Noise reduction devices

Abstract

To provide a relatively small noise reduction device that can effectively reduce the frequency range of human speech. [Solution] The noise reduction device 100 comprises a ventilation passage 24 for ensuring the wearer's breathing, with the mouth covered by a covering part (protective part 10), and a pair of noise reduction units connected to the ventilation passage 24. One of the pair of noise reduction units is a first noise reduction unit 30 that reduces low-frequency sounds from the mouth guided through the ventilation passage 24 using an active noise cancellation method, and the other of the pair of noise reduction units is a second noise reduction unit 40, 50 that reduces high-frequency sounds higher than low-frequency sounds from the mouth guided through the ventilation passage 24 using an interference tube method or a resonance tube method.

Description

Technical Field

[0001] The present invention relates to a sound attenuation device.

Background Art

[0002] Conventionally, there is known a technique for attenuating (reducing the sound) of the voice emitted from a person's mouth by collecting the voice (vowel) emitted from the person's mouth with a microphone and outputting a sound wave having a phase opposite to that of the collected voice by an active noise cancellation method (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In sound attenuation by the active noise cancellation method, it is required that the accuracy of synchronously outputting a sound wave having a phase opposite to that of the vowel is higher in the higher frequency range. However, since the frequency band of a person's voice is as wide as about 100 to 2 kHz, the sound attenuation by the active noise cancellation method in the higher frequency range of a person's voice may not be sufficient due to insufficient accuracy, and sound attenuation may not be sufficiently performed. <00′000″29>In addition, since the sound cancellation mask described in Patent Document 1 does not cover the mouth of the speaker, there is a problem that the speaker's voice leaks from between the mouth of the speaker and the sound cancellation mask.

[0005] Therefore, an object of the present invention is to provide a sound attenuation device that is relatively small and can effectively attenuate the frequency band of a person's voice.

Means for Solving the Problems

[0006] The noise reduction device of the present invention comprises a ventilation passage for ensuring the wearer's breathing, with the mouth covered by a covering, and a pair of noise reduction units connected to the ventilation passage, wherein one of the pair of noise reduction units is a first noise reduction unit that reduces low-frequency sounds from the mouth that are guided through the ventilation passage by an active noise cancellation method, and the other of the pair of noise reduction units is a second noise reduction unit that reduces high-frequency sounds higher than the low-frequency sounds from the mouth that are guided through the ventilation passage by an interference tube method or a resonance tube method. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a sound-reducing device that is relatively small and can effectively reduce the frequency range of human speech. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of how to use the noise reduction device according to this embodiment. [Figure 2] This figure shows an example of how to use the noise reduction device according to this embodiment. [Figure 3] This is a perspective view showing the external appearance of the noise reduction device according to the first embodiment, including the side in the positive Y-axis direction. [Figure 4] This is a perspective view showing the appearance of the noise reduction device according to the first embodiment, including the negative Y-axis side. [Figure 5] This is a cross-sectional view of the sound-reducing device according to the first embodiment, when cut by the YZ plane passing through the center in the X-axis direction. [Figure 6] This is a schematic diagram of the inside of the sound-reducing unit of the sound-reducing device according to the first embodiment, viewed from the positive Y-axis direction. [Figure 7] This figure shows the configuration of a verification model for explaining the noise reduction effect according to the first embodiment. [Figure 8] This figure shows the noise reduction effect according to the first embodiment. [Figure 9] This is a perspective view showing the appearance of the noise reduction device according to the second embodiment, including the side in the positive Y-axis direction. [Figure 10]This is a schematic diagram of the inside of the sound-reducing unit of the sound-reducing device according to the second embodiment, viewed from the positive Y-axis direction. [Figure 11] This figure shows the configuration of a verification model for explaining the noise reduction effect according to the second embodiment. [Figure 12] This figure shows the sound reduction effect according to the second embodiment. [Modes for carrying out the invention]

[0009] <First Embodiment> The embodiments for carrying out the present invention will be described in detail below with reference to the drawings. As shown in Figure 1, the noise reduction device 100 according to this embodiment is worn on the user's mouth and covers the user's mouth. The noise reduction device 100 is for reducing sounds, including the voice of the user. The noise reduction device 100 is equipped with a microphone 13 (see Figure 4) and collects sound using the microphone 13. Therefore, the noise reduction device 100 can collect sound using the microphone 13 so that the voice of the user is not heard by people around it. For example, when conducting a remote meeting in an office or at home, the noise reduction device 100 can reduce the possibility of the voice of the user being heard by people around it, thereby preventing the content of the conversation from being known to people around it or causing discomfort to people around it. The noise reduction device 100 may have, for example, an ear hook 200 for attaching the noise reduction device 100 to the user's mouth. The noise reduction device 100 may also be held in the user's hand and attached to the user's mouth.

[0010] As shown in Figure 2, the sound-reducing device 100 of this embodiment may be worn inside the cover mask 300 on the user's mouth. This reduces the visual discomfort caused by wearing the sound-reducing device 100. If the cover mask 300 is made of a material with high sound-insulating properties (thick cloth, rubber sheet layer, etc.), using the cover mask 300 together with the sound-reducing device 100 can further reduce noise. Also, if the cover mask 300 is made of a breathable material (mesh, non-woven fabric, etc.), comfort can be obtained when using the cover mask 300.

[0011] The noise reduction device 100 comprises a protective part 10 and a noise-reducing unit 20 attached to the protective part 10. The protective part 10 is provided in the portion of the noise reduction device 100 that is worn in the user's mouth. The protective part 10 is made of various soft materials with relatively low hardness, such as silicone. As shown in Figures 4 and 5, the protective part 10 has a bottomed cylindrical shape, and its cross-section parallel to the XZ plane is elliptical. As shown in Figure 5, the protective part 10 has a flat plate-shaped bottom 10a parallel to the XZ plane, and a mouth portion 10b that is positioned on the negative Y-axis side from the periphery of the bottom portion 10a and extends in the negative Y-axis direction, with the pipe diameter narrowing towards the negative Y-axis direction. The mouth portion 10b has an opening 11 at its end on the negative Y-axis side. The opening 11 is positioned to surround the user's mouth when the noise reduction device 100 is worn in the user's mouth. In other words, when the sound-reducing device 100 is attached to the user's mouth, the user's mouth is positioned within the opening 11 of the protective part 10 and covered by the sound-reducing device 100. The protective part 10 functions as a cover that surrounds the wearer's mouth.

[0012] The bottom portion 10a is provided with a through-hole 12 that penetrates the bottom portion 10a in the Y-axis direction and communicates with the space 10c surrounded by the protective portion 10 to the internal space of the sound-dampening unit 20. The through-hole 12 is located approximately at the center of the bottom portion 10a in the X-axis direction and is located on the positive side of the center in the Z-axis direction. The bottom portion 10a is also provided with a microphone 13 for collecting sound, including the voice of the user wearing the sound-dampening device 100. The microphone 13 is connected to a signal processing circuit and a communication interface (IF) (not shown), and the processing results from the signal processing circuit may be transmitted to an external device via the communication interface. In other words, by transmitting the sound collected by the microphone 13 to an external device, the microphone 13 functions as a communication microphone.

[0013] The sound absorption unit 20 has an elliptical column shape, and a cross-section parallel to the XZ plane is elliptical. The sound absorption unit 20 is located on the negative Y-axis side, and includes a first flat member 21 located on the negative Y-axis side and parallel to the XZ plane, and a second flat member 22 located on the positive Y-axis side and parallel to the XZ plane. The first flat member 21 and the second flat member 22 have substantially the same shape as the bottom 10a in the XZ plane. The sound absorption unit 20 further has a side member 23 connecting the first flat member 21 and the second flat member 22. As shown in FIGS. 5 and 6, the sound absorption unit 20 includes an air passage 24 inside the housing formed by the first flat member 21, the second flat member 22, and the side member 23.

[0014] As shown in FIGS. 5 and 6, the first flat member 21 is provided with a through hole 21a that penetrates the first flat member 21 in the Y-axis direction and communicates with the air passage 24. The through hole 21a is provided at a substantially central position of the first flat member 21 in the X-axis direction and on the positive side of the center in the Z-axis direction. The inner diameter of the through hole 21a is substantially the same as the inner diameter of the through hole 12. The through hole 21a is provided at a position overlapping the through hole 12 in the X-axis direction and the Z-axis direction and communicates with the through hole 12.

[0015] On the surface of the side member 23 on the negative Z-axis side, a through hole 23a that penetrates the surface in the Z-axis direction and communicates with the air passage 24 is provided. The through hole 23a is an opening on the outside air side of the air passage 24. Since the through hole 23a is provided on the surface of the side member 23 on the negative Z-axis side, the sound emitted from the user wearing the sound attenuation device 100 passes through the through hole 12, the through hole 21a, the air passage 24, and the through hole 23a and is emitted in the negative Z-axis direction. Therefore, the sound traveling in the forward direction (positive Y-axis direction) of the user can be reduced. The shape of the through hole 23a is substantially the same as the inner cross-sectional shape of the air passage 24.

[0016] The ventilation passage 24 is a hollow tube with a semi-elliptical internal cross-section and is located at the center of the sound-reducing unit 20 in the X-axis direction. One end of the ventilation passage 24, which is the inlet, communicates with the through-hole 21a, and the other end, which is the outlet, communicates with the through-hole 23a. The ventilation passage 24 extends linearly in the negative Z-axis direction from the inlet end to the outlet end. The ventilation passage 24 allows the user to release the air blown out of their mouth into the space outside the sound-reducing device 100 while the protective part 10 of the sound-reducing device 100 is tightly fitted around their mouth. In other words, when the user is wearing the sound-reducing device 100 and speaking, the air blown out of the user's mouth can be released into the space outside the sound-reducing device 100, thereby reducing the feeling of breathlessness when the user is wearing the first form of the sound-reducing device 100.

[0017] Furthermore, the through-hole 12 is positioned opposite the user's mouth when the user is wearing the sound-reducing device 100. This allows the air blown out from the user's mouth when the user is speaking to be released into the space outside the sound-reducing device 100 through the through-hole 12 positioned opposite the user's mouth. Therefore, the feeling of breathlessness experienced by the user while wearing the sound-reducing device 100 can be further reduced.

[0018] As shown in Figure 6, the sound-dampening unit 20 includes a first sound-dampening section 30 located on the positive X-axis side of the ventilation passage 24 inside the housing formed by the first surface member 21, the second surface member 22, and the side members 23. The first sound-dampening section 30 includes an amplifier board 31, a speaker 32, a speaker sound path 33, and a battery 34. The amplifier board 31 is driven by the battery 34, processes the sound collected by the microphone 13 with phase inversion, and emits the phase-inverted sound from the speaker 32. The phase-inverted sound emitted from the speaker 32 is emitted into the ventilation passage 24 via the speaker sound path 33. As shown in Figure 6, the sound-dampening unit 20 may also include sound-absorbing material 25 in the location where the first sound-dampening section 30 is provided inside the housing. In the example shown in Figure 6, the sound-absorbing material 25 is provided in the space behind the speaker 32 inside the housing of the sound-dampening unit 20, and absorbs sound that leaks into that space.

[0019] As shown in Figure 6, the sound-dampening unit 20 includes a second sound-reducing section 40 located on the negative X-axis side of the ventilation passage 24 inside the housing formed by the first surface member 21, the second surface member 22, and the side member 23. The second sound-reducing section 40 includes a neck section 41 and a resonant tube 42. The ventilation passage 24 communicates with the resonant tube 42 via the neck section 41 on the outlet side of the ventilation passage 24, beyond the joint 33a between the ventilation passage 24 and the speaker sound path 33.

[0020] The noise reduction device 100 is attached to the user's mouth, and when the user makes a sound, the sound enters the ventilation passage 24 through the through-holes 12 and 21a. The microphone 13 collects the sound emitted from the user. The amplifier board 31 processes the sound collected by the microphone 13 with phase inversion and emits the phase-inverted sound from the speaker 32. The phase-inverted sound emitted from the speaker 32 is emitted into the ventilation passage 24 via the speaker sound path 33. Inside the ventilation passage 24, the sound that entered the ventilation passage 24 through the through-holes 12 and 21a interferes with the phase-inverted sound emitted from the speaker 32, resulting in noise reduction. In this embodiment, the noise reduction by the first noise reduction unit 30 is described as noise reduction by the active noise canceling method.

[0021] Furthermore, when the sound-reducing device 100 is attached to the user's mouth and the user makes a sound, and the sound enters the ventilation passage 24 through the through-holes 12 and 21a, a resonant sound corresponding to a wavelength corresponding to the volume of the resonant tube 42 is generated inside the resonant tube 42. At the joint 41a between the ventilation passage 24 and the neck portion 41 (the end of the neck portion 41 on the positive X-axis side), the sound incident from the ventilation passage 24 to the neck portion 41 (incident sound) and the resonant sound generated inside the resonant tube 42 (emitted sound) interfere with each other, and a frequency sound corresponding to the volume of the resonant tube 42 is canceled out. In other words, the neck portion 41 and the resonant tube 42 constitute a Helmholtz resonator. As a result, at the through-hole 23a, a sound with a frequency corresponding to the volume of the resonant tube 42 (resonant frequency) is emitted at a reduced volume. In other words, in the sound-reducing device 100, the sound emitted by the user is emitted outside the sound-reducing device 100 with a frequency sound corresponding to the volume of the resonant tube 42 at a reduced volume. In this embodiment, the sound reduction by the second sound reduction unit 40 is referred to as sound reduction by the resonant tube method.

[0022] In addition, the ventilation passage 24 may be configured to communicate with the resonant tube 42 via the neck portion 41 on the inlet side of the ventilation passage 24, rather than the joint portion 33a. However, in this case, a separate microphone is required to collect the sound that has been reduced by the second noise reduction unit 40 for noise reduction using the active noise cancellation method. Therefore, a configuration in which the ventilation passage 24 is configured to communicate with the resonant tube 42 via the neck portion 41 on the outlet side of the ventilation passage 24, rather than the joint portion 33a, is preferable. In this configuration, the microphone for noise reduction using the active noise cancellation method and the microphone 13 that functions as a communication microphone can be used interchangeably.

[0023] Next, the noise reduction effects of the active noise cancellation method and the resonant tube method will be explained. In the verification models A to D shown in Figure 7, a sweep sound source of 20Hz to 20kHz is introduced from the sound source speaker 402 into the sound path duct 401, and the sound emitted from the outlet of the sound path duct 401 is observed by the microphone 403. The sound path duct 401 is a hollow tube with a circular internal cross-section. The sound path duct 401 has a length of 120mm from the sound inlet to the outlet and an internal diameter of 10mm.

[0024] Verification model A consists of a sound duct 401 to which the first and second noise reduction units are not connected. Verification model B consists of a sound duct 401 to which the first noise reduction unit 404 is connected, but the second noise reduction unit is not connected. Verification model C consists of a sound duct 401 to which the first noise reduction unit is not connected, but the second noise reduction unit 405 is connected. Verification model D consists of a sound duct 401 to which the first noise reduction unit 404 is connected, and the second noise reduction unit 405 is connected. The first noise reduction unit 404 reduces the sound emitted from the sound source speaker 402 by emitting sound into the sound duct 401 that has been phase-inverted from the sound emitted from the sound source speaker 402. In other words, the first noise reduction unit 404 performs noise reduction using an active noise cancellation method. The second sound-reducing section 405 consists of a neck section 405a and a volume of 6000 mm 3It has a resonant tube 405b. The sound-reducing device 100 of this embodiment has a volume of 6000 mm 3 The size is such that a resonant tube can be housed inside. The second sound reduction unit 405 reduces the frequency sound in the sound emitted from the sound source speaker 402 according to the volume of the resonant tube 405b. In other words, the second sound reduction unit 405 performs sound reduction using a resonant tube method. The frequency (resonant frequency) f1 of the sound reduced by the second sound reduction unit 405 is calculated by the following formula (1), and the frequency of the sound reduced by the second sound reduction unit 405 in verification models C and D is approximately 1.7 kHz.

[0025]

number

[0026] Figure 8 shows the observation results for verification models A to D. In the graph in Figure 8, the horizontal axis represents the frequency of the sound, and the vertical axis represents decibels (dB). The frequency range of the human voice is generally within the range of 100Hz to 2kHz. In other words, if there is a sound reduction effect in the 100Hz to 2kHz range, the sound reduction effect on the human voice is sufficient. In the entire range, the observation results for verification model A are -40dB or higher. In addition, in the observation results for verification model B, a sound reduction effect of up to 20dB by the first sound reduction unit 404 is observed in the 100Hz to 1kHz range of the human voice frequency band. However, as the frequency range increases to 1kHz or higher, the accuracy of the phase inversion processing by the first sound reduction unit 404 cannot keep up, and the sound reduction effect decreases. Therefore, in the observation results for verification model B, no sound reduction effect is obtained in the frequency range above 1kHz. Furthermore, observations from verification model C show that a significant noise reduction effect by the second noise reduction unit 405 is observed, peaking around 1.7 kHz within the human voice frequency range. The 1-2 kHz range within the human voice frequency range corresponds to high-pitched shouts and is perceived as extremely loud. The second noise reduction unit 405 can sufficiently reduce noise in this range. In addition, observations from verification model D show a combined noise reduction effect from the first noise reduction unit 404 and the second noise reduction unit 405. Therefore, a sufficient noise reduction effect was observed in the human voice frequency range.

[0027] The first sound-reducing section 30 of the sound-reducing device 100 of the first embodiment is configured to achieve a sound-reducing effect equivalent to that of the first sound-reducing section 404 in verification models B and D. Therefore, the sound-reducing device 100 of the first embodiment can achieve a sound-reducing effect of up to 20 dB in the 100 Hz to 1 kHz range of the human voice, similar to verification models B and D. Furthermore, the volume of the resonant tube 42 of the second sound-reducing section 40 of the sound-reducing device 100 of the first embodiment is 6000 mm, which is equivalent to the volume of the resonant tube 405b of the second sound-reducing section 405 in verification models C and D. 3It is set to this. Therefore, the noise reduction device 100 of the first embodiment can achieve a large noise reduction effect with a peak around 1.7 kHz in the frequency range of the human voice, similar to verification models C and D. Thus, the noise reduction device 100 of the first embodiment can sufficiently reduce noise in the 1-2 kHz range of the human voice, which is the region that is perceived as extremely loud, such as high-pitched shouts. As described above, the noise reduction device 100 of the first embodiment reduces noise in the low frequency range of the human voice (for example, the 100 Hz to 1 kHz range) by the first noise reduction unit 30, which is an active noise canceling method. Furthermore, the noise reduction device 100 of the first embodiment reduces noise in the high frequency range of the human voice (for example, above 1 kHz), where the noise reduction effect of the first noise reduction unit 30 is reduced, by the second noise reduction unit 40, which is a resonant tube method. Thus, the noise reduction device 100 of the first embodiment can sufficiently reduce noise in the frequency range of the human voice. Furthermore, the first sound reduction unit 30 may be configured to emit only the sound after phase inversion processing to reduce the low frequency range of the human voice from the speaker 32, without emitting the sound after phase inversion processing to reduce the high frequency range of the human voice frequency band from the speaker 32.

[0028] Furthermore, if one attempts to reduce the entire frequency range of the human voice using a resonant tube method, multiple resonant tubes are required, such as a resonant tube for reducing the low frequency range and a resonant tube for reducing the high frequency range. In this case, it may also be necessary to combine the resonant tube method with a resistance / expansion method that provides physical resistance to the sound path in the sound reducing device. As a result, the sound reducing device becomes larger. However, in the sound reducing device 100 according to the first embodiment, the low frequency range of the human voice (e.g., 100Hz to 1kHz) is reduced by an active noise canceling method. In addition, the high frequency range of the human voice (e.g., 1kHz to 2kHz) is reduced by a resonant tube method. Therefore, in this embodiment, multiple resonant tubes, a relatively large resonant tube for reducing the low frequency range, and a configuration for achieving sound reduction by a resistance / expansion method are not required, and the sound reducing device 100 can be made relatively small.

[0029] <Second Embodiment> Next, a second embodiment of the present invention will be described. In the second embodiment, the same reference numerals are used for components similar to those in the first embodiment, and their descriptions are omitted. As shown in Figures 9 and 10, the sound-reducing device 100 of the second embodiment includes a first sound-reducing section 30 similar to that of the first embodiment, located on the positive X-axis side of the ventilation passage 24 inside the housing formed by the first surface member 21, the second surface member 22, and the side member 23. The sound-reducing device 100 of the second embodiment also includes a second sound-reducing section 50 located on the negative X-axis side of the ventilation passage 24 inside the housing formed by the first surface member 21, the second surface member 22, and the side member 23. In other words, in the sound-reducing device 100 of the second embodiment, the second sound-reducing section 40 in the sound-reducing device 100 of the first embodiment is replaced by the second sound-reducing section 50. The second sound-reducing section 50 includes an interference tube 51. In the second embodiment, the ventilation passage 24 communicates with one end 51a, which is the inlet of the interference pipe 51, and the other end 51b, which is the outlet of the interference pipe 51, on the outlet side of the ventilation passage 24, beyond the joint 33a between the ventilation passage 24 and the speaker sound path 33.

[0030] The first sound guiding distance L1 is defined as the distance from one end of the ventilation passage 24, which is the entrance, to the vicinity of the other end 51b of the ventilation passage 24. The second sound guiding distance L2 is defined as the distance from one end of the ventilation passage 24, which is the entrance, through one end 51a of the interference pipe 51, through the inside of the interference pipe 51, to the other end 51b. The second sound guiding distance L2 is longer than the first sound guiding distance L1.

[0031] When the sound-reducing device 100 is attached to the user's mouth and the user makes a sound, the first sound-reducing unit 30 reduces the sound by causing interference between the sound that enters the ventilation passage 24 through the through-holes 12 and 21a and the phase-inverted sound emitted from the speaker 32, similar to the first embodiment. Furthermore, when the sound-reducing device 100 is attached to the user's mouth and the user makes a sound, causing the sound to enter the ventilation passage 24 through the through-holes 12 and 21a, the entered sound passes through the ventilation passage 24. The sound that enters the ventilation passage 24 is then entered into the interference pipe 51 from one end 51a. The sound that enters the interference pipe 51 then passes through the interference pipe 51 and is emitted into the ventilation passage 24 from the other end 51b. The first sound wave, which is a sound wave of speech that has passed through the inside of the ventilation passage 24 and reached the vicinity of the other end 51b, and the second sound wave, which is a sound wave of speech that has passed through the inside of the interference tube 51 and is emitted from the other end 51b, merge near the other end 51b of the ventilation passage 24. Since the second sound guiding distance L2 is longer than the first sound guiding distance L1, the second sound wave vibrates more than the first sound wave, and there is a phase difference between the second sound wave and the first sound wave. At the position where the first and second sound waves merge, the first sound wave and the second sound wave with a phase difference interfere with each other, causing the sound in the frequency range corresponding to the phase difference in the first sound wave to cancel each other out. As a result, at the position where the first and second sound waves merge, the sound with a peak in that frequency range in the first sound wave is attenuated and emitted.

[0032] The first guiding distance L1 and the second guiding distance L2 are set to values ​​that satisfy the following equation (2). f2 = c / 2·(L2-L1) ···(2) f2: Frequency at which sound is reduced from the user's voice. c:Sound speed When the above equation (2) is satisfied, the second sound reduction unit 50 can reduce the sound with a peak frequency f2 in response to the voice emitted by the user. In this embodiment, the sound reduction by the second sound reduction unit 50 is referred to as sound reduction by the interference tube method.

[0033] It is also possible that the ventilation passage 24 communicates with one end 51a, which is the inlet of the interference pipe 51, and the other end 51b, which is the outlet of the interference pipe 51, on the inlet side of the ventilation passage 24 beyond the joint 33a. However, in this case, a separate microphone is required to collect the sound that has been reduced in volume by the second noise reduction unit 50. Therefore, it is preferable that the ventilation passage 24 communicates with one end 51a, which is the inlet of the interference pipe 51, and the other end 51b, which is the outlet of the interference pipe 51, on the outlet side of the ventilation passage 24 beyond the joint 33a. In this configuration, the microphone for noise reduction using the active noise cancellation method and the microphone 13 that functions as a communication microphone can be used together.

[0034] Next, the noise reduction effect of the active noise cancellation method and the interference tube method in the second embodiment will be described. In verification models A and B, which are the same as in the first embodiment, and in verification models E and F shown in Figure 11, the sound of a sweep sound source from 20Hz to 20kHz is introduced from the sound source speaker 402 into the sound path duct 401, and the sound emitted from the outlet of the sound path duct 401 is observed by the microphone 403.

[0035] Verification model C consists of a sound duct 401 to which the first sound reduction unit is not connected, but the second sound reduction unit 406 is connected. Verification model F consists of a sound duct 401 to which the first sound reduction unit 404 is connected, and the second sound reduction unit 406 is connected. The length of the interference tube of the second sound reduction unit 406 is 120 mm. The sound reduction device 100 in this embodiment is sized to accommodate the interference tube of 120 mm in length. The second sound reduction unit 406 reduces the sound emitted from the sound source speaker 402, with a peak at a frequency corresponding to the length of the interference tube. In other words, the second sound reduction unit 406 performs sound reduction using an interference tube method.

[0036] Figure 12 shows the observation results for verification models A, B, C, and E. In the graph in Figure 12, the horizontal axis represents the frequency of the sound, and the vertical axis represents decibels (dB). The observation results for verification models A and B are the same as those for the first embodiment. In addition, in the observation results for verification model E, a large sound reduction effect by the second sound reduction unit 406 appears, peaking around 1.4 kHz in the frequency band of the human voice. The 1-2 kHz range of the human voice corresponds to high-pitched shouts and is a region that is perceived as extremely loud. The second sound reduction unit 406 can sufficiently reduce the sound in this region. Furthermore, in the observation results for verification model F, a sound reduction effect is observed that is the sum of the sound reduction effect by the first sound reduction unit 404 and the sound reduction effect by the second sound reduction unit 406. Therefore, a sufficient sound reduction effect was observed in the frequency band of the human voice.

[0037] The first sound-reducing section 30 of the sound-reducing device 100 of the second embodiment is configured to achieve a sound-reducing effect equivalent to that of the first sound-reducing section 404 in verification models B and F, similar to the first embodiment. Therefore, the sound-reducing device 100 of the second embodiment can achieve a maximum sound-reducing effect of 20 dB in the 100 Hz to 1 kHz range of the human voice frequency band, similar to verification models B and F. Furthermore, the frequency at which sound is reduced by the second sound-reducing section 50 of the sound-reducing device 100 of the second embodiment is set to be equivalent to the frequency at which sound is reduced by the second sound-reducing section 406 in verification models E and F. Therefore, the sound-reducing device 100 of the second embodiment can achieve a large sound-reducing effect with a peak around 1.4 kHz in the human voice frequency band, similar to verification models E and F. Consequently, the sound-reducing device 100 of the second embodiment can sufficiently reduce sound in the 1 to 2 kHz range of the human voice frequency band, which is the region that is perceived as extremely loud, such as high-pitched shouts. As described above, the noise reduction device 100 of the second embodiment reduces the low-frequency range (e.g., 100Hz to 1kHz) of the human voice frequency range by the first noise reduction unit 30, which is an active noise canceling method. Furthermore, the noise reduction device 100 of the second embodiment reduces the high-frequency range (e.g., 1kHz or higher) of the human voice frequency range where the noise reduction effect of the first noise reduction unit 30 is reduced by the second noise reduction unit 50, which is an interference tube method. Therefore, the noise reduction device 100 of the second embodiment can sufficiently reduce noise in the human voice frequency range.

[0038] Furthermore, if one attempts to reduce the entire frequency range of the human voice using an interference tube method, multiple interference tubes are required, such as an interference tube for reducing the low frequency range and an interference tube for reducing the high frequency range. Also, if the average frequency of a male voice, 500Hz, is reduced using an interference tube method, a relatively large interference tube with a length of 34cm is required, resulting in a large noise reduction device. However, in the noise reduction device 100 according to the second embodiment, the low frequency range of the human voice (e.g., 100Hz to 1kHz) is reduced using an active noise cancellation method. In addition, the high frequency range of the human voice (e.g., 1kHz to 2kHz) is reduced using an interference tube method. Therefore, in this embodiment, multiple resonance tubes and relatively large interference tubes for reducing the low frequency range are not required, and the noise reduction device 100 can be made relatively small.

[0039] As described above, the noise reduction device 100 according to this embodiment comprises a ventilation passage 24 for ensuring the wearer's breathing, with the mouth covered by a covering part (protective part 10), and a pair of noise reduction units connected to the ventilation passage 24. One of the pair of noise reduction units is a first noise reduction unit 30 that reduces low-frequency sounds from the mouth guided through the ventilation passage 24 using an active noise cancellation method, and the other of the pair of noise reduction units is a second noise reduction unit 40, 50 that reduces high-frequency sounds higher than the low-frequency sounds from the mouth guided through the ventilation passage 24 using an interference tube method or a resonance tube method. If the entire frequency range of sound emitted from a person's mouth is to be reduced in real time using an active noise cancellation method in the narrow space inside the mask, it is necessary to process the phase inversion of the sound at an extremely high speed. In particular, wavelengths become shorter as the frequency range increases, and it is necessary to control the interference of phase-inverted sound with the sound emitted from the human mouth with high precision and low latency, making it difficult to ensure sufficient noise reduction performance in the high-frequency range. However, in this embodiment, the high-frequency range is reduced by a resonant tube method or interference tube method, and the low-frequency range is reduced by an active noise cancellation method, thereby effectively extending the range in which noise can be reduced. Furthermore, in the noise reduction device 100 according to the first embodiment, the low-frequency range of the human voice is reduced by an active noise cancellation method. Furthermore, since the high-frequency range of the human voice is reduced by a resonant tube method, multiple resonant tubes, a relatively large resonant tube for reducing the low-frequency range, and a configuration for achieving noise reduction by resistance / expansion method are not required, so the noise reduction device 100 can be made relatively small. Furthermore, in the noise reduction device 100 according to the second embodiment, the low-frequency range of the human voice is reduced by an active noise cancellation method. Furthermore, because the interference tube method reduces the high-frequency range of human voices, this embodiment does not require multiple resonant tubes or relatively large interference tubes for reducing low frequencies, thus allowing the sound-reducing device 100 to be made relatively small. In addition, since the wearer's mouth is covered by the protective part 10, sound leakage from between the wearer's mouth and the sound-reducing device 100 can be suppressed. As described above, a sound-reducing device that is relatively small and can effectively reduce the frequency range of human voices can be provided.

[0040] In the noise reduction device 100 according to this embodiment, the first noise reduction unit 30 is connected to the ventilation passage 24 on the mouth side of the connection point between the ventilation passage 24 and the second noise reduction units 40 and 50. Therefore, the microphone used for collecting human voices in noise reduction using the active noise cancellation method can be used for both purposes and as a microphone for communication.

[0041] In the noise reduction device 100 according to this embodiment, the opening (through hole 23a) on the outside air side of the ventilation passage 24 is opened downwards. Therefore, the sound emitted from the wearer of the noise reduction device 100 passes through the ventilation passage 24 and the through hole 23a and is emitted downwards (negative Z-axis direction). This makes it possible to reduce the sound directed forward of the wearer (positive Y-axis direction).

[0042] In the noise reduction device 100 according to this embodiment, a pair of noise reduction units are provided on the left and right sides (positive X-axis direction side and negative X-axis direction side) of the ventilation passage 24. Therefore, the space inside the housing of the noise reduction device 100 can be effectively utilized, and the noise reduction device 100 can be made relatively compact.

[0043] The noise reduction device 100 according to this embodiment includes a microphone 13 inside the housing. Therefore, the noise reduction device 100 can be used when conducting remote meetings in an office or at home, and can reduce the amount of the user's voice heard by those around them. This makes it possible to prevent the content of the conversation from being known to those around, or to prevent causing discomfort to those around.

[0044] The above embodiments are provided as specific examples to facilitate understanding of the invention, and the present invention is not limited to these embodiments. Various modifications and changes are possible without departing from the spirit of the invention. For example, in the above embodiments, the sound-reducing device 100 is formed in a shape that covers the wearer's mouth while exposing the nose, but the sound-reducing device 100 may be formed in a shape that covers both the wearer's mouth and nose. In this case, the protective part 10 should be formed so that it surrounds both the wearer's mouth and nose. [Explanation of symbols]

[0045] 100...Sound reduction device, 10...Protective part (covering part), 24...Ventilation passage, 30...First sound reduction part, 40, 50...Second sound reduction part

Claims

1. A ventilation channel to ensure breathing for the wearer whose mouth is covered by the covering, A pair of sound-reducing units connected to the aforementioned ventilation passage, Equipped with, One of the pair of sound reduction units is a first sound reduction unit that reduces low-frequency sounds from the mouth that are guided through the air passage by an active noise cancellation method. A sound-reducing device in which the other of the pair of sound-reducing parts is a second sound-reducing part that reduces high-frequency sounds higher than the low-frequency sounds among the sounds from the mouth that are guided through the air passage by an interference tube method or a resonance tube method.

2. The sound-reducing device according to claim 1, wherein the first sound-reducing section is connected to the ventilation passage at a point closer to the mouth than the connection point between the ventilation passage and the second sound-reducing section.

3. The sound-reducing device according to claim 1, wherein the opening on the outside side of the ventilation passage is opened downward.

4. The noise reduction device according to claim 1, wherein the pair of noise reduction units are provided on the left and right sides of the ventilation passage.

5. The noise reduction device according to claim 1, comprising a microphone inside the housing.

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