JP2015152583A - System and method for evaluating noise reduction device performance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for evaluating noise reduction device performance, with enhanced evaluation accuracy by eliminating variation in an evaluation result which depends on positions of microphones.SOLUTION: The system for evaluating noise reduction device performance includes; oscillation means 3 for oscillating air in an annular cavity SP of a structure 1 having the annular cavity SP; a noise reduction device 2, arranged in the annular cavity SP, for reducing sound waves in the annular cavity SP; a plurality of microphones 4 arranged in the annular cavity SP; and an evaluation device 5 for calculating a performance value of the noise reduction device 2 based on sound waves measured by the plurality of microphones 4. When the annular cavity SP is divided into halves of a first region Ar1 and second region Ar2 at an oscillating position 3a of the oscillation means 3, the plurality of microphones 4 are arranged only in the first region Ar1 and the noise reduction device 2 is arranged only in the second region Ar2.

Description

  The present invention relates to a performance evaluation system and a performance evaluation method for a noise reduction device provided in a structure such as a tire having an annular cavity.

  With the spread of electric cars and hybrid cars, and the improvement in technology of conventional gasoline cars, the demand for noise reduction generated by tires has become stronger. In-tire cavity resonance is known as one of the noises generated in a tire, and it is known to provide a noise reduction device such as a sound absorbing material inside the tire as a countermeasure.

  However, the performance of the sound absorbing material or the like varies depending not only on the material but also on the shape of the sound absorbing material or the like and the application situation, so an evaluation method suitable for the use situation is required.

  An acoustic tube method is known as a conventional performance evaluation method for sound absorbing materials and the like. The acoustic tube method uses a device in which a vibrating means such as a speaker is provided at one end of a rod-shaped cylindrical tube, a sound absorbing material or the like is provided at the other end, and a plurality of microphones are provided at an intermediate portion. This is a method of calculating the sound absorption coefficient (performance value) of the sound absorbing material or the like based on the incident wave and the reflected wave that is attenuated by the sound absorbing material or the like and reaches the microphone. As an example of application of the acoustic tube method, for example, Patent Document 1 is cited.

  The acoustic tube method cannot be applied to a pneumatic tire as it is because a structure having an annular cavity whose propagation path of sound waves forms a closed loop, such as a pneumatic tire, is not a measurement target.

  Accordingly, as described in Non-Patent Document 1, the inventors of the present invention provide a speaker (vibration means) that excites air in a cavity of a structure modeled as a pneumatic tire, and an outer periphery in the cavity. The sound absorption rate (performance value) of the sound absorbing material or the noise reduction device is calculated based on the sound wave measured by the microphone using the sound absorbing material or the like pasted around the part and a plurality of microphones provided in the cavity. A method was proposed.

JP 2001-289707 A

Kyoto Polytechnic University Seiki Nakamura, Yosuke Tanaka, Takanori Kobayashi, Shigeru Murata, Development of sound absorption performance evaluation method in tires, Preprint of Lecture Presentation for 2012 Graduation Research of Japan Society of Mechanical Engineers Kansai Student Association ('13 .3), P15-4

  However, in the method described in Non-Patent Document 1, the sound absorption rate (performance value) of the sound absorbing material differs depending on the position where the microphone is arranged, and the measurement results vary. In order to ensure the stability of the measurement result, the measurement result must be constant regardless of the position of the microphone. That is, according to the contents described in Non-Patent Document 1, it has been found that the sound absorption rate of the sound absorbing material cannot be accurately grasped without variation.

  The present invention has been made paying attention to such a problem, and its purpose is to eliminate the variation of the evaluation result according to the position of the microphone and improve the evaluation accuracy of the noise reduction device performance evaluation system. And providing a performance evaluation method.

  In the above description, the noise in the tire is measured. However, the present invention is not limited to the tire, and can be applied to a structure other than a tire and having an annular cavity.

  As described in Non-Patent Document 1, when a sound absorbing material is attached around the inner surface of the annular tube structure, the first sound wave that reaches the microphone through the first region from the excitation position and the first position from the excitation position. Any of the second sound waves that reach the microphone through the two regions are affected by the sound absorbing material. Since the degree of the sound absorption effect received by the first sound wave and the second sound wave changes depending on the position of the microphone, it has been found that the measurement result changes depending on the position of the microphone. For this reason, it is considered that the performance value of the sound absorbing material has not been accurately evaluated.

  In order to achieve the above object, the present invention takes the following measures.

  That is, the performance evaluation system for a noise reduction device according to the present invention includes a vibration means for exciting air in a cavity of a structure having an annular cavity, and noise reduction arranged in the annular cavity to reduce sound waves in the annular cavity. Apparatus, a plurality of microphones arranged in the annular cavity, and an evaluation device that calculates a performance value of the noise reduction device based on sound waves measured by the plurality of microphones, and an excitation position by the excitation means Is divided into half of the first region and the second region, the plurality of microphones are disposed only in the first region, and the noise reduction device is disposed only in the second region. It is characterized by being.

  Further, the performance evaluation method of the noise reduction device according to the present invention includes a vibration means for exciting the air in the annular cavity with respect to a structure having the annular cavity, and noise that reduces sound waves in the annular cavity. A preparatory step of disposing a reduction device and a plurality of microphones in the annular cavity; an actual measurement step of vibrating the air via the vibration means and measuring the sound waves generated thereby by the plurality of microphones; A performance value calculation step of calculating a performance value of the noise reduction device by an evaluation device based on a measurement result of the microphone, and in the preparation step, the annular cavity is first defined with an excitation position by the excitation means as a boundary. When divided into one region and half of the second region, the plurality of microphones are disposed only in the first region, and the noise reduction device is disposed only in the second region.

  According to the above system and method, the microphone reduces the noise from the excitation position through the first region only through the first region and reaches the microphone without being affected by the noise reduction device, and from the excitation position through the second region. The second sound wave that reaches the microphone under the influence of the apparatus can be measured. As a result, the performance value of the noise reduction device can be accurately calculated. Moreover, if the microphone is arranged in the first region, the measurement accuracy is not impaired even if the position of the microphone is changed. Therefore, it is possible to improve evaluation accuracy by eliminating variations in evaluation results according to the position of the microphone.

  As a preferable application example of the present invention, the structure may be a pneumatic tire.

  As a preferable application example of the present invention, the noise reduction device may be a sound absorbing material.

  As a preferred application example of the present invention, the noise reduction device may be a resonance type noise reduction device having a resonator that reduces noise.

  As a preferred application example of the present invention, the noise reduction device may be an active noise control device that reduces noise by exciting a sound wave that cancels noise.

The figure which shows the performance evaluation system of the noise reduction apparatus of this invention. The figure regarding the structure which has an annular cavity, a vibration means, and a microphone. The flowchart which shows the performance evaluation method of the noise reduction apparatus of this invention. The figure which shows the measurement result at the time of placing a microphone in a certain position in the conventional method. The figure which shows the measurement result at the time of putting a microphone in the position different from FIG. 4A in the conventional method. The figure which shows the measurement result which varied the position of the microphone in this invention. The figure which shows the measurement result which varied the installation state of the noise reduction apparatus in this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[Noise reduction system performance evaluation system]
As shown in FIGS. 1 and 2, the performance evaluation system for the noise reduction device of the present embodiment is a system for evaluating the performance of the noise reduction device 2 provided in a tire or tire model that is a structure 1 having an annular cavity SP. (Apparatus). The structure 1 having the annular cavity SP means a structure in which a sound wave propagation path forms a closed loop like a pneumatic tire. In an example other than a pneumatic tire with a rim assembled, for example, an air duct having a closed loop provided in a building can be considered. In the present embodiment, an acrylic plate having a thickness of 5 mm is used, and a tire model manufactured as if it were a tire is used as a structure to be evaluated. The tire model has an outer diameter of 633 mm, an inner diameter of 370 mm, and a height (tire width) of 190 mm. Of course, an actual pneumatic tire may be assembled with a rim and applied with internal pressure.

  This system includes a vibration means 3 for vibrating air in a cavity of a structure having an annular cavity SP, a noise reduction device 2 disposed in the annular cavity SP and reducing sound waves of the annular cavity SP, and an annular cavity SP. It has the some microphone 4 arrange | positioned, and the evaluation apparatus 5 (control part) which calculates the performance value of the noise reduction apparatus 2 based on the sound wave measured with the some microphone 4. FIG.

  In the present embodiment, a speaker is used as the vibration means 3. The speaker is disposed outside the structure 1 (tire model), and indirectly excites the air in the annular cavity SP from the outside of the structure 1. Of course, a speaker may be arranged inside the structure 1 to directly excite the air in the cavity. Further, as the vibration means 3, air may be vibrated by a physical impact input means such as an impact input or a vibrator in addition to the speaker.

  In this embodiment, as the noise reduction device 2, the sound absorbing material 2 using a foamed urethane sheet is disposed in the annular cavity SP. When the annular cavity SP is divided into half of the first region Ar1 and the second region Ar2 with the vibration position 3a by the vibration means 3 as a boundary, the sound absorbing material 2 is disposed only in the second region. In the present embodiment, the sound absorbing material 2 is attached to the entire outer surface of the second region Ar2, but the sound absorbing material 2 may be provided only in a part of the second region Ar2.

  The plurality of microphones 4 are disposed only in the first region Ar1 of the annular cavity SP. In the present embodiment, two microphones 4 are provided, but there may be two or more. In the present embodiment, the microphone 4 is arranged on an intermediate portion (indicated by a dotted line) of the annular cavity SP, that is, on a diameter of 480 mm.

  The evaluation device 5 uses an information processing device such as a normal personal computer, and is configured to receive a signal from the microphone 4 and to output a signal to the vibration means 3 (speaker). In FIG. 1, a signal from the microphone 4 is input to the evaluation device 5 through various interfaces such as an amplifier 51 and a data logger 52 connected to the stabilized power supply 50. The evaluation device 5 calculates a performance value (sound absorption coefficient α) of the noise reduction device 2 (sound absorbing material 2) based on sound waves measured by the plurality of microphones 4.

第１項が入射波に関し、第２項が反射波に関する。 Specifically, since the annular cavity can be modeled into an acoustic tube, as shown in FIG. 2, the first sound wave w1 (clockwise in the figure) from the excitation position 3a to the microphone 4 through only the first region Ar1. And the second sound wave w2 (which is a counterclockwise sound wave in the drawing) from the excitation position 3a through the second region Ar2 to the microphone 4 as a reflected wave. Apply the transfer function method using. In the transfer function method, if the sound pressure in the acoustic tube is expressed as the sum of the sound pressure due to the incident wave and the sound pressure due to the reflected wave, the sound pressure at the reference plane (x = 0) is p ₀ and the wavelength constant is k. The following equations (1) and (2) represent the sound pressures p ₁ and p ₂ at each microphone. Each microphone position is x ₁ and x ₂ , respectively.

The first term relates to the incident wave, and the second term relates to the reflected wave.

The transfer function H _i related to the incident wave, the transfer function H _r related to the reflected wave, and the transfer function H ₁₂ between the two microphones are expressed by the following equations (3) to (5), respectively.

ｒ_ｒ及びｒ_ｉは、音響反射率ｒの実部と虚部である。 The acoustic reflectivity r is expressed by the following formula (6) using formulas (3) to (5).

r _r and r _i are a real part and an imaginary part of the acoustic reflectivity r.

The sound absorption coefficient α is expressed by the following equation (7). The sound absorption coefficient α can be said to be a performance value of the noise reduction device 2.

  The evaluation device 5 (control unit) calculates the sound absorption coefficient α (performance value of the noise reduction device) using the data measured by the microphone 4 and the above calculation formula.

[Noise reduction device performance evaluation method]
A method for evaluating the performance of a noise reduction device provided in a structure having an annular cavity using the above system will be described with reference to FIG.

  First, a preparation process is executed in step ST1 (see FIG. 3). As shown in FIG. 2, in the preparation step, a vibration reducing means 3 for vibrating the air in the annular cavity is installed on the structure 1 having the annular cavity SP, and the sound wave in the annular cavity is reduced. Two and a plurality of microphones 4 are arranged in the annular cavity SP. At this time, as shown in the figure, when the annular cavity SP is divided into half of the first region Ar1 and the second region Ar2 with the excitation position 3a by the excitation means 3 as a boundary, the plurality of microphones 4 are connected to the first microphone 4. It arrange | positions only to area | region Ar1, and arrange | positions the noise reduction apparatus 2 only to 2nd area | region Ar2.

  In the next step ST2, an actual measurement process is executed (see FIG. 3). In the actual measurement step, air is vibrated through the vibration means 3, and sound waves (w 1, w 2) generated thereby are measured by the plurality of microphones 4.

  In the next step ST3, a performance value calculation step is executed (see FIG. 3). In the performance value calculation step, the evaluation device 5 calculates the performance value of the noise reduction device 2 based on the measurement results of the plurality of microphones 4.

  The effects of the prior art and the present invention are shown below.

As described in Non-Patent Document 1, as a conventional technique, a sound absorbing material is attached to the entire outer periphery of an annular cavity of a tire model (structure 1). The sound absorbing material used has a bulk density of 24 kg / m ³ and a thickness of 25 mm. White noise was oscillated with a speaker, measured with two microphones, and recorded with a data logger through a 400 × amplifier. The sound absorption coefficient α was calculated for each frequency of the measurement result. FIG. 4 shows the measurement results with dots and the moving average lines of the measurement results. FIG. 4A shows the result of x = 188.4 mm (θ = 45 °). FIG. 4B shows the result of x = 376.8 mm (θ = 90 °). As shown in FIG. 2, x corresponds to the distance on the outer circumference based on x = 0 (θ = 0 °).
Comparing FIG. 4A and FIG. 4B, since the sound absorption coefficient α of both is greatly different, the performance value (sound absorption coefficient α) varies depending on the position of the microphone 4, and the evaluation accuracy varies.

On the other hand, in the present invention, the sound absorbing material has a thickness of 5 mm and is attached only to the second region (a half circumference of the tire model) as shown in FIG. In order to verify whether or not the measurement result depends on the microphone position, two microphones x1 and x2 were paired, and three microphone pair positions were tested. The first microphone pair position No. 0 was set to x ₁ = 0.051 mm and x ₂ = 0.0 mm. Second microphone pair position No. 1 was set to x ₁ = 0.086 mm and x ₂ = 0.035 mm. The third microphone pair position No. 2 was set to x ₁ = 0.121 mm and x ₂ = 0.07 mm. The result is shown in FIG. 5A. Comparing FIG. 5A and FIG. 4, it can be seen that the sound absorption coefficient α is almost the same regardless of the microphone position. Therefore, the evaluation accuracy can be improved by eliminating the variation in the evaluation result according to the position of the microphone.

  Next, in order to confirm whether or not the sound absorption coefficient α can be measured according to the state of attachment of the noise reduction device (sound absorbing material), the case where no sound absorbing material is attached and the thickness of the sound absorbing material is set to 5 mm. In this case, the measurement was performed in three patterns when the thickness was 10 mm. The result is shown in FIG. 5B. 5B, it was confirmed that the sound absorption rate α is higher when the sound absorbing material is provided than when the sound absorbing material is not provided, and the sound absorbing effect (performance value) is increased as the thickness of the sound absorbing material is increased.

  In FIGS. 5A and 5B, there are variations in the results at some frequencies. However, it is considered that resonance occurred in the frequency band, resulting in measurement variations.

  As described above, the performance evaluation system for the noise reduction device according to the present embodiment is arranged in the annular cavity SP and the vibration means 3 (speaker) for exciting the air in the cavity of the structure 1 having the annular cavity SP. A noise reduction device 2 (sound absorbing material 2) for reducing sound waves in the annular cavity SP, a plurality of microphones 4 arranged in the annular cavity SP, and a noise reduction device 2 (sound absorbing material 2) based on the sound waves measured by the plurality of microphones 4. And an evaluation device 5 that calculates a performance value of When the annular cavity SP is divided into half of the first area Ar1 and the second area Ar2 with the excitation position 3a by the excitation means 3 as a boundary, the plurality of microphones 4 are arranged only in the first area Ar1, and the noise reduction device 2 is arranged only in the second region Ar2.

  In the performance evaluation method of the noise reduction device according to the present embodiment, the vibration means 3 that vibrates the air in the annular cavity SP is installed on the structure 1 having the annular cavity SP, and the sound wave in the annular cavity SP is reduced. Preparatory step (ST1) of arranging the noise reduction device 2 and the plurality of microphones 4 in the annular cavity SP, and actual measurement in which air is vibrated through the vibration means 3 and the sound waves generated thereby are measured by the plurality of microphones 4. A step (ST2), and a performance value calculation step (ST3) in which the performance value (sound absorption coefficient α) of the noise reduction device 2 is calculated by the evaluation device based on the measurement results of the plurality of microphones 4. In the preparation step (ST1), when the annular cavity SP is divided into half of the first region Ar1 and the second region Ar2 with the vibration position 3a by the vibration means 3 as a boundary, only the first region Ar1 is used as the plurality of microphones 4. The noise reduction device 2 is arranged only in the second region Ar2.

  In the method of Non-Patent Document 1, when a sound absorbing material is pasted around the inner surface of the annular tube structure, the first sound wave that reaches the microphone from the excitation position through the first area and the second area from the excitation position. All of the second sound waves that reach the microphone via the sound are affected by the sound absorbing material. Since the degree of the sound absorption effect received by the first sound wave and the second sound wave changes depending on the position of the microphone, it has been found that the measurement result changes depending on the position of the microphone. For this reason, it is considered that the performance value of the sound absorbing material has not been accurately evaluated.

  On the other hand, according to the system and method having the above-described configuration, as shown in FIG. 2, the microphone 4 passes through only the first region Ar1 from the excitation position 3a and is not affected by the noise reduction device 2. The first sound wave w1 that arrives and the second sound wave w2 that reaches the microphone 4 under the influence of the noise reduction device 2 from the excitation position 3a through the second region Ar2 can be measured. Thereby, the performance value of the noise reduction device 2 can be accurately calculated. And if the microphone 4 is arrange | positioned in 1st area | region Ar1, even if the position of the microphone 4 changes, measurement accuracy will not be impaired. Therefore, regardless of the position of the microphone 4, it is possible to improve the evaluation accuracy by eliminating variations in the evaluation results.

  Furthermore, the structure 1 is preferably a pneumatic tire. Since the acoustic characteristics of the pneumatic tire can be taken into consideration, it is possible to evaluate the performance of the noise reduction device 2 that reduces the cavity resonance noise in the pneumatic tire, which is preferable.

  In the present embodiment, the noise reduction device 2 is a sound absorbing material 2. The sound absorbing material 2 reduces sound energy by converting sound energy (vibration energy) into other energy such as heat energy. As the sound absorbing material 2, porous materials such as foamed urethane, glass wool, rock wool, and soft urethane foam, porous plate materials such as soft fiberboard and wood cement board, nonwoven fabric, membrane materials such as canvas canvas and vinyl sheet, etc. Is available.

  As the noise reduction device 2, a resonance type noise reduction device having a resonator for reducing noise can be used. An example of this apparatus is a Helmholtz resonator.

  Further, as the noise reduction device 2, an active noise reduction device that has an oscillating means such as a speaker and reduces noise by oscillating a sound wave that cancels noise having an opposite phase to the noise from the oscillating means can be used. .

  As mentioned above, although embodiment of this invention was described based on drawing, it should be thought that a specific structure is not limited to these embodiment. The scope of the present invention is shown not only by the above description of the embodiments but also by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the present embodiment, the sound absorbing material 2 has a sheet shape with a constant thickness, but is not limited thereto. The thickness of the sound absorbing material may be changed. Moreover, the arrangement position of the sound absorbing material 2 may be continuous in the circumferential direction, or may be discontinuously arranged in the circumferential direction or the width direction. The shape of the sound absorbing material is a sheet shape, and the traveling direction of the sound wave is parallel to the sound absorbing material. However, the present invention is not limited to this, and for example, the sound absorbing material may be arranged so as to intersect the sound wave.

  The structure employed in each of the above embodiments can be employed in any other embodiment. The specific configuration of each unit is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

1. Structure (pneumatic tire, tire model)
2 ... Noise reduction device 3 ... Excitation means (speaker)
3a ... excitation position 4 ... microphone 5 ... evaluation device (control unit)
Ar1 ... first region Ar2 ... second region SP ... annular cavity

Claims (10)

Vibration means for exciting air in the cavity of a structure having an annular cavity;
A noise reduction device disposed in the annular cavity for reducing sound waves of the annular cavity;
A plurality of microphones disposed in the annular cavity;
An evaluation device that calculates a performance value of the noise reduction device based on sound waves measured by the plurality of microphones, and
When the annular cavity is divided into half of the first region and the second region with the excitation position by the excitation means as a boundary, the plurality of microphones are arranged only in the first region, and the noise reduction device A system for evaluating the performance of a noise reduction device, wherein the system is disposed only in the second region.   The performance evaluation system for a noise reduction device according to claim 1, wherein the structure is a pneumatic tire.   The performance evaluation system for a noise reduction device according to claim 1 or 2, wherein the noise reduction device is a sound absorbing material.   The performance evaluation system for a noise reduction device according to claim 1 or 2, wherein the noise reduction device is a resonance type noise reduction device having a resonator for reducing noise.   The noise reduction device performance evaluation system according to claim 1 or 2, wherein the noise reduction device is an active noise control device that reduces noise by exciting a sound wave that cancels noise. A vibration reducing means for vibrating air in the annular cavity is installed in a structure having an annular cavity, and a noise reduction device for reducing sound waves in the annular cavity and a plurality of microphones are provided in the annular cavity. Process,
An actual measurement process in which air is vibrated through the vibration means and sound waves generated thereby are measured by the plurality of microphones;
A performance value calculation step of calculating a performance value of the noise reduction device based on a measurement result of the plurality of microphones with an evaluation device,
In the preparation step, when the annular cavity is divided into half of the first region and the second region with the vibration position by the vibration means as a boundary, the plurality of microphones are disposed only in the first region, A method for evaluating the performance of a noise reduction device, wherein the noise reduction device is arranged only in the second region.   The performance evaluation method for a noise reduction device according to claim 6, wherein the structure is a pneumatic tire.   The performance evaluation method for a noise reduction device according to claim 6 or 7, wherein the noise reduction device is a sound absorbing material.   The performance evaluation method for a noise reduction device according to claim 6 or 7, wherein the noise reduction device is a resonance type noise reduction device having a resonator for reducing noise.   The noise evaluation apparatus according to claim 6 or 7, wherein the noise reduction apparatus is an active noise control apparatus that reduces noise by exciting a sound wave that cancels noise.

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