JPH04367897

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DESCRIPTION JPH04367897
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
active noise control apparatus for actively reducing noises of a cabin of an automobile, a cabin of
an aircraft and the like.
[0002]
2. Description of the Related Art Heretofore, as an active noise control apparatus of this type, for
example, there is one as shown in FIG. 8 described in JP-A-59-114597.
[0003]
This conventional device is applied to a passenger compartment of an aircraft or a similar closed
space, and is provided with loudspeakers 101a and 101b and microphones 103a and 103b in
the closed space, and noises are generated by the loudspeakers 101a and 101b. A control sound
to be interfered is generated, and the residual signal (residual noise) is measured by the
microphones 103a and 103b.
The loudspeakers 101a and 101b and the microphones 103a and 103b are connected to the
signal processor 105. The signal processor 105 measures the fundamental frequency of the
noise source measured by the fundamental frequency measuring means (not shown) and the
input signal from the microphones 103a and 103b. And to output a drive signal to the
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loudspeakers 101a and 101b so as to minimize the sound pressure level in the closed space.
[0004]
Here, two loudspeakers 101a and 101b and microphones 103a and 103b are provided in the
closed space, but for simplifying the explanation, one each of 101a and 103a is provided. It is
assumed that Assuming now that the transfer function from the noise source to the microphone
103a is H, the transfer function from the loudspeaker 101a to the microphone 103a is C, and the
sound source information signal generated by the noise source is Xp, the residual observed by
the microphone 103a The signal E becomes E = Xp ・ H + Xp ・ G ・ C. Here, G is a transfer
function required to mute. When the noise is completely canceled at the noise reduction target
point (the position of the microphone 103a), E = 0. このときGは、G=−H/Cとなる。
Usually, this operation is performed in the frequency domain using fast Fourier transform, and
the result is subjected to inverse Fourier transform to obtain an impulse response, which is set as
a filter coefficient in the adaptive filter 107 of the signal processor 105. This filter coefficient
finds G that minimizes the microphone detection signal E, and based on this G, the filter
coefficient in the adaptive filter 107 is adaptively updated. As a method of obtaining a filter
coefficient so as to minimize the microphone detection signal E, there is an LMS algorithm (Least
Mean Square) which is a kind of steepest descent method.
[0005]
On the other hand, as shown in FIG. 8, when a plurality of microphones are installed, control is
performed such that the total sum of signals detected by the microphones 103a and 103b is
minimized.
[0006]
In such control, when a pressure wave having a high sound pressure area and a low sound
pressure area is generated in the closed space, the high sound pressure area and the low sound
pressure area are determined by measurement or analysis, and the microphone 103a, It has been
found that optimum active noise control can be achieved if 103b is in or adjacent to the high
sound pressure region.
[0007]
However, in the interior of a car, etc., noise is in resonance at a certain frequency, engine rotation
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is increased, resonance is in another frequency, and the acoustic mode is Different from each
other, the acoustic mode at a certain frequency may be in the high sound pressure area, and the
acoustic mode at another frequency may be in the bass pressure area.
For this reason, even if a plurality of microphones are installed in the passenger compartment, in
one acoustic mode, one microphone is in the high sound pressure region, another microphone is
in the low sound pressure region, and in the other sound mode, the one microphone is the low
sound pressure It is in the area, and other microphones are in the high sound pressure area.
[0008]
Therefore, even if control is performed so as to minimize the total sum of signals detected by
each of the microphones, optimization of active noise control is required as long as the detected
noise includes a signal in the bass pressure region. There was a limit to
[0009]
Therefore, according to the present invention, residual noise detecting means are provided
respectively at predetermined plural places in the closed space, and when the noise generation
state of the noise source changes, the residual noise detecting means should detect the residual
noise according to the change. It is an object of the present invention to provide an active noise
control device capable of achieving further optimization by selecting.
[0010]
SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is
directed to a control sound source that causes a control sound to interfere with noise transmitted
from a noise source whose noise generation state changes into a substantially closed space. A
means for separately detecting residual noise after the interference, provided at a plurality of
predetermined locations in the closed space, a means for detecting a signal related to a noise
generation state of the noise source, and an output signal of the residual noise detection means
An active noise control device comprising: control means for outputting a signal for driving the
control sound source based on an output signal of noise occurrence state detection means, and
residual according to a change in noise occurrence state of the noise source. It is characterized in
that it comprises means for selecting the residual noise detecting means whose noise is to be
detected.
[0011]
In order to select the residual noise detection means to detect residual noise according to the
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change in the noise generation state of the noise source, the residual noise in the high sound
pressure region which changes according to the noise generation state of the noise source is
selected. It can be detected.
[0012]
EXAMPLES Examples of the present invention will be described below.
The description will be made with the interior space of a car as an example of a substantially
closed space.
[0013]
FIG. 1 schematically shows a passenger compartment 1. As a noise source for which noise
generation changes in such a car, for example, it refers to a power plant, and the power plant is a
transmission as an engine and a power transmission device. , Differential gear is housed
integrally.
[0014]
On the lower side of the front seats 3a and 3b in the passenger compartment 1, loudspeakers 5a
and 5b are provided as control sound sources for interfering the control sound with the noise
transmitted from the power plant.
In addition, residual noise after interference is separately detected at predetermined locations
inside the vehicle, for example, at the front right side of the dashboard 7, at the front left side, at
the rear right side and at the rear left side of the rear parcel shelf 10. Microphones 11a, 11b, 11c
and 11d are provided as means for detecting.
The loudspeakers 5a and 5b and the microphones 11a to 11d are connected to the control unit
13.
[0015]
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FIG. 2 is a block diagram showing a circuit configuration in the control unit 13. As shown in FIG.
[0016]
In the control unit 13, a control sound calculation unit 15 as control means and an input
switching circuit 17 as selection means are provided.
The control sound calculation unit 15 outputs signals for driving the loudspeakers 5a and 5b
based on the output signals of the microphones 11a to 11d and the output signal of the noise
occurrence state detection means 19.
The noise generation state detection means 19 detects an ignition signal of the engine from a
signal from a crank angle sensor or a high tension code, for example, and inputs it to the control
sound calculation unit 15 as a signal xp related to the noise generation state.
[0017]
The input switching circuit 17 selects the microphones 11a to 11d for detecting the residual
noise according to the change of the noise generation state of the noise source, and the ignition
from the detection means 19 together with the signals of the microphones 11a to 11d. A signal is
input.
[0018]
Next, optimization of the locations of the microphones 11a to 11d will be described.
[0019]
An example will be described of the muffled engine noise of a vehicle equipped with a 4-cycle 4cylinder engine, which is most commonly used as a passenger car.
[0020]
In a 4-cycle 4-cylinder engine, usually, the unbalance force is generated by the reciprocating
motion of a piston, a connecting rod, etc. inside the engine at the same frequency as the
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combustion cycle, which causes the engine to vibrate and generate noise in the passenger
compartment. Let
This noise is often referred to as "bomber" because it feels trapped in the cabin.
The frequency is the same as the combustion cycle, twice per engine revolution, that is, twice the
frequency of the engine revolution, and the current operating speed range of modern high
performance engines is 600 rpm to 7500 rpm. , Vibration between 20 Hz and 250 Hz.
Also, booming noise often becomes a problem especially at a frequency at which resonance
occurs in the vehicle interior, and in order to reduce the engine booming noise by interfering
with the control sound output from the loudspeakers 5a and 5b, the acoustic mode of the
resonance state is reduced. It is necessary to arrange the microphones 11a to 11d at positions
where they can be detected.
[0021]
Furthermore, in general, all corners of the eight corners always have high sound pressure areas
in any closed-loop cubical space, but in the case of a complex-shaped closed space as in a vehicle
interior There is no limitation to the high sound pressure area for any acoustic mode, and there is
a characteristic high sound pressure area according to the shape of each vehicle.
[0022]
FIGS. 3 (a) to 3 (d) show an example of the result of calculation of the acoustic mode generated in
the cabin of such a vehicle by the finite element method, and the black portion is the high sound
pressure region.
In such a vehicle, by arranging the microphones 11a to 11d as shown in FIG. 1, the microphones
11a and 11c become high sound pressure areas in FIG. 3A, and 11a, 11b and 11d in FIG. 3B. In
FIG. 3C, the position of the microphone 11a is in the high sound pressure region in the mode of
FIG. 3D, and in the mode of FIG. 3D, the positions of the microphones 11a to 11d are in the high
sound pressure region or the sound pressure is low. It is an area.
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However, according to the arrangement of the microphones 11a to 11d as shown in FIG. 1, the
position of any one of the microphones 11a to 11d can be a high sound pressure area in any
acoustic mode, and the position is high in the sound pressure level If control is performed using
signals from the microphones, accurate control can be performed without being influenced by
signals in the low region.
[0023]
There are two other conditions which should be satisfied for the arrangement of the
microphones.
One is not too many. This is because an increase in the number of microphones leads to an
increase in the calculation load of the control sound calculation unit 15, and as a result, an
increase in cost. Another condition is that the microphone does not come to the acoustic mode
node. Not only is it difficult to detect the acoustic mode due to noise at the position of the node
of the acoustic mode, but there is also a possibility that it will not be detected even if the control
mode is too loud and the acoustic mode thereby occurs.
[0024]
Therefore, in this embodiment, the acoustic modes of FIG. 3 are arranged as shown in FIG.
[0025]
If the space to be controlled is different, the arrangement of the microphones is determined
according to the change of the acoustic mode of the space.
[0026]
Next, the operation will be described.
[0027]
The input switching circuit 17 shown in FIG. 2 selects which one of the microphones 11a to 11d
to use according to the fundamental frequency of the ignition signal 21 sent from an engine
control unit (not shown).
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[0028]
Taking the acoustic mode shown in FIG. 3 as an example, the microphones 11a and 11c in the 85
Hz mode in (a), the microphones 11a, 11b and 11 d in 110 Hz in (b), and the microphone 11 d in
142 Hz for (c). , (D) operates to select the microphone 11a.
[0029]
FIG. 4 shows a flow chart of such a microphone selection procedure. In step S1, an ignition signal
is input, and it is determined whether or not 85 Hz in step S2. If 85 Hz, microphones 11a and
11c are selected in step S3. A selection is made.
If it is determined in step S2 that the frequency is not 85 Hz, it is determined in step S4 whether
the frequency is 110 Hz. If it is 110 Hz, the microphones 11a, 11b and 11d are selected in step
S5.
If it is determined in step S4 that the frequency is not 110 Hz, the process proceeds to step S6, in
which it is determined whether the frequency is 142 Hz. If 142 Hz, the microphone 11d is
selected in step S7.
If it is determined in step S6 that the frequency is not 142 Hz, the process proceeds to step S8, in
which it is determined whether the frequency is 203 Hz. If 203 Hz, the microphone 11a is
selected in step S9.
If it is determined in step S8 that the frequency is not 203 Hz, no booming noise occurs and the
process returns to step S1.
[0030]
Thus, the sound pressure in the high sound pressure region is selectively detected in any of the
acoustic modes, and control is performed such that the sum of the detected signals is minimized.
[0031]
Next, the control method will be described.
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[0032]
Now, the noise signal detected by the l-th microphone 11a (-11d) by the above-mentioned
method is el (n), and the l-th microphone 11a (-when there is no control sound from the
loudspeakers 5a and 5b) 11d) detects the noise signal detected by epl (n), j-th (j = 1, j = 1,
transfer function FIR (finite impulse response) function) between the m-th loudspeaker 5a (5b)
and the l-th evaluation point 1, 2,..., Ic -1) filter coefficients lmim when the terms are represented
by digital filters, a reference signal, that is, a sound source information signal xp (n), and a
reference signal xp (n) Assuming that the ith coefficient (i = 0, 1, 2, ..., Ik -1) of the adaptive filter
that drives (18b) is Wmi,
[0033]
[Equation 1]
[0034]
The following holds.
Here, the terms with (n) are all sample values at sampling time n, L is the number of microphones
11a to 11d (four in this embodiment), and M is the number of loudspeakers 5a and 5b (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 of the adaptive filter (filter order).
[0035]
In the above equation (1), the term ΣWmi · xp (n−j−i) (= ym) on the right side is obtained
when the signal xp is input to the filter (coefficient Wm) for each output channel in the adaptive
filter The signal energy input to the m-th speaker 5a (5b) is output as acoustic energy from the
speaker 5a (5b). Represents the signal when the l-th microphone 11a (˜11 d) is reached via the
transfer function Clm in the passenger compartment 1, and further, the entire right side of Cl
Cl Clm j · {W Wmi · xp (n−j−i)} Since the arrival signal to the l-th microphone 11a (to 11 d) is
added up for all the speakers, it represents the total sum of secondary sounds reaching the l-th
evaluation point.
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However, in the embodiment of the present invention, the arrival signal is zero except for the
selected speaker.
[0036]
Next, the evaluation function (variable to be minimized) Je is
[0037]
[Equation 2]
[0038]
【0038】とおく。
[0039]
Then, in order to obtain the filter coefficient Wm which minimizes the evaluation function Je, the
LMS algorithm is adopted in this embodiment.
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.
[0040]
[Equation 3]
[0041]
From equation (1),
[0042]
[Equation 4]
[0043]
Therefore, assuming that the right side of the equation (4) is rlm (n-1), the equation for rewriting
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the filter coefficient can be obtained by the following equation (5).
[0044]
[Equation 5]
[0045]
Here, α is a convergence coefficient, and is concerned with the speed at which the filter
converges optimally and the stability at that time.
[0046]
By performing such control, when a booming sound is generated in each acoustic mode, the
sound pressure is measured in the high sound pressure region, and control is performed so as to
minimize this. It can be done effectively.
[0047]
FIG. 5 shows another embodiment.
In this embodiment, the ignition signal is also input to the control sound calculation unit 15.
Therefore, in the embodiment of FIG. 5, it is possible to calculate only for the signal of the
selected microphone, which enables faster and more accurate calculation.
[0048]
FIG. 6 shows still another embodiment, in which the signal of the microphone 11d is analyzed by
the frequency analysis circuit 23, and the information of the frequency which is the main
component of noise is input switching circuit 17 and control sound calculation unit 15 Supply to
the
The position of the microphone 11d is the antinode of each acoustic mode, the frequency of the
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main component of the noise synchronized with the engine rotational speed can be reliably
analyzed, and the selection of the microphones 11a to 11d can be switched using this frequency.
The input to the frequency analysis circuit 23 can be performed by providing a dedicated
microphone separately instead of the signal from the microphone 11 d.
[0049]
FIG. 7 shows still another embodiment, wherein a reference signal xp concerning noise
generation state is inputted from the noise generation state detecting means 19 to the frequency
analysis circuit 23, and the frequency is analyzed to obtain an input switching circuit 17 And the
control sound calculation unit 15.
Therefore, in this embodiment, accurate and quick switching is possible because the reference
signal regarding the noise generation state is used.
[0050]
The present invention is not limited to the above embodiment.
For example, in the above embodiment, the case of selecting the input of channels 1 to 3 from
four microphones and outputting the control sound has been described, but the number of
microphones input to the input switching circuit 17 The number of input channels sent and the
number of output channels sent to the loudspeaker as control sounds can be fixed to a specific
one.
Further, although the noise control has been described for the sake of convenience in the above
embodiment, the control object is vibration accompanied by a resonance phenomenon, the
microphone can be used as a vibration sensor, and the speaker can be similarly applied as any
vibration actuator.
[0051]
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As is apparent from the foregoing, according to the configuration of the present invention, it is
possible to select the residual noise detection means for detecting the residual noise according to
the change in the noise generation state of the noise source. Silence control can be performed
more effectively.
[0052]
Brief description of the drawings
[0053]
1 is a schematic overall configuration perspective view according to an embodiment of the
present invention.
[0054]
2 is the same block diagram.
[0055]
3 is an explanatory view of the acoustic mode.
[0056]
4 is a flowchart.
[0057]
5 is a block diagram according to another embodiment.
[0058]
6 is a block diagram according to another embodiment.
[0059]
7 is a block diagram according to another embodiment.
[0060]
8 is a block diagram according to the conventional example.
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[0061]
Explanation of sign
[0062]
1 compartment (substantially closed space) 5a, 5b Loudspeakers (control sound sources) 11a to
11d Microphones (residual noise detection means) 15 control sound source calculation unit
(control means) 17 input switching circuit (selection means) 19 noise occurrence state detection
means
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