JP7283010B2 - Sound source identification method - Google Patents

Description

The present invention relates to a sound source localization method.

A microphone array is known in which a large number of microphones are arranged vertically and horizontally on a plane. The sound pressure of the noise generated from the rotating tires is simultaneously measured with a large number of microphones that make up such a microphone array, and the measured data is subjected to acoustic holography processing to determine the sound pressure at the contact area of the tire. A method for obtaining the distribution is known (see Patent Document 1, for example). In such a method, a microphone array 112 is often arranged in front of or behind the rotating tire T, as shown in FIG. Also, what is intended to be measured in such a method is the sound pressure of noise generated from the contact portion G of the tire T. FIG.

Japanese Patent No. 5089253

In such a method, if the microphone array 112 is separated from the ground contact portion G of the tire T, the sound pressure of not only the noise generated from the ground contact portion G of the tire T but also the sound pressure of other background noise is However, there was a problem that the sound source could not be specified accurately. For example, when the microphone array 112 is arranged in front or behind the tire T as shown in FIG. 8, the reflected sound between the tread surface T1 of the tire T and the surface D1 of the drum D rotating the tire T is It was a loud dark noise.

In order not to measure the sound pressure of such background noise, it is necessary to measure the sound pressure near the contact portion G of the tire T. However, since the microphone array 112 is a large array consisting of a large number of microphones, it cannot be placed close to the ground contact portion G of the tire T.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sound source identifying method capable of reducing the influence of background noise.

The sound source probing method of the embodiment measures the sound pressure of noise at a plurality of measurement positions away from the tire while rotating the tire, and uses acoustic holography based on the measurement data to determine the sound pressure distribution at the ground contact portion of the tire. and identifying the sound source of the noise based on the sound pressure distribution, wherein the sound pressure is sequentially measured at a plurality of measurement positions using a movable mobile microphone, and the sound pressure at each measurement position by the mobile microphone is measured. In the measurement, the measurement is started and ended based on a predetermined reference signal, and using a fixed microphone whose position is fixed, the sound pressure is measured in synchronization with the measurement at each measurement position by the mobile microphone, and the mobile microphone and the measurement data of the fixed microphone, and the phase difference between the frequency analysis data of the measurement data of the mobile microphone at each measurement position and the corresponding frequency analysis data of the measurement data of the fixed microphone to obtain the phase difference caused by the difference in the measurement position among the phase differences between the frequency analysis data of the measurement data of the mobile microphone at each measurement position, and the phase difference caused by the difference in the measurement position Acoustic holography using the phase difference is used to determine the sound pressure distribution at the ground contact portion of the tire, and the measurement position by the moving microphone is a location under the tire in front or behind the tire. .

According to the sound source probing method of the embodiment, the measurement range of the mobile microphone can be narrowed, and the sound pressure can be measured near the sound source, so that the influence of background noise can be reduced. .

FIG. 2 is a diagram showing how the sound source probing method of the embodiment is implemented; The figure which looked at the tire from the axial direction. FIG. 2 is a diagram showing how the sound source probing method of the embodiment is implemented; The figure seen from the arrow A direction of FIG. A conceptual diagram of a sound source probing device. FIG. 4 is a diagram showing measurement positions and movement paths of mobile microphones; The flowchart of the whole sound source probing method. Flowchart of measurement of sound pressure. Image diagram of acoustic holography processing. The figure which shows the state of the conventional sound source identification method. The figure which looked at the tire from the axial direction.

Embodiments will be described based on the drawings. It should be noted that the embodiment described below is merely an example, and any suitable modifications within the scope of the present invention are included in the scope of the present invention.

1 and 2 show the state of sound source probing in this embodiment. Although not shown, the tread surface T1 of the tire T is formed with a large number of grooves. When the drum D rotates while the tire T is in contact with (grounds on) the drum D, the tire T rotates in the direction opposite to the rotation direction of the drum D, and noise is generated from the grooves of the contact portion G of the tire T. . The sound source probing method of this embodiment is a method of identifying the position of the noise source at that time.

<Regarding the Sound Source Probing Device of the Embodiment>
FIG. 3 shows an example of a sound source probing device 10 used for carrying out the sound source probing method of this embodiment. The sound source probing device 10 has one movable microphone 12 and one fixed microphone 14 as devices for measuring the sound pressure of noise.

The sound source probing device 10 also includes an acoustic holography device 16 to which the mobile microphone 12 and the fixed microphone 14 are connected, a computer 18 to which the acoustic holography device 16 is connected, and an output such as a display for outputting the calculation results of the computer 18. a device 20; Further, the sound source tracking device 10 has a reference signal device 22 for acquiring a reference signal, which will be described later, and a movement control device 24 for moving the mobile microphone 12 . A reference signal device 22 and a motion control device 24 are connected to the computer 18 .

As the mobile microphone 12, one having a small measuring portion at the tip is used. For example, the mobile microphone 12 may be a probe microphone, a 1/2, 1/4 or 1/8 inch microphone (i.e., a tip measuring portion diameter 2, 1/4 or 1/8 inch microphones), or MEMS (Micro-Electrical-Mechanical Systems) microphones.

The mobile microphone 12 is arranged so that the measuring portion at the tip thereof approaches the contact portion G of the tire T to the drum D. As shown in FIG. The measurement position of the sound pressure by the mobile microphone 12 (that is, the position of the measuring portion at the tip of the mobile microphone 12) is preferably 25 mm to 100 mm (including 25 mm and 100 mm) away from the ground contact portion G of the tire T.

Specific locations of the mobile microphone 12 include, for example, a location in front of or behind the tire T, a location in the axial direction (width direction) of the tire T, and the like. A preferred location for the mobile microphone 12 is in front of or behind the tires. A more preferable placement location for the mobile microphone 12 is a location below the tire T in front or behind the tire T as shown in FIG. It is a place sandwiched between the surface D1 of the drum D).

Mobile microphone 12 is held by a portion of motion controller 24 and is moved by motion controller 24 . The movement control device 24 is, for example, a robot. The measuring part of the mobile microphone 12 moves on a plane having a predetermined area. This plane is the sound pressure measurement plane 30 by the moving microphone 12 (see FIG. 2). The measurement plane 30 is, for example, a plane perpendicular to the traveling direction of noise generated from the ground contact portion G of the tire T, and in the front-rear direction of the tire T when the mobile microphone 12 is arranged in front or behind the tire T. is a plane perpendicular to

FIG. 4 shows an enlarged sound pressure measurement plane 30 by the mobile microphone 12 . In FIG. 4, the moving path of the mobile microphone 12 is indicated by a dashed line, and the stop position is indicated by a circle. The movement path describes a grid (preferably a grid forming squares as in FIG. 4).

The mobile microphone 12 stops at all the stop positions shown in FIG. 4, but the route of movement is not limited. As an example, as shown by the arrows in FIG. 4, the mobile microphone 12 moves to the right on the topmost (first row) movement path and moves to the left on the second (second row) movement path from the top. Then, the third row moves to the right, the fourth row moves to the left, and so on, and stops at all stop positions during that movement.

The mobile microphone 12 performs sound pressure measurements while stopped at each stop position. That is, the stop positions circled in FIG. 4 are sound pressure measurement positions. A measurement surface 30 is defined as a portion surrounded by the outermost measurement position and movement path in FIG.

The distance L between adjacent measurement positions (that is, the stop position of the mobile microphone 12) is preferably 1 mm to 10 mm (including 1 mm and 10 mm), and preferably 4 mm to 5 mm (including 4 mm and 5 mm). More preferred. The movement path and stop position of the mobile microphone 12 as described above are set in advance in the sound source tracking device 10 .

The position where the fixed microphone 14 is fixed may be anywhere as long as the noise generated from the ground contact portion G of the rotating tire T can be measured. For example, as shown in FIG. ) is fixed to the fixed microphone 14 . Although various microphones can be applied as the fixed microphone 14, for example, a 1/2, 1/4 or 1/8 inch microphone is used.

The reference signal device 22 is, for example, a rotary encoder provided on the rotating shaft S of the tire T as shown in FIG. When the tire T and its rotary shaft S rotate, a pulse signal corresponding to the rotation angle of the rotary shaft S is generated from the rotary encoder and sent to the computer 18 . For example, one pulse signal is generated each time the tire T and its rotation axis S rotate one round, ie, 360°.

This pulse signal is used as a reference signal for starting and ending sound pressure measurement by the mobile microphone 12 . Therefore, the relationship between the start of measurement by the mobile microphone 12 and the pulse signal and the relationship between the end of measurement by the mobile microphone 12 and the pulse signal are set in advance. For example, a predetermined pulse signal (for example, the first pulse) after the mobile microphone 12 moves to a new measurement position is set as a reference signal for starting measurement, and another predetermined pulse signal after the mobile microphone 12 moves to the new measurement position is set as a reference signal for starting measurement. A (for example, second or third) pulse signal is set as a reference signal for ending the measurement.

The acoustic holography device 16 acquires sound pressure measurement data from the mobile microphone 12 and the fixed microphone 14, performs frequency analysis and acoustic holography processing, etc., which will be described later, and calculates the sound pressure distribution at the ground contact portion G of the tire T. do. The computer 18 also controls the connected acoustic holography device 16 and movement control device 24 . Then, the sound pressure distribution at the ground contact portion G of the tire T obtained by the acoustic holography device 16 is output to the output device 20 .

<Regarding the sound source probing method of the embodiment>
FIG. 5 shows a rough flow of the sound source probing method of this embodiment. First, the tire T rotates (S1), and then the sound pressure is measured by the moving microphone 12 and the fixed microphone 14 (S2). Next, based on the sound pressure measurement data, the sound pressure distribution at the ground contact portion G of the tire T is calculated using acoustic holography (S3). Next, the sound source is specified based on the sound pressure distribution in the contact portion G of the tire T (S4).

To explain in detail, first, the tire T is arranged so as to contact the drum D as shown in FIGS. 1 and 2 . Next, the rotation of the drum D starts, and the rotation of the tire T in contact with the drum D starts (S1). When the tire T starts rotating, noise begins to be generated. Also, a pulse signal is generated as a reference signal according to the rotation angle of the tire T and the rotating shaft S. FIG.

FIG. 6 shows the flow of the next sound pressure measurement step (S2). FIG. 6 shows sound pressure measurement by the mobile microphone 12 . First, the mobile microphone 12 moves to the first measurement position (S2-1) and waits at that measurement position (S2-2). Then, when a reference signal for starting measurement is issued during standby (YES in S2-3), the mobile microphone 12 starts measuring sound pressure (S2-4). Next, when the measurement end reference signal is issued during sound pressure measurement (YES in S2-5), the mobile microphone 12 ends the sound pressure measurement (S2-6). As a result, the mobile microphone 12 performs measurement from when the measurement start reference signal is issued until when the measurement end reference signal is issued. After that, if the measurement at all the measurement positions has not been completed (NO in S2-7), the mobile microphone 12 moves to the next measurement position (S2-1), and steps S2-2 to S2-6 are performed. is performed again. If measurements at all measurement positions have been completed (YES in S2-7), step S2 for sound pressure measurement is completed.

On the other hand, the sound pressure measurement by the fixed microphone 14 should be performed at least simultaneously with the sound pressure measurement by the mobile microphone 12 . Therefore, the fixed microphone 14 may continuously measure the sound pressure from the start of measurement at the first measurement position by the mobile microphone 12 to the end of measurement at the last measurement position. Alternatively, the stationary microphone 14 may also start or end a measurement whenever the mobile microphone 12 starts or ends a measurement based on the reference signal.

Since the measurement by the mobile microphone 12 and the measurement by the fixed microphone 14 are performed synchronously in this manner, the measurement data at each measurement position by the mobile microphone 12 and the corresponding measurement data by the fixed microphone 14 are linked. be done. That is, measurement data at a certain measurement position by the mobile microphone 12 (referred to as "moving microphone data") and measurement data obtained by the fixed microphone 14 while the mobile microphone 12 is measuring at the measurement position ("fixed microphone data"). ) are linked.

Next, the step (S3) of obtaining the sound pressure distribution at the ground contact portion G of the tire T using acoustic holography based on the sound pressure measurement data will be described.

When sound pressure is measured by a microphone array as described in Background Art, measurements are performed simultaneously with each microphone placed at each measurement position. Therefore, between the frequency analysis data of the measurement data at each measurement position (however, between the waveform data of the same frequency), only the phase difference caused by the difference in the measurement position exists as the phase difference. Here, frequency analysis data is waveform data for each frequency obtained by frequency analysis of measurement data.

On the other hand, in the present embodiment, as described above, one mobile microphone 12 performs measurement at each measurement position while moving. Therefore, between the frequency analysis data of the moving microphone data at each measurement position (however, between the waveform data of the same frequency), there is a phase difference caused by the difference in the measurement position and a phase difference caused by the difference in the measurement time. contains a difference. Therefore, in order to enable the same acoustic holography processing as when sound pressure is measured by a microphone array, processing is performed to eliminate the phase difference caused by the difference in measurement time. With this processing, it can be considered that the sound pressure is measured simultaneously by the mobile microphone 12 at all measurement positions.

Specifically, first, frequency analysis is performed on the mobile microphone data and the fixed microphone data to obtain respective frequency analysis data. Then, the phase difference between the frequency analysis data of the mobile microphone data at each measurement position and the corresponding frequency analysis data of the fixed microphone data (that is, linked to the mobile microphone data) (however, the phase difference between the waveform data of the same frequency is phase difference) is obtained. This phase difference is called a "microphone phase difference". Microphone phase differences are determined for all measurement positions. Also, the microphone phase difference can be obtained for all frequencies, but may be obtained only for a specific frequency of interest. Note that the microphone phase difference may be calculated each time sound pressure measurement at each measurement position is completed in step S2 of sound pressure measurement.

Next, the phase difference between the microphone phase differences for different measurement positions (but the phase difference between the microphone phase differences for the same frequency) is determined. The phase difference between the microphone phase differences can be obtained for all frequencies, but may be obtained only for a specific frequency of interest.

Since the mobile microphone data and the fixed microphone data are measured at the same time, the microphone phase difference does not include the phase difference caused by the difference in measurement time. Therefore, the phase difference caused by the difference in measurement time is eliminated from the phase difference between the microphone phase differences. Therefore, the phase difference between the microphone phase differences is the phase difference caused by the difference in the measurement positions.

This will be described by taking as an example data processing for two measurement positions, the first and second points. First, let the phase of the waveform data of frequency f1 with the frequency analysis data of the mobile microphone data at the first measurement position be ω _m1 , and the corresponding fixed microphone (that is, at the time of measurement at the first measurement position) Let ω _f1 be the phase of the waveform data of the frequency f1 of the frequency analysis data of the data. At this time, the microphone phase difference for the frequency f1 at the first measurement position (that is, the waveform data of the frequency f1 with the frequency analysis data of the moving microphone data at the first measurement position and the fixed microphone data corresponding to it) The phase difference between the frequency analysis data of frequency f1 and the waveform data of frequency f1) Δω ₁ is
_Δω1 = _ωm1 - _ωf1
is.

Next, the phase ω _m2 of the waveform data of the frequency f1 of the frequency analysis data of the moving microphone data at the second measurement position is the phase difference Δω _p caused by the difference in the position with respect to the phase ω _m1 . Since the phase difference Δω _t caused by the difference in time is added,
ω _m2 = ω _m1 + Δω _p + Δω _t
becomes. Further, the phase ω _f2 of the waveform data of the frequency _f1 of the frequency analysis data of the fixed microphone data at the time of measurement at the second measurement position is the phase difference Δω Since only _t is added,
ω _f2 = ω _f1 + Δω _t
becomes. At this time, the microphone phase difference for the frequency f1 at the second measurement position (that is, the waveform data of the frequency f1 with the frequency analysis data of the moving microphone data at the second measurement position and the fixed microphone data corresponding to it) The phase difference between the frequency analysis data of frequency f1 and the waveform data of frequency f1) Δω ₂ is
Δω ₂ = ω _m2 − ω _f2 = (ω _m1 + Δω _p + Δω _t ) − (ω _f1 + Δω _t ) = ω _m1 − ω _f1 + Δω _p
is.

When the phase difference Δω _2-1 between the microphone phase differences is calculated from the microphone phase differences Δω ₁ and Δω ₂ for the first and second measurement positions thus obtained,
Δω _2-1 =Δω ₂ −Δω ₁ =(ω _m1 −ω _f1 +Δω _p )−(ω _m1 −ω _f1 )=Δω _p
becomes. Thus, it can be seen that the phase difference Δω _2-1 between the microphone phase differences is equal to the phase difference Δω _p caused by the difference in measurement position.

If the acoustic holography processing is performed using the phase difference resulting from the difference in the measurement positions obtained in this way, the sound pressure is measured simultaneously at all the measurement positions using the microphone array, and the acoustic holography is performed based on the measurement data. You can get the same result as if you did the processing.

The NAH (Near Field Acoustic Holography) method or the like that has already been established is used in the acoustic holography processing. Briefly, in acoustic holography processing, the sound pressure distribution on the sound source plane is calculated based on the phase and level of the frequency analysis data of the measurement data at each measurement position on the measurement plane (measurement data that can be regarded as being measured simultaneously at each measurement position). is calculated. 7, the Fourier transform P(k x , k y , z ₁ ) of the sound pressure distribution p( _x , _y , z ₁ ) on the measurement plane and the transmission from the sound source plane to the measurement plane From the inverse characteristic H ⁻¹ of the function H, the sound pressure distribution p(x, y, 0) on the sound source surface is calculated. In the present embodiment, the sound pressure distribution in the plane including the contact portion G of the tire T is obtained from the sound pressure distribution measured by the mobile microphone 12 on the measurement plane 30 described above. This sound pressure distribution can be obtained for all frequencies, but may be obtained only for a particular frequency of interest.

In the next sound source identification step (S4), the highest sound pressure portion in the sound pressure distribution on the surface including the ground contact portion G of the tire T is identified as the noise source of that frequency. Any groove or sipe on the tread surface T1, for example, is identified as the noise source. The identification of the sound source may be performed by a person looking at the sound pressure distribution, or may be performed by the computer 18 . A designer of the tire T can change the design of the tread pattern of the tire T based on the result of specifying the sound source.

<About the effect of the embodiment>
As described above, in this embodiment, the mobile microphone 12 sequentially measures the sound pressure at a plurality of measurement positions, and the fixed microphone 14 measures the sound pressure in synchronism with the measurement at each measurement position by the mobile microphone 12. be. Then, the mobile microphone data and the fixed microphone data are subjected to frequency analysis, and the phase difference between the frequency analysis data of the mobile microphone data and the frequency analysis data of the corresponding fixed microphone data at each measurement position is obtained as the microphone phase difference. A phase difference between phase differences is obtained as a phase difference caused by a difference in measurement positions. Then, since the sound pressure distribution at the ground contact portion G of the tire T is calculated by acoustic holography based on the phase difference caused by the difference in the measurement positions, the sound pressure distribution is the same as when the sound pressure is measured simultaneously at each measurement position. is obtained.

That is, in the present embodiment, the sound pressure is measured in order at each measurement position by the mobile microphone 12, but by performing the subsequent processing using the fixed microphone data, the sound pressure is measured by a microphone array consisting of a large number of microphones. You can get the same result as

Here, since the microphone array is formed by arranging a large number of microphones, even if the adjacent microphones are brought into close contact with each other, the size of the microphone array exceeds a predetermined size, and cannot be made smaller.

In contrast, in this embodiment, the distance between adjacent measurement positions of the mobile microphone 12 (in other words, the moving distance of the mobile microphone 12) can be arbitrarily determined. It can also be set to a distance shorter than the distance between microphones. Therefore, the area of the measurement surface 30 by the mobile microphones 12 can be made smaller than the area of the microphone array.

Since the area of the measurement surface 30 by the mobile microphones 12 can be reduced in this way, the measurement surface 30 by the mobile microphones 12 can be positioned in places where the microphone array cannot be placed, for example, under the tires T in front of or behind the tires T. It can also be set in narrow places such as As a result, the measurement plane 30 by the mobile microphone 12 can be set closer to the contact portion G of the tire T than the microphone array. As a specific example, the measurement plane 30 by the mobile microphone 12 can be set at a location near the ground contact portion G of the tire T, such as 25 mm to 100 mm, in front or behind the tire T.

Since the measurement plane 30 by the mobile microphone 12 can be set close to the ground contact portion G of the tire T in this manner, the background noise entering the mobile microphone 12 can be reduced. For example, by setting the measurement plane 30 by the mobile microphone 12 under the tire T at the front or rear of the tire T so as to approach the ground contact portion G, the distance between the tread surface T1 of the tire T and the surface D1 of the drum D can be prevented from entering the moving microphone 12. Therefore, according to the present embodiment, it is possible to identify the sound source while reducing the influence of the background noise.

In addition, since the measurement is started and ended based on the reference signal as described above in the measurement at each measurement position by the mobile microphone 12, the measurement conditions by the mobile microphone 12 at each measurement position can be matched.

More specifically, as described above, the configuration is such that a pulse signal is generated based on the rotation of the tire T, and the pulse signal is measured a predetermined time (for example, the first time) after the mobile microphone 12 moves to each measurement position. A reference signal for starting is set, and another predetermined pulse signal (for example, the second or third time) after the mobile microphone 12 moves to each measurement position is set as a reference signal for ending measurement. At each measurement position, the mobile microphone 12 performs measurement from when the measurement start reference signal is issued until when the measurement end reference signal is issued. Therefore, it is possible to measure the sound pressure during the same number of rotations of the tire T at all measurement positions.

<Regarding a modified example of the embodiment>
Modification 1 will be described first.

In Modification 1, the rotation speed of the tire T is used instead of the pulse signal in the above embodiment as the reference signal that serves as a reference for starting and ending measurement by the mobile microphone 12 . For this purpose, a tachometer for measuring the rotational speed of the tire T is provided as the reference signal device 22 .

A first rotation speed and a second rotation speed, which are two different rotation speeds of the tire T, are set in advance as reference signals. Then, at each measurement position, the mobile microphone 12 performs measurement while the rotation speed of the tire T is from the first rotation speed to the second rotation speed.

As a specific example, a first rotational speed is set as a reference signal for starting measurement, and a second rotational speed slower than the first rotational speed is set as a reference signal for ending measurement. Then, the tire T is rotated on the drum D at a high speed higher than the first rotation speed, and the power of the motor for rotating the drum D is turned off. Then, the rotational speeds of the drum D and tire T gradually decrease. Measurement by the mobile microphone 12 is started when the rotation speed of the tire T has decreased to the first rotation speed, and measurement by the mobile microphone 12 ends when the rotation speed of the tire T has further decreased to the second rotation speed. This makes it possible to specify the noise source when the rotation speed of the tire T is the average speed between the first rotation speed and the second rotation speed with the motor sound turned off.

As another specific example, a first rotation speed is set as a reference signal for starting measurement, and a second rotation speed faster than the first rotation speed is set as a reference signal for ending measurement. Then, the rotation speed of the tire T is gradually increased, and when the rotation speed of the tire T increases to the first rotation speed, measurement by the mobile microphone 12 is started, and the rotation speed of the tire T further increases to the second rotation speed. When the measurement by the mobile microphone 12 ends. This makes it possible to identify the noise source when the rotation speed of the tire T is accelerated from the first rotation speed to the second rotation speed.

In Modification 1, instead of the tire T rotation speed, the drum D rotation speed may be used as the reference signal.

Next, modification 2 will be described.

In Modification 2, instead of the pulse signal in the above embodiment, the axial force acting on the rotation axis S of the tire T is used as the reference signal for starting and ending the measurement by the mobile microphone 12 . For this purpose, an axial force meter for measuring the axial force acting on the rotating shaft S of the tire T is provided as the reference signal device 22 .

A predetermined amount of axial force is set in advance as a reference signal. At each measurement position, the mobile microphone 12 performs measurement while the measured axial force is equal to or greater than the predetermined magnitude. That is, when the axial force gradually increases and exceeds the predetermined magnitude, the measurement of the mobile microphone 12 is started, and when the axial force gradually decreases and falls below the predetermined magnitude, the movable microphone is measured. 12 measurements are completed. Since the magnitude of the axial force corresponds to the braking/driving force, this method makes it possible to identify the noise source when a braking force or driving force greater than or equal to a predetermined magnitude is generated.

D... drum, D1... surface of drum, G... contact part, S... rotating shaft, T... tire, T1... tread surface, 10... sound source probe, 12... moving microphone, 14... fixed microphone, 16... acoustic holography device , 18... Computer, 20... Output device, 22... Reference signal device, 24... Movement control device, 30... Measuring plane, 112... Microphone array

Claims (6)

While rotating the tire, the sound pressure of the noise is measured at a plurality of measurement positions away from the tire, and based on the measured data, acoustic holography is used to determine the sound pressure distribution at the ground contact portion of the tire, and based on the sound pressure distribution. In the sound source probing method for identifying the source of the noise,
measuring the sound pressure in turn at a plurality of measurement positions using a movable mobile microphone;
starting and ending the measurement based on a predetermined reference signal when measuring at each measurement position by the mobile microphone;
Using a fixed microphone whose position is fixed, measure the sound pressure in synchronization with the measurement at each measurement position by the moving microphone,
frequency analysis of the measurement data of the mobile microphone and the measurement data of the fixed microphone, and frequency analysis data of the measurement data of the mobile microphone at each measurement position and frequency analysis data of the corresponding measurement data of the fixed microphone; thereby obtaining the phase difference caused by the difference in the measurement position among the phase differences between the frequency analysis data of the measurement data of the mobile microphone at each measurement position,
Acoustic holography is used to determine the sound pressure distribution at the ground contact portion of the tire using the phase difference resulting from the difference in the measurement position ;
A sound source localization method , wherein the position measured by the mobile microphone is a location under the tire in front of or behind the tire . 2. The sound source exploration method according to claim 1 , wherein the position to be measured by said mobile microphone is a position 25 mm to 100 mm away from the ground contact portion of said tire. 3. The sound source localization method according to claim 1, wherein the distance between adjacent measurement positions by said moving microphone is 1 mm to 10 mm. A pulse signal based on tire rotation is generated,
The pulse signal for a predetermined time after the mobile microphone has moved to each measurement position is set as the reference signal for starting measurement, and the pulse signal for another predetermined time after the mobile microphone has moved to each measurement position is set as the reference signal for starting measurement. set as the reference signal for the end of measurement,
4. The mobile microphone according to any one of claims 1 to 3 , wherein at each measurement position, the mobile microphone performs measurement from when the reference signal for starting measurement is issued until when the reference signal for ending measurement is issued. Sound source probing method. Two different tire rotation speeds, a first rotation speed and a second rotation speed, are set in advance as the reference signal, and at each measurement position, the tire rotation speed changes from the first rotation speed to the second rotation speed. A sound source localization method according to any one of claims 1 to 3 , wherein the mobile microphone makes measurements until time. Claims 1 to 3 , wherein an axial force of a predetermined magnitude is set in advance as the reference signal, and the mobile microphone performs measurement while the axial force measured at each measurement position is equal to or greater than the predetermined magnitude. The sound source probing method according to any one of 1.

Images