Cancellation Device

Abstract

A canceling device according to one aspect of the present invention is designed to cancel noise arriving at a region near a speaker, and includes at least two speakers 1 and one reference microphone 3. The canceling device is configured such that an acoustic signal emitted from a sound emission direction and an acoustic signal emitted from a direction opposite thereto of the same speaker collide with each other, the at least two speakers 1 and the reference microphone 3 are disposed on the same plane, the at least two speakers 1 emit canceling sound for canceling the noise in conjunction with each other, and the plane includes a boundary between the sound emission direction of the two speakers 1 and the direction opposite to the sound emission direction.

Description

[Technical field]

[0001] The present invention relates to noise canceling technology. [Background technology]

[0002] The process of canceling noise by emitting a signal having a phase opposite to that of the noise arriving in the viewing area is called noise canceling (see, for example, Non-Patent Document 1).

[0003] There are many audio devices on the market that have noise cancellation functions. However, these audio devices often only cancel noise in a very small area, such as the listening area near the ear or inside the ear canal, as with headphones and earphones.

[0004] This is because, when trying to cancel noise over an area larger than a very small area, it is necessary to combine multiple speakers (including both multiple speakers with the same characteristics and a combination of speakers of different sizes), and the non-noise signals emitted from the speakers are picked up by a microphone that collects noise in order to generate a signal to cancel the noise, resulting in feedback being generated by the signals emitted from the speakers.

[0005] An object of the present invention is to provide a noise canceling device that can cover an area wider than the vicinity of the ears and is less susceptible to howling caused by signals emitted from speakers.

[0006] This is because, when trying to cancel noise over an area larger than a very small area, it is necessary to combine multiple speakers (including both multiple speakers with the same characteristics and a combination of speakers of different sizes), and the non-noise signals emitted from the speakers are picked up by a microphone that collects noise in order to generate a signal to cancel the noise, resulting in feedback being generated by the signals emitted from the speakers. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Hideo Yuasa, "Digital goods that help you work: Make effective use of your travel time with noise-canceling headphones," [online], June 21, 2019, [Retrieved March 22, 2021], Internet<URL:https: / / www.nttcom.co.jp / comware_plus / column / digital_goods / 201906.html> Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a cancellation device, which is a noise canceling device that can target an area wider than the vicinity of the ears and is less likely to cause howling due to signals emitted from speakers. [Means for solving the problem]

[0009] A cancellation device according to one aspect of the present invention is a cancellation device that cancels noise arriving in an area near a speaker, and includes at least two speakers and one reference microphone. The cancellation device is configured so that an acoustic signal emitted from the sound emission direction of the same speaker collides with an acoustic signal emitted from the opposite direction. The at least two speakers and the reference microphone are arranged on the same plane, and the at least two speakers work in conjunction to emit cancellation sounds that cancel the noise. The plane includes a boundary between the sound emission direction of the two speakers and the opposite direction to the sound emission direction. The reference microphone is arranged at a position where the phase characteristic from the speaker to the error microphone is inverse to the phase characteristic from the speaker to the reference microphone, instead of on a plane. . Effect of the Invention

[0010] This allows the target area to be larger than the area near the ears, making it less likely that feedback caused by signals emitted from the speakers will occur. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of an example of a cancellation device. [Diagram 2] FIG. 2 is a front view of an example of a cancellation device. [Diagram 3] FIG. 3 is a left side view of an example of the cancellation device. [Figure 4] FIG. 4 is a plan view of an example of a cancellation device. [Diagram 5] FIG. 5 is a rear view of an example of a cancellation device. [Figure 6] FIG. 6 is a diagram for explaining how feedback from a speaker to a reference microphone can be suppressed. [Figure 7] FIG. 7 is a diagram showing an example of an experimental result. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail. In the drawings, components having the same functions are designated by the same reference numerals, and duplicated explanations will be omitted.

[0013] [Cancellation device and method] As shown in Figures 1 to 5, the cancellation device includes, for example, a speaker 1, a fixed plate 2, and a reference microphone 3. In the example of Figures 1 to 5, the number of speakers 1 is four.

[0014] Fig. 1 is a perspective view of an example of a cancellation device. Fig. 2 is a front view of an example of a cancellation device. Fig. 3 is a left side view of an example of a cancellation device. Fig. 4 is a plan view of an example of a cancellation device. Fig. 5 is a rear view of an example of a cancellation device.

[0015] The fixed plate 2 is made of aluminum, for example. The fixed plate 2 has sound emission holes 21. Four speakers 1 are attached to the positions of the sound emission holes 21 of the fixed plate 2. At least two speakers 1 are required. The multiple speakers 1 are installed on the same plane. For example, the multiple speakers 1 are evenly arranged on the same plane in a lattice or honeycomb pattern.

[0016] In the example of Figures 1 to 5, each sound emission hole 21 is composed of seven holes. The speaker 1 is attached so that the center of the central hole of these seven holes coincides with the center of the speaker 1. In the example of Figures 1 to 5, the speaker 1 is fixed to the fixing plate 2 with screws.

[0017] In addition, if there is an obstruction in the way of the sound traveling through the air from the speaker 1 to the ear, the sound quality may be impaired. To avoid this, the sound emission hole 21 is provided.

[0018] By arranging the sound emission holes 21 with high symmetry with respect to the center of the speaker 1, the generated sound field becomes more uniform, which is more preferable from the viewpoint of sound quality. However, the arrangement of the holes is not limited to this example. For example, the sound emission holes 21 do not have to be arranged at positions that are completely symmetrical with respect to the center of the speaker 1. For example, the sound emission holes 21 may be configured with six holes arranged in a star shape (one in the center and five around).

[0019] The relationship between the sound emission hole 21 and the speaker 1 is not particularly limited, but the sound emission hole 21 is provided in a position close to the speaker 1, for example.

[0020] The number and arrangement of the sound emission holes 21 and the speakers 1 are not limited to those described above.

[0021] The reference microphone 3 is placed at a symmetrical position with respect to the + and - sound fields generated by the speaker 1. The symmetrical position can be anywhere on the same plane as mentioned above, but it is better if it is a position where it can record the sound coming directly from the noise (without hitting or reflecting off various objects on the way).

[0022] In Figures 1 to 5, the reference microphone 3 is arranged above the centre of the fixed plate 2. The reference microphone 3 is supported, for example, by an extension extending from the fixed plate 2. In Figures 1 to 5, the extension is not shown.

[0023] 1 to 5, the reference microphone 3 is placed on the same plane as the speaker 1. This plane can be said to be a plane that includes the boundary between the sound emission direction of the speaker 1 and the opposite direction to the sound emission direction. As long as the reference microphone 3 is placed on the same plane as the speaker 1, it does not have to be placed above the speaker 1. For example, the reference microphone 3 may be placed next to the fixed plate 2.

[0024] A signal processing device (not shown) is connected to the cancellation device. The signal collected by the reference microphone 3 is input to the signal processing device. The signal processing device performs predetermined sound signal processing (so-called ANC processing) such as phase inversion, time delay, and emphasis of a specific frequency on the signal collected by the reference microphone 3 to cancel the signal collected by the reference microphone, and inputs the signal after the sound signal processing to the speaker 1.

[0025] The speaker 1 emits a sound based on the input signal. In other words, the speaker 1 emits a cancellation sound that cancels noise in conjunction with the input signal.

[0026] As shown in Fig. 1 to Fig. 5, the cancellation device is configured so that an acoustic signal emitted from the sound emitting direction of the same speaker 1 collides with an acoustic signal emitted from the opposite direction. For example, the cancellation device or the speaker 1 does not have a speaker box. As a result, + and - sound fields are generated in front of and behind the speaker 1, respectively.

[0027] By placing the reference microphone 3 symmetrically with respect to the + and - sound fields generated by the speaker 1, the signals reaching the reference microphone 3 from the speaker 1 cancel each other out at the position of the reference microphone 3. This makes it possible to reduce or eliminate the leakage of sound from the speaker 1 to the reference microphone 3.

[0028] In order to reduce noise over a wide area, it is important to generate a wide and uniform sound field using multiple speakers 1 as secondary sound sources. In this case, by arranging all the speakers 1 on the same plane, even in a situation where there are multiple speakers 1, the reference microphone 3 can be arranged symmetrically with respect to the + and - sound fields generated by the speakers 1.

[0029] With these configurations, the cancellation device can cancel noise arriving in an area near the speaker 1. More specifically, the cancellation device can suppress noise such as noise in an area in front of the cancellation device F (see Figs. 3 and 4).

[0030] Increasing the number of speakers 1 allows noise to be cancelled over a wider area. Increasing the distance between the speakers 1 allows noise to be cancelled over a wider area. On the other hand, narrowing the distance between the speakers 1 allows the noise cancelling performance to be improved in the area between the multiple speakers 1.

[0031] [Variations] Although the embodiments of the present invention have been described above, the specific configurations are not limited to these embodiments, and it goes without saying that the present invention includes appropriate design changes and the like as long as they do not deviate from the spirit of the present invention.

[0032] For example, the cancellation device may be applied to light waves and radio waves.

[0033] The cancellation device may further include an error microphone 4 for checking the effect of the cancellation. The error microphone 4 is indicated by a dotted line in Figures 1 to 5. The error microphone 4 is disposed, for example, in the center in front of the speaker 1.

[0034] In this case, the reference microphone 3 is placed in a position where the phase characteristic from the speaker 1 to the error microphone 4 is inverse phase to the phase characteristic from the speaker 1 to the reference microphone 3, instead of on the plane on which the speaker 1 is placed. For example, the reference microphone 3 is placed in an area in the opposite direction from the area to be cancelled, with the speaker 1 as the reference.

[0035] This also reduces the amount of noise that leaks from the speaker 1 to the reference microphone 3, making feedback less likely to occur.

[0036] For example, as shown in Fig. 6, when the error microphone 4 is placed in front of the speaker 1, the reference microphone 3 is placed on the back of the speaker 1. In Fig. 6, the speaker 1 is not shown to simplify the drawing. Instead, in Fig. 6, the plane on which the speaker 1 is placed is indicated by the reference symbol 1'. In Fig. 6, the error microphone 4 is placed in front of the speaker 1, at a position 15 cm from the plane 1' on which the speaker 1 is placed. Also, in Fig. 6, the reference microphone 3 is placed on the back of the speaker 1, at a position 10 cm from the plane 1' on which the speaker 1 is placed.

[0037] As shown in FIG. 6, in front of the speaker 1, a waveform B (shown by a solid line in FIG. 6) that is in phase with a waveform A (shown by a dashed line in FIG. 6) of the reference microphone 3 is generated.

[0038] As a result, a waveform C (indicated by a dashed line in FIG. 6) that is in phase with the waveform B is generated on the rear surface of the speaker 1.

[0039] In this case, if the wavelength of the noise is long, in other words, if the frequency of the noise is low, even if the noise and the control sound output from the speaker 1 are added together at the position of the error microphone 4, no howling occurs and the noise can be canceled.

[0040] Furthermore, if the positions of the reference microphone 3 and the error microphone 4 are approximately symmetrical with respect to the plane 1' on which the speaker 1 is placed, and the 1 / 4 wavelength of the simulated noise to be controlled is longer than the distance between the plane 1' on which the speaker 1 is placed and the reference microphone 3 and the distance between the plane 1' on which the speaker 1 is placed and the error microphone 4, then the noise can be suppressed even if the reference microphone 3 is placed behind the speaker 1.

[0041] Needless to say, other modifications can be made without departing from the spirit of the present invention.

[0042] [Experimental Example] An experiment was conducted to confirm the effectiveness of the proposed arrangement of the reference microphone 3. The results of this example experiment are described below. The cancellation device used in this experiment is the same as that shown in Figures 1 to 5 and described in the section "Cancellation Device and Method," except for the position of the reference microphone 3.

[0043] The Filtered-X LMS algorithm (tap length 2400, alpha=0.001, leakage=0.01) was used to design the filter that generates the secondary sound source reproduced sound from the signal collected by the reference microphone 3. Sine waves of 100, 200, 300, 400, and 600 Hz were used as simulated noise.

[0044] The error microphone 4 was placed in front of the speaker 1, at a position 15 cm away from the plane 1' on which the speaker 1 was placed.

[0045] The reference microphone 3 was placed in the following locations: (1) above the speaker 1 on the same plane as the speaker 1, (2) to the side of the speaker 1 on the same plane as the speaker 1, (3) halfway between the plane on which the speaker 1 is placed and the error microphone 4, and (4) behind the speaker 1, 10 cm from the plane 1' on which the speaker 1 is placed.

[0046] FIG. 7 shows the amount of noise suppression [dB] at the error microphone 4 when the reference microphone 3 is placed at each of the positions (1) to (4).

[0047] FIG. 7 shows that in the cases of (1) and (2), in other words, when the reference microphone 3 is placed on the same plane as the speaker 1, noise can be stably suppressed regardless of the frequency of the simulated noise.

[0048] In addition, in the case of (4), in other words, when the reference microphone 3 is placed behind the speaker 1, it can be seen that noise can be suppressed when the frequency is low (in this experimental example, when the frequency is 400 Hz or less).

Claims

1. A cancellation device for canceling noise arriving in an area near a speaker, comprising: The cancellation device includes at least two speakers and a reference microphone; The canceling device is configured so that an acoustic signal emitted from a sound emitting direction of the same speaker and an acoustic signal emitted from an opposite direction collide with each other, The at least two speakers and the reference microphone are arranged on the same plane; The at least two speakers work in conjunction with each other to emit a cancellation sound that cancels the noise, the plane includes a boundary between a sound emission direction of the two speakers and a direction opposite to the sound emission direction, further comprising an error microphone for verifying the effectiveness of the cancellation; The reference microphone is disposed on the plane, but at a position where a phase characteristic from the speaker to the error microphone is inversely phase to a phase characteristic from the speaker to the reference microphone. Cancellation device.

2. The cancellation device of claim 1, The reference microphone is disposed in an area opposite to the area in which the noise is to be canceled with respect to the speaker. Cancellation device.

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