Sound System

Abstract

Provided is a sound system for users who use a seat in an aircraft, an automobile, or the like, said sound system being such that sound that cannot be heard by surrounding users is played back without the use of earphones or headphones. This sound system includes a speaker system configured from one speaker unit that emits sound on the basis of a sound signal from a specified sound source, and said sound system is such that the sound emitted from the speaker unit can be heard in a region in the vicinity of the speaker unit where the sound ought to be audible, and via the traveling around to a front surface direction of a sound emitted from the speaker unit in a rear surface direction, the sound emitted from the speaker unit in the front surface direction and the sound emitted from the speaker unit in the rear surface direction cancel each other out in a front surface direction region distant from the speaker unit.

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 an acoustic system that includes a speaker system composed of one speaker unit that emits sound based on an acoustic signal from a predetermined sound source, wherein the sound emitted from the speaker unit can be heard in an area near the speaker unit where it should be audible, and the sound emitted from the speaker unit toward the rear wraps around toward the front, so that the sound emitted from the speaker unit toward the front and the sound emitted from the speaker unit toward the rear cancel each other out in the front area away from the speaker unit. 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 block diagram showing an example of the configuration of an acoustic system 200. [Figure 16] 1 is a diagram showing an example of the configuration of a speaker unit 1221 to which a baffle plate 1222 is attached. [Figure 17] FIG. 1 is a block diagram showing an example of the configuration of a telephone conference device to which an audio system 200 is applied. 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] <Second embodiment> In this embodiment, an audio system will be described that applies the experimental results of Condition 2 and Condition 3 described in <Technical Background>. That is, the audio system of this embodiment is configured using a speaker system consisting of one speaker unit.

[0032] Hereinafter, acoustic system 200 will be described with reference to Fig. 15. Fig. 15 is a block diagram showing the configuration of acoustic system 200. As shown in Fig. 15, acoustic system 200 includes a playback device 210 and a speaker system 220. Speaker system 220 includes one speaker unit 1221 to which a baffle plate 1222 is attached.

[0033] The baffle plate 1222 is a member for lengthening the path through which sound emitted from the speaker unit 1221 in the direction opposite to the user direction (i.e., toward the rear) travels back toward the user direction (i.e., toward the front), in other words, for preventing sound from traveling back from the rear of the speaker unit (see FIG. 16). The range in which sound emitted from the speaker unit 1221 to which the baffle plate 1222 is attached can be heard (so-called sweet spot) is larger than the range in which sound emitted from the speaker unit 1221 to which the baffle plate 1222 is not attached can be heard. Therefore, if the sweet spot is sufficiently large, there is no need to attach the baffle plate 1222 to the speaker unit 1221.

[0034] The operation of the acoustic system 200 will be described below with reference to FIG.

[0035] The reproduction device 210 outputs an acoustic signal obtained based on the reproduction object.

[0036] The speaker system 220 receives an acoustic signal output by the playback device 210 and emits sound based on the acoustic signal. The sound emitted from the speaker unit 1221 can be heard in an area near the speaker unit 1221 that should be audible (i.e., near the front of the speaker unit 1221), but cannot be heard in other areas (for example, an area in the front direction away from the speaker unit 1221, or an area to the side of the speaker unit 1221). The reason why the sound can be heard near the front of speaker unit 1221 but cannot be heard in a frontal area far from speaker unit 1221 is that the sound emitted from speaker unit 1221 in the direction toward the user and the sound emitted from speaker unit 1221 in the direction opposite to the user are in opposite phase with each other, and the sound emitted from speaker unit 1221 in the direction opposite to the user wraps around toward the user, so that the sound emitted from speaker unit 1221 in the direction toward the user and the sound emitted from speaker unit 1221 in the direction opposite to the user do not cancel each other out near the front of speaker unit 1221, but do cancel each other out in a frontal area far from speaker unit 1221. As described above, the baffle plate 1222 is a component that lengthens the path that the sound emitted from the speaker unit 1221 toward the rear travels around to the front of the speaker unit 1221, and the area that should be audible becomes larger as the size of the baffle plate 1222 increases.

[0037] The sound system 200 may include a microphone (not shown) for picking up the user's voice. This microphone is installed in an area other than the area to be audible. By installing the microphone in an area other than the area to be audible, the microphone picks up only the user's voice without picking up the sound emitted from the speaker unit 1221. FIG. 17 is a diagram showing an example of the configuration of a conference call device to which the sound system 200 is applied. The conference call device of FIG. 17 includes a speaker unit to which a baffle plate is attached, a microphone for picking up the user's voice, a connector for connecting a cable for taking in an acoustic signal from a remote location, and an operation unit for operating the conference call device. The size of the baffle plate may be determined in consideration of the size of the area to be audible and the size allowable in terms of the design of the conference call device. In addition, in order to shorten the distance between the area to be audible and the conference call device, the speaker unit may be at a predetermined angle with respect to the ground surface of the conference call device. In order to make it easier to pick up the user's voice, the microphone should be placed in front of the speaker unit (i.e., on the side where the user is located) in an area other than the area that should be audible. In addition, if the conference call device has an echo cancellation function, the microphone for picking up the reference sound and error sound should also be placed in the front. A member for holding the speaker unit may be attached to the back of the speaker unit. In this case, a member with a mesh structure, for example, should be used to prevent the sound emitted from the back of the speaker unit from being obstructed from wrapping around to the front.

[0038] 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.

[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 that is composed of one speaker unit that emits sound based on an acoustic signal from a predetermined sound source. An audio system comprising: The sound emitted from the speaker unit can be heard in an area near the speaker unit where the sound should be audible, the speaker unit is not housed in a speaker box, and a member for holding the speaker unit is attached to the speaker box; Since the sound emitted from the speaker unit in the rear direction wraps around to the front direction, the sound emitted from the speaker unit in the front direction and the sound emitted from the speaker unit in the rear direction cancel each other out in the front direction area far from the speaker unit, Further, the present invention includes a microphone for picking up a user's voice and a microphone for picking up a reference sound or an error sound, The microphone for picking up the user's voice and the microphone for picking up the reference sound or the error sound are both installed in front of the speaker unit in an area other than the area to be audible. Sound system.

2. An acoustic system as claimed in claim 1, The speaker unit has a member for holding the speaker unit attached to a rear surface of the speaker unit, The member that holds the speaker unit is a member that does not impede the sound emitted from the speaker unit toward the rear from escaping toward the front. An audio system characterized by:

3. 2. The audio system of claim 1, A baffle plate is attached to the speaker unit, The baffle plate is a member for lengthening a path through which sound emitted from the speaker unit toward the rear side returns to the front side of the speaker unit, The larger the baffle plate, the larger the area that should be audible. An audio system characterized by:

4. 2. The audio system of claim 1, The speaker unit is at a predetermined angle to the ground surface of the sound system. An audio system characterized by:

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