JPH08194489A - Active silencing system and device equipped with the same - Google Patents

Abstract

PURPOSE: To shorten the system delay as a physical restriction by sensing the noise information signal, and predicting a future noise signal arising thereafter on the basis of the obtained signal. CONSTITUTION: A controller 4 predicts in advance a future noise signal on the basis of the reference signal obtained with a reference sensor 2, and noises are reduce by performing phase coordination and inversion of the signal so that the noise make destructive interference with the applied sonic wave at the desired silencing point As noise information of a noise source 1 a sensing signal S1 is emitted from the reference sensor 2 and converted into digital signal by an A/D converter 41 so that a reference signal S2 is provided, and the future noise signal is predicted from time to time by a future signal predicting means 42 on the basis of the reference signal S2 so that a predict signal S3 is prepared. Then a speaker control signal S4 is produced by an inverted phase signal producing means 43, analogized by a D/A converter 44, and amplified by a power amplifier 45. and application sonic wave is emitted from a speaker 3 so that the noise is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction system for reducing noise, and a device using the same, for generating random noise such as fluid noise, such as vehicle noise and air conditioner noise. The present invention relates to a system and a device for reducing active muffling.

[0002]

2. Description of the Related Art Conventionally, as a method of reducing noise in a vehicle or noise emitted from equipment such as an air conditioner, a so-called passive method using a structural design of a vehicle body or using a sound absorbing material or a sound insulating material is used. Was common. On the other hand, active noise control technology has recently attracted attention, in which a secondary sound having the same amplitude as that of the noise is artificially created and the sound is actively extinguished by using the interference of waves.

The basic idea of this active noise control is old and dates back to the 1930s. Since then, it has been studied by various researchers, and recently, with the development of the field of digital signal processing, it has been adapted to actual products.

A noise control method relating to active noise control is disclosed in P. A. Nelson / S. J. LMS (Least by Eliot
Mean Square: There is a least mean square method algorithm (published patent 1-501344). This algorithm is 1950
Most of the recent studies on active noise control, which were systematized by Widrow and rich in versatility, used this algorithm. The present invention is also basically based on the use of this algorithm, and the prior art will be described accordingly.

First, before starting the muffling operation, the value of the transfer function between the speaker input signal which is the additional sound source and the output signal of the error microphone which is the muffling sensor installed at the position to be muffled is identified. Next, during the mute operation, the reference sensor detects the reference signal according to the noise information, and the reference signal is input to the speaker through the adaptive filter in the controller to generate the additional sound wave. LMS in the controller using
The algorithm reduces the noise level at the error microphone position by sequentially updating the coefficient of the adaptive digital filter so that the square value of the error microphone output signal is minimized. The transfer function and the adaptive digital filter each have a finite impulse response (FI).
R) A filter is used.

[0006]

In such an active noise reduction method and device, it is necessary to install a noise reduction sensor at the muffling point, and when a future time series signal cannot be predicted, a reference sensor detects it. It is necessary to create an additional sound wave generated from the speaker before the generated sound wave reaches the position of the muffling sensor. Therefore, when the noise to be silenced is aperiodic, even if there is a high-speed DSP, there is system delay such as speaker delay and filter delay. Therefore, the reference sensor and the speaker are separated by the delay. There was a fundamental constraint (causality) that it had to be.

An object of the present invention is to propose an active muffling system and apparatus that alleviates the causality by making an improved future prediction by paying attention to such points.

[0008]

In order to achieve the above object, the present invention predicts a future noise signal from a past time series signal based on a noise signal detected by a reference sensor. The prediction signal is phase-guaranteed and muted so that the predicted signal will cause destructive interference with the additional sound wave emitted from the speaker at the desired silencing point.

[0009]

The information signal of noise can be sensed, and the noise signal in the future can be predicted based on the signal, so that the system delay, which is a physical constraint condition, can be shortened.

[0010]

【Example】

(Embodiment 1) An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the overall construction of an active noise canceling apparatus according to the present invention. The active silencer shown in the figure generates a reference sensor 2 such as a microphone that obtains information on the noise 1, and a sound wave (additional sound wave) having the same phase as the sound wave propagating from the noise 1 to reduce the noise. A speaker 3 that is an additional sound source and a controller 4 that controls generation of an additional sound wave from the speaker 3 for reducing noise at a desired silencing point are provided.

The controller 4 predicts a future noise signal in advance based on a reference signal which is information of noise obtained by the reference sensor 2, and phase the noise and the additional sound wave so as to cause destructive interference at a desired silencing point. It functions to reduce noise by matching and inverting signals.

In the controller 4, as shown in an excerpted form in FIG. 2, the detection signal s1 output from the reference sensor 2 as the noise information of the noise source 1 is converted into a digital signal by the A / D converter 41, and is converted into a reference signal. Signal s2, future signal prediction means 4
2, the noise signal of the future is successively predicted based on the reference signal s2, and the prediction signal s3 is created.

Next, the anti-phase signal generating means 43 uses the predicted signal s3 to generate the speaker control signal s4 for generating the additional sound wave having the anti-phase same amplitude, and the D / A converter 4 is generated.
4, and the power amplifier 45 amplifies it to generate additional sound waves from the speaker 3 to reduce noise.

FIG. 3 shows a control processing flow chart for predicting such a series of noise signals and creating an antiphase signal.

First, the noise signal is previously stored in the storage medium. When the time series signal from the noise detected by the reference sensor is given by x _-N , x _{-N + 1} , x _{-N + 2} , ..., x _-2 , x _-1 , x ₀ , n steps ahead Consider the case of predicting x _n of. D-dimensional vector {X _-i } from time series

[0017]

## _EQU00001 ## X- _i = [x- _i , x- _i-1 , x- _i-2 , ..., X- _{i-d + 1} ] (Equation 1), which is defined as a d-dimensional phase space. To do. d is the embedding dimension. A vector {X ₀ } corresponding to the current time-series data x ₀ is used as a reference vector, a vector in the vicinity of the reference vector is searched from a vector composed of past noise signal data in the memory, and local fitting is performed. Make predictions. That is, if the vector of past data {X _-j } is used, the predicted value {X _n } is

[0018]

[Equation 2] ‖X _−j −X ₀ ‖… (Equation 2) is calculated to be the minimum.

[0019]

[Number 3] _{X n = X -m + A -m} (X 0 -X -m) ... ( number 3) and can be expressed. Here, A _−m is the Jacobian matrix at time −m. The phase is adjusted so that destructive interference occurs at the desired sound deadening point, and the sound is emitted from the additional sound source and muted.

The present prediction method is effective when the noise signal from the noise source is unsteady.

(Embodiment 2) This embodiment relates to a noise signal prediction method.

The second embodiment is also constructed similarly to the first embodiment, and the reference sensor 2 detects a noise signal. Before performing the noise reduction operation, noise is learned from the detection signal in advance, the noise signal is predicted as a certain function, and stored in the predictor.

During the muffling operation, after ensuring the phase so that the additional sound wave and the noise signal may cause destructive interference at the muffling point, the signal is converted into an opposite phase and radiated from the speaker.

This method is effective when the noise signal from noise is stationary.

(Embodiment 3) Regarding Embodiment 1 or 2, when the distance between the reference sensor and the speaker is short, the transfer function between the reference sensor output and the speaker input is identified before the muffling operation as shown in FIG. Keep it.

Howling can be prevented by subtracting the convolution value of the transfer function and the speaker control signal from the speaker control signal s4 from the output signal s2 from the reference sensor.

(Embodiment 4) FIG. 5 is a diagram in which a function for adjusting the speaker control signal s4 output from the anti-phase signal generating means 43 is added according to the volume of the sound deadening in the embodiment 1, 2, or 3. Is.

A muffling sensor 10 for detecting an error after muffling is installed at a desired muffling point, and an output signal of the muffling sensor 10 is converted into a digital signal by an A / D converter 48 and input to an anti-phase signal generating means 43. . In the anti-phase signal generation means 43,
The magnitude of the input signal is monitored, and the speaker control signal is adjusted as necessary to stabilize the sound volume at the position of the sound deadening sensor.

(Embodiment 5) FIG. 6 is a diagram in which a function for judging whether or not the muffling operation is normally performed is added to the embodiment 1, 2, or 3.

The difference between the signal s1 from the noise detected by the reference sensor 2 and the speaker control signal s4, or the ratio thereof, is calculated, and a reference value is set to that value. It can be judged as above. Reset the system in case of abnormality.

(Embodiment 6) FIG. 7 shows a perspective view of a high-speed vehicle equipped with the future prediction type active noise reduction system of the present invention. A current collector 7 is mounted on the roof 6 of the vehicle body 5. The current collector 7 is surrounded by a current collector cover 8,
Electric power for running the vehicle 5 is collected from the overhead line 9. Then, when air collides with the current collector 7 or the current collector cover 8 when the vehicle body 5 travels at high speed, the flow separation causes
Fluid noise is generated from these. This device includes a reference sensor 2 installed on a collector cover 8 and a controller 4 that predicts future noise from the detection signal and generates an additional sound wave.
And a speaker 3 which is an additional sound source controlled by the output signal of the controller 4. The reference sensor 2 detects noise having a high correlation with the noise to be silenced, and the detected signal is input to the controller 4. Speaker 3
The number and position of the sound sources are determined depending on the frequency of the sound deadening target and the number of fluid sound sources.

With the above-mentioned configuration, as shown in FIG. 2, in the controller 4, the detection signal s1 output from the reference sensor 2 is converted into a digital signal by the A / D converter 41 to form the reference signal s2, which will be used in the future. The reference signal s by the signal predicting means 42
The future noise signal is sequentially predicted based on 2, and the prediction signal s3
Create

Next, the anti-phase signal generating means 43 uses the predicted signal s3 to generate a speaker control signal s4 for generating an additional sound wave having the same anti-phase amplitude, and the D / A converter 4 is generated.
4, and the power amplifier 45 amplifies it to generate additional sound waves from the speaker 3 to reduce noise.

[0034]

According to the present invention, the system delay can be shortened by predicting the future noise signal based on the noise information, so that the causality, which is a principle constraint condition for aperiodic noise, can be relaxed. , The whole system can be made compact.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an active silencer according to the present invention.

FIG. 2 is a block diagram showing details of the active silencer shown in FIG.

FIG. 3 is a flowchart showing an example of control processing in the active silencer shown in FIG.

FIG. 4 is a block diagram showing an overall configuration when a howling prevention function means is added to the active silencer shown in FIG.

5 is a block diagram showing an overall configuration when a function of confirming a silencing operation is added to the active silencing device shown in FIG.

FIG. 6 is a block diagram showing an overall configuration when a silencer sensor is attached to the active silencer shown in FIG.

FIG. 7 is a perspective view when the present invention is applied to a high speed vehicle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Noise source, 2 ... Sensor, 3 ... Speaker, 4 ... Controller, 42 ... Future signal prediction means, 43 ... Anti-phase signal generation means, 47 ... Silence operation confirmation means.

Front page continued (72) Inventor Masami Naito 2520, Akanuma, Hatoyama-cho, Hiki-gun, Saitama Inside Hitachi Research Laboratories (72) Inventor Naoki Tanaka 2520, Akunuma, Hatoyama-cho, Hiki-gun, Saitama Corporation In the laboratory

Claims (8)

[Claims] 1. A reference sensor for detecting noise information, an additional sound source for outputting a sound wave of the same amplitude in an opposite phase to a sound wave reaching a desired sound deadening region, and noise for reducing the desired sound deadening region. In an active noise reduction system provided with a controller for generating an additional sound wave, in the controller, with respect to a time series signal reaching the reference sensor, using past time series signal data, predicts a future time series signal, An active sound deadening system characterized by generating the additional sound wave based on a predicted value. 2. The active muffling system according to claim 1, wherein a muffling sensor for detecting an error after muffling at a desired muffling point is installed. 3. An active muffling system according to claim 1, wherein a noise signal is learned in advance, the entire noise waveform is predicted as a function based on the learning data, and an additional sound wave is generated from the predicted signal. 4. The noise information according to claim 1 or 2, wherein noise information is stored in a storage medium, and each time the time-series signal reaches the reference sensor, prediction is performed from the stored noise information based on the time-series signal. An active noise reduction system that searches for a signal and generates an additional sound wave from the predicted signal. 5. The transfer function between the additional sound source and the reference sensor according to claim 1, 2, 3 or 4, which is identified before the muffling operation, and the transfer function and the additional sound source input signal are identified during the muffling operation. An active noise reduction system that prevents howling by subtracting the convolution value from the reference sensor. 6. The active muffling system according to claim 1, wherein it is determined whether the muffling operation is normal based on the difference between the signal output from the reference sensor and the input signal to the additional sound source or the magnitude of the ratio. 7. An active silencer equipped with the active silencer system according to claim 1, 2, 3, 4, 5 or 6. 8. A high-speed vehicle equipped with the active silencer according to claim 7.