Fault diagnosis method, noise measuring device, and fault diagnosis system

Abstract

To accurately discriminate timing at which a fault has occurred in a noise meter.SOLUTION: The present invention relates to a noise measuring device 20 that includes a noise meter 10 having a main microphone 11 capable of measuring noise and a sub-microphone 21 capable of measuring noise simultaneously with the main microphone 11. The present invention also relates to a fault diagnosis system 1 that includes this noise measuring device 20 and a fault diagnosis device 30 capable of diagnosing a fault of the main microphone 11. The present invention further relates to a fault diagnosis method for diagnosing a fault of the main microphone 11. In the fault diagnosis system 1 and method, the presence of a fault in the main microphone 11 of the noise meter 10 is diagnosed on the basis of comparison between the main and sub noise data obtained by each of the main and sub microphones 11, 21, in each of a plurality of recording periods.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fault diagnosis method for diagnosing a fault in a microphone, and further to a sound level measuring device including a sound level meter having a microphone, and a fault diagnosis system capable of diagnosing a fault in the microphone of the sound level meter. [Background technology]

[0002] Sound level meters with microphones are used for various purposes such as monitoring noise pollution, designing noise-free environments, etc. For example, to continuously monitor aircraft noise around airports, local governments and other organizations install sound level meters around airports, and the noise data continuously measured by these sound level meters is recorded and managed. Summary of the Invention [Problem to be solved by the invention]

[0003] When a sound level meter measures noise continuously as described above, the sound level meter is generally inspected periodically at regular intervals such as every six months or every year. However, for example, if no malfunction is found in the sound level meter during one six-month inspection, but a malfunction of the sound level meter, particularly a malfunction of the microphone, occurs during the inspection six months later, it becomes unclear when in the six months between these inspections the malfunction occurred.

[0004] In this case, there is a possibility that all of the noise data continuously measured by the sound level meter over the past six months has been affected by the malfunction, and so there is a risk that all of this noise data will become unusable.In contrast, if it were possible to know at what point in time between the regular inspection before and after the malfunction occurred the sound level meter malfunction, particularly the microphone malfunction, occurred, it would be possible to determine that the noise data from the regular inspection before the malfunction occurred until the sound level meter malfunction occurred was not affected by the malfunction, and would remain usable.

[0005] In view of this situation, it is desirable to provide a fault diagnosis method for diagnosing a fault in a sound level meter that can accurately determine when a fault in the sound level meter occurred, and in particular, it is desirable to provide a fault diagnosis method that can accurately determine when a fault in the sound level meter occurred without having to perform an inspection that involves directly touching the actual sound level meter.

[0006] It is also desirable to be able to accurately determine when a malfunction of a sound level meter occurs in a sound level measuring device having a sound level meter and in a fault diagnosis system for diagnosing malfunctions in the sound level meter. In particular, it is desirable to be able to accurately determine when a malfunction of the sound level meter occurs in a sound level measuring device and a fault diagnosis system without having to carry out an inspection that involves directly touching the actual sound level meter. [Means for solving the problem]

[0007] In order to solve the above problem, one embodiment of a fault diagnosis method is a fault diagnosis method for diagnosing a fault in a main microphone, and includes a recording step of recording main noise data based on noise measured by the main microphone and secondary noise data based on noise measured by a secondary microphone simultaneously with the measurement of the noise of the main microphone, for each of a plurality of recording periods that differ from each other over time, and a fault diagnosis step of diagnosing the presence or absence of a fault in the main microphone, for each recording period, based on a noise contrast that compares the main and secondary noise data recorded in that recording period. The noise contrast includes either or both of a time noise contrast that compares main and secondary noise waveforms that respectively represent noise levels based on the noises measured by the main and secondary microphones on a time axis, and a frequency noise contrast that compares the noise levels based on the noises measured by the main and secondary microphones on a frequency axis.

[0009] A fault diagnosis system according to one embodiment includes: noise The sound level meter includes a sound measuring device and a fault diagnosis device configured to be able to diagnose a fault in a main microphone of the sound level meter, and the fault diagnosis device is configured to be able to diagnose the presence or absence of a fault in the main microphone based on a noise contrast that compares the main and secondary noise data recorded in each of a plurality of recording periods that differ from one another over time. The noise measuring device comprises a sound level meter having a main microphone configured to be able to measure noise and whose position is fixed, and an auxiliary microphone configured to be able to measure the same noise as the noise to be measured by the main microphone simultaneously with measuring the noise of the main microphone, in order to obtain auxiliary noise data to be compared with main noise data obtained based on the noise measured by the main microphone, and whose position is fixed. The noise contrast includes either or both of a time noise contrast that compares main and auxiliary noise waveforms which respectively represent noise levels based on the noises measured by the main and auxiliary microphones on a time axis, and a frequency noise contrast that compares noise levels based on the noises measured by the main and auxiliary microphones on a frequency axis. Effect of the Invention

[0010] In the fault diagnosis method according to one aspect, it is possible to accurately determine the timing when a fault occurred in a sound level meter. In particular, in the fault diagnosis method according to one aspect, it is possible to accurately determine the timing when a fault occurred in a sound level meter without performing an inspection that involves directly touching the actual sound level meter.

[0011] In the noise measuring device and fault diagnosis system according to one aspect, it is possible to accurately determine the timing when a malfunction of the sound level meter occurs. In particular, in the noise measuring device and fault diagnosis system according to one aspect, it is possible to accurately determine the timing when a malfunction of the sound level meter occurs without performing an inspection that involves directly touching the actual sound level meter. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram of a fault diagnosis system according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view showing a schematic exploded state of a sound level meter and a sub-microphone of a sound level measuring device according to one embodiment. [Diagram 3] FIG. 3 is a perspective view showing a schematic view of a sound level meter and a sub-microphone of a sound level measuring device according to one embodiment, with part of the windscreen and the cover omitted. [Figure 4] Each of Figures 4(a) to 4(c) is a graph showing the results of comparing main and secondary noise data based on noise including event noise when the sensitivity of the main microphone is reduced by 0.5 dB relative to the sensitivity of the secondary microphone in a first example and Example 1 of an embodiment, where Figure 4(a) is a graph showing main and secondary noise waveforms representing the noise levels of the main and secondary noise data on the time axis, Figure 4(b) is a graph showing the difference in noise levels between the main and secondary noise data in multiple frequency bands and overall values, and Figure 4(c) is a graph showing MSC (magnitude squared coherence) values ​​based on the noise levels of the main and secondary noise data in multiple frequency bands and overall values. [Diagram 5]Figures 5(a) to 5(c) are graphs showing the results of comparing main and secondary noise data based on noise including event noise when the sensitivity of the main microphone is reduced by 1.0 dB relative to the sensitivity of the secondary microphone in a second example of an embodiment and in Example 2. Figure 5(a) is a graph showing main and secondary noise waveforms representing the noise levels of the main and secondary noise data on the time axis. Figure 5(b) is a graph showing the difference in noise levels between the main and secondary noise data in multiple frequency bands and overall values. Figure 5(c) is a graph showing MSC values ​​based on the noise levels of the main and secondary noise data in multiple frequency bands and overall values. [Figure 6] Figures 6(a) to 6(c) are graphs showing the results of comparing main and secondary noise data based on noise including event noise when the sensitivity of the main microphone is reduced by 1.5 dB relative to the sensitivity of the secondary microphone in a third example and example 3 of an embodiment, where Figure 6(a) is a graph showing main and secondary noise waveforms representing the noise levels of the main and secondary noise data on the time axis, Figure 6(b) is a graph showing the difference in noise levels between the main and secondary noise data in multiple frequency bands and overall values, and Figure 6(c) is a graph showing MSC values ​​based on the noise levels of the main and secondary noise data in multiple frequency bands and overall values. [Figure 7] Figures 7(a) to 7(c) are graphs showing the results of comparing main and secondary noise data based on noise including event noise when the sensitivity of the main microphone was reduced by 2.0 dB relative to the sensitivity of the secondary microphone in a fourth example of an embodiment and in Example 4, where Figure 7(a) is a graph showing main and secondary noise waveforms representing the noise levels of the main and secondary noise data on the time axis, Figure 7(b) is a graph showing the difference in noise levels between the main and secondary noise data in multiple frequency bands and overall values, and Figure 7(c) is a graph showing MSC values ​​based on the noise levels of the main and secondary noise data in multiple frequency bands and overall values. [Figure 8]Figures 8(a) to 8(c) are graphs showing the results of comparing main and secondary noise data based on noise including event noise when the sensitivity of the main microphone is reduced by 2.5 dB relative to the sensitivity of the secondary microphone in a fifth example and a fifth example of an embodiment, where Figure 8(a) is a graph showing main and secondary noise waveforms representing the noise levels of the main and secondary noise data on the time axis, Figure 8(b) is a graph showing the difference in noise levels between the main and secondary noise data in multiple frequency bands and overall values, and Figure 8(c) is a graph showing MSC values ​​based on the noise levels of the main and secondary noise data in multiple frequency bands and overall values. [Figure 9] Figures 9(a) to 9(c) are graphs showing the results of comparing main noise data including noise due to a failure with auxiliary noise data not including noise due to a failure in Example 6 of an embodiment and Example 6, where Figure 9(a) is a graph showing main and auxiliary noise waveforms representing the noise levels of the main and auxiliary noise data on the time axis, Figure 9(b) is a graph showing the difference in noise levels between the main and auxiliary noise data in multiple frequency bands and overall values, and Figure 9(c) is a graph showing the MSC value based on the noise levels of the main and auxiliary noise data in multiple frequency bands and overall values. [Figure 10] Figures 10(a) to 10(c) are graphs showing the results of comparing main and auxiliary noise data based on background noise when the same 50 dB pink noise was added to noise measured by the main and auxiliary microphones in Example 7 of an embodiment, respectively. Figure 10(a) is a graph showing main and auxiliary noise waveforms representing the noise levels of the main and auxiliary noise data on the time axis, Figure 10(b) is a graph showing the difference in noise levels between the main and auxiliary noise data in multiple frequency bands and overall values, and Figure 10(c) is a graph showing the MSC value based on the noise levels of the main and auxiliary noise data in multiple frequency bands and overall values. [Figure 11]Figures 11(a) to 11(c) are graphs showing the results of comparing main and auxiliary noise data based on background noise when different pink noises of 60 dB were added to noise measured by the main and auxiliary microphones in Example 8 of an embodiment and Example 8, respectively. Figure 11(a) is a graph showing main and auxiliary noise waveforms representing the noise levels of the main and auxiliary noise data on the time axis, Figure 11(b) is a graph showing the difference in noise levels between the main and auxiliary noise data in multiple frequency bands and overall values, and Figure 11(c) is a graph showing MSC values ​​based on the noise levels of the main and auxiliary noise data in multiple frequency bands and overall values. [Figure 12] FIG. 12 is a flowchart for explaining an outline of a fault diagnosis method according to one embodiment. [Figure 13] FIG. 13 is a flowchart for explaining an example of a fault diagnosis process of the fault diagnosis method according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A noise measuring device, a fault diagnosis system including the same, and a fault diagnosis method according to an embodiment will be described below.

[0014] "Outline of noise measurement device and fault diagnosis system" 1 to 11, a noise measuring device 20 and a fault diagnosis system 1 according to this embodiment will be generally described. The noise measuring device 20 and the fault diagnosis system 1 according to this embodiment are generally configured as follows.

[0015] As shown in Fig. 1, the fault diagnosis system 1 includes a sound level meter 10 having a main microphone 11 configured to be able to measure noise. The fault diagnosis system 1 further includes a noise measuring device 20 having the sound level meter 10. As shown in Figs. 1 to 3, the noise measuring device 20 has a sub-microphone 21 configured to be able to measure noise simultaneously with measuring the noise of the main microphone 11, in order to obtain sub-noise data for comparison with main noise data obtained based on noise measured by the main microphone 11.

[0016] Furthermore, the sound level measuring device 20 and fault diagnosis system 1 according to this embodiment can be roughly configured as follows. As shown in Figures 2 and 3, the sound level meter 10 has a microphone connecting member 12 formed in an elongated shape. The main microphone 11 is disposed at a tip end 12a of the microphone connecting member 12 in the longitudinal direction. The sub-microphone 21 is disposed on an outer peripheral surface 12b of the microphone connecting member 12.

[0017] The sound level meter 10 has a windscreen 13. The main and secondary microphones 11, 21 are disposed inside the windscreen 13. However, it is also possible to dispose the main microphone inside the windscreen and the secondary microphone outside the windscreen. In this case, the secondary microphone can also be disposed inside a separate windscreen.

[0018] The auxiliary microphone 21 is preferably installed so that the auxiliary noise data obtained thereby is as equal as possible to the main noise data obtained by the main microphone 11. The correlation between the main and auxiliary noise data, which is required to be as equal as possible in this manner, is preferably determined to such an extent that a failure of the main microphone 11 can be diagnosed.

[0019] As shown in Fig. 1, the fault diagnosis system 1 also includes a fault diagnosis device 30 configured to be able to diagnose a fault in the main microphone 11 of the sound level meter 10. As shown in Fig. 4 to Fig. 11, the fault diagnosis device 30 is configured to be able to diagnose the presence or absence of a fault in the main microphone 11 for each of a plurality of recording periods that differ over time, based on a noise contrast that compares the main and secondary noise data recorded in the recording periods.

[0020] 4 to 11(a), in the fault diagnosis device 30, the noise contrast includes a time noise contrast that compares a main noise waveform and a sub-noise waveform that respectively represent on a time axis the noise levels based on the noises measured by the main microphone 11 and the sub-microphone 21. With reference to Figs. 4 to 11(b) and (c), in the fault diagnosis device 30, the noise contrast includes a frequency noise contrast that compares on a frequency axis the noise levels based on the noises measured by the main microphone 11 and the sub-microphone 21. Details of Figs. 4 to 11 will be described later.

[0021] With reference to (b) of Figures 4 to 11, such a fault diagnosis device 30 diagnoses the presence of a fault in the main microphone 11 when, in a time-noise contrast, the main noise waveform includes an event pulse waveform that makes the noise level higher than the background noise, and the auxiliary noise waveform includes an event pulse waveform that makes the noise level higher than the background noise at the same timing as the event pulse waveform of the main noise waveform, and when, in a frequency-noise contrast, the absolute value d of the difference between the noise levels based on the event pulse waveforms of the main and auxiliary noise waveforms is greater than a predetermined noise difference threshold d1 in at least one of a plurality of frequency bands and / or the overall value.

[0022] The noise difference threshold d1 can be set according to the amount of change in sensitivity determined as a criterion for diagnosing a failure of the main microphone 11. For example, the noise difference threshold d1 can be set to increase as the amount of change in sensitivity determined as a criterion for diagnosing a failure of the main microphone 11 increases. For example, the noise difference threshold d1 can be set to 0.5 dB, 1.0 dB, 1.5 dB, 2.0 dB, and 2.5 dB when the amount of change in sensitivity is ±0.5 dB, ±1.0 dB, ±1.5 dB, ±2.0 dB, and ±2.5 dB, respectively. However, the noise difference threshold is not limited to these.

[0023] 9(a), the fault diagnosis device 30 diagnoses that the main microphone 11 is faulty when the main noise waveform includes an impact pulse waveform in which the noise level is higher than that of the secondary noise waveform at a specific pulse width in a time-noise comparison. The pulse width of the impact pulse waveform is preferably in the range of 0.1 to 2.0 seconds.

[0024] An example of an impact pulse waveform is an impact pulse waveform caused by noise generated when a failure occurs in the main microphone 11. In particular, an impact pulse waveform caused by noise generated when a failure occurs in the main microphone 11 tends to be a pulse waveform that increases the noise level at the above-mentioned pulse width. The minimum value of the pulse width of the impact pulse waveform can be determined based on the fact that the period of the equivalent sound level can be set to a minimum of 0.1 seconds. The maximum value of the pulse width of the impact pulse waveform can be determined based on the tendency that the pulse width of noise instantaneously generated when a failure occurs in the main microphone 11 is 2 seconds or less.

[0025] Furthermore, there is a noticeable tendency that the pulse width of the impact pulse waveform caused by noise generated when a failure occurs in the main microphone 11 is around 1.0 seconds. Based on this noticeable tendency, in order to identify the noise generated when a failure occurs in the main microphone 11, the minimum value of the pulse width of the impact pulse waveform can be 0.5 seconds, preferably 0.7 seconds, more preferably 0.8 seconds, and even more preferably 0.9 seconds. Furthermore, the maximum value of such a pulse width can be 1.5 seconds, preferably 1.3 seconds, more preferably 1.2 seconds, and even more preferably 1.1 seconds.

[0026] Referring to Figures 10(c) and 11(c), the fault diagnosis device 30 diagnoses that the main microphone 11 is faulty when the MSC value m calculated from noise data based on background noise measured by the main and sub microphones 11, 21, respectively, in at least one of a plurality of frequency bands and / or the overall value in the frequency noise contrast is smaller than a predetermined coherence threshold m1.

[0027] For example, the coherence threshold m1 can be set in consideration of the variation in the MSC value m calculated from noise data based on background noise detected by the main and sub microphones 11 and 21 under normal conditions. For example, the coherence threshold m1 can be set to 0.2. However, the coherence threshold is not limited to this. For example, the coherence threshold can be appropriately set within the range of 0.1 to 0.9.

[0028] In this embodiment, the MSC value m is calculated as follows. (1) The main audio signal from the main microphone 11 and the sub audio signal from the sub microphone 21 are divided on the time axis into predetermined frame lengths. (2) Using a fast Fourier transform or the like, the power spectra of the main and secondary audio signals and the average values ​​of the cross spectra between the main and secondary audio signals are calculated for all the divided frames. (3) In each frequency band, an energy sum A of the power spectrum average value of the main audio signal, an energy sum B of the power spectrum average value of the secondary audio signal, and an energy sum C of the absolute value of the cross spectrum average value are calculated. (4) In each frequency band, the MSC value is calculated from the energy sum A of the power spectrum average value of the main audio signal, the energy sum B of the power spectrum average value of the secondary audio signal, and the energy sum C of the absolute value of the cross-spectral average value, based on the following (Equation 1).

[0029] MSC value = C 2 / (A×B) (Formula 1)

[0030] Here, (a) of Fig. 4 to Fig. 11 are graphs shown as first to eighth examples of this embodiment, respectively. In (a) of Fig. 4 to Fig. 11, solid lines X1 to X8 indicate main noise waveforms, dashed lines Y1 to Y8 indicate auxiliary noise waveforms, vertical axis L indicates equivalent noise level (dB), and horizontal axis T indicates time (s (seconds)). In particular, (a) of Fig. 4 to Fig. 11 shows main and auxiliary noise waveforms in which equivalent noise levels (LAeq, 1s) of main and auxiliary noise data measured every 1s are respectively represented on a time axis of 30 seconds.

[0031] Figures 4 to 11(b) are graphs shown as first to eighth examples of this embodiment, respectively. In each of Figures 4 to 11(b), the vertical axis D represents the difference (dB) based on the equivalent noise levels of the main and secondary noise data, and the horizontal axis F represents frequency (Hz). Each of Figures 4 to 11(b) shows the difference (dB) based on the equivalent noise levels of the main and secondary noise data in five frequency bands with center frequencies of 250 Hz, 500 Hz, 1 kHz, 2 kHz, and 4 kHz in a 1 / 1 octave band.

[0032] In each of Figures 4 to 11(b), the points marked "OA" on the horizontal axis F indicate the differences (dB) based on the overall values ​​of the equivalent A-weighted sound level of the main and auxiliary noise data. In particular, the graphs in Figures 4(b) to 11(b) each show the differences in the regions above the 90th percentile of the equivalent A-weighted sound level (LAeq,1s) of the main and auxiliary noise data over a 30-second period for multiple frequency bands and overall values.

[0033] Figures 4 to 11(c) are also graphs shown as the first to eighth examples of this embodiment, respectively. In each of Figures 4 to 11(c), the vertical axis M represents the MSC value m based on the equivalent noise level of the main and secondary noise data, and the horizontal axis F represents frequency (Hz). Each of Figures 4 to 11(c) shows the MSC value m based on the equivalent noise level of the main and secondary noise data in five frequency bands with center frequencies of 250 Hz, 500 Hz, 1 kHz, 2 kHz, and 4 kHz in a 1 / 1 octave band.

[0034] In each of Figures 4 to 11(c), the points marked with "OA" on the horizontal axis F indicate the MSC value m based on the overall value of the equivalent A-weighted sound level of the main and auxiliary noise data. In particular, each of Figures 4 to 11(c) shows the MSC value m based on the average value of the cross spectrum and power spectrum in the region below the 10th percentile of the equivalent A-weighted sound level (LAeq,1s) of the main and auxiliary noise data over 30 seconds for multiple frequency bands and overall values.

[0035] However, Fig. 4 to Fig. 11 only show the first to eighth examples of this embodiment, respectively, and the graphs used for the time noise contrast and / or frequency noise contrast are not limited to these. For example, the sampling period of the equivalent sound pressure level may be other than 1 s. The noise level may be the single-exposure sound pressure level, the percentile sound pressure level, the weighted equivalent average perceived sound pressure level, etc., instead of the equivalent sound pressure level. For example, the recording period is 30 seconds in these graphs, but the recording period is not limited to these.

[0036] In the first to eighth examples of this embodiment described above, the equivalent continuous-tone sound level (dB) measured every 1 second is recorded for 30 seconds for each of the main and auxiliary noise data in each recording period. In the first, second, and third examples of this embodiment, a band-pass filter of 200 Hz to 4 kHz is applied to the main noise data and the auxiliary noise data.

[0037] In the first to eighth examples of this embodiment, the multiple frequency bands are defined by 1 / 1 octave bands. However, the multiple frequency bands can also be defined by 1 / n octave bands (n is an integer of 2 or more).

[0038] "Details of Fault Diagnosis System 1" 1, the fault diagnosis system 1 can be configured in detail as follows. In the fault diagnosis system 1, a noise measuring device 20 having a sound level meter 10 constitutes a measurement station that is placed in the vicinity of a noise measurement target. For example, the noise measuring device 20 can be placed in the vicinity of an airport, a main road, an expressway, a railway, a factory, a power plant, etc.

[0039] The fault diagnosis device 30 is placed away from the noise measuring device 20. The fault diagnosis device 30 is configured to be able to communicate with the noise measuring device 20 by wireless or wired communication means. The fault diagnosis device 30 can form part of a central station that allows centralized management of noise data, or part of a maintenance and inspection device used by a person or contractor who maintains and inspects the noise measuring device 20. However, the fault diagnosis device can also be configured integrally with the noise measuring device. The fault diagnosis device can also be placed adjacent to the noise measuring device, in which case the fault diagnosis device can also form part of the measurement station.

[0040] "Details of noise measurement equipment and sound level meters" 1 to 3, the noise measuring device 20 and the sound level meter 10 can be configured in detail as follows. As shown in Figs. 1 to 3, the main microphone 11 of the sound level meter 10 is an ECM (Electret Condenser Microphone) 11. The sub-microphone 21 of the sound level measuring device 20 is a MEMS (Micro Electro Mechanical Systems) microphone 21.

[0041] However, the main microphone and the sub microphone are not limited to this. For example, the main microphone can be a MEMS microphone, etc. For example, the sub microphone can be an ECM, etc. In this case, the noise measuring device may have a preamplifier for the sub microphone.

[0042] The microphone connecting member 12 is a preamplifier 12 configured to be capable of amplifying a signal from the main microphone 11. As shown in Figures 2 and 3, a tip end 12a of the microphone connecting member 12 is configured to be electrically and mechanically connectable to the main microphone 11. As shown in Figure 3, a base end 12c in the longitudinal direction of the microphone connecting member 12 is configured to be electrically and mechanically connectable to a main connection cable 14.

[0043] 2 and 3, the sub-microphone 21 is disposed at a longitudinal intermediate portion 12d of the microphone connecting member 12. The sub-microphone 21 is also electrically and mechanically connected to the sub-connecting cable 15. The noise measuring device 20 has one sub-microphone 21. However, the noise measuring device may have multiple sub-microphones. In this case, the multiple sub-microphones may be disposed at intervals in the circumferential direction of the microphone connecting member.

[0044] 1, the sound level meter 10 has a sound level meter main body 16 that is electrically connected to the main microphone 11 via a main connection cable 14 and a microphone connection member 12. The sound level meter main body 16 includes electronic components, electric components, etc. for providing various functions of the sound level meter 10.

[0045] 2, the sound level meter 10 has a cover 17 configured to cover the main microphone 11 and the microphone connecting member 12 from the tip portion 12a side of the microphone connecting member 12. The cover 17 can also cover the sub microphone 21. The cover 17 has a mesh portion 17a configured to allow air to pass through while preventing the passage of water and / or dust.

[0046] The windscreen 13 is disposed so as to cover the cover 17 from the tip 12a side of the microphone connecting member 12, together with the main microphone 11, the sub microphone 21, and the microphone connecting member 12. As shown in Fig. 2, the windscreen 13 has an internal cavity 13a capable of accommodating the main microphone 11, the sub microphone 21, the microphone connecting member 12, and the cover 17. The windscreen 13 also has an opening 13b formed to open the internal cavity 13a to the outside of the windscreen 13.

[0047] 2, the sound level meter 10 has an intermediate collar 18 configured to support the microphone connecting member 12 from its base end 12c side. The intermediate collar 18 has a through hole 18a that passes through the microphone connecting member 12 in the longitudinal direction. The intermediate collar 18 supports the microphone connecting member 12c from its base end 12c side with the base end 12c of the microphone connecting member 12 and the main connection cable 14 passing through the through hole 18a.

[0048] 2 and 3, the sound level meter 10 has a mounting collar 19 configured to support the cover 17 and the intermediate collar 18 from the base end 12c side of the microphone connecting member 12. The mounting collar 19 has a through hole 19a that passes through the microphone connecting member 12 in the longitudinal direction. The mounting collar 19 supports the cover 17 and the intermediate collar 18 from the base end 12c side of the microphone connecting member 12 with the main and auxiliary connecting cables 14, 15 passing through the through hole 19a. The mounting collar 19 also has a slit 19b formed to allow the main and auxiliary connecting cables 14, 15 to be drawn out to the outside of the sound level meter 10.

[0049] 1, sound level measuring device 20 has an audio interface 22 that is electrically connected to main microphone 11 via main connection cable 14, microphone connection member 12, and sound level meter main body 16, and is also electrically connected to secondary microphone 21 via secondary connection cable 15. Audio interface 22 can receive signals from main and secondary microphones 11, 21. Note that sound level meter main body 16, and in particular the audio signal output section of sound level meter main body 16, are electrically connected to audio interface 22 by a cable (not shown).

[0050] The noise measuring device 20 has a noise data management unit 23 configured to manage main and secondary noise data based on signals from the main and secondary microphones 11, 21, respectively. The noise data management unit 23 is configured to receive signals from the main and secondary microphones 11, 21 via an audio interface 22.

[0051] The noise data management unit 23 is configured to be able to record the main and secondary noise data for a plurality of recording periods. The main and secondary noise data can also be recorded in the fault diagnosis device instead of in the noise data management unit of the noise measuring device. The main and secondary noise data can also be recorded in the fault diagnosis device in addition to in the noise data management unit of the noise measuring device.

[0052] The noise data management unit 23 is also configured to be able to communicate with the fault diagnosis device 30 by wireless or wired communication means. The noise data management unit 23 can be configured to include electronic components such as a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), flash memory, an input interface, an output interface, and an electric circuit in which such electronic components are arranged. Furthermore, as shown in Fig. 3, the noise measuring device 20 has a support member 24 configured to be able to support the sound level meter 10 from below. The support member 24 is attached to the mounting collar 19 of the sound level meter 10 from below.

[0053] "Details of fault diagnosis device" 1, the fault diagnosis device 30 can be specifically configured as follows: As described above, the fault diagnosis device 30 can diagnose the presence or absence of a fault in the main microphone 11 based on a noise contrast that compares main and secondary noise data in each of a plurality of recording periods that differ from one another over time.

[0054] In the fault diagnosis device 30, it is possible to diagnose that a fault has occurred in the main microphone 11 at the timing of the recording period during which it is first determined that the main microphone 11 has a fault, among a plurality of recording periods. In this case, it can be determined that the main noise data in the recording period after the recording period during which it is first determined that the main microphone 11 has a fault is affected by the fault, while it can be determined that the main noise data in the recording period prior to the recording period during which it is first determined that the main microphone 11 has a fault is not affected by the fault, and as a result, it can be effectively utilized.

[0055] The fault diagnosis device 30 is configured to be able to determine, in a time-noise contrast, whether or not the main and auxiliary noise waveforms include an event pulse waveform that makes the noise level higher than the background noise at the same timing. The fault diagnosis device 30 is configured to be able to determine, in a frequency-noise contrast, whether or not the absolute value d of the difference between the noise levels based on the event pulse waveforms of the main and auxiliary noise waveforms is greater than a noise difference threshold d1 in at least one of a plurality of frequency bands and / or the overall value.

[0056] The fault diagnosis device 30 is configured to be able to determine, in a time-noise comparison, whether or not the main noise waveform includes an impact pulse waveform in which the noise level is increased more than that of the auxiliary noise waveform at the specific pulse width. The fault diagnosis device 30 is configured to be able to determine, in a frequency-noise comparison, whether or not the MSC value m calculated from noise data based on background noises measured by the main and auxiliary microphones 11, 21 is smaller than a predetermined coherence threshold m1 in at least one of a plurality of frequency bands and / or an overall value.

[0057] Such a fault diagnosis device 30 can be configured to include electronic components such as a CPU, RAM, ROM, flash memory, an input interface, an output interface, and the like, and an electric circuit in which such electronic components are arranged.

[0058] "Outline of fault diagnosis method" The fault diagnosis method according to this embodiment will be outlined with reference to Figures 12 and 13. Such a fault diagnosis method is outlined as follows.

[0059] 12, the fault diagnosis method diagnoses a fault in the main microphone 11. In this fault diagnosis method, main noise data based on noise measured by the main microphone 11 and secondary noise data based on noise measured by the secondary microphone 12 simultaneously with the measurement of the noise by the main microphone 11 are recorded in each of a plurality of recording periods that differ from each other over time (recording step S1). In each recording period, it is diagnosed whether or not a fault has occurred in the main microphone 11 based on a noise comparison that compares the main and secondary noise data recorded in that recording period (fault diagnosis step S2).

[0060] In the fault diagnosis step S2 of such a fault diagnosis method, a noise comparison can be performed similarly to the fault diagnosis device 30, and the presence or absence of a fault in the main microphone 11 can be diagnosed similarly to the fault diagnosis device 30.

[0061] 13, the fault diagnosis process S2 in each recording period can be performed, for example, as follows: In a time noise comparison, it is determined whether or not the main and secondary noise waveforms contain an event pulse waveform at the same timing (first stage S21 of the event noise determination process).

[0062] If the main and auxiliary noise waveforms contain event pulse waveforms at the same timing (YES), it is determined whether the absolute value d of the difference between the noise levels based on the event pulse waveforms of the main and auxiliary noise waveforms is greater than the noise difference threshold d1 in at least one of the multiple frequency bands and / or the overall value in the frequency noise comparison (second stage S22 of the event noise determination process).If the absolute value d of the difference between the noise levels is greater than the noise difference threshold d1 in at least one of the multiple frequency bands and / or the overall value (YES), it is determined that the main microphone 11 has a malfunction (malfunction determination process S23).

[0063] If the absolute value d of the difference between the noise levels is equal to or less than the noise difference threshold d1 in at least one of the multiple frequency bands and / or the overall value (NO), it is determined whether or not the main noise waveform includes an impact pulse waveform that increases the noise level more than the auxiliary noise waveform at the specific pulse width in the time-noise comparison (noise determination step S24). Even if the main and auxiliary noise waveforms do not include an event pulse waveform at the same timing in the first stage S21 of the event noise determination step (NO), it is determined whether or not the main noise waveform includes an impact pulse waveform in the time-noise comparison (noise determination step S24). If the main noise waveform includes an impact pulse waveform (YES), it is determined that the main microphone 11 has a malfunction (malfunction determination step S23).

[0064] If the main noise waveform does not include an impact pulse waveform (NO), it is determined whether the MSC value m calculated from noise data based on background noise measured by the main and sub microphones 11, 21 in at least one of a plurality of frequency bands and / or the overall value in the frequency noise comparison is smaller than the coherence threshold m1 (background noise determination step S25). If the MSC value m is smaller than the coherence threshold m1, it is determined that the main microphone 11 is faulty (fault determination step S23). If the MSC value m is equal to or greater than the coherence threshold m1, it is determined that the main microphone 11 is not faulty (no fault determination step S26).

[0065] However, in such a failure diagnosis process, the presence or absence of a failure of the main microphone can also be diagnosed by only the event noise determination process, only the noise determination process, or only the background noise determination process. The presence or absence of a failure of the main microphone can also be diagnosed by a combination of two of the event noise determination process, the noise determination process, and the background noise determination process.

[0066] According to the above, the noise measuring device 20 of this embodiment comprises a sound level meter 10 having a main microphone 11 configured to be able to measure noise, and a sub-microphone 21 configured to be able to measure noise simultaneously with the measurement of noise by the main microphone 11, in order to obtain sub-noise data for comparison with main noise data obtained based on the noise measured by the main microphone 11.

[0067] By using such sound level measuring device 20 to record main noise data based on noise measured by the main microphone 11 and secondary noise data based on noise measured by the secondary microphone 21 during each of a number of continuous recording periods and then comparing the main and secondary noise data recorded during each recording period, it is possible to accurately determine in which of the multiple recording periods a malfunction of the main microphone 11 occurred. In particular, it is possible to accurately determine the timing at which a malfunction of the sound level meter 10 occurred, without having to perform an inspection that involves direct contact with the actual sound level meter 10.

[0068] In the noise measuring device 20 of this embodiment, the sound level meter 10 is provided with a microphone connecting member 12 formed in an elongated shape, the main microphone 11 is arranged at the longitudinal end 12a of the microphone connecting member 12, and the sub-microphone 21 is arranged on the outer peripheral surface 12b of the microphone connecting member 12.

[0069] In such a noise measuring device 20, the sub microphone 21 can be placed near the main microphone 11, which can improve the correlation between the main and sub noise data based on the noises measured by the main and sub microphones 11, 21. This makes it possible to clearly detect differences between such main and sub noise data that arise due to trouble, and as a result, it is possible to accurately determine in which of multiple recording periods the failure of the main microphone 11 occurred.

[0070] In the noise measuring device 20 and fault diagnosis method according to this embodiment, the main and auxiliary microphones 11, 21 are disposed inside the windscreen 13. Therefore, the main and auxiliary microphones 11, 21 can be disposed in a similar environment, which results in an improved correlation between the main and auxiliary noise data based on the noises measured by the main and auxiliary microphones 11, 21, respectively.

[0071] The fault diagnosis system 1 of this embodiment includes the above-mentioned noise measuring device 20, and a fault diagnosis device 30 configured to be able to diagnose a fault in the main microphone 11 of the sound level meter 10, and the fault diagnosis device 30 is configured to be able to diagnose the presence or absence of a fault in the main microphone 11, for each of a plurality of recording periods that differ over time, based on a noise contrast that compares the main and secondary noise data recorded in those recording periods.

[0072] The fault diagnosis method of this embodiment is a fault diagnosis method for diagnosing a fault in the main microphone 11, and includes a recording step S1 for recording main noise data based on noise measured by the main microphone 11 and secondary noise data based on noise measured by the secondary microphone 21 simultaneously with the measurement of the noise by the main microphone 11 over a plurality of different recording periods over time, and a fault diagnosis step S2 for diagnosing the presence or absence of a fault in the main microphone 11 based on a noise contrast that compares the main and secondary noise data recorded in each recording period.

[0073] In such a fault diagnosis system and method, main noise data based on noise measured by the main microphone 11 and secondary noise data based on noise measured by the secondary microphone 21 are recorded in each of a plurality of continuous recording periods. Therefore, by referring to the comparison results of the main and secondary noise data recorded in each recording period, it is possible to accurately determine in which of the plurality of recording periods a fault occurred in the main microphone 11. In particular, it is possible to accurately determine the timing at which a fault occurred in the main microphone 11, without inspecting the main microphone 11 by directly touching it.

[0074] In the fault diagnosis system 1 and fault diagnosis method according to the present embodiment, the noise contrast includes a time noise contrast that compares main and auxiliary noise waveforms which respectively represent on a time axis the noise levels based on the noises measured by the main and auxiliary microphones 11, 21, and a frequency noise contrast that compares on a frequency axis the noise levels based on the noises measured by the main and auxiliary microphones 11, 21, respectively. The main microphone 11 is diagnosed as having a fault when, in the time noise contrast, the main noise waveform includes an event pulse waveform which makes the noise level higher than the background noise, and the auxiliary noise waveform includes an event pulse waveform which makes the noise level higher than the background noise, at the same timing as the event pulse waveform of the main noise waveform, and when, in the frequency noise contrast, the absolute value d of the difference between the noise levels based on the event pulse waveforms of the main and auxiliary noise waveforms is greater than a predetermined event noise difference threshold d1 in at least one of a plurality of frequency bands and / or the overall value.

[0075] In such a fault diagnosis system 1 and fault diagnosis method, a decrease in the sensitivity of the main microphone 11 can be sensitively detected from a change in the event noise data that may be included in the main and secondary noise data during multiple recording periods, and as a result, it can be accurately determined in which of the multiple recording periods a fault in the main microphone 11 occurred.

[0076] In the fault diagnosis system 1 and fault diagnosis method of this embodiment, the noise contrast includes a time-noise contrast that compares main and auxiliary noise waveforms that respectively represent on a time axis the noise levels based on the noises measured by the main and auxiliary microphones 11, 21, and if the time-noise contrast shows that the main noise waveform includes an impact pulse waveform in which the noise level is increased compared to the auxiliary noise waveform with a pulse width of 0.1 seconds to 2.0 seconds, the main microphone 11 is diagnosed as having a fault.

[0077] In such a fault diagnosis system 1 and fault diagnosis method, for example, by utilizing pulse noise that may be included in the main noise data due to a failure of the main microphone 11 during multiple recording periods, it is possible to accurately determine in which of multiple recording periods a failure of the main microphone 11 occurred.

[0078] In the fault diagnosis system 1 and fault diagnosis method of this embodiment, the noise contrast includes a frequency noise contrast that compares noise levels based on the noise measured by the main and sub-microphones 11, 21 on a frequency axis, and if the MSC value m calculated from noise data based on the background noise measured by the main and sub-microphones 11, 21 in at least one of a plurality of frequency bands and / or the overall value in the frequency noise contrast is smaller than a predetermined coherence threshold m1, the main microphone 11 is diagnosed as having a fault.

[0079] In such a fault diagnosis system 1 and fault diagnosis method, it is possible to accurately determine in which of the multiple recording periods a fault in the main microphone 11 occurred by utilizing a large amount of background noise data that may be contained in the main and secondary noise data during multiple recording periods.

[0080] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and the present invention can be modified and changed based on the technical concept thereof. EXAMPLES

[0081] Examples 1 to 8 will be described. In Examples 1 to 5, the event noise judgment steps S21 and S22 were used to diagnose whether the main microphone 11 had a malfunction. In Example 6, the noise judgment step S24 was used to diagnose whether the main microphone 11 had a malfunction. In Examples 7 and 8, the background noise judgment step S25 was used to diagnose whether the main microphone 11 had a malfunction.

[0082] "Examples 1 to 5" Examples 1 to 5 will now be described. In each of the noise measuring devices 20 of Examples 1 to 5, the main microphone 11 of the sound level meter 10 was an ECM 11, the sub-microphone 21 of the sound level measuring device 20 was a MEMS microphone 21, the sub-microphone 21 was disposed on the outer circumferential surface 12b of the microphone connecting member 12, and the main and sub-microphones 11, 21 were disposed inside the windscreen 13. In Examples 1 to 5, the sensitivity of the main microphone 11 was reduced by 0.5 dB, 1.0 dB, 1.5 dB, 2.0 dB, and 2.5 dB relative to the sensitivity of the sub-microphone 21, respectively.

[0083] In each of Examples 1 to 5, the difference in noise level between the main and auxiliary noise data was confirmed in multiple frequency bands and overall values ​​during one recording period. One recording period was 30 seconds. The multiple frequency bands were five frequency bands with center frequencies of 250 Hz, 500 Hz, 1 kHz, 2 kHz, and 4 kHz in 1 / 1 octave bands. The difference in noise level between the main and auxiliary noise data was taken as the difference in the region above the 90th percentile of the equivalent continuous A-weighted sound level (LAeq,1s) of the main and auxiliary noise data.

[0084] As a result of such confirmation, the graphs in Fig. 4 to Fig. 8(b) for Examples 1 to 5 were obtained. Referring to Fig. 4 to Fig. 8(b), as the amount of decrease in the sensitivity of the main microphone 11 relative to the sensitivity of the sub microphone 21 was increased between 0.5 dB and 2.5 dB, the above difference (dB) increased in each frequency band and overall value. In particular, the difference increased significantly in the overall value. Based on these results, it was confirmed that the presence or absence of a malfunction of the main microphone 11 can be diagnosed using the event noise judgment steps S21 and S22 by setting the noise difference threshold d1 in accordance with the amount of change in sensitivity determined as a criterion for diagnosing a malfunction of the main microphone 11.

[0085] "Example 6" A description will now be given of Example 2. The noise measuring device 20 of Example 6 was similar to the noise measuring devices 20 of Examples 1 to 5, except that the sensitivities of the main and sub microphones 11, 21 were made the same. In Example 6, an impact pulse waveform equivalent to pulse noise that may occur when the main microphone 11 fails was intentionally added to the main microphone 11.

[0086] In Example 6, the main and auxiliary noise waveforms, which respectively represent the equivalent sound level (LAeq, 1s) of the main and auxiliary noise data measured every 1s on the time axis of one recording period, were compared. One recording period was 30 seconds.

[0087] As a result of such confirmation, the graph of Fig. 10(a) relating to Example 6 could be obtained. In Fig. 10(a), it was clear that the main noise data indicated by the solid line X6 contained an impact pulse waveform, whereas the secondary noise data indicated by the dashed line Y6 did not contain an impact pulse waveform. From such a result, it was confirmed that the presence or absence of a malfunction of the main microphone 11 could be diagnosed using the noise determination process S24.

[0088] "Examples 7 and 8" Examples 7 and 8 will now be described. The noise measuring device 20 in each of Examples 7 and 8 was similar to the noise measuring device 20 in each of Examples 1 to 5, except that the sensitivities of the main and sub microphones 11, 21 were the same. In Example 7, the same 50 dB pink noise was added to the noise measured by the main and sub microphones 11, 21. In Example 8, different 60 dB pink noise was added to the noise measured by the main and sub microphones 11, 21.

[0089] In each of Examples 7 and 8, the MSC value m based on the main and auxiliary noise data was confirmed in multiple frequency bands and overall values ​​during one recording period. One recording period was 30 seconds. The multiple frequency bands were five frequency bands with center frequencies of 250 Hz, 500 Hz, 1 kHz, 2 kHz, and 4 kHz in 1 / 1 octave bands. The MSC value m based on the main and auxiliary noise data was the MSC value m based on the average value of the cross spectrum and power spectrum in the region below the 10th percentile of the equivalent sound level (LAeq,1s) of the main and auxiliary noise data.

[0090] As a result of such confirmation, the graphs of Fig. 10(c) and Fig. 11(c) for Examples 7 and 8, respectively, could be obtained. Referring to Fig. 10(c) and Fig. 11(c), it was found that the MSC value m of Example 8 was smaller than the MSC value m of Example 7 in each frequency band and overall value. These results confirmed that if the coherence threshold m1 is set taking into consideration the variation in the MSC value m calculated from noise data based on background noise confirmed by the main and sub microphones 11, 21 under normal conditions, it is possible to diagnose the presence or absence of a malfunction of the main microphone 11 using the above background noise determination step S25. [Explanation of symbols]

[0091] Reference Signs List 1...fault diagnosis system, 10...sound level meter, 11...main microphone, 12...microphone connecting member, 12a...tip portion, 12b...outer peripheral surface, 13...windscreen, 20...noise measuring device, 21...sub-microphone, 30...fault diagnosis device d...Absolute value of the difference between the noise levels based on the event pulse waveforms of the main and secondary noise waveforms, d1...Noise difference threshold m...magnitude squared coherence value (MSC value), m1...coherence threshold S1: Recording process, S2: Fault diagnosis process

Claims

1. 1. A method for diagnosing a fault in a main microphone, comprising: a recording step of recording main noise data based on the noise measured by the main microphone and secondary noise data based on the noise measured by the secondary microphone simultaneously with the measurement of the noise by the main microphone, for each of a plurality of recording periods different from each other over time; a fault diagnosis step of diagnosing whether or not the main microphone is faulty based on a noise contrast that compares the main and secondary noise data recorded during each recording period; Including, The noise contrast includes either or both of a time noise contrast that compares main and auxiliary noise waveforms that respectively represent noise levels based on the noises measured by the main and auxiliary microphones on a time axis, and a frequency noise contrast that compares noise levels based on the noises measured by the main and auxiliary microphones on a frequency axis. Fault diagnosis method.

2. the noise contrast includes the time noise contrast and the frequency noise contrast, 2. The fault diagnosis method according to claim 1, wherein the main microphone is diagnosed as having a fault when, in the time-noise contrast, the main noise waveform includes an event pulse waveform that makes the noise level higher than background noise, and the auxiliary noise waveform includes an event pulse waveform that makes the noise level higher than background noise at the same timing as the event pulse waveform of the main noise waveform, and when, in the frequency noise contrast, an absolute value of a difference between the noise levels based on the event pulse waveforms of the main and auxiliary noise waveforms is greater than a predetermined noise difference threshold in at least one of a plurality of frequency bands and / or an overall value.

3. the noise contrast comprises the temporal noise contrast, 3. The fault diagnosis method according to claim 1, wherein the main microphone is diagnosed as having a fault when the main noise waveform includes an impact pulse waveform in which the noise level is increased with a pulse width of 0.1 seconds to 2.0 seconds compared to the secondary noise waveform in the time-noise contrast.

4. the noise contrast comprises the frequency noise contrast, The fault diagnosis method according to any one of claims 1 to 3, wherein the main microphone is diagnosed as being faulty when a magnitude-squared coherence value calculated from noise data based on background noise measured by the main and auxiliary microphones in at least one of a plurality of frequency bands and / or an overall value in the frequency noise contrast is smaller than a predetermined coherence threshold value.

5. The fault diagnosis method according to any one of claims 1 to 4, wherein the main and auxiliary microphones are arranged inside a windscreen.

6. A noise measuring device comprising: a sound level meter having a main microphone configured to be capable of measuring noise and having a fixed position; and a secondary microphone configured to be capable of measuring the same noise as the noise to be measured by the main microphone at the same time as measuring the noise of the main microphone, in order to obtain secondary noise data to be compared with main noise data obtained based on the noise measured by the main microphone, and having a fixed position; a fault diagnosis device configured to be able to diagnose a fault in the main microphone of the sound level meter; Equipped with the fault diagnosis device is configured to be able to diagnose the presence or absence of a fault in the main microphone based on a noise contrast comparing the main and secondary noise data recorded in each of a plurality of recording periods that differ from one another over time, The noise contrast includes either or both of a time noise contrast that compares main and auxiliary noise waveforms that respectively represent noise levels based on the noises measured by the main and auxiliary microphones on a time axis, and a frequency noise contrast that compares noise levels based on the noises measured by the main and auxiliary microphones on a frequency axis. Fault diagnosis system.

7. the sound level meter has a microphone connection member formed in an elongated shape, The main microphone is disposed at a tip end of the microphone connection member in a longitudinal direction, 7. The noise measuring device according to claim 6, wherein the sub-microphone is disposed on an outer circumferential surface of the microphone connecting member.

8. 8. A noise measuring device according to claim 6, further comprising a windscreen in which the main and sub microphones are disposed.

9. the noise contrast includes the time noise contrast and the frequency noise contrast, 7. The fault diagnosis system according to claim 6, wherein the main microphone is diagnosed as having a fault when, in the time noise contrast, the main noise waveform includes an event pulse waveform that makes the noise level higher than background noise, and the auxiliary noise waveform includes an event pulse waveform that makes the noise level higher than background noise at the same timing as the event pulse waveform of the main noise waveform, and when, in the frequency noise contrast, an absolute value of a difference between the noise levels based on the event pulse waveforms of the main and auxiliary noise waveforms is greater than a predetermined noise difference threshold in at least one of a plurality of frequency bands and / or an overall value.

10. the noise contrast comprises the temporal noise contrast, 10. The fault diagnosis system according to claim 6 or 9, wherein the main microphone is diagnosed as having a fault when the main noise waveform includes an impact pulse waveform in which the noise level is increased more than the secondary noise waveform in a pulse width of 0.1 seconds to 2.0 seconds in the time-noise contrast.

11. the noise contrast comprises the frequency noise contrast, 11. The fault diagnosis system according to claim 6, wherein the main microphone is diagnosed as being faulty when a magnitude-squared coherence value calculated from noise data based on background noise measured by the main and auxiliary microphones in at least one of a plurality of frequency bands and / or an overall value in the frequency noise contrast is smaller than a predetermined coherence threshold value.

Images