JPH04283798A - Noise control system - Google Patents

Abstract

PURPOSE:To form a sound elimination zone nearby the ear of a person at all times even if the head moves. CONSTITUTION:A signal process part 2 filtrates a signal observed by a noise observation part 1 so as to generate a secondary sound, which decreases sound pressure inputted to a remaining noise observation part 4, by a secondary sound source part 3. At this time, a coefficient update part 5 updates the filter coefficient of the signal process part 2. A transfer function estimation part 7, on the other hand, varies a transfer function Cj, used by the coefficient update part 5, momentarily corresponding to the motion of the residual noise observation part 4 according to the position information of the residual noise observation part 4 to update the filter coefficient of the signal process part 2 so that a square error decreases. Consequently, when the residual noise observation part 4 is used while fitted to the head of the person, the sound elimination zone can be formed nearby the ear of the person at all times even if the head moves.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention generates a secondary sound that cancels out noise.
This invention relates to a noise control system that attenuates noise at a certain point.

0002

[Prior Art] For example, in the document ``Realization of Active Noise Control Chair, Report of Institute of Electrical Information and Communication Engineers Study Group EA90-2,'' for example, a sound that cancels out noise is generated as a secondary sound. A noise control system for controlling noise is disclosed. FIG. 4 is a diagram showing an example of the configuration of this type of conventional noise control system. The noise control system in FIG. 4 includes a noise observation unit 51 such as a microphone that observes a noise-causing signal at a noise source 50 and converts it into an electrical signal x(n), and an electric signal obtained by the noise observation unit 51. A signal processing unit 52 that performs signal processing on the signal x(n) using an appropriate digital filter, and a signal s(n) as a result of signal processing by the signal processing unit 52.
A secondary sound source unit 53 such as a speaker that generates secondary sound according to the
is placed at the point where you want to remove the noise, and the noise source 50
The noise y(n) propagated from the secondary sound source section 53 and the secondary sound as control sound propagated from the secondary sound source section 53 are combined and input as residual noise, and the sound pressure is converted into an electrical signal and output signal e(n). A residual noise observation section 54 such as a microphone to output, and a coefficient updating section 55 that updates the filter coefficient of the digital filter in the signal processing section 52 based on the output signal e(n) from the residual noise observation section 54 are provided. , the signal processing unit 52 based on the output signal e(n) from the residual noise observation unit 54.
By updating the filter coefficients of the signal and performing appropriate signal processing such that the output signal e(n) becomes zero, noise in the vicinity of the point where the residual noise observation unit 54 is placed can be removed. ing. Note that in each of the above signals, n represents time.

0003

[Problems to be Solved by the Invention] In the conventional noise control system described above, although control is performed such that the output signal e(n) becomes zero, the coefficient updating section 55 uses LMS (Least Mean Square). An algorithm that updates coefficients using the least squares error method is often used. That is, in the system configuration of FIG. 4, the output signal e(n) from the residual noise observation unit 54 at time n is expressed by the following equation.

0004

[Math 1]

[0005] Here, Cj is a transfer function between the secondary sound source section 53 and the residual noise observation section 54, and the convolution of s(n-j) and the transfer function Cj is input to the residual noise observation section 54. This becomes a secondary sound signal. Further, wi(n) is a filter coefficient of a digital filter in the signal processing unit 52, and in the LMS algorithm, adaptive signal processing is performed to update wi(n) for each sample.

[0006] That is, the LMS in the coefficient update section 55
In the algorithm, the squared error σ(n
), that is, {e(n)}2, decreases with time n, so that the filter coefficient wi is updated for each sample. More specifically, in equation 1,
When e(n) is squared, it becomes a quadratic equation related to wi, so in the LMS algorithm, when the squared error σ(n) is viewed as a quadratic equation related to wi, it goes down the quadratic surface Z of the following equation. Thus, the filter coefficient wi is updated for each sample.

[0007]

[Math 2]

In this case, the coefficient wi(n+1) of the filter at time (n+1) is given by the following equation, where α is the convergence coefficient.

[0009]

[Math 3]

As can be seen from Equation 3, in order to update wi(n), a transfer function Cj between the secondary sound source section 53 and the residual noise observation section 54 is required for calculation. This transfer function C
Generally, j is measured in advance using a system identification method, and in order to apply the above-mentioned LMS algorithm to obtain a predetermined silencing effect, the transfer function Cj that has been measured and set must be It is necessary to ensure that it does not change even while the system is running. That is, in the conventional noise control system, it is necessary to fix the positions of the secondary sound source section 53 and the residual noise observation section 54 so that the once set transfer function Cj does not change. However, if the point from which noise is to be removed is, for example, near the ears of a person doing a predetermined task, and the residual noise observation section 54, such as a microphone, is attached near the ears of the person, if the person's head moves. ,
Along with this, the residual noise observation section 54 also moves. At this time, the transfer function Cj changes and the LMS algorithm does not work effectively, and as a result, wi(n) is not necessarily updated in the direction in which σ(n) decreases, making it impossible to obtain a noise reduction effect. There was a case.

[0011] As described above, in the conventional noise control system,
Cases in which the sound can be effectively silenced only at the once fixed position of the residual noise observation unit 54, and if the position of the residual noise observation unit 54 moves, the noise reduction effect cannot be obtained at that position of the residual noise observation unit 54. There was a problem that there was.

[0012] The present invention aims to provide a noise control system that can always form a silencing zone near the human ear even if the head moves, when trying to mute the sound near the human ear. There is.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a noise observation means for observing noise at a noise generation source, and a predetermined filtering process for a signal obtained by the noise observation means. a signal processing means; a secondary sound source means for generating a secondary sound according to a signal resulting from signal processing by the signal processing means; and a secondary sound source means arranged at a point where noise is to be removed;
residual noise observation means for observing residual noise when noise propagated from the noise source and secondary sound as control sound propagated from the secondary sound source are combined and input as residual noise; coefficient updating means for updating the filter coefficients in the signal processing means based on the observed residual noise; a position detection means for detecting position information of the residual noise observation means; and a secondary sound source according to the position information of the residual noise observation means. transfer function processing means for determining a transfer function between the means and the residual noise observation means and providing it to the coefficient updating means; It is characterized in that it uses a transfer function sent from a function processing means.

Further, the transfer function processing means estimates a transfer function based on the position information when the position information of the residual noise observation means is sent, and provides the estimated transfer function to the coefficient updating means. It is characterized by

Further, the transfer function processing means includes a transfer function holding means for holding transfer functions for each position measured in advance at various positions of the residual noise observation means, and position information detected by the position detection means. The present invention is characterized by comprising transfer function updating means for reading a corresponding transfer function from the transfer function holding means and applying it to the coefficient updating means.

[0016]

[Operation] In the noise control system as described above, a residual noise observation means is placed at the point where noise is to be removed, and the noise propagated from the noise source and the secondary sound propagated from the secondary sound source are combined with this. Allow residual noise to be input. The secondary sound is input as a control sound that cancels out the noise. Therefore, the signal processing means performs a predetermined filtering process on the signal obtained by the noise observation means in a direction that reduces the residual noise. Give it to the next sound source means. At this time, the coefficient updating means updates the filter coefficients based on the observation results of the residual noise so that the residual noise becomes smaller. By the way, this update process includes a transfer function between the secondary sound source means and the residual noise observation means, and this transfer function is determined by the position of the residual noise observation means being moved by the position detection means and the transfer function processing means. Then, the filter coefficients are changed accordingly, so the filter coefficients can always be updated optimally.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a block diagram of a first embodiment of a noise control system according to the present invention. Referring to FIG. 1, the noise control system of the first embodiment includes a noise observation section 1 such as a microphone that observes a noise-causing signal at a noise source 50 and converts it into an electrical signal x(n). , noise observation section 1
A signal processing section 2 performs signal processing on the electrical signal x(n) obtained by using an appropriate digital filter, and a secondary sound corresponding to the signal s(n) as a result of signal processing by the signal processing section 2. A secondary sound source unit 3 such as a speaker that generates noise, noise y(n) propagated from the noise generation source 50 and a secondary sound as a control sound propagated from the secondary sound source unit 3 is placed at a point where the noise is to be removed. Based on the residual noise observation unit 4 such as a microphone that converts the sound pressure as residual noise into an electrical signal and outputs it as an output signal e(n), and the output signal e(n) from the residual noise observation unit 4. A coefficient updating unit 5 that updates the filter coefficients of the digital filter in the signal processing unit 2; a position detection unit 6 that detects the position of the residual noise observation unit 4; and a position of the residual noise observation unit 4 detected by the position detection unit 6. A transfer function estimating section 7 is provided which estimates a transfer function between the secondary sound source section 3 and the residual noise observation section 4 based on the equation, and provides the estimated transfer function to the coefficient updating section 5.

As the noise observation unit 1, a sensor that detects sound waves generated from a machine or the like and converts them into electrical signals may be used, or a sensor that detects sound waves generated from a machine or the like and converts them into electrical signals, or a sensor that detects sound waves generated from a machine or the like and converts the sound waves into electrical signals, or a sensor that detects sound waves generated from a machine or the like and converts them into electrical signals, or a sensor that detects sound waves generated from a machine etc. In such a case, the noise observation unit 1 may be one that converts the rotational speed of a motor directly into an electrical signal x(n) that has an electrical frequency, or When noise is generated by the noise, a vibration pickup or the like that converts the vibration into an electric signal x(n) is used as the noise observation unit 1.

Further, the signal processing unit 2 is configured to filter the signal x(n) observed by the noise observation unit 1 so that the sound pressure input to the residual noise observation unit 4 is reduced, and the coefficient The updating section 5 updates the filter coefficients of the signal processing section 2 using, for example, an LMS algorithm, that is, a coefficient updating algorithm using the least square error method.

The position detecting unit 6 also detects the position of the residual noise observing unit 4. For this purpose, for example, it measures the distance from the secondary sound source unit 3, which is the most important position information, and The relative position of the residual noise observation section 4 with respect to the next sound source section 3 is detected. When detecting the position of the residual noise observation unit 4 relative to the secondary sound source unit 3, the position detection unit 6, for example, It has an ultrasonic sensor 10 attached to the observation part 4, and generates a burst wave etc. from the ultrasonic generator 9 at each discrete time and constantly measures the time until it reaches the ultrasonic sensor 10. The distance between the residual noise observation section 4 and the secondary sound source section 3 is calculated from the measured time, and the position of the residual noise observation section 4 is thereby detected.

[0021] Furthermore, the transfer function estimating unit 7 includes a position detecting unit 6
When the position of the residual noise observation section 4 is detected as the distance from the secondary sound source section 3, the transfer function is estimated based on this distance.

Next, the processing operation of the noise control system having such a configuration will be explained. In this first embodiment, based on the position information of the residual noise observation unit 4 detected by the position detection unit 6, the transfer function estimation unit 7 updates the coefficient update unit 5 according to the movement of the residual noise observation unit 4. The transfer function Cj to be used is changed from moment to moment, thereby updating the filter coefficient wi(n) in the signal processing section 2 in a direction that reduces the square error σ(n).

More specifically, before system operation, the residual noise observation section 4 is positioned at the initial position, and the distance between the secondary sound source section 3 and the residual noise observation section 4 at this time is initially set as L0. Then, the transfer function C0 at that position is measured in advance. When the system is in operation, the position detection unit 6 detects the position of the residual noise observation unit 4 at time n as the distance L(n) from the secondary sound source unit 3. In this case, the transfer function estimation unit 7 calculates the transfer function at time n using the following formula based on the initial values L0 and C0 of the distance and transfer function, and the distance L(n) detected by the position detection unit 6. Estimate Cj(n).

[0024]

[Math 4]

[0025] Here, sf is the sampling frequency, vs
is the speed of sound. Equation 4 represents the secondary sound source section 3 and the residual noise observation section 4.
The transfer function Cj(n) is estimated based on the assumption that sound waves are mainly propagated by direct sound between the secondary sound source section 3 and the residual noise observation section 4. When the influence of reflection is not so large, the transfer function C
A sufficiently good approximation of j(n) can be obtained by estimating equation 4. In addition, in Equation 4, the coefficient (L0/L(n)) is
This is determined from the physical fact that the strength of a spherical sound wave is inversely proportional to the distance from the sound source, and d is based on the fact that the delay increases with distance.

When the transfer function estimator 7 estimates the transfer function Cj(n) at time n using Equation 4, the estimated transfer function Cj(n) is sent to the coefficient updater 5. The coefficient update unit 5 updates the filter coefficient wi(n) at time n using Equation 3, that is, using the LMS algorithm.
Cj(n
) is used to update the filter coefficient wi(n).

As described above, in the first embodiment, the coefficient updating process in the coefficient updating section 5 includes the transfer function between the secondary sound source section 3 and the residual noise observation section 4, but the transfer function is fixed as the transfer function. By using the transfer function estimated according to the change in the position of the residual noise observation unit 4, the LMS
By making the algorithm work effectively, the squared error σ(n) of equation 2
The filter coefficient wi(n) can always be optimally updated in the direction that decreases the filter coefficient wi(n).

FIG. 2 is a block diagram of a second embodiment of the noise control system according to the present invention. Note that in FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. In this second embodiment, instead of the transfer function estimation unit 7 of the first embodiment,
A transfer function holding section 11 and a transfer function updating section 12 are provided.

The transfer function holding unit 11 includes a residual noise observation unit 4
The transfer function at each position when the is positioned at various positions is measured in advance and stored.

Further, the transfer function updating section 12 reads the transfer function at the position of the residual noise observation section 4 detected by the position detecting section 6 from the transfer function holding section 11 and provides it to the coefficient updating section 5. .

In such a configuration, before the system starts the noise control operation, that is, the silencing operation, for example, the space where the noise is to be controlled is cut out at appropriate grid intervals, and the residual noise observation unit 4 is installed at each grid point. Then, the transfer function from the secondary sound source section 3 to each residual noise observation section 4 is measured in advance for each residual noise observation section 4. Assuming that the distances from the secondary sound source section 3 to each of the residual noise observation sections 4 are L1, L2,..., Lm, the above measurements determine that each distance is L1, L2,..., Lm, respectively.
The transfer functions C(1), C(2), ..., C(m
) are obtained in advance, and these are stored in the transfer function holding unit 11 as shown in FIG.
Keep it like this.

After that, the system starts the noise control operation, and at time n, the position information of the residual noise observation unit 4 is transmitted from the position detection unit 6 to the transfer function as the distance L(n) from the secondary sound source unit 3, for example. When given to the update unit 12, the transfer function update unit 12 searches which distance is the closest to this distance L(n) among the distances held in the transfer function holding unit 11, A transfer function corresponding to the distance is read from the transfer function holding unit 11. For example, if the distance L(n) sent from the position detection unit 6 is between L1 and L2 and closer to L2, the transfer function C(2) corresponding to L2 is read and the coefficient is updated. Part 5 is given.

[0033] Also, the residual noise observation unit 4 moves and the next time (
n+1), if the position information from the position detection unit 6, that is, the distance L(n+1), becomes closer to L1, for example, the transfer function update unit 12 changes the position information to L1 at the next time (n+1). The corresponding transfer function C(1) is read from the transfer function holding section 11 and given to the coefficient updating section 5.

In the coefficient updating unit 5, the filter coefficient wi(n
) is updated by equation 3, that is, by the LMS algorithm, but at this time, the coefficient update unit 5 uses Cj(n) updated by the transfer function update unit 12 instead of the fixed transfer function Cj. Update filter coefficients wi(n).

In this way, in the second embodiment as well, the residual noise observation section 4 does not use a fixed transfer function.
By using a transfer function that is updated according to a change in the position of , the LMS algorithm can be made to work effectively, and the filter coefficients wi(n) can always be optimally updated in a direction that reduces the squared error of Equation 2.

In each of the embodiments described above, even if the transfer function changes during system operation, the filter coefficient w is always updated in a direction that reduces the output signal e(n). This allows the residual noise observation unit 4 to be placed near the human ear in order to muffle the sound near the human ear.
Even if a person's head moves in accordance with the task and the residual noise observation section 4 moves accordingly, the output signal e(n) will follow the movement and decrease in the direction. Since the filter coefficient wi(n) is updated, it is possible to always form a muffling zone near the ear.

In each of the above-described embodiments, in order to simplify the explanation, there is only one noise source, and the secondary sound source section 3,
Although one residual noise observation section 4 is provided, the present invention can be applied in the same manner even when a plurality of noise generation sources, secondary sound source sections, or residual noise observation sections are provided.

Further, in the position detecting section 6, specifically, it is preferable to use a plurality of ultrasonic generators 9. For example, four ultrasonic generators 9 are used. This number is the minimum number at which the position in the space can be uniquely determined once the distance from each point in the three-dimensional space is determined. Note that if there are three points, the number of positions allowed in space is narrowed down to two, so in practice, three points are often sufficient. Each of the four ultrasonic generators 9 generates ultrasonic waves of different frequencies, and the ultrasonic sensor 10 attached to the residual noise observation section 4 receives these ultrasonic waves. By measuring how long it takes the sound of each frequency to arrive, the distance from each ultrasonic generator 9 to the residual noise observation section 4 can be determined. Since the position is determined when the distance from the four points in the three-dimensional space is determined, the position of the residual noise observation section 4 can be known in this way.

[0039]

[Effects of the Invention] As explained above, according to the present invention,
Even if the coefficient updating process in the coefficient updating means includes a transfer function between the secondary sound source means and the residual noise observation means, the position information of the residual noise observation means is detected and transmitted according to this position information. Since the function is updated, the coefficients can be updated optimally at all times. For example, the residual noise observation means can be attached near a person's ear, and the residual noise observation means can be moved as the person's head moves. Even so, it is possible to always form a silencing zone near the residual noise observation means, that is, the human ears.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a first embodiment of a noise control system according to the present invention.

FIG. 2 is a configuration diagram of a second embodiment of the noise control system according to the present invention.

FIG. 3 is a diagram illustrating an example of a transfer function holding unit.

FIG. 4 is a diagram showing a configuration example of a conventional noise control system.

[Explanation of symbols]

1 Noise Observation Department 2 Signal processing section 3 Secondary sound source section 4 Residual noise observation department 5 Coefficient update section 6 Position detection section 7 Transfer function estimation section 11 Transfer function holding unit 12 Transfer function update section

Claims (3)

[Claims] Claim 1: A noise observation means for observing noise at a noise generation source; a signal processing means for performing a predetermined filtering process on a signal obtained by the noise observation means; A secondary sound source means that generates a secondary sound according to a signal is placed at a point where noise is to be removed, and the noise propagated from the noise source and the secondary sound as a control sound propagated from the secondary sound source are combined. residual noise observation means for observing residual noise when inputting it as residual noise;
coefficient updating means for updating a filter coefficient in the signal processing means based on the residual noise observed by the residual noise observation means; a position detection means for detecting position information of the residual noise observation means; and a position detection means for detecting position information of the residual noise observation means. and transfer function processing means for determining a transfer function between the secondary sound source means and the residual noise observation means and providing it to the coefficient updating means, and the coefficient updating means performs the transfer function necessary for updating the filter coefficients. A noise control system characterized in that a transfer function sent from the transfer function processing means is used as the function. 2. The noise control system according to claim 1, wherein the transfer function processing means estimates the transfer function based on the position information when the position information of the residual noise observation means is sent, and calculates the estimated transfer function. A noise control system characterized in that a function is given to a coefficient updating means. 3. The noise control system according to claim 1, wherein the transfer function processing means includes transfer function holding means for holding transfer functions for each position measured in advance at various positions of the residual noise observation means; 1. A noise control system comprising: transfer function updating means for reading a transfer function corresponding to position information detected by the position detecting means from transfer function holding means and applying it to coefficient updating means.