Noise reduction device and cleaner

Abstract

To provide a noise reduction device with which size can be reduced and noise can be effectively reduced. This noise reduction device (1) comprises: a pipe part (2) having a first air passage (16) for transmitting noise in a first transmission direction and a second air passage (17) for transmitting the noise in a second transmission direction different from the first transmission direction; a reference microphone (5) to which sound in the first air passage is input; and a speaker (6) for outputting sound to the second air passage.

Description

Noise reduction devices and vacuum cleaners

[0001] The present invention relates to a noise reduction device and a vacuum cleaner.

[0002] Active noise control (ANC) is known to reduce noise by generating a sound that cancels the noise. For example, ANC is performed using a speaker, a reference microphone, and an error microphone to reduce noise. Another known ANC method is an ANC feedforward method that uses a feedback canceller to suppress the effects of acoustic feedback (see, for example, Patent Document 1).

[0003] Japan “Unexamined Japanese Patent Publication No. 10-190590”

[0004] When using ANC to reduce noise transmitted through a pipe, the smaller the system, the shorter the distance between the reference microphone and the speaker. This means that the time required to calculate the phase of the sound output from the speaker that cancels out the noise becomes shorter, limiting how small the system can be. Furthermore, the effects of acoustic feedback become greater, making it more susceptible to feedback.

[0005] An object of one aspect of the present invention is to provide a noise reduction device that is compact and can effectively reduce noise.

[0006] In order to solve the above problem, a noise reduction device according to one embodiment of the present invention includes a pipe section having a first air passage that transmits noise emitted by a noise source in a first transmission direction, and a second air passage that communicates with the first air passage via a space and transmits the noise in a second transmission direction different from the first transmission direction, a reference microphone to which sound in the first air passage is input, and a speaker that outputs sound to the second air passage.

[0007] In order to solve the above problem, a noise reduction device according to one aspect of the present invention comprises a pipe section having a first air passage that transmits noise emitted by a noise source in a first transmission direction, and a second air passage that communicates with the first air passage via a space and transmits the noise in a second transmission direction different from the first transmission direction, the pipe section having an inner pipe and an outer pipe, the inner pipe forming the first air passage inside a first inner surface of the inner pipe, and the outer pipe forming the second air passage between a second inner surface of the outer pipe and a first outer surface of the inner pipe.

[0008] According to one aspect of the present invention, it is possible to achieve miniaturization and effectively reduce noise.

[0009] FIG. 1 is a configuration diagram showing an example of a noise reduction device according to a first embodiment. FIG. 2 is a cross-sectional view of the noise reduction device. FIG. 3 is a configuration diagram showing another example of a noise reduction device. FIG. 4 is a diagram explaining details and operation of a control unit of a noise reduction device according to a second embodiment. FIG. 5 is a schematic diagram showing the structure of a part of a vacuum cleaner according to a third embodiment. FIG. 6 is a schematic diagram showing the overall structure of the vacuum cleaner. FIG. 7 is a schematic diagram showing the positions of a speaker and a reference microphone of a noise reduction device in the vacuum cleaner. FIG. 8 is a schematic diagram showing the positions of a speaker and a reference microphone of a noise reduction device in the vacuum cleaner. FIG. 9 is a configuration diagram showing an example of a noise reduction device according to a fourth embodiment. FIG. 10 is a cross-sectional view of the noise reduction device. FIG. 11 is a diagram showing how sound traveling from a speaker to a reference microphone is reduced by the noise reduction device. FIG. 12 is a diagram showing various structures of a reflection suppression section of the noise reduction device. FIG. 13 is a diagram explaining a shielding section of the noise reduction device. FIG. 14 is a configuration diagram showing another example of a noise reduction device. FIG. 14 is a diagram showing how sound traveling from a speaker to a reference microphone is reduced by the noise reduction device.

[0010] [First Embodiment] Hereinafter, one embodiment of the present invention will be described in detail.

[0011] Fig. 1 is a configuration diagram showing an example of a noise reduction device 1 according to a first embodiment. As shown in Fig. 1, the noise reduction device 1 includes a pipe section 2, a reference microphone 5, a control section 50, a speaker 6, and an error microphone 7. A noise source 9 is located at one end of the pipe section 2. The noise source 9 is a device that generates noise.

[0012] Such a noise reduction device 1 is provided in a noise-generating device such as a vacuum cleaner or an air conditioner. In this case, the noise source 9 is, for example, a blower. The blower includes a motor that rotates a fan. The noise includes the sound of wind and the sound of the motor.

[0013] 1 , the noise source 9 may be covered with a cover 10. The cover 10 is connected to one end of the pipe section 2. The cover 10 is preferably made of a sound-absorbing material such as urethane or felt. By covering the noise source 9, the cover 10 can confine the noise inside the pipe section 2.

[0014] The pipe section 2 transmits noise emitted by the noise source 9. The pipe section 2 is a cylindrical member having an internal cavity. The internal cavity of the pipe section 2 functions as a transmission passage (air passage) for transmitting the noise emitted by the noise source 9. Specifically, the pipe section 2 has a first air passage 16 that transmits the noise emitted by the noise source 9 in a first transmission direction, and a second air passage 17 that communicates with the first air passage 16 via a space 19 and transmits the noise in a second transmission direction different from the first transmission direction. The first air passage 16 includes an input section 5a through which a reference microphone 5 (described later) acquires sound. The second air passage 17 includes an output section 6a through which a speaker 6 (described later) outputs sound. The pipe section 2 has, for example, a cylindrical or rectangular shape. One end of the pipe section 2 faces the noise source 9. The end of the pipe section 2, opposite the noise source 9 and downstream in the noise transmission direction, is closed. 1 , in a configuration in which a cover 10 that covers a noise source 9 is connected to one end, one end of the pipe portion 2 is open. Hereinafter, the noise source 9 side of the pipe portion 2 may be referred to as the upstream side (upstream side in the first transmission direction), and the opposite side may be referred to as the downstream side (downstream side in the first transmission direction). The downstream side of the pipe portion 2 has a double-pipe structure.

[0015] 2 is a cross-sectional view of the noise reduction device 1. As shown in FIG. 2, the pipe section 2 includes an inner pipe 3 and an outer pipe 4.

[0016] The inner pipe 3 transmits noise and has an open downstream end 31 (first end). In this example, the inner pipe 3 also has an open upstream end 32 (third end) to which a cover 10 that covers the noise source 9 is connected.

[0017] The outer pipe 4 is inserted onto the outer periphery of the inner pipe 3 on the downstream side in the power transmission direction, with a distance between it and the outer periphery of the inner pipe 3. In other words, the outer pipe 4 is formed to be larger in diameter and shorter than the inner pipe 3. The outer pipe 4 extends downstream of the downstream end 31 of the inner pipe 3. In other words, the downstream end 41 (second end) of the outer pipe 4 is located downstream of the downstream end 31 of the inner pipe 3. The downstream end 41 of the outer pipe 4 is closed, and the upstream end 42 (fourth end) is open.

[0018] As a result, the inner pipe 3 forms a first air passage 16 (which transmits noise in a first transmission direction) inside the first inner circumferential surface 36 of the inner pipe 3. The outer pipe 4 forms a second air passage 17 (which transmits noise in a second transmission direction) between the second inner circumferential surface 46 of the outer pipe 4 and the first outer circumferential surface 37 of the inner pipe 3. That is, by inserting the outer pipe 4 into the outer periphery of the inner pipe 3 on the downstream side in the transmission direction, the downstream side of the pipe section 2 has a double-pipe structure, forming the first air passage 16 and the second air passage 17. Noise output from the noise source 9 is transmitted through the first air passage 16 in the first transmission direction, changes direction in the space 19, transmitted through the second air passage 17 in the second transmission direction, and output to the outside from the upstream end 42 of the outer pipe 4. In the example shown in FIG. 2 , the second transmission direction is opposite to the first transmission direction. As a result, noise emitted from the downstream end 31 of the inner pipe 3 in the first transmission direction is redirected (i.e., diffracted) to the second transmission direction, making it less likely to be transmitted to the second air passage 17.

[0019] The speaker 6 outputs sound under the control of the control unit 50. The speaker 6 outputs sound toward the inside of the pipe section 2. The speaker 6 outputs sound that includes a sound that reduces noise. Specifically, the speaker 6 outputs sound that is in the opposite phase to the noise that propagates inside the pipe section 2. The noise emitted by the noise source 9 is propagated inside the inner pipe 3. The noise propagated inside the inner pipe 3 is further propagated inside the outer pipe 4. The noise propagated inside the outer pipe 4 is canceled out by the sound output from the speaker 6. Therefore, the noise output from the downstream end of the pipe section 2 is reduced.

[0020] The speaker 6 is located in the outer pipe 4. The speaker 6 is arranged with its diaphragm facing in a direction intersecting the transmission direction. Specifically, the speaker 6 outputs sound to the space (second air passage 17) between the outer pipe 4 and the inner pipe 3, which form a double-pipe structure in the pipe section 2. An output part 6a, from which the sound of the speaker 6 is output to the inside of the pipe section 2, is located on the side surface of the outer pipe 4.

[0021] As shown in the example in Fig. 2, the speaker 6 is directly connected to the pipe section 2 (specifically, the outer pipe 4). In this case, the output part 6a serves as the diaphragm of the speaker 6. The speaker 6 may also be disposed inside a branch pipe that branches off from the pipe section 2. In this case, the sound output by the speaker 6 is transmitted to the inside of the pipe section 2 through an opening of the branch pipe. The output part 6a serves as the opening of the branch pipe.

[0022] The reference microphone 5 acquires sound from inside the inner pipe 3 (first air passage 16). An input portion 5a where the reference microphone 5 acquires sound is located on the side surface of the inner pipe 3. In the example shown in Fig. 2, the reference microphone 5 is located in the inner pipe 3. Note that, like the speaker 6, the reference microphone 5 may be disposed inside a branch pipe that branches off from the pipe section 2 (specifically, the inner pipe 3).

[0023] According to the above configuration, noise transmitted through the first air passage 16 enters and is transmitted through the second air passage 17, which has a different noise transmission direction from the first air passage 16. This makes it possible to shorten the actual separation distance between the reference microphone 5 and the speaker 6 while ensuring a long distance on the noise transmission path between the reference microphone 5 and the speaker 6. Therefore, the noise reduction device 1 can be made smaller while ensuring sufficient processing time for ANC.

[0024] Furthermore, since the speaker 6 outputs sound to the second air passage 17, the sound emitted from the speaker 6 is prevented from going directly toward the reference microphone 5, thereby suppressing howling.

[0025] The error microphone 7 picks up sound from inside the pipe section 2 at a position where the noise emitted by the noise source 9 and the sound output by the speaker 6 join together. Specifically, the error microphone 7 is located in a portion of the outer pipe 4 that extends downstream from the downstream end of the inner pipe 3. The error microphone 7 picks up sound from the overlapping portion of the outer pipe 4 where it overlaps with the inner pipe 3. The provision of the error microphone 7 allows ANC to be performed with high accuracy even if the shape of the pipe section 2 changes or the temperature fluctuates.

[0026] The control unit 50 controls the sound output from the speaker 6. The control unit 50 is, for example, a processor such as a CPU (Central Processing Unit) or a logic circuit (hardware) formed in an integrated circuit (IC (Integrated Circuit) chip). The control unit 50 performs active noise control (ANC) to reduce noise by generating a sound that cancels out the noise. For example, the control unit 50 performs ANC using the speaker 6, the reference microphone 5, and the error microphone 7 to reduce noise transmitted inside the pipe unit 2.

[0027] In ANC, the control unit 50 controls the sound output from the speaker 6 based on the sound input to the reference microphone 5 and the error microphone 7. Specifically, for example, the control unit 50 outputs a sound that reduces noise, such as a sound that is in antiphase with the noise, from the speaker 6 based on the sound input to the reference microphone 5 and the error microphone 7. The control unit 50 controls the sound output from the speaker 6 so as to reduce the volume of the sound input to the error microphone 7, i.e., the reduced noise. As a result, the noise transmitted inside the pipe section 2 is reduced, and the reduced noise is output from the outlet of the pipe section 2 (the upstream end 42 of the outer pipe 4).

[0028] According to the noise reduction device 1, the pipe section 2 is disposed near the noise source 9, with one end of the pipe section 2 facing the noise source 9, and the noise emitted by the noise source 9 can be transmitted inside the pipe section 2 by the pipe section 2. The noise transmitted inside the pipe section 2 can then be canceled out by the speaker 6. This reduces the noise output from the outlet of the pipe section 2 (the upstream end 42 of the outer pipe 4). The noise reduction device according to the first embodiment also includes a cover 10 that covers the noise source 9. Covering the noise source 9 with the cover 10 enhances the noise reduction effect.

[0029] The noise reduction device 1 further includes a wall 11. The wall 11 is provided at the downstream end 41 of the outer pipe 4. The wall 11 forms a space 19 between the downstream end 31 of the inner pipe 3 and the downstream end 41 of the outer pipe 4. Therefore, the first air passage 16 formed inside the inner pipe 3 communicates with the second air passage 17 formed between the first outer circumferential surface 37 of the inner pipe 3 and the second inner circumferential surface 46 of the outer pipe 4 via the space 19. Noise transmitted through the first air passage 16 is transmitted to the space 19. The noise transmitted to the space 19 is diffused in the space 19. The noise diffused in the space 19 can reach the second air passage 17 by being diffracted toward the second air passage 17 or reflected by the wall 11. The noise that reaches the second air passage 17 is transmitted through the second air passage 17 in the opposite direction to the first air passage 16. This reduces noise transmission to the second air passage 17.

[0030] It is preferable that a sound-absorbing material be provided on the inside of the wall 11. Noise emitted from the downstream end 31 of the inner pipe 3 that reaches the wall 11 is absorbed by the sound-absorbing material in the wall 11. Furthermore, by providing the wall 11 with a sound-absorbing material, the noise that reaches the wall 11 is reflected by the wall 11 and prevented from reaching the second air passage 17. This further reduces noise. Therefore, the sound output from the speaker 6 (sound that cancels out the noise transmitted to the second air passage) can be reduced, further suppressing howling.

[0031] The diameter of the outer pipe 4 is preferably 5 cm or less at the output portion 6a where sound is output from the speaker 6. By making the diameter of the outer pipe 4 at the output portion 6a 5 cm or less, the sound output from the speaker 6 (typically sound of 4 kHz or less) can be transmitted one-dimensionally in the direction of sound propagation inside the pipe portion 2 (specifically, the second air passage 17), allowing ANC to be performed with high accuracy.

[0032] The distance L in the first transmission direction (axial direction of the pipe portion 2) between the downstream end 31 of the inner pipe 3 and the downstream end 41 of the outer pipe 4 is preferably equal to or less than the inner diameter of the inner pipe 3. In other words, the width of the space 19 in the first transmission direction is preferably equal to or less than the inner diameter of the inner pipe 3. This makes it possible to suppress pressure loss of the exhaust gas discharged from the inner pipe 3. It is also possible to suppress the generation of new noise due to the exhaust gas being turned back.

[0033] Note that the noise reduction device 1 does not need to perform ANC (i.e., it does not need to have the reference microphone 5 and the speaker 6) as long as it has the double-pipe structure (first air passage 16 and second air passage 17) of the pipe portion 2 described above. As described above, by having at least the double-pipe structure of the pipe portion 2, the noise reduction device 1 can make it difficult for noise transmitted through the first air passage 16 to be transmitted to the second air passage 17. In other words, noise can be effectively reduced.

[0034] Fig. 11 is a structural diagram showing another example of a noise reduction device (designated noise reduction device 1A). As shown in Fig. 11, the outlet of the pipe section 2 in noise reduction device 1A, i.e., the upstream end 42 of the outer pipe 4, has a gradually expanding diameter shape with an opening area that gradually widens. This structure of the upstream end 42 of the outer pipe 4 makes it possible to suppress the generation of new noise due to exhaust gases at the exhaust outlet. Furthermore, even if there is noise that cannot be silenced by ANC, it is possible to suppress the reflection of that noise at the exhaust outlet. Therefore, it is possible to suppress the noise from becoming a cause of howling.

[0035] (Controller of Noise Reduction Device) Fig. 4 is a diagram illustrating the details and operation of the controller 50 of the noise reduction device according to the second embodiment. Note that in Fig. 4, the cover 10, the pipe section 2, and the treble reduction section 12 are omitted.

[0036] The control unit 50 has a signal amplification conversion unit 502, an AGC (Automatic Gain Control) unit 503, a noise filter unit 504, a low-pass filter (LPF) 505, an input filter unit 506, a feedback cancellation node 507, an adaptive filter 508, a transfer function H learning unit 509, an output filter unit 510, a DAC (Digital to Analog Converter) 511, a feedback canceller 512, an FBC gain compensation unit 513, a secondary path estimation filter 514, a secondary path correction node 515, a signal amplification conversion unit 516, an AGC unit 517, an error sound filter unit 518, a low-pass filter (LPF) 519, an input filter unit 520, a transfer function F learning unit 521, a sound signal generation unit 522, and a transfer function S learning unit 523.

[0037] The reference microphone 5 receives the noise emitted by the noise source 9 and outputs the noise source signal to the signal amplification and conversion unit 502 .

[0038] The signal amplification and conversion unit 502 includes a programmable gain amplifier (PGA) and an analog-to-digital converter (ADC). The PGA amplifies the noise source signal output by the reference microphone 5. The PGA can switch the amplification factor. The PGA switches the amplification factor in response to an instruction from the AGC unit 503. The ADC converts the signal amplified by the PGA into a digital signal.

[0039] The AGC unit 503 controls the gain of the reference microphone 5. Specifically, the AGC unit 503 changes the amplification factor of the PGA of the signal amplification conversion unit 502. The AGC unit 503 receives the signal output by the ADC of the signal amplification conversion unit 502 and determines the amplification factor of the PGA. The AGC unit 503 determines the amplification factor of the PGA in accordance with the signal output by the ADC. For example, the AGC unit 503 determines the amplification factor of the PGA using AGC so that the dynamic range of the PGA is maximized. For example, the AGC unit 503 performs the following process regarding AGC. The AGC unit 503 detects the output of the ADC of the signal amplification conversion unit 502 for each first period (e.g., 5.21 μs), calculates the square mean value for each second period (e.g., 1.33 ms) from the sum of the squares of multiple (e.g., 256) detected outputs, and calculates a moving average value from the calculated multiple square mean values. The AGC unit 503 determines at regular intervals whether the calculated moving average value is greater than a predetermined target range and the current value of the amplification factor of the PGA of the signal amplification conversion unit 502 is not the minimum value, and if the calculated moving average value is greater than the predetermined target range and the current value of the amplification factor of the PGA of the signal amplification conversion unit 502 is not the minimum value, reduces the value of the amplification factor of the PGA of the signal amplification conversion unit 502 by a predetermined value. In addition, the AGC unit 503 determines at regular intervals whether the calculated moving average value is smaller than a preset target range and the current value of the amplification factor of the PGA of the signal amplification conversion unit 502 is not the maximum value, and if the calculated moving average value is smaller than the preset target range and the current value of the amplification factor of the PGA of the signal amplification conversion unit 502 is not the maximum value, it increases the value of the amplification factor of the PGA of the signal amplification conversion unit 502 by a predetermined value.

[0040] The noise filter unit 504 filters the signal output by the ADC to generate a filtered noise signal h(n). The noise filter unit 504 includes a low-pass filter (LPF) 505 that performs decimation, and an input filter unit 506.

[0041] The feedback cancellation node 507 generates a feedback-canceled noise signal x(n) from the filtered noise signal h(n) and an FBC (Feedback Control) gain compensation signal d(n). The feedback cancellation node 507 generates the feedback-canceled noise signal x(n), for example, by subtracting the FBC gain compensation signal d(n) from the filtered noise signal h(n).

[0042] The adaptive filter 508 generates an anti-noise signal y(n) from the feedback-canceled noise signal x(n). The anti-noise signal y(n) includes information for reducing the noise emitted by the noise source 9. The adaptive filter 508 is, for example, a dynamically operating digital filter. The adaptive filter 508 has a transfer function H that generates the anti-noise signal y(n) from the feedback-canceled noise signal x(n). The transfer function H is learned from the filtered error signal k(n) of the error microphone 7 and the secondary path estimation filtered signal r(n) of the feedback-canceled noise signal x(n). The transfer function H is learned by the transfer function H learning unit 509. A specific example will be described. The filtered noise signal h(n) that has passed through the noise filter unit 504 is processed by the adaptive filter 508 to obtain the anti-noise signal y(n). The anti-noise signal y(n) passes through the output filter unit 510 and the DAC 511 and is input to the speaker 6, which then emits a control sound. The control sound emitted by the speaker 6 interacts with the noise that has passed through the primary path. The sound resulting from the interaction of the noise that has passed through the primary path and the control sound emitted by the speaker 6 is input to the error microphone 7. The transfer function H is trained so as to reduce the sound input to the error microphone 7. Here, it is preferable to train the transfer function H based on the secondary path estimation filtered signal r(n) output from the secondary path estimation filter 514, which imitates the characteristics of the additional path including the output filter unit 510, the secondary path, and the error sound filter unit 518. This is because a transfer function H can be obtained that can remove the influence of the additional path including the output filter unit 510, the secondary path, and the error sound filter unit 518 and accurately cancel out the noise that has passed through the primary path.

[0043] The output filter section 510 filters the anti-noise signal y(n) and includes a low-pass filter that performs interpolation.

[0044] A DAC (Digital to Analog Converter) 511 converts the signal filtered by the output filter unit 510 into an analog signal and outputs it to the speaker 6 .

[0045] The speaker 6 receives the analog signal from the DAC 511 and emits a control sound. The speaker 6 emits a sound that cancels out the noise that has passed through the primary path at the control point. The noise that has been controlled at the control point, i.e., the reduced noise, is then output from the pipe section 2 and reaches the user.

[0046] The feedback canceller 512 generates a feedback suppression signal i(n) from the anti-noise signal y(n). The feedback suppression signal i(n) includes information regarding the input of the sound output from the speaker 6 to the reference microphone 5. A portion of the sound output from the speaker 6 is input to the reference microphone 5 through a feedback path. The feedback canceller 512 is, for example, a dynamically operating digital filter. The feedback canceller 512 has a transfer function F that generates the feedback suppression signal i(n) from the anti-noise signal y(n). The transfer function F generates a signal by estimating the input of the sound output from the speaker 6 to the reference microphone 5. The transfer function F is learned during the path estimation operation and stored in the feedback canceller 512.

[0047] The FBC gain compensation unit 513 generates an FBC gain compensation signal d(n) from the feedback suppression signal i(n). The FBC gain compensation signal d(n) includes information about the input of sound output from the speaker 6 to the reference microphone 5. The FBC gain compensation unit 513 generates the FBC gain compensation signal d(n) from the feedback suppression signal i(n) and a correction coefficient Z. For example, the correction coefficient Z is generated from the amplification factor WMEAS of the PGA of the signal amplification conversion unit 502 acquired during path estimation and the current amplification factor WANC of the PGA of the signal amplification conversion unit 502. The amplification factor WMEAS is a fixed value, and the amplification factor WANC is a variable value. For example, the correction coefficient Z is obtained by dividing the current amplification factor WANC of the PGA of the signal amplification conversion unit 502 by the amplification factor WMEAS of the PGA of the signal amplification conversion unit 502 acquired during path estimation. For example, the FBC gain compensation signal d(n) is obtained by multiplying the feedback suppression signal i(n) by a correction coefficient Z. The gain WMEAS is an example of the gain setting value of the reference microphone 5 acquired during path estimation. The gain WANC is the current gain setting value of the reference microphone 5.

[0048] The secondary path estimation filter 514 generates a secondary path estimation filtered signal r(n) from the feedback-canceled noise signal x(n). The secondary path estimation filter 514 is, for example, a dynamically operating digital filter. The secondary path estimation filter 514 has a transfer function S that generates the secondary path estimation filtered signal r(n) from the feedback-canceled noise signal x(n). The transfer function S generates a signal by estimating the input of the sound output from the speaker 6 to the error microphone 7. The transfer function S is learned during the path estimation operation and stored in the secondary path estimation filter 514.

[0049] The secondary path correction node 515 generates the secondary path correction signal e(n) from the secondary path estimated filtered signal r(n) and the filtered error signal k(n). For example, the secondary path correction node 515 obtains the secondary path correction signal e(n) by subtracting the filtered error signal k(n) from the secondary path estimated filtered signal r(n).

[0050] The noise (error sound) after being controlled by the control point is input to the error microphone 7 , and the error microphone 7 outputs the error sound signal to the signal amplification conversion unit 516 .

[0051] The signal amplification / conversion unit 516 includes a PGA and an ADC. The PGA amplifies the error sound signal output by the error microphone 7. The PGA can switch the amplification factor. The PGA switches the amplification factor in response to an instruction from the AGC unit 517. The ADC converts the signal amplified by the PGA into a digital signal.

[0052] The AGC unit 517 controls the gain of the error microphone 7. Specifically, the AGC unit 517 changes the amplification factor of the PGA of the signal amplification conversion unit 516. The AGC unit 517 receives the signal output by the ADC of the signal amplification conversion unit 516 and determines the amplification factor of the PGA of the signal amplification conversion unit 516. The AGC unit 517 determines the amplification factor of the PGA of the signal amplification conversion unit 516 in accordance with the signal output by the ADC of the signal amplification conversion unit 516. The AGC unit 517 determines the amplification factor of the PGA of the signal amplification conversion unit 516, for example, so that the dynamic range of the PGA of the signal amplification conversion unit 516 is maximized.

[0053] The error sound filter unit 518 filters the signal output by the ADC of the signal amplification and conversion unit 516 to generate a filtered noise signal k(n). The error sound filter unit 518 includes, for example, a low-pass filter (LPF) 519 that performs thinning, and an input filter unit 520.

[0054] The transfer function F learning unit 521 learns the transfer function F from the post-feedback cancellation noise signal x(n) and the output a(n) of the sound signal generating unit 522. The transfer function F learning unit 521 implements least mean squares (LMS), recursive least mean squares (RLMS), normalized least mean squares (NLMS), or any other suitable algorithm.

[0055] The transfer function S learning unit 523 learns the transfer function S from the filtered error signal k(n) and the output a(n) of the sound signal generator. The transfer function S learning unit 523 implements least mean squares (LMS), recursive least mean squares (RLMS), normalized least mean squares (NLMS), or any other suitable algorithm.

[0056] The transfer function H learning unit 509 learns the transfer function H from the filtered error signal k(n) and the secondary path estimated filtered signal r(n). The transfer function H learning unit 509 implements least mean squares (LMS), recursive least mean squares (RLMS), normalized least mean squares (NLMS), or any other suitable algorithm.

[0057] (Path Estimation) Here, path estimation in ANC, learning of transfer function F, and learning of transfer function S will be described. Path estimation is to estimate the path of sound propagating inside pipe 401. The path of sound propagating inside pipe 401 includes a feedback path and a secondary path.

[0058] The route estimation is performed, for example, before shipping a product equipped with the noise reduction device 1. Note that the route estimation may also be performed after shipping the product based on an instruction from a user.

[0059] During path estimation, the amplification factor of the PGA in each of the signal amplification conversion unit 502 and the signal amplification conversion unit 516 is fixed.

[0060] The sound signal generating unit 522 outputs, for example, a uniform random number signal. The sound signal generating unit 522 outputs a random number signal using, for example, a random number signal having a specific frequency distribution. The speaker 6 emits sound based on the random number signal emitted by the sound signal generating unit 522. The sound emitted by the speaker 6 is transmitted to the feedback path and the secondary path.

[0061] (Learning of Transfer Function F) Sound output from the speaker 6 and transmitted through the feedback path is input to the reference microphone 5. The signal output from the reference microphone 5 is processed by the signal amplification and conversion unit 502 and the noise filter unit 504, and a filtered noise signal h(n) is output to the feedback cancellation node 507. Meanwhile, the feedback canceller 512 receives the output a(n), which is a random number signal having a specific frequency distribution, and outputs a feedback suppression signal i(n) based on the currently stored transfer function F. The FBC gain compensation unit 513 generates an FBC gain compensation signal d(n) from the feedback suppression signal i(n). The feedback cancellation node 507 calculates the difference between the filtered noise signal h(n) and the FBC gain compensation signal d(n) to generate a feedback-canceled noise signal x(n).

[0062] Furthermore, the output a(n) of the sound signal generator 522 is input to the transfer function F learning unit 521. The transfer function F learning unit 521 learns the transfer function F from the post-feedback-canceled noise signal x(n) and the output a(n) of the sound signal generator 522. At this time, for example, a wideband random number signal uncorrelated with the noise source signal is input to the feedback canceller 512, and the output is compared with a signal that has passed through the feedback path and noise filter unit 504 and a signal that has passed through the feedback canceller 512 and FBC gain compensation unit 513, and the filter coefficients of the feedback canceller 512, i.e., the transfer function F, are learned in a direction that reduces the post-feedback-canceled noise signal x(n), which is the difference between the two. By using the various algorithms described above, the transfer function F learning unit 521 can bring the filter coefficients of the feedback canceller 512 closer to the characteristics of the path including the feedback path and noise filter unit 504. The learned transfer function F is stored in the feedback canceller 512.

[0063] (Learning of Transfer Function S) The sound output from speaker 6 and transmitted through the secondary path is input to error microphone 7. The signal output from error microphone 7 is processed by signal amplification and conversion unit 516 and error sound filter unit 518, and the filtered error signal k(n) output from error sound filter unit 518 is output to secondary path correction node 515. Meanwhile, secondary path estimation filter 514 receives output a(n), which is a random number signal having a specific frequency distribution, and generates secondary path estimation filtered signal r(n) based on the currently stored transfer function S. Secondary path correction node 515 calculates the difference between secondary path estimation filtered signal r(n) and filtered error signal k(n) to generate secondary path correction signal e(n). Secondary path correction signal e(n) is input to transfer function S learning unit 523. Transfer function S learning unit 523 learns transfer function S from secondary path correction signal e(n) and output a(n) from sound signal generator 522. At this time, for example, a wideband random number signal uncorrelated with the noise source signal is input to the secondary path estimation filter 514, and the output is compared with a signal passed through the secondary path and error sound filter unit 518 and a signal passed through the secondary path estimation filter 514, and the filter coefficients of the secondary path estimation filter 514, i.e., the transfer function S, are learned in a direction that reduces the secondary path correction signal e(n), which is the difference between the two. The transfer function S learning unit 523 can bring the filter coefficients of the secondary path estimation filter 514 closer to the characteristics of the path including the secondary path and error sound filter unit 518 by using the various algorithms described above. The learned transfer function S is stored in the secondary path estimation filter 514.

[0064] <ANC Operation> Next, the process during ANC operation will be described.

[0065] During ANC operation, AGC is performed on the reference microphone 5 and the error microphone 7, and the gain of the PGA of each of the signal amplification conversion unit 502 and the signal amplification conversion unit 516 is variable. That is, the AGC unit 503 controls the gain of the reference microphone 5. Specifically, the AGC unit 503 changes the gain of the PGA of the signal amplification conversion unit 502. The AGC unit 517 also controls the gain of the error microphone 7. Specifically, the AGC unit 517 changes the gain of the PGA of the signal amplification conversion unit 516.

[0066] The sound input to the reference microphone 5 is processed by the signal amplification and conversion unit 502, the noise filter unit 504, and the feedback cancellation node 507, and the post-feedback cancellation noise signal x(n) output from the feedback cancellation node 507 is input to the adaptive filter 508.

[0067] The anti-noise signal y(n) generated by the adaptive filter 508 is input to the output filter unit 510, which filters the anti-noise signal y(n), and the DAC 511 converts the signal filtered by the output filter unit 510 into an analog signal and outputs it to the speaker 6. The speaker 6 receives the analog signal from the DAC 511 and emits a control sound, thereby reducing the noise emitted by the noise source 9.

[0068] The anti-noise signal y(n) generated by the adaptive filter 508 is input to the feedback canceller 512, which generates a feedback suppression signal i(n) from the anti-noise signal y(n) and outputs it to the FBC gain compensation unit 513. The FBC gain compensation unit 513 generates an FBC gain compensation signal d(n) from the feedback suppression signal i(n) and a correction coefficient Z and outputs it to the feedback cancellation node 507. For example, the correction coefficient Z is obtained by dividing the current amplification factor WANC of the PGA of the signal amplification conversion unit 502 by the amplification factor WMEAS of the PGA of the signal amplification conversion unit 502 acquired during path estimation. Furthermore, for example, the FBC gain compensation signal d(n) is obtained by multiplying the feedback suppression signal i(n) by the correction coefficient Z.

[0069] The sound input to the error microphone 7 is processed by the signal amplification and conversion unit 516 and the error sound filter unit 518, and the filtered error signal k(n) output from the error sound filter unit 518 is input to the transfer function H learning unit 509.

[0070] The sound input to the reference microphone 5 is processed by the signal amplification and conversion unit 502, the noise filter unit 504, the feedback cancellation node 507, and the secondary path estimation filter 514, and the secondary path estimation filtered signal r(n) output from the secondary path estimation filter 514 is input to the transfer function H learning unit 509.

[0071] The transfer function H learning unit 509 learns the transfer function H from the filtered error signal k(n) and the secondary path estimated filtered signal r(n).

[0072] In noise reduction device 1 according to the second embodiment, the amplification factor (volume) of the PGA in each of signal amplification conversion units 502 and 516 is fixed during path estimation, and the amplification factor of the PGA in each of signal amplification conversion units 502 and 516 is made variable during ANC operation, and FBC gain compensation signal d(n) is compensated by multiplying feedback inhibition signal i(n) by a gain that offsets the fluctuating gain.

[0073] According to the noise reduction device of the second embodiment, the volumes of the reference microphone and the error microphone can be fixed during path estimation, and AGC operation can be performed during ANC operation. This makes it possible to make full use of the dynamic ranges of the reference microphone and the error microphone, maximize the sensitivity of the reference microphone and the error microphone, and maximize the effect of ANC. In particular, by maximizing the sensitivity of the error microphone, it is possible to minimize noise after reduction by the sound output from the speaker as a result of ANC.

[0074] (Treble-Pitch Reduction Section) Fig. 5 is a schematic diagram showing the structure of part (motor 202 and noise reduction device 1) of vacuum cleaner 110 according to the third embodiment. As shown in Fig. 5, noise reduction device 1 may further include treble-pitch reduction section 12.

[0075] The treble reduction unit 12 is located between the noise reduction device 1 and the noise source 9. The treble reduction unit 12 reduces high-frequency sounds (2 KHz or higher) contained in the noise emitted by the noise source. The treble reduction unit 12 is provided, for example, inside the inner pipe 3 upstream of the reference microphone 5, and is an absorbing material capable of absorbing high-frequency sounds.

[0076] Noise that passes through the treble reduction section 12 and is transmitted to the downstream end of the pipe section 2 becomes low-frequency sound, with high-frequency sounds reduced by the treble reduction section 12. The sound output from the speaker 6 to cancel out such noise also becomes low-frequency sound. Low-frequency sounds are less likely to be diffracted than high-frequency sounds. Therefore, noise emitted from the downstream end 31 of the inner pipe 3 is diffracted and less likely to be transmitted to the second air passage 17. In addition, the sound from the speaker 6 is less likely to be transmitted to the reference microphone 5 on the upstream side of the inner pipe 3. Therefore, providing the noise reduction device 1 with the treble reduction section 12 can further suppress feedback.

[0077] 5 , the reference microphone 5 may be provided on the outer circumferential surface of the outer pipe 4. The reference microphone 5 acquires sound at an input part 5a located on the side surface of the inner pipe 3 via a branch pipe 3a branching off from the inner pipe 3. The branch pipe 3a is located in the second air passage and connects the outside of the outer pipe 4 with the inside of the inner pipe 3.

[0078] 5, the outer pipe 4 may extend upstream so that the upstream end 42 of the outer pipe 4 is located upstream of the cover 10. The upstream end 42 of the outer pipe 4 is open and functions as a blowing section 403, which will be described later.

[0079] Fig. 6 is a schematic diagram showing the overall structure of vacuum cleaner 110. As shown in Fig. 6, vacuum cleaner 110 includes suction section 121, extension tube 141, filter section 131, motor 202, cover 10, noise reduction device 1, blow-out section 403, handle 122, display section 601, and operation section 701.

[0080] Suction unit 121 sucks in a fluid. Suction unit 121 includes extension tube 141 extending from filter unit 131 and a nozzle provided at the tip of extension tube 141. Suction unit 121 sucks in dust along with air from the nozzle, and the sucked air and dust pass through the inside of the extension tube and are introduced into filter unit 131. Air is an example of a fluid.

[0081] The filter unit 131 removes dust from the fluid sucked by the suction unit 121. Specifically, for example, the filter unit 131 separates the sucked dust from the air using a cyclone method.

[0082] The motor 202 includes a blower that generates suction force, and drives the blower to cause a fluid flow. Specifically, for example, the motor 202 drives the blower to suck dust together with air from the suction portion 121 into the filter portion 131.

[0083] The cover 301 covers the motor 202. The cover 301 has an opening 302, which is connected to the upstream end of the pipe portion 2 of the noise reduction device 1.

[0084] The motor sound emitted by the motor 202 is transmitted as noise to the pipe section 2. In other words, the motor 202 is an example of the noise source 9 described in the first embodiment. The cover 301 that covers the motor 202 is the cover 10 described in the first embodiment. The motor 202 and the pipe section 2 communicate with each other to form an exhaust path. The fluid sucked into the suction section 121 and the noise of the motor 202 are output to the exhaust path.

[0085] The noise reduction device 1 is located between the motor 202 (noise source 9) and the blowout section 403, and reduces the noise of the motor 202 transmitted through the exhaust path.

[0086] The blowout section 403 blows out the fluid that has flowed out from the filter section 131 and the noise of the motor 202. The blowout section 403 is the upstream end 42 of the outer pipe 4. The blowout section 403 opens toward the suction section 121. That is, the blowout section 403 opens toward the side opposite the user when the vacuum cleaner 110 is in use. As a result, the fluid passing through the exhaust path is discharged from the blowout section 403 toward the side opposite the user. Therefore, the user does not feel uncomfortable when using the vacuum cleaner 110. Furthermore, even if noise is output from the blowout section 403, the noise is directed toward the side opposite the user, thereby reducing the volume of the noise heard by the user.

[0087] The control unit 50 of the noise reduction device 1 is provided inside the cover 301 and controls the vacuum cleaner 110. The control unit 50 performs ANC, which reduces noise by generating a sound that cancels out the noise. For example, the control unit 50 performs ANC using the speaker 6, the reference microphone 5, and the error microphone 7, and reduces noise transmitted inside the pipe unit 2. The processing by the control unit 50 is the same as in the second embodiment, so a description thereof will be omitted.

[0088] When noise is reduced by ANC, if the noise increases, the control unit 50 increases the amount of noise reduction by increasing the volume of the sound output from the speaker 6. As a result, the level of noise heard by the user may not change, or may only change slightly. In this way, even if the power of the vacuum cleaner 110 is increased to strengthen the suction force, the level of noise heard by the user may not change, making it difficult for the user to understand the operating status of the vacuum cleaner 110. Therefore, the control unit 50 may control the sound output from the speaker 6 so that the amount of noise reduction does not increase beyond a predetermined value even if the power of the vacuum cleaner 110 increases and the noise level increases. The control unit 50 detects the level of the power of the vacuum cleaner 110, for example, from the rotation speed of the motor 202 or the control amount of the motor 202. The control unit 50 also detects the level of noise, for example, from the volume of sound input to the reference microphone 5.

[0089] The display unit 601 displays a screen including the status (for example, the status of clogging) of the vacuum cleaner 110. The operation unit 701 accepts user operations.

[0090] 7 is a schematic diagram showing the positions of the speaker 6 and the reference microphone 5 of the noise reduction device 1 in the vacuum cleaner 110. The vacuum cleaner 110 is formed by a rod-shaped body 111, a suction part 121 provided at the bottom of the rod-shaped body 111, and a handle 122 provided at the top of the rod-shaped body 111. The extension tube 141, the filter part 131, the motor 202, and the noise reduction device 1 described above are located on the rod-shaped body 111.

[0091] Rod-shaped body 111 is rotatably connected to suction portion 121. Rod-shaped body 111 is inclined with respect to the vertical direction toward the side where the user operating vacuum cleaner 110 is located when suction portion 121 is in contact with the floor surface. The user operates vacuum cleaner 110 by grasping handle 122 provided on the upper part of rod-shaped body 111 with suction portion 121 in contact with the floor surface. In the example shown in FIG. 7 , handle 122 is inclined further toward the floor relative to rod-shaped body 111 so that the user can easily grip it when suction portion 121 is in contact with the floor surface. Hereinafter, the surfaces of rod-shaped body 111 and handle 122 that face the floor when in use will be referred to as the bottom surface, and the surfaces opposite the bottom surface will be referred to as the top surface.

[0092] The display unit 601 is provided on the upper surface of the rod-shaped body 111 (the noise reduction device 1 in the example shown in FIG. 7 ) so that it can be easily seen by a user using the vacuum cleaner 110. Similarly, the operation unit 701 is provided on the upper surface of the handle 122 so that it can be easily operated by a user using the vacuum cleaner 110. Meanwhile, the speaker 6 and the reference microphone 5 are provided on the lower surface of the rod-shaped body 111 (specifically, the noise reduction device 1) that faces the floor during use. In other words, the speaker 6 and the reference microphone 5 are provided on the opposite side (back side) of the rod-shaped body 111 from the side on which the display unit 601 or the operation unit 701 is located. In other words, the speaker 6 and the reference microphone 5 are provided on the surface of the rod-shaped body 111 where the handle 122 is bent (inclined) relative to the rod-shaped body 111.

[0093] As a result, the speaker 6 and the reference microphone 5 are positioned between the vacuum cleaner 110 and the user when the vacuum cleaner 110 is in use. This reduces the possibility that the speaker 6 and the reference microphone 5, which are precision machines, will collide with something. Furthermore, even if the vacuum cleaner 110 is placed on its side on the floor so that the underside of the rod-shaped body 111 faces the floor, the speaker 6 and the reference microphone 5 are positioned in the space formed by the rod-shaped body 111 and the handle 122, and therefore can avoid contact with the floor. Furthermore, even if the vacuum cleaner 110 is placed on its side on the floor so that the side of the rod-shaped body 111 touches the floor, the diameter of the rod-shaped body 111 is larger than the width of the speaker 6 and the reference microphone 5, and therefore the speaker 6 and the reference microphone 5 can avoid contact with the floor.

[0094] In other words, the speaker 6 and the reference microphone 5 may be provided on a surface facing a straight line L1 connecting the end 122a of the handle 122 opposite the base end (the connection portion between the noise reduction device 1 and the handle 122) and the connection portion 161 between the suction portion 121 and the rod-shaped body 111 (see FIG. 7). In particular, the speaker 6 and the reference microphone 5 should be located closer to the main body of the vacuum cleaner 110 than the straight line L1. This further reduces the possibility that the speaker 6 and the reference microphone 5, which are precision machines, will collide with an object or the floor.

[0095] FIG. 8 is a schematic diagram showing the positions of the speaker 6 and reference microphone 5 of the noise reduction device 1A in the vacuum cleaner 110 (when the vacuum cleaner 110 is equipped with the noise reduction device 1A described above). In the noise reduction device 1A, the upstream end 42 of the outer pipe 4 (i.e., the blowout portion 403) has a gradually expanding diameter, with an opening area that gradually widens. In this case, the speaker 6 and the reference microphone 5 may be provided on a surface facing a line L2 connecting the end 122a of the handle 122 opposite the base end and the upstream end 42 of the outer pipe 4 on the underside of the rod-shaped body 111. Specifically, the speaker 6 and the reference microphone 5 are preferably located closer to the main body of the vacuum cleaner 110 than the line L2. This further reduces the possibility that the speaker 6 and the reference microphone 5, which are precision machines, will collide with an object or the floor.

[0096] [Embodiment 2] Another embodiment of the present invention will now be described in detail. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0097] Fig. 9 is a configuration diagram showing an example of a noise reduction device according to the fourth embodiment. As shown in Fig. 9, the noise reduction device 1 includes a pipe section 2, a reference microphone 5, a control section 50, a speaker 6, and an error microphone 7. A noise source 9 is located at one end of the pipe section 2.

[0098] The cavity inside the pipe section 2 functions as a transmission passage that transmits noise emitted by the noise source 9 from the upstream side closer to the noise source 9 to the downstream side farther from the noise source 9. The pipe section 2 is, for example, cylindrical or rectangular. One end of the pipe section 2 faces the noise source 9. The end of the pipe section 2 is open on the downstream side in the noise transmission direction, opposite the noise source 9. As in the example shown in FIG. 9 , in a configuration in which a cover 10 covering the noise source 9 is connected to one end, the pipe section 2 is open on both ends. Hereinafter, the noise source 9 side of the pipe section 2 may be referred to as the upstream side (upstream side in the noise transmission direction), and the opposite side may be referred to as the downstream side (downstream side in the noise transmission direction). The downstream side of the pipe section 2 has a double-pipe structure.

[0099] Fig. 10 is a cross-sectional view of the noise reduction device 1. As shown in Fig. 10, the pipe section 2 includes an inner pipe 3 and an outer pipe 4. The inner pipe 3 transmits noise and has an open downstream end. In this example, both ends of the inner pipe 3 are open.

[0100] The outer pipe 4 is inserted onto the outer periphery of the inner pipe 3 on the downstream side in the power transmission direction, with a distance between it and the outer periphery of the inner pipe 3. In other words, the outer pipe 4 is formed to have a larger diameter and be shorter than the inner pipe 3. The outer pipe 4 extends downstream of the downstream end 31 of the inner pipe 3. The outer pipe 4 has an open downstream end 41 and a closed upstream end 42.

[0101] The speaker 6 outputs sound under the control of the control unit 50. The speaker 6 outputs sound toward the inside of the pipe section 2. The speaker 6 outputs sound that includes a sound that reduces noise. Specifically, the speaker 6 outputs sound that is in the opposite phase to the noise that propagates inside the pipe section 2. The noise emitted by the noise source 9 is propagated inside the inner pipe 3. The noise propagated inside the inner pipe 3 is further propagated inside the outer pipe 4. The noise propagated inside the outer pipe 4 is canceled out by the sound output from the speaker 6. Therefore, the noise output from the downstream end of the pipe section 2 is reduced.

[0102] The speaker 6 is located in the outer pipe 4. The speaker 6 is arranged with its diaphragm facing in a direction intersecting the transmission direction. Specifically, the speaker 6 outputs sound to the space between the outer pipe 4 and the inner pipe 3, which form a double-pipe structure in the pipe section 2. An output section 6a, from which the sound of the speaker 6 is output to the inside of the pipe section 2, is located on the side surface of the outer pipe 4.

[0103] 10 , the speaker 6 is directly connected to the pipe section 2 (specifically, the outer pipe 4). In this case, the output part 6a serves as the diaphragm of the speaker 6. The speaker 6 may also be disposed inside a branch pipe that branches off from the pipe section 2. In this case, the sound output by the speaker 6 is transmitted to the inside of the pipe section 2 through an opening of the branch pipe. The output part 6a serves as the opening of the branch pipe.

[0104] The diameter of the outer pipe 4 is preferably 5 cm or less at the output portion 6a where sound is output from the speaker 6. By making the diameter of the outer pipe 4 at the output portion 6a 5 cm or less, the sound output from the speaker 6 (typically sound of 4 kHz or less) can be transmitted one-dimensionally in the direction of sound propagation inside the pipe portion 2, allowing ANC to be performed with high accuracy.

[0105] The reference microphone 5 acquires sound from inside the pipe section 2 at an input section 5a located upstream of the output section 6a in the transmission direction. Specifically, the reference microphone 5 is located in the inner pipe 3. The reference microphone 5 acquires sound from inside the inner pipe 3. The input section 5a from which the reference microphone 5 acquires sound is located on the side of the inner pipe 3. Note that the reference microphone 5, like the speaker 6, may be disposed inside a branch pipe branching off from the pipe section 2 (specifically, the inner pipe 3).

[0106] The error microphone 7 picks up sound from inside the pipe section 2 at a position where the noise emitted by the noise source 9 and the sound output by the speaker 6 join together. Specifically, the error microphone 7 is located in a portion of the outer pipe 4 that extends downstream from the downstream end of the inner pipe 3. The error microphone 7 picks up sound from a non-overlapping portion of the outer pipe 4 that does not overlap with the inner pipe 3. The provision of the error microphone 7 allows ANC to be performed with high accuracy even if the shape of the pipe section 2 changes or the temperature fluctuates.

[0107] The noise reduction device 1 further includes a reflection suppression unit 8. The reflection suppression unit 8 is provided at the downstream open end 41 of the pipe unit 2 (specifically, the outer pipe 4) and suppresses sound reflection at the end 41. This suppresses sound reflection at the outlet of the pipe unit 2, thereby reducing the amount of sound returning to the reference microphone 5 and suppressing feedback. The reflection suppression unit 8 has various structures for suppressing sound reflection at the end 41 (see FIG. 12 ).

[0108] The control unit 50 controls the sound output from the speaker 6. The control unit 50 is, for example, a processor such as a CPU (Central Processing Unit) or a logic circuit (hardware) formed in an integrated circuit (IC (Integrated Circuit) chip). The control unit 50 performs active noise control (ANC) to reduce noise by generating a sound that cancels out the noise. For example, the control unit 50 performs ANC using the speaker 6, the reference microphone 5, and the error microphone 7 to reduce noise transmitted inside the pipe unit 2.

[0109] In ANC, the control unit 50 controls the sound output from the speaker 6 based on the sound input to the reference microphone 5 and the error microphone 7. Specifically, for example, the control unit 50 outputs a sound that reduces noise, such as a sound that is in antiphase with the noise, from the speaker 6 based on the sound input to the reference microphone 5 and the error microphone 7. The control unit 50 controls the sound output from the speaker 6 so that the volume of the sound input to the error microphone 7, i.e., the reduced noise, is reduced. As a result, the noise transmitted inside the pipe 2 is reduced, and the reduced noise is output from the downstream end of the pipe 2. Note that the details and operation of the control unit 50 are the same as those in the second embodiment, and therefore will not be described again.

[0110] According to the noise reduction device 1, the pipe 2 is disposed near the noise source 9, with one end of the pipe 2 facing the noise source 9, and the noise emitted by the noise source 9 can be transmitted inside the pipe 2 by the pipe 2. The noise transmitted inside the pipe 2 can then be canceled out by the speaker 6. This reduces the noise output from the downstream end of the pipe 2. The noise reduction device according to the fourth embodiment further includes a cover 10 that covers the noise source 9. Covering the noise source 9 with the cover 10 enhances the noise reduction effect.

[0111] Fig. 11 is a diagram showing how the noise reduction device 1 reduces sound traveling from the speaker 6 to the reference microphone 5. As shown in Fig. 11, the noise reduction device 1 is provided with a shielding portion 13 that blocks sound traveling from the speaker 6 to the reference microphone 5. In the example shown in Fig. 11, the overlapping portion of the inner pipe 3 that overlaps with the outer pipe 4 (more specifically, the portion of the inner pipe 3 that is covered by the outer pipe 4 when viewed from the normal direction of the outer surface of the outer pipe 4) functions as the shielding portion 13. The shielding portion 13 is provided between the reference microphone 5 and the speaker 6 inside the pipe portion 2. This makes it more difficult for the sound of the speaker 6 output from the output part 6a by the shielding portion 13 to return to the reference microphone 5, thereby suppressing feedback.

[0112] Furthermore, the reflection of the sound from the speaker 6 that has been transmitted to the downstream end of the pipe section 2 at that end is suppressed by the reflection suppression section 8. This reduces the amount of sound output from the speaker 6 that returns to the reference microphone 5, thereby suppressing feedback.

[0113] As shown in FIG. 11 , the pipe section 2 of the noise reduction device 1 can also be interpreted as being provided with a first transmission passage 21 and a second transmission passage 22. The first transmission passage 21 is a passage that transmits noise emitted by the noise source 9 from the upstream side to the downstream side. The second transmission passage 22 is a passage that communicates with the first transmission passage 21 at one end via a communication opening 18 and is closed at the other end. In this case, the communication opening 18 opens toward the downstream side. In other words, the speaker 6 outputs sound from the communication opening 18 toward the first transmission passage 21 via the second transmission passage 22. In other words, the reference microphone 5 receives sound from the first transmission passage 21 upstream of the communication opening 18.

[0114] Because the communication port 18 opens toward the downstream side, the sound from the speaker 6 traveling toward the first transmission path 21 through the communication port 18 is less likely to return to the reference microphone 5 side, thereby suppressing howling. Note that "opening toward the downstream side" also includes opening toward a direction between the direction along the noise transmission direction and the direction perpendicular to the noise transmission direction.

[0115] 11 , the inner pipe 3 forms a portion of the first transmission passage 21 therein. The outer pipe 4 forms a second transmission passage in the overlapping portion where it overlaps with the inner pipe 3, and forms a portion of the first transmission passage in the non-overlapping portion where it does not overlap with the inner pipe. In other words, the first transmission passage 21 is the interior of the inner pipe 3 and the interior of the outer pipe 4 in the non-overlapping portion. The second transmission passage 22 is the space between the outer surface of the inner pipe 3 and the inner surface of the outer pipe 4 in the overlapping portion. The communication opening 18 opens in a direction along the noise transmission direction.

[0116] (Reflection suppression section) Fig. 12 is a diagram showing various structures of the reflection suppression section 8. The reflection suppression section 8 is an opening member that gradually (specifically, radially) widens the opening area of ​​the open end. Such a structure of the reflection suppression section 8 can effectively suppress reflection of the sound from the speaker 6 that has been transmitted to the downstream end of the pipe section 2. Note that a reflection suppression section 8A may be provided instead of the reflection suppression section 8. The reflection suppression section 8A is an opening member that gradually (specifically, linearly) widens the opening area of ​​the open end.

[0117] A reflection suppression unit 8B may be provided instead of the reflection suppression unit 8. The reflection suppression unit 8B is a cylindrical member having a side wall provided with a plurality of holes. In the side wall, a plurality of holes of a constant diameter may be provided at a constant density, or the density of the plurality of holes of a constant diameter may be gradually increased toward the downstream side, or the diameters of a plurality of holes arranged at a constant interval may be gradually increased toward the downstream side. Furthermore, in the side wall, a plurality of slits of a constant width may be provided at constant intervals, or the widths of the plurality of slits arranged at a constant interval may be gradually increased toward the downstream side. By diffusing the sound of the speaker 6 through the plurality of holes, reflection of the sound of the speaker 6 can be effectively suppressed.

[0118] (Shielding portion) Figure 13 is a diagram illustrating the shielding portion 13 of the noise reduction device 1. Reference numeral 5001 in Figure 13 is an enlarged cross-sectional view of the noise reduction device 1 showing the shielding portion 13 (a cross-sectional view taken along a cut surface perpendicular to the diaphragm of the speaker 6). Reference numeral 5002 in Figure 13 is a cross-sectional view taken along the line A-A of reference numeral 5001 showing the shielding portion 13.

[0119] The shielding portion 13 may be provided at least between the input portion 5a and the output portion 6a in the transmission path so as to shield sound traveling from the output portion 6a to the input portion 5a. Figures 9 to 11 show a double-pipe structure formed by an inner pipe 3 and an outer pipe 4 as an example of a structure for providing such a shielding portion 13. Figure 13, on the other hand, shows such a shielding portion 13 more conceptually. In Figure 13, the noise reduction device 1 includes a pipe 4A with a shielding portion 13 provided therein.

[0120] As shown in FIG. 13 , the shielding portion 13 may be provided so as to block the upstream side located upstream of the output portion 6a from the front side facing the output portion 6a (the diaphragm of the speaker 6). In other words, the shielding portion 13 defines a space within the pipe 4A that does not include the input portion 5a but includes at least a portion of the output portion 6a, with the upstream side of the space blocked by the shielding portion 13 and the downstream side of the space not blocked by the shielding portion 13. In the example shown in FIG. 13 , the shielding portion 13 includes a first portion 13a and a second portion 13b. The first portion 13a extends upstream from a position facing the output portion 6a, and both ends of the first portion 13a in a vertical cross section connect to the inner surface of the pipe 4A. The second portion 13b blocks the space between the inner surface of the pipe 4A and the upstream end of the first portion 13a. This makes it possible to prevent the sound from the speaker 6 output from the output portion 6 a from returning to the reference microphone 5 side.

[0121] The shielding portion 13 may be provided so as to extend downstream to a position downstream of the output portion 6a (see FIGS. 9 to 11). This blocks not only the sound emitted from the front of the output portion 6a but also the sound diffusing from the output portion 6a, thereby preventing the sound from returning to the reference microphone 5.

[0122] 14 is a configuration diagram showing another example of the noise reduction device 1. The noise reduction device 1 may further include a treble reduction section 12.

[0123] The treble reduction unit 12 is located between the noise reduction device 1 and the noise source 9. The treble reduction unit 12 reduces high-frequency sounds (2 KHz or higher) contained in the noise emitted by the noise source. The treble reduction unit 12 is provided, for example, inside the inner pipe 3 upstream of the reference microphone 5, and is an absorbing material capable of absorbing high-frequency sounds.

[0124] FIG. 15 is a diagram showing how the noise reduction device 1 including the treble reduction unit 12 reduces sound traveling from the speaker 6 toward the reference microphone 5. The noise that passes through the treble reduction unit 12 and is transmitted to the downstream end of the pipe 2 becomes low-frequency sound, with high-frequency sounds reduced by the treble reduction unit 12. The sound output from the speaker 6 to cancel out such noise also becomes low-frequency sound. Low-frequency sounds are less likely to be diffracted than high-frequency sounds. Therefore, as shown in FIG. 15, sound from the speaker 6 that is blocked by the shielding unit 13 is less likely to be diffracted by the shielding unit 13 and return to the reference microphone 5. Therefore, providing the noise reduction device 1 with the treble reduction unit 12 can further suppress feedback.

[0125] (Vacuum Cleaner) FIG. 16 is a block diagram of a vacuum cleaner according to a fifth embodiment.

[0126] The vacuum cleaner 110 includes a suction section 121 , a filter section 131 , a motor 202 , a cover 301 , the noise reduction device 1 described in the fourth embodiment, and a blow-out section 403 .

[0127] Suction unit 121 sucks in a fluid. Suction unit 121 includes an extension tube extending from filter unit 131 and a nozzle provided at the tip of the extension tube. Suction unit 121 sucks in dust along with air from the nozzle, and the sucked air and dust pass through the inside of the extension tube and are introduced into filter unit 131. Air is an example of a fluid.

[0128] The filter unit 131 removes dust from the fluid sucked by the suction unit 121. Specifically, for example, the filter unit 131 separates the sucked dust from the air using a cyclone method.

[0129] The motor 202 includes a blower that generates suction force, and drives the blower to cause a fluid flow. Specifically, for example, the motor 202 drives the blower to suck dust together with air from the suction portion 121 into the filter portion 131.

[0130] The cover 301 covers the motor 202. The cover 301 has an opening 302, which is connected to the upstream end of the pipe portion 2 of the noise reduction device 1.

[0131] The motor sound emitted by the motor 202 is transmitted as noise to the pipe section 2. In other words, the motor 202 is an example of the noise source 9 described in the fourth embodiment. The cover 301 that covers the motor 202 is the cover 10 described in the fourth embodiment. The motor 202 and the pipe section 2 communicate with each other to form an exhaust path. The fluid sucked into the suction section 121 and the noise of the motor 202 are output to the exhaust path.

[0132] The noise reduction device 1 is located between the motor 202 (noise source 9) and the blowout section 403, and reduces the noise of the motor 202 transmitted through the exhaust path.

[0133] The blowing section 403 blows out the fluid flowing out from the filter section 131 and the noise of the motor 202. The blowing section 403 is connected to the downstream end of the pipe section 2.

[0134] The control unit 50 of the noise reduction device 1 is provided inside the cover 301 and controls the vacuum cleaner 110. The control unit 50 performs ANC, which reduces noise by generating a sound that cancels out the noise. For example, the control unit 50 performs ANC using the speaker 6, the reference microphone 5, and the error microphone 7, and reduces noise transmitted inside the pipe unit 2. The processing by the control unit 50 is the same as in the second embodiment, so a description thereof will be omitted.

[0135] When noise is reduced by ANC, if the noise increases, the control unit 50 increases the amount of noise reduction by increasing the volume of the sound output from the speaker 6. As a result, the level of noise heard by the user may not change, or may only change slightly. In this way, even if the power of the vacuum cleaner 110 is increased to strengthen the suction force, the level of noise heard by the user may not change, making it difficult for the user to understand the operating status of the vacuum cleaner 110. Therefore, the control unit 50 may control the sound output from the speaker 6 so that the amount of noise reduction does not increase beyond a predetermined value even if the power of the vacuum cleaner 110 increases and the noise level increases. The control unit 50 detects the level of the power of the vacuum cleaner 110, for example, from the rotation speed of the motor 202 or the control amount of the motor 202. The control unit 50 also detects the level of noise, for example, from the volume of sound input to the reference microphone 5.

[0136] [Summary] The noise reduction device according to aspect 1 of the present invention comprises a pipe section having a first air passage that transmits noise emitted by a noise source in a first transmission direction, and a second air passage that communicates with the first air passage via a space and transmits the noise in a second transmission direction different from the first transmission direction, a reference microphone into which sound in the first air passage is input, and a speaker that outputs sound to the second air passage.

[0137] According to the above configuration, noise transmitted through the first air passage enters and is transmitted through the second air passage, which has a different noise transmission direction from the first air passage. This makes it possible to shorten the actual separation distance between the reference microphone and the speaker while ensuring a long distance on the noise transmission path between the reference microphone and the speaker. This allows the noise reduction device to be miniaturized while ensuring sufficient processing time for ANC.

[0138] Furthermore, since the speaker outputs sound to the second air passage, the sound emitted from the speaker is prevented from traveling directly toward the reference microphone, thereby suppressing howling and effectively reducing noise.

[0139] In a noise reduction device according to aspect 2 of the present invention, in the above-mentioned aspect 1, the pipe section may have an inner pipe and an outer pipe, the inner pipe forming the first air passage inside a first inner circumferential surface of the inner pipe, and the outer pipe forming the second air passage between a second inner circumferential surface of the outer pipe and a first outer circumferential surface of the inner pipe.

[0140] According to the above configuration, the first air passage and the second air passage can be formed by inserting the outer pipe around the outer periphery of the downstream side of the inner pipe. In this case, the second transmission direction is typically opposite to the first transmission direction. Therefore, noise emitted from the downstream end of the inner pipe in the first transmission direction is redirected (i.e., diffracted) into the second transmission direction and is less likely to be transmitted to the second air passage. Therefore, noise can be reduced before ANC is performed.

[0141] In a noise reduction device according to aspect 3 of the present invention, in the above-described aspect 2, the second end, which is the downstream end of the outer pipe in the first transmission direction, may be located downstream of the first end, which is the downstream end of the inner pipe, and further, a wall portion may be provided at the second end to prevent the noise from being transmitted downstream in the first transmission direction, thereby forming the space between the first end and the second end.

[0142] According to the above configuration, the first air passage formed inside the inner pipe communicates with the second air passage formed between the first outer peripheral surface of the inner pipe and the second inner peripheral surface of the outer pipe via a space. Noise transmitted through the first air passage is transmitted to the space. The noise transmitted to the space is diffused in the space. Of the noise diffused in the space, only diffracted portions are transmitted through the second air passage in the opposite direction to the first air passage. This reduces noise transmission to the second air passage.

[0143] A noise reduction device according to Aspect 4 of the present invention is the same as that of Aspect 3, and may further include a sound absorbing material provided on the inside of the wall portion.

[0144] According to the above configuration, noise emitted from the downstream end of the inner pipe that reaches the wall is absorbed by the sound-absorbing material in the wall. Furthermore, by providing the sound-absorbing material in the wall, the noise that reaches the wall is reflected by the wall and prevented from reaching the second air passage. This further reduces noise. Therefore, the sound output from the speaker can be reduced, further suppressing feedback.

[0145] In a noise reduction device according to Aspect 5 of the present invention, in any of Aspects 2 to 4 described above, the outer pipe may have a diameter of 5 cm or less at an output portion where sound from the speaker is output into the second air passage.

[0146] According to the above configuration, by making the diameter of the outer pipe at the output point 5 cm or less, the sound output from the speaker can be transmitted one-dimensionally in the direction of sound propagation inside the pipe section 2 (specifically, the second air passage 17), allowing ANC to be performed with high accuracy.

[0147] A noise reduction device according to a sixth aspect of the present invention is based on the fourth aspect, and may be configured such that the distance between the first end and the second end in the first transmission direction is equal to or less than the inner diameter of the inner pipe.

[0148] According to the above configuration, it is possible to suppress pressure loss of the exhaust gas discharged from the inner pipe, and also to suppress the generation of new noise due to the exhaust gas being turned back.

[0149] In the noise reduction device according to aspect 7 of the present invention, in the above aspects 2 to 6, the fourth end portion, which is the end portion of the outer pipe downstream in the second transmission direction, may have an expanding diameter shape in which the opening area gradually increases.

[0150] With the above configuration, it is possible to suppress new noise caused by exhaust gases at the exhaust outlet. Furthermore, even if there is noise that cannot be silenced by the ANC, it is possible to suppress the reflection of that noise at the exhaust outlet. Therefore, it is possible to prevent that noise from becoming a cause of howling.

[0151] A noise reduction device according to aspect 8 of the present invention comprises a pipe section having a first air passage that transmits noise emitted by a noise source in a first transmission direction, and a second air passage that communicates with the first air passage via a space and transmits the noise in a second transmission direction different from the first transmission direction, the pipe section having an inner pipe and an outer pipe, the inner pipe forming the first air passage inside a first inner circumferential surface of the inner pipe, and the outer pipe forming the second air passage between a second inner circumferential surface of the outer pipe and a first outer circumferential surface of the inner pipe.

[0152] According to the above configuration, noise transmitted through the first air passage along the first transmission direction is unlikely to change direction and be transmitted to the second air passage in the second transmission direction. By confining the noise in the space between the first air passage and the second air passage, it is possible to reduce noise output to the outside.

[0153] A vacuum cleaner according to aspect 9 of the present invention is a vacuum cleaner having a suction section that sucks in a fluid, a filter section that removes dust from the fluid sucked in by the suction section, and a blow-out section that blows out the fluid that flows out from the filter section, and is equipped with a noise source having a motor that causes the flow of the fluid, and a noise reduction device according to aspects 1 to 7 above, wherein the noise reduction device is located between the noise source and the blow-out section.

[0154] According to the above configuration, it is possible to provide a vacuum cleaner equipped with a noise reduction device that can reduce noise from a noise source that is transmitted through the pipe together with the fluid that has flowed out of the filter.

[0155] A vacuum cleaner according to aspect 10 of the present invention may be the same as in aspect 9 above, further comprising a treble reduction section between the noise reduction device and the noise source that reduces sounds of 2 kHz or higher contained in the noise emitted by the noise source.

[0156] According to the above configuration, noise that passes through the treble reduction section and is transmitted to the downstream end of the pipe section becomes low-frequency sound, with high-frequency sounds reduced by the treble reduction section. The speaker sound output to cancel out such noise also becomes low-frequency sound. Low-frequency sounds are less likely to be diffracted than high-frequency sounds. Therefore, the speaker sound is less likely to be diffracted and return to the reference microphone. Therefore, providing a treble reduction section in the noise reduction device can further suppress feedback.

[0157] A vacuum cleaner according to aspect 11 of the present invention is, in the above-mentioned aspects 9 or 10, provided with a rod-shaped body on which the filter section and the noise source are located and which is rotatably connected to the suction section, and which is inclined relative to the vertical direction when the suction section is in contact with the floor surface for use, wherein the noise reduction device is located on the rod-shaped body, and the speaker and the reference microphone are provided on the surface of the rod-shaped body that faces the floor when in use.

[0158] According to the above configuration, the speaker and the reference microphone are positioned between the vacuum cleaner and the user when the vacuum cleaner is in use, which reduces the possibility that the speaker and the reference microphone, which are precision machines, will collide with an object or the floor.

[0159] A vacuum cleaner according to aspect 12 of the present invention is, in the above-mentioned aspects 9 or 10, provided with a rod-shaped body on which the filter section and the noise source are located and which is rotatably connected to the suction section, and which is inclined relative to the vertical direction when the suction section is in contact with the floor surface for use, and a handle provided on the upper part of the rod-shaped body, wherein the noise reduction device is located on the rod-shaped body, and the speaker and the reference microphone may be provided on a surface of the rod-shaped body opposite a straight line connecting the end of the rod-shaped body opposite the base end of the handle and the connection between the suction section and the rod-shaped body.

[0160] According to the above configuration, the possibility that the speaker and the reference microphone, which are precision machines, will collide with an object or the floor can be further reduced.

[0161] A noise reduction device according to aspect 13 of the present invention comprises a pipe section having a transmission passage formed therein that transmits noise emitted by a noise source from an upstream side closer to the noise source to a downstream side farther from the noise source, a speaker that outputs sound toward the inside of the transmission passage, and a reference microphone that inputs sound within the transmission passage from an input section that is located upstream of an output section from which the sound of the speaker is output into the transmission passage, and a shielding section is provided between the input section and the output section within the transmission passage to shield sound traveling from the output section to the input section.

[0162] According to the above configuration, the shielding portion makes it difficult for the sound of the speaker output from the output portion to return to the reference microphone side, thereby suppressing howling.

[0163] The shielding portion of the noise reduction device according to aspect 14 of the present invention may be arranged in the above-described aspect 13 so as to block the upstream side located upstream of the output portion from the front side facing the output portion.

[0164] According to the above configuration, it is possible to prevent the sound of the speaker output from the output portion from returning to the reference microphone side.

[0165] The shielding portion of the noise reduction device according to Aspect 15 of the present invention may be provided in Aspects 13 or 14 above so as to extend to a downstream side located downstream of the output portion.

[0166] According to the above configuration, not only the sound coming from the front of the output unit but also the diffused sound can be blocked, and the sound can be prevented from returning to the reference microphone side.

[0167] A noise reduction device according to aspect 16 of the present invention comprises a pipe section having formed therein a first transmission passage that transmits noise emitted by a noise source from an upstream side closer to the noise source to a downstream side farther from the noise source, and a second transmission passage that is connected to the first transmission passage at one end via a communication opening and has a closed other end; a speaker that outputs sound from the communication opening through the second transmission passage toward the inside of the first transmission passage; and a reference microphone to which sound from within the first transmission passage upstream of the communication opening is input, the communication opening opening toward the downstream side.

[0168] According to the above configuration, the sound from the speaker that travels through the communication opening into the first transmission path is less likely to return to the reference microphone, thereby suppressing howling.

[0169] The pipe portion of the noise reduction device according to aspect 17 of the present invention may, in accordance with aspect 16 above, have an inner pipe that forms a portion of the first transmission passage therein, and an outer pipe that is inserted around the outer periphery of the inner pipe with a distance between it and the outer periphery of the inner pipe, extends downstream beyond the downstream end of the inner pipe, and has its upstream end closed, thereby forming the second transmission passage in the overlapping portion that overlaps with the inner pipe and forming a portion of the first transmission passage in the non-overlapping portion that does not overlap with the inner pipe.

[0170] According to the above configuration, by inserting the outer pipe onto the outer periphery of the downstream side of the inner pipe, a first transmission passage can be formed inside the inner pipe and inside the outer pipe in the non-overlapping portion, and a second transmission passage can be formed in the space between the outer surface of the inner pipe 3 and the inner surface of the outer pipe in the overlapping portion. In other words, a noise reduction device that can suppress howling can be realized simply by inserting the outer pipe onto the outer periphery of the downstream side of the inner pipe.

[0171] The noise reduction device of aspect 18 of the present invention may be, in the above-mentioned aspect 17, further include an error microphone located in a portion of the outer pipe extending downstream of the downstream end of the inner pipe, into which sound from the non-overlapping portion is input.

[0172] According to the above configuration, by providing the error microphone, ANC can be performed with high accuracy even if the shape of the pipe portion changes or the temperature changes.

[0173] The noise reduction device according to Aspect 19 of the present invention is, in Aspects 13 to 18 above, further comprising a reflection suppression section at the downstream open end of the pipe section, which suppresses sound reflection at the end.

[0174] According to the above configuration, it is possible to suppress the reflection of sound at the outlet of the pipe section, so that the amount of sound returning to the reference microphone side is reduced, and thus howling can be suppressed.

[0175] The anti-reflection portion of the noise reduction device according to Aspect 20 of the present invention may be an opening member in Aspect 19 above that gradually widens the opening area of ​​the opened end portion.

[0176] According to the above configuration, it is possible to effectively prevent the sound from the speaker that has been transmitted to the downstream end of the pipe section from being reflected.

[0177] A vacuum cleaner according to aspect 21 of the present invention is a vacuum cleaner having a suction section that sucks in a fluid, a filter section that removes dust from the fluid sucked in by the suction section, and a blow-out section that blows out the fluid that flows out from the filter section, and is equipped with a noise source having a motor that causes the flow of fluid, and a noise reduction device according to any one of aspects 1 to 8 above, wherein the noise reduction device is located between the noise source and the blow-out section.

[0178] According to the above configuration, it is possible to provide a vacuum cleaner equipped with a noise reduction device that can reduce noise from a noise source that is transmitted through the pipe together with the fluid that has flowed out of the filter.

[0179] A vacuum cleaner according to aspect 22 of the present invention may be the same as in aspect 21 above, further comprising a treble reduction section between the noise reduction device and the noise source that reduces sounds of 2 kHz or higher contained in the noise emitted by the noise source.

[0180] According to the above configuration, noise that passes through the treble reduction section and is transmitted to the downstream end of the pipe section becomes low-frequency sound, with high-frequency sounds reduced by the treble reduction section. The speaker sound output to cancel out such noise also becomes low-frequency sound. Low-frequency sounds are less likely to be diffracted than high-frequency sounds. Therefore, the speaker sound is less likely to be diffracted and return to the reference microphone. Therefore, providing a treble reduction section in the noise reduction device can further suppress feedback.

[0181] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0182] DESCRIPTION OF SYMBOLS 1, 1A Noise reduction device 2 Pipe section 3 Inner pipe 4 Outer pipe 5 Reference microphone 5a Input section 6 Speaker 6a Output section 7 Error microphone 9 Noise source 11 Wall section 12 Treble reduction section 16 First air passage 17 Second air passage 19 Space 31 Downstream end (first end) of inner pipe 41 Downstream end (second end) of outer pipe 42 Upstream end (fourth end) of outer pipe 36 First inner circumferential surface 37 First outer circumferential surface 46 Second inner circumferential surface 50 Control section 110 Vacuum cleaner 111 Rod-shaped body 122 Handle 122a End of handle 161 Connection section 202 Motor

Claims

1. A noise reduction device comprising: a pipe section having a first air passage that transmits noise emitted by a noise source in a first transmission direction, and a second air passage that communicates with the first air passage via a space and transmits the noise in a second transmission direction different from the first transmission direction; a reference microphone to which sound from within the first air passage is input; and a speaker that outputs sound to the second air passage.

2. A noise reduction device as described in claim 1, wherein the pipe section has an inner pipe and an outer pipe, the inner pipe forms the first air passage inside a first inner surface of the inner pipe, and the outer pipe forms the second air passage between a second inner surface of the outer pipe and a first outer surface of the inner pipe.

3. A noise reduction device as described in claim 2, wherein a second end, which is the end on the downstream side in the first transmission direction of the outer pipe, is located downstream of a first end, which is the end on the downstream side of the inner pipe, and a wall portion is provided at the second end to prevent the noise from being transmitted downstream in the first transmission direction, thereby forming the space between the first end and the second end.

4. A noise reduction device according to claim 3, wherein a sound absorbing material is provided on the inside of said wall portion.

5. A noise reduction device according to claim 2, wherein the diameter of said outer pipe at the output portion where the sound from said speaker is output into said second air passage is 5 cm or less.

6. A noise reduction device as described in claim 4, wherein the distance between said first end and said second end in said first transmission direction is equal to or less than the inner diameter of said inner pipe.

7. A noise reduction device as described in claim 5, wherein a fourth end portion, which is the end portion of said outer pipe downstream in said second transmission direction, has a diameter-expanding shape in which the opening area gradually increases.

8. A noise reduction device comprising a pipe section having a first air passage that transmits noise emitted by a noise source in a first transmission direction, and a second air passage that communicates with the first air passage via a space and transmits the noise in a second transmission direction different from the first transmission direction, wherein the pipe section has an inner pipe and an outer pipe, wherein the inner pipe forms the first air passage inside a first inner peripheral surface of the inner pipe, and the outer pipe forms the second air passage between a second inner peripheral surface of the outer pipe and a first outer peripheral surface of the inner pipe.

9. A vacuum cleaner having a suction section that sucks in a fluid, a filter section that removes dust from the fluid sucked in by the suction section, and a blowing section that blows out the fluid that flows out from the filter section, comprising: a noise source having a motor that causes a flow of the fluid; and a noise reduction device according to claim 1, wherein the noise reduction device is positioned between the noise source and the blowing section.

10. The vacuum cleaner according to claim 9, further comprising a treble reduction section between said noise reduction device and said noise source, for reducing sounds of 2 KHz or higher contained in the noise emitted by said noise source.

11. A vacuum cleaner as described in claim 9, comprising a rod-shaped body on which the filter section and the noise source are located, which is rotatably connected to the suction section, and which is inclined with respect to the vertical direction when the suction section is in contact with a floor surface for use, the noise reduction device being located on the rod-shaped body, and the speaker and the reference microphone being provided on a surface of the rod-shaped body that faces the floor when in use.

12. A vacuum cleaner as described in claim 9, comprising: a rod-shaped body on which the filter section and the noise source are located, which is rotatably connected to the suction section, and which is inclined with respect to the vertical direction when the suction section is in contact with a floor surface for use; and a handle provided on an upper part of the rod-shaped body, wherein the noise reduction device is located on the rod-shaped body, and the speaker and the reference microphone are provided on a surface of the rod-shaped body facing a straight line connecting the end of the rod-shaped body opposite the base end of the handle and the connection between the suction section and the connection section of the rod-shaped body.

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