Sound System

Abstract

An acoustic system that has: a control system that generates control signals for eliminating noise from noise signals near the head of a user using a seat; a muting speaker system that is disposed near the head of the user using the seat and includes an M number of speaker units that emit sound on the basis of the control signals; and an emission suppression unit that includes at least a sound absorbing material that readily absorbs sound having at least a prescribed frequency, said emission suppression unit being configured such that sound having at least the prescribed frequency and emitted from the muting speaking system is unlikely to be emitted to other than the ears of the user. An mth muting speaker unit is disposed such that the sound emitted from the mth muting speaker unit in an mth muting user direction is muted at locations other than locations near the head of the user using the seat, as a result of sound, emitted from the mth speaker unit, wrapping around in a direction opposite to the mth muting user direction.

Description

[Technical field]

[0001] The present invention relates to a technique for reducing noise inside vehicles such as aircraft and automobiles. [Background technology]

[0002] Conventionally, when users are bothered by noise while watching movies or listening to music on an airplane, they have used earphones or headphones with a noise canceling function (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] In-flight entertainment / JAL First Class, [online], [searched on March 16, 2020], 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] Therefore, an object of the present invention is to provide a technique for reducing noise heard when seated in a vehicle seat without using earphones or headphones. [Means for solving the problem]

[0006] One aspect of the present invention is an acoustic system comprising: a control system, where M is an integer greater than or equal to 1, that generates a control signal for canceling noise from a noise signal (hereinafter referred to as a noise signal) at a location close to the head of a user using a seat; a noise-reduction speaker system including M speaker units (hereinafter referred to as noise-reduction speaker units) that are installed at locations close to the head of a user using a seat and emit sound based on the control signal; and a radiation suppression unit that includes at least a sound-absorbing material that is likely to absorb only sounds with frequencies above a predetermined value, and is configured to prevent sounds with frequencies above the predetermined value emitted from the noise-reduction speaker units from being radiated to anywhere other than the user's ears. The M silencer speaker units are designated as the first silencer speaker unit, ..., Mth silencer speaker unit, the direction in which the mth silencer speaker unit faces the user is designated the mth silencer user direction (m = 1, ..., M), and the mth silencer speaker unit (m = 1, ..., M) is positioned so that sound emitted from the mth silencer speaker unit in the mth silencer user direction is muted in all locations except near the head of the user using the seat by the wraparound of sound emitted from the mth silencer speaker unit in the opposite direction to the mth silencer user direction. Effect of the Invention

[0007] According to the present invention, it is possible to reduce noise heard when seated in a vehicle seat. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an active noise control system. [Diagram 2] 3A and 3B are diagrams for explaining the directivity of sound emitted from a speaker unit. [Diagram 3] FIG. 1 is a diagram showing an example of an audio system installed in an aircraft seat. [Figure 4] FIG. 5 is a block diagram showing an example of the configuration of an audio system 500. [Diagram 5] FIG. 2 is a diagram illustrating an example of the arrangement of a reference microphone and an error microphone. [Figure 6]FIG. 5 is a block diagram showing an example of the configuration of an audio system 501. [Figure 7] FIG. 5 is a block diagram showing an example of the configuration of an audio system 502. [Figure 8] 5 is a diagram showing an example of the configuration of a sound-proof speaker system 520 to which a member 5222 is attached. [Figure 9] FIG. 1 is a diagram showing an example of an audio system installed in an aircraft seat. [Figure 10] FIG. 1 is a block diagram showing an example of the configuration of an acoustic system 1000. [Figure 11] 1 is a block diagram showing an example of the configuration of an acoustic system 100. FIG. [Figure 12] FIG. 2 is a block diagram showing an example of the configuration of an audio system 102. [Figure 13] 12 is a diagram showing an example of the configuration of a speaker unit pair 122 to which a member 1222 is attached. [Figure 14] FIG. 2 is a block diagram showing an example of the configuration of an audio system 104. [Figure 15] FIG. 2 is a block diagram showing an example of the configuration of an acoustic system 200. [Figure 16] FIG. 2 is a block diagram showing an example of the configuration of an audio system 300. [Figure 17] FIG. 2 is a block diagram showing an example of the configuration of an audio system 106. [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. 2 is a block diagram showing an example of the configuration of an audio system 108. [Figure 20] FIG. 5 is a block diagram showing an example of the configuration of an audio system 530. [Figure 21] 5 is a diagram showing an example of the configuration of a sound-absorbing speaker unit to which members 5230 and 5240 and a sound-absorbing material 5250 are attached. [Figure 22] FIG. 13 is a diagram showing an experimental result of the fifth embodiment. [Diagram 23] FIG. 13 is a diagram showing an experimental result of the fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 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.

[0010] <Technical background> In order to reduce the noise heard when seated in an aircraft seat, active noise control, which is one of the noise reduction technologies, is used (see Non-Patent Documents 1 and 2).

[0011] (Reference Non-Patent Document 1: ANC Noise Reduction Test System, [online], [searched March 16, 2020], Internet<URL: https: / / micronet.jp / product / anc / index.html> ) (Reference Non-Patent Document 2: Active Noise Control (Institute of Electronics, Information and Communication Engineers, "Forest of Knowledge", Group 2, Part 6, Chapter 6), [online], [searched on March 16, 2020], Internet<URL: http: / / www.ieice-hbkb.org / files / 02 / 02gun_06hen_06.pdf> ) Fig. 1 is a diagram showing an example of the configuration of an active noise control system. The active noise control system includes a microphone (hereinafter referred to as a reference microphone) that collects noise, a controller that generates a control signal for canceling the noise from a signal (hereinafter referred to as a noise signal) output from the reference microphone, and a noise canceling speaker that emits a sound based on the control signal. The active noise control system may further include a microphone (hereinafter referred to as an error microphone) that collects the sound that could not be completely canceled, and may feed back a signal (hereinafter referred to as an error signal) output from the error microphone to the controller, which may then generate a control signal using the error signal as well.

[0012] Since the main components of noise inside an aircraft are concentrated in the low frequency range, if the noise reduction speaker is not of a certain size, it will not be able to reproduce low frequency sounds sufficiently, and sufficient noise reduction effect will not be obtained. However, if the noise reduction speaker is too large, it will be difficult to use it in an aircraft seat. In addition, if the sound from the noise reduction speaker is picked up by the reference microphone, the sound signal from the noise reduction speaker will be included in the noise signal, which is a problem that the noise reduction performance will be deteriorated.

[0013] In order to solve these two problems, in the present invention, a speaker unit is used instead of a speaker to emit a sound based on a control signal (see FIG. 2).

[0014] 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.

[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 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. When a speaker is used, positive sound waves are emitted in all directions from the speaker, while negative sound waves do not go outside the speaker box. In contrast, when only a speaker unit is used, negative sound waves are also emitted because there is no speaker box. In this case, the positive and negative sound waves are in an opposite phase relationship with each other, so the positive and negative sound waves cancel each other out, but in the vicinity of the speaker unit, the negative sound waves cannot wrap around in time, so the positive sound waves remain. If the remaining positive sound waves and the noise are in an anti-phase relationship, the positive sound waves and the noise will cancel each other out, resulting in a noise reduction effect in the vicinity of the speaker unit.

[0016] In other words, by installing a speaker unit close to the user's ears without using a speaker box, noise reduction in the aircraft can be achieved. In addition, since the area in which positive sound waves remain is limited to a relatively narrow area such as the vicinity of the speaker unit, leakage to the reference microphone is also suppressed, and deterioration of noise reduction performance can also be suppressed.

[0017] The form in which only the speaker unit is installed has the advantage that the installation space can be minimized because the speaker box is not used. In addition to this advantage, the form in which only the speaker unit is installed has the advantage that it produces lower-frequency sounds than the form in which it is installed in combination with the speaker box. The reason for this is explained below. Generally, when the speaker unit is stored in the speaker box, the negative sound waves do not go outside the speaker box, but when the speaker unit is stored in the speaker box, the negative sound waves are trapped inside the speaker box, and the air vibrations of the negative sound waves that have nowhere to go suppress the cone of the speaker unit and interfere with the next vibration of the cone. As a result, even if the speaker unit is stored in the speaker box, low-frequency sounds will not be produced. Therefore, it is possible to fill the inside of the speaker box with sound-absorbing material, but this effect is not sufficient for low-frequency sounds, and the speaker box must be made somewhat large in order to produce low-frequency sounds. In other words, in the end, if a speaker box that is small enough to be installed in an airplane seat is used, sufficient low-frequency sounds will not be produced.

[0018] First Embodiment A system that reproduces an acoustic signal 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 acoustic signal to be reproduced by an acoustic system is, for example, an acoustic signal obtained from data recorded on a CD, DVD, or record, data received via the Internet, or a signal received via radio or television broadcast.

[0019] Hereinafter, an acoustic system that reduces noise by reproducing a control signal generated from a noise signal obtained from noise around a user in the vicinity of a speaker system will be described. When such an acoustic system is used as an acoustic system for a user using a seat on an aircraft, for example, a system that can reduce noise around the user using the seat can be provided. FIG. 3 is a diagram showing an example of an acoustic system installed on an aircraft seat. The acoustic system in FIG. 3 is arranged so that the speaker system is located near the head of a seated user. Such an acoustic system can be installed in vehicles other than aircraft, such as automobiles and trains, and in chairs used in homes and commercial facilities, 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.

[0020] The acoustic system 500 will be described below with reference to FIG. 4. FIG. 4 is a block diagram showing the configuration of the acoustic system 500. As shown in FIG. 4, the acoustic system 500 includes a control system 510 and a noise-reducing speaker system 520. The control system 510 includes K (K is an integer of 1 or more) reference microphones 511, L (L is an integer of 0 or more) error microphones 512, and a control signal generating device 514. Here, as explained in <Technical Background>, the reference microphone and the error microphone are a microphone that picks up noise and a microphone that picks up sounds that could not be completely eliminated, respectively. The error microphone is used for updating the filter, and is often used in practice. The minimum number of microphones required for the acoustic system 500 is 1 (when K=1, L=0). FIG. 5 is a diagram showing the arrangement of the reference microphone and the error microphone when K=4, L=2. As shown in FIG. 5, it is preferable to arrange the reference microphone at a position where the noise arrives before the error microphone. In addition, since the error microphone is ideally placed at the position of the user's ear, it is preferable to place it as close to the ear as possible. In addition, the noise-reducing speaker system 520 includes one noise-reducing speaker unit 5221 that is a speaker unit that emits sound based on a control signal. The noise-reducing speaker system 520 is installed in a position close to the head of the user who uses the seat.

[0021] The direction in which the mute speaker unit 5221 faces the user is defined as the mute user direction, and the mute speaker unit 5221 is arranged so that sound emitted from the mute speaker unit 5221 in the mute user direction is mute in places other than near the head of the user using the seat by the wraparound of sound emitted from the mute speaker unit 5221 in the opposite direction to the mute user direction. Here, the mute user direction refers to the front direction of the mute speaker unit 5221. Also, the opposite direction to the mute user direction refers to the rear direction of the mute speaker unit 5221.

[0022] The operation of the acoustic system 500 will be described below with reference to FIG.

[0023] The control system 510 generates and outputs a control signal for canceling noise from a signal (hereinafter referred to as a noise signal) obtained from noise at a location close to the head of a user occupying a seat in the aircraft. More specifically, the reference microphone 511 picks up the noise at a location close to the head of the user occupying the seat in the aircraft, and outputs the noise signal obtained by converting the noise into an electrical signal. The error microphone 512 picks up sound that has not been completely cancelled at a location very close to the head of the user, and outputs an error signal obtained by converting the sound that has not been completely cancelled into an electrical signal. The control signal generating device 514 receives the noise signal and the error signal as inputs, generates a control signal from the noise signal using the error signal, and outputs the control signal. The control signal may be a signal that has approximately the same amplitude as the noise signal and is in the opposite phase.

[0024] The silent speaker system 520 receives the control signal output by the control system 510 and emits a sound based on the control signal. More specifically, the silent speaker unit 5221 receives the control signal and emits a sound based on the control signal.

[0025] According to an embodiment of the present invention, it is possible to reduce noise heard when seated in an aircraft seat.

[0026] <Second embodiment> The acoustic system 500 of the first embodiment uses only one mute speaker unit, so the range in which noise is reduced is narrow. Here, an acoustic system including two or more mute speaker units will be described so that the mute speaker units can be installed close to each of the user's ears.

[0027] Hereinafter, the acoustic system 501 will be described with reference to Fig. 6. Fig. 6 is a block diagram showing the configuration of the acoustic system 501. As shown in Fig. 6, the acoustic system 501 includes a control system 510 and a noise cancelling speaker system 520, similar to the acoustic system 500. However, the acoustic system 501 differs from the acoustic system 500 in that the noise cancelling speaker system 520 includes M (M is an integer equal to or greater than 2) noise cancelling speaker units 5221. The same control signal is input to the M noise cancelling speaker units 5221.

[0028] Hereinafter, the M mute speaker units are referred to as the first mute speaker unit, ..., M-th mute speaker unit. The direction in which the m-th mute speaker unit faces the user is referred to as the m-th mute user direction (m=1, ..., M), and the m-th mute speaker unit (m=1, ..., M) is arranged so that the sound emitted from the m-th mute speaker unit in the m-th mute user direction is mute in places other than the place close to the head of the user using the seat by the wraparound of the sound emitted from the m-th mute speaker unit in the opposite direction to the m-th mute user direction. Here, the m-th mute user direction refers to the front direction of the m-th mute speaker unit 5221. The opposite direction to the m-th mute user direction refers to the rear direction of the m-th mute speaker unit 5221.

[0029] The operation of the silent speaker system 520 will be described below with reference to FIG.

[0030] The mute speaker system 520 receives the control signal output by the control system 510 and emits a sound based on the control signal. More specifically, the m-th mute speaker unit 5221 (m=1, ..., M) receives the control signal and emits a sound based on the control signal.

[0031] In this embodiment, M is an integer of 2 or more, but if M=1, the embodiment coincides with the first embodiment.

[0032] According to an embodiment of the present invention, it is possible to reduce noise heard when seated in an aircraft seat.

[0033] <Third embodiment> In the acoustic system 501 of the second embodiment, the range in which noise is reduced is widened by increasing the number of sound-reducing speaker units. Here, an acoustic system having a structure in which the range in which noise is reduced by one sound-reducing speaker unit is widened will be described.

[0034] Hereinafter, the acoustic system 502 will be described with reference to Fig. 7. Fig. 7 is a block diagram showing the configuration of the acoustic system 502. As shown in Fig. 7, the acoustic system 502 includes a control system 510 and a noise cancelling speaker system 520, similar to the acoustic system 501. However, the acoustic system 502 differs from the acoustic system 501 in that a member 5222 is attached to an m-th noise cancelling speaker unit 5221 (m=1, ..., M).

[0035] The structure of the mth sound-reduction speaker unit 5221 (m=1, . . . , M) will be described below with reference to FIG.

[0036] A member 5222 is attached to the mth silencing speaker unit 5221 to lengthen the path of sound emitted from the mth silencing speaker unit 5221 in the direction opposite to the mth silencing user direction and wrapping around to the mth silencing user direction (see FIG. 8). The member 5222 may be, for example, a member such as a partition plate that prevents sound from wrapping around from the back of the speaker unit. This member 5222 is attached to prevent interference of sound waves and to widen the range in which noise is reduced.

[0037] The mth silencing speaker unit 5221 to which the member 5222 is attached has a wider range in which noise is reduced compared to the mth silencing speaker unit 5221 of the second embodiment.

[0038] According to an embodiment of the present invention, it is possible to reduce noise heard when seated in an aircraft seat.

[0039] <Fourth embodiment> In the first to third embodiments, an acoustic system (a noise reduction acoustic system) for reducing noise around a user occupying an aircraft seat has been described. These noise reduction acoustic systems can be combined with an acoustic system (a reproduction acoustic system) that reproduces sound based on an acoustic signal obtained from an object to be reproduced so that only a user in the vicinity of the speaker system can hear it. Here, the object to be reproduced refers to data or signals 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 signals received via radio or television broadcasting.

[0040] FIG. 9 shows an example of an acoustic system combining a noise reduction acoustic system and a reproduction acoustic system. FIG. 9 is a diagram showing an example of an acoustic system installed on an aircraft seat. The speaker system of the reproduction acoustic system in FIG. 9 is installed on the seat so as to sandwich the head of a seated user, and the speaker unit pair is arranged so as to be located near the left and right ears. On the other hand, the muffling speaker system of the noise reduction acoustic system is installed on the seat so as to be located behind the head of the seated user. The acoustic system can be installed in vehicles other than aircraft, such as automobiles and trains, and in reclining chairs, and can also be installed in a wearable form, such as on the shoulder. In addition, the reproduction acoustic system may be configured to install a driver unit pair in which two driver units are arranged side by side, which corresponds to the above speaker unit pair, in each of the left and right units of headphones or earphones, similar to the noise reduction acoustic system. Headphones are generally roughly divided into two types, open-type (open-air type) and closed-type (closed type). It is expected that sound leakage will be reduced by applying the above technology to the open-type, which is particularly concerned about sound leakage.

[0041] The acoustic system 1000 will be described below with reference to Fig. 10. Fig. 10 is a block diagram showing the configuration of the acoustic system 1000. The acoustic system 1000 includes a noise reduction acoustic system and a reproduction acoustic system. The noise reduction acoustic system can be the acoustic system 500, the acoustic system 501, the acoustic system 502, or the acoustic system 530 described below. On the other hand, the reproduction acoustic system can be the acoustic system 100, the acoustic system 102, the acoustic system 104, the acoustic system 106, the acoustic system 108, the acoustic system 200, or the acoustic system 300 described below.

[0042] Each embodiment of the reproduction sound system will be described below.

[0043] {Form 1: Sound System 100} The acoustic system 100 will be described below with reference to FIG. 11. FIG. 11 is a block diagram showing the configuration of the acoustic system 100. As shown in FIG. 11, 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.

[0044] 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.

[0045] 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.

[0046] The operation of the acoustic system 100 will be described below with reference to FIG.

[0047] 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.

[0048] 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 opposite phase relationship, 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.

[0049] 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.

[0050] {Form 2: Sound System 102} The acoustic system 100 has a narrow sweet spot, which is the range in which the emitted sound can be heard. Here, an acoustic system having a structure that widens the sweet spot will be described.

[0051] Hereinafter, the acoustic system 102 will be described with reference to Fig. 12. Fig. 12 is a block diagram showing the configuration of the acoustic system 102. As shown in Fig. 12, the acoustic system 102 includes a playback device 110 and a speaker system 120, similar to the acoustic system 100. However, the acoustic system 102 differs from the acoustic system 100 in that a member 1222 is attached to the speaker unit pair 122.

[0052] The structure of the n-th speaker unit pair 122 (n=1, . . . , N) will be described below with reference to FIG.

[0053] A member 1222 is attached to the n-th speaker unit pair 122 to lengthen the path of sound that is emitted from the positive speaker unit 1221 and the negative speaker unit 1221 of the n-th speaker unit pair 122 in the direction opposite to the n-th user direction and that wraps around toward the user (see FIG. 13). The member 1222 may be, for example, a member such as a partition plate that prevents sound from wrapping around from the back of the speaker unit. This member 1222 is attached not to prevent sound from wrapping around, but to increase the phase difference between sound wrapping around from the back and sound from the front, in other words, to lengthen the path of the wrapping sound.

[0054] The nth speaker unit pair 122 to which the member 1222 is attached has a wider sweet spot than the nth speaker unit pair 122 of form 1.

[0055] {Form 3: Sound System 104} Since high-frequency sounds have short wavelengths, it is difficult for the phases of sounds coming around from the back to match with sounds coming from the front. Therefore, high-frequency sounds are characterized by being less likely to be eliminated in the vicinity of the speaker unit or in a relatively distant location other than the vicinity, compared to low-frequency sounds. Since the positive speaker unit 1221 and the negative speaker unit 1221 of the speaker unit pair 122 constituting the acoustic system 100 are not housed in a speaker box, the above-mentioned characteristic results in a wide range in which high-frequency sounds can be heard, which can lead to sound leakage. Here, an acoustic system having a structure that makes it difficult for high-frequency sounds to leak outside the vicinity of the speaker system will be described.

[0056] The acoustic system 104 will be described below with reference to FIG. 14. FIG. 14 is a block diagram showing the configuration of the acoustic system 104. As shown in FIG. 14, the acoustic system 104 includes a playback device 110 and a speaker system 120, similar to the acoustic system 100. However, the acoustic system 104 differs from the acoustic system 100 in that a tweeter 1223 is attached to each of the positive speaker unit 1221 and the negative speaker unit 1221 of the speaker unit pair 122. Here, a tweeter is a speaker unit for reproducing high-frequency signals. Note that the tweeter 1223 is attached to the positive speaker unit 1221 and the negative speaker unit 1221 in a manner that prevents sound from leaking from the back, as if it were stored in a speaker box.

[0057] The operation of the speaker system 120 will be described below with reference to FIG.

[0058] 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 a tweeter 1223 attached to the positive speaker unit 1221, and emits a sound based on the 2nth acoustic signal from the negative speaker unit 1221 and a tweeter 1223 attached to the negative speaker unit 1221.

[0059] Higher frequency sounds have the tendency to travel in a more directional direction, but because the tweeter 1223 is designed so that sound does not leak out from the back, the high frequency sounds emitted from the tweeter 1223 can be prevented from leaking in all directions.

[0060] {Form 4: Sound System 200} The tweeter is a speaker unit for reproducing high-frequency signals. Therefore, it is possible to input only high-frequency signals to the tweeter by band splitting processing. Here, an audio system that performs band splitting processing will be described.

[0061] The acoustic system 200 will be described below with reference to Fig. 15. Fig. 15 is a block diagram showing the configuration of the acoustic system 200. As shown in Fig. 15, the acoustic system 200 includes a playback device 110, a band splitting device 210, and a speaker system 120. The band splitting device 210 includes N band splitting sections 212 (i.e., a first band splitting section 212, ..., an Nth band splitting section 212). The acoustic system 200 differs from the acoustic system 104 in that it includes the band splitting device 210.

[0062] The operations of the band splitting device 210 and the speaker system 120 will be described below with reference to FIG.

[0063] The band splitting device 210 receives as input the first acoustic signal, the second acoustic signal, ..., the 2Nth acoustic signal output by the playback device 110, and outputs a first high-frequency signal that is the high-frequency signal of the first acoustic signal and a first low-frequency signal that is the low-frequency signal, a second high-frequency signal that is the high-frequency signal of the second acoustic signal and a second low-frequency signal that is the low-frequency signal, ..., a 2Nth high-frequency signal that is the high-frequency signal of the 2Nth acoustic signal and a 2Nth low-frequency signal that is the low-frequency signal. More specifically, the nth band splitting unit 212 (n = 1, ..., N) receives the 2n-1th acoustic signal and the 2nth acoustic signal as input, generates a 2n-1 high-frequency signal that is the high-frequency signal of the 2n-1th acoustic signal and a 2n-1 low-frequency signal that is the low-frequency signal, generates a 2n high-frequency signal that is the high-frequency signal of the 2nth acoustic signal and a 2n low-frequency signal that is the low-frequency signal, and outputs the 2n-1 high-frequency signal, the 2n-1 low-frequency signal, the 2n high-frequency signal, and the 2n low-frequency signal.

[0064] The speaker system 120 receives as input the first high-frequency signal, the first low-frequency signal, the second high-frequency signal, the second low-frequency signal, ..., the 2Nth high-frequency signal, and the 2Nth low-frequency signal output by the band splitting device 210, and emits sound based on the first high-frequency signal, sound based on the first low-frequency signal, sound based on the second high-frequency signal, sound based on the second low-frequency signal, ..., sound based on the 2Nth high-frequency signal, and sound based on the 2Nth low-frequency signal. More specifically, the nth speaker unit pair 122 (n = 1, ..., N) receives the 2n-1th high-frequency signal, the 2n-1th low-frequency signal, the 2nth high-frequency signal, and the 2nth low-frequency signal as input, and emits sound based on the 2n-1th low-frequency signal and sound based on the 2n-1th high-frequency signal from the positive speaker unit 1221 and the tweeter 1223 associated with the positive speaker unit 1221, respectively, and emits sound based on the 2nth low-frequency signal and sound based on the 2nth high-frequency signal from the negative speaker unit 1221 and the tweeter 1223 associated with the negative speaker unit 1221, respectively.

[0065] {Form 5: Sound System 300} In the acoustic system 200, speaker units having tweeters 1223 attached to the positive speaker unit 1221 and the negative speaker unit 1221 are used. Here, an acoustic system using a speaker unit pair including two speaker units and one tweeter, instead of using a speaker unit pair including two speaker units with tweeters attached, will be described.

[0066] The acoustic system 300 will be described below with reference to FIG. 16. FIG. 16 is a block diagram showing the configuration of the acoustic system 300. As shown in FIG. 16, the acoustic system 300 includes a reproduction device 110, a band splitting device 310, and a speaker system 320. The band splitting device 310 includes N band splitting sections 312 (i.e., a first band splitting section 312, ..., an Nth band splitting section 312). The speaker system 320 includes N speaker unit pairs 322 (i.e., a first speaker unit pair 322, ..., an Nth speaker unit pair 322). The speaker unit pair 322 includes two speaker units (i.e., a positive speaker unit 1221 and a negative speaker unit 1221) and a tweeter 3221. The audio system 300 differs from the audio system 200 in that it includes a band splitting device 310 and a speaker system 320 instead of the band splitting device 210 and the speaker system 120 .

[0067] Tweeter 3221 is preferably housed in a speaker box to prevent sound from leaking from the rear. Speaker system 320 is installed in a position close to the head of a user using the seat.

[0068] The direction in which the nth speaker unit pair 322 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 322 (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, the negative speaker unit 1221, and the tweeter 3221 of the nth speaker unit pair 322. Moreover, the direction opposite to the n-th user direction refers to the rear direction of the positive speaker unit 1221 , the negative speaker unit 1221 , and the tweeter 3221 of the n-th speaker unit pair 322 .

[0069] In addition, the positive speaker unit 1221 and the negative speaker unit 1221 of the nth speaker unit pair 322 (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.

[0070] The operations of the band splitting device 310 and the speaker system 320 will be described below with reference to FIG.

[0071] The band splitting device 310 receives as input the first acoustic signal, second acoustic signal, ..., 2Nth acoustic signal output by the playback device 110, and outputs a first high-frequency signal which is the high-frequency signal of the first acoustic signal, a first low-frequency signal which is the low-frequency signal, a second low-frequency signal which is the low-frequency signal of the second acoustic signal, ..., a 2N-1 high-frequency signal which is the high-frequency signal of the 2N-1th acoustic signal, a 2N-1 low-frequency signal which is the low-frequency signal, and a 2N low-frequency signal which is the low-frequency signal of the 2Nth acoustic signal. More specifically, the nth band splitting unit 312 (n = 1, ..., N) receives the 2n-1th acoustic signal and the 2nth acoustic signal as input, generates a 2n-1 high-frequency signal that is a high-frequency signal of the 2n-1th acoustic signal and a 2n-1 low-frequency signal that is a low-frequency signal, generates a 2n low-frequency signal that is the low-frequency signal of the 2nth acoustic signal, and outputs the 2n-1 high-frequency signal, the 2n-1 low-frequency signal, and the 2n low-frequency signal.

[0072] The speaker system 320 receives as input the first high-frequency signal, the first low-frequency signal, the second low-frequency signal, ..., the 2N-1th high-frequency signal, the 2N-1th low-frequency signal, and the 2Nth low-frequency signal output by the band splitting device 310, and emits sound based on the first high-frequency signal, sound based on the first low-frequency signal, sound based on the second low-frequency signal, ..., sound based on the 2N-1th high-frequency signal, sound based on the 2N-1th low-frequency signal, and sound based on the 2Nth low-frequency signal. More specifically, the nth speaker unit pair 322 (n = 1, ..., N) receives the 2n-1th high-frequency signal, the 2n-1th low-frequency signal, and the 2nth low-frequency signal as input, emits sound based on the 2n-1th high-frequency signal from the tweeter 3221, emits sound based on the 2n-1th low-frequency signal from the positive speaker unit 1221, and emits sound based on the 2nth low-frequency signal from the negative speaker unit 1221.

[0073] Form 6: Sound System 106 The acoustic system 104 is a system that is less susceptible to leakage of high-frequency sounds by using a speaker unit 1221 equipped with a tweeter 1223. Here, an acoustic system that is less susceptible to leakage of high-frequency sounds will be described, which uses a member with sound-absorbing properties instead of a speaker unit equipped with a tweeter.

[0074] Hereinafter, the acoustic system 106 will be described with reference to Fig. 17. Fig. 17 is a block diagram showing the configuration of the acoustic system 106. As shown in Fig. 17, the acoustic system 106 includes a playback device 110 and a speaker system 120, similar to the acoustic system 104. However, the acoustic system 106 differs from the acoustic system 104 in that the acoustic system 106 uses a speaker unit 1221 without a tweeter 1223 instead of a speaker unit 1221 with a tweeter 1223, and in that a member 1224 is attached to the speaker unit pair 122.

[0075] Hereinafter, the structure of the n-th speaker unit pair 122 (n=1, . . . , N) will be described with reference to FIG.

[0076] A member 1224 is attached to the n-th speaker unit pair 122 to absorb sounds emitted from the positive speaker unit 1221 and the negative speaker unit 1221 of the n-th speaker unit pair 122 in the direction opposite to the n-th 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 except for the front surface.

[0077] Form 7: Sound System 108 The acoustic system 106 is a system that is less susceptible to leakage of high-frequency sounds by using the speaker unit 1221 to which the member 1224 is attached. Here, an acoustic system that is less susceptible to leakage of high-frequency sounds is described by storing each of the speaker units of the speaker unit pair in a speaker box with holes, instead of using a speaker unit pair to which a sound-absorbing material is attached.

[0078] Hereinafter, acoustic system 108 will be described with reference to Fig. 19. Fig. 19 is a block diagram showing the configuration of acoustic system 108. As shown in Fig. 19, acoustic system 108 includes a playback device 110 and a speaker system 120, similar to acoustic system 106. Acoustic system 108 differs from acoustic system 106 in that acoustic system 108 includes a speaker unit pair 122 including a speaker unit 1221 housed in a speaker box 1225, instead of speaker unit pair 122 to which member 1224 is attached.

[0079] Hereinafter, the structure of the n-th speaker unit pair 122 (n=1, . . . , N) will be described with reference to FIG.

[0080] The positive speaker unit 1221 and the negative speaker unit 1221 of the n-th speaker unit pair 122 are each housed in a speaker box 1225. Note that the speaker box 1225 has a large number of holes formed therein.

[0081] According to an embodiment of the present invention, it is possible to reduce the noise heard when seated in an aircraft seat, and also to reproduce sounds that can be heard only in a very limited range, namely, in the vicinity of the speaker system.

[0082] <Fifth embodiment> The following description will focus on the differences from the second embodiment. As described above, a noise reduction audio system is an audio system for reducing noise around a user using a seat, and is an audio system that emits a cancellation sound that cancels out noise reaching the seat so that the noise cancellation effected by the cancellation sound only affects a specified range in the vicinity of the user using the seat.

[0083] High-frequency sounds tend to travel in straight lines, making them less likely to diffract and less likely to be in phase with each other. Therefore, compared to low-frequency sounds, high-frequency sounds may not be silenced in the vicinity of the speaker unit or at relatively distant locations. To solve this problem, the acoustic system of this embodiment uses physical ingenuity to direct high-frequency cancellation sounds only to the area from the noise-reduction speaker unit to the ear (toward the user), and absorbs the high-frequency cancellation sounds in directions other than the ear from the noise-reduction speaker unit using sound-absorbing material.

[0084] The acoustic system 530 will be described below with reference to FIG. 20. FIG. 20 is a block diagram showing the configuration of the acoustic system 530. As shown in FIG. 20, the acoustic system 530 includes a control system 510 and M sound-reduction speaker systems 520, similar to the acoustic system 501. However, the acoustic system 530 differs from the acoustic system 501 in that a radiation suppression unit is attached to the M sound-reduction speaker units. The radiation suppression unit includes at least a sound-absorbing material 5250, and in this embodiment, includes members 5230 and 5240 (see FIG. 20 and FIG. 21). The sound-absorbing material 5250 is made of a material, shape, and structure that is easy to absorb only sounds with frequencies equal to or higher than a predetermined value. The radiation suppression unit is configured to be provided with the sound-absorbing material 5250 so that sounds (canceling sounds) with frequencies equal to or higher than a predetermined value emitted from the sound-reduction speaker units are less likely to be radiated to places other than the user's ears. As described in the first embodiment, the mute speaker unit 5221 is arranged so that the sound emitted from the mute speaker unit 5221 in the mute user direction is mute at locations other than the location near the head of the user using the seat due to the wraparound of the sound emitted from the mute speaker unit 5221 in the opposite direction to the mute user direction. However, high-frequency sounds tend to travel in a straight line, so it is difficult to mute them by this wraparound. Therefore, in this embodiment, the sound absorbing material 5250 absorbs sounds of frequencies that do not cause wraparound (high-frequency sounds). Therefore, it is sufficient for the sound absorbing material 5250 to absorb high-frequency sounds that tend to travel in a straight line, and the predetermined value is set so that sounds of frequencies equal to or higher than the predetermined value do not cause wraparound.

[0085] The members 5230 and 5240 sandwich the M number of mute speaker units 5221 from the front and rear, respectively. Furthermore, the members 5230 and 5240 sandwich the sound absorbing material 5250 on the edge of the surface sandwiching the M number of mute speaker units 5221. In other words, the members 5230 and 5240 sandwich the sound absorbing material 5250 on the side surface of the space sandwiched between the members 5230 and 5240. The members 5230 and 5240 may be members like the partition plate of the third embodiment. The member 5230 that sandwiches the M number of mute speaker units 5221 from the front is provided with a hole so that sound can escape, and the member 5240 that sandwiches the M number of mute speaker units 5221 from the rear is not provided with a hole so that sound cannot escape. The sound absorbing material 5250 is a material that has a higher sound absorbing effect at higher frequencies and has less sound absorbing effect at lower frequencies.

[0086] With this configuration, high-frequency cancellation sounds, which have a high degree of directivity, are radiated only to the ears through the holes in member 5230. Because sound-absorbing material 5250 and member 5240 prevent the diffusion of high-frequency cancellation sounds, the high-frequency cancellation sounds are not radiated to the sides and rear of M sound-reduction speaker units 5221. On the other hand, low-frequency cancellation sounds, which have a high degree of diffusivity, will wrap around to the rear even if there are no holes in member 5230. The low-frequency cancellation sounds will pass through sound-absorbing material 5250, wrap around to the rear, and cancel each other out in places other than the vicinity, being eliminated.

[0087] The operations of the control system 510 and the silent speaker system 520 are similar to those in the second embodiment.

[0088] According to an embodiment of the present invention, it is possible to reduce noise heard when seated in an aircraft seat.

[0089] 20, M mute speaker units 5221 are covered with one radiation suppression section, but it is not necessary to cover them with one radiation suppression section. For example, M mute speaker units 5221 may be covered with M radiation suppression sections, or two of M mute speaker units 5221 may be configured as mute speaker unit pairs, and each mute speaker unit pair may be covered with M / 2 radiation suppression sections.

[0090] <Experimental Results> The experimental results of the noise reduction sound system according to the fifth embodiment will be described below. A car equipped with the noise reduction sound system was driven, a dummy head was placed in the passenger seat, two sound-reducing speaker units were placed so as to sandwich the dummy head from the left and right (see FIG. 3), microphones were placed on the ears of the dummy head, and road noise was measured.

[0091] Fig. 22 shows road noise at the left ear position, and Fig. 23 shows road noise at the right ear position. By applying the noise reduction acoustic system, road noise was reduced by 7.78 dB at the left ear position and by 7.87 dB at the right ear position.

[0092] <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. M is an integer equal to or greater than 1; a control system that generates a control signal for canceling noise from a signal of noise at a position close to the head of a user using a seat (hereinafter referred to as a noise signal); a silent speaker system including M speaker units (hereinafter referred to as silent speaker units) that are installed near the head of a user using the seat and emit sounds based on the control signals; A radiation suppression unit includes at least a sound absorbing material that is easy to absorb only sounds having frequencies equal to or higher than a predetermined value, and is configured to make it difficult for sounds having frequencies equal to or higher than the predetermined value emitted from the noise-reducing speaker unit to be radiated to any location other than the user's ears, The M mute speaker units are designated as a first mute speaker unit, ..., an M-th mute speaker unit, The direction in which the m-th mute speaker unit faces the user is defined as the m-th mute user direction (m=1, . . . , M), an m-th mute speaker unit (m=1, ..., M) is arranged so that a sound emitted from the m-th mute speaker unit in the m-th mute user direction can be heard only at a location close to the head of the user by a wraparound of a sound emitted from the m-th mute speaker unit in the opposite direction to the m-th mute user direction, and the sound is muted at a location other than the location close to the head of the user using the seat; N is an integer equal to or greater than 1; a reproduction device including an n-th reproduction unit (n=1, ..., N) that outputs a 2n-1-th acoustic signal that is an acoustic signal obtained based on an object to be reproduced, and a 2n-th acoustic signal that is an acoustic signal in antiphase with the 2n-1-th acoustic signal; a speaker system including an n-th speaker unit pair (n=1, ..., N) including a speaker unit that emits a sound based on a 2n-1-th acoustic signal and a speaker unit that emits a sound based on a 2n-th acoustic signal, the speaker system being installed in a position close to a head of a user using the seat; The front direction of each speaker unit faces the user. Sound system.

2. M is an integer equal to or greater than 1; a control system that generates a control signal for canceling noise from a signal of noise at a position close to the head of a user using a seat (hereinafter referred to as a noise signal); a silent speaker system including M speaker units (hereinafter referred to as silent speaker units) that are installed near the head of a user using the seat and emit sounds based on the control signals; A radiation suppression unit includes at least a sound absorbing material that is easy to absorb only sounds having frequencies equal to or higher than a predetermined value, and is configured to make it difficult for sounds having frequencies equal to or higher than the predetermined value emitted from the noise-reducing speaker unit to be radiated to any location other than the user's ears, The M mute speaker units are designated as a first mute speaker unit, ..., an M-th mute speaker unit, The direction in which the m-th mute speaker unit faces the user is defined as the m-th mute user direction (m=1, . . . , M), an m-th mute speaker unit (m=1, ..., M) is arranged so that a sound emitted from the m-th mute speaker unit in the m-th mute user direction can be heard only at a location close to the head of the user by a wraparound of a sound emitted from the m-th mute speaker unit in the opposite direction to the m-th mute user direction, and the sound is muted at a location other than the location close to the head of the user using the seat; The m th ... The sound absorbing material is sandwiched between two members at a side surface of a space sandwiched between the two members, The member in the m silencing user direction has a hole so that sound can escape, and the member in the opposite direction to the m silencing user direction has no hole so that sound cannot escape. Sound system.

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