Sound 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

[0006] , ,

[0005] ,

[0001] The present invention relates to a sound reproduction technology that can be used in an audio system installed in a seat of an aircraft, an automobile, or the like.

Background Art

[0002] Conventionally, users have used earphones or headphones to watch movies and listen to music on an aircraft (see Non-Patent Document 1). This is because when using a speaker, the reproduced sound reaches the surroundings of the user, which causes inconvenience to other users.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, wearing earphones or headphones is troublesome for users. In addition, there are users who do not like to wear them because their hairstyles are messed up or for other reasons. There are also users who dislike the pressure on their ears caused by wearing them. Furthermore, wearing earphones or headphones for a long time may also make users feel tired of listening.

[0005] In order to eliminate the need to wear earphones or headphones, it is also conceivable to synthesize a virtual sound field using wavefront synthesis technology. In this case, however, it is necessary to prepare a large-scale speaker array, which is not practical.

[0006] Therefore, the present invention aims to provide an acoustic system for users of seats in aircraft, automobiles, etc., that reproduces sounds that cannot be heard by surrounding users without using earphones or headphones. [Means for solving the problem]

[0007] One aspect of the present invention is a wearable acoustic system including a speaker system that includes at least one speaker unit pair, each including a speaker unit that emits 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 sound based on an acoustic signal in opposite phase to the acoustic signal (hereinafter referred to as a negative speaker unit), wherein the speaker unit pair is configured such that the positive speaker unit and the negative speaker unit of the speaker unit pair, which are located at the front when viewed from the front of the speaker unit pair, 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 in the forward direction, the sound based on an acoustic signal in opposite phase to the acoustic signal is emitted from the negative speaker unit in the forward direction, and an audible region is formed for each speaker unit pair. [Effects of the Invention]

[0008] According to the present invention, it is possible to reproduce sounds that can only be heard within a very limited and narrow range. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram illustrates the directivity of sound emitted from a speaker. [Figure 2] This diagram illustrates the directivity of sound emitted from a speaker unit. [Figure 3] This is a diagram illustrating the sound emitted from a speaker unit pair. [Figure 4] This diagram illustrates the directivity of sound emitted from a pair of speaker units. [Figure 5]It is a diagram showing the state of the experiment (the positional relationship between the speaker and the microphone). [Figure 6] It is a diagram showing the state of the experiment (the positional relationship between the speaker unit and the microphone). [Figure 7] It is a diagram showing the state of the experiment (the positional relationship between the speaker unit pair and the microphone). [Figure 8] It is a diagram showing the state of the experiment (other measurement positions). [Figure 9] It is a diagram showing the experimental result (condition 1). [Figure 10] It is a diagram showing the experimental result (condition 2). [Figure 11] It is a diagram showing the experimental result (condition 3). [Figure 12] It is a diagram showing the experimental result (condition 4). [Figure 13] It is a diagram showing an example of an acoustic system installed in an aircraft seat. [Figure 14] It is a block diagram showing an example of the configuration of the acoustic system 100. [Figure 15] It is a diagram showing an example of the configuration of a speaker unit pair. [Figure 16] It is a diagram showing an example of the configuration of a speaker unit pair. [Figure 17] It is a diagram showing an example of the configuration of a speaker unit pair. [Figure 18A] It is a diagram showing an example of the configuration of a speaker unit pair. [Figure 18B] It is a diagram showing an example of the configuration of a speaker unit pair. [Figure 18C] It is a diagram showing an example of the configuration of a speaker unit pair. [[ID=四十八]]

Embodiments for Carrying Out the Invention

[0010] [[ID=五十二]] [[ID=五十三]]Hereinafter, embodiments of the present invention will be described in detail. Components having the same function are denoted by the same reference numerals, and redundant descriptions are omitted.[[ID=五十四]] [[ID=五十五]]

[0011] [[ID=五十六]] [[ID=五十七]]<Technical Background>[[ID=五十八]] First, the directivity of the sound emitted from the speaker will be described. Next, the directivity of the sound emitted from the pair of speaker units of the present invention will be described. Finally, the results of an experiment to confirm the effects of the pair of speaker units of the present invention will be described.

[0012] 《1: Directivity of Sound Emitted from Speaker》 Normally, a speaker is composed of a speaker unit and a speaker box. The speaker unit is a component including a diaphragm that converts an acoustic signal, which is an electrical signal, into air vibrations (that is, generates sound waves). The speaker box is a component that houses the speaker unit.

[0013] When an acoustic signal is input to the speaker, the diaphragm of the speaker unit vibrates, and sound waves are radiated in both directions in which the diaphragm vibrates. Here, the sound waves radiated to the outside of the speaker box (that is, the front direction of the speaker unit) are called positive sound waves, and the sound waves radiated to the inside of the speaker box (that is, the back direction of the speaker unit) are called negative sound waves. The negative sound waves are sound waves with a phase opposite to that of the positive sound waves. FIG. 1 is a diagram for explaining the directivity of the sound emitted from the speaker. As shown in FIG. 1, the positive sound waves are radiated omnidirectionally from the speaker, while the negative sound waves do not come out of 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 Pair of Speaker Units》 Here, first, the directivity of the sound emitted from the speaker unit, which is a bare speaker, will be described. FIG. 2 is a diagram for explaining the directivity of the sound emitted from the speaker unit. In the case of only the speaker unit, different from the case of the speaker, negative sound waves are radiated from the back of the speaker unit hidden inside the speaker box. Therefore, as shown in FIG. 2, the sound emitted from the speaker unit has a characteristic of bidirectionality.

[0015] The present invention utilizes this bidirectional property. This will be explained in detail below. First, as shown in Figure 3, two speaker units are placed side by side to form a speaker unit pair. When acoustic signals with opposite polarity are input to this speaker unit pair, the diaphragms of the two speaker units vibrate, and sound is emitted based on these two acoustic signals. As a result, as shown in Figure 4, sound is canceled out in all directions except in the vicinity of the speaker unit pair. In other words, sound is canceled out only at positions sufficiently far from the speaker unit pair, and sound is not canceled out in the vicinity of the speaker unit pair. The reason why sound is not canceled out in the vicinity of the speaker unit pair is that in the vicinity of the speaker unit pair, the phases of the sound waves radiated from the front of the speaker unit and the sound waves that wrap around from the back do not align.

[0016] In other words, by inputting a predetermined acoustic signal to one speaker unit constituting a speaker unit pair and an acoustic signal with the opposite phase to that predetermined acoustic signal to the other speaker unit, it becomes possible to create a situation where sound is only audible in the vicinity of the speaker unit pair, and sound is not audible to other users, by utilizing the property that sound is only audible in the vicinity of the speaker unit pair.

[0017] 《3: Experimental Results》 This section describes the results of an experiment measuring the frequency characteristics of a speaker, a speaker unit, and a pair of speaker units. The experiment used a speaker with a diaphragm diameter of 4.5 cm (see Figure 5), a speaker unit with the speaker box removed (see Figure 6), and two of these speaker units placed side-by-side (see Figure 7). Microphones were set up under the following four conditions to measure the frequency characteristics in the vicinity of the speaker, speaker unit, and pair of speaker units.

[0018] (Condition 1) 5 cm from the front of the speaker (Condition 2) Position 5 cm from the front of the speaker unit (Condition 3) Position 2 cm from the front of the speaker unit (Condition 4) Position 2 cm from the front of the speaker unit pair Furthermore, for comparison purposes, microphones were also placed 100 cm from the front, back, and side of the speaker, speaker unit, and speaker unit pair under all conditions (see Figure 8).

[0019] The experimental results are described 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; one curve indicated by an 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 at 5 cm or 2 cm from the front have a very high gain because they are located near speakers, etc. Therefore, for clarity, the curve at 5 cm from the front is plotted at -25 dB compared to the three curves at 100 cm. Similarly, the curve at 2 cm from the front is plotted at -32 dB. Comparing Figure 9 and Figure 10, it can be seen that 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 at 5 cm from the front and the other three curves. This difference is more pronounced at lower frequencies. Furthermore, comparing Figure 11 and Figure 12, it can be seen that the speaker unit pair exhibits a larger difference between the curve at 2cm from the front and the other three curves compared to the speaker unit alone.

[0020] Based on the experiments described above, it was confirmed that the sound emitted from the speaker unit pair of the present invention is audible only in the vicinity of the speaker unit pair.

[0021] <First Embodiment> An acoustic system is a system that reproduces an acoustic signal obtained from a playback object. An acoustic system includes a speaker system to emit the acoustic signal as sound (hereinafter, this sound will be referred to as sound based on the acoustic signal). Here, the speaker system is a device that converts the acoustic signal, which is an analog signal, into sound. The playback object refers to data or signals from which an acoustic signal can be obtained through predetermined processing, such as data recorded on CDs, DVDs, or records, data received via the internet, or signals received via radio or television broadcasts.

[0022] This section describes an acoustic system that reproduces sound based on acoustic signals obtained from an object, so that only users near the speaker system can hear it. In other words, the sound reproduced by the acoustic system is inaudible to users other than those near the speaker system. If such an acoustic system is used, for example, as an acoustic system for users using an airplane seat, it is possible to provide a system in which only the user using that seat can hear the reproduced sound. Figure 13 shows an example of an acoustic system installed in an airplane seat. The acoustic system in Figure 13 is installed in the seat so as to surround the head of the seated user, with two speaker unit pairs positioned near the left and right ears. Such an acoustic system can also be installed in vehicles other than airplanes, such as cars and trains, as well as in reclining chairs, and can also be installed in a wearable form, such as resting on the shoulders. Alternatively, a driver unit pair consisting of two driver units side by side, equivalent to the speaker unit pair described above, may be installed in each left and right unit of headphones or earphones. Headphones are generally classified into two main types: open-air and closed-back. Applying the above technology to open-back headphones, which are particularly prone to sound leakage, is expected to reduce sound leakage.

[0023] The sound system 100 will be described below with reference to Figure 14. Figure 14 is a block diagram showing the configuration of the sound system 100. As shown in Figure 14, the sound system 100 includes a playback device 110 and a speaker system 120. The playback device 110 includes N playback units 112 (i.e., a first playback unit 112, ..., the nth playback unit 112) (where N is an integer of 1 or more). The speaker system 120 also includes N speaker unit pairs 122 (i.e., a first speaker unit pair 122, ..., the 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). The negative speaker unit 1221 receives an acoustic signal that is in opposite phase to the acoustic signal input to the positive speaker unit 1221. The speaker system 120 is installed near the head of the user occupying 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). The positive speaker unit 1221 and negative speaker unit 1221 of the nth speaker unit pair 122 (n=1, …, N) are arranged such that sound emitted from the positive speaker unit 1221 in the opposite direction to the nth user direction and sound emitted from the negative speaker unit 1221 in the opposite direction to the nth user direction are transmitted to the nth user direction by wrapping around. Here, the nth user direction is the direction in front of the positive speaker unit 1221 and negative speaker unit 1221 of the nth speaker unit pair 122. The direction opposite to the nth user direction is the direction in front of the positive speaker unit 1221 and negative speaker unit 1221 of the nth speaker unit pair 122.

[0025] Furthermore, the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 122 (n=1, …, N) are positioned such that the sound emitted from the positive speaker unit 1221 and the sound emitted from the negative speaker unit 1221 cancel each other out so that they cannot be heard by users of other seats.

[0026] The operation of the sound system 100 will be described below in accordance with Figure 14.

[0027] The playback device 110 takes the first acoustic signal, third acoustic signal, ..., second N-1 acoustic signal, which are acoustic signals obtained based on the object to be reproduced, as input and outputs the first acoustic signal, second acoustic signal, ..., second N acoustic signal. More specifically, the nth playback unit 112 (n=1, ..., N) takes the second n-1 acoustic signal as input, generates the second n acoustic signal, which is an acoustic signal with the opposite phase to the second n-1 acoustic signal, from the second n-1 acoustic signal, and outputs the second n-1 acoustic signal and the second n acoustic signal. The second n-1 acoustic signal and the second n 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 takes the first, second, ..., second-nth acoustic signals output by the playback device 110 as input and emits sounds based on the first acoustic signal, sounds based on the second acoustic signal, ..., second-nth acoustic signal. More specifically, the nth speaker unit pair 122 (n=1, ..., N) takes the second-n-1st acoustic signal and the second-nth acoustic signal as input and emits the sound based on the second-n-1st acoustic signal from the positive speaker unit 1221 and the sound based on the second-nth acoustic signal from the negative speaker unit 1221. Since the second-n-1st acoustic signal and the second-nth acoustic signal are in opposite phase to each other, as explained in <Technical Background>, the sound can only be heard in the vicinity of the seat where the speaker system 120 is installed. For example, in the case where N=2, if the first and third sound signals are the right channel and left channel sound signals of a certain sound source, respectively, then stereo sound can be heard only in the vicinity of the seat where the speaker system 120 is installed.

[0029] Furthermore, the sound emitted from the positive speaker unit 1221 of the nth speaker unit pair 122 towards the nth user and the sound emitted from the positive speaker unit 1221 of the nth speaker unit pair 122 in the opposite direction to the nth user are in opposite phase to each other. Similarly, the sound emitted from the negative speaker unit 1221 of the nth speaker unit pair 122 towards the nth user and the sound emitted from the negative speaker unit 1221 of the nth speaker unit pair 122 in the opposite direction to the nth user are in opposite phase to each other.

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

[0031] (Example of speaker unit pair configuration) The positive and negative speaker units in a single speaker unit pair are generally located very close to each other. Furthermore, identical speaker units are used for both the positive and negative speaker units to ensure they have the same acoustic characteristics. Alternatively, instead of using identical speaker units, an acoustic signal processed to achieve the same acoustic characteristics for both the positive and negative speaker units may be input.

[0032] This section describes an example of a speaker unit pair configuration from the perspective of the positional relationship between the positive and negative speaker units.

[0033] In all of the configuration examples described below, the speaker unit pair is configured such that sound emitted from the positive speaker unit in the opposite direction to the user (i.e., towards the rear) and sound emitted from the negative speaker unit in the opposite direction to the user (i.e., towards the rear) wraps around to the user (i.e., towards the front).

[0034] Configuration Example 1: Figure 15 shows an example of a speaker unit pair configuration 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 faces of the positive and negative speaker units 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 and negative speaker units 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 faces of the positive and negative speaker units of the speaker unit pair located at the front, when viewed from the front of the speaker unit pair, in the example of Figure 15, refer to the faces where the parts of the cone-shaped diaphragms that make up the positive and negative speaker units, which are closest when viewed from the front (i.e., the bottom surfaces of the two cones), are in contact. As can be seen in Figure 15, the positive and negative speaker units are usually placed in very close proximity, adjacent to each other.

[0035] Configuration Example 2: Figure 16 shows an example of a speaker unit pair configuration in which the positive and negative speaker units are arranged side by side. More specifically, the speaker unit pair is configured such that, when viewed from the front of the speaker unit pair, the faces of the positive and negative speaker units of the frontmost speaker unit 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 and negative speaker units of the speaker unit pair when viewed from the front of the speaker unit pair is parallel to the direction horizontal to the ground surface of the speaker unit pair. As can be seen in Figure 16, the positive and negative speaker units are usually placed in a very close position, adjacent to each other.

[0036] Configuration Example 3: Figure 17 shows an example of a speaker unit pair configuration in which the positive and negative speaker units are tilted diagonally and arranged side by side. More specifically, the speaker unit pair is configured such that the faces of the positive and negative speaker units of the speaker unit pair located at the front, when viewed from the front of the speaker unit pair, form a plane that makes a predetermined angle θ (where 0 < θ < π / 2) with the ground surface of the speaker unit pair, and the arrangement of the positive and negative speaker units of the speaker unit pair, when viewed from the front of the speaker unit pair, is parallel to the direction horizontal to the ground surface of the speaker unit pair. As can be seen in Figure 17, the positive and negative speaker units are usually placed in a very close positional relationship, adjacent to each other.

[0037] Configuration Example 4: Figures 18A, 18B, and 18C show an example of a speaker unit pair configuration in which a positive speaker unit and a negative speaker unit are tilted diagonally and arranged in a single row front to back. Figure 18A is a view of the positive and negative speaker units from the front, Figure 18B is a view of the positive and negative speaker units from the rear, and Figure 18C is a view of the positive and negative speaker units from the side. More specifically, the speaker unit pair is configured such that the face of the positive speaker unit of the speaker unit pair located at the very front when viewed from the front of the speaker unit pair, and the face of the negative speaker unit of the speaker unit pair located at the very front when viewed from the front of the speaker unit pair, are parallel to a plane that makes a predetermined angle θ (where 0 < θ < π / 2) with respect to the ground surface of the speaker unit pair. Here, the positive speaker unit (negative speaker unit) of a speaker unit pair, when viewed from the front, refers to the surface of the cone-shaped diaphragm that makes up the positive speaker unit (negative speaker unit), specifically the surface that is in contact with the front view (i.e., the bottom surface of one cone) in the example in Figure 18A. As can be seen in Figures 18A, 18B, and 18C, the positive and negative speaker units are usually positioned very close to each other, almost adjacent. Also, as can be seen in Figure 18C, when viewed from directly above, the positive and negative speaker units appear to overlap. When the positional relationship between the positive and negative speaker units is as close as shown in Figure 18C, the volume occupied by the speaker units can be reduced, making it possible to miniaturize the sound system.

[0038] As in Configuration Examples 3 and 4, when the positive and negative speaker units are positioned at an angle, the audible range may shift from the desired range due to this angled arrangement. In such cases, it is advisable to control the directivity of the acoustic signal so that the position of the user's ear is included in the audible range. Any method can be used for directivity control; for example, filtering using an FIR (Finite Impulse Response) filter can be used. In this case, the FIR filter should be designed using the speaker unit closest to the audible range as the reference.

[0039] <Note> The above-described embodiments of the present invention are presented for illustrative and descriptive purposes. They are not intended to be exhaustive, nor are they intended to limit the invention to the strict form disclosed. Modifications and variations are possible from the above teachings. The embodiments are selected and presented to provide the best illustration of the principles of the present invention and to enable those skilled in the art to utilize the invention in various embodiments and with various modifications to suit thoughtful practical use. All such modifications and variations are within the scope of the present invention as defined by the appended claims, interpreted in accordance with the fairly, lawfully, and equitably given width.

Claims

1. A speaker system comprising at least one speaker unit pair, each including a speaker unit that emits sound based on an acoustic signal from a predetermined sound source (hereinafter referred to as a positive speaker unit) and a speaker unit that emits sound based on an acoustic signal with the opposite phase to the aforementioned acoustic signal (hereinafter referred to as a negative speaker unit). An acoustic system including, The speaker unit pair is configured such that, when viewed from the front of the speaker unit pair, the frontmost surfaces of the diaphragms of the positive speaker unit and the negative speaker unit are aligned on a plane perpendicular to the ground surface of the speaker unit pair, the arrangement of the diaphragms of the positive speaker unit and the negative speaker unit is parallel to the direction horizontal to the ground surface of the speaker unit pair, and the diaphragms of the positive speaker unit and the negative speaker unit are adjacent to each other. The aforementioned speaker unit pair is of the open type, Sound based on the aforementioned acoustic signal is emitted forward from the positive speaker unit, and sound based on an acoustic signal with the opposite phase to the aforementioned acoustic signal is emitted forward from the negative speaker unit. One audible region is formed for each of the speaker unit pairs. A wearable audio system.

2. The acoustic system according to claim 1, The positive and negative speaker units of the aforementioned speaker unit pair are speaker units with substantially identical acoustic characteristics. An acoustic system characterized by the following features.

3. The acoustic system according to claim 1, The speaker unit pair is configured such that sound emitted from the positive speaker unit towards the rear and sound emitted from the negative speaker unit towards the rear wrap around to the front. An acoustic system characterized by the following features.

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