JP2021043472A - Active noise control device - Google Patents

Abstract

To provide a non-closed type active noise control device that can effectively eliminate random noise such as road noise and is suitable for use in a vehicular cabin and the like.SOLUTION: An active noise control device detects noise, and delays the phase of a signal of the detected noise in a low-frequency band. Since in the non-closed type noise control device, a phenomenon in which the phase of the signal of noise in the low-frequency band advances occurs, correction of delaying the phase with correction means for compensation is performed. Then, noise is reduced by outputting a noise reduction sound on the basis of the signal of noise whose phase is corrected.SELECTED DRAWING: Figure 6

Description

The present invention relates to an active noise control technique.

There is known an active noise control technology that cancels external noise with the sound output from a speaker. For example, Patent Document 1 describes an open-type vehicle interior noise reducing device that reduces vehicle interior noise by a feedforward type active noise control. Further, Patent Document 2 describes a noise canceling device for closed headphones that reduces the noise level by outputting a noise canceling signal from a speaker by a feedback method.

Japanese Unexamined Patent Publication No. 9-288489 Japanese Unexamined Patent Publication No. 2007-259246

In the passenger compartment, it is required to mute random noise such as road noise of a car. Since the method of Patent Document 1 performs feedforward control, a reference signal is required. However, in feedforward control, it is difficult to obtain a sufficient muffling effect because the correlation between the reference signal and random noise such as road noise is low and the causality is not satisfied. Therefore, in order to mute the road noise, it is desirable to perform feedback control that does not require a reference signal.

In this respect, since the method of Patent Document 2 performs feedback control, the effect of silencing random noise is high. However, since the device of Patent Document 2 is a closed headphone type, there is a feeling of pressure on the ears, and since the outside sound cannot be heard, it is not suitable for use in the vehicle interior.

Examples of the problems to be solved by the present invention include the above. An object of the present invention is to provide a non-sealed active noise control device that can effectively mute random noise such as road noise and is suitable for use in a vehicle interior or the like.

According to the first aspect of the present invention, in an active noise control device having a non-sealed structure and performing feedback control, a detection means for detecting noise and a gain of the detected noise signal in a low frequency band can be obtained. It is characterized by having a correction means for increasing and an output means for outputting a noise reduction sound for reducing the noise based on the corrected noise signal.

The configurations of the closed type and non-closed type active noise control devices are schematically shown. The noise canceling effect of the closed type and non-sealed type noise control devices is shown. The configuration of the closed noise control device and the characteristics of the shelf filter are shown. The characteristics of the closed type and simple open type noise control devices are shown. The characteristics of the simple open type noise control device and the noise canceling effect are shown. The configuration of the non-sealed noise control device according to the embodiment is shown. The characteristics of the low boost filter are shown.

The characteristics of the noise control device and the noise canceling effect according to the embodiment are shown. It is a flowchart of the noise control processing by the noise control device which concerns on Example. The noise canceling effect of the simple open type and non-sealed type noise control devices is shown. It is a top view which shows the example which mounted the noise control device which concerns on embodiment on a vehicle. An example of arranging the speaker and the microphone is shown. A modification of the noise control device according to the embodiment is shown.

In a preferred embodiment of the present invention, an active noise control device having a non-sealed structure and performing feedback control determines a detection means for detecting noise and a phase of the detected noise signal in a low frequency band. It has a correction means for delaying and an output means for outputting a noise reduction sound for reducing the noise based on the corrected noise signal.

The active noise control device described above detects noise and delays the phase of the detected noise signal in the low frequency band. In a non-sealed noise control device, a phenomenon occurs in which the phase of a noise signal advances in a low frequency band, so correction is performed by delaying the phase by a correction means to cancel the phase. Then, the noise is reduced by outputting the noise reduction sound based on the phase-corrected noise signal. In a preferred example, the active noise control device described above is provided in the vehicle interior.

In one aspect of the active noise control device, the correction means corrects with a filter having a characteristic of increasing the gain while delaying the phase as the frequency becomes lower in the low frequency band. As a result, the phase in the low frequency band can be appropriately corrected.

In another aspect of the active noise control device, the output means is a speaker having a cabinet, and the low frequency band in which noise can be controlled is changed according to the capacity of the cabinet provided with the speaker.

In another aspect of the active noise control device described above, the low frequency band in which noise control is possible is changed according to the size or weight of the diaphragm of the output means.

In another aspect of the active noise control device described above, it is preferable that the distance between the detection means and the output means is as close as possible. This makes it possible to widen the control band in which the noise reduction effect can be obtained. Preferably, the distance between the detection means and the output means is set to the minimum as long as the detection means does not come into contact with the output means at the maximum amplitude of the diaphragm of the output means.

In another aspect of the active noise control device, the direction in which the gain of the directivity of the detection means is high is directed to the direction of the output means. As a result, the control band from which the noise reduction effect can be obtained can be widened.

In a preferred example, the detection means and the output means are installed one by one at the positions of the left and right ears of the user.

Another aspect of the active noise control device is that the output means and the detection means can be three-dimensionally arranged at a position according to the state of the listener while maintaining the distance between the output means and the detection means. As a result, even when the position of the active noise control device changes according to the state of the user, the distance between the output means and the detection means can be maintained, and the noise reduction effect can be maintained.

In another aspect of the active noise control device, the detection means is provided between the output means and the protective material. This makes it possible to prevent the user's ears and the like from coming into direct contact with the detection means.

Another aspect of the active noise control device described above has a partially sealed structure. As a result, the phase advance of the noise signal in the low frequency band can be suppressed, and the control band in which the noise reduction effect can be obtained can be widened.

Another preferred embodiment of the present invention is an active noise control method executed by an active noise control device having a non-sealed structure and performing feedback control, wherein a detection step for detecting noise and a detection step are performed. It has a correction step of delaying the phase of the detected noise signal in the low frequency band, and an output step of outputting a noise reduction sound for reducing the noise based on the corrected noise signal. Also in this method, the phase of the noise signal that advances in the low frequency band due to the non-sealed structure is offset by delaying the phase by the correction means. Then, the noise is reduced by outputting the noise reduction sound based on the corrected noise signal.

In another preferred embodiment of the present invention, a program executed by an active noise control device having a non-sealed structure, including a computer and performing feedback control, is a detection means for detecting noise, detected. The computer functions as a correction means for delaying the phase of a noise signal in a low frequency band and an output means for outputting a noise reduction sound for reducing the noise based on the corrected noise signal. By executing this program on a computer, the above-mentioned active noise control device can be realized. This program can be stored and handled in a storage medium.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[1] Closed Type and Simple Open Type Noise Control Device FIG. 1A schematically shows the configuration of a closed type active noise control device (hereinafter, also simply referred to as “noise control device”). The closed-type noise control device 3 has a headphone-type housing 5, and is worn so as to cover the user 1's ear 2. The noise control device 3 is provided with an internal unit 4 such as a speaker, a microphone, and a filter unit inside the housing 5. The internal unit 4 is configured to perform feedback-type active noise control. However, in such a closed type noise control device 3, since the ear 2 of the user 1 is covered by the housing 5, it is not suitable for being worn by a driver or the like in the vehicle interior.

FIG. 1B schematically shows the configuration of a non-sealed (open type) noise control device. Specifically, the non-sealed noise control device 6 shown in FIG. 1 (B) is composed of only the internal unit 4 by removing the housing 5 of the closed noise control device 3 shown in FIG. 1 (A). It is a thing. In order to distinguish from the non-sealed noise control device according to the embodiment described later, this non-sealed (open type) noise control device is referred to as a "simple open type" noise control device 6. Since the simple open type noise control device 6 does not have a housing that covers the ears 2 of the user 1, the user 1 who wears the noise control device 6 can hear external sounds without any trouble, and is suitable for use in a vehicle interior or the like.

However, it has been found that when the housing 5 is removed from the closed type noise control device 3 to form the simple open type noise control device 6, the problem that the muffling effect is lowered in the low frequency range always occurs. It was. FIG. 2 is a graph showing a noise canceling effect (also simply referred to as “cancellation effect” or “silence effect”) by a closed type and a simple open type noise control device. Specifically, FIG. 2 (A) shows the canceling effect of the closed noise control device 3 shown in FIG. 1 (A), and FIG. 2 (B) shows the simple open type noise shown in FIG. 1 (B). The canceling effect of the control device 6 is shown. In FIGS. 2 (A) and 2 (B), the horizontal axis represents the frequency and the vertical axis represents the canceling effect. The canceling effect is greater toward the bottom of the figure and smaller toward the top. That is, when the value on the vertical axis is negative, the sound is muted, and when the value on the vertical axis is positive, the sound is increased.

As shown in FIG. 2A, the closed noise control device 3 has a noise canceling effect in all bands. On the other hand, as shown in FIG. 2B, in the simple open type noise control device 6, the noise canceling effect is reduced and the sound is increased in the band indicated by the broken line 70 in the low frequency band. The cause of this will be described.

FIG. 3A shows the circuit configuration of the closed noise control device 3 shown in FIG. 1A. The closed noise control device 3 is configured as a feedback circuit including an adder 11, a speaker 12, a microphone 13, and a shelf filter (Self Filter) 14. The transfer function from the speaker 12 to the microphone 13 is defined as "C". Further, the characteristics from the speaker 12 to the shelf filter 14 indicated by the arrow 80 are referred to as a “circular transfer function”.

FIG. 3B shows the frequency characteristics and the phase characteristics of the shelf filter 14 shown in FIG. 3A. The shelf filter 14 reduces the gain (power) in the high frequency range as shown by the broken line 90, and maintains the phase near 0 degrees (°) as shown by the broken line 91 so as not to cause a phase delay.

FIG. 4A shows the frequency characteristics and the phase characteristics of the closed noise control device 3 configured as shown in FIG. 3A. In the case of the closed type noise control device 3, the frequency characteristic is substantially flat, and the phase characteristic also has no phase fluctuation from the low range to the middle range. As a result, the desired noise reduction effect can be obtained in the closed noise control device 3.

On the other hand, consider a simple open type noise control device 6 in which the housing 5 is removed from the closed type noise control device 3 while keeping the circuit configuration shown in FIG. 3 (A). The frequency characteristics and phase characteristics of the simple open type noise control device 6 are as shown in FIG. 4 (B). In the simple open type noise control device 6, the gain in the low frequency band decreases as shown by the broken line 71 in FIG. 4B, and the phase advances in the low frequency band accordingly as shown by the broken line 72. Due to this, as shown in FIG. 2B, the canceling effect is reduced in the low frequency range in the simple open type noise control device 6.

This point will be described in detail. FIG. 5 shows the frequency characteristics and phase characteristics of the one-round transfer function of the simple open type noise control device 6, and the canceling effect. The one-round transmission characteristic is indicated by the arrow 80 in FIG. 3 (A). The cancel effect indicates the sound pressure at the position of the microphone 13.

Based on the feedback control theory, the condition for canceling noise in the feedback circuit of FIG. 3 (A) is in the one-round transfer function.
(Condition 1) The phase is within ± 90 degrees, and (Condition 2) The gain is large.
Will be. If condition 1 is not satisfied, the sound will be increased. Further, when the condition 1 is not satisfied, the larger the gain, the larger the volume increase. Examining this point, in the phase characteristics of the one-circle transfer function shown in FIG. 5, as shown by the broken line 74, the phase exceeds ± 90 degrees in the low frequency range, and the sound is increased because the condition 1 is not satisfied. It ends up. Further, in the frequency characteristics, as shown by the broken line 73, the condition 1 is not satisfied in the same band and the gain is in the vicinity of 0 dB, so that the sound is increased and the gain is close to the oscillation (the gain is not satisfied in the condition 1). As a result, as shown by the broken line 75 in the graph of the canceling effect, there is no canceling effect in the low frequency range, and the sound is increased by about 10 dB.

[2] Non-sealed noise control device according to the embodiment (configuration)
From the above, in this embodiment, a filter is added to the feedback control circuit in order to prevent the above-mentioned decrease in the canceling effect. FIG. 6 shows the configuration of the non-sealed noise control device 10 according to the embodiment. The noise control device 10 according to the embodiment is referred to as a "non-sealed type" to distinguish it from the above-mentioned simple open type noise control device 6.

The non-sealed noise control device 10 includes a low boost filter 15 in addition to the configuration of the closed noise control device 3 shown in FIG. 3 (A). FIG. 7A shows the frequency characteristic and the phase characteristic of the low boost filter 15. As shown in the frequency response, the low boost filter 15 increases the low frequency gain. More specifically, the lower the frequency, the higher the gain. Further, as shown by the broken line 76 of the phase characteristic, the low boost filter 15 delays the phase. In FIG. 6, the positions of the shelf filter 14 and the low boost filter 15 may be exchanged.

In the above configuration, the speaker is an example of the output means of the present invention, the microphone 13 is an example of the detection means of the present invention, and the low boost filter 15 is an example of the correction means of the present invention.

FIG. 8 shows the frequency characteristics and phase characteristics of the one-round transfer function of the non-sealed noise control device 10, and the canceling effect. This one-round transfer function is indicated by the arrow 81 in FIG. In the frequency characteristics, as shown by the broken line 77, the gain is increased in the low frequency range and becomes 0 dB or more. This is because, as described above, the low boost filter 15 has a characteristic of increasing the gain in the low frequency range. Further, in the phase characteristic, as shown by the broken line 78, the phase is corrected in the low frequency range, and the phase is in an ideal state of 0 degrees. This is because, as described above, the low boost filter 15 has a property of delaying the phase. That is, by inserting the low boost filter 15, the characteristic of the simple open type noise control device 6 shown in FIG. 5 is compensated for the lack of gain in the low frequency range in the frequency characteristic shown by the broken line 73, and the broken line is delayed by delaying the phase. The phase advance in the phase characteristic shown in 74 is canceled out. In this way, the low boost filter 15 makes the phase within ± 90 degrees and the gain becomes 0 dB or more, so that the above-mentioned conditions 1 and 2 are satisfied. As a result, as shown by the broken line 79 in FIG. 8, the canceling effect in the low frequency range is ensured.

The low boost filter 15 is configured as, for example, a filter in which four primary filters shown in FIG. 7B are connected in series. In this case, the number of low boost filters 15 is determined to realize the phase delay required to cancel the phase lead generated in the simple open type noise control device 6.

(motion)
Next, the operation of the non-sealed noise control device 10 according to the embodiment will be described. FIG. 9 is a flowchart of noise control processing by the noise control device 10. This process is performed by the components of the noise control device 10 shown in FIG.

First, the microphone 13 collects ambient noise (step S10). The collected signal is supplied to the low boost filter 15, and the low boost filter 15 corrects the low-frequency phase and gain of the signal as described above (step S11). Next, the shelf filter 14 suppresses the phase delay while lowering the gain in the high frequency range of the signal (step S12). The output of the shelf filter 14 is input to the adder 11, and the adder calculates a difference from the target value 0 to generate a cancel signal having a phase opposite to that of noise and supplies it to the speaker 12. Then, the speaker 12 outputs a noise reduction sound (also referred to as “cancellation sound”) having a phase opposite to the noise based on the cancel signal. This cancels the noise.

Although the circuit of the noise control device 10 is shown as an analog circuit in FIG. 6, this may be configured as a digital circuit. Specifically, an A / D converter is provided on the output side of the microphone 13, a D / A converter is provided on the input side of the speaker 12, and the adder 11, the shelf filter 14, and the low boost filter 15 are configured as digital circuits. To do. Further, the parts other than the speaker 12 and the microphone 13 may be configured by a computer such as a DSP.

(Noise canceling effect)
FIG. 10A shows the canceling effect of the simple open type noise control device 6 having no low boost filter, and FIG. 10B shows the canceling effect of the non-sealed noise control device 10 having the low boost filter. Is shown. As shown by the broken line 83 in FIG. 10A, when the low boost filter is not provided, the canceling effect is reduced in the low frequency range and the sound is increased. On the other hand, as shown by the broken line 84 in FIG. 10B, the low-frequency canceling effect is ensured by providing the low boost filter.

(Example of installation)
Next, an installation example of the non-sealed noise control device 10 according to the embodiment will be described. FIG. 11 shows an example in which the noise control device 10 is mounted on the vehicle 20. In this example, the noise control device 10 is installed on the driver's seat side of the vehicle. Specifically, a pair of left and right speakers 12 and a microphone 13 are attached to the driver's seat. For example, the speaker 12 and the microphone 13 are provided on the left and right sides of the headrest of the driver's seat. As a result, the speaker 12 and the microphone 13 are located near the left and right ears of the user sitting in the driver's seat.

Further, the noise control device 10 includes a speaker amplifier 21 for amplifying a signal supplied to the speaker 21, a filter unit 22, and a microphone amplifier 23 for amplifying an output signal of the microphone 13. The filter unit 22 includes a shelf filter 14, a low boost filter 15, an adder 11, and the like in the feedback control circuit shown in FIG.

Random noise such as road noise is generated when the vehicle is driven. By installing the non-sealed noise control device 10 in the vehicle interior in this way, random noise such as road noise is canceled by the driver's ear. , Can be made inaudible to the driver.

The speaker 12 is usually configured as a speaker having a cabinet, a so-called box-shaped speaker. In this case, by increasing the capacity (volume) of the cabinet constituting the speaker, the low frequency side of the frequency band (hereinafter, referred to as “control band”) in which the noise control device 10 can obtain the canceling effect can be widened. It will be possible. Further, by making the diaphragm provided in the speaker 12 larger or lighter, it is possible to widen the low frequency side of the control band.

Next, the distance between the speaker 12 and the microphone 13 will be described. The closer the distance between the speaker 12 and the microphone 13 is, the more the frequency at which the phase starts to rotate can be moved to the high frequency side in the phase characteristic of the one-round transfer function. Therefore, by making the distance between the speaker 12 and the microphone 13 as close as possible, the control band can be expanded to the high frequency side. Actually, since the diaphragm and the microphone 13 must not come into contact with each other when the speaker 12 is driven, the speaker 12 and the microphone 13 are the minimum within a range in which the speaker 12 and the microphone do not come into contact with each other at the maximum amplitude of the diaphragm of the speaker 12. It is preferable that the speaker is installed at a distance of.

At the time of actual riding, the user three-dimensionally adjusts the positions of the seat and the headrest in the front-rear direction, the left-right direction, and the up-down direction according to the height of the sitting height and the angle according to the position of the ears. At this time, it is preferable that the noise control device 10 is configured so that the position can be three-dimensionally adjusted to a position according to the user's state while maintaining the distance between the speaker 12 and the microphone 13. That is, it is preferable to attach the speaker 12 and the microphone 13 to the seat, the headrest, etc. so that the user can adjust the seat, the headrest, and the like three-dimensionally while maintaining the distance between the speaker 12 and the microphone 13.

Next, the orientations of the speaker 12 and the microphone 13 will be described. FIG. 12A shows an example of the relationship between noise and the direction of the speaker 12. When the wave surface W1 of noise such as node noise moves as shown in FIG. 12A, the noise is canceled in the region 85 in front of the speaker 12. In this case, when the wave surface W2 of the cancel sound output from the speaker 12 coincides with the direction of the wave surface W1 of the noise, the muffling control space can be widened.

Therefore, since the normal microphone 13 has a directivity characteristic, as shown in FIG. 12B, the speaker 12 and the microphone 13 are directed so that the direction 86 in which the gain of the directivity characteristic of the microphone 13 is high faces the direction of the speaker 12. Are placed relatively. As a result, the microphone picks up more noise behind the speaker, and the muffling control space can be widened.

FIG. 13A schematically shows a noise control device 10a provided with a protective material as a modification of the noise control device 10. Usually, a net-like protective material is provided in front of the diaphragm of the speaker 12. In this example, the microphone 13 is arranged between the net-like protective material 25 that covers the front of the diaphragm of the speaker 12 and the speaker 12. That is, the speaker 12 and the microphone 13 are arranged inside the net-like protective material 25. This makes it possible to prevent the user's ears and the like from coming into direct contact with the microphone 13.

FIG. 13B schematically shows a partially sealed noise control device 10b as another modification of the noise control device 10. In this example, the noise control device 10b has a housing 9 whose upper side is open, and a speaker 12, a microphone 13, and the like are housed therein. In this way, by making it a partially sealed type, it is possible to suppress the degree of phase advance in the low frequency range as compared with the simple open type noise control device 6, so that the control band can be expanded. Become.

[3] Modification example In the above embodiment, the non-sealed noise control device 10 is mounted on a vehicle, but instead, it is mounted on a moving body such as an airplane or a train to reduce ambient noise. Is also possible.

3 Sealed noise control device 5, 9 housing 6 Simple open type noise control device 10 Non-sealed noise control device 12 Speaker 13 Microphone 14 Shelf filter 15 Low boost filter 21 Speaker amplifier 22 Filter part 23 Microphone amplifier 25 Protective material

Claims (1)

In an active noise control device that has a non-sealed structure and performs feedback control,
Detection means to detect noise and
A correction means that increases the gain of the detected noise signal in the low frequency band, and
An output means that outputs a noise-reducing sound that reduces the noise based on the corrected noise signal, and
An active noise control device characterized by having.

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