JP2886397B2 - Active noise control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise control device for eliminating noise generated in a duct or other conduit.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a configuration of a conventional active noise control device disclosed in, for example, JP-A-3-36897 and JP-A-2-70195.

In FIG. 3, reference numeral 1 denotes noise from a noise source;
Is a duct for ventilation, and 3 is a control unit composed of components 10 to 17. Reference numeral 4 denotes a microphone (hereinafter abbreviated as a microphone) that detects noise 1 propagating from the upstream side to the downstream side in the duct 2 and converts the noise into an electric signal. Purse,
Reference numeral 6 denotes a noise cancellation confirmation microphone for confirming that noise 1 has been eliminated, reference numeral 7 denotes a microphone amplifier for increasing the output of the noise cancellation confirmation microphone 6, and reference numeral 8 denotes a duct in the propagation direction of the noise 1. The microphone 2 is installed between the microphone 4 installed on the upstream side and the noise cancellation confirmation microphone 6 installed on the downstream side of the microphone 2, and has a phase opposite to that of the noise 1 propagating in the duct 2 and having the same sound pressure. The secondary speaker 9 to be generated is a secondary speaker driving amplifier connected to the secondary speaker 8.

Next, the configuration inside the control unit 3 will be described.
Reference numeral 10 denotes an A / D converter that converts an analog output signal of the microphone amplifier 5 into a digital signal. Reference numeral 11 denotes a howling prevention digital filter that outputs a howling prevention signal.
Reference numeral 2 denotes a subtractor that takes the difference between the output of the A / D converter 10 and the output of the howling prevention digital filter 11.

Reference numeral 13 denotes an adaptive digital filter which outputs a signal such that the output of the noise cancellation confirmation microphone 6 becomes minimum (silence) based on a transfer function given by inputting the output of the subtracter 12, and 14 A digital filter for delay which receives an output of the subtractor 12 as an input, and 15 is a digital filter 14
And an output signal of an A / D converter 16 for converting an analog output signal of the microphone amplifier 7 into a digital signal, and outputting data for updating a coefficient of the adaptive digital filter 13. A filter coefficient updating unit 17 converts the digital output signal of the adaptive digital filter 13 into an analog signal and supplies the analog signal to the secondary speaker 8 via the secondary speaker driving amplifier 9. The output of the adaptive digital filter 13 is input to the digital filter 11 for howling prevention.

Next, the operation will be described. The noise 1 passing through the duct 2 is detected by the microphone 4 and converted into an electric signal. This electric signal is amplified by the microphone amplifier 5 and input to the control unit 3. On the other hand, on the downstream side, the sound at the site is detected by the noise cancellation confirmation microphone 6 and converted into an electric signal. This electric signal is amplified by the microphone amplifier 7 and input to the control unit 3.

The control unit 3 converts the drive signal based on the two input signals so that the output through the noise cancellation confirmation microphone 6 and the microphone amplifier 7 is minimized, that is, the noise 1 is minimized. Generate. This drive signal is amplified by the secondary speaker driving amplifier 9 and supplied to the secondary speaker 8. As a result, the secondary speaker 8 generates a sound having the same sound pressure in the opposite phase to the noise 1 in the duct 2 and causes the noise to interfere with the noise 1.
Acts to mute the sound. Due to the canceling interference action, the noise 1 becomes extremely low downstream of the noise cancellation confirmation microphone 6.

Next, a more detailed operation of the control unit 3 will be described. A system identification is performed from the secondary speaker driving amplifier 9 through the secondary speaker 8, through the duct 2, to the noise cancellation confirmation microphone 6 and the microphone amplifier 7. The digital filter 14 has been replaced.

Similarly, the microphone 4 is passed from the secondary speaker driving amplifier 9 through the secondary speaker 8 and the inside of the duct 2.
, The system identification up to the microphone amplifier 5 is performed, and this is replaced by a digital filter 11 for howling prevention as a transfer function Hr. These digital filters 1
Each of the digital filters 1 and 14 functions as a fixed filter. In particular, the howling preventing digital filter 11 functions to prevent howling between the microphone 4 and the secondary speaker 8.

The noise 1 is detected by the microphone 4 and converted into an electric signal. This electric signal is amplified by a microphone amplifier 5, further converted into a digital signal by an A / D converter 10, input to a subtractor 12, and output from a howling prevention digital filter 11, and a howling prevention signal. And the difference is taken. The output signal of the subtractor 12 passes through the digital filter 14 and is incorporated in a coefficient updating algorithm for specifying the transfer function C by the adaptive filter coefficient updating unit 15. As a result, the adaptive filter coefficient update unit 15 determines the coefficient for specifying the transfer function to be applied to the adaptive digital filter 13 based on the coefficient update algorithm so that the input signal from the noise cancellation confirmation microphone 6 is minimized. Is determined, and the coefficient of the adaptive digital filter 13 is updated according to the change in the propagation characteristic of the propagation path and the change in the characteristic of the control system.

On the other hand, the adaptive digital filter 13 converts the input signal output from the subtractor 12 into a drive signal having predetermined amplitude and phase characteristics based on a transfer function based on given coefficients. The drive signal of the adaptive digital filter 13 is converted into an analog signal by a D / A converter 17 and radiated from the secondary speaker 8 into the duct 2 through the secondary speaker drive amplifier 9 as a sound-absorbing sound wave. You.

At the same time, the adaptive digital filter 13
Is output from the digital filter 11 for howling prevention.
To the subtractor 12 as a signal for preventing howling. As described above, the coefficient of the adaptive digital filter 13 is updated in accordance with the change in the propagation characteristics of the propagation region and the change in the characteristics of the control system. It is possible to follow a change in characteristics of the microphone 6 and a change in propagation characteristics due to a change in temperature in the duct 2.

[0013]

Since the conventional active noise control device is constructed as described above, the transfer function at the time of system identification from the secondary speaker driving amplifier 9 to the microphone amplifier 5 is used. Hr and the transfer function C for system identification from the secondary speaker driving amplifier 9 to the microphone amplifier 7
However, although the digital filters 11 and 14 are fixed filters, the digital filters 11 and 14 cannot follow the change despite the change due to the change in the propagation characteristic due to the temperature change in the duct 2. There were problems such as stability.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is possible to prevent the occurrence of howling by causing a transfer function at the time of system identification to follow a temperature change in a noise propagation space, An object of the present invention is to obtain an active noise control device capable of stabilizing a system.

[0015]

An active noise control device according to the present invention is installed in a pipeline, and is arranged from an upstream side to a downstream side thereof.
Detects noise propagating toward the side and converts it into an electrical signal
Noise detecting microphone, and the noise detecting microphone
Installed on the downstream side of the pipeline with respect to
Noise cancellation confirmation microphone to confirm that noise has been erased
Microphone, the microphone for noise detection and the noise
Installed between the erasure confirmation microphone and the
The same phase and the same sound pressure as the noise propagating in the pipe
And a noise detection microphone.
The first to convert the analog output signal of
A / D converter and the noise cancellation confirmation microphone
A to convert the analog output signal of
/ D converter and how to output howling prevention signal
A digital filter for preventing ringing, and the first A / D converter;
Of the converter and the howling prevention digital filter
A subtractor that takes the difference between the outputs,
Based on the given transfer function, the noise cancellation confirmation
Suitable for outputting a signal that minimizes the output of the
Input of the adaptive digital filter and the output of the subtractor
A digital filter for delay,
Filter output signal and the output signal of the second A / D converter.
Update the coefficients of the adaptive digital filter based on
An adaptive filter coefficient updating unit for outputting data;
The digital output signal of the adaptive digital filter
D / A converter for converting the signal into
An active noise control device comprising:
Prevention digital filter and delay digital filter
Adaptive howling prevention with variable coefficients instead of data
Filter for adaptive delay and digital filter for adaptive delay
Between the noise detection microphone and a secondary speaker.
A temperature sensor that detects the temperature in the pipeline, and at the time of system identification
According to the temperature detected by the temperature sensor.
The adaptive howli by shifting on the
And digital filter for adaptive delay
Transfer function to update the coefficients of the
And a troll unit .

[0016]

According to the active noise control apparatus of the present invention, when there is a temperature change at the time of system identification, the propagation characteristic of the propagation region changes, and the coefficient of the transfer function of the adaptive digital filter is changed by following the change. Is shifted to the lower tap side when the temperature changes to the higher side, and shifted to the higher tap side when the temperature changes to the lower side, and its transfer function is adapted to the temperature change.

[0017]

【Example】

Embodiment 1 FIG. In FIG. 1, the same or corresponding parts as those of the conventional example are denoted by the same reference numerals 1 to 10, 12, 15 to 17, and the description thereof is omitted, and 11a and 14a are adaptive digital filters whose coefficients can be changed respectively. The adaptive digital filter 11a for preventing howling is connected between the output terminal of the adaptive digital filter 13 and the (−) side input terminal of the subtractor 12, and the adaptive digital filter 14a is connected to the output terminal of the subtractor 12 It is connected between the input terminals of the pattern filter coefficient updating unit 15.

Reference numeral 18 denotes a temperature sensor installed between the microphone 4 and the speaker 8 for detecting the temperature in the duct 2 and outputting a signal corresponding to the temperature. Reference numeral 19 denotes an amplifier for increasing the output of the temperature sensor 18. The amplifier 20 receives the temperature signal output from the amplifier 19 and updates the transfer functions Hr and C in accordance with the temperature signal, that is, in accordance with the detected temperature in the duct 2. This is a transfer function control unit that updates the coefficients of the adaptive digital filters 11a and 14a.

Next, the operation of the first embodiment will be described with reference to FIG. Adaptive digital filters 11a and 14a operate in place of the digital filters 11 and 14 shown in FIG. 3, respectively, and the basic operation for silencing is the same as in the conventional example. The temperature in the duct 2 (passage of the noise 1) between the microphone 4 and the speaker 8 is detected by the temperature sensor 18 and converted into a temperature signal. This temperature signal is amplified by the amplifier 19 and input to the transfer function control unit 20.

The transfer function control unit 20 provides a transfer function for system identification from the secondary speaker driving amplifier 9 to the microphone amplifier 7 according to the temperature represented by the input temperature signal at the time of system identification. C and the transfer function Hr at the time of system identification from the secondary speaker driving amplifier 9 to the microphone amplifier 5 is updated, and the adaptive digital filter 14a (corresponding to the transfer function C) is updated so as to have the updated transfer function. ) And 11a (corresponding to the transfer function Hr) are updated by the temperature sensor 18 according to the temperature change detected at the time of system identification.

The adaptive digital filter 11a provides an appropriate howling prevention signal to the subtracter 12 by making the transfer function Hr appropriate for the temperature change even when the temperature in the duct 2 changes. Output to prevent howling. Further, even if the temperature in the duct 2 changes, the adaptive digital filter 14a makes the coefficient of the adaptive digital filter 13 appropriate by making the transfer function C appropriate for the temperature change. Stabilize the system.

Next, a more detailed operation example of the coefficient update will be described. The temperature in the duct 2 at the time when the identification of each system is performed is sensed by the temperature sensor 18. A temperature signal corresponding to this temperature is output from the temperature sensor 18, amplified by the amplifier 19 and input to the transfer function control unit 20, where it is stored as T ₀ ° C.

When the temperature in the duct 2 at the time of system identification changes from T ₀ ° C to T _A ° C during the operation of the active noise control device, the noise propagation space characteristic in the duct 2 changes and follows the change. To this end, the transfer function control unit 20 calculates the following equation. S = (331.5 + 0.61 × T ₀ ) / (331.5 + 0.61 × T _A ) Transfer coefficients Hr and C of the adaptive digital filters 11 a and 14 a are calculated by the transfer function by the ratio of S. The controller unit 20 shifts on the tap number. The coefficient at the N-th tap at the time of the previous system identification is shifted to the [N × S] tap at the time of the current system identification.

For example, when T ₀ = 0 ° C. and T _A = 50 ° C., S = (331.5 + 0.61 × 0) / (331.5 + 0.61 × 50) = 0.92 Therefore, at the tenth tap, The coefficient is 9 at 10 × 0.92 ≒ 9
Shift to the tap, and the coefficient at the 20th tap is 20 × 0.
The coefficient shifts to the 18th tap when 92 ≒ 18, and the coefficient at the 100th tap shifts to the 92nd tap when 100 × 0.92 = 92.

FIG. 2 shows a shift state of the transfer function coefficient with respect to the tap length when the temperature changes from T ₀ = 0 ° C. to T _A = 50 ° C. In FIG. 2, the horizontal axis represents the tap length, the vertical axis represents the transfer coefficient, the upper curve represents the impulse response of the transfer function C or Hr when T ₀ = 0 ° C., and the lower curve changes to T _A = 50 ° C. Transfer function C or H
This shows the impulse response of r. As can be understood from a comparison between the two, the curve at 50 ° C. is shifted to the shorter tap length as compared to 0 ° C.

[0026]

As described above, according to the present invention, the active noise control apparatus has the adaptive digital filter to which the transfer function at the time of system identification is applied, and the temperature at the time of system identification in the noise path is obtained. Since the configuration is such that the coefficient of the adaptive digital filter is updated in accordance with the change, it is possible to prevent howling and to improve the stability of the system.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an active noise control device according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a shift state of a transfer coefficient according to an embodiment of the present invention.

FIG. 3 is a configuration diagram showing a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Noise 3 Control part 4 Microphone 5 Microphone amplifier 6 Microphone for noise cancellation confirmation 7 Microphone amplifier 8 Secondary speaker 9 Secondary speaker drive amplifier 10 A / D converter 11a Adaptive digital filter for howling prevention Reference Signs List 12 subtracter 13 adaptive digital filter 14a adaptive digital filter 15 adaptive filter coefficient update unit 16 A / D converter 17 D / A converter 18 temperature sensor 19 amplifier 20 transfer function control unit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G10K 11/178 F16L 55/04

Claims (1)

(57) [Claims] Claims: 1. Installed in a pipeline, from upstream to downstream
Detects noise propagating toward the side and converts it into an electrical signal
A noise detection microphone, and a lower part of the conduit with respect to the noise detection microphone.
Installed on the upstream side to confirm that noise has been eliminated
A noise cancellation confirmation microphone, the noise detection microphone, and the noise cancellation confirmation microphone.
Installed between the microphone and the microphone
A second phase generating a sound having the same sound pressure in the opposite phase as the noise in the pipe;
And the analog output signal of the noise detection microphone
A first A / D converter for converting into a digital signal, and an analog output signal of the noise cancellation confirmation microphone
A / D converter for converting the signal into a digital signal, and a howling preventing data for outputting a howling preventing signal.
A digital filter, the output of the first A / D converter, and the howling prevention
A subtractor for taking the difference between the output of the digital filter, based on the transfer function given by an output of said subtractor
And the output of the noise cancellation confirmation microphone is minimum.
An adaptive digital filter that outputs a signal as follows, and a delay digital filter that receives an output of the subtractor as an input
When the output signal of the digital filter for the delay and the second A
Based on the output signal of the A / D converter.
Adaptive filter that outputs data to update filter coefficients
A coefficient updating section, and an analog output section of the adaptive digital filter.
D / A conversion to be converted to a log signal and given to the secondary speaker
In active noise control system that includes a changer, digital filter for feedback prevention and for the delay
Adaptive type that can change coefficient instead of digital filter
Digital filter for howling prevention and data for adaptive delay
Digital filter, and a conduit between the noise detection microphone and a secondary speaker
And temperature sensor for detecting the temperature of the inner temperature detected by the temperature sensor at the time of system identification
By shifting on the tap number, depending on
The adaptive type howling prevention digital filter and the adaptive
Update each coefficient of adaptive delay digital filter
Active noise control apparatus characterized by further comprising a transfer function control unit that.