A sound absorption coefficient measurement system and method based on laser vibration measurement

Abstract

The present invention belongs to the field of sound absorption coefficient measurement, specifically, a sound absorption coefficient measurement system and method based on laser vibration measurement, the method comprising: placing the material to be tested on one side of a standing wave tube and sealing it, connecting it to a loudspeaker on the other side of the standing wave tube, opening a transparent area on the standing wave tube, and designing a soft film in the tube wall of the transparent area; placing two probes of the laser vibrometer at a certain distance at different positions of the soft film; the loudspeaker generates a sound wave of a certain frequency f; the laser vibrometer measures the vibration of two different points on the soft film material to obtain vibration data; the sound pressure values ​​at different positions are calculated based on the vibration data, and the sound absorption coefficient of the material to be tested is calculated based on the sound pressure value. The problem of accurately measuring the sound absorption coefficient of the material is solved, and the advantages of high precision and good real-time performance are obtained. Applying laser vibration measurement technology to measure the sound absorption coefficient of materials is a brand-new solution.

Description

Technical Field

[0001] The invention belongs to the field of sound absorption coefficient measurement, and in particular to a sound absorption coefficient measurement system and method based on laser vibrometer. Background Art

[0002] With the rapid development of economic construction, the process of urban modernization is also accelerating. In the process of urban construction, some noises, such as traffic noise, construction noise, etc., are flooding people's daily lives. This has a great impact on people's physical and mental health. Therefore, how to control noise pollution to create a quiet and comfortable personal space is increasingly concerned and desired by people. Using sound-absorbing materials to control noise pollution is a very effective way in terms of economy, complexity, and effectiveness. For sound-absorbing materials, the sound absorption coefficient strictly describes the material's absorption effect on sound, and the larger the sound absorption coefficient, the better the sound absorption effect of the material. Therefore, how to accurately measure the sound absorption coefficient of the material is the first basic problem to be faced. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a sound absorption coefficient measurement system based on laser vibration measurement to solve the problem of accurately measuring the sound absorption coefficient of a material.

[0004] The present invention is achieved in this way.

[0005] A method for measuring sound absorption coefficient based on laser vibration measurement, the method comprising:

[0006] The material to be tested is placed on one side of a standing wave tube and sealed, and connected to a speaker on the other side of the standing wave tube. A transparent area is provided on the standing wave tube, and a soft film is designed inside the tube wall of the transparent area.

[0007] Two probes of the laser vibrometer are placed at different positions of the soft film at a certain distance;

[0008] The loudspeaker produces a sound wave of a certain frequency f;

[0009] The laser vibrometer measures the vibration at two different points on the soft film material to obtain vibration data;

[0010] The sound pressure values ​​at different positions are calculated based on the vibration data, and the sound absorption coefficient of the tested material is calculated based on the sound pressure values.

[0011] Furthermore, different frequencies f are set, and the sound absorption coefficients at different frequencies are calculated, and the arithmetic mean of these sound absorption coefficients is calculated to obtain the average sound absorption coefficient of the material.

[0012] Further, the sound pressure values ​​at different positions are calculated according to the vibration data, and the sound absorption coefficient of the tested material is calculated according to the sound pressure values, including: assuming that the sound pressures at the two probes are P1 and P2 respectively, and calculating the sound absorption coefficient according to the following formula:

[0013] The transfer function of the incident wave H I for:

[0014]

[0015] The transfer function of the reflected wave H R for:

[0016]

[0017] The reflection coefficient is:

[0018]

[0019] Where L1 is the distance between the probes closest to the material being tested, and L2 is the distance between the two probes. c is the speed of sound, H 12 is the transfer function from the first probe to the second probe:

[0020]

[0021] Where S 11 is the auto-power spectrum of the sound pressure P1, S 22 is the auto-power spectrum of the sound pressure P2, S 12 is the cross power spectrum of sound pressure P1 and sound pressure P2; S 21 is the cross power spectrum of sound pressure P2 and sound pressure P1;

[0022] The sound absorption coefficient at frequency f is calculated based on the relationship between the material's sound absorption coefficient α(f) and the reflection coefficient r(f):

[0023] α(f)=1-|r(f)| 2 .

[0024] Furthermore, the specific frequencies include: 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz.

[0025] A sound absorption coefficient measurement system based on laser vibration measurement, the system comprising:

[0026] A standing wave tube, where the material to be tested is placed on one side of the standing wave tube and is closed, and the other side of the standing wave tube is open for connection with a speaker. A certain area in the middle of the standing wave tube is designed to be transparent for conducting laser light; a soft film is designed inside the tube wall in the transparent area for assisting in measuring the sound pressure signal at that location;

[0027] A loudspeaker produces a sound wave of a certain frequency f;

[0028] The laser vibrometer measures the vibration of two different points on the soft film material by placing two probes at a certain distance from each other to obtain vibration data.

[0029] The PC receives the vibration data measured by the laser vibrometer and calculates the sound pressure values ​​at different positions, and obtains the sound absorption coefficient of the tested material based on the sound pressure values.

[0030] Furthermore, the speaker generates sound waves of specific frequencies under the control of waveforms of different frequencies output by the signal generator.

[0031] Furthermore, the signal generator uses six sound wave frequencies of 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz to output a sine wave signal to drive the speaker to generate corresponding sound waves.

[0032] Furthermore, it also includes an adaptive power amplifier board: used to amplify the sine wave signal output by the signal generator and increase the driving current.

[0033] Furthermore, the laser vibrometer uploads the obtained vibration parameters to the data adapter card. The data adapter is a transfer mechanism between the PC and the underlying system. On the one hand, it is used to parse the commands issued by the PC to control the signal generator or the laser vibrometer, and on the other hand, it transmits the data measured by the underlying system to the PC.

[0034] Furthermore, the PC computer calculates the sound pressure values ​​at different positions, and the process of calculating the sound absorption coefficient of the detected material according to the sound pressure values ​​includes:

[0035] Let the sound pressure at the two probes be P1 and P2 respectively, and calculate the sound absorption coefficient according to the following formula:

[0036] The transfer function of the incident wave H I for:

[0037]

[0038] The transfer function of the reflected wave H R for:

[0039]

[0040] The reflection coefficient is:

[0041]

[0042] Where L1 is the distance between the probes closest to the material being tested, and L2 is the distance between the two probes. c is the speed of sound, H 12 is the transfer function from the first probe to the second probe:

[0043]

[0044] Where S 11 is the auto-power spectrum of the sound pressure P1, S 22 is the auto-power spectrum of the sound pressure P2, S 12 is the cross power spectrum of sound pressure P1 and sound pressure P2; S 21 is the cross power spectrum of sound pressure P2 and sound pressure P1;

[0045] The sound absorption coefficient at frequency f is calculated based on the relationship between the material's sound absorption coefficient α(f) and the reflection coefficient r(f):

[0046] α(f)=1-|r(f)| 2 .

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The advantages of the invention are discussed in terms of equipment and method.

[0049] This system measures the sound absorption coefficient based on the transfer function method. Existing measurement systems based on the transfer function method all use multiple microphones to collect the sound pressure of the reflected sound waves at different positions in the standing wave tube. When using a microphone to collect the sound pressure in the standing wave tube, a hole must be opened on the standing wave tube, and the size of the hole needs to fit closely with the microphone. The requirements for mechanical technology to produce the required aperture and hole position on the standing wave tube will be very high, which increases the cost of the system. In addition, the number of holes is limited. When the number of holes is limited, the situation in which the algorithm can be verified is very limited. Finally, since the sound pressure caused by the reflected sound wave is very weak, in order to effectively detect the weak signal, a high-performance microphone is required, which greatly increases the cost of the system. This system uses a non-contact method to measure the sound pressure of the reflected wave, which means that this system does not need to open a hole on the standing wave tube, and the selection of the observation point is arbitrary, so the application of the system is very flexible. Furthermore, the laser vibrometer is highly sensitive to vibration information and can well observe the vibration of the standing wave tube wall caused by the reflected wave sound pressure, thereby making a more accurate measurement of the sound absorption coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A system block diagram provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] See also Figure 1 As shown, the present invention is a sound absorption coefficient measurement system based on laser vibration measurement, including a standing wave tube, a speaker, a signal generator, a laser vibrometer (including a probe), a microphone, a multi-channel high-frequency acquisition card, a data adapter card and a PC computer. Among them:

[0053] Standing wave tube: One side of the standing wave tube is open to connect to the speaker, and the other side is closed. The outer wall of the standing wave tube is designed to be rigid, and the standing wave tube is designed to be transparent in a certain area in the middle. The material of the rigid lens is selected. When the wall of the standing wave tube is set to be transparent, the laser emitted by the laser vibrometer can pass through the standing wave tube and hit the soft film inside the tube, so as to collect the vibration information of the soft film caused by the sound pressure. The soft film is an amplification of the vibration signal caused by the sound pressure. When the vibration signal is amplified, the laser vibrometer can better collect the vibration information, which is also conducive to the suppression of the introduced noise. This is used to maximize the conduction of the laser sent by the vibrometer. A soft film is designed inside the wall of the transparent area to assist in measuring the sound pressure signal at that position.

[0054] Speaker: When working, the speaker is placed on the opening side of the waveguide and is tightly coupled with the opening side. The speaker mainly generates sound waves of specific frequencies under the control of waveforms of different frequencies output by the signal generator.

[0055] Signal generator: The arithmetic mean of the sound absorption coefficients at the six sound wave frequencies of 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz and 4000Hz is used to represent the average sound absorption coefficient of a certain material. The signal generator is used to output the sine wave signals of the above 6 frequencies to drive the speaker to generate the corresponding sound waves.

[0056] Adaptive power amplifier board: used to amplify the sine wave signal output by the signal generator and increase the driving current, so that it can normally drive the speaker to produce the desired sound wave.

[0057] Laser vibrometer: The laser vibrometer has two probes. When the speaker sends a sound wave signal, the vibrometer uses the two probes to measure the vibration parameters of the soft film material at different positions, such as velocity, displacement and acceleration, and uploads the obtained vibration parameters to the data adapter card.

[0058] Data adapter card: This module is the transfer mechanism between the PC and the underlying system. On the one hand, it is used to parse the commands issued by the PC to control the work of the signal generator or laser vibrometer, and on the other hand, it uploads the data measured by the underlying system, such as vibration parameters, to the PC according to the established PCI protocol.

[0059] PC: This module is the core control mechanism of the whole system. The developed software is installed in the PC. The generation of control commands and the analysis of received data are completed in the developed software. After the data analysis is completed, the software displays the calculation results on the screen.

[0060] The present invention provides a method for measuring sound absorption coefficient based on laser vibration measurement, the method comprising:

[0061] The material to be tested is placed on one side of a standing wave tube and sealed, and connected to a speaker on the other side of the standing wave tube. A transparent area is provided on the standing wave tube, and a soft film is designed inside the tube wall of the transparent area.

[0062] Two probes of the laser vibrometer are placed at different positions of the soft film at a certain distance;

[0063] The loudspeaker produces a sound wave of a certain frequency f;

[0064] The laser vibrometer measures the vibration at two different points on the soft film material to obtain vibration data;

[0065] The sound pressure values ​​at different positions are calculated based on the vibration data, and the sound absorption coefficient of the tested material is calculated based on the sound pressure values.

[0066] Set different frequencies f, calculate the sound absorption coefficients at different frequencies, and calculate the arithmetic mean of these sound absorption coefficients to obtain the average sound absorption coefficient of the material. The specific steps are:

[0067] (1) First, under the control of the PC, the signal generator drives the speaker to generate a sound wave of a specific frequency f. When the sound wave passes through the material to be tested, part of it is absorbed and part of it is reflected. The reflected sound wave propagates in the standing wave tube and drives the soft film material to vibrate. The laser vibrometer measures the vibration at two different points on the soft film material and uploads the measured vibration data to the PC through the data adapter card.

[0068] (2) The vibration data uploaded by the laser vibrometer contains information about the reflected sound pressure. The software in the PC calculates the sound pressure values ​​at different positions based on the vibration data, and sets the sound pressures at the first probe 1 and the second probe 2 to be P1 and P2 respectively. The sound absorption coefficient can be calculated using the following formula.

[0069] The transfer function of the incident wave HI for

[0070]

[0071] The transfer function of the reflected wave H R for

[0072]

[0073] The reflection coefficient is

[0074]

[0075] Where L1 is the distance between the probes closest to the material being tested, L2 is the distance between the two probes, c is the speed of sound, H 12 is the transfer function from the first probe 1 to the second probe 2. Therefore, we only need to know H 12 The reflection coefficient r(f) can be calculated.

[0076] and:

[0077]

[0078] Where S 11 is the autopower spectrum of sound pressure 1, S 22 is the autopower spectrum of sound pressure 2, S 12 is the cross power spectrum of sound pressure P1 and sound pressure P2,

[0079] S 21 is the cross power spectrum of sound pressure P2 and sound pressure P1. Since sound pressure P1 and sound pressure P2 can be measured, H 12 can be calculated. Therefore, the reflection coefficient r(f) can be calculated by the above formula.

[0080] The relationship between the sound absorption coefficient α(f) and the reflection coefficient r(f) of the material is:

[0081] α(f)=1-|r(f)| 2 ,

[0082] Therefore, the sound absorption coefficient α(f) at frequency f can be calculated by combining the above formulas.

[0083] (3) Set different frequencies f and calculate the sound absorption coefficients at different frequencies. Then calculate the arithmetic mean of these sound absorption coefficients to obtain the average sound absorption coefficient of the material. After the average sound absorption coefficient is completed, it will be displayed on the screen of the PC computer.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring sound absorption coefficient based on laser vibration measurement, characterized in that: The method includes: The material to be tested is placed on one side of a standing wave tube and sealed, and connected to a speaker on the other side of the standing wave tube. A transparent area is provided on the standing wave tube, and a soft film is designed inside the tube wall of the transparent area. Two probes of the laser vibrometer are placed at different positions of the soft film at a certain distance; The loudspeaker produces a sound wave of a certain frequency f; The laser vibrometer measures the vibration at two different points on the soft film material to obtain vibration data; The sound pressure values ​​at different positions are calculated based on the vibration data, and the sound absorption coefficient of the tested material is calculated based on the sound pressure values.

2. The method for measuring sound absorption coefficient based on laser vibration measurement according to claim 1, characterized in that: Set different frequencies f, calculate the sound absorption coefficients at different frequencies, and calculate the arithmetic mean of these sound absorption coefficients to obtain the average sound absorption coefficient of the material.

3. The method for measuring sound absorption coefficient based on laser vibration measurement according to claim 1, characterized in that: The sound pressure values ​​at different positions are calculated based on the vibration data. The sound absorption coefficient of the tested material is calculated based on the sound pressure values. Let the sound pressures at the two probes be P1 and P2 respectively, and calculate the sound absorption coefficient according to the following formula: The transfer function of the incident wave H I for: The transfer function of the reflected wave H R for: The reflection coefficient is: Where L1 is the distance between the probes closest to the material being tested, and L2 is the distance between the two probes. c is the speed of sound, H 12 is the transfer function from the first probe to the second probe: Where S 11 is the auto-power spectrum of the sound pressure P1, S 22 is the auto-power spectrum of the sound pressure P2, S 12 is the cross power spectrum of sound pressure P1 and sound pressure P2; S 21 is the cross power spectrum of sound pressure P2 and sound pressure P1; The sound absorption coefficient at frequency f is calculated based on the relationship between the material's sound absorption coefficient α(f) and the reflection coefficient r(f): α(f)=1-|r(f)| 2 。 4. The method for measuring sound absorption coefficient based on laser vibration measurement according to claim 1, characterized in that: The specific frequencies include: 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz and 4000Hz.

5. A sound absorption coefficient measurement system based on laser vibration measurement, characterized in that: The system includes: A standing wave tube, where the material to be tested is placed on one side of the standing wave tube and is closed, and the other side of the standing wave tube is open for connection with a speaker. A certain area in the middle of the standing wave tube is designed to be transparent for conducting laser light; a soft film is designed inside the tube wall in the transparent area for assisting in measuring the sound pressure signal at that location; A loudspeaker produces a sound wave of a certain frequency f; The laser vibrometer measures the vibration of two different points on the soft film material by placing two probes at a certain distance from each other to obtain vibration data. The PC receives the vibration data measured by the laser vibrometer and calculates the sound pressure values ​​at different positions, and obtains the sound absorption coefficient of the tested material based on the sound pressure values.

6. The sound absorption coefficient measurement system based on laser vibration measurement according to claim 5, characterized in that: The loudspeaker generates sound waves of specific frequencies under the control of waveforms of different frequencies output by the signal generator.

7. The sound absorption coefficient measurement system based on laser vibration measurement according to claim 6, characterized in that: The signal generator uses six sound wave frequencies of 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz to output a sine wave signal to drive the speaker to generate corresponding sound waves.

8. The sound absorption coefficient measurement system based on laser vibration measurement according to claim 7, characterized in that: It also includes an adaptive power amplifier board: used to amplify the sine wave signal output by the signal generator and increase the driving current.

9. The sound absorption coefficient measurement system based on laser vibration measurement according to claim 6, characterized in that: The laser vibrometer uploads the obtained vibration parameters to the data adapter card, which is a transfer mechanism between the PC and the underlying system. On the one hand, it is used to parse the commands issued by the PC to control the signal generator or the laser vibrometer, and on the other hand, it transmits the data measured by the underlying system to the PC.

10. The sound absorption coefficient measurement system based on laser vibration measurement according to claim 5, characterized in that: The PC computer calculates the sound pressure values ​​at different positions, and the process of calculating the sound absorption coefficient of the tested material according to the sound pressure values ​​includes: Let the sound pressure at the two probes be P1 and P2 respectively, and calculate the sound absorption coefficient according to the following formula: The transfer function of the incident wave H I for: The transfer function of the reflected wave H R for: The reflection coefficient is: Where L1 is the distance between the probes closest to the material being tested, and L2 is the distance between the two probes. c is the speed of sound, H 12 is the transfer function from the first probe to the second probe: Where S 11 is the auto-power spectrum of the sound pressure P1, S 22 is the auto-power spectrum of the sound pressure P2, S 12 is the cross power spectrum of sound pressure P1 and sound pressure P2; S 21 is the cross power spectrum of sound pressure P2 and sound pressure P1; The sound absorption coefficient at frequency f is calculated based on the relationship between the material's sound absorption coefficient α(f) and the reflection coefficient r(f): α(f)=1-|r(f)| 2 。

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