simulations or experiments and stored in a storage unit (not shown) in association with the positional relationship between the speaker unit pair and the position of the user's auditory organs. Instead of selecting a filter, filters may be calculated sequentially so that the directionality of the sound emitted by the speaker unit pair is directed toward the position of the user's auditory organs.

[0055] (Example of directivity control) As shown in FIG. 23, when the position where the user's auditory organs are located is lower than the position where the speaker unit pair is located, the speaker unit pair is controlled so that the directivity of the sounds emitted is directed in a lower direction.

[0056] As shown in FIG. 24, when the position where the user's auditory organs are located is higher than the position where the speaker unit pair is located, the speaker unit pair is controlled so that the directivity of the sounds emitted from the speaker unit pair is directed in a high direction.

[0057] As shown in FIG. 25, when the position where the user's auditory organs are located is approximately the same height as the position where the speaker unit pair is located, the directivity of the sound emitted by the speaker unit pair is controlled so that the user can hear the sound at a point equidistant from the positive speaker and the negative speaker. Note that when the position where the user's auditory organs are located is approximately the same height as the position where the speaker unit pair is located, this means that the position where the user's auditory organs are located is on a plane formed by points equidistant from the positive speaker and the negative speaker (i.e., the intermediate region in the second embodiment). A filter designed to minimize the area where the directivity is not suitable (the area where sound pressure is low) between the positive speaker and the negative speaker is selected. Note that in this case, there is a trade-off: the smaller the area where the directivity is not suitable (the area where sound pressure is low), the greater the sound leakage to the surroundings.

[0058] As shown in Fig. 26, when the position of the user's auditory organs is at approximately the same height as the position of the positive speaker or the negative speaker, the directivity of the sound emitted by the speaker unit pair is controlled so that the area that the user can hear is reduced. By controlling in this way, it is possible to reduce sound leakage to the surroundings.

[0059] For example, filters for realizing directivity such as those shown in FIGS. 23 to 26 are calculated in advance through simulations or experiments, and stored in a memory unit (not shown) in association with the positions of the auditory organs. The position acquisition unit 330 acquires the positions of the user's auditory organs, selects a corresponding filter from the memory unit (not shown) based on the positional relationship between the speaker unit pair and the acquired positions of the user's auditory organs, and sets the selected file in the directivity control device 210.

[0060] The directivity control device 210 performs processing using the filter selected by the position acquisition unit 330. The processing itself in the directivity control device 210 is the same as in the second embodiment, and therefore a description thereof will be omitted.

[0061] As explained in the second embodiment, the positive speaker and the negative speaker emit sounds in predetermined directions so that they are in opposite phase to each other in a region that should not be audible. Also, as explained in the first embodiment, the positive speaker unit and the negative speaker unit are speakers without the speaker box, and are arranged so that the sound emitted from the positive speaker unit in the direction opposite to the nth user direction and the sound emitted from the negative speaker unit in the direction opposite to the nth user direction are transmitted to the nth user direction by wraparound.

[0062] According to an embodiment of the present invention, it is possible to reproduce sounds that can only be heard in a very limited range, such as in the vicinity of the speaker system, and to appropriately control the directionality to match the location of the user's auditory organs. The present embodiment may be combined with the modified example of the second embodiment.

[0063] Furthermore, in this embodiment, an example of N=2 has been described, but N may be either 1 or an integer of 3 or greater, and even when N is an integer of 2 or greater, local playback is possible and the directionality can be appropriately controlled according to the position of the user's auditory organs.

[0064] In this embodiment, the sound system is installed on a partition, but it may also be installed on a wall or digital signage. In short, in an environment where multiple users of different heights are using the system, it is sufficient to be able to control the directionality of a pair of speaker units arranged on a single plane in order to form an area that is inaudible to other users, including other users in adjacent positions, and audible only to the target user.

[0065] <Variation 1> In this embodiment, a partition is installed behind the sofa on which the user sits, but the sound system may also be incorporated into a partition installed between users (for example, a partition installed in a library or coworking space as shown in FIG. 27). As shown in FIG. 28, directivity control similar to that of the third embodiment can be performed for each channel.

[0066] <Fourth embodiment> FIG. 21 is a diagram showing an example of an audio system installed behind a partition. The audio system in FIG. 21 is installed behind a partition, with two speaker unit pairs arranged horizontally, and the two speaker units included in each speaker unit pair arranged vertically. In this example, a partition is installed behind the sofa on which the user sits. Before describing the details of this embodiment, an overview will be provided. Generally, a speaker array is composed of a large number of speakers, and an audio signal that has undergone array signal processing to emit an audio signal with desired characteristics is emitted from each speaker. In other words, the processing is performed by selecting speakers belonging to the speaker array. In this embodiment, a speaker array located in a position that is most convenient for the user to listen is selected from among multiple speaker arrays. This is because, as described in the previous embodiments, this audio system is configured to be listened to only in the immediate vicinity of the user. Therefore, depending on the height and seating position of the user, it may be impossible for the user to listen without moving the speaker position itself. In order to solve this problem, this embodiment is characterized in that a plurality of speaker arrays are prepared and the user selects the speaker array itself depending on the viewing position. For ease of explanation, the speaker unit pair has been described here as the speaker array.

[0067] The acoustic system 400 will be described below with reference to Fig. 29. Fig. 29 is a block diagram showing the configuration of the acoustic system 300. As shown in Fig. 29, the acoustic system 400 includes a playback device 410, a selection unit 430, a control unit 450, and a speaker system 120.

[0068] The operation of the acoustic system 400 will be described below with reference to FIG. The acoustic system 400 receives as input a first acoustic signal, which is an acoustic signal obtained based on a reproduction target object.

[0069] The playback device 410 receives as input a first acoustic signal, which is an acoustic signal obtained based on a playback object, and outputs a first acoustic signal and a second acoustic signal. The playback device 410 includes a first playback unit 112, which receives as input the first acoustic signal, generates from the first acoustic signal a second acoustic signal, which is an acoustic signal of opposite phase to the first acoustic signal, and outputs the second acoustic signal. The first acoustic signal and the second acoustic signal are input to the positive speaker unit 1221 and the negative speaker unit 1221 of the n-th (n=1, 2, ..., N) speaker unit pair 122, respectively. In this embodiment, N is any integer equal to or greater than 2.

[0070] The selection unit 430 selects one of the speaker unit pairs according to the position of the user's auditory organs and the position of the speaker unit pair, and outputs the selection result to the control unit 450.

[0071] First, the selection unit 430 acquires the positions of the user's auditory organs. The positions may be acquired by any method. For example, the positions of the user's auditory organs may be acquired by estimation or selection using a method similar to that used by the position acquisition unit 330 of the third embodiment.

[0072] Next, the selection unit 430 selects the speaker unit pair that is closest to the position where the user's auditory organs are located, and outputs the selection result to the control unit 450. For example, the selection unit 430 may measure and obtain the positions of each speaker unit pair in advance, store them in a storage unit (not shown), and select the speaker unit pair that corresponds to the position that is the shortest distance from the obtained position where the user's auditory organs are located.

[0073] Control unit 450 performs control so that the first acoustic signal is emitted only from the positive speaker of the selected speaker unit pair, and the second acoustic signal is emitted only from the negative speaker of the selected speaker unit pair, and speaker system 120 receives the first acoustic signal and the second acoustic signal as input, and, under the control of control unit 450, emits sound based on the first acoustic signal from positive speaker 1221 of the selected speaker unit pair, and emits sound based on the second acoustic signal from negative speaker 1221 of the selected speaker unit pair. Because the first acoustic signal and the second acoustic signal are in an anti-phase relationship, as explained in <Technical Background>, the sounds can only be heard in the vicinity of the selected speaker unit pair.

[0074] In this embodiment, the sound system is installed on a partition, but it may also be installed on a wall or digital signage. In short, in an environment used by multiple users in different positions, it is sufficient to arrange multiple speaker unit pairs on a single plane and select a speaker unit pair to form an area that is inaudible to other users, including other users in adjacent positions, and is audible only to the target user.

[0075] In the present embodiment, the selection unit 430 selects one speaker unit pair, but if there are two or more users, it may be configured to select speaker unit pairs equal to the number of detected users, and the control unit 450 may control the sound to be emitted from all selected speaker unit pairs.

[0076] Furthermore, this embodiment may be combined with the third embodiment. In this case, the selection unit 430 of this embodiment selects one speaker unit pair from N speaker unit pairs, and the directivity control device 210 of the third embodiment provides directivity from the position of the selected speaker unit pair toward the position of the user's auditory organs, and sound is emitted from the selected speaker unit pair under the control of the control unit 450.

[0077] <Modification> The acoustic system in Fig. 30 is installed on a partition, with two speaker unit pairs arranged vertically and two speaker units included in each speaker unit pair arranged horizontally. The other configurations are the same as those of the fourth embodiment. 31 is installed on a partition, with two speaker unit pairs arranged side by side in the horizontal direction, and the two speaker units included in each speaker unit pair also arranged side by side in the horizontal direction. The other configurations are the same as those of the fourth embodiment.

[0078] Fifth Embodiment In the acoustic system of the second embodiment, only one speaker unit pair can reproduce a one-channel (monaural) acoustic signal. If two-channel (stereo) acoustic signals are to be reproduced, at least two speaker unit pairs are required.

[0079] In this embodiment, an audio system capable of reproducing two-channel (stereo) audio signals using one speaker unit pair will be described. Before going into details, an overview of the invention according to this embodiment will be described. As described above, an audio system in which a positive speaker unit (hereinafter also referred to as the first speaker) and a negative speaker unit (hereinafter also referred to as the second speaker) are in opposite phase to each other and neither speaker has a speaker box is realized. In this embodiment, the first speaker and the second speaker each have two roles. For simplicity of explanation, the speaker that emits an audio signal for listening is referred to as the main speaker, and the other speaker is referred to as the cancellation speaker. The first speaker plays the role of a left-channel main speaker and a right-channel cancellation speaker, and the second speaker plays the role of a left-channel cancellation speaker and a right-channel main speaker. By giving directionality to the signals emitted from the first and second speakers so that they can perform these functions, a single speaker unit pair can reproduce stereo sound signals that can only be heard in the vicinity. In this embodiment, the sound signal obtained based on the object to be reproduced is a two-channel (stereo) sound signal.

[0080] FIG. 31 is a diagram showing an example of an audio system according to this embodiment installed behind a partition. The audio system in FIG. 31 is installed behind a partition, with two speaker unit pairs arranged side by side horizontally, and the two speaker units included in each speaker unit pair also arranged side by side horizontally. Note that while a partition is used as an example here, the invention may also be applied to a car seat, a train seat, an office chair, or a speaker unit pair installed on a separator or digital signage. In short, the invention described in this embodiment may be applied to any audio system that uses fewer speakers than the first embodiment and reproduces stereo audio signals that can only be heard by those in close proximity.

[0081] The acoustic system 500 will be described below with reference to Fig. 32. Fig. 32 is a block diagram showing the configuration of the acoustic system 500. As shown in Fig. 32, the acoustic system 500 includes a playback device 510, a directivity control device 530, a synthesis device 540, and a speaker system 520.

[0082] Playback device 510 includes N (where N is an integer equal to or greater than 1) playback sections 512 (that is, first playback section 512, ..., Nth playback section 512).

[0083] The directivity control device 530 includes 2N directivity control units 532 (that is, the L1-th directivity control unit 532-L, . . . , the LN-th directivity control unit 532-L, the R1-th directivity control unit 532-R, . . . , the RN-th directivity control unit 532-R).

[0084] The combining device 540 includes 2N combining sections 542 (that is, an L1 combining section 542-L, . . . , an LN combining section 542-L, an R1 combining section 542-R, . . . , an RN combining section 542-R).

[0085] Speaker system 520 includes N speaker unit pairs 522 (i.e., first speaker unit pair 522, ..., Nth speaker unit pair 522). Each speaker unit pair 522 includes two speaker units (i.e., speaker unit 5221 for Lch and speaker unit 5221 for Rch). Speaker system 520 is installed on a partition near the head of a user using the sofa.

[0086] Furthermore, the speaker unit 5221 for Lch and the speaker unit 5221 for Rch of the nth speaker unit pair 522 (n=1, ..., N) are positioned in a positional relationship such that the sounds emitted from the speaker unit 5221 for Lch and the sounds emitted from the speaker unit 5221 for Rch are cancelled out by each other so that they cannot be heard by users using other seats.

[0087] The operation of the acoustic system 500 will be described below with reference to FIG.

[0088] The playback device 510 receives as input two-channel audio signals obtained based on the object to be played back: an L1 audio signal and an R1 audio signal, an L3 audio signal and an R3 audio signal, ..., an L(2N-1) audio signal and an R(2N-1) audio signal, and outputs an L1 audio signal and an R1 audio signal, an L2 audio signal and an R2 audio signal, ..., an L(2N) audio signal and an R(2N) audio signal. More specifically, the nth reproducer 512 (n = 1, ..., N) receives the L(2n-1)th acoustic signal and the R(2n-1)th acoustic signal as input, generates an L(2n)th acoustic signal from the L(2n-1)th acoustic signal that is an acoustic signal of opposite phase to the L(2n-1)th acoustic signal, generates an R(2n)th acoustic signal from the R(2n-1)th acoustic signal that is an acoustic signal of opposite phase to the R(2n-1)th acoustic signal, and outputs the L(2n-1)th acoustic signal and the R(2n-1)th acoustic signal and the R(2n-1)th acoustic signal. The L(2n-1)th acoustic signal and the L(2n)th acoustic signal are input to the Ln directivity control unit 532-L, and the R(2n-1)th acoustic signal and the R(2n)th acoustic signal are input to the Rn directivity control unit 532-R.

[0089] The directivity control device 530 receives as input the L1 acoustic signal and the R1 acoustic signal, the L2 acoustic signal and the R2 acoustic signal, ..., the L(2N) acoustic signal and the R(2N) acoustic signal output by the playback device 510, and outputs an L1-processed acoustic signal obtained by signal processing the L1 acoustic signal, an L2-processed acoustic signal obtained by signal processing the L2 acoustic signal, ..., an L(2N)-processed acoustic signal obtained by signal processing the L(2N) acoustic signal, an R1-processed acoustic signal obtained by signal processing the R1 acoustic signal, an R2-processed acoustic signal obtained by signal processing the R2 acoustic signal, ..., an R(2N)-processed acoustic signal obtained by signal processing the R(2N) acoustic signal.

[0090] More specifically, the Lnth directivity control unit 532-L (n = 1, ..., N) receives the L(2n-1)th acoustic signal and the L(2n)th acoustic signal as input, and performs predetermined signal processing to generate an L(2n-1)th processed acoustic signal from the L(2n-1)th acoustic signal, generate an L(2n)th processed acoustic signal from the L(2n)th acoustic signal, and output the L(2n-1)th processed acoustic signal and the L(2n)th processed acoustic signal by performing predetermined signal processing.

[0091] Similarly, the Rnth directivity control unit 532-R (n = 1, ..., N) receives the R(2n-1)th acoustic signal and the R(2n)th acoustic signal as input, and performs predetermined signal processing to generate an R(2n-1)th processed acoustic signal from the R(2n-1)th acoustic signal, generate an R(2n)th processed acoustic signal from the R(2n)th acoustic signal, and output the R(2n-1)th processed acoustic signal and the R(2n)th processed acoustic signal by performing predetermined signal processing. Here, the predetermined signal processing is processing for controlling the directivity described in the second embodiment, and includes, for example, filtering processing having coefficients as will be described next.

[0092] A more detailed explanation follows. The audible and inaudible regions need to be designed depending on the case. For example, consider the case of installation in a car seat (hereinafter referred to as seat S). The Ln directivity control unit 532-L ensures that the position where the left ear of a user using seat S is located is included in the audible region, and that other positions are included in the inaudible region. The Rn directivity control unit 532-R ensures that the position where the right ear of a user using seat S is located is included in the audible region, and that other positions are included in the inaudible region. Therefore, for example, the Ln directivity control unit 532-L ensures that the filter coefficient value approaches 0 for a microphone installed in a region that includes the left seat adjacent to seat S but does not include the position where the left ear of a user using seat S is located. The Rn directivity control unit 532-R ensures that the filter coefficient value approaches 0 for a microphone installed in a region that includes the right seat adjacent to seat S but does not include the position where the right ear of a user using seat S is located. In essence, the filter coefficient of a microphone placed in an area where it is assumed that the user's ears are located should be controlled to approach 1, and / or the filter coefficient of a microphone placed in an area where it is assumed that the user's ears are not located should be controlled to approach 0. In other words, the filter should be configured so that the loudest possible sound arrives in the area where it is assumed that the user's ears are located, and so that the quietest possible sound arrives in the area where it is assumed that the user's ears are not located.

[0093] As a result, the Lnth directivity control unit (n=1, ..., N) performs signal processing so that the sound emitted from the speaker unit for the Lch of the nth speaker unit pair and the sound emitted from the speaker unit for the Rch of the nth speaker unit pair can be heard in an area near the nth speaker unit pair that should be audible (for example, the position where the user's left ear is located), but cannot be heard in an area that should not be audible.

[0094] Similarly, the Rnth directivity control unit (n = 1, ..., N) performs signal processing so that the sound emitted from the speaker unit for Rch of the nth speaker unit pair and the sound emitted from the speaker unit for Lch of the nth speaker unit pair can be heard in an area near the nth speaker unit pair that should be audible (for example, the position where the user's right ear is located), but cannot be heard in an area that should not be audible. Figures 33 and 34 are diagrams explaining the areas that should be audible and the areas that should not be audible. A speaker unit for Rch and a speaker unit for Lch are placed horizontally on a partition. Here, it is assumed that the user's head is positioned near the center of the speaker unit pair. Stereo playback is possible with a speaker unit pair consisting of two speaker units by reproducing the stereo L channel using the directivity for the L channel created in advance with a fixed filter, and reproducing the stereo R channel using the directivity for the R channel.

[0095] The L(2n-1)th processed audio signal is an audio signal for making the R channel directivity audible in a region (hereinafter also referred to as the first region) to the left of the direction in which the user faces as viewed from the center of the speaker unit pair. The R(2n)th processed audio signal is an audio signal for making the R channel directivity inaudible in a region (hereinafter also referred to as the fourth region) to the right of the direction in which the user faces as viewed from the center of the speaker unit pair.

[0096] Similarly, the R(2n-1)th processed acoustic signal is an acoustic signal for making the L channel directivity audible in a region (hereinafter also referred to as the third region) to the right of the direction in which the user faces as viewed from the center of the speaker unit pair. The L(2n)th processed acoustic signal is an acoustic signal for making the L channel directivity inaudible in a region (hereinafter also referred to as the second region) to the left of the direction in which the user faces as viewed from the center of the speaker unit pair.

[0097] The synthesis device 540 receives as input the L1-processed acoustic signal, the L2-processed acoustic signal, ..., the L(2N)-processed acoustic signal, and the R1-processed acoustic signal, the R2-processed acoustic signal, ..., the R(2N)-processed acoustic signal, and synthesizes these signals to obtain an L1-processed acoustic signal, an L2-processed acoustic signal, ..., the LN-th processed acoustic signal, and an R1-processed acoustic signal, an R2-processed acoustic signal, ..., the RN-th processed acoustic signal, which it outputs.

[0098] More specifically, the Ln-th synthesis unit 542-L (n=1, ..., N) receives the L(2n-1)-th processed acoustic signal and the R(2n)-th processed acoustic signal as input, synthesizes these signals, and obtains the Ln-th synthesized acoustic signal. Similarly, the Rn synthesis unit 542-R (n = 1, ..., N) receives the R(2n-1)th processed acoustic signal and the L(2n)th processed acoustic signal as input, synthesizes these signals, and obtains the Rnth synthesized acoustic signal.

[0099] The speaker system 520 receives as input the L1 synthesized acoustic signal, the L2 synthesized acoustic signal, ..., the LN synthesized acoustic signal, and the R1 synthesized acoustic signal, the R2 synthesized acoustic signal, ..., the RN synthesized acoustic signal output by the synthesizing device 540, and emits sound based on the L1 synthesized acoustic signal, sound based on the L2 synthesized acoustic signal, ..., the LN synthesized acoustic signal, and sound based on the R1 synthesized acoustic signal, sound based on the R2 synthesized acoustic signal, ..., the RN synthesized acoustic signal. More specifically, the n-th speaker unit pair 522 (n = 1, ..., N) receives as input the Ln synthesized acoustic signal and the Rn synthesized acoustic signal, and emits sound based on the Ln synthesized acoustic signal from the Lch speaker unit 5221, and emits sound based on the Rn synthesized acoustic signal from the Rch speaker unit 5221. The component of the Ln-th synthesized audio signal based on the L(2n-1)-th processed audio signal and the component of the Rn-th synthesized audio signal based on the L(2n)-th processed audio signal are in opposite phase to each other, and the component of the Rn-th synthesized audio signal based on the R(2n-1)-th processed audio signal and the component of the Ln-th synthesized audio signal based on the R(2n)-th processed audio signal are in opposite phase to each other, so that, as explained in <Technical Background>, sound can only be heard near the seat where speaker system 520 is installed. For example, when N=1, if the L1-th audio signal and the R1-th audio signal, which are two-channel audio signals obtained based on the playback object, are the left channel audio signal and the right channel audio signal of a certain sound source, respectively, stereo sound can only be heard near the position where speaker system 520 is installed.

[0100] Sixth Embodiment FIG. 35 is a diagram showing an example of an audio system according to this embodiment installed behind a partition. The audio system in FIG. 35 is installed behind a partition, and M speaker units are arranged at equal distances in the horizontal and vertical directions. The distance between two adjacent speaker units in the horizontal and vertical directions is a distance that allows localized sound emission when the two adjacent speaker units emit a first acoustic signal and a second acoustic signal. In this example, the partition is installed behind the sofa on which the user sits. M is any integer greater than or equal to 3.

[0101] The acoustic system 600 will be described below with reference to Fig. 36. Fig. 36 is a block diagram showing the configuration of the acoustic system 600. As shown in Fig. 36, the acoustic system 600 includes a playback device 410, a selection unit 630, a control unit 650, and a speaker system 620.

[0102] The operation of the acoustic system 600 will be described below with reference to FIG. The acoustic system 400 receives as input a first acoustic signal, which is an acoustic signal obtained based on a reproduction target object.

[0103] The playback device 410 receives a first acoustic signal, which is an acoustic signal obtained based on a playback object, as input, and outputs a first acoustic signal and a second acoustic signal. The playback device 410 includes a first playback unit 112, which receives the first acoustic signal as input, generates from the first acoustic signal a second acoustic signal, which is an acoustic signal of opposite phase to the first acoustic signal, and outputs the second acoustic signal. The first acoustic signal and the second acoustic signal are input to an m-th (n=1, 2, ..., M) speaker unit.

[0104] The selection unit 630 selects any two adjacent speaker units according to the position of the user's auditory organs and the position of the speaker unit pair, and outputs the selection result to the control unit 650.

[0105] First, the selection unit 630 acquires the positions of the user's auditory organs. The positions may be acquired by any method. For example, the positions of the user's auditory organs may be acquired by estimation or selection using a method similar to that of the selection unit 630 in the fourth embodiment.

[0106] Next, the selection unit 630 selects two adjacent speaker units that are closest to the position of the user's auditory organs, and outputs the selection result to the control unit 650. In other words, two speaker units are selected from a group of speaker units prepared in advance to provisionally form a speaker unit pair. For example, the selection unit 630 may measure and determine the position of each speaker unit in advance, store the position in a storage unit (not shown), and select two adjacent speaker units that correspond to positions that are closest to the acquired position of the user's auditory organs.

[0107] Control unit 650 performs control so that the first acoustic signal is emitted from only one speaker of the selected speaker units, and the second acoustic signal is emitted from only the other speaker of the selected speaker units, and speaker system 620 receives the first acoustic signal and the second acoustic signal as input, and, under the control of control unit 650, emits sound based on the first acoustic signal from one selected speaker unit 1221, and emits sound based on the second acoustic signal from the other selected speaker unit 1221. Because the first acoustic signal and the second acoustic signal are in an anti-phase relationship, as explained in <Technical Background>, the sounds can only be heard in the vicinity of the selected speaker unit pair.

[0108] In the present embodiment, the selection unit 430 selects two speaker units, but if there are two or more users, the number of speaker units selected may be two times the number of detected users, and the control unit 650 may be configured to control the sound to be emitted from all selected speaker units. This embodiment may be combined with the third and fifth embodiments.

[0109] Seventh Embodiment 37 is a diagram showing an example of the sound system of this embodiment installed in a vehicle. Note that the vehicle referred to here is a vehicle that a person rides in and moves by rotating wheels driven by human power or electricity, such as a stroller, baby carriage, or wheelchair.

[0110] In the sound system shown in Figure 37, a pair of speaker units are installed side by side on the inside of the stroller hood. The side facing the seat where the baby sits is the inside, and the opposite side is the outside.

[0111] As shown in Figure 38, the speaker unit pair may be installed side by side on the stroller's side structure, or may be installed side by side near the connection between the stroller's side structure and the canopy. In this case, the speaker unit pair may be placed either on the outside or inside of the stroller, or on either the left or right side. This arrangement has the advantage that the change in the audible range is small when the canopy is open or closed, allowing continuous listening without the need for a mechanism such as filter switching, which will be described later.

[0112] Furthermore, the speaker unit pair may be installed horizontally alongside the backrest as shown in Figure 39. This arrangement has the advantage that a wide audible area can be formed horizontally, making it less likely that the baby will lose their hearing even if they move their head.

[0113] Furthermore, the speaker unit pair may be arranged side by side on the inside of the front bar as shown in Figure 39. This arrangement has the advantage that if a wide audible range is achieved (by adding components that increase the distance until diffraction occurs, for example), infants can continue to listen even if they move their face or body.

[0114] The speaker unit pair may be installed horizontally alongside the backrest as shown in Figure 40. This arrangement has the advantage that a wide vertical audible area can be formed, making it less likely that an infant's face will be unable to hear even if it slides down.

[0115] The acoustic system 700 will be described below with reference to Fig. 41. Fig. 41 is a block diagram showing the configuration of the acoustic system 700. As shown in Fig. 41, the acoustic system 700 includes a playback device 110, a position acquisition unit 730, a directivity control device 210, and a speaker system 120. The acoustic system 700 differs from the acoustic system 300 in that it includes the position acquisition unit 730.

[0116] The position acquisition unit 730 changes the directionality of the directionality control processing performed by the directionality control device 210 depending on the position where the user's auditory organs are located and the position where the speaker unit pair is located, so that the directionality of the sound emitted by the speaker unit pair is directed toward the position where the user's auditory organs are located. The operation of the position acquisition unit 730 will be described below with reference to FIG.

[0117] The position acquisition unit 730 changes the directionality of the directionality control processing performed by the directionality control device 210 depending on the position where the user's auditory organs are located and the position where the speaker unit pair is located, so that the directionality of the sound emitted by the speaker unit pair is directed toward the position where the user's auditory organs are located.

[0118] First, the position acquisition unit 730 acquires the position where the user's auditory organs are located or the position where the speaker unit pair is located. Note that the position may be acquired by any method. Below, an example in which the position acquisition unit 730 estimates a position and an example in which the user selects a position will be described.

[0119] (Acquisition method 1 (location estimation)) For example, a pressure sensor is installed in the backrest and it is estimated that the user's (baby's) head is located in a position where strong pressure is applied. For example, the position acquisition unit 730 estimates the position of the user's head and estimates the position of the auditory organs from the head position. Note that the head position may be estimated by any method.

[0120] For example, a camera or the like is used to capture an image of the user's head, feature amounts are extracted from the captured image, and the position of the user's head or auditory organs is estimated from the extracted feature amounts. Also, for example, if a speaker unit pair is installed on the hood as shown in Figure 37, the position of the speaker unit pair installed on the hood is detected from physical structures such as the state of gears that operate in conjunction with the opening and closing of the hood.

[0121] (Acquisition method 2 (user selection)) For example, the position acquisition unit 730 may have a selection unit such as a button not shown, and a user (such as a parent pushing a stroller) may select the position of the user's (infant's) head or auditory organs via the selection unit, and the position of the user's (infant's) auditory organs may be acquired from the selection results.

[0122] Next, the position acquisition unit 730 selects a filter that directs the directionality of the sound emitted by the speaker unit pair toward the position where the user's auditory organs are located, and sets the selected filter as the filter to be used in the directivity control device 210. In essence, the position acquisition unit 730 changes the filter to be used in the directivity control device 210 according to the positional relationship between the speaker unit pair and the position where the user's auditory organs are located, thereby changing the area that should be audible and the area that should not be audible, and can be designed so that the position where the user's auditory organs are located (the position where it is assumed that they exist) becomes the area that should be audible, and the position where the user's auditory organs are not located (the position where it is assumed that they do not exist) becomes the area that should not be audible.

[0123] By adopting such a configuration, an appropriate region can be set as the audible region. Note that the acoustic signal reproduced in this embodiment may be an acoustic signal (such as a mother's heartbeat or white noise) intended for a user (baby).

[0124] <Variation 1> In this modified example, as shown in Figures 39 and 40, a pair of speaker units is installed on the backrest of the stroller, an attachment such as a buggy board is attached to the outside of the back of the stroller, and the user (infant) is assumed to ride on the buggy board.

[0125] The stroller is configured so that sound emitted from the speaker's backrest reaches the outside of the stroller. For example, the entire or part of the back of the stroller's backrest is made of a mesh structure. Also, for example, the stroller's backrest is made of a material that allows sound based on low-frequency acoustic signals to pass through.

[0126] With this configuration, both the user (baby) in the stroller and the user (child) on an attachment such as a buggy board can hear and hear the sound based on the acoustic signal. Note that even if there is no attachment such as a buggy board, there is an advantage in that it is easy to check whether the user (parent) pushing the stroller is emitting sound or not.

[0127] <Variation 2> In this modification, as shown in Fig. 42, a pair of speaker units is installed horizontally on a bar that spans between the front and rear seats of an upright double stroller. With this configuration, two users (infants) can listen to music simultaneously using two speaker pairs. Note that although the two seats face forward in Fig. 42, even if the front seat faces backward and the front and rear seats are arranged facing each other, the same effect can be achieved by installing a pair of speaker units horizontally on a bar that spans between the front and rear seats of the stroller.

[0128] <Variation 3> As shown in Fig. 42, the speaker unit pair may be installed side by side on the pusher (parent) side of the bar used to push the stroller. With such an arrangement, the speaker unit pair can be targeted at the user (parent) pushing the stroller. It goes without saying that in the strollers shown in Figs. 37 and 38, the speaker unit pair may also be installed side by side on the pusher (parent) side of the bar used to push the stroller. Furthermore, the speaker unit pair may be installed in combination with the speaker unit pairs described in the seventh embodiment and all modified examples. By installing a combination of speaker unit pairs facing the user (parent) pushing the stroller and the user (infant) pushing the stroller, there is an advantage in that the user (parent) pushing the stroller can easily check whether or not they are emitting sound to the user (infant).

[0129] <Additional Notes> The foregoing description of the embodiments of the present 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 were chosen and described to provide the 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 uses 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

1. At least two speaker unit pairs are provided, each of which includes a positive speaker that does not include a speaker box and a negative speaker that does not include a speaker box, and which emit acoustic signals in opposite phases to each other to form an extremely narrow audible area in which sound can be heard only in the vicinity of the speaker unit pairs; a selection unit that selects one of the speaker unit pairs according to the position of the user's auditory organs and the positions of the speaker unit pairs; a control unit that controls the speaker unit pair so that an acoustic signal of a predetermined sound source (hereinafter referred to as a first acoustic signal) is emitted only from the positive speaker of the selected speaker unit pair, and an acoustic signal having an opposite phase to the first acoustic signal (hereinafter referred to as a second acoustic signal) is emitted only from the negative speaker of the selected speaker unit pair, At least two of the speaker unit pairs are arranged horizontally so as to emit sound in approximately the same direction, and in the vicinity of each of the at least two speaker unit pairs, the sound waves emitted from the front of the positive speaker and the negative speaker and the sound waves coming around from the back are designed so that the positive and negative phases of the sound waves are in a completely opposite relationship and do not overlap, The positive speaker and the negative speaker of each of at least two speaker unit pairs are arranged side by side in a vertical direction; The positive speaker is positioned closer to the user's ear than the negative speaker. Sound system.

2. The acoustic system of claim 1, The speaker further includes a direction control unit that controls directionality so that an intermediate region between the positive speaker and the negative speaker becomes an audible region. Sound system.

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