JPH0588685A - Electronic sound elimination system - Google Patents

Abstract

PURPOSE:To provide the stand-alone type electronic sound elimination system which can follow up large variation in the noise level in an air duct and has high performance. CONSTITUTION:A sound wave which is opposite in phase and equal in sound pressure to a sound wave propagated in the air duct 1 from a noise source is generated and the operation of sound wave interference is utilized to positively eliminate the propagated sound wave by this electronic sound elimination system. In this system, an input level adjusting circuit 61 which adjusts the level of the input signal from a sensor microphone 2 and an output level adjusting circuit 63 which adjusts the level of the driving signal outputted by a controller 6 to a speaker 3 are added, and the level adjusting circuits 61 and 63 are automatically controlled by a level control circuit 64. Namely, the level control circuit 64 controls the input level adjusting circuit 61 according to the input signal from the sensor microphone 2 so that the input signal to the controller 6 is optimized and also controls the output level adjusting circuit 63 corresponding to the level adjustment of the input level adjusting circuit 61. Consequently, even when the noise level greatly varies, the input level to the controller 6 is optimized to obtain desired sound elimination effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic silencing system, and more particularly to an electronic silencing system that actively silences a propagating sound wave propagating in an air duct by sound wave interference.

[0002]

2. Description of the Related Art An electronic noise suppression system called active noise control is used in which noise propagating in a ventilation path is silenced by adding sound waves of opposite phase and same amplitude. FIG. 2 is a block diagram showing an example of a conventional electronic silencing system. This electronic silencing system includes a sensor microphone 2 for detecting noise information in the air duct 1, a speaker 3 for canceling a propagating sound wave in the air duct 1, an error microphone 4 for detecting an error after canceling the propagating sound wave, The controller 5 is configured to generate a drive signal to be given to the speaker 3.

The controller 5 includes amplifiers 11, 12, 1
3, A / D converters 21 and 22, a D / A converter 23, an adder 31, digital filters 41, 42 and 43, and an arithmetic circuit 51. The noise signal indicating the noise detected by the sensor microphone 2 is sent to the amplifier 11, A /
It is added to the adder 31 via the D converter 21. The output signal from the digital filter 41 is added to the other input of the adder 31, and the adder 31 adds these input signals and outputs the added signal x (n) to the digital filters 42 and 43. Output. The digital filter 41 is for canceling the acoustic feedback given to the sensor microphone 2 by the sound wave from the speaker 3.

By the way, the digital filter 42 can be realized by an FIR filter having variable tap weights (filter coefficients) and an adaptive algorithm for controlling the FIR filter. The adaptive algorithm is the input x (n) and the error microphone 4. From the information of the error output e (n) input via the amplifier 13 and the A / D converter 22, the energy of the error output e (n) is minimized under some evaluation criteria. Adjust the filter coefficient of.

Next, a method for setting the filter coefficient of the digital filter 42 to the optimum value will be described. The output y (n) of the digital filter 42 is given by the convolution of the input x (n) and the filter coefficient w _i . The error output e (n) can be expressed as Can be expressed as In the equation (2), r (n) is a reference signal filtered by the digital filter 43 showing the transmission characteristic from the speaker 3 to the error sensor 4, Is.

[0006] The following vector representation for the sake of simplicity, R = [r (n) , r (n-1), ... r (n-I + 1)] T W = [w O, w 1, ... w I- ₁ ] ^T , the above equation (2) can be expressed by the following equation: e (n) = d (n) + ^RT · W (4)

Here, the mean square error (MSE: mean-squ)
are error) E [e (n) ² ], J = E [e (n) ² ] = E [d (n) ² ] + 2W ^T E [R ^T d (n) ] + W ^T E [R ^T R] W (5), and MSE becomes a quadratic function of the filter coefficient. The second derivative is the first, and if the derivative is set to 0, the minimum value J
A solution with _min is obtained.

Now, it is a steepest descent algorithm.
In the Filtered-xLSM algorithm, the estimated amount of MSE J
Instantaneous squared error e (n) as²By using itself, the introduction of J
Estimate of number (gradient ∇) ∇_nIs given byFound by ∇_nWith the adaptive digital filter
The filter coefficient of ilta is recursively updated by
Go W_{n + 1}= W_n+ Μ (-∇_n) = W_n-2 μR_n ^Te (n) (7) where μ is a positive scalar and is corrected in each iteration.
It is a parameter that controls the size of the quantity. In particular, the value of μ
Adjustable convergence speed and stability by making variable
Yes, this is VS-LMS (Variable Step-Least Mean
 Square) algorithm, which is also used in the present invention.
There is. Equation (7) above is the gradient vector (∇ _n) Opposite direction
Sequentially (in the direction of the steepest descent of the error surface)
It means updating, and if you continue this, finally MSE
Is the minimum value J_minAnd the filter coefficient has an optimum value.
Becomes

In FIG. 2, the arithmetic circuit 51 includes a reference signal r (n) added from the digital filter 43.
And the error microphone 4 to the amplifier 13 and the A / D converter 22.
From the error signal e (n) added via
The filter coefficient W (z) is calculated based on the equation, and the filter coefficient W (z) of the digital filter 42 is updated with this filter coefficient W (z).

The digital filter 42 receives the input signal x (n)
And a given filter coefficient W (z) are convolved to output a driving signal y (n) of the speaker 3, which driving signal y (n) is passed through the D / A converter 23 and the amplifier 12. It is added to the speaker 3.

[0011]

By the way, in the above-mentioned electronic muffling system, in order to maximize the muffling volume, the noise level in the air duct 1 is measured in advance by using a voltage measuring device such as an oscilloscope at the time of test operation, The amplifiers 11, 12, and 13 of the controller 5 adjust the gain, and the controller 5
The input level to and the output level from the controller 5 are optimized. The gains of the amplifiers 11, 12, and 13 are fixed after being adjusted during the test run.

However, the normal electronic silencing system is
In many cases, they are installed in series, and when the upstream electronic muffling system fails, the noise level in the air duct rises, so the input level of the downstream electronic muffling system controller is the optimum value. However, there was a drawback that the volume of sound disappeared. In addition, there is a problem that auxiliary equipment such as an oscilloscope is required at the time of test operation, and a specialized engineer is required to manage the controller input level.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a higher performance stand-alone type electronic silencing system capable of following a large change in the noise level in the air duct. And

[0014]

In order to achieve the above-mentioned object, the present invention generates a sound wave having the same sound pressure and a phase opposite to that of a sound wave propagating from a noise source propagating in an air duct, thereby causing sound wave interference. In the electronic silencing system that actively silences the propagating sound wave by utilizing the action of, the sensor microphone that detects the propagating sound wave from the noise source propagating in the air passage and the sound wave that cancels the propagating sound wave are emitted. Based on input signals from the sensor microphone and the error microphone, the speaker having the speaker microphone, the error microphone arranged downstream of the speaker for detecting a sound wave propagated from the speaker and the noise source, and the digital filter. A controller that creates a drive signal to be given to the speaker so that the input signal from the error microphone is minimized, and the sensor microphone that is input to the controller Input level adjusting means for adjusting the level of the input signal, output level adjusting means for adjusting the level of the drive signal output from the controller to the speaker, and to the controller based on the input signal from the sensor microphone. And a level control means for controlling the output level adjusting means in response to the level adjustment by the input level adjusting means.

[0015]

According to the present invention, the input level adjusting means for adjusting the level of the input signal from the sensor microphone and the output level adjusting means for adjusting the level of the drive signal to the speaker output from the controller are provided with the conventional electronic silencer. In addition to the system, these level adjusting means are automatically controlled by the level control means. That is, the level control means controls the input level adjusting means based on the input signal from the sensor microphone so that the input signal to the controller becomes optimum, and corresponds to the level adjustment by the input level adjusting means. The output level adjusting means is controlled. As a result, the input level to the controller is optimized even if the noise level in the air passage changes significantly, and the desired noise reduction effect is obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an electronic silencing system according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of an electronic silencing system according to the present invention. The same parts as those of the electronic silencing system shown in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 1, the electronic silencing system includes an input level adjusting circuit 6 in a controller 6.
1, 62, an output level adjusting circuit 63, and a level control circuit 64 are added, which is a difference from the electronic silence system of FIG. The input level adjusting circuit 61 is arranged between the amplifier 11 and the A / D converter 21, and the input voltage input from the sensor microphone 2 via the amplifier 11 is 6d.
It is configured to be variable up to 30 dB in B step. Similarly, the input level adjusting circuit 62 is arranged between the amplifier 13 and the A / D converter 22, and the input voltage input from the error microphone 4 via the amplifier 13 is up to 30 dB in 6 dB steps. It is configured to be variable. Further, the output level adjusting circuit 63
The output voltage, which is arranged between the D / A converter 23 and the amplifier 12, is output from the digital filter 42 via the D / A converter 23 by a maximum of 30d in 6dB steps.
It is configured to be variable up to B.

The output voltage of the input level adjusting circuit 61 is applied to the level control circuit 64, and the level control circuit 64 sets the voltage level to an optimum value for performing digital processing in the subsequent stage. Input level adjustment circuit 6
Control level adjustment at 1. That is, the level control circuit 6
4 obtains the average value of the input voltage level for a certain period of time, and when this average value becomes 6 dB or more larger than the preset optimum level, the input level adjusting circuit 61
The output voltage from is controlled by 6dB, and conversely,
When the average value obtained as described above becomes 6 dB or more smaller than the preset optimum level, the output voltage from the input level adjusting circuit 61 is controlled to increase by 6 dB.

Further, the level control circuit 64 controls the input level adjusting circuit 61 to decrease or increase the output voltage from the input level adjusting circuit 61 by 6 dB, and at the same time outputs the output voltage from the other input level adjusting circuit 62. The input level adjusting circuit 62 is controlled to decrease or increase by 6 dB, and the output level adjusting circuit 63 is controlled to increase or decrease the output voltage from the output level adjusting circuit 63 by 6 dB. That is, the output level adjusting circuit 63 is the input level adjusting circuit 6
Contrary to 1, 62, when these output voltages are controlled to decrease by 6 dB, they are controlled to increase by 6 dB,
When the output voltage of the input level adjusting circuits 61 and 62 is controlled to increase by 6 dB, it is controlled to decrease by 6 dB.

In this way, the input level adjusting circuits 61, 6
By controlling the output level adjusting circuit 63 and the output level adjusting circuit 63, the input levels of the A / D converters 21 and 22 of the controller 6 can always be set to optimum values, and the output level of the D / A converter 23 can be set. Can be set to an optimum value, and even if the noise level in the air duct changes significantly, the effect is that the mute level does not deteriorate.

In this embodiment, the level adjusting circuit is changed every 6 dB steps, but it has been confirmed by experiments that the mute volume does not deteriorate within this range.
Further, although the input level adjusting circuit 62 is provided in the present embodiment, it may be omitted. Further, the amount of change in the noise level in the air duct is determined by the average value for a certain fixed time, but the same effect can be obtained by controlling using the instantaneous amount of change such as the peak value. it can.

[0022]

As described above, according to the electronic muffling system of the present invention, the controller input voltage and output voltage can be automatically optimized even if the noise level in the air duct changes significantly, and therefore, it is always possible. You can expect the optimum muffling. In addition, since auxiliary equipment such as an oscilloscope is not required and a specialized technician is not required, the adjustment at the time of test operation can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an electronic silencing system according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional electronic silencing system.

[Explanation of symbols]

 1 ... Blower 2 ... Sensor microphone 3 ... Speaker 4 ... Error microphone 6 ... Controller 11, 12, 13 ... Amplifier 21, 22 ... A / D converter 23 ... D / A converter 41, 42, 42 ... Digital filter 51 ... arithmetic circuit 61, 62 ... input level adjusting circuit 63 ... output level adjusting circuit 64 ... level control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Matsuda 1-1-14 Kanda Uchida, Chiyoda-ku, Tokyo Within Hirit Plant Construction Co., Ltd. Company Koganei factory

Claims (2)

[Claims] 1. A sound wave having the same sound pressure and a phase opposite to that of a sound wave propagating from a noise source propagating in the air duct is generated, and the sound wave interference is actively silenced by utilizing the action of sound wave interference. In the electronic silencing system, a sensor microphone that detects a sound wave propagating from a noise source propagating in the air passage, a speaker that emits a sound wave for canceling the sound wave, and is disposed on the downstream side of the speaker, An error microphone that detects a sound wave propagating from a speaker and the noise source, and a digital filter, and the speaker is configured to minimize the input signal from the error microphone based on the input signals from the sensor microphone and the error microphone. A controller that creates a drive signal to be given, and a first input level that adjusts the level of the input signal from the sensor microphone input to the controller. Adjusting means, output level adjusting means for adjusting the level of the drive signal to the speaker output from the controller, and the first input signal to the controller based on the detection signal from the sensor microphone so as to optimize the input signal to the controller. An electronic silencer, comprising: a level control means for controlling the first input level adjusting means and for controlling the output level adjusting means in response to the level adjustment by the first input level adjusting means. system. 2. A second input level adjusting means for adjusting the level of an input signal from the error microphone input to the controller, wherein the level control means adjusts the level of the first input level adjusting means. Corresponding to the second
The electronic silencing system according to claim 1, wherein the input level adjusting means is controlled.