Microphone device

Abstract

To provide a microphone device of which a size can be reduced.SOLUTION: A microphone device comprises a plurality of microphones 20. When an interval from the two microphones 20 of the plurality of microphones 20 is d, a SN ratio in a single body of each microphone 20 is MicSNR, a sound speed is c, a frequency of a processing object is f, an azimuth angle of an operation seat against the plurality of microphones 20 is θ, the minimum azimuth angle as a detection object is Δθ, a voltage amplitude of an output signal of each microphone 20 using an output voltage when receiving a sound in 94 dBA as a reference is A, the following equation is satisfied: Δτ=d / c{sin(θ+Δθ)-sinθ}, and a differential voltage effective ratio EDER is regulated by a formula 1, an interval d is set to a value so as to satisfy d<c / 2f and EDER>0.7.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a microphone device. [Background technology]

[0002] A technology has been proposed that allows a driver to operate an air conditioner and other devices in a vehicle cabin without having to look away from the direction of travel of the vehicle. Various noises are generated while driving. In response to this, a voice enhancement technology using a microphone array with multiple microphones has been proposed to increase the signal-to-noise ratio, i.e., the strength of the operator's voice signal relative to the noise, and make it easier to recognize the contents of the operator's speech (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-149612 A Summary of the Invention [Problem to be solved by the invention]

[0004] When installing a microphone device in a vehicle, the space available for installation is limited, so the device needs to be compact. On the other hand, if the microphones are arranged closely together, the time difference and amplitude difference between the signals of the microphones become small compared to the electrical noise generated by the microphones themselves, so there is a risk that the performance of the microphone array cannot be maintained.

[0005] Therefore, it is desirable to set the microphone spacing to a value that allows the device to be made smaller while still ensuring performance. However, Patent Document 1 does not consider the minimum microphone spacing that allows the device to maintain performance.

[0006] In view of the above, an object of the present disclosure is to provide a microphone device that can be miniaturized. [Means for solving the problem]

[0007] In order to achieve the above object, according to one aspect of the present disclosure, a microphone device includes a plurality of microphones (20, 21, 22), and when a distance between two of the plurality of microphones is d, a signal-to-noise ratio of a single microphone is MicSNR, a sound speed is c, a frequency to be processed is f, an azimuth angle of an operator's seat relative to the plurality of microphones is θ, a minimum azimuth angle to be detected is Δθ, a voltage amplitude of an output signal of the microphone based on an output voltage when a sound of 94 dBA is received is A, and Δτ=d / c{sin(θ+Δθ)-sinθ}, and a differential voltage effectiveness ratio EDER is defined by Equation 1, the distance d is d<c / 2f、かつ、EDER> It is set to a value satisfying 0.7.

[0008]

number

[0009] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a front view of a microphone device according to a first embodiment. [Diagram 2] FIG. 13 is a diagram for explaining a method for detecting an azimuth angle. [Diagram 3] FIG. 13 is a diagram showing the relationship between azimuth angle and angular resolution. [Figure 4] FIG. 13 is a diagram for explaining a method for detecting an azimuth angle. [Diagram 5] FIG. 13 is a diagram showing the relationship between azimuth angle and angular resolution. [Figure 6] FIG. 4 is a diagram showing an output signal of a microphone. [Figure 7] FIG. 4 is a diagram showing a voltage difference of an output signal of a microphone. [Figure 8] FIG. 11 is a diagram showing the relationship between frequency and differential voltage effectiveness rate. [Figure 9] FIG. 13 is a diagram for explaining a required angular resolution. [Figure 10] FIG. 13 is a diagram showing the relationship between the microphone spacing and the differential voltage effectiveness rate. [Figure 11] FIG. 13 is a diagram showing the relationship between the microphone spacing and the differential voltage effectiveness rate. [Figure 12] FIG. 13 is a diagram showing the relationship between the microphone spacing and the differential voltage effectiveness rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0012] (First embodiment) A first embodiment will be described. The microphone device of this embodiment is mounted on a vehicle and used for voice recognition operations. As shown in FIG. 1, the microphone device includes a substrate 10, a microphone 20, and a signal processing unit 30.

[0013] The substrate 10 is a rectangular plate-like member made of resin, etc. The microphone device is mounted in a vehicle by fixing the substrate 10 to a dashboard, an overhead console, or the like.

[0014] The microphone 20 receives sound waves and outputs a signal corresponding to the sound pressure of the received sound waves. As the microphone 20, a MEMS (Micro Electro Mechanical Systems) microphone or the like is used.

[0015] The microphone 20 is a microphone with a high S / N ratio. Specifically, if the ratio of the output signal and self-noise of the microphone 20 based on 94 dBA and 1 kHz is defined in dB as the S / N ratio MicSNR, the S / N ratio MicSNR is 70 dB or more, for example, 78 dB. Note that the voltage (hereinafter referred to as LSB voltage) corresponding to the LSB (least significant bit) of an ADC (analog-digital converter) 31 described later is set smaller than the output voltage due to the self-noise of the microphone 20.

[0016] The microphone device includes a plurality of microphones 20. Specifically, the number of microphones 20 is 2, where n is a natural number. n The microphones 20 are arranged in an array in two or three directions at an angle to each other.

[0017] In this embodiment, eight microphones 20 are arranged on the substrate 10. Four of the eight microphones 20 are arranged at each corner of the substrate 10. The remaining four are arranged between the microphones 20 arranged at the corners of the substrate 10. That is, the eight microphones 20 are arranged in a rectangular shape.

[0018] The signal processing unit 30 processes the output signal of the microphone 20, and includes an ADC 31, a microcomputer 32, and an interface 33. The signal processing unit 30 is disposed in the center of the multiple microphones 20 that are arranged in a rectangular shape.

[0019] The ADC 31 converts an analog voltage signal output by the microphone 20 into a digital signal. The ADC 31 performs AD conversion on the output signal of the microphone 20. The digital signal generated by the ADC 31 is input to the microcomputer 32.

[0020] The microcomputer 32 performs voice enhancement processing or noise reduction processing based on the digital signal generated by the ADC 31 .

[0021] The interface 33 connects the microphone device to other devices. A signal generated by the voice enhancement process by the microcomputer 32 is transmitted to other devices via the interface 33.

[0022] The effect obtained by arranging the microphones 20 in a rectangular shape will be described. As shown in FIG. 2, of the eight microphones 20, two adjacent microphones 20 are microphones 21 and 22. The distance between the microphones 21 and 22 is d. The azimuth angle of the direction of arrival of the sound wave with respect to the normal to the surface of the substrate 10 is θ. Specifically, the azimuth angle θ is the azimuth angle of the operator's seat with respect to the substrate 10 and the multiple microphones 20. c is the speed of sound. If the time difference between the signals detected by the microphones 21 and 22 is τ, then τ=(d / c)sinθ.

[0023] When the azimuth angle of the sound wave changes by Δθ relative to the azimuth angle θ, the change in the time difference between the output signals of the microphones 21 and 22 is defined as Δτ. Since τ+Δτ=1 / c·{dsin(θ+Δθ)}, Δτ=(d / c)·sin(θ+Δθ)-τ=(d / c){sin(θ+Δθ)-sinθ}.

[0024] For example, the relationship between the azimuth angle θ and |Δτ| when Δθ=5° is as shown in Figure 3. If Δθ is the minimum azimuth angle to be detected by the microphone device, Δτ represents the angular resolution in the time domain. As shown in Figure 3, when θ=90°, Δτ≒0, that is, the angular resolution is almost 0.

[0025] In an automobile cabin, the operator's voice is reflected by the interior walls and reaches the microphone device from various directions. Therefore, in order to identify the direction of the sound source and to separate the operator's voice from noise and emphasize the voice, it is necessary to make the angular resolution greater than 0.

[0026] In this embodiment, as shown in Fig. 4, some of the microphones 20 are arranged in a direction different from that of the microphones 21 and 22 shown in Fig. 2. Specifically, when the direction in which the microphones 21 and 22 are arranged is defined as a first direction, some of the microphones 20 are arranged in a second direction perpendicular to the first direction.

[0027] As a result, the Δτ characteristics are as shown in Fig. 5. That is, in the vicinity of θ=90° where the angular resolution of microphones 21 and 22 is 0, the angular resolution of two microphones 20 shown in Fig. 4 is maximized, and the two types of Δτ characteristics complement each other in angular resolution. In Fig. 5, the solid line indicates Δτ in microphones 21 and 22, and the dashed line indicates Δτ of microphone 20 shown in Fig. 4.

[0028] In this way, by arranging multiple microphones 20 along two mutually inclined axes, it is possible to obtain characteristics in which the angular resolutions are mutually complementary, thereby preventing the angular resolution of the entire microphone device from becoming zero.

[0029] Furthermore, by arranging multiple microphones 20 in a rectangular shape and lining them up along two perpendicular axes, it is possible to prevent the occurrence of azimuth angles in all 360° directions where the angular resolution becomes extremely small and the effect of speech enhancement or noise suppression decreases.

[0030] As described above, in this embodiment, eight microphones 20 are arranged on the substrate 10. However, by providing at least three microphones 20 and arranging one microphone 20 away from the straight line connecting the other two microphones 20, it is possible to suppress a decrease in angular resolution. By arranging the multiple microphones 20 so that the straight line connecting the two microphones 20 and the straight line connecting the two microphones 20 including the other one microphone 20 are perpendicular to each other, it is possible to suppress a decrease in angular resolution in all directions.

[0031] Furthermore, by providing at least four microphones 20, the microphones 20 can be arranged in a rectangular shape to suppress a decrease in angular resolution. The microphones 20 may also be arranged three-dimensionally. For example, at least four microphones 20 may be provided, and one of the four microphones 20 may be arranged at a location away from a plane passing through the other three microphones 20. Even when the microphones 20 are arranged in this manner, a decrease in angular resolution can be suppressed. Furthermore, when the microphones 20 are arranged in this manner, the detection capability can be improved.

[0032] The lower limit of the distance d will now be described. As shown in FIG. 6, a voltage difference ΔE occurs in the voltages of the output signals of the two microphones 20 according to the time difference Δτ. If there is no noise in the output signals, the time difference Δτ can be detected based on this voltage difference ΔE. However, in reality, noise is superimposed on the output signals due to electrical noise from the microphones 20 themselves. The present inventors have studied the relationship between the magnitude of the electrical noise of the microphones 20 and whether or not Δτ can be detected.

[0033] Assume that the two output signals shown in Fig. 6 are sine waves with amplitude A and frequency f. In this case, ignoring the initial phase, the voltage difference ΔE is ΔE=Asin(2πft)-Asin{2πf(t-Δτ)}=2Asin(πfΔτ)·cos{πf(2t-Δτ)}, where t is the time and π is the constant of the circumference of a circle. In other words, the voltage difference ΔE is expressed as a cosine function with an amplitude of 2Asin(πfΔτ).

[0034] When d = 6 mm, θ = 0° Δθ = 3°, f = 1 kHz, and A = 1, Δτ = 91 ms. The voltage difference ΔE at this time is shown in Figure 7. Note that the amplitude is shown in decibels with amplitude A as the reference of 0 dB.

[0035] The waveforms shown in Fig. 7 are in an ideal state without electrical noise, and in an actual circuit, a certain amount of electrical noise is superimposed on the waveforms shown in Fig. 7. For example, when a microphone 20 with an S / N ratio of 60 dB is used, electrical noise with an effective amplitude of 0.001, i.e., -60 dB, is superimposed on the reference amplitude of 1.00, i.e., 94 dBA, of the input signal to the microphone 20. In this case, in the waveforms shown in Fig. 7, signals with amplitudes of -60 dB or less are buried in electrical noise, and it is considered that the time difference cannot be detected.

[0036] Here, the amplitude of the reference electrical noise is defined as the reference amplitude Ath, and the ratio of the time during which the voltage difference ΔE is equal to or greater than the reference amplitude Ath to the time of the entire signal is defined as the effective delta-E ratio (EDER). In other words, if the period of the voltage difference ΔE is T1 and the length of time during one period during which ΔE is equal to or greater than the reference amplitude Ath is T2, then EDER=T2 / T1. For example, if the reference amplitude Ath is -60 dB, T2 is the time shown in Figure 7. EDER=100% indicates that the voltage difference ΔE can be completely detected, and EDER=0% indicates that the voltage difference ΔE is buried in noise and cannot be detected.

[0037] EDER is a function of frequency f, amplitude A, and SNR MicSNR, and the lower the frequency f and the larger the amplitude of the electrical noise, the smaller the EDER. For example, when d = 6 mm, θ = 0°, and Δθ = 3°, the EDER is as shown in Figure 8.

[0038] For EDER to be 0 or more, it is necessary that the amplitude term is not buried in the electrical noise of the microphone 20. In other words, it is necessary to satisfy 2Asin(πfΔτ)≧10^(-MicSNR / 20). Here, the amplitude A is the relative effective voltage amplitude of the output signal of the microphone 20 when the voltage when a sound of 94 dBA is received is 0 dB, that is, the reference amplitude is 1.0.

[0039] Since EDER is expressed as a periodic cosine function, the ratio of time when the amplitude is equal to or greater than a certain value can be calculated by calculating the ratio of time in the range from 0 to π / 2. Let Amp>0, Amp=|2Asin(πfΔτ)|, and φ be the phase angle at which |ΔE| reaches a certain voltage value Const. Amp·cosφ=Const, and φ=cos -1 (Const / Amp), so in the range 0 to π / 2, EDER=cos -1 (Const / Amp) / (π / 2), where Const=10^(-MicSNR / 20) and Amp≧Const. That is, EDER is defined by Equation 1.

[0040]

number

[0041] In addition, in the formula 1, the frequency f is the lowest frequency of the frequency band to be processed by the signal processing unit 30, and for example, f≧100Hz. Since the noise entering the microphone 20 during vehicle driving has a very large low-frequency component, the voice recognition device is provided with a filter that reduces the volume of the low-frequency band to reduce the consumption of the dynamic range of the ADC. The lowest frequency f is the cutoff frequency of this filter. In addition, in the formula 1, the amplitude A is the relative effective voltage amplitude of the output signal of the microphone 20 when the amplitude of the signal output by the microphone 20 when receiving a sound of 94 dBA is 0 dB, that is, the reference amplitude is 1.0. The effective voltage amplitude can be calculated by 1 / √2×voltage amplitude.

[0042] It is desirable that the dynamic range of the ADC 31 is larger than the dynamic range of the microphone 20. If the sound pressure at the rated maximum output of the microphone 20 is MicMAX, then the dynamic range of the microphone 20 is (MicMAX-94)+MicSNR. If the number of conversion bits of the ADC 31 is m, then the dynamic range of the ADC 31 is 20×log 10 (2 m −1). The dynamic range of the ADC31 may be smaller than the dynamic range of the microphone 20. In this case, MicSNR in Equation 1 is replaced with the pseudo SN ratio of the ADC31 calculated from the dynamic range of the ADC31. The dynamic range of the ADC31 may be equal to the dynamic range of the microphone 20. The dynamic range of the ADC31 being larger than the dynamic range of the microphone 20 is the same as the LSB voltage of the ADC31 being smaller than the self-noise of the microphone 20. As described above, in this embodiment, the LSB voltage of the ADC31 is smaller than the self-noise of the microphone 20, but the LSB voltage of the ADC31 may be larger than the self-noise of the microphone 20. The LSB voltage of the ADC31 may be equal to the self-noise of the microphone 20.

[0043] Traditionally, microphones for voice recognition have been placed near the steering column, but in recent years they have been moved closer to the mouths of the driver and passenger in the front seats, such as in the overhead console or near the headliner.

[0044] It is considered that it is possible to separate and recognize the sound source if it is possible to distinguish the size of a human face with respect to Δθ. The distance between the board 10 and the operating seat, more specifically, the distance between the microphone 20 arranged on the board 10 and the mouth of the operator, is L [m]. Since the width of a human face is about 156 mm, if θ=0°, it is considered that it is possible to reduce noise if it is possible to distinguish Δθ, where Δθ=arctan(0.078 / L).

[0045] For example, as shown in Fig. 9, when the distance L is about 0.3 m, it is considered that noise reduction is possible if about ±13° can be distinguished for the direct sound, based on arctan(0.078 / 0.3) ≒ 13°. Also, when the distance L is about 0.4 m, it is considered that noise reduction is possible if about ±11° can be distinguished for the direct sound, based on arctan(0.078 / 0.4) ≒ 11°.

[0046] The relationship between the frequency f, the signal-to-noise ratio MicSNR, and the lower limit of the distance d is, for example, as shown in Figures 10 to 12. Figures 10 to 12 are graphs of EDER when f=400 Hz, 200 Hz, and 100 Hz, θ=0°, and Δθ=14°, respectively.

[0047] As shown in FIG. 10, at f=400 Hz, EDER>0.7 is achieved when MicSNR=54 dB, d>2.6 mm, or when MicSNR=44 dB, d>8.2 mm.

[0048] As shown in FIG. 11, at f=200 Hz, EDER>0.7 is achieved when MicSNR=44 dB, d>17 mm, when MicSNR=54 dB, d>5.0 mm, or when MicSNR=64 dB, d>1.7 mm.

[0049] As shown in FIG. 12, at f=100 Hz, EDER>0.7 is achieved when MicSNR=44 dB, d>33 mm, when MicSNR=54 dB, d>10 mm, or when MicSNR=64 dB, d>3.2 mm.

[0050] In this way, EDER is specified by the frequency f, the signal-to-noise ratio MicSNR, the azimuth angle θ, the minimum azimuth angle Δθ, and the amplitude A. Then, by determining the condition of the distance d where EDER>0.7, it is possible to reduce the distance d within a range where the performance of the microphone device can be ensured, thereby making the microphone device more compact.

[0051] The upper limit of the interval d will be described. The larger the interval d is, the higher the directivity of the microphone device can be enhanced. On the other hand, when the interval d exceeds 1 / 2 of the wavelength of the sound with frequency f, spatial aliasing occurs. That is, assuming that the wavelength of the sound with frequency f input to the microphone 20 is λ, spatial aliasing occurs when d > λ / 2 = (c / f)·(1 / 2). Therefore, it is desirable to set the interval d to a value that satisfies d < c / 2f.

[0052] Although the audible sound of humans is said to be about 20 Hz to 20 kHz, for voice, in ITU-T (International Telecommunication Union - Telecommunication sector), the frequency band of the telephone is defined as 300 Hz to 3.4 kHz. Therefore, in order to maintain the voice recognition performance, it is desirable to set the upper limit of the frequency f to 3.4 kHz and make d < c / 2f within this range of the frequency f.

[0053] Assuming the Celsius temperature is deg_c, c = 331.5 + 0.61×deg_c. At room temperature, for example, 25°C, c ≒ 347 m / s. At this time, the maximum value of the interval d that can suppress spatial aliasing for frequencies f up to 3.4 kHz is 347 [m / s] / 3.4 [kHz] × 1 / 2 ≒ 51 [mm].

[0054] In fact, voice includes a wide frequency band and determines the direction of sound arrival using not only a single frequency but also the upper and lower frequency bands. Therefore, it is not necessary for the interval d to satisfy d < λ / 2. However, it is desirable to suppress the occurrence of spatial aliasing in the band containing a large amount of voice information.

[0055] Also, in order to miniaturize while maintaining the performance of the microphone device, it is desirable to make EDER approach 0.7. For example, it is desirable to set the interval d so that 0.8 > EDER.

[0056] Regarding the upper and lower limits of the distance d, it is sufficient that the distance d between at least one pair of adjacent microphones 20 satisfies the above condition. That is, the distance d between some microphones 20 does not necessarily have to satisfy the above condition.

[0057] As described above, in this embodiment, by setting the interval d so as to satisfy EDER>0.7, it is possible to prevent the difference between the output signals of the multiple microphones from being buried in self-noise. Therefore, by reducing the interval d within a range that satisfies EDER>0.7, it is possible to miniaturize the microphone device while maintaining the voice recognition performance.

[0058] Furthermore, according to the above embodiment, the following effects can be obtained.

[0059] (1) At least three microphones 20 are provided, and one microphone 20 is disposed away from the straight line connecting the other two microphones 20. This makes it possible to suppress a decrease in angular resolution.

[0060] (2) A line connecting two microphones 20 and a line connecting two microphones 20 including one other microphone 20 are perpendicular to each other. This makes it possible to suppress a decrease in angular resolution.

[0061] (3) The signal processing unit 30 is disposed at the center of the microphones 20 arranged in a rectangular shape. This makes it possible to prevent the substrate 10 from becoming large.

[0062] (4) The number of microphones is 2 n In digital processing, if the number of data pieces is a power of 2, there are no wasted digits when expressed in binary, and processing can be done efficiently with the same memory capacity and communication bandwidth resources.

[0063] (5) The microphone 20 is a MEMS microphone. This allows the microphone 20 to be small, inexpensive, and have less variation in characteristics compared to a dynamic microphone, a condenser microphone, an ECM (Electron Condenser Microphone), or the like.

[0064] (Other embodiments) It should be noted that the present disclosure is not limited to the above-described embodiment, and can be modified as appropriate. In addition, in the above-described embodiment, it goes without saying that the elements constituting the embodiment are not necessarily essential, except when they are specifically stated as essential or when they are clearly considered essential in principle. In addition, in the above-described embodiment, when the numbers, values, amounts, ranges, etc. of the components of the embodiment are mentioned, they are not limited to the specific numbers, except when they are specifically stated as essential or when they are clearly limited to a specific number in principle. In addition, in the above-described embodiment, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., except when they are specifically stated or when they are limited to a specific shape, positional relationship, etc. in principle.

[0065] (In view of the present disclosure) [First viewpoint] 1. A microphone device comprising: A plurality of microphones (20), The distance between two of the microphones is d, The signal-to-noise ratio of the microphone alone is defined as MicSNR. Let the speed of sound be c, The frequency to be processed is f. The azimuth angle of the operator's seat with respect to the plurality of microphones is θ, The minimum azimuth angle to be detected is Δθ. The voltage amplitude of the output signal of the microphone is defined as A based on the output voltage when a sound of 94 dBA is received, and the amplitude of the output signal of the microphone is defined as A when the output voltage is set to 0 dB. As Δτ=d / c{sin(θ+Δθ)-sinθ}, When the differential voltage effectiveness ratio EDER is defined by Equation 1, The distance d is d<c / 2f、かつ、EDER> Microphone equipment set to a value satisfying 0.7. [Second viewpoint] The interval d is, when f≦3.4 kHz, d<c / 2f、かつ、EDER> The microphone device according to the first aspect, wherein the difference is set to a value satisfying 0.7. [Third Perspective] The distance between the microphone and the operator's seat is L [m]. The distance d is, when θ=0° and Δθ=arctan(0.078 / L),<c / 2f、かつ、EDER> The microphone device according to the first or second aspect, wherein the difference is set to a value satisfying 0.7. [Fourth viewpoint] The distance d is d when L = 0.3 m.<c / 2f、かつ、EDER> The microphone device according to the third aspect, wherein the difference is set to a value satisfying 0.7. [Fifth viewpoint] The interval d is, when MicSNR ≧ 70 dB, d<c / 2f、かつ、EDER> The microphone device according to any one of the first to fourth aspects, wherein the ratio is set to a value satisfying 0.7. [Sixth viewpoint] It is installed in vehicles and used for voice recognition, The interval d is, when f≧100Hz, d<c / 2f、かつ、EDER> The microphone device according to any one of the first to fifth aspects, wherein the ratio is set to a value satisfying 0.7. At least three of the microphones are provided; The microphone device according to any one of the first to sixth aspects, wherein one of the microphones is disposed away from a straight line connecting the other two of the microphones. [Eighth viewpoint] A straight line connecting the two microphones; The microphone device according to a seventh aspect, wherein a straight line connecting two of the microphones including the other one of the microphones is perpendicular to the straight line connecting the other one of the microphones. [Ninth viewpoint] At least four of the microphones are provided; The microphone device according to an eighth aspect, wherein the plurality of microphones are arranged in a rectangular shape. [10th viewpoint] The microphone device according to a ninth aspect, further comprising a signal processing unit (30) arranged at a central portion of the plurality of microphones arranged in the rectangular shape. [Eleventh viewpoint] Let n be a natural number, The number of microphones is 2 n The microphone device according to any one of the first to tenth aspects, [12th viewpoint] The microphone device according to an eleventh aspect, comprising eight of the microphones. [13th viewpoint] At least four of the microphones are provided; The microphone device according to any one of the first to twelfth aspects, wherein one of the four microphones is disposed at a location away from a plane passing through the other three microphones. [14th viewpoint] The microphone device according to any one of the first to thirteenth aspects, wherein the microphone is a MEMS microphone. [Explanation of symbols]

[0066] 20, 21, 22 Microphones

Claims

1. 1. A microphone device comprising: A plurality of microphones (20, 21, 22) are provided; The distance between two of the microphones is d, The signal-to-noise ratio of the microphone alone is MicSNR, The speed of sound is c, The frequency to be processed is f, The azimuth angle of the operator's seat with respect to the plurality of microphones is θ, The minimum azimuth angle to be detected is Δθ. The voltage amplitude of the output signal of the microphone based on the output voltage when receiving a sound of 94 dBA is A, As Δτ=d / c{sin(θ+Δθ)−sinθ}, When the differential voltage effective ratio EDER is defined by Equation 1, A microphone device in which the distance d is set to a value that satisfies d<c / 2f and EDER>0.

7. [0010]

2. 2. The microphone device according to claim 1, wherein the interval d is set to a value that satisfies d<c / 2f and EDER>0.7 when f≦3.4 kHz.

3. The distance between the microphone and the operator's seat is L [m], 2. The microphone device according to claim 1, wherein the distance d is set to a value that satisfies d<c / 2f and EDER>0.7 when θ=0° and Δθ=arctan(0.078 / L).

4. 4. The microphone device according to claim 3, wherein the distance d is set to a value that satisfies d<c / 2f and EDER>0.7 when L=0.3 m.

5. 2. The microphone device according to claim 1, wherein the distance d is set to a value that satisfies d<c / 2f and EDER>0.7 when MicSNR is 70 dB or higher.

6. It is installed in vehicles and used for voice recognition, 2. The microphone device according to claim 1, wherein the interval d is set to a value that satisfies d<c / 2f and EDER>0.7 when f≧100 Hz.

7. At least three of the microphones are provided; 2. The microphone device according to claim 1, wherein one of the microphones is disposed away from a straight line connecting the other two of the microphones.

8. A straight line connecting the two microphones; The microphone device according to claim 7 , wherein a line connecting the two microphones including the other one of the microphones is perpendicular to the line connecting the two microphones.

9. At least four of the microphones are provided; The microphone device according to claim 8 , wherein the plurality of microphones are arranged in a rectangular shape.

10. 10. The microphone device according to claim 9, further comprising a signal processing unit (30) disposed at a center of the plurality of microphones arranged in a rectangular shape.

11. Let n be a natural number, The number of microphones is two. ｎ 2. The microphone device according to claim 1,

12. The microphone device according to claim 11, comprising eight of the microphones.

13. At least four of the microphones are provided; 2. The microphone device according to claim 1, wherein one of the four microphones is disposed away from a plane passing through the other three microphones.

14. The microphone device according to claim 1 , wherein the microphone is a MEMS microphone.

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