JP2007292667A - Device for measuring acoustic characteristics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device capable of measuring acoustic characteristics in a space noncontact and close to a sample, without destructing the sample. <P>SOLUTION: A computing part 8 drives a speaker 4 at a prescribed frequency of signal to generate a plane wave from the speaker 4 in an acoustic tube 5 having a particle velocity sensor 2 and a microphone 3 in an opening end 5a side, and having the speaker 4 in a closed end 5b side. The computing part 8 measures the acoustic characteristics of the sample 6 arranged adjacently with a prescribed space with respect to an opening end 5a, based on output signals from the particle velocity sensor 2 and the microphone 3. The particle velocity sensor 2 and the microphone 3 are arranged inside the acoustic tube 5 with an equal distance from the sample 6, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acoustic characteristic measuring apparatus, and more particularly to an apparatus for measuring acoustic characteristics such as acoustic impedance of a sample (measurement object) surface.

  In the development of vehicles and the like, a CAE (Computer Aided Engineering) technique that can predict vibration noise more quickly and more accurately at the development stage is desired.

  In general, when predicting vehicle noise, modeling (1) to (3) focusing on (1) sound source, (2) transmission structure, and (3) evaluation point, theoretical calculation (boundary Element method, finite element method), it is necessary to accurately measure and apply each boundary condition in performing this calculation.

  For example, in order to obtain the acoustic impedance (Z) of the sample surface, there has been a two-microphone type acoustic measurement device (see, for example, Patent Document 1).

  In the measurement of acoustic characteristics by such a two-microphone method, it is necessary to destroy the sample and pack it in the acoustic tube, and to press the sample from the back, and the acoustic tube and the sample are brought into contact with each other. It was. Therefore, there is a problem that the sample is damaged or damaged.

  In addition, such a conventional two-microphone system detects the phase lag between the incident wave and the reflected wave with respect to the sample, so the interval between the two microphones needs to be sufficiently long, and the acoustic tube becomes huge. There was also a problem.

  As described above, in the acoustic characteristic measuring apparatus according to Patent Document 1, it is necessary to destroy the sample, and it is necessary to directly contact the sample, and further, it is necessary to lengthen the acoustic tube. In order to solve this problem, an acoustic characteristic measurement method using a particle velocity sensor and a microphone has been reported (for example, see Non-Patent Document 1).

  Such an acoustic characteristic measurement method of Non-Patent Document 1 will be described with reference to FIG.

  As shown in FIG. 1 (1), the acoustic characteristic measuring apparatus 10 is configured such that the particle velocity sensor 2 and the microphone 3 are both arranged at an equal distance d from the sample 6 in order to measure the acoustic characteristics in an open space, and their outputs. The signals are given to the calculation unit 8 as channels CH1 and CH2, respectively. The calculation unit 8 further applies random noise N to the speaker 4 via the amplifier 7, so that the output sound wave from the speaker 4 is simultaneously applied to the particle velocity sensor 2 and the microphone 3 through a space of length l. It is like that.

Fig. 2 (2) shows the relationship between the particle velocity sensor 2, microphone 3, speaker 4, and sample 6.To measure the acoustic impedance Z in a normal environment, the sound source speaker 4 is measured. The sound pressure P and the particle velocity U of the surface of the sample 6 as the target material are necessary, and these are detected by the microphone 3 and the particle velocity sensor 2, respectively, so the acoustic impedance Z is
Z = P / U ・ ・ ・ Formula (1)
Can be obtained.

The acoustic admittance β is obtained from the acoustic impedance Z, and the reflectance γ and the sound absorption coefficient α are also obtained.
Japanese Patent Laid-Open No. 2003-83805 Teruo Iwase, Koichi Yoshihisa, “Measuring Method of Sound Reflection and Absorption Characteristics Based on the Particle Velocity and its Applications to Measurements on Such as Drainage Pavement of Road Surface”, Inter-noise 2003, p.697-704

  In Non-Patent Document 1 described above, the acoustic characteristics in an open space are measured, and therefore the acoustic characteristics in a closed space cannot be measured. Therefore, for example, when measuring the acoustic characteristics in the car, if the measurement method in this open space is applied as it is, the reflected wave will be reflected in a complicated shape because the car has a complicated shape, and the measurement will be accurate. I can't.

  In order to avoid this, when measuring the acoustic characteristics of these automobile parts in a measurement room equipped with acoustic equipment, prepare a huge measurement room and destroy the sample from the vehicle into a predetermined shape and place it in a predetermined position. There was a need to place.

  Accordingly, an object of the present invention is to provide an acoustic characteristic measuring apparatus that can measure acoustic measurements in a narrow closed space without destroying the sample and without contact with the sample.

  In order to achieve the above object, an acoustic characteristic measuring apparatus according to the present invention has a particle velocity sensor and a microphone on the open end side, an acoustic tube having a speaker inside the closed end, and a plane wave generated from the speaker. The loudspeaker is driven with a signal of a predetermined frequency, and the output signals from the particle velocity sensor and microphone are input at this time, and the acoustic characteristics of the sample placed close to the opening end at a predetermined proximity interval are calculated. The particle velocity sensor and the microphone are both disposed in the acoustic tube at an equal distance from the sample.

  That is, in the present invention, a plane wave is generated in the acoustic tube by driving the speaker with a signal having a predetermined frequency. This plane wave propagates through the acoustic tube to become an incident wave to the sample. In this case, the particle velocity sensor and microphone are placed in each acoustic tube equidistant from the sample, and close from the closed end of the acoustic tube to the sample. Therefore, the acoustic tube substantially forms a closed tube at both ends so that the reflected wave from the sample has substantially the same trajectory as the incident wave. It becomes a standing wave to follow.

  Therefore, when this plane wave (incident wave and reflected wave) passes through the particle velocity sensor and the microphone, as described in FIG. Acoustic characteristics can be measured.

  The above particle velocity sensor and microphone have directivity for the plane wave, so that even if there is a gap between the acoustic tube and the sample, the sound wave entering from the gap is made invalid and only the incident wave and reflected wave are made. The acoustic characteristics can be obtained in response to the above.

  The particle velocity sensor described above is at least two heat rays, provided that the particle velocity detection direction by both heat rays and the central axis of the acoustic tube are the same. Good. As a result, the particle velocity sensor is given directivity in the central axis direction of the acoustic tube (directivity only for incident waves and reflected waves).

  Further, the predetermined frequency is equal to or lower than the lowest natural frequency of the acoustic tube.

  The acoustic tube preferably has a length of 150 to 300 mm and an inner diameter of 40 to 70 mm.

  As described above, according to the acoustic characteristic measuring apparatus according to the present invention, since the two-microphone system is not adopted, the acoustic tube can be made small and can be handled even in a narrow closed space such as in an automobile.

  In addition, in the measurement of acoustic characteristics using the conventional two-microphone method, it is necessary to pack the sample into an acoustic tube, and the sample needs to be destroyed. The sample can be measured in a non-destructive state, and the acoustic characteristics of the sample are not changed by contact, and the acoustic characteristics data can be obtained with higher accuracy and in accordance with the actual usage. It becomes possible.

  Further, since the particle velocity sensor and the microphone are arranged in the acoustic tube, the handling property is high, and the acoustic tube can protect these sensors in use. Furthermore, since the configuration is simple and small, it is possible to directly measure a sample such as an automobile material or a building material on site.

  FIG. 1 shows an embodiment of an acoustic characteristic measuring apparatus 1 according to the present invention. This embodiment is different from the conventional acoustic characteristic measuring apparatus 10 shown in FIG. 4 (1) in that a particle velocity sensor 2, a microphone 3, and a speaker 4 are provided in an acoustic tube 5. The acoustic tube 5 is arranged at a certain distance D without contacting the sample 6 and has a length L. The interval D is preferably as close as possible within a range in which the acoustic tube 5 does not affect the acoustic characteristics of the sample, and is, for example, 1 cm or less. Thus, by bringing the acoustic tube 5 as close as possible to the sample 6, the acoustic tube 5 is substantially closed at both ends.

  The particle velocity sensor 2 and the microphone 3 are installed on the side of the open end 5a of the acoustic tube 5 and inserted into the tube, and are provided at substantially the same distance from the sample 6. The speaker 4 is a sealed speaker that is attached to the closed end 5b of the acoustic tube 5 and is fixed so as to output sound waves to the open end 5a.

  Instead of such a sealed speaker 4, as shown in FIG. 2, the speaker 4 may be connected to the opening end 5b of the acoustic tube 5 using a flexible tube 9. In this case, since the speaker 4 can be arranged at a different position from the acoustic tube 5, the measurement is easy even when the sample 6 is in a narrow place.

  The microphone 3 can be a condenser type.

  Here, the sound wave measured by the particle velocity sensor 2 and the microphone 3 uses both an incident wave and a reflected wave with respect to the sample 6. For this purpose, since the incident wave and the reflected wave are preferably standing waves having the same sound pressure mode as much as possible, it is necessary to generate a plane wave from the speaker 4. For this reason, the signal given from the arithmetic unit 8 to the speaker 4 via the amplifier 7 is a predetermined frequency signal.

  That is, the incident wave used for the measurement is a sound wave having the lowest fixed frequency of the acoustic tube 5 as an upper limit frequency, so that the incident wave and the reflected wave in the acoustic tube 5 can be a plane wave. The acoustic characteristics can be obtained by measuring the incident wave and the reflected wave.

Regarding this upper limit frequency, if the acoustic tube 5 is closed at both ends, the cross section of the acoustic tube 5 is circular, the radius is a, and the sound velocity c is the upper limit frequency Fc is
Fc = 0.586c / 2a ... Formula (2)
Given in.

Also, if the cross-sectional shape is rectangular, if the length in the long side direction is b,
Fc = c / 2b (3)
(See “Noise Prevention Design and Simulation” published on April 18, 1987 by Applied Technology Publishing Co., Ltd.).

  In the embodiment shown in FIGS. 1 and 2, as described above, the distance between the acoustic tube 5 and the sample 6 is very close with D = 1 cm or less, and the acoustic tube 5 is substantially closed at both ends. Therefore, a plane wave can be generated if it is below the natural frequency given by the above formula (2) or formula (3).

  Further, since the particle velocity sensor 2 and the microphone 3 measure the plane wave of the incident wave and the reflected wave generated in the acoustic tube 5 in the cross-sectional direction of the acoustic tube 5, the length of the acoustic tube 5 in the longitudinal direction is measured. If it is known, it may be a columnar shape or any columnar shape as long as it is a columnar shape.

  Thus, the plane wave generated from the speaker 4 driven by the calculation unit 8 passes through the particle velocity sensor 2 and the microphone 3 as an incident wave or a reflected wave, so that the output signals of the particle velocity sensor 2 and the microphone 3 are calculated. Part 8 is given as channels CH1 and CH2. Then, as described above with reference to FIG. 4 (2), the calculation unit 8 calculates acoustic admittance, acoustic impedance, reflectance, or sound absorption coefficient as acoustic characteristics, as shown in the above equation (1). The arithmetic unit 8 can obtain these acoustic characteristics by fast Fourier analysis (FFT) or the like.

  Here, the particle velocity sensor 2 and the microphone 3 have directivity with respect to the plane wave. This directivity is directivity with respect to both the direction of the incident wave and the direction of the reflected wave.

  That is, the incident wave passes through the particle velocity sensor 2 and the microphone 3 and is applied to the sample 6, and the reflected wave from the sample 6 with respect to this incident wave is sent to the particle velocity sensor 2 and the microphone 3 in the acoustic tube 5. In other words, there is a portion that exits from the interval D, and there is a portion that exits from the interval D, but some sound waves leak from the periphery of the acoustic tube 5.

  However, since the leaked sound wave has nothing to do with the acoustic characteristics of the sample 6, it is necessary that the particle velocity sensor 2 and the microphone 3 do not detect it.

  For this reason, the particle velocity sensor 2 and the microphone 3 have directivity in both the direction of the incident wave and the direction of the reflected wave (directivity in directions opposite to each other), so that only the incident wave and the reflected wave from the sample 6 are detected. can do.

  FIG. 3 is an enlarged view of the structure of the particle velocity sensor 2. As shown in the figure, the particle velocity sensor 2 has hot wires 21 and 22 protruding into the acoustic tube 5, and the particle velocity sensor 2 determines the particle velocity based on the temperature difference detected by these hot wires 21 and 22. To detect. In this case, the particle velocity detection direction determined by the arrangement of the heat rays 21 and 22 and the central axis of the acoustic tube 5 (axis connecting the speaker 4 and the opening 5a) are arranged in parallel. Thereby, the particle velocity sensor 2 has directivity with respect to both the incident wave and the reflected wave described above. In this case, the heat rays 21 and 22 of the particle velocity sensor 2 need only detect the velocity in the traveling direction of the incident wave, and need not be limited to two.

  As described above, when the acoustic characteristics of the sample 6 are measured by the particle velocity sensor 2 and the microphone 3, the particle velocity detection direction of the particle velocity sensor 2 is set as the traveling direction of the incident wave of the speaker 4 incident on the acoustic tube 5. Therefore, it is possible to measure acoustic characteristics by plane waves moving in a closed space in which the microphone 3 and the particle velocity sensor 2 are disposed in the acoustic tube 5.

  This eliminates the need for a measurement space such as a huge measurement chamber, as compared to the conventional 2-microphone method and when measuring acoustic characteristics in an open space, and does not destroy the sample 6 without contact with the acoustic tube 5. Since it can be measured easily and non-destructively just by placing it in the vicinity of one side, it becomes a simple and compact configuration, and it is possible to measure the sample as it is in the field, such as automobile materials and building materials. .

  The particle velocity sensor 2 and the microphone 3 may be provided integrally with the acoustic tube 5.

  In addition, when a sample is investigated and measured in the field, by adopting an acoustic tube of this size, it is possible to reduce the size and measure a sound of about 500 Hz to 5 kHz.

  It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that various modifications can be made by those skilled in the art based on the description of the scope of claims.

It is the block diagram which showed one Example of the acoustic characteristic measuring apparatus which concerns on this invention. It is the block diagram which showed another Example of the acoustic characteristic measuring apparatus which concerns on this invention. It is the figure which showed roughly the structure of the particle velocity sensor used for the acoustic characteristic measuring apparatus which concerns on this invention. FIG. 10 is a block diagram showing an acoustic characteristic device known as a conventional example (Non-Patent Document 1).

Explanation of symbols

1 Acoustic characteristic measuring device
2 Particle velocity sensor
3 Microphone
4 Speaker
5 Acoustic tube
5a Open end
5b Closed end
6 Sample (material to be measured)
7 Amplifier
8 Calculation unit
9 Flexible tube
21, 22 Hot wire In the figure, the same symbols indicate the same or corresponding parts.

Claims (5)

An acoustic tube having a particle velocity sensor and a microphone on the open end side, and a speaker on the closed end side;
The speaker is driven with a signal of a predetermined frequency so that a plane wave is generated from the speaker, and at this time, an output signal from the particle velocity sensor and the microphone is input and arranged at a predetermined proximity interval from the opening end. And a calculation unit for calculating the acoustic characteristics of the sample,
An apparatus for measuring acoustic characteristics, wherein the particle velocity sensor and the microphone are both disposed in the acoustic tube at an equal distance from the sample. In claim 1,
An acoustic characteristic measuring apparatus, wherein the particle velocity sensor and the microphone have directivity with respect to the plane wave. In claim 1,
The particle velocity sensor is provided with at least two heat rays, the particle velocity detection direction by both heat rays being arranged so that the central axis of the acoustic tube is parallel, acoustic characteristic measurement apparatus. In claim 1,
The acoustic characteristic measuring apparatus, wherein the predetermined frequency is equal to or lower than a lowest natural frequency of the acoustic tube. In claim 1,
An acoustic characteristic measuring apparatus, wherein the acoustic tube has a length of 150 mm to 300 mm and an inner diameter of 40 mm to 70 mm.

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