This part of GB/T18696 specifies the method for determining the sound absorption coefficient, reflection factor and surface acoustic impedance or surface acoustic admittance of sound-absorbing materials and structures at normal incidence. These data are determined based on the standing wave diagram generated by the superposition of the incident sinusoidal plane wave and the plane wave reflected from the test piece under normal incidence conditions in the impedance tube. Since only a small amount of sound-absorbing material is required as the test piece, it is particularly suitable for parameter research and design of sound-absorbing materials. GB/T 18696.1-2004 Measurement of sound absorption coefficient and acoustic impedance in acoustic impedance tubes Part 1: Standing wave ratio method GB/T18696.1-2004 standard download decompression password: www.bzxz.net
This part of GB/T18696 specifies the method for determining the sound absorption coefficient, reflection factor and surface acoustic impedance or surface acoustic admittance of sound-absorbing materials and structures at normal incidence. These data are determined based on the standing wave diagram generated by the superposition of the incident sinusoidal plane wave and the plane wave reflected from the test piece under normal incidence conditions in the impedance tube. Since only a small amount of sound-absorbing material is needed as a test piece, it is particularly suitable for parameter research and design of sound-absorbing materials.

ICS 17. 140. 01
National Standard of the People's Republic of China
GB/T 18696.1--2004
Acoustics--Determination of sound absorption coefficientand impedance in impedance tubes--Part 1 : Method using standing wave ratio(ISO 10534-1:1996,MOD)
Promulgated on 2004-05-13
Implementation by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on 2004-12-01
GB/T 18696 "Determination of sound absorption coefficient and acoustic impedance in impedance tubes" is divided into two parts: Part 1: Standing wave ratio method; Part 2: Transfer function method.
GB/T 18696. 1-2004
This part is Part 1 of GB/T 18696, and the international standard ISO 10534-1: 1996 Acoustics—Determination of sound absorption efficiency and impedance in impedance tubes-- Part 1, Method using standing wave ratio is adopted.
During the process of revision and adoption, several necessary modifications were made to the ISO original text: -\- According to the definition, in the main text of the standard, "acoustic impedance" was changed to "acoustic impedance". However, in order to correspond with ISO, the name of the standard was not changed. The original 3.5 "impedance in the reference plane" and 3.8 "surface impedance" were deleted because these two terms never appeared again:
Appendix A.2 of the first part "Measurement of sound velocity, wavelength and characteristic impedance" adopts the method of Article 7.2 of IS010534-2:1998 text (i.e. Article 8.2 of GB/T18696.2-2002); - The constant 250 in Formula 29) is obtained from 0.75c, and it is better to use 0.75c; - The original Article 6.5 involves sound level meter. The new and old versions of the sound level meter standard are in the replacement stage. The provisions for the 0-level sound level meter are no longer in use, and this article only mentions the 0-level sound level meter incidentally, so it is deleted. An introduction is added.
Appendix A, Appendix B and Appendix C of this part are normative appendices. Appendix D of this part is an informative appendix.
This part is proposed by the Chinese Academy of Sciences.
This part is under the jurisdiction of the National Technical Committee for Acoustics Standardization (CSBTS/TC.17). The main drafting units of this part are the Institute of Acoustics of the Chinese Academy of Sciences and the Institute of Acoustics of Nanjing University. The main drafters of this part are Li Xiaodong, Dai Genhua, Mao Dongxing and Xu Xin. This part is entrusted to the Acoustics Foundation Subcommittee of the National Technical Committee for Acoustics Standardization for interpretation. GB/T 18696.1—2004
The standing wave ratio method is used to determine the sound absorption coefficient, reflection factor and surface acoustic impedance or surface acoustic admittance of sound-absorbing materials and structures under normal incidence in an impedance tube. Since the instruments used in this part can all be analog instruments, and only a small amount of sound-absorbing material is needed as test pieces, it is adopted by merchants and testing units.
This part and GB/T18696.2-2002 form the "Measurement of sound absorption coefficient and acoustic impedance in impedance tube" series of standards. The methods specified in this series of standards are significantly different from the reverberation case sound absorption measurement method specified in ISO354. The impedance tube method is limited to the test of normal incidence parameters, and the test piece area should be as large as the cross-section of the impedance tube. The reverberation chamber method measures the random incidence absorption coefficient, which can be used to test materials with different structures in the lateral and normal directions, and requires a larger area of ​​the test piece. For materials with local reactions, the random incidence sound absorption coefficient can be converted from the measurement results of the impedance tube method. 1 Scope
GB/T 18696. 1---2004
Determination of sound absorption coefficient and acoustic impedance in acoustic impedance tubes Part 1: Standing wave ratio method
1.1 This part of GB/T 18696 specifies the method for determining the sound absorption coefficient, reflection factor and surface acoustic impedance or surface acoustic admittance of sound absorbing materials and structures under normal incidence. These data are determined based on the standing wave diagram produced by the superposition of the incident sinusoidal plane wave and the plane wave reflected from the test piece under normal incidence in the impedance tube. Since only a small amount of sound absorbing material is required as the test piece, it is particularly suitable for parameter research and design of sound absorbing materials.
1.2 The method in this part has some important differences compared with the method for measuring sound absorption coefficient in a reverberation chamber (see ISO 354). The impedance tube method can be used to determine both the sound absorption coefficient and the acoustic impedance or acoustic admittance. This method stipulates that the sound wave is incident normally on the surface of the test piece. The reverberation chamber method (under ideal conditions) determines the random incident sound absorption coefficient. The impedance tube method is based on the existence of a plane wave generated by an incident sound. Under these conditions, it gives accurate measurements (except for measurement errors and installation errors). The determination of the sound absorption coefficient in the reverberation chamber is based on some simplifying and approximate assumptions about the sound field and the size of the test piece. Therefore, sound absorption coefficients greater than 1 are sometimes obtained. The impedance tube method requires the test piece to be as large as the cross section of the impedance tube. The reverberation chamber method requires relatively large test pieces. At the same time, the reverberation tube method can also be used for test pieces with significant non-uniform structures in the lateral direction and/or perpendicular to the surface. Measurements made in the impedance tube on such non-uniform test pieces must be interpreted with caution (see 9.1).
For the calculation method of converting the test results of the impedance tube method (normal incidence) to random incident conditions, see the Appendix). 1.3 Because laboratories are now equipped with computers, this part of ISO 14001 uses numerical calculation methods instead of table search methods. Some of the quantities in the formulas of this part are complex numbers. The quantity of the diagonal function is expressed in degrees. 2 Normative references
The clauses in the following documents become clauses of this part through the reference of this part. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this part. However, parties to an agreement based on this part are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version applies to this part. GB/T 3240-1982 Common frequencies in acoustic measurements (ncqIS) 266: 1975) IS0351 Measurement of sound absorption in acoustic mixing chambers 3 Definitions and symbols
This part uses the following definitions and symbols
Normal incidence sound absorption coefficient (α) normal incidence (sound) absorption coefficient The ratio of the sound power of a normally incident plane wave entering the surface of the test piece to the incident sound power. 3.2
Normal incidence sound pressure reflection factor (r) normalincidence (sound) pressurereflectionfactor Reference plane [The complex ratio of the reflected wave amplitude of a normal incident plane wave to the incident wave amplitude. 3.3
Reference plane reference plane is used to measure the pressure reflection factor or surface acoustic impedance 7. Or surface acoustic admittance G, the cross section of the tube. If the surface of the test piece is a plane, it is usually taken as the reference plane. The base surface is assumed to be at = 0, see Figure 1, 3. 4
acoustic roughness impedance (Z,(r)) specific acoustic impedance The ratio of the sound pressure p(±) at a point in the sound field to the particle velocity \) (pointing to the surface of the specimen), 3.5
surface normal acoustic impedance (Z,) normal surface specific acuustic impedance The ratio of the complex sound pressure (0) of a sound wave of a certain frequency on the reference surface to the normal component of the complex sound particle velocity 0). 3.6
surface normal acoustic admittance (G,) normalsurfacespecificacousticmittance The ratio of the normal component of the complex sound particle velocity 0) of a sound wave of a certain frequency on the reference surface to the complex sound pressure 0). 3.7
(Acoustic) characteristic impedance (Z,）(acoustic)characleristic impedance The ratio of the effective sound pressure of a plane free-traveling wave at a certain point in the medium to the effective sound particle velocity passing through that point, mainly Z
Where:
P—medium (air) density, kg/m
c,---sound speed in medium (air), m/s:
Specific acoustic impedance (z)
normalized specific acoustic impedance The ratio of the surface normal acoustic impedance Z to the (medium) acoustic characteristic impedance B: 1 = 2./2
Specific acoustic admittance (g)normalized specific acoustic admittance The product of the surface normal acoustic admittance G and the (medium) acoustic] characteristic impedance Z: gG,· Z
Standing wave ratio (s) ratio
On the standing wave diagram without attenuation, the ratio of the amplitude force m of the maximum sound pressure value to the amplitude force of the minimum sound pressure value: s=|Pmx 1/pmin
(Taking into account the attenuation) standing wave ratio (s.) standing wave ratio (with attennation) On the standing wave diagram with attenuation, the ratio of the sound pressure amplitude force (x,) at the nth sound pressure maximum value to the sound pressure amplitude i(Tma,n) at the nth sound pressure minimum value (see Figure 1): wwW.bzxz.Net
s, =/ p(rm.) I /I p(rn.) |
Obviously, 1 takes different values ​​at different times.
(Free field) wave number (k)
is defined as:
where:
sound wave angular velocity;
at --- wave frequency;
-sound speed in air.
(free-field)wavenumber
ke — w/ce - 2-element f/ce
The wavenumber of the node is a complex number, so it can be written as: In the formula,
k,= .
——the real part of k (2/,), that is, the phase constant; n——the wavelength of the sound wave; the imaginary part of
k.-.., that is, the attenuation constant, the unit is Np/m. Note: In the following, if " " is added in the upper right corner of the variable pier, it means taking its real part, and if *\\ is added, it means taking its imaginary part. 3.13
Reflection (cycles) phase angle phase of reflection (factor) complex reflection factor r is expressed by its amplitude 1rl and phase angle: r =r'+ir\=[re\ =rl.cose+ising) where:
r'-rb .cosd
r\-{rlsins
$arc tan(r\/r')
working frequency range (f) workingfrequencyrange The range of sound wave frequencies that are effectively measured in the impedance tube: fi
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