JP2008040410A - Active type noise reducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active type noise reducing device in which stable operations are obtained even though acoustic transmission characteristics are fluctuated by the change with time and external noise is mixed much, and an ideal noise reducing effect is provided by detecting a case when noise other than control object frequency is amplified and uncomfortable sound is generated. <P>SOLUTION: The active type noise reducing device which cancels noise by radiated sound from an electroacoustic transducing means 111 which is driven based on output of a noise control processing circuit 101 composed of two one-tap digital filters, includes a control changing means 117 in which, an output signal Vd of a processing circuit 112 composed of two one-tap digital filters with an output signal Va of a noise control processing circuit 101 as input, is compared with a signal Vs in which the output signal Vd and the output signal Va are added, and according to a comparison result, a control method of the noise control processing circuit 101 is changed, and it is prevented that the noise of frequency different from the control frequency is amplified and generated as the uncomfortable sound. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an active noise reduction device for reducing noise by causing signals having opposite phases and equal amplitudes to interfere with unpleasant noise that remarkably includes a specific frequency that occurs with the rotation of an engine or the like. In particular, in the present invention, even if there is a change in the noise state or an external environment change of the active noise reduction device, it is possible to operate even in a place where the environment changes rapidly by suppressing the increase in noise at frequencies other than the target reduced frequency component. An object is to realize an active noise reduction device capable of performing the above.

  As such a conventional technique, there is known a method of detecting an input / output signal of an electroacoustic transducer such as a speaker included in an active noise reduction apparatus to detect the generation of noise exceeding the propagation noise. For example, it is disclosed by patent document 1 and the principle figure is FIG. In the figure, a sound wave propagation path 1 is provided with a first microphone 2 for detecting noise and a second microphone 3 for evaluating a silencing effect. Further, a mute speaker 4 is provided between the first and second microphones 2 and 3. A control device 5 is provided between the first microphone 2 and the mute speaker 4. Further, between the silencer speaker 4 and the control device 5, there are input / output signal detection means 6 for detecting the input signal of the silencer speaker 4, averaging means 7 for averaging the detected output signals, and an averaged output signal. Comparing means 8 for comparing the values and a stopping means 9 for stopping the operation of the active noise reduction apparatus upon receiving the comparison output signal are provided.

Next, the operation will be described. In the above configuration, the propagation noise is first detected by the first microphone 2 and input to the control device 5. In addition, an evaluation signal for evaluating the silencing effect from the second microphone 3 is input to the control device 5. The control device 5 outputs a drive signal to the mute speaker 4 so that the output of the second microphone 3 becomes zero due to the mutual interference between the muffled sound wave emitted from the mute speaker 4 and the propagation noise. Further, the signal to the mute speaker 4 is detected by the input / output signal detection means 6, the detection signal is averaged by the averaging means 7, and the average output signal is compared with the set value input to the comparison means 8. Here, if there is a change in noise or a change in the external environment, the control system is disturbed, and the muffler speaker 4 outputs noise above the propagation noise, and if it is determined that the average output signal is larger than the set value, The comparison means 8 outputs the result, and the stop means 9 for stopping the operation of the active noise reduction device according to the output signal stops the operation of the control device 5.
JP-A-4-282695

  However, the active noise reduction device according to the above-described prior art operates when an output exceeding a preset set value is detected, and even if the average output signal is less than the set value, it interferes with the propagation noise. If a sound wave that becomes noise without being output is output, the output sound wave is added to the propagation noise, and as a result, the noise increases and the noise may deteriorate as an unpleasant sound. Further, when a temporary disturbance or the like occurs and the control system returns to the initial state after a lapse of time, once the increase in noise is detected and the control is stopped, the control cannot be performed again.

  According to a first aspect of the present invention, there is provided a noise frequency detecting means for detecting a noise frequency of a noise source in order to actively reduce noise caused by rotation of an engine or the like, and the frequency detecting means. A sine wave generating means for generating a sine wave having the same frequency as the detected noise frequency, a cosine wave generating means for generating a cosine wave, and outputs from the sine wave generating means and the cosine wave generating means, respectively. A noise control signal obtained by adding outputs from the first one-tap digital filter, the second one-tap digital filter, and the first one-tap digital filter and the second one-tap digital filter is made to interfere with the noise. And an electroacoustic conversion means for converting the control sound signal as a control sound signal and a position near the position where the noise is reduced, and the interference result between the noise and the control sound signal is measured. An acoustoelectric converting means for converting an electric signal as a signal, and the error signal from the acoustoelectric detecting means and the sine wave generating means for the coefficients of the first one-tap digital filter and the second one-tap digital filter In the active noise control device for reducing the noise at the position of the acoustoelectric conversion means by sequentially updating with a reference signal created by a sine wave signal from the cosine wave signal from the cosine wave generation means, A third one-tap digital filter and a fourth one-tap digital filter that process the outputs from the sine wave generation unit and the cosine wave generation unit, and a third one-tap digital filter and a fourth one-tap digital filter, respectively. A first control state signal obtained by adding outputs, a second control state obtained by adding the first control state signal and the noise control signal. Coefficients of the third one-tap digital filter and the fourth one-tap digital filter with the signal, the second control state signal, the sine wave signal from the sine wave generation unit, and the cosine wave signal from the cosine wave generation unit Coefficient update means for sequentially updating the control state and control change means for changing the control state of the active noise control device, and the control change means by comparing the first control state signal and the second control state signal. The control state of the active noise control device is changed.

  According to the active noise reduction apparatus of the first aspect of the present invention, the noise control signal centered on the frequency of the original noise in the processing circuit using the first and second adaptive one-tap digital filters. To reduce the noise by interfering with the original noise, but for some reason that the processing circuit generates a control signal component different from the frequency of the original noise and enters a sound-increasing state. A processing circuit for generating a noise control signal by using a third and a fourth adaptive type 1-tap digital filter and determining by dividing and comparing the control signal into a frequency component of noise and a frequency component other than that. An active noise reduction device with high safety can be realized with a simple configuration in which an unpleasant sound increase phenomenon can be suppressed by changing the control state.

  As described above, according to the present invention, when the current transfer characteristic of the active noise reduction device is significantly changed from the initial transfer characteristic, a sound increase is generated at a frequency different from the control target frequency, resulting in a silencing effect. If the unpleasant sound due to the increased sound becomes louder than that, the control method is optimally controlled by detecting the control state and controlling the coefficient updating means of the digital filter, and the output of the abnormal signal is suppressed to suppress the abnormal signal output. The generation of abnormal noise can be suppressed, and an ideal noise reduction effect can be obtained.

  Hereinafter, an active noise reduction device according to the present invention will be described with reference to embodiments.

  FIG. 1 is a block diagram showing a configuration of an active noise reduction apparatus according to an embodiment of the present invention.

  There is a sine wave generating means 102 for generating a sine wave of a specific frequency related to noise based on a signal from a noise source, and a cosine wave generating means 103 for generating a cosine wave of the same frequency. The first one-tap digital filter 104 and the second one-tap digital filter 105 that process the outputs of the sine wave generation unit 102 and the cosine wave generation unit 103, respectively, are simulated to the sine wave generation unit 102 and the cosine wave generation unit 103, respectively. It comprises two coefficient updating means 106 and 107 to which an output multiplied by the transfer characteristic 108 and an output from an acoustoelectric conversion means 109 for detecting noise such as a microphone are inputted. Each of these coefficient updating means is a first one tap. The coefficients of the digital filter 104 and the second one-tap digital filter 105 are sequentially updated. The output of the processing circuit 101 is amplified by the power amplifier 110 and applied to the electroacoustic conversion means 111 such as a speaker. In addition, the processing circuit 112 processes a third 1-tap digital filter 113 and a fourth 1-tap digital filter 114 that process the outputs of the sine wave generation unit 102 and the cosine wave generation unit 103, the sine wave generation unit 102, and A second control state in which the noise control signal output from the processing circuit 101 is added to the first control state signal obtained by adding the output from the cosine wave generation means 103 and the outputs from the two one-tap digital filters 113 and 114. It comprises two coefficient update means 115 and 116 that receive signals, and these coefficient update means update the coefficients of the third 1-tap digital filter 113 and the fourth 1-tap digital filter 114, respectively. The first control state signal and the second control state signal are input to the control change means 117, and the control change means 117 compares the two control state signals so that the control change means 117 can control the control state of the processing circuit 101. Has changed.

  Here, the input / output characteristics of the processing circuit 101 in FIG. 1 will be described in order to explain the noise reduction mechanism in the embodiment of the present invention shown in FIG.

FIG. 2 is a block diagram of the processing circuit 101 in FIG. 1 in which the connection from the output to the input is removed, and the input / output characteristics of the processing circuit 101 will be described using the notation described here. Here, the input signal of the processing circuit 101 is cos (ωt + α), and the values obtained by multiplying the generated signals of the sine wave generating means 102 and the cosine wave generating means 103 by the simulated transfer characteristic C ^ are sin (ω ₀ t + β) and cos (ω ₀ t + β) (in order to simplify the explanation, the amplitude gain of the simulated transfer characteristic is 1). The coefficient updating means 106 and 107 generally update the coefficients of the two one-tap digital filters 104 and 105 by the LMS algorithm, respectively, but the coefficient updating formulas use the current coefficients of the two one-tap digital filters. Represented by Bn and An respectively

  Here, μ is a small coefficient value called a convergence coefficient. Also,

It expresses with the exponent expression and advances the calculation.

  First, the changes ΔAn and ΔBn of the coefficients An and Bn of the adaptive filter are expressed by the following equations.

Here, when ω ₀ + ω = ωx, ω ₀ −ω = ωy, α + β = θ, α−β = γ

  Here, An and Bn, which are sequentially updated, are obtained by integrating the above equations.

It becomes. Also, if the integration constant of A and B is 0 and ω is in the vicinity of ω ₀ , ωx >> ωy, so if the term of ωx is ignored

It becomes.

  Since signals from the sine wave generating means 102 and the cosine wave generating means 103 are added to this, the outputs Ea and Eb from the two 1-tap digital filters are respectively

Therefore, the output Et (= Ea + Eb) is

That is, Equation (1) is a signal that is output with cos (ωt + α) added as an input. When ω <ω ₀ , the phase is −β−90 ° from the input signal, and when ω ₀ <ω, the input signal. It shows that the phase changes by -β + 90 °. When ω = ω ₀ , the phase is 180 ° −β.

  FIG. 3 shows the input / output characteristics f (ω) of the processing circuit 101.

f (ω) = {μ / 2 (ω ₀ −ω)} / {− (β + π / 2)}.

Here, assuming that the actual transfer characteristic from the processing circuit 101 to the position of the noise detection device 109 is σ (ω) and the characteristic is expressed as shown in FIG. 4 in the vicinity of ω ₀ , arg {σ (ω ₀ )} = β and | σ (ω ₀ ) | = 1 (= 0 dB), that is, when the simulated transmission characteristic is substantially equal to the actual transmission characteristic, the phase characteristic of the output signal in the noise detection device 109 is as shown in FIG. It becomes like this.

Here, consider a case where the actual transfer function changes. For _{example, arg {(0 ω) σ} } σ is changed = beta + 60 when it becomes a °, the phase characteristic of the output signal at noise detection apparatus 109 becomes FIG 6, omega ₀ a phase of 0 ° at a slightly lower frequency It turns out that it is. This indicates that the transfer characteristic from the output to the input in the noise detection device 109 is positive feedback. When a signal different from the control target frequency is input, the signal is sufficiently attenuated by the filter. It can be seen that the signal is amplified and output from the electroacoustic transducer 111 depending on circumstances. When σ changes to arg {σ (ω ₀ )} = β−60 °, the phase characteristic of the output signal in the noise detection device 109 is FIG. 7, and the phase is slightly higher than ω ₀ . It turns out that it is 0 degree. Similarly, it can be seen that when a signal different from the frequency to be controlled is input, the signal is not sufficiently attenuated by the filter and is amplified in some cases and output from the electroacoustic transducer 111.

  As described above, when noise at a frequency near the control frequency is large due to a change in transfer characteristics, the noise at the control frequency is reduced, but the noise at a frequency different from the control frequency is amplified to obtain an optimum mute The effect cannot be obtained. Also, when the noise at the control frequency is smaller than the other noises and the control effect is not felt, if there is noise at a frequency that is different from the control frequency but in the vicinity, even if the noise is slightly amplified, the entire sound is muted. The effect cannot be obtained. In such a case, it is necessary to perform operations such as stopping the noise control or reducing the convergence coefficient μ to suppress the sound increase.

  Next, a mechanism for detecting the control state will be described.

  FIG. 8 is a block diagram of the processing circuit 112 excluding the connection from the input to the output, and performs the same operation as when β = 0 in the processing circuit 101 described above. That is, for input cos (ωt + α)

To get the output The output of the processing circuit 112 is 90 ° behind the input signal when ω <ω ₀ , and advances 90 ° when 180 ° ω> ω ₀ when ω = ω ₀ . It can also be seen that the amplitude gain becomes infinite when ω ₀ = ω, and decreases in inverse proportion to | ω ₀ −ω | as ω moves away from ω ₀ .

  FIG. 9 is a characteristic diagram example of the transfer characteristic Et / Ei of the block diagram of FIG. 8 calculated as described above.

  Next, the transfer characteristic of the processing circuit 112 will be described. FIG. 10 is a block diagram illustrating a state in which the output of the block diagram of FIG. 8 is fed back to the input so that the processing circuit 112 performs the same operation as the operation in the block diagram of FIG. The transfer function is represented by F (s) and has the characteristics shown in FIG. The transfer characteristic of this block diagram is

It is represented by FIG. 11 shows an example of frequency characteristics represented by this (formula).

From this, it can be seen that the processing circuit 112 has the characteristics of a band pass filter centered on ω ₀ . It can also be seen that the phase is 180 ° at ω ₀ . That is, in FIG. 1, when the noise control signal Va from the processing circuit 101 mainly includes a frequency component of ω ₀ , the first control state signal Vd that is the output of the processing circuit 112 is 180 ° in phase with the output Va. The second control state signal Vs (= Va + Vd), which is the sum of these two signals, becomes very small. Here, the frequency characteristic of Vd with respect to Va is

Therefore, FIG. 11 is obtained. Further, the frequency characteristics of Vs with respect to Va are calculated from the results so far and are as shown in FIG. FIG. 13 compares the amplitude gains of these characteristics. The control change means 117 compares Vd and Vs, and when Vd is large, determines that normal noise reduction processing is being performed, and controls the processing circuit 101 to perform normal operation. However, when the sound increase at a frequency other than the control frequency is more effective than the noise suppression at the control frequency, the output Va from the processing circuit 101 includes a relatively large number of frequency components ω ′ different from ω ₀ . At this time, since the processing circuit 112 has the characteristics of a band pass filter, the first control state signal Vd at that time becomes smaller with respect to the input, and the second control state signal Vs becomes larger. That is, in FIG. 13, Vs / Va> Vd / Va. At this time, the control change means 117 compares Vd and Vs, and when Vs is large, determines that the control is not appropriate, and changes the control conditions of the processing circuit 101 such as stopping the control or reducing the convergence coefficient μ. It is possible to prevent an unpleasant state due to an increase in noise.

  As described above, according to the present invention, when the current transfer characteristic of the active noise reduction device is significantly changed from the initial transfer characteristic, a sound increase is generated at a frequency different from the control target frequency, resulting in a silencing effect. If the unpleasant sound due to the increased sound becomes louder than that, the control method is optimally controlled by detecting the control state and controlling the coefficient updating means of the digital filter, and the output of the abnormal signal is suppressed to suppress the abnormal signal output. The generation of abnormal noise can be suppressed, and an ideal noise reduction effect can be obtained.

1 is a block diagram of an active noise reduction apparatus according to an embodiment of the present invention. Block diagram for calculating the transfer characteristic of the processing circuit 101 The figure which shows the example of a transfer characteristic in the block diagram of FIG. The figure which shows the example of a transfer characteristic from the processing circuit 101 to the noise detection apparatus 109 The figure which shows the transfer characteristic in the block diagram of FIG. 2 in the case of having the transfer characteristic of FIG. The figure which shows the transfer characteristic example 1 in the block diagram of FIG. 2 when a transfer characteristic changes from FIG. The figure which shows the transfer characteristic example 2 in the block diagram of FIG. 2 when a transfer characteristic changes from FIG. Block diagram of processing circuit 112 The figure which shows the example of a transfer characteristic in the block diagram of FIG. Block diagram for determining the characteristics of a processing circuit including negative feedback The figure which shows the example of a characteristic of a noise control signal and a 1st control state signal The figure which shows the example of a characteristic of a noise control signal and a 2nd control state signal The figure which shows the comparison of the amplitude gain of FIG. 11 and FIG. System diagram of a conventional active noise reduction device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Noise propagation path 2 1st microphone 3 2nd microphone 4 Mute speaker 5 Control apparatus 6 Input / output signal detection means 7 Averaging means 8 Comparison means 9 Stop means to stop operation of active noise reduction apparatus 101 For noise reduction Processing circuit 102 Sine wave generation means 103 Cosine wave generation means 104 1 tap digital filter 105 1 tap digital filter 106 coefficient update means 107 coefficient update means 108 Simulated transfer characteristic 109 Noise detection means 110 Power amplifier 111 First conversion means 112 Divergence detection Processing circuit 113 1-tap digital filter 114 1-tap digital filter 115 coefficient updating means 116 coefficient updating means 117 divergence detection device

Claims (5)

In order to actively reduce noise caused by rotation of an engine or the like, noise frequency detection means for detecting the noise frequency of the noise source, and a sine having the same frequency as the noise frequency detected by the frequency detection means A sine wave generating means for generating a wave, a cosine wave generating means for generating a cosine wave, and a first one-tap digital filter and a second one tap for processing outputs from the sine wave generating means and the cosine wave generating means, respectively. A digital filter, and an electroacoustic conversion means for converting a noise control signal obtained by adding outputs from the first one-tap digital filter and the second one-tap digital filter as a control sound signal for causing interference with the noise; Sound that is arranged in the vicinity of the position where noise is reduced and that converts an interference result between the noise and the control sound signal into an electric signal as an error signal The first and the second one-tap digital filters include the error signal from the acoustoelectric detection means, the sine wave signal from the sine wave generation means and the cosine wave. In the active noise control apparatus for reducing the noise at the position of the acoustoelectric conversion means by sequentially updating with a reference signal created by the cosine wave signal from the generating means, the sine wave generating means and the cosine wave generating A first control state in which the outputs of the third one-tap digital filter and the fourth one-tap digital filter and the outputs of the third one-tap digital filter and the fourth one-tap digital filter, which respectively process the outputs from the means, are added A second control state signal obtained by adding the signal, the first control state signal, and the noise control signal; the second control state signal; and Coefficient updating means for successively updating the coefficients of the third 1-tap digital filter and the fourth 1-tap digital filter with the sine wave signal from the chord wave generation means and the cosine wave signal from the cosine wave generation means, and the active noise Control change means for changing the control state of the control device is provided, and the control state of the active noise control device is changed by the control change means by comparing the first control state signal and the second control state signal. An active noise reduction device characterized by that. 2. The active noise reduction apparatus according to claim 1, wherein the control change means compares the first control state signal with the second control state signal from the electroacoustic conversion means of the active noise control apparatus. An active noise reduction apparatus characterized by stopping the control sound signal. 2. The active noise reduction apparatus according to claim 1, wherein the control change unit compares the first control state signal and the second control state signal to compare the first one tap of the active noise control device. An active noise reduction apparatus characterized by changing a value of a convergence coefficient in coefficient update of a digital filter and a second one-tap digital filter. 2. The active noise reduction apparatus according to claim 1, wherein the control change unit compares the first control state signal with the second control state signal to obtain a value of the reference signal of the active noise control apparatus. An active noise reduction device characterized by being changed. 2. The active noise reduction apparatus according to claim 1, further comprising storage means for storing the number of times that a comparison value between the first control state signal and the second control state signal exceeds a threshold value and a noise frequency at that time. An active noise reduction apparatus, wherein the control change means changes the control state of the active noise control apparatus based on the contents of the storage means.

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