TWI779171B - Active noise control system - Google Patents

Abstract

This invention provides for an active noise control system capable of reducing the sound pressures of a plurality of dominant frequencies included in noise and the like at once.

An active noise control system include a controller 3 for creating and outputting a control sound AS for reducing the control target sound S including three predetermined dominant frequencies a'-c' observed by the microphone 2, and a speaker 4 for emitting the control sound, wherein, the controller includes a single band-pass filter 5 transmitting all three dominant frequencies, two control sound signal creation means 6b, 6c serially are arranged, create control sound signals sb, sc of opposite phases individually for the two dominant frequencies and superimposes the control sound signal of opposite phase to the band-pass signal sp so that the two dominant frequencies can be canceled from the band-pass signals output from the band-pass filter; a single final control sound signal creation means 6a is provided in series with the control sound signal creation means and creates a control sound signal sa of opposite phase with respect to the remaining one dominant frequency in the band-pass signal; and a superimposing means 7 superimposes control sound signals of opposite phases and creates and outputs the control sound.

Description

Active Noise Control System

The present invention relates to an active noise control system capable of reducing the sound pressure of a plurality of dominant frequencies contained in noise etc. at one go.

Patent Documents 1 and 2 are known as prior art related to active noise control. The "system for active noise control using parallel adaptive filters" of Patent Document 1 is an active noise control system, and this system is a system that includes a plurality of adaptive filters, and the plurality of adaptive filters The filter is constituted by receiving the same input signal representing an undesired audio frequency respectively, and receiving an update signal of each, and the plurality of adaptive filters is used to generate a plurality of output signals based on the same input signal each of the plurality of output signals is independently adjusted based on an update signal for each of the plurality of output signals, at least one of the plurality of output signals is used to correspond to the undesired audio frequency An anti-noise signal formed by counteracting interference to drive speakers to produce sound waves.

The "Active Noise Control System and Active Noise Control Method" of Patent Document 2 includes a microphone for measuring noise, a controller for producing and outputting a control sound for reducing noise, and a control device for emitting the control sound. The loudspeaker, and the controller is equipped with: a band-pass filter that allows only the frequency components in the frequency band of the control target to pass through the noise; an adaptive filter that estimates the dominant frequency of the control target from the frequency components that pass through the band-pass filter ; and a control signal calculation unit, which is based on the phase delay of each frequency of the controller measured in advance, and uses time control to perform phase correction for the phase delay of the dominant frequency of the control object, and then produces the control of the opposite phase sound.

[Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2010-161770

[Patent Document 2] Japanese Patent Laid-Open No. 2015-225130

Active noise control systems (hereinafter referred to as ANC) are increasingly being used in construction sites as noise countermeasures against engine sounds of bucket excavators, crane trucks, and the like. The above-mentioned engine sound system is mainly the sound pressure of a single frequency, which has a great impact on the surroundings. The currently known ANC only uses a single dominant frequency as the object of noise reduction, and the effect has also been confirmed.

However, for construction machinery, there are many engine sounds that emit a plurality of dominant frequencies rather than a single dominant frequency. In addition, the dominant frequency fluctuates according to the operation of the construction machine, and the range of fluctuation and the sound pressure greatly differ from construction machine to construction machine. In the conventional ANC, a single dominant frequency is used as the object. Therefore, with respect to noise having a plurality of dominant frequencies, the sound pressure of the dominant frequencies other than the single dominant frequency targeted cannot be reduced, resulting in a possibility that a sufficient effect cannot be obtained.

A plurality of ANCs whose target frequencies are different can be used, but when each speaker is installed, there may be a case where sound interferes. It is also conceivable to synthesize the sounds from each ANC, but it is necessary to completely synchronize the plurality of ANCs.

The present invention was invented in view of the above-mentioned known problems, and its purpose is to provide an active noise control system that can reduce the sound pressure of a plurality of dominant frequencies contained in noise and the like at one go.

The feature of the active noise control system of the present invention is that it has: a microphone, which observes the control object sound that contains N predetermined dominant frequencies sent from the sound source; a controller, which makes and outputs it to reduce A control sound for the control object sound observed by the microphone; and a loudspeaker, which emits the above-mentioned control sound input from the controller; The N predetermined dominant frequencies contained in the input control object sound are transmitted together; the control sound signal production means is aimed at the N predetermined dominant frequencies output from the band-pass filter. The band-pass signal can be arranged in series (N-1) in order to cancel (N-1) predetermined dominant frequencies from the band-pass signal, and for (N-1) of the band-pass signal Any one of the predetermined dominant frequencies is individually produced with an anti-phase control tone signal, and the anti-phase control tone signal is superimposed on the band-pass signal; a final control tone signal production means, It is arranged in series in the control tone signal production means, and for the above-mentioned bandpass signal of the above-mentioned control tone signal with (N-1) anti-phase overlap processing by the control tone signal production means In the remaining 1 predetermined dominant frequency, the control tone signal of the opposite phase is produced; and the overlapping means is aimed at the input from the (N-1) control tone signal production means and 1 final control tone signal production means The above-mentioned control sound signals of N opposite phases are superimposed to produce and output the above-mentioned control sound; the above-mentioned control sound input from the overlapping means is emitted from the above-mentioned loudspeaker.

The present invention is characterized in that the above-mentioned controller includes a computing device.

The present invention is characterized in that: the means for producing the control tone signal is to produce the control tone signal of opposite phase for the predetermined dominant frequency among the plurality of predetermined dominant frequencies in the band-pass signal which has the largest sound pressure level.

The present invention is characterized in that: the number of N predetermined dominant frequencies included in the controlled object sound and the number of each dominant frequency and its range of variation are obtained through prior investigation, and the above-mentioned band-pass filter is set to pass through frequency range.

The active noise control system of the present invention can reduce the sound pressure of multiple dominant frequencies contained in noise etc. in one fell swoop.

1‧‧‧Sound source

2‧‧‧Microphone

3‧‧‧Controller

4‧‧‧Speaker

5‧‧‧Single bandpass filter

6a‧‧‧Final control tone signal production means

6b, 6c‧‧‧Control sound signal production means

7‧‧‧overlapping means

8‧‧‧Output line

9a, 9b‧‧‧Signal overlapping part

10‧‧‧Microphone

11‧‧‧generator

12‧‧‧exhaust pipe

AS‧‧‧Control tone

S‧‧‧Control object sound

a'~c'‧‧‧Established dominant frequency

sa~sc‧‧‧inverted control tone signal

sp‧‧‧bandpass signal

FIG. 1 is an explanatory diagram for explaining an example of the variation characteristic of the dominant frequency of the control object sound set as the object in the active noise control system of the present invention.

Fig. 2 is an explanatory diagram illustrating a preferred embodiment of the active noise control system of the present invention.

FIG. 3 is a flow chart illustrating the processing steps for a single dominant frequency applicable to the active noise control system of the present invention.

FIG. 4 is a graph showing frequency characteristics of noise (engine sound) near the exhaust pipe of the sound source as an application example of the active noise control system shown in FIG. 2 .

Fig. 5 is a schematic diagram showing the arrangement of confirmation microphones in an application example.

Fig. 6 is a graph showing the phase state of the engine sound and the speaker sound in the applicable example.

Fig. 7 is a graph showing time series changes before and after the control start point of the band sound pressure including the dominant frequency in an applicable example.

Fig. 8 is a graph illustrating the effect of the active noise control system in the applicable example.

Hereinafter, a preferred embodiment of the active noise control system of the present invention will be described in detail with reference to the accompanying drawings.

Regarding the plurality of dominant frequencies, there is the first case where the dominant frequency itself changes, and the second case where the dominant frequency basically does not change but has a large sound pressure change. The ANC of the present invention is aimed at the first case. system.

The first case is the noise of generators, etc., where the engine speed changes due to the load, and as shown in Figure 1, the sound pressure changes of the plurality of dominant frequencies a', b', c' are relatively small , the frequency of each dominant frequency a'~c' is a large change. In other words, regarding the multiple sounds heard in the noise, the "size of the sound" basically does not change, but the "height of the sound" changes.

The dominant frequencies a'~c' of the engine sound of construction machinery are determined by the engine speed. There is a possibility that the plurality of dominant frequencies a' to c' of the engine sound may change greatly in a short period of time due to the load. Therefore, it is preferable that the calculation time of the tone of the anti-phase is extremely short.

FIG. 2 is an explanatory diagram illustrating a preferred embodiment of the ANC of the present invention. As shown in the block diagram in Fig. 2, the ANC system of the present embodiment is mainly constituted in the following manner, promptly has: microphone 2, it comprises N (3) to the sound source (noise source) 1 that sends out Observing the control object sound (noise) S of the predetermined dominant frequency a', b', c'; the controller 3, which produces and outputs the control sound AS for reducing the control object sound S observed by the microphone 2; And the speaker 4, which emits the control sound AS input from the controller 3; and the controller 3 is equipped with: a single band-pass filter 5, which makes the N contained in the control object sound S input from the microphone 2 (3) pre-determined dominant frequencies a'~c' pass through together; the control tone signal production means 6b, 6c, etc. contain N (3) pre-determined for the output of the band-pass filter 5 The band-pass signal sp of the dominant frequency a'~c' can be set in series in such a way that the self-passing signal sp can offset (N-1) (2) predetermined dominant frequencies b', c' (N-1) (2), and for any of the (N-1) (2) predetermined dominant frequencies b', c' in the band-pass signal sp, respectively make anti-phase The control tone signals sb, sc, and the antiphase control tone signals sb, sc are superimposed on the bandpass signal sp; a final control tone signal production means 6a, which is arranged in series on these control tone signals The signal production means 6b, 6c, and for the remaining one predetermined dominant frequency a' in the band-pass signal sp, the control tone signal sa of the opposite phase is produced, and the band-pass signal sp is obtained by the control tone signal production means 6b, 6c are overlapped with (N-1) (2) control tone signals sb, sc of opposite phases; and overlapping means 7, which are made from these (N-1) (2) The N (3) anti-phase control tone signals sa, sb, and sc input by the control tone signal production means 6b, 6c and one final control tone signal production means 6a overlap to produce and output the control tone AS; and The speaker 4 emits the control sound AS input from the superimposing means 7 .

The controller 3 is constituted by a computer or the like provided with a computing device, and is desirably constituted by one. The reason for this is that when using a plurality of controllers 3 (computers, etc.), it is difficult to completely synchronize all of them. The controller 3 digitizes the analog signal of the control object sound S input from the microphone 2 , and outputs the analog signal of the control sound AS output from the superimposing means 7 to the speaker 4 .

The ANC of this embodiment is a system that sequentially calculates antiphase signals sa~sc for a plurality of dominant frequencies a'~c', and the calculation time of the control sound S is shorter than that of the conventional system for a single dominant frequency. The ANC is slightly longer, but it can widen the frequency range that can reduce the noise S. Even if the dominant frequency a'~c' changes greatly, the noise S can be reduced correspondingly.

A single bandpass filter 5 that passes N predetermined dominant frequencies a' to c' together is connected in series to the microphone 2 .

On the output line 8 that outputs the bypass signal sp from the self-pass filter 5, (N-1) control tone signals arranged sequentially in a manner called the first segment and the second segment are connected in series. Production means 6b, 6c and a final control sound signal production means 6a of the final stage.

The control sound signal production means 6b, 6c and the final control sound signal production means 6a are for each of the N predetermined dominant frequencies a'-c', respectively and individually produce N control sound signals sa~sc.

The control sound signal generating means 6a to 6c have signal overlapping portions 9a, 9b connected to the output line 8 between the control sound signal generating means of the next stage, respectively.

The control tone signal production means 6b, 6c are both superimposed on the band-pass signal sp with the produced control tone signals sb, sc, and offset the predetermined dominant frequency b corresponding to the control tone signals sb, sc in the band-pass signal sp ', c'.

For example, the first-stage control tone signal production means 6c offsets a predetermined dominant frequency c' from the band-pass signal sp input to the second-stage control tone signal production means 6b. Similarly, the second-stage control tone signal production means 6b is to cancel a predetermined dominant frequency b' from the band-pass signal sp input to the final control tone signal production means 6a of the third section. Therefore, when processing N predetermined dominant frequencies a'~c' as objects, (N-1) control tone signal production means 6b, 6c are used to cancel (N-1) A dominant frequency b', c'.

If the band-pass signal sp is compared between the control tone signal producing means 6b, 6c of each stage, the number of dominant frequencies decreases by one each time the control tone signal producing means 6b, 6c passes through. The band-pass signal sp including the remaining one predetermined dominant frequency a' is input to the Nth final control tone signal producing means 6a of the final stage.

The final control tone signal production means 6a is to produce the control tone signal sa for the remaining predetermined dominant frequency a'.

Also, the N number of these control sound signal generating means 6b, 6c and the final control sound signal generating means 6a are connected in parallel to a single overlapping means 7 in parallel. The superposition means 7 for producing a single control sound AS by superimposing the control sound signals sa~sc is connected to the speaker 4 .

In short, the ANC of this embodiment is provided with a single band-pass filter 5 that has a wider range of variation than that produced by a plurality of dominant frequencies a'~c', and the output of the band-pass filter 5 is connected in series The control sound signal generating means 6a~6c are arranged in a row to prevent the undesirable interference between filters caused by setting a plurality of bandpass filters.

The ANC of this embodiment is based on a plurality of dominant frequencies a'~c', and is composed of a processing module (bandpass filter 5 and control tone signal production means 6a~6c) for a single dominant frequency. . Referring to FIG. 3 , the processing steps performed by the processing module targeting a single dominant frequency will be outlined.

When estimating the dominant frequency, in order to limit the estimation range and shorten the time spent in estimation, the control object sound (input signal) obtained by observing the microphone (control microphone) (step 1) is used to limit the dominant frequency Bandpass filter of the guessed range (step 2). Thereby, the predetermined dominant frequency included in the controlled target sound input from the microphone is transmitted.

The N "predetermined" dominant frequencies included in the control object sound refer to the number of pre-acquired and mastered and the changes between each dominant frequency and the frequency in the construction site and other surveys conducted in advance. The dominant frequency of the range (amplitude) refers to the dominant frequency to be weakened by the control tone signal of the opposite phase in the ANC of this embodiment. Based on the results of previous investigations, the band-pass filter 5 is set to pass the frequency range.

For the signal passing through the band-pass filter, use the well-known least mean square (LMS, Least Mean Square) algorithm to estimate the dominant frequency in the time domain (along the time axis) (step 3).

The signal (signal of dominant frequency) passing through the band-pass filter changes in amplitude and phase relative to the signal of dominant frequency contained in the input signal observed by the microphone, and it is in the actual noise that is the object of weakening The sound of dominant frequency (observed by the microphone) does not have the same amplitude and opposite phase, and the bass pressure cannot be properly reduced.

Therefore, with regard to the ANC used, the correction values (due to the phase shift generated by the devices such as the microphone 2, the controller 3, the speaker 4, etc., and the band-pass filter 5, Phase shift generated by electronic processing such as LMS algorithm) (step 4), use the measured correction value to correct the signal passing through the band-pass filter (step 5), and output the corrected signal To the speaker (speaker for control) (step 6), make the sound of the dominant frequency of the weakened object and the control sound emitted from the speaker have the same amplitude and opposite phase.

The time spent in estimating the dominant frequency varies according to the value of the step size parameter in the LMS algorithm, but by selecting the parameter value suitable for controlling the speed of the change of the object sound, even within 1 second at 30Hz, It can fully follow the sound pressure change of 20dB.

Returning to Fig. 2, the ANC of this embodiment will be described in more detail. In the illustrated example, a situation in which there are three dominant frequencies a' to c' of the control object sound S is shown. The dominant frequencies a'~c' of the control object sound S are not limited to three, and may be several or more than two.

The ANC in this embodiment corresponds to the case where the dominant frequencies a'~c' vary greatly and the sound pressure varies relatively little. In the case of large changes in the dominant frequencies a'~c', it is difficult to capture the sound of the changed dominant frequency if it is a band-pass filter with a narrow frequency bandwidth.

In this embodiment, the control target sound S input from the microphone 2 is passed through the bandpass filter 5 having a relatively large frequency range at one time, and then the control sound signal production means 6b, 6c and the final control tone signal generating means 6a perform the process of producing control tone signals sa~sc of opposite phases.

At this time, the means 6b and 6c for producing control sound signals are to produce anti-phase signals for the predetermined dominant frequency among the plurality of predetermined dominant frequencies a'~c' in the band-pass signal sp, respectively, for which the sound pressure level is the largest. Control tone signal.

For example, in the first control sound signal generating means 6c, the first control sound signal sc of opposite phase is calculated and produced for the predetermined dominant frequency c' having the largest sound pressure level in the bandpass signal sp. Using the first control sound signal sc, the sound of a predetermined dominant frequency c' is attenuated from the band-pass signal sp output through the band-pass filter 5 .

In this way, the band-pass signal sp becomes a signal in which the dominant frequency c' having the largest sound pressure level among the three predetermined dominant frequencies a'~c' is cancelled.

Immediately afterwards, the second control tone signal production means 6b is aimed at the established dominant frequency b' with the largest sound pressure level in the band-pass signal sp passing through the first control tone signal production means 6c after the sound pressure level is relatively large. , calculate and produce the second control tone signal sb of opposite phase. Using the second control sound signal sb, the sound of a predetermined dominant frequency b' is weakened from the band-pass signal sp passing through the first control sound signal generating means 6c.

Thereby, the band-pass signal sp passed through the second control tone signal generating means 6b becomes a signal in which two dominant frequencies b', c' among the three predetermined dominant frequencies a'~c' are canceled. In this way, the same processing is repeated sequentially by the plurality of control sound signal generating means 6b, 6c.

The band-pass signal sp output from the second control tone signal production means 6b contains a signal of a predetermined dominant frequency a', and the final control tone signal production means 6a is calculated for the predetermined dominant frequency a' And make the third control tone signal sa of anti-phase.

The superposition means 7 is for the 3 anti-phase control sound signals sa~sc produced and inputted by using the first and second control sound signal making means 6b, 6c and the final control sound signal making means 6a. These are summed and superimposed to create one control sound AS.

The superposition means 7 outputs the one control sound AS to the speaker 4, and the speaker 4 emits the input control sound AS.

It can be said that the ANC system of this embodiment is constituted such that the control sound signal generating means 6b, 6c and the final control sound signal generating means 6a have the same function, and the control sound signal generating means 6a~6c are set with Signal overlapping sections 9a, 9b.

Also, the greater the number of predetermined dominant frequencies to be targeted, the more effectively the control target sound can be suppressed, but the greater the number, the longer it takes until the control sound AS is output. The number of predetermined dominant frequencies to be targeted is determined by the above-mentioned preliminary investigation, but at this time, it is desirable to consider the capability of the controller 3 (calculation device).

The ANC of this embodiment described above targets a plurality of predetermined dominant frequencies a'~c' contained in the control object sound S such as noise, even if these dominant frequencies a'~c' occur In the case of changes, it is also possible to reasonably produce all predetermined dominant frequencies a' by using the sequence processing performed by the serially connected plurality of control tone signal production means 6b, 6c and the final control tone signal production means 6a. The plurality of control tone signals sa~sc of c', and output the control tone AS which overlaps the control tone signals sa~sc, so the sound pressure of the plurality of predetermined dominant frequencies a'~c' can be effectively reduced.

The ANC of this embodiment is to sequentially calculate the control tone signal sa~ of the opposite phase of each dominant frequency a'~c' by using a plurality of control tone signal production means 6b, 6c and the final control tone signal production means 6a sc, therefore, the processing time tends to be longer than that of the case where a single dominant frequency is the object. Therefore, it is desired to be used for less noise in which the dominant frequency frequently changes, such as the engine sound of a generator.

"Application and Effect"

Hereinafter, an example in which the ANC of this embodiment is applied to the noise of a generator with a small change in sound pressure will be described. The sound source of the engine sound of the generator is the exhaust pipe, and the microphone and the speaker are arranged near the exhaust pipe.

In FIG. 4 , the frequency characteristics of the noise (sound pressure) of the generator measured in advance in the vicinity of the exhaust pipe in order to determine a predetermined dominant frequency are shown. It can be seen that the engine sound system as the control object sound contains a plurality of dominant frequencies with a sound pressure of about 100~120dB in 70~180Hz.

In FIG. 5, the position of the confirmation microphone 10 for confirming the noise cancellation effect of ANC is shown. The confirmation microphone 10 was installed at a position 2 m away from the exhaust pipe 12 of the generator 11 in a horizontal distance and at a height of 1.2 m.

The measurement results are shown in Fig. 6 to Fig. 8 . FIG. 6 shows the relationship between the generator sound (control target sound) S near the exhaust pipe and the control sound (output sound) AS near the speaker when ANC is activated. During the measurement, the engine speed of the generator was 1600 rpm, and the main noise S of about 70 Hz, about 150 Hz, and about 160 Hz was generated from the exhaust pipe 12 . With respect to the generator sound S, the control sound AS of the speaker is basically in antiphase.

In FIG. 7 , time-series changes in sound pressure (80 Hz band and 160 Hz band) in bands including predetermined dominant frequencies of 70 Hz, 150 Hz, and 160 Hz are shown. There is no ANC control up to the control start point shown in the figure, and there is ANC control after the control start point. It is possible to confirm the reduction of the sound pressure of the dominant frequency after starting the ANC control. From the start of the control, the sound pressure of the band corresponding to each dominant frequency began to decrease, and the effect was displayed in about 0.6 seconds.

FIG. 8 shows the sound pressure at the position of the confirming microphone 10 according to the presence or absence of ANC. In the 80Hz band and 160Hz band that contain the predetermined dominant frequency, the reduction can be about 9dB and 8dB, respectively.

1‧‧‧Sound source

2‧‧‧Microphone

3‧‧‧Controller

4‧‧‧Speaker

5‧‧‧Single bandpass filter

6a‧‧‧Final control tone signal production means

6b, 6c‧‧‧Control sound signal production means

7‧‧‧overlapping means

8‧‧‧Output line

9a, 9b‧‧‧Signal overlapping part

AS‧‧‧Control sound

S‧‧‧Control object sound

a'~c'‧‧‧Established dominant frequency

sa~sc‧‧‧inverted control tone signal

sp‧‧‧bandpass signal

Claims (5)

A kind of active noise control system, it is characterized in that, it has: Microphone, it is sent from the sound source to contain the control object sound that contains N predetermined dominant frequencies to observe; Controller, its production and output are used to reduce The control sound of the control object sound observed by the microphone; and the speaker, which emits the above-mentioned control sound input from the controller; the above-mentioned controller is equipped with: a single band-pass filter, which enables The N predetermined dominant frequencies contained in the control object sound are passed through together; the control sound signal production means, which is aimed at the band communication that contains N predetermined dominant frequencies output from the band-pass filter No., (N-1) numbers can be set in series in order to cancel (N-1) predetermined dominant frequencies from the band-pass signal, and for the (N-1) predetermined frequency in the band-pass signal For any one of the dominant frequencies, the control tone signal of the opposite phase is produced individually, and the control tone signal of the opposite phase is superimposed on the band-pass signal; a final control tone signal production means, its series Set in the control tone signal production means in a row, and for the above-mentioned band-pass signals of the above-mentioned control tone signal with (N-1) anti-phase overlap processing by the control tone signal production means The remaining 1 predetermined dominant frequency is used to produce control tone signals of opposite phases; and overlapping means, which are aimed at the N inputted from the (N-1) control tone signal production means and 1 final control tone signal production means. The above-mentioned control sound signals of opposite phases are superimposed to produce and output the above-mentioned control sound; and the above-mentioned control sound input from the overlapping means is emitted from the above-mentioned speaker. The active noise control system according to claim 1, wherein the above-mentioned controller includes a computing device. Such as the active noise control system of claim 1, wherein, the above-mentioned control sound signal production means is respectively for the predetermined dominant frequency among the plurality of predetermined dominant frequencies in the above-mentioned band-pass signal, which has the largest sound pressure level, and produces anti-phase Bit of the above-mentioned control tone signal. Such as the active noise control system of claim 2, wherein, the above-mentioned control sound signal production means is respectively for the predetermined dominant frequency among the plurality of predetermined dominant frequencies in the above-mentioned band-pass signal, which has the largest sound pressure level, and produces anti-phase Bit of the above-mentioned control tone signal. The active noise control system according to any one of claims 1 to 4, wherein the number of N predetermined dominant frequencies included in the controlled object sound and the number of dominant frequencies and their changes are obtained through prior investigation Amplitude is the range of frequencies that are set to pass through the above-mentioned bandpass filter.

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