JPH04263297A - Active noise controller - Google Patents

Abstract

PURPOSE:To reduce noise at an evaluation point even when a residual noise detecting means is provided spatially at a distance from the evaluation point. CONSTITUTION:The active noise controller is equipped with a control sound source which generates a control sound to interfere with the noise, the means 14 which is provided spatially at a distance from the evaluation point where the noise is to be reduced and detects the residual noise, a means 10 which detects a signal regarding the noise generation state of a noise source, and a control means 28 which outputs a signal for driving the control sound source 18 according to the output signal of the residual noise detecting means 14 and the output signal of the noise generation state detecting means 10. The control means 28 estimates the residual noise at the evaluation point according to the detected residual noise and specific ratios between the noise source and control sound source 18, and evaluation point and residual noise detecting means 14 and generates an output based on the signal of the estimated residual noise and the output signal of the noise generation state detecting means 10.

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 actively reducing noise in automobile cabins, aircraft cabins, etc.

0002

2. Description of the Related Art Conventionally, as an active type noise control device of this type, there is, for example, one shown in FIG. 6 of British Patent Publication No. 2149614.

This conventional device is applied to an aircraft cabin or similar closed space, and is equipped with loudspeakers 103a, 103b, 103c and microphones 105a, 105b, 105c, 105d in a closed space 101. Control sounds that interfere with noise are generated by speakers 103a, 103b, and 103c, and residual signals (residual noise) are measured by microphones 105a, 105b, 105c, and 105d. These loudspeakers 103a, 103b, 103c and microphones 105a, 105b, 105c, 105d are connected to a signal processor 107, which uses the fundamental frequency of the noise source measured by the fundamental frequency measuring means and the microphones 105a, 105b. , 105c, 105
loudspeakers 103a, 1 to minimize the sound pressure level in the closed space 101.
It outputs a drive signal to 03b and 103c.

Here, in the closed space 101, three loudspeakers 103a, 103b, 103c and four microphones 105a, 105b, 105c, 105d are provided.
It is assumed that one each of a and 105a is provided. Let the transfer function from the noise source to the microphone 105a be H, and from the loudspeaker 103a to the microphone 105a
Let C be the transfer function up to C, and let Xp be the sound source information signal generated by the noise source, then the residual signal E observed by the microphone 105a is E=Xp.H+Xp.G.C. Here, G is a transfer function necessary for silencing. When the noise is completely canceled at the point to be muted (the position of the microphone 105a), E=0. At this time, G becomes G=-H/C. Usually, this calculation is performed in the frequency domain using fast Fourier transform, and the impulse response is obtained by inverse Fourier transform of the result, and the signal processor 1
07 as the filter coefficient. This filter coefficient is determined by determining G that minimizes the microphone detection signal E, and based on this G, the filter coefficient in the signal processor 107 is adaptively updated. As a method for finding filter coefficients to minimize the microphone detection signal E, the LMS algorithm (Least
Mean Square).

Furthermore, as shown in FIG. 6, when a plurality of microphones are installed, each microphone 105a, 10
Control is performed so that the sum of the signals detected at 5b, 105c, and 105d is minimized. That is, each position of the microphones 105a, 105b, 105c, and 105d is an evaluation point at which noise reduction should be attempted.

[0006]

[Problems to be Solved by the Invention] However, in many cases, it is not possible to place the microphone within the work area of the passenger, such as the driver's seat of a vehicle where many instrument operations are required, and cavity resonance occurs in a closed space room, so it is difficult to locate the microphone and the work position. There may be cases where it is not possible to match the evaluation scores. In other words, even if the evaluation point is set at the passenger's ear position, if the microphone is located spatially away from the passenger's ear position, even if the sound pressure level is controlled to the minimum at the microphone position, the sound pressure level at the passenger's ear position will be The problem is that it does not become the minimum.

Therefore, the present invention makes it possible to reduce noise at the evaluation point even if the evaluation point and the residual noise detection means are located at a spatially distant position.

[0008]

[Means for Solving the Problem] In order to solve the above problem, the invention of claim 1 provides a control sound source that generates control sound that interferes with noise, and a control sound source that is located at a position spatially distant from an evaluation point that aims to reduce noise. means for detecting residual noise, means for detecting a signal related to the noise generation state of the noise source, and driving the control sound source based on the output signal of the residual noise detection means and the output signal of the noise generation state detection means. an active noise control device comprising: a control means for outputting a signal to detect the detected residual noise; The residual noise at the evaluation point is estimated based on a predetermined ratio, and the output is performed based on the estimated residual noise signal and the output signal of the noise generation state detection means.

[0009] The invention according to claim 2 also includes a control sound source that generates a control sound that interferes with noise, and a means for detecting residual noise E that is provided at a position spatially distant from an evaluation point for achieving a low noise range. , means for detecting a signal Xp relating to the noise generation state of the noise source; and control means for outputting a signal for driving the control sound source based on the output signal of the residual noise detection means and the output signal of the noise generation state detection means. An active noise control device comprising: an evaluation point when only the noise source is operated; a sound pressure ratio A between the residual noise detection means; and an evaluation when only the control sound source is operated. Using the previously measured value of the sound pressure ratio B between the point and the residual noise detection means and the transfer characteristic H between the noise source and the residual noise detection means, [E]=(B-A)・H・Xp +A・The present invention is characterized in that the residual noise [E] at the evaluation point is estimated by correcting E, and control is performed so as to reduce JE=Σ[E]2.

0010

[Operation] According to the invention of claim 1, the control means is configured to detect the residual noise at the evaluation point based on the detected residual noise and the predetermined ratio between the noise source, the control sound source, the evaluation point and the residual noise detection means. It is possible to estimate the residual noise and output a signal for driving the control sound source based on the estimated residual noise signal and the output signal of the noise generation state detection means.

According to the second aspect of the invention, the control means determines the evaluation point when only the noise source is operated, the sound pressure ratio A between the residual noise detection means, and the evaluation point when only the control sound source is operated. Using the previously measured value of the sound pressure ratio B between the residual noise detection means and the transfer characteristic H between the noise source and the residual noise detection means, [E]=(B-A)・H・Xp +A・E The residual noise [E] at the evaluation point can be estimated by performing the correction, and control can be performed to reduce JE=Σ[E]2.

0012

[Embodiment] An embodiment of the present invention will be described below. In addition,
The explanation will be given using the interior space of a vehicle as an example.

In FIG. 1, 12 indicates a vehicle, 4 indicates a power plant of the vehicle 12 as a noise source, and 6' indicates a passenger compartment as an acoustic space. The power plant 4 integrally houses an engine, a transmission as a power transmission device, and a differential gear. The vehicle 12 is also equipped with the active noise control device 8 of this embodiment.

The active noise control device 8 includes an engine noise information detection sensor 10 constituting a noise generation state detection means.
Microphones 14a to 14c as residual noise detection means arranged in the vehicle interior 6', a controller 16 installed at a predetermined position in the vehicle 12, and a loudspeaker 18a as a control sound source installed in the vehicle interior 6'. 18b.

The engine noise information detection sensor 10 can be, for example, a vibration sensor or a crank angle signal sensor fixed to the outer surface of the engine. The microphones 14a to 14c are installed at the front, center, and rear positions of the ceiling of the vehicle compartment 6', respectively, and output analog voltage noise signals ea corresponding to the residual noise (sound pressure) at each installation position.
, eb and ec are output respectively. Detection signals from the engine noise information detection sensor 10 and the microphones 14a to 14c are individually supplied to the controller 16.

The loudspeakers 18a and 18b are installed below the front instrument panel of the vehicle interior 6' and behind the rear seat, and receive drive signals output from the controller 16 to listen to the vehicle interior. Control sound (acoustic signal) is output to 6'.

As shown in FIG. 1, the controller 16 includes an amplifier 22 for voltage amplifying the input signal g, and an A/D converter 23 for digitally converting the output signal of the amplifier 22.
, a reference signal extraction means 24 which inputs the conversion output of this A/D converter 23 and extracts only periodic components correlated with the noise frequency as a reference signal xp; and a noise signal ea as input residual noise; Amplifiers 26a to 26c that voltage amplify eb and ec, and amplifiers 26a to 26
c and the reference signal x from the reference signal extraction means 24
A speaker control unit 28 as a control means that generates drive signals ya and yb for noise control based on the noise control unit 28 and power amplifies the drive signals ya and yb from the speaker control unit 28 and outputs them to the loud speakers 18a and 18b, respectively. It is provided with amplifiers 30a and 30b for supplying the power.

The reference signal extraction means 24 constitutes a noise generation state detection means together with the sensor 10, and as shown in FIG. It has a digital filter 36 whose filter coefficients can be updated, and the above-mentioned signal g is branched and inputted, and this input waveform g
a subtracter 40 that calculates a residual signal R by subtracting the output waveform xp of the filter 36 from the subtracter 40; and an adaptive processor 44 that updates the filter coefficients of the digital filter 36 using the residual signal R from the subtracter 40. have. In this embodiment, the adaptive processor 44 changes the filter coefficients of the digital filter 36 so that the square value of the residual signal R is minimized using the LMS algorithm, which will be described later.

As a result, when g is the engine surface vibration waveform, only the periodic component, which is the main cause of interior noise, can be obtained. Further, when g is the detected crank angle pulse, xp may be obtained by directly generating a sine wave having a frequency that is an integral multiple of the pulse interval without using the circuit 24.

On the other hand, as shown in FIG. 2, the speaker control section 28 includes a digital filter 48 which receives the reference signal xp outputted from the reference signal extraction means 24 of FIG.
and an adaptive filter 50, and microphones 14a to 14c.
A/D converters 52a to 52c that input noise signals ea to ec from the A/D converters 52a to 52c;
a microprocessor 54 which inputs the conversion signal obtained by the above conversion signal and the output signal γlm of the digital filter 48, and a D/A converter 5 which D/A converts the processed signals ya, yb of the adaptive filter 50 and outputs the D/A converters to the amplifiers 30a, 30b.
6a and 56b.

Of these, the digital filter 48 inputs the reference signal xp and generates a filtered reference signal γlm (described later) according to a transfer function related to the combination of the microphones 14a to 14c and the speakers 18a, 18b. 4) , (5)) is generated. The adaptive filter 50 has individual filters corresponding to the output channels to the speakers 18a and 18b, receives the reference signal xp, performs adaptive signal processing based on the filter coefficients set at that time, and generates a speaker drive signal. It outputs ya and yb respectively. The microprocessor 54 is
The noise signals ea to ec and the filtered reference signal γlm are input, and the filter coefficients of the adaptive filter 50 are changed using the LMS algorithm.

[0022] Here, the noise control method and reference signal generation method in this embodiment will be explained.

In the above, the residual noise ea to ec is expressed by the difference between the sound pressure caused by the noise source and the sound pressure caused by the additional sound source. Active noise control works to minimize this error, but the detection position of the residual noise ea ~ ec is only the microphone installation part due to the restriction of the mounting position of the microphones 14a ~ 14c, and it is an evaluation point for noise reduction. , for example, cannot be used as a human working position. Therefore, unless the residual noise is corrected in any way, the sound may become louder at the working position of the person, which is disadvantageous, especially when standing waves occur.

The embodiment of the present invention is characterized in that the residual noise is corrected by the calculation procedure described below, and the sound at the working position of the person is controlled to be minimized.

That is, conventionally, the residual noise that is actively controlled at the microphone position is replaced by the residual noise at the working position by the method described below. ” is a technique.

In this case, in order to simplify the explanation, a case of one microphone and one speaker will be described as an example.

(1) By activating only the loudspeaker, the transmission characteristics between the loudspeaker and the microphone and the transmission characteristics between the loudspeaker and the work position (evaluation point) are correlated in the frequency domain.

In FIG. 3, C1(ω) is the transfer characteristic between the loudspeaker 63 and the microphone 64, and C2(ω)
is the transfer characteristic between the loudspeaker 63 and the working position 65, Y1(ω), Y2(ω), and S(ω) are the microphone 64 position, the sound pressure at the working position, and the loudspeaker signal (for example, the driving voltage ) shows the frequency characteristics of In addition, lowercase letters in the figure indicate the same characteristics in each time domain.

[0029]

[Math 1]

In other words, the loudspeaker 63 is
(control sound source) and the work position 65 (evaluation point) is the transfer characteristic C2 (ω) between the loudspeaker 63 (control sound source) and the microphone 64 (residual noise detection means) C1 (ω) and the sound pressure ratio A(ω) (predetermined ratio) between the loudspeaker 63 (control sound source), the operating position (evaluation point), and the microphone 64 (residual noise detection means) position. .

(2) By generating only noise, the transmission characteristics between the noise source and the microphone and the transmission characteristics between the noise source and the work position are correlated in the frequency domain.

In FIG. 4, H1(ω) is the transfer characteristic between the noise source 62 and the microphone 64, H2(ω) is the transfer characteristic between the noise source 62 and the working position 65, Z1(ω),
Z2(ω) and Xp(ω) are the microphone positions, respectively.
Shows the sound pressure at the working position and the frequency characteristics of the sound source information signal. In addition, lowercase letters in the figure indicate the same characteristics in each time domain.

[0033]

[Math 2]

That is, according to equation (2), the transfer characteristic H2 (ω) between the noise source 62 and the work position 65 (evaluation point) is the transfer characteristic H1 between the noise source 62 and the microphone 64 (residual noise detection means). (ω), the noise source 62 and the working position 65 (
evaluation point) and the position of the microphone 64 (residual noise detection means) B(ω) (predetermined ratio).

Here, there is no problem before or after the steps (1) and (2) above.

(3) The relationship between the residual noise at the microphone position and the working position is expressed in the frequency domain.

In FIG. 5, E1(ω) indicates the sound pressure at the microphone position, and E2(ω) indicates the sound pressure at the working position. In addition, lowercase letters in the figure indicate the same characteristics in each time domain.

Since the sound pressure at the microphone position = the sound pressure due to the noise source + the sound pressure due to the loudspeaker, E1 (
ω)=H1(ω)・Xp(ω)+C1(ω)・S(ω)
…■ Similarly, the sound pressure at the working position is E2(ω)=H2(ω)・Xp(ω)+C2(
ω)・S(ω) …■ Substituting the ■formula into the ■formula, C2(ω)=A(ω)・of the ■formula obtained in (1) above
If C1(ω) is used, E2(ω)=H2(ω)・Xp(ω)
+A(ω)・[E1(ω)−H1(ω)・Xp
(ω)] This is also the equation H2(ω)=B(ω)・H1
Substituting (ω), it is expressed as follows.

E2(ω)=B(ω)・H1(ω)・Xp(ω
) +A(ω)・[E1(ω)−H1(ω)
・Xp(ω)] = [A(ω)+B(ω)]
・[H(ω)+Xp(ω)] +A(ω)・
E1(ω) =F(ω)・[H1(ω)・Xp(ω)]
+A(ω)・E1(ω)...■However, F(ω)=B(ω)-A(ω).

That is, E2((ω) is [E
], H1(ω) is the same H, Xp (ω) is the same Xp
, A(ω) corresponds to the same A, and E1(ω) corresponds to the same E, and the sound pressure ratio A, B as a predetermined ratio and the transfer characteristic H between the noise source and the residual noise detection means are using [E
]=(B−A)·H·Xp +A·E is corrected to estimate the residual noise [E] at the evaluation point (work position).

[0041] When this is inversely Fourier transformed and expressed on the time axis, it becomes as follows.

[0042]

[Math 3]

[0043] The uppercase letters in the expression ``■'' and the lowercase letters in the expression ``■'' correspond to each other.

Here, i and j are the number of taps required to express h1, a, or b, respectively (the number of filters necessary to express the transfer characteristic). In actual calculations, f (frequency), h1 (transfer characteristic), and a (sound pressure ratio) are known. Therefore, by calculating the convolution of f and h1 in advance, the calculation of the first term on the right side of equation (2) can be performed at a sufficiently practical speed. That is, f'=
It is sufficient to set f*h1 and calculate e2 = f'*xp +a*e1.

Furthermore, it is necessary that f satisfies causality, and for this purpose, the position of the microphone may be set so that A and B are causal. Specifically, the microphone 6 is connected to the noise source 62 and the loudspeaker 63.
It is effective to set position 4 to a point closer to the work position.

[0046] In the embodiment shown in Fig. 1, a plurality of speakers are used, but in that case, the microphone position should be positioned closer to the noise source and the loudspeaker than the working position, and separate systems should be installed. settings and performs the control described above.

By the above calculation, the residual noise e1 detected at the microphone position can be replaced by e2 at the working position. As a result, the active noise control effect can be maximized without placing a microphone in a local work zone (for example, a work area such as a driver's seat) in a substantially closed space filled with certain constant noises.

Returning to FIGS. 1 and 2 again, we will discuss the case where the device is composed of a plurality of microphones and a plurality of speakers. The noise signal [e] described below means the noise signal at the working position corrected as described above. It is written as [e] to distinguish it from the previous one.

First, the control method carried out by the speaker control section 28 will be explained.

Now, the noise signal corrected from the noise signal detected by the l-th microphone 14a (~14c) by the method described above is calculated as [el (n)] when there is no control sound from the loudspeakers 18a and 18b. The correction value due to the noise signal detected by the l-th microphone 14a (~14c) is [epl(n)], and the transfer function between the m-th loudspeaker 18a (18b) and the l-th evaluation point, that is, the work position ( FIR (finite impulse response) function)
When the j-th term (j=0, 1, 2..., Ic -1) is expressed as a digital filter, the filter coefficient is Clmj
, a reference signal, that is, a sound source information signal xp (n), and a reference signal xp (n) are input to the m-th loudspeaker 18.
i-th (i=0
, 1, 2, ..., IK-1) as Wmi,

[
0051

[Math 4]

##EQU1## holds true. Here, the term with (n) is
Both are sample values at sampling time n, and
L is the number of microphones 14a to 14c (3 in this embodiment)
M is the number of loudspeakers 18a and 18b (2 in this embodiment), IC is the number of taps (filter order) of the transfer function Clm expressed by the FIR digital filter, and IK
is the number of taps (filter order) of the adaptive filter 50.

In the above formula (1), “Σ Wmi・
xp (n-j-i)'' (=ym) is the filter (coefficient Wm
) represents the output when the signal xp is input to
The term Clmj . represents the signal when reaching the L-th evaluation point via the transfer function Clm, and further,
“Σ Σ Clmj ・{Σ Wmi・xp (
Since the entire right side of ``n-j-i)'' is the sum of the signals arriving at the l-th evaluation point for all speakers,
represents the sum of secondary sounds that reach the th evaluation point.

Although it has been described here that the evaluation point is set one by one for the l-th microphone, it may be set at one specific point, or it may be set at a point close to each microphone.

Next, the evaluation function (variable to be minimized) J
e,

[0056]

[Math 5]

[0057] That is, it corresponds to JE=Σ[E]2 in the frequency domain of claim 2.

In order to find the filter coefficient Wm that minimizes the evaluation function Je, this embodiment employs the LMS algorithm. That is, the filter coefficient Wmi is updated with a value obtained by partially differentiating the evaluation function Je with respect to each filter coefficient Wmi.

[0059] Therefore, from equation (2),

[0060]

[Math 6]

From equation (1),

[0062]

[Math 7]

Therefore, the right side of this equation (4) is rlm
(ni), the filter coefficient rewriting formula can be obtained from the following formula (5).

[0064]

[Math. 8]

Here, α is a convergence coefficient, and is involved in the speed at which the filter optimally converges and the stability at that time.

[0066] By doing this, for example, one microphone can be installed at a predetermined location in the interior of an automobile, and this microphone can be used to reduce noise at the spatially distant ear positions of the occupants. Therefore, the number of microphones can be significantly reduced, and costs can be significantly reduced.

[0067] In the above-described embodiment, the ear position was calculated using one predetermined point, but the ear position can also be estimated by detecting the seat slide position or the angle of the backrest.

[0068] Furthermore, the driver's condition is imaged by a camera,
Ear positions can also be calculated by image analysis.

Further, in this embodiment, the sound pressure ratio and transfer function were calculated for the ear position of one passenger, but it is of course possible to perform the calculation for multiple people.

[0070]

As is clear from the above, according to the configuration of the present invention, even if the residual noise detection means is provided at a position spatially distant from the evaluation point where noise reduction is to be performed, the noise reduction at the evaluation point can be achieved. can be reliably achieved. This is particularly effective when controlling high-frequency noise that has short wavelengths and large local sound pressure changes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram according to an embodiment of the present invention.

FIG. 2 is a block diagram of main parts according to this embodiment.

FIG. 3 is a perspective view showing in block form the main parts according to an embodiment of the present invention.

FIG. 4 is a perspective view showing in block form the main parts according to an embodiment of the present invention.

FIG. 5 is a block diagram showing main parts according to an embodiment of the present invention.

FIG. 6 is a block diagram according to a conventional example.

[Explanation of symbols]

8 Active noise control device 10 Engine noise information detection sensor (noise generation state detection means) 14 Microphone (residual noise detection means) 18 Loudspeaker (control sound source) 24 Reference signal detection means (noise generation state detection means) 2
8 Speaker control section (control means)

Claims (2)

[Claims] 1. A control sound source that generates a control sound that interferes with noise, a means for detecting residual noise that is provided at a position spatially distant from an evaluation point for noise reduction, and a signal regarding the noise generation state of the noise source. and a control means for outputting a signal for driving the control sound source based on the output signal of the residual noise detection means and the output signal of the noise generation state detection means. The control means estimates the residual noise at the evaluation point based on the detected residual noise and a predetermined ratio between the noise source and the control sound source and the evaluation point and the residual noise detection means, An active noise control device characterized in that the output is performed based on the estimated residual noise signal and the output signal of the noise generation state detection means. 2. A control sound source that generates a control sound that interferes with noise, a means for detecting residual noise E that is provided at a position spatially distant from an evaluation point for achieving a low noise range, and a noise generation state of the noise source. and a control means for outputting a drive signal for driving the control sound source based on the output signal of the residual noise detection means and the output signal of the noise generation state detection means. The control device includes an evaluation point when only the noise source is operated, a sound pressure ratio A between the residual noise detection means, an evaluation point when only the control sound source is operated, and the residual noise detection means. [E]=(
An active type characterized in that the residual noise [E] at the evaluation point is estimated by correcting B-A)・H・Xp +A・E, and control is performed to reduce JE=Σ[E]2 Noise control device.