Acoustics--Attenuation of sound during propagation outdoors--Part 1:Calculation of the absorption of sound by the atmosphere
Some standard content:
GB/T 17247.1—2000
This standard is formulated based on ISO9613-1:1993, one of the series of standards of the International Organization for Standardization, "Acoustic outdoor sound propagation attenuation Part 1: Calculation of atmospheric sound absorption". It is equivalent to the international standard in terms of technical content and is compiled in accordance with the provisions of GB/T1.1-1993 "Guidelines for standardization work Unit 1: Rules for drafting and expressing standards Part 1: Basic provisions for standard compilation". ISO9613-2:1993, the second series of standards, "Acoustic outdoor sound propagation attenuation Part 2: General calculation method", was equivalently formulated as the national standard GB/T17247.2-1998 "Acoustic outdoor sound propagation attenuation Part 2: General calculation method" in 1998. The formulation of this standard is conducive to the integration with international standards.
Appendix A, Appendix B, Appendix C, Appendix D, Appendix E and Appendix F of this standard are all suggestive appendices for reference only. This standard was proposed by the Chinese Academy of Sciences. This standard is under the jurisdiction of the National Technical Committee for Acoustics Standardization. This standard was drafted by the Institute of Acoustics, Chinese Academy of Sciences, Peking University. The main drafters of this standard are Dai Genhua and Luan Guidong. This standard is entrusted to the National Technical Committee for Acoustics Standardization Technical Committee for Acoustics for interpretation. 292
GB/T17247.1—2000
ISO Foreword
The International Organization for Standardization (ISO) is a worldwide federation of national standardization committees (ISO member states). The formulation of international standards is usually completed by ISO technical committees. Each member state has the right to participate in a technical committee when it is interested in a standard determined by a technical committee. Governmental and non-governmental organizations associated with ISO may also participate in the work. The International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) maintain close cooperation in all aspects of electrotechnical standardization. Draft international standards adopted by each technical committee shall be circulated to each member state for voting. A draft international standard requires at least 75% of the member states to vote in favor before it can be published as an international standard. The international standard ISO9613-1 was drafted by the ISO/TC43 (Acoustics) Technical Committee SC1 (Noise). ISO9613, under the general title "Acoustics: Outdoor Sound Propagation Attenuation", consists of the following two parts: Part 1: Calculation of Atmospheric Sound Absorption
Part 2: General Calculation Method
Appendices AB, C, D, E and F of this part of ISO9613 are indicative and for reference only. 293
1 Scope
National Standard of the People's Republic of China
Acoustics-Attenuation of sound during propagation outdoors-Part 1: Calculation of the absorption of sound by the atmosphereGB/T _17247: 1. 2000
eqv ISO 9613-1 : 1993
This standard specifies the calculation method for the sound attenuation caused by atmospheric absorption when the sound emitted by an outdoor sound source propagates through the atmosphere under various meteorological conditions.
For pure sound, the atmospheric absorption attenuation is expressed as an attenuation coefficient related to four variables, namely, the acoustic frequency, atmospheric temperature, humidity and air pressure. The calculated attenuation coefficients are listed in the table. The air pressure in the table is 1 standard atmosphere (101.325 kPa), and the ranges of the other three variables are often followed in predicting outdoor sound propagation, namely:
frequency, 50 ~ 10 kHz;
temperature, -20 ~ +50 ℃;
relative humidity, 10% ~ 100%.
For a wider range of variables for special purposes, such as ultrasonic cheeks in scaled model studies, and low air pressure when sound propagates from high to ground, calculation formulas are also proposed.
For broadband sound, fractional octave bandpass filters (such as 1/3 octave bandpass filters) are often used for analysis. This standard stipulates that the method of pure tone with frequency as the center frequency of the band is used to calculate the atmospheric absorption attenuation. In addition, an alternative spectral integration method is described in Appendix D. The sound spectrum may be broadband and have no obvious discrete frequency components, or it may be a synthesis of broadband sound and discrete frequency sound. This standard applies to atmospheres with uniform meteorological conditions and can also be used to determine the correction of sound pressure levels measured to take into account the differences between atmospheric absorption losses under different meteorological conditions. This standard can be extended to inhomogeneous atmospheres, especially atmospheres with meteorological conditions that vary with altitude above the ground, which is discussed in Appendix C.
This standard only considers the main absorption mechanism of the atmosphere without significant fog or pollution. The calculation of sound attenuation caused by other mechanisms other than atmospheric absorption, such as refraction or ground reflection, is described in GB/T17247.2-1998. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard by reference in this standard. When this standard was published, the versions shown were valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T3240-1982 Frequencies commonly used in acoustic measurements GB/T3241-1998 Octave and fractional octave filters GB/T17247.2-1998 Acoustics Attenuation of outdoor sound propagation Part 2: General calculation method
ISO2533:1975 Standard atmosphere
Approved by the State Administration of Quality and Technical Supervision on March 16, 2000 294
Implemented on December 1, 2000
3 Symbols ||t t||Sound frequency, Hz
Center frequency of frequency band, Hz
Molar concentration of water vapor, %
Baseline ambient atmospheric pressure, kPa
Initial sound pressure, Pa
Instantaneous sound pressure, Pa
Baseline sound pressure, 20μPa
Ambient atmospheric pressure, kPa
Sound propagation distance, m
Ambient atmospheric temperature, K
Baseline atmospheric temperature, K
GB/T 17247.1-—2000
Pure tone sound attenuation coefficient caused by atmospheric absorption, dB/m Note 1: For convenience, this standard uses the shorter term "attenuation coefficient" instead of the above full name to refer to α. aL
Attenuation due to atmospheric absorption, dB
Reference atmospheric conditions
4.1 Components
Atmospheric absorption is very sensitive to the composition of the atmosphere, especially to the widely varying concentration of water vapor. The standard molar concentrations or volume percentages of the three normally fixed major components of pure, dry atmosphere at sea level are 0.78084, 0.209476 and 0.000314 respectively (taken from ISO2533). The remaining trace elements of dry atmosphere add up to only 0.00937 and have no significant effect on atmospheric absorption. In calculating atmospheric absorption, this standard assumes that the standard molar concentrations of these three major components of dry atmosphere remain constant over an altitude range of at least 50 km above mean sea level. However, the molar concentration of water vapor, which has a major influence on atmospheric absorption, varies greatly near the surface, varying by more than two orders of magnitude from sea level to an altitude of 10 km. 4.2 Atmospheric pressure and temperature
The reference ambient atmospheric pressure adopted in this standard is the international standard atmospheric pressure at mean sea level, i.e. 101.325 kPa; the reference atmospheric temperature T. is 293.15 K (20°C). The most reliable data supporting this standard are obtained at this temperature. 5 Pure sound attenuation coefficient due to atmospheric absorption
5.1 Basic expression of attenuation
After a pure sound propagates through the atmosphere for a distance s, its instantaneous sound pressure p will decay exponentially from the initial sound pressure pi due to the absorption of the atmosphere, assuming that the attenuation formula of plane sound waves in free space
pt = pexp(- 0. 115 1 α s)
is used.
Note 2: exp(-0. 115 1 αs) represents the exponential formula e-(a.1151an), and the constant 0.115 1 is obtained from 1/[10 lg(e=)]. 5.2 Attenuation of sound pressure level
For a pure tone with a frequency of , propagating from a starting point where the sound pressure is force to a point where the sound pressure is p, the attenuation of the sound pressure level in decibels due to atmospheric absorption is L(f)
aL(f)= 10 lg(p\/p)= αsdB
6 Calculation steps of pure tone attenuation coefficient
6.1 Variables
GB/T 17247.1--2000
The acoustic and atmospheric variables encountered in the calculations are the sound frequency, ambient atmospheric temperature, water vapor mole concentration, and ambient atmospheric pressure. Their symbols and units are given in Chapter 3.
Note 3: For a given sample of moist atmosphere, the water vapor mole concentration is the ratio (expressed as a percentage) of the number of kilomoles (kilogram molecular weight) of water vapor to the sum of the number of dry moles of water vapor in the dry atmosphere. According to Avogadro's law, the water vapor mole concentration is also the ratio of the partial pressure of water vapor to the atmospheric pressure.
Note 4: For meteorological conditions usually observed near mean sea level, the water vapor mole concentration ranges from 0.2% to 2%, but drops to much less than 0.01% at altitudes above 10 km.
6.2 Formulas
As described in Appendix A, the atmospheric absorption attenuation is related to two relaxation frequencies: the oxygen relaxation frequency fo and the nitrogen relaxation frequency fn. fro and fn are expressed in Hz and are calculated by the following formula:
fo =2[24 + 4.04 × 10 h %]
JiN -TT
+,[]\×[9 + 280 hexp(- 4.170[()-\ 1]].
The atmospheric absorption attenuation coefficient α is expressed in dB/m and is calculated by the formula [1.84 ×10-(会)()\]+()
× (0.012 75[exp (= 22 391)8.686f
×[fo +()' + 0.106 8[exp(=3 52.9]][n + ()])T
Calculation.
In equations (3) to (5), pr = 101.325 kPa, T. = 293.15 K. (3)
(4)
(5)
Equations (3) to (5) are combined to form a formula that is suitable for calculation and concise in form. It gives the contribution of various physical mechanisms, see Appendix A. 6.3 Calculation of attenuation coefficient
Equations (3), (4) and (5) are the calculations of the selected variable values. All the formulas necessary for the attenuation coefficients of pure sounds due to atmospheric absorption. Although the values of atmospheric temperature and atmospheric pressure may not be given in the units of measurement given in Chapter 3, conversion factors for converting them to Kelvin and kilopascals, respectively, are readily available. On the other hand, humidity data are rarely given in the form of molar concentrations of water vapor. Appendix B provides information for converting humidity expressed in relative humidity, dew point temperature, and other units of measurement to the corresponding molar concentrations. For actual non-uniform atmospheres, the uniform atmosphere assumed in the formula in 6.2 can be used to approximate them, and the method will be discussed in Appendix C. 6.4 Attenuation coefficient table
For given T, h, and f at standard atmospheric pressure (101.325 kPa), Table 1 lists the pure sound attenuation coefficients due to atmospheric absorption, which are calculated from equations (3), (4), and (5). For ease of use in outdoor sound propagation over a propagation distance of several kilometers, dB/km is used as the unit in the table. The values in the table are expressed in exponential form with a base of 10 in order to maintain accuracy at low frequencies. The user of Table 1 should not interpolate between the variables or extrapolate outside the range of the variables, but should use equations (3) to (5) to calculate the specific pure tone attenuation coefficient under the required conditions.
Note 5: For convenience, the frequencies in Table 1 are the band frequencies of 1/3 octave bandpass filters (see GB/T3240-1982 and GB/T3241-1998), but the attenuation coefficients are calculated for the exact center frequency of the band, f (Hz). The general expression for f is fm = 1 000(1036/10)*
where 1 000 Hz is the exact reference frequency; b is a rational fraction, which is the bandwidth identifier of a certain fractional octave bandpass filter. For example, b=1/3 represents a 1/3 octave bandpass filter, and so on. For the purposes of Table 1, the index is an integer ranging from -13 to +10, corresponding to the common frequencies from 50 Hz to 10 kHz. For the ultrasonic frequency range from 10 kHz to 1 MHz, the values of in equation (6) range from +10 to +30 when calculating the exact 1/3 octave band center frequency. Note 6: The relative humidity in the first row of Table 1 is the relative value of the saturated vapor pressure above the liquid water surface at each temperature. The saturated vapor pressure is calculated by the formula used in the preparation of international meteorological reports [z, see Appendix B. 296
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