GBJ 88-1985 Standard for the measurement of sound absorption coefficient and acoustic impedance using the standing wave tube method
Some standard content:
Engineering Construction Standard Full-text Information System
National Standard of the People's Republic of China
Standing Wave Tube Method Sound Absorption Coefficient
And Acoustic Impedance Ratio Measurement Specification
GBJ88—85
1986Beijing
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National Standard of the People's Republic of China
Standing Wave Tube Method Sound Absorption Coefficient
And Acoustic Impedance Ratio Measurement Specification
GBJ88—85
Editor: Tongji University
Approval Department: National National Planning Commission Effective Date: June 1, 1986
Engineering Construction Standards Full Text Information System
Engineering Construction Standards Full Text Information System
Notice on the Release of "Standing Wave Tube Method Sound Absorption Coefficient and Acoustic Impedance Measurement Specification"
Standards [1986] No. 04
According to the requirements of the former National Construction Commission (81) Jianfa Shezi No. 546, the National Acoustic Standardization Technical Committee is responsible for the centralized organization, and Tongji University will work with relevant units to compile the "Standing Wave Tube Method Sound Absorption Coefficient and Acoustic Impedance Measurement Specification", which has been reviewed by the National Acoustic Standardization Technical Committee. The "Standing Wave Tube Method Sound Absorption Coefficient and Acoustic Impedance Measurement Specification" GBJ88-85 is now approved as a national standard and will be implemented from June 1986.
The specific interpretation of this specification is the responsibility of Tongji University. State Planning Commission
December 31, 1985
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Preparation Instructions
This specification is prepared by the National Acoustic Standardization Technical Committee and entrusted to Tongji University in accordance with the requirements of the former National Capital Construction Committee (81) Jianfa Shezi No. 546.
In the process of preparing this specification, the preparation unit investigated and studied the practical experience and research results of relevant domestic units, collected and analyzed similar foreign measurement standards and relevant technical information, conducted relatively systematic comparative tests and corresponding theoretical analysis on some important contents, and put forward the draft for soliciting opinions. The opinions of relevant domestic units were widely solicited, and a symposium was held. After repeated revisions, the draft for submission was put forward. After discussion and agreement by the Architectural Acoustics Subcommittee of the National Acoustic Standardization Technical Committee, it was finally reviewed and finalized by the National Acoustic Standardization Technical Committee.
This specification consists of five chapters and seven appendices. The contents include: measurement equipment, measurement methods, measurement range and measurement requirements.
During the implementation of this specification, we hope that all units will pay attention to accumulating information and summarizing experience. If you find any need for modification or supplementation, please send your opinions and relevant information to the Institute of Acoustics of Tongji University for reference in future revisions. Tongji University
December 1985
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Chapter 1
Chapter 2
Basic Measurement Equipment
Section 1 Measuring Device
Section 2 Standing Wave Tube
Section 3
Section 4
Sound Source System
Detector
Output Indicator
Section 5
Chapter 3 Measurement Methods| |tt||Section 1
General requirements
Section 2 Measurement of sound absorption coefficient
Section 3 Measurement of normal acoustic impedance
Chapter 4 Measurement range
Section 1 Measurement range of sound absorption coefficient
Section 2
Measurement frequency range
Chapter 5
Measurement requirements
Section 1 Preparation and installation of test pieces
Section 2 Measurement procedure
Section 3 Measurement error…
Expression of measurement results·||t t||Section 4
Appendix—
Typical Test Piece Installation
Appendix 2
Relative Position of Acoustic Center of Detector
Appendix 3
Relationship Table between Standing Wave Ratio (s) and Its Reciprocal (n), Sound Pressure Level Difference (L) and Sound Absorption Coefficient (α)
Appendix 4
Extension of Lower Limit of Measurement Frequency
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(15)
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Appendix 5 Management Channel attenuation causes the change of the minimum value Appendix VI Calculation of normal acoustic impedance ratio diagram
Appendix VII Explanation of terms used in this specification...
Additional explanation:
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Chapter 1 General
Article 1.0.1 In order to unify the standing wave tube measurement and facilitate the mutual comparison of the measurement data, this specification is specially formulated.
Article 1.0.2 This specification is applicable to sound-absorbing materials and sound-absorbing components that absorb airborne sound. The sound absorption coefficient and normal acoustic impedance ratio at normal incidence are measured using a standing wave tube. Engineering Construction Standard Full Text Information System
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Chapter 2 Basic Measurement Equipment
Section 1 Measurement Device
Article 2.1.1 The equipment for standing wave tube measurement shall consist of standing wave tube, sound source system, detector and output indication device, as shown in Figure 2.1..1. Probe
Standing wave tube
City frequency signal
Generator
Speaker box
Microphone
mmmarym
Indication device
Figure 2.1, 1 Typical device of standing wave tube measurement equipment Article 2.1.2 The test piece and the sound source device shall be placed at both ends of the standing wave tube respectively. The surface of the test piece shall be perpendicular to the axis of the standing wave tube. Section 2 Standing wave tube
Article 2.2.1 The cross section inside the standing wave tube shall generally be circular or square. The cross-sectional area should be uniform, and its deviation should not be greater than 0.2%. Article 2.2.2 The wall of the standing wave tube should be made of dense and rigid materials. The inner surface of the wall should be smooth and free of fine cracks. Article 2.2.3 The standing wave tube can be divided into two sections: one is the specimen section, which is used to install the specimen, and the other is the test section, which is the main body of the standing wave tube. The cross-section and wall thickness of the two sections must be exactly the same, and they should be coaxially connected.
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If the specimen section and the main body of the standing wave tube are an integral structure, the passage on the tube wall for loading and unloading the specimen must be tightly sealed with a thick cover plate; the cover plate should be well fixed, and its sound insulation performance should be better than or close to the sound insulation performance of the tube wall. If the specimen section is a cylindrical detachable structure, the end face of the open end must be flat and can be closely combined with the main body of the standing wave tube. The bottom plate of the closed end shall be made of a solid material with a thickness of more than 10 mm. The bottom plate and the side wall shall be tightly fitted and shall be able to move smoothly in the test tube. The test tube and the main body of the standing wave tube shall be relatively fixed, and the outer side of the pipe connection shall be tightly sealed with a sleeve. The requirements for typical test device can be implemented according to Appendix 1. Article 2.2.4 The ratio of the length of the standing wave tube to the inner diameter of the circular section or the side length of the square section should be within the range of 1015.
Article 2.2.5 The standing wave tube shall be installed on the ground or on a stand. When a detachable test tube is used, the test tube shall be equipped with an additional support device. Section 3 Sound Source System
Article 2.3.1 The sound source system shall consist of an audio signal generator, a power amplifier, a loudspeaker, etc.
Article 2.3.2 The loudspeaker shall be installed in a box connected to the standing wave tube. The wall of the box should be made of thick material, and the wall and the speaker should be padded with vibration isolation material; the box should be filled with sound-absorbing material. Article 2.3.3 The speaker box can be directly installed at the end of the standing wave tube, or it can be installed on a 45° or 90° elbow. The box and the standing wave tube should be tightly combined and padded with vibration isolation material. There should be no sudden change in the cross-sectional area of the channel at the connection. Article 2.3.4 The speaker must be excited with a pure tone signal. The excitation signal is generally generated by an audio signal generator and should be amplified before being fed to the speaker. The frequency of the signal should use the center frequency of the 1/3 octave series. Article 2.3.5 During the test, the amplitude and frequency of the pure tone signal should remain stable. In the same measurement, the drift of the signal amplitude should not be greater than 0.2 decibels; the drift of the frequency should not be greater than 0.5%.
Article 2.3.6 The frequency of the signal should be able to be accurately measured; its accuracy should be better than that of the Engineering Construction Standard Full Text Information System
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Note: If only the sound absorption coefficient is measured, its accuracy can be appropriately reduced. Section 4 Detector
Article 2.4.Article 1 The main body of the detector is a movable microphone. The microphone can be installed directly in the standing wave tube or outside the tube with the help of a probe tube. The total cross-sectional area of the part of the detector installed in the tube should not be greater than 5% of the cross-sectional area of the standing wave tube. Article 2.4.2 The detector must isolate all other sound transmission channels that communicate with the outside except the sound-receiving surface. The sound-receiving surface of the detector must be perpendicular to the axis of the standing wave tube.
Article 2.4.3 The acoustic center of the detector should be able to move along the axis of the standing wave tube; the relative ratio of the distance from the axis to the inner diameter of the circular section or the side length of the square section should not be greater than 10%. The relative position of the acoustic center of the detector should be calibrated in advance and can generally meet the requirements of Appendix 2.
Article 2.4.4 The detector should be equipped with a scale or a transmission reading device. Compared with the wavelength corresponding to the upper limit of the measurement frequency, the accuracy of the distance measurement should be better than 1%. Article 2.4.5 The microphone part of the detector must be isolated from vibration, and it should be ensured that there will be no rigid contact with the wall of the standing wave tube or the speaker during the movement of the detector.
Article 2.4.6 When using a probe tube for detection, the wall thickness of the probe tube should not be less than 1/8 of the tube diameter. Vibration isolation should be performed between the probe tube and the microphone. Section 5 Output Indicator Device
Article 2.5.1 The output indicator device should generally consist of a signal amplifier, an attenuator, a filter and an indicator. Article 2.5.2 The cable that feeds the receiving signal from the detector to the output indicator device must be a shielded cable.
Article 2.5.3 During the test, the working state of the signal amplifier should remain stable. In the same measurement, the drift of the amplifier gain should not be greater than 0.2 dB. Engineering Construction Standard Full Text Information System
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Under normal working conditions, the distortion of the amplifier should not be greater than 3%. Article 2.5.4 The attenuator should be able to change the relative strength of the signal continuously or in steps. The stepped attenuator should be calibrated in advance, and its measurement accuracy should be better than 0.2 decibels.
Article 2.5.5 The attenuation of the filter for frequencies that deviate from the center frequency by one octave should be increased by more than 30 decibels. When the detector is at the maximum sound pressure level in the standing wave tube, the harmonic frequency component of the received signal after amplification and filtering should be more than 50 decibels lower than the fundamental frequency component.
Article 2.5.6 The indicator should be equipped with a reading device and should be able to accurately measure the relative ratio of the received signal or the corresponding level difference; its measurement accuracy should be better than 2% or 0.2 decibels.
Article 2.5.7 The reading device of the indicator can directly read the value according to the size of the indicator indication (such as the deflection angle of the pointer, the level of the received signal, etc.); it can also use a calibrated attenuator to change the strength of the received signal so that it indicates a given value on the indicator, and then read the value according to the attenuation of the attenuator. Article 2.5.8 The indication of the indicator should be able to change rapidly with the change of the received signal; when using a sound level meter to indicate and read, it is generally not appropriate to use the "slow gear" measurement. Engineering Construction Standard Full Text Information System
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Chapter 3
Measurement Method
Section 1
General Requirements
Article 3.1.1 The measurement of the standing wave tube must be carried out successively at the two places with the maximum sound pressure and the minimum sound pressure, and then a relative comparison is made. Generally, the detector should be moved to the place with the maximum sound pressure for debugging, and then the detector should be moved to the place with the minimum sound pressure for measurement. During the movement, the experimental conditions of the sound source and receiving system must remain unchanged. Article 3.1.2 The relative ratio between the maximum and minimum sound pressure in the standing wave tube, that is, the standing wave ratio, is determined by the relative ratio of the voltage of the corresponding receiving signal. Article 3.1.3 When the acoustic center of the detector is at the surface of the specimen, the position reading of the detector should be used as the starting point for measuring the moving distance, and the provisions of Appendix 2 can generally be followed. The position reading when the acoustic center of the detector moves to the first minimum of sound pressure should be the distance from the surface of the specimen to the first minimum of sound pressure; this distance should be expressed in units of half the wavelength of the sound wave, and the corresponding value is the phase factor, which can be calculated as follows: =2/2
引——the distance from the surface of the specimen to the first minimum of sound pressure (meters); 2/2——half the wavelength of the sound wave (meters);
6——the phase factor is the relative ratio of the distance from the surface of the specimen to the first minimum of sound pressure to the half wavelength of the sound wave.
Article 3.1.4 When measuring the relative normal acoustic impedance, the room temperature should be observed and recorded. The speed of sound in air should be determined according to the following formula:
c=331.3+0.6t
c-speed of sound in air (m/s);
t-room temperature (℃).
Article 3.1.5 For a given frequency, the half-wavelength of the sound wave should be determined according to the following formula: Engineering 6 Construction Standard Full Text Information System3. When the acoustic center of the detector is at the surface of the specimen, the position reading of the detector should be used as the starting point for measuring the moving distance. Generally, the provisions of Appendix 2 can be followed. The position reading when the acoustic center of the detector moves to the first minimum of sound pressure should be the distance from the surface of the specimen to the first minimum of sound pressure; this distance should be expressed in units of half the wavelength of the sound wave, and the corresponding value is the phase factor, which can be calculated as follows: =2/2
引——the distance from the surface of the specimen to the first minimum of sound pressure (meters); 2/2——half the wavelength of the sound wave (meters);
6——the phase factor, which is the relative ratio of the distance from the surface of the specimen to the first minimum of sound pressure to the half wavelength of the sound wave.
Article 3.1.4 When measuring the relative normal acoustic impedance, the room temperature should be observed and recorded. The speed of sound in air should be determined as follows:
c=331.3+0.6t
c——the speed of sound in air (meters/second);
t——room temperature (℃).
Article 3.1.5 For a given frequency, the half-wavelength of the sound wave should be determined according to the following formula: Engineering 6 Construction Standard Full Text Information System3. When the acoustic center of the detector is at the surface of the specimen, the position reading of the detector should be used as the starting point for measuring the moving distance. Generally, the provisions of Appendix 2 can be followed. The position reading when the acoustic center of the detector moves to the first minimum of sound pressure should be the distance from the surface of the specimen to the first minimum of sound pressure; this distance should be expressed in units of half the wavelength of the sound wave, and the corresponding value is the phase factor, which can be calculated as follows: =2/2
引——the distance from the surface of the specimen to the first minimum of sound pressure (meters); 2/2——half the wavelength of the sound wave (meters);
6——the phase factor, which is the relative ratio of the distance from the surface of the specimen to the first minimum of sound pressure to the half wavelength of the sound wave.
Article 3.1.4 When measuring the relative normal acoustic impedance, the room temperature should be observed and recorded. The speed of sound in air should be determined as follows:
c=331.3+0.6t
c——the speed of sound in air (meters/second);
t——room temperature (℃).
Article 3.1.5 For a given frequency, the half-wavelength of the sound wave should be determined according to the following formula: Engineering 6 Construction Standard Full Text Information System
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