Noise reduction device and cleaner

Abstract

To provide a noise reduction device capable of effectively reducing noise.SOLUTION: A noise reduction device (1) comprises: a pipe part (2) inside which a transmission passage for transmitting noise from an upstream side to a downstream side is formed; a loudspeaker (6) that outputs sound toward the transmission passage; and a reference microphone (5) into which sound of an input site (5a) is input. Between the input site and an output site (6a), a shielding part (11) is provided which shields sound from the output site toward the input site.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] It is known to perform ANC (Active Noise Control) that reduces 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. In addition, in ANC, an ANC feedforward method is also known that uses a feedback canceller to suppress the influence of acoustic feedback (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-190590 Summary of the Invention [Problem to be solved by the invention]

[0004] When using ANC to reduce noise transmitted through a pipe, the smaller the size of the device, the smaller 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 to cancel out the noise becomes shorter, limiting how small the device can be. In addition, the effect of acoustic feedback becomes greater, making it easier for feedback to occur.

[0005] An object of one aspect of the present invention is to provide a noise reduction device that can effectively reduce noise. [Means for solving the problem]

[0006] In order to solve the above problems, a noise reduction device according to one embodiment 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 inside the transmission passage, and a reference microphone to which sound within the transmission passage from an input section that is located upstream of an output section where the sound of the speaker is output into the transmission passage is input, and a shielding section is provided between the input section and the output section in the transmission passage to shield sound traveling from the output section to the input section.

[0007] In order to solve the above problems, a noise reduction device according to one embodiment of the present invention comprises a pipe section having a first transmission passage that transmits noise emitted by a noise source from an upstream side close to the noise source to a downstream side far from the noise source, and a second transmission passage having one end connected to the first transmission passage via a communication port and the other end closed, a speaker that outputs sound from the communication port through the second transmission passage toward inside the first transmission passage, and a reference microphone to which sound from inside the first transmission passage upstream of the communication port is input, and the communication port opens toward the downstream side. Effect of the Invention

[0008] According to one aspect of the present invention, noise can be effectively reduced. [Brief description of the drawings]

[0009] [Figure 1] 1 is a configuration diagram showing an example of a noise reduction device according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the noise reduction device. [Diagram 3] 5 is a diagram showing how the noise reduction device reduces sound traveling from a speaker to a reference microphone. FIG. [Figure 4] 3A to 3C are diagrams showing various structures of the reflection suppression portion of the noise reduction device. [Diagram 5] 3A and 3B are diagrams illustrating a shielding portion of the noise reduction device. [Figure 6] FIG. 11 is a configuration diagram showing another example of a noise reduction device. [Figure 7] 5 is a diagram showing how the noise reduction device reduces sound traveling from a speaker to a reference microphone. FIG. [Figure 8] 7 is a diagram illustrating the details and operation of a control unit of a noise reduction device according to a second embodiment. FIG. [Figure 9] FIG. 11 is a block diagram of a vacuum cleaner according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Embodiment 1] 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 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 device that generates noise, 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 the 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 desirably configured to include 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 the noise generated by the noise source 9. The pipe section 2 is a tubular member having a cavity inside. The cavity inside the pipe section 2 functions as a transmission passage that transmits the noise generated by the noise source 9 from the upstream side close to the noise source 9 to the downstream side far 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 on the downstream side in the noise transmission direction, opposite to the noise source 9, is open. As in the example shown in FIG. 1, in a configuration in which a cover 10 covering the noise source 9 is connected to one end, the pipe section 2 is open at 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 transmission direction), and the opposite side may be referred to as the downstream side (downstream side in the transmission direction). The downstream side of the pipe section 2 has a double pipe structure.

[0015] Fig. 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. The inner pipe 3 transmits noise and has an open downstream end. In this example, both ends of the inner pipe 3 are open.

[0016] The outer pipe 4 is inserted into the outer periphery of the inner pipe 3 on the downstream side in the 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 than the inner pipe 3 and to 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.

[0017] 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 including a sound that reduces noise. Specifically, the speaker 6 outputs sound that is in the opposite phase to the noise transmitted inside the pipe section 2. The noise emitted by the noise source 9 is transmitted inside the inner pipe 3. The noise transmitted inside the inner pipe 3 is further transmitted inside the outer pipe 4. The noise transmitted 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.

[0018] 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 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.

[0019] 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 be disposed inside a branch pipe branching 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.

[0020] The diameter of the outer pipe 4 is preferably 5 cm or less at the output part 6a where the sound of the speaker 6 is output. By making the diameter of the outer pipe 4 at the output part 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 sound traveling direction inside the pipe part 2, and ANC can be performed with high accuracy.

[0021] The reference microphone 5 picks up 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 picks up sound from inside the inner pipe 3. The input section 5a from which the reference microphone 5 picks up 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).

[0022] The error microphone 7 picks up sound 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 beyond 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 changes.

[0023] The noise reduction device 1 further includes a reflection suppression section 8. The reflection suppression section 8 is provided at an open end 41 on the downstream side of the pipe section 2 (specifically, the outer pipe 4), and suppresses sound reflection at the end 41. This makes it possible to suppress sound reflection at the outlet of the pipe section 2, thereby reducing the amount of sound returning to the reference microphone 5 side and suppressing howling. The reflection suppression section 8 has various structures for suppressing sound reflection at the end 41 (see FIG. 4).

[0024] 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 ANC (Active Noise Control) to reduce noise by generating a sound that cancels 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.

[0025] In the 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 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 sound input to the error microphone 7, i.e., the reduced noise, is reduced in volume. This reduces the noise transmitted inside the pipe section 2, and the reduced noise is output from the downstream end of the pipe section 2.

[0026] According to the noise reduction device 1, the pipe section 2 is disposed near the noise source 9, one end of the pipe section 2 is directed toward 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 cancelled out by the speaker 6. This makes it possible to reduce the noise output from the downstream end of the pipe section 2. The noise reduction device according to the first embodiment further includes a cover 10 that covers the noise source 9. Covering the noise source 9 with the cover 10 enhances the effect of reducing noise.

[0027] FIG. 3 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. 3, the noise reduction device 1 is provided with a shielding section 11 that shields sound traveling from the speaker 6 to the reference microphone 5. In the example shown in FIG. 3, an overlapping portion of the inner pipe 3 that overlaps with the outer pipe 4 (more specifically, a 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 section 11. The shielding section 11 is provided between the reference microphone 5 and the speaker 6 inside the pipe section 2. This makes it difficult for the sound of the speaker 6 output from the output part 6a by the shielding section 11 to return to the reference microphone 5 side, thereby suppressing howling.

[0028] Furthermore, reflection of the sound of the speaker 6 transmitted to the downstream end of the pipe section 2 at the 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.

[0029] As shown in FIG. 3, the pipe section 2 of the noise reduction device 1 can be interpreted as being provided with a first transmission passage 16 and a second transmission passage 17. The first transmission passage 16 is a passage that transmits the noise generated by the noise source 9 from the upstream side to the downstream side. The second transmission passage 17 is a passage that communicates with the first transmission passage 16 at one end via a communication port 18 and has a closed other end. At this time, the communication port 18 opens toward the downstream side. In other words, the speaker 6 outputs sound from the communication port 18 toward the first transmission passage 16 through the second transmission passage 17. In other words, the reference microphone 5 receives sound from the first transmission passage 16 upstream of the communication port 18.

[0030] Since communication port 18 opens toward the downstream side, the sound of speaker 6 traveling toward first transmission passage 16 through communication port 18 is less likely to return to reference microphone 5, 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.

[0031] In the example shown in Fig. 3, the inner pipe 3 forms a part of the first transmission passage 16 inside. The outer pipe 4 forms a second transmission passage in the overlapping portion where it overlaps with the inner pipe 3, and forms a part 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 16 is the inside of the inner pipe 3 and the inside of the outer pipe 4 in the non-overlapping portion. The second transmission passage 17 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 port 18 opens in a direction along the noise transmission direction.

[0032] (Reflection suppressor) FIG. 4 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 the reflection of the sound of the speaker 6 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.

[0033] A reflection suppression section 8B may be provided instead of the reflection suppression section 8. The reflection suppression section 8B is a cylindrical member having a side wall in which a plurality of holes are provided. 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 diameter of the plurality of holes arranged at a constant interval may be gradually increased toward the downstream side. In addition, in the side wall, a plurality of slits of a constant width may be provided at a constant interval, or the width 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 from the plurality of holes, reflection of the sound of the speaker 6 can be effectively suppressed.

[0034] (shielding part) Fig. 5 is a diagram illustrating the shielding portion 11 of the noise reduction device 1. Reference numeral 5001 in Fig. 5 is an enlarged cross-sectional view (a cross-sectional view taken along a cut surface perpendicular to the diaphragm of the speaker 6) of the noise reduction device 1 showing the shielding portion 11. Reference numeral 5002 in Fig. 5 is a cross-sectional view taken along the line AA of reference numeral 5001 showing the shielding portion 11.

[0035] The shielding portion 11 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. In Figs. 1 to 3, a double-pipe structure formed by an inner pipe 3 and an outer pipe 4 is shown as an example of a structure for providing such a shielding portion 11. Meanwhile, Fig. 5 shows such a shielding portion 11 more conceptually. In Fig. 5, the noise reduction device 1 includes a pipe 4A in which the shielding portion 11 is provided.

[0036] As shown in FIG. 5, the shielding portion 11 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 11 defines a space inside the pipe 4A that does not include the input portion 5a and includes at least a part of the output portion 6a, and the upstream side of the space is blocked by the shielding portion 11, and the downstream side of the space is not blocked by the shielding portion 11. In the example shown in FIG. 5, the shielding portion 11 includes a first portion 11a and a second portion 11b. The first portion 11a extends upstream from a position facing the output portion 6a, and both ends of the first portion 11a in the vertical cross section are connected to the inner surface of the pipe 4A. The second portion 11b blocks the space between the inner surface of the pipe 4A and the upstream end of the first portion 11a. This makes it possible to prevent the sound of the speaker 6 output from the output part 6a from returning to the reference microphone 5 side.

[0037] The shielding portion 11 may be provided so as to extend to a downstream side located downstream of the output portion 6a (see Figs. 1 to 3). This makes it possible to shield not only the sound coming from the front of the output portion 6a but also the sound diffusing from the output portion 6a, thereby suppressing the sound from returning to the reference microphone 5 side.

[0038] (Treble reduction section) 6 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.

[0039] The treble reduction section 12 is located between the noise reduction device 1 and the noise source 9. The treble reduction section 12 reduces high-frequency sounds (2 KHz or higher) contained in the noise emitted by the noise source. The treble reduction section 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.

[0040] FIG. 7 is a diagram showing how the noise reduction device 1 including the treble reduction section 12 reduces the sound traveling from the speaker 6 to the reference microphone 5. The noise that passes through the treble reduction section 12 and is transmitted to the downstream end of the pipe section 2 becomes a low-frequency sound in which high-frequency sounds are reduced by the treble reduction section 12. The sound of the speaker 6 output to cancel such noise also becomes a low-frequency sound. Here, low-frequency sounds are less likely to be diffracted than high-frequency sounds. Therefore, as shown in FIG. 7, the sound of the speaker 6 blocked by the shielding section 11 is less likely to diffract the shielding section 11 and return to the reference microphone 5. Therefore, by providing the treble reduction section 12 in the noise reduction device 1, howling can be further suppressed.

[0041] (Control unit of noise reduction device) Fig. 8 is a diagram illustrating the details and operation of the control unit 50 of the noise reduction device according to the second embodiment. Note that in Fig. 8, the illustration of the cover 10, the pipe portion 2, and the treble reduction portion 12 is omitted.

[0042] 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.

[0043] Noise emitted from a noise source 9 is input to the reference microphone 5 , and the reference microphone 5 outputs a noise source signal to a signal amplification conversion unit 502 .

[0044] The signal amplification 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 upon receiving an instruction from the AGC unit 503. The ADC converts the signal amplified by the PGA into a digital signal.

[0045] 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 a 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 by following the signal output by the ADC. For example, the AGC unit 503 determines the amplification factor of the PGA so that the dynamic range of the PGA is maximized using AGC. 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 (for example, 5.21 μs), calculates the square average value for each second period (for example, 1.33 ms) from the square sum of the detected multiple (for example, 256) outputs, and calculates a moving average value from the calculated multiple square average values. The AGC unit 503 determines at regular intervals whether the calculated moving average value is greater 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 minimum value, and if the calculated moving average value is greater 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 minimum value, reduces the value of the amplification factor of the PGA of the signal amplification conversion unit 502 by a predetermined value. Also, the AGC unit 503 determines at regular intervals whether the calculated moving average value is less 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 less 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, increases the value of the amplification factor of the PGA of the signal amplification conversion unit 502 by a predetermined value.

[0046] 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 thinning, and an input filter unit 506.

[0047] 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) by, for example, subtracting the FBC gain compensation signal d(n) from the filtered noise signal h(n).

[0048] 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 generated by the noise source 9. The adaptive filter 508 is, for example, a digital filter that operates dynamically. 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 that imitates the characteristics of the auxiliary path including the output filter unit 510, the secondary path, and the error sound filter unit 518. This is because a transfer function H that can remove the influence of the auxiliary 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 can be obtained.

[0049] The output filter unit 510 filters the anti-noise signal y(n) and includes a low-pass filter that performs interpolation.

[0050] A digital to analog converter (DAC) 511 converts the signal filtered by the output filter unit 510 into an analog signal, and outputs it to the speaker 6 .

[0051] The speaker 6 receives the analog signal from the DAC 511 and emits a control sound. The speaker 6 emits a sound that cancels the noise that has passed through the primary path at the control point. Then, the noise that has been controlled at the control point, i.e., the reduced noise, is output from the pipe section 2 and reaches the user.

[0052] 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 by the speaker 6 to the reference microphone 5. A part of the sound output by 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 estimates the input of the sound output by the speaker 6 to the reference microphone 5 to generate a signal. The transfer function F is learned during the path estimation operation and stored in the feedback canceller 512.

[0053] 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 on the input of the sound output by 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 at the time of path estimation and the current amplification factor WAN C of the PGA of the signal amplification conversion unit 502. The amplification factor WMEAS is a fixed value, and the amplification factor WAN C is a variable value. For example, the correction coefficient Z is obtained by dividing the amplification factor WAN C of the PGA of the signal amplification conversion unit 502 at the time of path estimation by the amplification factor WMEAS of the PGA of the signal amplification conversion unit 502 acquired at the time of path estimation. For example, the FBC gain compensation signal d(n) is obtained by multiplying the feedback suppression signal i(n) by the correction coefficient Z. The gain factor WMEAS is an example of the setting value of the gain of the reference microphone 5 acquired at the time of path estimation. The gain factor WAN C is the current setting value of the gain of the reference microphone 5.

[0054] The secondary path estimation filter 514 generates a secondary path estimation filtered signal r(n) from the feedback cancellation noise signal x(n). The secondary path estimation filter 514 is, for example, a digital filter that operates dynamically. The secondary path estimation filter 514 has a transfer function S that generates the secondary path estimation filtered signal r(n) from the feedback cancellation noise signal x(n). The transfer function S generates a signal by estimating the input of the sound output by 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.

[0055] The secondary path correction node 515 generates a 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).

[0056] Noise (error sound) after being controlled by the control point is input to error microphone 7 , and error microphone 7 outputs the error sound signal to signal amplification conversion unit 516 .

[0057] 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 upon receiving an instruction from the AGC unit 517. The ADC converts the signal amplified by the PGA into a digital signal.

[0058] 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.

[0059] The error sound filter unit 518 filters the signal output by the ADC of the signal amplification 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.

[0060] 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.

[0061] 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 generating unit. 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.

[0062] 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.

[0063] (Route Estimation) Here, a description will be given of path estimation in ANC, learning of transfer function F, and learning of transfer function S. 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.

[0064] The route estimation is performed, for example, before the shipment of a product equipped with the noise reduction device 1. Note that the route estimation may be performed based on an instruction from a user after the shipment of the product.

[0065] During path estimation, the amplification factor of the PGA of each of the signal amplification and conversion unit 502 and the signal amplification and conversion unit 516 is fixed.

[0066] 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 generates a sound based on the random number signal generated by the sound signal generating unit 522. The sound generated by the speaker 6 is transmitted to the feedback path and the secondary path.

[0067] (Learning the transfer function F) The sound output from the speaker 6 and transmitted to the feedback path is input to the reference microphone 5. The signal output from the reference microphone 5 is processed by the signal amplification 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).

[0068] Furthermore, the output a(n) of the sound signal generating unit 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 feedback-canceled noise signal x(n) and the output a(n) of the sound signal generating unit 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 passed through the feedback path and the noise filter unit 504 and a signal passed through the feedback canceller 512 and the FBC gain compensation unit 513, and the filter coefficient of the feedback canceller 512, i.e., the transfer function F, is learned in a direction that reduces the difference, that is, the feedback-canceled noise signal x(n). The transfer function F learning unit 521 can make the filter coefficient of the feedback canceller 512 closer to the characteristics of the path including the feedback path and the noise filter unit 504 by using the various algorithms described above. The learned transfer function F is stored in the feedback canceller 512.

[0069] (Learning the transfer function S) The sound output from the speaker 6 and transmitted through the secondary path is input to the error microphone 7. The signal output from the error microphone 7 is processed by the signal amplification 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 output to the secondary path correction node 515. On the other hand, the secondary path estimation filter 514 takes as input the output a(n) which is a random number signal with a specific frequency distribution, and generates a signal r(n) after the secondary path estimation filter based on the currently stored transfer function S. The secondary path correction node 515 calculates the difference between the signal r(n) after the secondary path estimation filter and the filtered error signal k(n), and generates a secondary path correction signal e(n). The secondary path correction signal e(n) is input to the transfer function S learning unit 523. The transfer function S learning unit 523 performs learning of the transfer function S from the secondary path correction signal e(n) and the output a(n) of the sound signal generation unit 522. At this time, for example, a broadband random number signal uncorrelated with the noise source signal is input to the secondary path estimation filter 514, and the output thereof is compared with the signal passing through the secondary path and the error sound filter unit 518 and the signal passing through the secondary path estimation filter 514, and the filter coefficient of the secondary path estimation filter 514, that is, the transfer function S, is learned in the direction of reducing the secondary path correction signal e(n) which is the difference. The transfer function S learning unit 523 can approximate the filter coefficient of the secondary path estimation filter 514 to the characteristics of the path including the secondary path and the error sound filter unit 518 by using the above various algorithms. The learned transfer function S is stored in the secondary path estimation filter 514.

[0070] <ANC operation> Next, the processing during the operation of ANC will be described.

[0071] During ANC operation, AGC is performed on the reference microphone 5 and the error microphone 7, and the amplification factor of the PGA of each of the signal amplification conversion unit 502 and the signal amplification conversion unit 516 becomes variable. That is, 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. In addition, 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.

[0072] 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.

[0073] 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.

[0074] 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 WAN C 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 at the time of path estimation. Also, for example, the FBC gain compensation signal d(n) is obtained by multiplying the feedback suppression signal i(n) by the correction coefficient Z.

[0075] The sound input to the error microphone 7 is processed by a signal amplification conversion unit 516 and an error sound filter unit 518 , and the filtered error signal k(n) output from the error sound filter unit 518 is input to a transfer function H learning unit 509 .

[0076] 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.

[0077] A transfer function H learning unit 509 learns a transfer function H from the filtered error signal k(n) and the secondary path estimation filtered signal r(n).

[0078] In noise reduction device 1 of the second embodiment, the amplification factor (volume) of the PGA of each of signal amplification conversion units 502 and 516 is fixed during path estimation, and the amplification factor of each of the PGA of signal amplification conversion units 502 and 516 is made variable during ANC operation, and the FBC gain compensation signal d(n) is compensated by multiplying the feedback inhibition signal i(n) by a gain that offsets the varied gain amount.

[0079] 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 the most of the dynamic range of the reference microphone and the error microphone, and maximize the sensitivity of the reference microphone and the error microphone, thereby maximizing the effect of the ANC. In particular, by maximizing the sensitivity of the error microphone, it is possible to minimize the noise after reduction by the sound output from the speaker as a result of the ANC.

[0080] (vacuum cleaner) FIG. 9 is a block diagram of a vacuum cleaner according to the third embodiment.

[0081] The vacuum cleaner 110 comprises a suction section 121, a filter section 131, a motor 202, a cover 301, the noise reduction device 1 described in the first embodiment, and a blowing section 403.

[0082] 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 together 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.

[0083] 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 by a cyclone method.

[0084] The motor 202 includes a blower that generates a suction force, and drives the blower to cause a flow of a fluid. 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.

[0085] The cover 301 covers the motor 202. The cover 301 has an opening 302, and the opening 302 is connected to the upstream end of the pipe section 2 of the noise reduction device 1.

[0086] The motor sound generated by the motor 202 is transmitted to the pipe section 2 as noise. That is, the motor 202 is an example of the noise source 9 described in the first embodiment. The cover 301 covering 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.

[0087] The noise reduction device 1 is located between the motor 202 (noise source 9) and the blowing section 403, and reduces the noise of the motor 202 transmitted through the exhaust path.

[0088] The blowing section 403 blows out the fluid flowing out from the filter section 131 and noise of the motor 202. The blowing section 403 is connected to the end of the pipe section 2 on the downstream side.

[0089] 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 to reduce noise by generating a sound that cancels 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 of the control unit 50 is similar to that of the second embodiment, so a description thereof will be omitted.

[0090] When noise is reduced by ANC, if the noise becomes louder, the control unit 50 increases the amount of noise reduction by increasing the sound output from the speaker 6. As a result, the loudness of the noise heard by the user may not change, or may change only slightly. In this way, even if the power of the vacuum cleaner 110 is increased to strengthen the suction force, the loudness of the noise heard by the user may not change, and the user may have difficulty in understanding the operating state 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 is not increased from a predetermined value even if the power of the vacuum cleaner 110 increases and the noise becomes louder. The control unit 50 detects the magnitude of the power of the vacuum cleaner 110, for example, from the number of rotations of the motor 202 or the control amount of the motor 202. The control unit 50 also detects the loudness of the noise, for example, from the loudness of the sound input to the reference microphone 5.

[0091] 〔summary〕 The noise reduction device of aspect 1 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 inside the transmission passage, and a reference microphone to which sound within the transmission passage from an input section that is located upstream of an output section at which the sound of the speaker is output into the transmission passage is input, and a shielding section is provided between the input section and the output section in the transmission passage to shield sound traveling from the output section to the input section.

[0092] 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, thereby suppressing howling.

[0093] The shielding portion of the noise reduction device according to aspect 2 of the present invention may be arranged in the above-mentioned aspect 1 so as to block the upstream side located upstream of the output portion from the front side facing the output portion.

[0094] 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.

[0095] In the noise reduction device according to the third aspect of the present invention, in the first or second aspect, the shielding portion may be provided so as to extend to a downstream side located downstream of the output portion.

[0096] 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.

[0097] A noise reduction device according to a fourth aspect of the present invention comprises a pipe section having a first transmission passage formed therein, which transmits noise emitted by a noise source from an upstream side close to the noise source to a downstream side far from the noise source, and a second transmission passage having one end connected to the first transmission passage via a communication port and the other end closed, a speaker which outputs sound from the communication port through the second transmission passage toward inside the first transmission passage, and a reference microphone to which sound from inside the first transmission passage upstream of the communication port is input, and the communication port opens toward the downstream side.

[0098] According to the above configuration, sound from the speaker traveling into the first transmission passage through the communication opening is less likely to return to the reference microphone side, making it possible to suppress howling.

[0099] The pipe section of a noise reduction device according to aspect 5 of the present invention may, in accordance with aspect 4 above, comprise: 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 and extends downstream beyond the downstream end of the inner pipe, and has its upstream end blocked, thereby forming the second transmission passage in an overlapping portion that overlaps with the inner pipe, and forming a portion of the first transmission passage in a non-overlapping portion that does not overlap with the inner pipe.

[0100] According to the above configuration, by inserting the outer pipe into 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 into the outer periphery of the downstream side of the inner pipe.

[0101] The noise reduction device of aspect 6 of the present invention, in accordance with aspect 5 above, may further comprise an error microphone located in a portion of the outer pipe extending downstream beyond the downstream end of the inner pipe, into which sound from the non-overlapping portion is input.

[0102] According to the above configuration, by providing an error microphone, ANC can be performed with high accuracy even if the shape of the pipe section changes or the temperature changes.

[0103] The noise reduction device according to a seventh aspect of the present invention, in accordance with any of the first to sixth aspects described above, may further include a reflection suppression section at the downstream open end of the pipe section, which suppresses sound reflection at the end.

[0104] According to the above configuration, since sound reflection at the outlet of the pipe section can be suppressed, the amount of sound returning to the reference microphone side is reduced, and feedback can be suppressed.

[0105] The reflection suppressing portion of the noise reduction device according to aspect 8 of the present invention may be an opening member in the above-mentioned aspect 7 that gradually widens the opening area of ​​the opened end portion.

[0106] According to the above configuration, it is possible to effectively prevent the sound of the speaker transmitted to the downstream end of the pipe section from being reflected.

[0107] A vacuum cleaner according to aspect 9 of the present invention has 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, and is equipped with a noise source having a motor that causes a flow of fluid, and a noise reduction device according to any of aspects 1 to 8 above, wherein the noise reduction device is positioned between the noise source and the blowing section.

[0108] 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 portion.

[0109] A vacuum cleaner according to a tenth aspect of the present invention may be configured in such a way that, in the above-mentioned ninth aspect, a treble reduction section is provided between the noise reduction device and the noise source, which reduces sounds of 2 KHz or higher contained in the noise emitted by the noise source.

[0110] According to the above configuration, the noise transmitted through the treble reduction section to the downstream end of the pipe section becomes a low-frequency sound with high-frequency sounds reduced by the treble reduction section. The sound of the speaker output to cancel such noise also becomes a low-frequency sound. Here, low-frequency sounds are less likely to be diffracted than high-frequency sounds. Therefore, the sound of the speaker is less likely to be diffracted and return to the reference microphone. Therefore, by providing a treble reduction section in the noise reduction device, howling can be further suppressed.

[0111] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the respective embodiments. [Explanation of symbols]

[0112] 1 Noise reduction device 2 Pipe section 3 Inner pipe 4 Outer pipe 5 Reference Microphone 5a Input site 6 Speakers 6a Output part 7 Error Mic 8, 8A, 8B Reflection suppressor 9. Noise Sources 11 Shielding part 16 First Transmission Passage 17 Second Transmission Passage 110 Vacuum cleaner 121 Suction section 131 Filter section 202 Motor 403 Blowing section

Claims

1. a pipe portion having a transmission passage formed therein for transmitting noise generated by a noise source from an upstream side close to the noise source to a downstream side far from the noise source; a speaker that outputs sound toward the inside of the transmission path; a reference microphone to which sound in the transmission passage is input, the sound being from an input portion located upstream of an output portion at which the sound of the speaker is output into the transmission passage; A noise reduction device in which a blocking portion is provided between the input portion and the output portion in the transmission path, for blocking sound traveling from the output portion to the input portion.

2. The noise reduction device according to claim 1 , wherein the shielding portion is provided so as to block an upstream side located on the upstream side of the output portion from a front side facing the output portion.

3. The noise reduction device according to claim 2 , wherein the shielding portion is provided so as to extend to a downstream side located downstream of the output portion.

4. a pipe section having therein a first transmission passage for transmitting noise generated by a noise source from an upstream side close to the noise source to a downstream side far from the noise source, and a second transmission passage having one end communicating with the first transmission passage via a communication port and the other end closed; a speaker that outputs sound from the communication port toward the inside of the first transmission passage through the second transmission passage; a reference microphone to which a sound in the first transmission passage upstream of the communication port is input, The communication port of the noise reduction device opens toward the downstream side.

5. The pipe portion is an inner pipe that defines a portion of the first transmission passage therein; 5. The noise reduction device according to claim 4, further comprising: an outer pipe that is inserted around an outer periphery of the inner pipe with a distance between it and an outer periphery surface 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 an overlapping portion that overlaps with the inner pipe and forming part of the first transmission passage in a non-overlapping portion that does not overlap with the inner pipe.

6. 6. The noise reduction device according to claim 5, further comprising an error microphone located in a portion of the outer pipe extending downstream beyond the downstream end of the inner pipe, into which sound of the non-overlapping portion is input.

7. 5. A noise reduction device according to claim 1, further comprising a reflection suppressing portion at the downstream open end of the pipe portion, the reflection suppressing portion suppressing sound reflection at the end.

8. The noise reduction device according to claim 7 , wherein the anti-reflection portion is an opening member that gradually widens an opening area of ​​the open end portion.

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 blow-out section that blows out the fluid that flows out from the filter section, a noise source having a motor for inducing a flow of fluid; The noise reduction device according to claim 1 or 4, The noise reduction device is located between the noise source and the blowing portion of the vacuum cleaner.

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

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