JPH1011073A - Microphone system and silencer using this system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect only a sound wave transmitting in the direction of one side out of sound waves transmitting in the bidirection. SOLUTION: Two microphones A, B are provided along the direction of transmission of a sound wave in a duct 20 in which sound waves P1 , P2 are transmitted in the bi-direction. A signal being almost equivalent to a signal obtained by collecting only the sound wave P1 with the microphone A can be obtained by performing the prescribed operation by an operation section 70 for sound collection signals outputted from the microphones A, B. Further, the operation section 70 is constituted with a delay circuit 71 delaying a sound collection signal of the microphone B, a subtracter 72 subtracting an output of this delay circuit 71 from a sound collection signal of the microphone A, and a compensation amplifier 73 amplifying an output of this subtracter 72 with the prescribed amplification factor G.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone system for picking up a sound wave propagating in a sound wave propagation path such as a duct, and more particularly to a microphone system suitable for use in a muffler for actively muffling the sound wave. And an active silencer using the same.

[0002]

2. Description of the Related Art The above-mentioned active silencer attenuates a sound wave propagating in the duct by causing a sound wave propagating in the duct to interfere with a sound wave having substantially the same magnitude and opposite phase. For example, it is applied to muffle noise such as exhaust noise generated from an engine. Conventionally, as this silencer, for example, there is one as shown in FIG.

In FIG. 1, reference numeral 1 denotes a noise source such as an engine, for example. The noise generated from the noise source 1 passes through the inside of a duct 2 from the left side to the right side in FIG. It propagates toward the outlet and is discharged from the duct outlet 2a. A primary microphone (hereinafter, referred to as a reference microphone) 3 is coupled to the duct 2, and the reference microphone 3 collects (detects) noise propagating in the duct 2. An electric signal output from the reference microphone 3, that is, a so-called noise signal, is supplied to a filter 4, where the signal is filtered based on a predetermined filter transfer function, and then supplied to a speaker 6 via an amplifier 5. The speaker 6
A sound wave corresponding to the output of the filter 4 (amplifier 5) is provided so as to be radiated to the downstream side of the noise from the position where the reference microphone 3 is coupled in the duct 2.

That is, in this silencer, the noise emitted from the speaker 6 is canceled by causing the noise to interfere with the noise. Therefore, in the filter 4, a filtering process is performed on the collected sound signal output from the reference microphone 3 so that the radiated sound of the speaker 6 is substantially equal to the noise and has an opposite phase relationship. Is set in the filter 4.

Further, a secondary microphone (hereinafter, referred to as an error microphone) 107 is coupled to the duct 2 downstream of the position where the speaker 6 is provided, for example, near the duct outlet 2a. . The error microphone 107 picks up (detects) the sound pressure level after the noise is canceled by the sound emitted from the speaker 6.
An electric signal output from the error microphone 107, a so-called error signal, is supplied to the control device 8. Also,
The noise signal output from the reference microphone 3 is filtered by a filter 9 different from the filter 4 and supplied to the control device 8. Note that the filter transfer function W of the filter 9 is obtained by previously identifying a transfer function from the input section of the speaker 6 to the output section of the error microphone 107 with necessary accuracy. The control device 8 updates and controls the filter transfer function of the filter 4 such that the error signal is minimized, that is, the noise discharged from the duct 2 approaches zero as much as possible.

The filter 4 and the control device 8 are:
For example, it is composed of a DSP (Digital Signal Processing Unit), a CPU (Central Processing Unit), etc.
The P and the CPU operate according to a program stored in a storage unit such as a memory (not shown). When the filter 4 and the control device 8 are configured by the DSP and the CPU in this manner, the input / output of each signal (the noise signal, the error signal, and the output signal of the filter 4) to the filter 4 is originally A / D. Although a converter and a D / A converter are required, this is a natural technique and is not specifically illustrated here.

As described above, the noise generated from the noise source 1 propagates through the duct 2 and passes through the duct outlet 2a.
However, since the acoustic impedance changes abruptly in the vicinity of the duct outlet 2a, some of the noise is reflected at the duct outlet 2a as shown by an arrow 10a in FIG. 6, for example. Some components travel in the opposite direction (from the right side to the left side in the figure). Further, in the duct 2, in addition to the noise, for example, an arrow 10b shown in FIG.
As shown by, there is also external noise entering from outside through the duct outlet 2a.

[0008] As described above, the duct outlet 2
When there is a reflected sound or external noise at a, the reference microphone 3 for collecting the noise of the noise source 1 and the sound pressure level after canceling the noise by the radiated sound of the speaker 6. The error microphone 107 collects the reflected sound and the external noise at the same time. In particular, regarding the error microphone 107 provided near the duct outlet 2a, the above-mentioned reflected sound and external noise have a very large effect. As a result, there is a problem that the silencing control of the silencing device is hindered and a sufficient silencing effect cannot be obtained.

In order to solve this problem, of the sound waves propagating in the duct 2, only the sound waves propagating in one direction indicated by an arrow 10 in FIG. 6 are collected by the reference microphone 3 and the error microphone 107. Although good, conventionally, there has been no microphone that can collect only the sound wave propagating in one direction among the sound waves propagating in a pipe such as the duct 2 in two directions (in opposite directions).

[0010]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a microphone system capable of picking up only a sound wave propagating in one direction among sound waves propagating in a pipe such as the duct 2 in both directions. The purpose is to do. In addition, by using this microphone system for an active silencer, more accurate silencing control can be realized as compared to the conventional silencer shown in FIG. 5, and a more reliable silencing effect can be obtained. It is also an object of the present invention to provide a silencer.

[0011]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is directed to a sound wave propagation path in which sound waves propagate in both directions. First and second microphones that are coupled at a predetermined interval along the
And a predetermined operation is performed on the collected sound signal output from each of the second microphones, and among the collected sound signals output from the first microphone, the sound wave propagation path is directed to one of the directions. And a calculating means for outputting a signal substantially equivalent to a signal component corresponding to only the sound wave propagating through the loudspeaker.

That is, the first and second microphones pick up sound waves propagating in the sound wave propagation path at two different points separated by a predetermined distance in the propagation direction. Then, the arithmetic means performs a predetermined arithmetic operation on the collected sound signals output from the first and second microphones, respectively. A signal that is substantially equivalent to that of collecting only sound waves propagating in one of the directions is output.

According to a second aspect of the present invention, in the microphone system according to the first aspect, the arithmetic means includes a transfer function between the second microphone and the first microphone in the sound wave propagation path. Processing means having a transfer function substantially equivalent to: and processing a collected sound signal output from the second microphone based on the transfer function;
Subtraction means for subtracting the signal processed by the processing means from the collected sound signal output from the first microphone; and subtraction by the subtraction means, among the collected sound signals output from the first microphone. And compensating means for compensating for the subtraction of the signal component corresponding to only the sound wave propagating from the first microphone side toward the second microphone side.

[0014] The compensation means is, for example,
Predetermined compensation using the transfer function between the first microphone and the second microphone and the transfer function between the second microphone and the first microphone as parameters for the result of the subtraction performed by the subtraction means. It is configured to multiply the coefficient.

That is, the processing means processes the sound pickup signal output from the second microphone based on a transfer function substantially equivalent to a transfer function between the second microphone and the first microphone. Therefore, the signal processed by the processing means transmits the sound wave (sound pressure) at the position where the second microphone is provided in the sound wave propagation path to the position where the first microphone is provided. The first
It can be considered that the signal is substantially equivalent to a signal obtained by picking up sound with the microphone. That is, of the signals processed by this processing means, the signal component corresponding to only the sound wave propagating from the second microphone side to the first microphone side is the signal component of the sound pickup signal output from the first microphone. Among them, the signal is a signal substantially equivalent to a signal component corresponding to only a sound wave propagating from the second microphone side toward the first microphone side. On the other hand, among signals processed by the processing means, a signal component corresponding to only a sound wave propagating from the first microphone side toward the second microphone side is a signal component of the collected sound signal output from the second microphone. Among them, a signal component corresponding to only a sound wave propagating from the first microphone side toward the second microphone side is further processed based on the transfer function of the processing means.

The subtracting means subtracts the signal processed by the processing means from the sound pickup signal output from the first microphone. By this subtraction, signal components corresponding to only sound waves propagating from the second microphone side toward the first microphone side in the collected sound signals output from the first microphone are almost completely removed. Will be. On the other hand, among the collected sound signals output from the first microphone, a signal component corresponding to only a sound wave propagating from the first microphone side to the second microphone side is output from the second microphone. Of the collected sound signals, the signal component corresponding to only the sound wave propagating from the first microphone side toward the second microphone side is subtracted by the amount processed by the processing means.

Therefore, the above subtraction is compensated for by the compensation means. Thus, a signal component corresponding to only a sound wave propagating from the first microphone side toward the second microphone side is derived from the collected sound signals output from the first microphone.

That is, according to the second aspect of the present invention, of the sound waves propagating bidirectionally through the sound wave propagation path by the first microphone, the second sound waves are transmitted from the first microphone side to the second sound waves.
, A signal substantially equivalent to collecting only sound waves propagating toward the microphone side can be obtained.

According to a third aspect of the present invention, in the microphone system according to the second aspect, the sound wave propagation path is:
A loss element for propagation of the sound wave between the first and second microphones is eliminated. For example, without interposing anything between the first and second microphones,
By forming the inside of the sound wave propagation path smoothly without any irregularities and further forming the inner wall of the sound wave propagation path with a (rigid) material such as a metal which has strong reflection to sound, the above-mentioned loss element is reduced. Can be eliminated.

That is, since there is no element that gives a loss to the propagation of the sound wave between the first and second microphones in the sound wave propagation path, almost no sound wave is generated between the first and second microphones. Does not decay. Therefore, the transfer function between the first and second microphones is represented by a function relating only to the time required for the sound wave to propagate between the first and second microphones. Therefore, when performing each processing in the processing means and the compensating means using the transfer function, it is not necessary to consider the attenuation component of the sound wave, and the propagation necessary for the sound wave to propagate between the first and second microphones. Only the time (delay time) needs to be considered.

According to a fourth aspect of the present invention, there is provided a noise propagation path for propagating noise input from one end and outputting the noise from the other end.
A reference microphone coupled to the noise propagation path for picking up the noise and outputting a noise signal according to the reference microphone; first filter means for filtering the noise signal based on a predetermined filter transfer function; The first
A speaker which is driven by an output signal of the filter means and emits sound to the downstream side of the noise from the reference microphone in the noise propagation path, and is coupled to the downstream side of the noise from the speaker in the noise propagation path. And an error microphone that picks up the sound after causing the noise emitted from the speaker to interfere with the noise and outputs an error signal corresponding thereto, and the noise signal from an input portion of the speaker to an output portion of the error microphone. A second filter means for filtering and outputting a noise operation signal according to a transfer function of the first filter means, and a filter of the first filter means for receiving the error signal and the noise operation signal so as to minimize the error signal. Control means for controlling a transfer function, wherein one or both of the reference microphone and the error microphone are provided. But it is characterized in that comprising a microphone system according to claim 1, 2 or 3.

That is, in the muffling device, muffling control is performed based on the noise signal output from the reference microphone and the error signal output from the error microphone. By forming the reference microphone and the error microphone with the microphone system according to claim 1, 2 or 3, the reference microphone collects only the noise that is to be collected, and the error microphone includes the error microphone. ,
It is possible to collect only the error sound pressure after silencing, which is the target of sound collection. Therefore, even if the noise propagating in the noise propagation path is reflected at the other end of the noise propagation path, or external noise enters the noise propagation path from the outside via the other end, these reflected sounds and Normal silencing control can be realized without being affected by external noise and the like.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a microphone system according to the present invention and a silencer using the same will be described with reference to FIGS.

The microphone system according to the present invention, as shown in FIG. 2, for example, when there are sound waves P ₁ and P ₂ propagating in the duct 20 in two directions, _one of these sound waves P ₁ and P ₂ Sound wave P ₁ or P propagating in the direction
It is intended to pick up only ₂ Therefore, in order to realize this, for example, as shown in FIG. 3, a predetermined distance L [m] is set for a duct 20 having a constant inner diameter along its length direction, that is, along the propagation direction of a sound wave. Consider a model in which two microphones A and B are arranged separated by.

The alternate long and short dash line 20a shown in the figure is an imaginary reference plane that crosses the duct 20 perpendicularly to its length direction (the propagation direction of the sound waves P ₁ and P ₂ ). The two microphones A and B are disposed at points a and b at equal intervals (that is, L / 2) on both sides of the microphone. Therefore, the respective a
Between the point and the point b, the shape inside the duct 20 is
The plane is substantially symmetric with respect to the reference plane 20a. It is also assumed that the two microphones A and B have the same standard, for example.

In FIG. 3, the sound pressure generated at the point a by the sound wave P ₁ is p _1a (t), the sound pressure generated at the point b by the sound wave P ₁ is p _1b (t), and the sound generated at the point a by the sound wave P ₂ . Pressure
_2a (t), the sound pressure generated at point b by the sound wave P ₂ is p _2b (t)
Then, the sound pressures p _A (t) and p _B (t) collected (detected) by the microphones A and B can be expressed by the following equations 1 and 2, respectively.

[0027]

## EQU1 ## p _A (t) = p _1a (t) + p _2a (t)

[0028]

## EQU2 ## p _B (t) = p _1b (t) + p _2b (t)

Here, assuming that the sound speed is c [m / s], the time τ required for the sound waves P ₁ and P ₂ to propagate between the points a and b in the duct 20 is τ = L / c [s]. Then, using this time τ, a transfer function related to only the sound wave propagation time between the points a and b is expressed as ex
p [-jωτ] (where ω is the angular velocity). Therefore, the transfer function from point a to point b in the duct 20 is expressed as C _ab · exp [-j
ωτ], and assuming that the transfer function from point b to point a in the duct 20 is C _ba · exp [−jωτ], p _2a (t), p
_1b (t) is expressed as in the following equations 3 and 4, respectively.
Here, j is an imaginary unit, and j ² = −1.

[0030]

## EQU3 ## p _2a (t) = p _2b (t) · C _ba · exp [-jωτ]

## EQU4 ## p _1b (t) = p _1a (t) · C _ab · exp [-jωτ]

Equations (3) and (4) are respectively expressed by the above equations (1) and (4).
Substituting into Equation 2, the following Equations 5 and 6 are obtained.

[0032]

P _A (t) = p _1a (t) + p _2b (t) · C _ba · exp [-jωτ]

[0033]

P _B (t) = p _1a (t) · C _ab · exp [-jωτ] + p _2b (t)

Then, p _2b (t) is deleted from the above equations 5 and 6, and the equation for p _1a (t) is rearranged.
Can be obtained.

[0035]

## _EQU7 ## p _1a (t) = ｛p _A (t) −p _B (t) · C _ba · exp
[-jωτ]｝ / {1-C _ab · C _ba · exp [-2jωτ]｝

As described above, p _1a (t) in _Equation 7 is given by
The sound pressure is generated at point a by sound wave P ₁ propagating in one direction, that is, from point a to point b, of sound waves P ₁ and P ₂ propagating in the duct 20 in both directions. Then, from this equation 7, the sound pressure p _1a (t) is determined by the two microphones A and B.
The sound pressures p _A (t) and p _B (t) picked up by
Transfer functions C _ab · exp [−jωτ] and C _ba · exp [−jω existing between the microphones A and B (between the points a and b).
τ] can be derived.

As described above, the shape of the duct 20 is symmetric with respect to the reference plane 20a between the reference plane 20a and points a and b. Therefore, the above transfer functions C _ab .exp [-jωτ], C _ba.
Of exp [-jωτ], part except the function exp [-jωτ] according to wave propagation time between the point a and point b C _ab, for C _ba, be satisfied C _ab = C _ba. Then, C _ab = C _ba =
Assuming C, Equation 7 is simplified as Equation 8 below.

[0038]

## _EQU8 ## p _1a (t) = ｛p _A (t) −p _B (t) · C · exp [-j
ωτ]｝ / {1-C ² · exp [-2jωτ]｝

Further, the inside of the duct 20, especially the points a and b
Since the space between the points is a one-dimensional sound field, nothing intervenes between the points a and b, there is no unevenness inside, and the inner wall has a strong reflection against sound, such as a metal (rigid). ) If it is made of a material, there is almost no element that causes a loss in the propagation of the sound waves P ₁ and P ₂ . Therefore, the sound waves P ₁ , P
₂ propagates between the points a and b with little attenuation. In this case, among the transfer functions, the C (a function excluding exp [-jωτ] related to the transfer time) can be assumed to be C ≒ 1, and particularly, the distance L between the points a and b is short. Indeed, this function C more closely approximates unity. Therefore,
In this case, the above equation (8) is further simplified as in the following equation (9).

[0040]

## EQU9 ## p _1a (t) = ｛p _A (t) −p _B (t) · exp [-jω
τ]｝ / {1-exp [-2jωτ]｝

That is, as can be seen from Equation 9, the sound pressure p _1a
(t) is the sound pressure p collected by each of the microphones A and B.
_A (t), and p _B (t), the transfer function relating only to the propagation time required for sound waves between the point a and point b is propagated exp [-jω
τ].

By the way, in order to realize the relationship expressed by the above equation (9), for example, an apparatus as shown in FIG. 1 may be configured. That is, a sound pickup signal obtained by picking up sound pressure p _B (t) by the microphone B is supplied to the delay circuit 71. Delay circuit 71
Delays the supplied sound pickup signal by an amount corresponding to the time τ required for the sound wave P ₂ to propagate from the point b to the point a. That is, the delay circuit 71 functions as a filter that processes the collected sound signal from the microphone B based on the above-described transfer function exp [-jωτ] relating only to the sound wave propagation time.

Then, in the subtracter 72, the output of the delay circuit 71 is subtracted from the collected sound signal obtained by collecting the sound pressure p _A (t) by the microphone A.

Further, the output of the subtracter 72 is amplified by a compensation amplifier 73 at a predetermined amplification rate (compensation coefficient) G.
(Compensate). The gain G of the compensation amplifier 73 is G = 1 / {1-exp [-2jωτ]}.

[0045] With this arrangement, the number 9 is realized, i.e. out of the sonic P _1, P ₂ that propagates duct 20 in both directions, to a point by waves P ₁ propagating toward the point b from point a A signal equivalent to the sound pressure p _1a (t) generated by the microphone A alone can be obtained.

The delay circuit 71, the subtractor 72, and the compensation amplifier 73 in FIG. 1 correspond to the processing means, the subtraction means, and the compensation means, respectively. The delay circuit 71, the subtracter 72, and the amplifier 73 form an operation unit 70 corresponding to the operation means described in the claims. Then, the operation unit 70
And two microphones A and B constitute a microphone system 7. Note that the arithmetic unit 70 is configured by the above-described DSP and CPU.

FIG. 4 shows an example in which the microphone system 7 shown in FIG. 1 is applied to a muffler. For example, the error microphone 107 in the muffler shown in FIG.
In place of the microphone system 7 described above. The remaining configuration is the same as that of FIG. 5 described above, and thus the same reference numerals are given to the same components, and detailed description thereof will be omitted.

That is, by using the microphone system 7 as an error microphone, the microphone system 7 is less affected by the reflected sound of the noise at the duct outlet 2a and the external noise that enters the duct 2 through the duct outlet 2a. Can be. Therefore, there is an effect that normal silencing control can be realized and a more reliable silencing effect can be obtained as compared with the related art.

Of course, not limited to the error microphone,
The microphone signal 7 can also be used for the reference microphone 3. However, the influence of the reflected sound and the external noise on the reference microphone 3 is far less than the influence on the error microphone and is very small. Therefore, the microphone system 7 is applied only to the error microphone.

In the present embodiment, the case where the microphone system 7 is applied to a muffling device has been described. However, in the technical field of detecting sound pressure in a duct, the present technology can be applied to other than the muffling device. Applicable.

Further, in the present embodiment, the configuration for realizing Equation 9 has been described with reference to FIGS. 1 and 4, but the present invention is not limited to this. For example, transmission between a point and b point in the duct 20 functions C _ab · exp [-jωτ], when the C _ba · exp [-jωτ] is present, the number 7 described above (the C _ab ≠ C _ba The same effect as described above can be obtained by configuring a microphone system that realizes (case) or Equation 8 (C _ab = C _ba ≠ 1).

The calculations based on the above equations 7, 8 and 9 may be performed for all the frequencies (angular velocity ω) of the sound waves P ₁ and P ₂ propagating in the duct 20, or for some of the frequencies. Only the above calculation may be performed. For example, in the case of a silencer, the above calculation may be performed for all frequencies to be silenced, or the above calculation may be performed only for frequencies where the influence of the above-mentioned reflected sound or external noise is particularly large.

Further, when the calculation is performed based on the above equations 7, 8, and 9, depending on the frequency (angular velocity ω) (for example, when ω ≒ 0), the denominator of each equation (that is, ｛1−exp [− 2jω
τ]｝) becomes 0 or approximates 0, resulting in an uncertain state. In such an uncertain state, since normal silencing control cannot be performed, in actual silencing control,
It is desirable to perform the above calculation only for frequencies other than the frequency causing the above-mentioned uncertain state.

Equations (7), (8) and (9) represent the sound wave P ₁
The is a calculation formula for the sound pressure p _1a (t) occurring in a point, not only the sound pressure p _1a (t), using the equations (1) through 4 described above, other sound pressure p _1b (t ), P _2a (t) and p _2b (t) may be calculated, and a microphone system for realizing them may be configured.

[0055]

According to the microphone system of the first aspect of the present invention, the first microphone and the second microphone are spaced apart from each other by a predetermined distance in the sound wave propagation direction with respect to the sound wave propagation path.
And two microphones.
Then, the first microphone outputs a signal substantially equivalent to that of collecting only sound waves propagating in either one of the sound waves propagating in the sound wave propagation path in both directions. That is, according to the first aspect of the present invention, even if a sound wave propagates in both directions in the sound wave propagation path, it is possible to collect only the sound wave propagating toward one of the sound waves. is there.

According to the second aspect of the present invention, of the sound waves propagating in the sound wave propagation path in both directions by the first microphone, the sound waves are directed from the first microphone side to one side toward the second microphone side. It is possible to obtain a signal substantially equivalent to collecting only the propagating sound wave.

According to the third aspect of the present invention, when each processing is performed in the above-described processing means and compensation means, it is not necessary to consider the attenuation component of the sound wave, and the sound wave is generated by the first and second sound waves.
Only the propagation time (delay time) necessary to propagate between the microphones need to be considered. Accordingly, there is an effect that each processing in the processing means and the compensating means can be simplified as compared with the second aspect of the present invention.

According to the muffler of the fourth aspect of the present invention, the reference microphone and the error microphone are formed by the microphone system of the first, second or third aspect. It is possible to pick up only the noise that is the target of the sound, and to pick up only the error sound pressure after the noise that is the target of the error microphone. Therefore, even if the noise propagating in the noise propagation path is reflected at the other end of the noise propagation path, or external noise enters the noise propagation path from the outside via the other end, these reflected sounds and Normal silencing control can be realized without being affected by external noise and the like. Therefore, there is an effect that a more reliable silencing effect can be obtained as compared with the above-described related art.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a microphone system according to the present invention.

FIG. 2 is an explanatory diagram of the embodiment.

FIG. 3 is an explanatory diagram of the embodiment.

FIG. 4 is a schematic configuration diagram showing an example in which the microphone system of the embodiment is applied to a muffling device.

FIG. 5 is a schematic configuration diagram of a conventional silencer.

FIG. 6 is a diagram showing the effects of noise reflection and external noise in a conventional silencer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Noise source 2 Duct 3 Reference microphone (primary microphone) 4 Filter 5 Amplifier 6 Speaker 7 Microphone system 8 Control means 70 Calculation part (Calculation means) 71 Delay part (Processing means) 72 Subtraction part (Subtraction means) 73 Multiplication part ( Compensation means)

Claims (4)

[Claims] 1. A first and a second microphone that are coupled to a sound wave propagation path in which a sound wave propagates in both directions at a predetermined interval along a propagation direction of the sound wave and that collects the sound wave. And performing a predetermined operation on the collected sound signals output from the first and second microphones, respectively, and selects one of the sound wave propagation paths among the collected sound signals output from the first microphone. And a calculating means for outputting a signal substantially equivalent to a signal component corresponding to only a sound wave propagating in one direction. 2. The arithmetic means has a transfer function substantially equivalent to a transfer function between the second microphone and the first microphone in the sound wave propagation path, and based on the transfer function, Processing means for processing a collected sound signal output from the second microphone; subtraction means for subtracting the signal processed by the processing means from the collected sound signal output from the first microphone; Of the signal collected from the first microphone, the signal component corresponding to only the sound wave propagating from the first microphone side toward the second microphone side is subtracted. The microphone system according to claim 1, further comprising: a compensating means for compensating. 3. The microphone system according to claim 2, wherein the sound wave propagation path excludes a loss element for propagation of the sound wave between the first and second microphones. 4. A noise propagation path for transmitting noise input from one end and outputting the noise from the other end, and coupled to the noise propagation path to collect the noise and output a noise signal corresponding thereto. A second microphone, first filter means for filtering the noise signal based on a predetermined filter transfer function, and a first filter means driven by an output signal of the first filter means to be higher than the first microphone in the noise propagation path. A speaker that emits sound to the downstream side of the noise; and a speaker that is coupled to the noise propagation path on the downstream side of the noise from the speaker and collects the sound after the noise emitted from the speaker interferes with the noise. Outputs an error signal corresponding to the sound 2
A second microphone, and second filter means for filtering a noise signal from the first microphone with a transfer function from an input unit of the speaker to an output unit of the second microphone to output a noise operation signal, Control means for controlling a filter transfer function of the first filter means so that the error signal and the noise calculation signal are inputted and the error signal is minimized.
A muffling device, wherein one or both of the secondary microphone and the secondary microphone comprise the microphone system according to claim 1, 2 or 3.