Acoustic system

Abstract

To provide an acoustic system for passengers seated in seats in aircraft or automobiles that reproduces sound that cannot be heard by other passengers without the need for earphones or headphones.SOLUTION: A wearable acoustic system includes at least one speaker unit pair including a positive speaker unit that emits sound based on an acoustic signal of a predetermined sound source and a negative speaker unit that emits sound based on an acoustic signal that is in phase opposite to the acoustic signal, the speaker unit pair is configured such that the positive speaker unit and the negative speaker unit of the speaker unit pair located at the forefront when viewed from the front are adjacent to each other, the speaker unit pair is open type, the sound based on the acoustic signal is emitted from the positive speaker unit, and the sound based on the acoustic signal that is in phase opposite to the acoustic signal is emitted from the negative speaker unit in the front direction, and an audible area is formed for each speaker unit pair.SELECTED DRAWING: Figure 15

Description

[Technical field]

[0001] The present invention relates to a sound reproduction technology that can be used in audio systems installed in seats of aircraft, automobiles, etc. [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 surroundings of the user, 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 on 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 bothersome for users. Some users do not like wearing them because they mess up their hair. Others dislike the pressure they put on their ears. Furthermore, wearing earphones or headphones for long periods of time can cause users to feel tired after listening to them.

[0005] To eliminate the need to wear earphones or headphones, it is possible to synthesize a virtual sound field using wave field synthesis technology; however, this would require the preparation of a large-scale speaker array, which is not realistic.

[0006] Therefore, an object of the present invention is to provide an audio system for a user seated in an airplane, automobile, etc., that reproduces sounds that cannot be heard by surrounding users without the need for earphones or headphones. [Means for solving the problem]

[0007] One aspect of the present invention is a wearable acoustic system that includes a speaker system including at least one speaker unit pair including a speaker unit (hereinafter referred to as a positive speaker unit) that emits sound based on an acoustic signal of a predetermined sound source and a speaker unit (hereinafter referred to as a negative speaker unit) that emits sound based on an acoustic signal that is in phase opposite to the acoustic signal, wherein the speaker unit pair is configured so that the positive speaker unit and the negative speaker unit of the speaker unit pair that are located foremost when viewed from the front of the speaker unit pair are adjacent to each other, the speaker unit pair is an open type, the sound based on the acoustic signal is emitted in the front direction from the positive speaker unit, and the sound based on an acoustic signal that is in phase opposite to the acoustic signal is emitted in the front direction from the negative speaker unit, and an audible area is formed for each speaker unit pair. Effect of the Invention

[0008] According to the present invention, it is possible to reproduce sounds that can only be heard in a very limited range. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram for explaining the directivity of a sound emitted from a speaker. [Diagram 2] 3A and 3B are diagrams for explaining the directivity of sound emitted from a speaker unit. [Diagram 3] 1A and 1B are diagrams for explaining sounds emitted from a speaker unit pair. [Figure 4] 1A and 1B are diagrams for explaining the directivity of sounds emitted from a speaker unit pair. [Diagram 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 the microphone). [Figure 8] FIG. 13 is a diagram showing the experimental conditions (other measurement positions). [Figure 9] FIG. 13 is a diagram showing experimental results (condition 1). [Figure 10] FIG. 13 is a diagram showing experimental results (condition 2). [Figure 11] FIG. 13 is a diagram showing experimental results (condition 3). [Figure 12] FIG. 13 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] FIG. 2 is a diagram illustrating an example of a configuration of a speaker unit pair. [Figure 16] FIG. 2 is a diagram illustrating an example of a configuration of a speaker unit pair. [Figure 17] FIG. 2 is a diagram illustrating an example of a configuration of a speaker unit pair. [Figure 18A] FIG. 2 is a diagram illustrating an example of a configuration of a speaker unit pair. [Figure 18B] FIG. 2 is a diagram illustrating an example of a configuration of a speaker unit pair. [Figure 18C] FIG. 2 is a diagram illustrating an example of a configuration of a speaker unit pair. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail. Note that components having the same functions are given the same reference numbers and duplicated explanations will be omitted.

[0011] <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 effect of the speaker unit pair of the present invention will be described.

[0012] 1: Directivity of sound emitted from a speaker Typically, a speaker is made up of a speaker unit and a speaker box. The speaker unit is a component that includes a diaphragm that converts an acoustic signal, which is an electrical signal, into vibrations in the air (i.e., generates sound waves). The speaker box is a component that houses the speaker unit.

[0013] 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 vibration of the diaphragm. Here, sound waves emitted to the outside of the speaker box (i.e., toward the front of the speaker unit) are called positive sound waves, and sound waves emitted to the inside of the speaker box (i.e., toward the back of the speaker unit) are called negative sound waves. Negative sound waves are sound waves with a phase opposite to that of positive sound waves. Figure 1 is a diagram for 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 go outside the speaker box. As a result, the sound emitted from the speaker can be heard over a wide range.

[0014] 2: Directivity of sound emitted from a pair of speaker units Here, we will first explain the directivity of sound emitted from a speaker unit, which is a bare speaker. Figure 2 is a diagram for explaining the directivity of sound emitted from a speaker unit. In the case of only a speaker unit, unlike the case of a speaker, negative sound waves are emitted from the back of the speaker unit hidden inside the speaker box. Therefore, as shown in Figure 2, the sound emitted from the speaker unit has a bidirectional characteristic.

[0015] In the present invention, this bidirectionality is utilized. A specific description will be given below. First, as shown in FIG. 3, two speaker units are arranged to form a speaker unit pair. When acoustic signals with opposite positive and negative relationships are input to the speaker unit pair, the diaphragms of the two speaker units vibrate and emit sounds based on these two acoustic signals. Then, as shown in FIG. 4, sounds are eliminated in all directions except for the vicinity of the speaker unit pair. In other words, sounds are eliminated only at positions sufficiently far away from the speaker unit pair, and sounds are not eliminated in the vicinity of the speaker unit pair. The reason why sounds are not eliminated in the vicinity of the speaker unit pair is because the phases of the sound waves radiated from the front of the speaker unit and the sound waves wrapping around from the back are not aligned in the vicinity of the speaker unit pair.

[0016] 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 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.

[0017] 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. In the experiment, the following speakers, speaker units, and speaker unit pairs were used: a speaker with a diaphragm with a diameter of 4.5 cm (see Fig. 5), a speaker with the speaker box removed leaving only the speaker unit (see Fig. 6), and two of the speaker units arranged side by side (see Fig. 7). In addition, microphones were placed under the following four conditions to measure the frequency characteristics near the speaker, speaker unit, and speaker unit pair.

[0018] (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) 2cm from the front of the speaker unit pair In addition, for comparison purposes under all conditions, microphones were placed 100 cm from the front, back, and side of the speaker, speaker unit, and speaker unit pair (see Figure 8).

[0019] The experimental results are explained below. Figures 9, 10, 11, and 12 are diagrams showing the experimental results, and are diagrams showing the relationship between frequency and attenuation under conditions 1, 2, 3, and 4, respectively. Each diagram shows four curves, of which one curve indicated by an arrow is a sound picked up by a microphone located 5 cm or 2 cm from the front, and the other three curves are sounds picked up by microphones located 100 cm from the front, back, and side. The curves located 5 cm or 2 cm from the front are located near a speaker, etc., so the gain is very large. Therefore, to make it easier to see, the curve located 5 cm from the front is plotted at -25 dB lower than the three curves located 100 cm. Similarly, the curve located 2 cm from the front is plotted at -32 dB. Comparing Figures 9 and 10, when a speaker is used, there is almost no difference between the four curves, while when a speaker unit is used, there is a difference between the curve located 5 cm from the front and the other three curves. This difference is more pronounced in the lower frequencies. Also, comparing Figure 11 with Figure 12, we can see that the difference between the curve 2 cm from the front and the other three curves is larger for the speaker unit pair than for the speaker unit itself.

[0020] 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.

[0021] First Embodiment A system that reproduces an acoustic signal obtained based on an object to be reproduced is called an acoustic system. An acoustic system includes a speaker system for emitting the acoustic signal as sound (hereinafter, this sound is referred to as sound based on an acoustic signal). Here, a speaker system is a device that converts an analog acoustic signal into sound. An object to be reproduced is data or a signal from which an acoustic signal can be obtained by a predetermined process, such as data recorded on a CD, DVD, or record, data received via the Internet, or a signal received via a radio or television broadcast.

[0022] Here, an acoustic system that reproduces sound based on an acoustic signal obtained from a reproduction target object so that only a user in the vicinity of the speaker system can hear it will be described. In other words, the reproduced sound of the acoustic system cannot be heard by users other than the user in the vicinity of the speaker system. When such an acoustic system is used as an acoustic system for a user using a seat in an aircraft, for example, a system can be provided in which only the user using the seat can hear the reproduced sound. FIG. 13 is a diagram showing an example of an acoustic system installed on an aircraft seat. The acoustic system in FIG. 13 is installed on a seat so as to sandwich the head of a seated user, and two speaker unit pairs are arranged so as to be located near the left and right ears. Note that such an acoustic system can be installed in vehicles other than aircraft, such as automobiles and trains, reclining chairs, and the like, and can also be installed in a wearable form, such as on the shoulder. In addition, a driver unit pair in which two driver units are arranged side by side, which corresponds 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 types: open-air and closed. By applying the above technology to open-air headphones, in which sound leakage is a particular concern, it is expected that sound leakage will be reduced.

[0023] 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., a first playback unit 112, ..., an Nth playback unit 112). The speaker system 120 includes N speaker unit pairs 122 (i.e., a first speaker unit pair 122, ..., an Nth speaker unit pair 122). The 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 of an acoustic signal input to the positive speaker unit 1221 is input to the negative speaker unit 1221. The speaker system 120 is installed in a position close to the head of a user using the seat.

[0024] 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 a sound emitted from the positive speaker unit 1221 in the direction opposite to the nth user direction and a 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. Also, 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.

[0025] 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 are cancelled out by each other so that they cannot be heard by users using other seats.

[0026] The operation of the acoustic system 100 will be described below with reference to FIG.

[0027] The reproducing device 110 receives a first acoustic signal, a third acoustic signal, ..., a 2N-1th acoustic signal, which are acoustic signals obtained based on a reproduction target, as input, and outputs a first acoustic signal, a second acoustic signal, ..., a 2Nth acoustic signal. More specifically, the nth reproducing unit 112 (n=1, ..., N) receives the 2n-1th acoustic signal as input, generates a 2nth acoustic signal, which is an acoustic signal in opposite phase to the 2n-1th acoustic signal, from 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.

[0028] The speaker system 120 receives 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 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. Since the 2n-1th acoustic signal and the 2nth acoustic signal are in an anti-phase relationship with each other, as described in <Technical Background>, the sound 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 respectively the right channel acoustic signal and the left channel acoustic signal of a certain sound source, the stereo sound can be heard only in the vicinity of the seat where the speaker system 120 is installed.

[0029] 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 opposite direction to the n-th user direction have an opposite phase relationship. 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 opposite direction to the n-th user direction have an opposite phase relationship.

[0030] According to an embodiment of the present invention, it is possible to reproduce sounds that can be heard only in a very limited narrow range, namely, in the vicinity of the speaker system.

[0031] (Example of speaker unit pair configuration) The positive speaker unit and the negative speaker unit included in one speaker unit pair are basically located very close to each other. The same speaker unit is used for the positive speaker unit and the negative speaker unit so that they have the same acoustic characteristics. Instead of using the same speaker unit, an audio signal that has been signal-processed may be input so that the acoustic characteristics of the positive speaker unit and the negative speaker unit are the same.

[0032] Here, an example of the configuration of a speaker unit pair will be described from the viewpoint of the positional relationship between the positive speaker unit and the negative speaker unit.

[0033] In any of the configuration examples described below, the speaker unit pair is configured so that sound emitted from the positive speaker unit in the direction opposite to the user (i.e., toward the rear), and sound emitted from the negative speaker unit in the direction opposite to the user (i.e., toward the rear), reverberates toward the user (i.e., toward the front).

[0034] Configuration example 1: Fig. 15 is a diagram showing an example of the configuration of a speaker unit pair in which a positive speaker unit and a negative speaker unit are arranged vertically. More specifically, the speaker unit pair is configured such that the surfaces of the positive speaker unit and the negative speaker unit of the speaker unit pair located at the forefront when viewed from the front of the speaker unit pair form a single plane perpendicular to the ground surface of the speaker unit pair, and the arrangement of the positive speaker unit and the negative speaker unit of the speaker unit pair when viewed from the front of the speaker unit pair is parallel to the direction perpendicular to the ground surface of the speaker unit pair. Here, the surfaces of the positive speaker unit and the negative speaker unit of the speaker unit pair located at the forefront when viewed from the front of the speaker unit pair refer to the surfaces of the cone-shaped diaphragms constituting the positive speaker unit and the negative speaker unit that are in contact with each other when viewed from the front (i.e., the bottom surfaces of the two cones). As can be seen from FIG. 15, the positive speaker unit and the negative speaker unit are usually arranged in a very close positional relationship, such as next to each other.

[0035] Configuration Example 2: Fig. 16 is a diagram showing an example of the configuration of a speaker unit pair in which a positive speaker unit and a negative speaker unit are arranged side by side. More specifically, the speaker unit pair is configured such that the surfaces of the positive speaker unit and the negative speaker unit of the speaker unit pair located at the front when viewed from the front of the speaker unit pair form a single plane perpendicular to the ground surface of the speaker unit pair, and the arrangement of the positive speaker unit and the negative speaker unit of the speaker unit pair when viewed from the front of the speaker unit pair is parallel to the horizontal direction to the ground surface of the speaker unit pair. As can be seen from Fig. 16, the positive speaker unit and the negative speaker unit are usually arranged in a very close positional relationship, such as next to each other.

[0036] Configuration Example 3: Fig. 17 is a diagram showing an example of the configuration of a speaker unit pair in which a positive speaker unit and a negative speaker unit are arranged side by side at an angle. More specifically, the speaker unit pair is configured such that the surfaces of the positive speaker unit and the negative speaker unit of the speaker unit pair located at the front when viewed from the front of the speaker unit pair are planes that form a predetermined angle θ (where 0<θ<π / 2) with the ground surface of the speaker unit pair, and the arrangement of the positive speaker unit and the negative speaker unit of the speaker unit pair when viewed from the front of the speaker unit pair is parallel to a horizontal direction with respect to the ground surface of the speaker unit pair. As can be seen from Fig. 17, the positive speaker unit and the negative speaker unit are usually arranged in a very close positional relationship, such as next to each other.

[0037] Configuration Example 4: Figures 18A, 18B, and 18C are diagrams showing an example of the configuration of a speaker unit pair in which a positive speaker unit and a negative speaker unit are inclined obliquely and arranged in a line from front to back. Figure 18A is a diagram showing the positive speaker unit and the negative speaker unit from the front, Figure 18B is a diagram showing the positive speaker unit and the negative speaker unit from the rear, and Figure 18C is a diagram showing the positive speaker unit and the negative speaker unit from the side. More specifically, the speaker unit pair is configured so that the surface of the positive speaker unit of the speaker unit pair located at the forefront when viewed from the front of the speaker unit pair and the surface of the negative speaker unit of the speaker unit pair located at the forefront when viewed from the front of the speaker unit pair are parallel to a plane that forms a predetermined angle θ (where 0<θ<π / 2) with the ground plane of the speaker unit pair. Here, the surface of the positive speaker unit (negative speaker unit) of the speaker unit pair located at the front when viewed from the front of the speaker unit pair refers to the surface of the cone-shaped diaphragm constituting the positive speaker unit (negative speaker unit) that is in contact with the part (i.e., the bottom surface of one cone) that is at the front when viewed from the front, in the example of FIG. 18A. As can be seen from FIG. 18A, FIG. 18B, and FIG. 18C, the positive speaker unit and the negative speaker unit are usually arranged in a very close positional relationship, such as adjacent to each other. Also, as can be seen from FIG. 18C, when the positive speaker unit and the negative speaker unit are viewed from directly above, the positive speaker unit and the negative speaker unit appear to overlap each other. When the positional relationship of the positive speaker unit and the negative speaker unit is very close to the extent shown in FIG. 18C, the volume occupied by the speaker unit can be reduced, and therefore the acoustic system can be made compact.

[0038] When the positive speaker unit and the negative speaker unit are arranged at an angle as in configuration example 3 and configuration example 4, the area to be audible may deviate from the desired area due to the oblique arrangement. In such a case, it is preferable to control the directionality of the acoustic signal so that the position of the user's ear is included in the area to be audible. Any method can be used for the directionality control, and for example, filtering using an FIR (Finite Impulse Response) filter can be used. In this case, it is preferable to design the FIR filter based on a speaker unit close to the area to be audible.

[0039] <Additional Notes> The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings. The embodiments have been chosen and depicted to provide a best illustration of the principles of the invention and to enable those skilled in the art to utilize the invention in various embodiments and with various modifications as may be suitable for the practical use contemplated. All such modifications and variations are within the scope of the invention as defined by the appended claims interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. A speaker system including at least one speaker unit pair including a speaker unit that emits a sound based on an acoustic signal of a predetermined sound source (hereinafter referred to as a positive speaker unit) and a speaker unit that emits a sound based on an acoustic signal of an opposite phase to the acoustic signal (hereinafter referred to as a negative speaker unit). An audio system comprising: the speaker unit pair is configured such that a positive speaker unit and a negative speaker unit of the speaker unit pair located at the front as viewed from the front direction of the speaker unit pair are adjacent to each other; The speaker unit pair is an open type, a sound based on the acoustic signal is emitted from the positive speaker unit in a front direction, and a sound based on an acoustic signal having an opposite phase to the acoustic signal is emitted from the negative speaker unit in a front direction; An audible area is formed for each pair of speaker units. Wearable sound system.

2. 2. The audio system of claim 1, The positive speaker unit and the negative speaker unit of the speaker unit pair are speaker units having substantially the same acoustic characteristics. An audio system characterized by:

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