This standard specifies a method for measuring the sound intensity component perpendicular to the measurement surface, which should surround the noise source being measured. This method can be used for any sound source with a fixed measurement surface. This method can be used in a test environment for on-site or special purposes. GB/T 16404.2-1999 Acoustics Determination of sound power level of noise source by sound intensity method Part 2: Scanning measurement GB/T16404.2-1999 Standard download decompression password: www.bzxz.net
This standard specifies a method for measuring the sound intensity component perpendicular to the measurement surface, which should surround the noise source being measured. This method can be used for any sound source with a fixed measurement surface. This method can be used in a test environment for on-site or special purposes.

GB/T16404.2—1999
This standard is equivalent to the international standard ISO9614-2:1996 "Acoustic sound intensity method for the determination of sound power level of noise sources".
According to the specific conditions of my country, this standard has made appropriate modifications to some of the provisions of the international standard. Appendix A and Appendix B of this standard are standard appendices. Appendix C, Appendix D, Appendix E and Appendix F of this standard are all indicative appendices. This standard is proposed and coordinated by the National Technical Committee for the Promotion of Acoustic Standards. The drafting unit of this standard: Institute of Acoustics, Chinese Academy of Sciences. The main drafters of this standard: Cheng Mingkun and Li Yimin. 244
Part 2: Scanning
GB/T16404.2—1999
ISO Foreword
The International Organization for Standardization (ISO) is a worldwide joint organization composed of national standardization committees (ISO member states). The formulation of international standards is usually completed by ISO technical committees. Each member country has the right to participate in a technical committee when it is interested in a standard determined by a technical committee. International organizations, both governmental and non-governmental, that are 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 technical committees shall be distributed to member countries for voting. Draft international standards require at least 75% of the votes of member countries to be published as international standards. International standard ISO9614-2 was drafted by ISO/TC43 Acoustics Technical Committee SC1 Noise Subcommittee. The general title of ISO9614 is "Acoustics - Part 1: Measurements at discrete points, Part 2: Scanning measurements; Determination of sound power levels of noise sources by sound intensity method", which consists of the following three parts: Part 3 Precision method for scanning measurements. Appendices A and B are standard appendices, and Appendices C, D, E and F are indicative and for reference only. 245
GB/T16404.2—1999
The sound power value radiated by a sound source is equal to the integral of the scalar product of the sound intensity vector and the corresponding surface element vector on any surface surrounding the sound source over the entire surface. At present, the national standards for the measurement of sound power level of noise sources, such as GB/T3767, GB/T3768, GB/T6881, GB/T6882, etc., all use sound pressure level as the basic quantity for measurement. The relationship between the sound intensity level and the sound pressure level at any point depends on the characteristics of the sound source, the characteristics of the measurement environment, and the arrangement of the measurement point relative to the sound source. Therefore, when formulating the measurement method, the above national standards must specify the characteristics of the sound source, the characteristics of the test environment, and the restrictions on use, in order to ensure that the sound power level measurement meets the specified uncertainty. However, the methods specified in the above national standards are sometimes not applicable. For example: a) If high-precision measurement is required, expensive special facilities (such as reverberation chambers, anechoic chambers, and semi-anechoic chambers) are required, and large equipment often cannot be installed and operated in such facilities. b) There may be non-measured sound sources with high noise. The purpose of this standard is to specify a method for measuring the sound power level of a sound source within a specified uncertainty range without as many restrictions as the above national standards. This standard method is mainly used for on-site sound power level measurement. In fact, it is a function of the environment. Therefore, in some cases, the sound power level of the same sound source measured under other conditions will be different. It is recommended that testers using this standard should receive appropriate training and have certain experience. This standard is a supplement to GB/T16404 and GB/T3767, GB/T3768, GB/T6881, GB/T6882 standards. It differs from GB/T3767, GB/T3768, GB/T6881, GB/T6882 standards as follows: a) The basic quantity measured is sound intensity, and sound pressure needs to be measured at the same time. b) The uncertainty of the sound power level measured by the method specified in this standard is graded according to the auxiliary tests specified in the standard and the corresponding calculation results.
c) Due to the limitations of the current sound intensity measurement equipment that complies with the IEC1043 standard, the 1/3 octave measurement frequency range is limited to 50Hz to 6.3kHz. The A-weighted value of the limited band is determined by the values ​​of each octave band or 1/3 octave band rather than by direct measurement of the A-weighting.
The integral of the scalar product of the sound intensity vector and the corresponding surface element vector over the entire surface surrounding the sound source gives the sum of the sound power directly radiated into the air by all sound sources within the measurement surface, which does not include the radiated sound of sound sources outside the measurement surface. In fact, this is true as long as the measured source and other sound sources outside the measurement surface are steady in time. When there are other sound sources outside the measurement surface, any system with sound absorption characteristics within the surface will absorb part of the energy incident on it. The total sound power absorbed within the measurement surface is negative, which will cause errors in the sound power measurement. Therefore, in order to minimize such errors, any sound absorbing materials in the measurement surface that are not related to the sound source must be removed. The method is based on sampling the sound intensity field perpendicular to the measurement surface by continuously moving a sound intensity probe along one or more prescribed routes. The sampling error is a function of the spatial variation of the normal sound intensity component on the measurement surface, which depends on the directivity of the sound source, the selected sampling surface, the scanning method and speed of the probe, and the distance of the sound source outside the measurement surface. At a measurement point, the measurement accuracy of the normal component of the sound intensity is closely related to the difference between the local sound pressure level and the local normal sound intensity level. When the angle between the sound intensity vector of a measurement point and the normal direction of the measurement surface is close to 90°, the difference will become very large. In other words, the local sound pressure level mainly comes from the sound source outside the measurement surface, and has almost nothing to do with the pure sound energy flow of the sound source being measured, just like the reverberation field in a hood, or the sound field will be strongly resistive due to the presence of near fields and/or standing waves. Although the external sound energy flow entering the measuring surface through part of the measuring surface will be offset by the sound energy flow flowing out through the remaining measuring surface in principle, it will still have an adverse effect on the accuracy of sound power measurement. This situation is mainly caused by the presence of a strong external sound source close to the measuring surface.
1 Range circle
National Standard of the People's Republic of China
Acoustics-Determination of sound power levelsof noise sources using sound intensity-Part 2:Measurement by scanning
Acoustics-Determination of sound power levelsof noise sources using sound intensity-Part 2:Measurement by scanningGB/T16404.2—1999
eqvISo9614-2.1996
1.1 This standard specifies a method for measuring the sound intensity component perpendicular to the measuring surface. The measuring surface should surround the noise source to be measured. The measuring surface is divided into a number of adjacent surface elements. The surface integral of the sound intensity perpendicular to the measuring surface is approximated by scanning the sound intensity probe on each surface element along a continuous path covering the surface element to a certain extent. The measuring instrument measures the average normal sound intensity component and the mean square sound pressure during each sweep. The sweep may be operated manually or by a mechanical system. The weighted sound power level of a limited frequency band is calculated from the measured octave band or one-third octave band values. This method can be used for any sound source with a defined fixed measurement surface. On this measurement surface, the noise generated by the measured sound source and other significant external sound sources, as defined in 3.13, should be steady in time. The measurement surface is selected according to the size and shape of the sound source. This method can be used in field or special purpose test environments.
This standard specifies auxiliary methods for determining the accuracy level, which are listed in Appendix B. If the accuracy of the results obtained by this method does not meet the requirements of this standard, the test procedure should be modified in the specified manner. This standard does not apply to any cheek strap where the measured sound power is negative. 1.2 This standard can be used for sound sources in any environment where changes in the environment over time do not cause the accuracy of the sound intensity measurement to degrade to an unacceptable level, or where the sound intensity measuring probe does not encounter unacceptably high or unstable airflow (see 5.2.2, 5.3 and 5.4).
This standard is not applicable to situations where the test conditions are so severe that the requirements of this standard cannot be met, such as when the external noise level may exceed the dynamic performance of the measuring instrument or vary greatly during the test. NOTE 1 In such cases, other methods, such as the method of determining the sound power level by surface vibration level specified in GB/T 16539, may be more appropriate. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard by reference in this standard. At the time of publication of this standard, the versions shown are valid. All standards are subject to revision, and parties using this standard should investigate the possibility of using the latest version of the following standards. GB/T14573.1~14573.4—1993 Acoustics Statistical methods for determining and verifying specified noise radiation values ​​for machinery and equipment (eqv ISO 7574-1~7574-4:1985) GB/T 15173—1994 Sound calibrator (eqv IEC 1014:1989) ISO 12001:1996 Acoustics—Noise emitted by mechanical equipment—Drafting and expressing a noise test specification IEC 1043:1993 Electroacoustics—Sound intensity measuring instrument—Measurement using a sound pressure microphone Approved by the State Administration of Quality and Technical Supervision on March 8, 1999 and implemented on September 1, 1999
3 Definitions
This standard adopts the following definitions
3.1 Sound pressure level sound pressure level GB/T 16404. 2 --- 1999
3.1.1 Sound pressure level (L,) sound pressure level The ratio of the sound pressure to the reference sound pressure is 20 times the logarithm to the base 10, the reference sound pressure is 20μPa, and the sound pressure level is expressed in decibels, symbol dB. 3.1.2 Segment-average sound pressure level (L,) Segment-average sound pressure level The ratio of the spatial average sound pressure on segment i to the reference sound pressure is 20 times the logarithm to the base 10. Expressed in decibels, symbol dB. 3.2 Instantaneous sound intensity (I(t)) instantaneous sound intensity The sound energy per unit time at a point in the sound field that passes through a unit area perpendicular to the direction of the particle velocity. The instantaneous sound intensity at a point in the sound field is a vector, which is equal to the product of the instantaneous sound pressure at that point and the instantaneous particle velocity. Where: I(t)—instantaneous sound intensity, W/m;
p(t)—instantaneous sound pressure, Pa;
u(t)—instantaneous particle velocity, m/s.
3.3 Sound intensity (1) sound intensityI(t) = p(t) · u(t)
The average value of the instantaneous sound intensity I(t) in a steady-state sound field within a certain time T: I
Where: T
-integration time.
I(t)dt
1 is the amplitude of the vector I, which can be positive or negative. The sign indicates the directionality, and the positive sign indicates the positive direction of the energy flow. 1I| is the absolute value of the vector amplitude.
3.4 ​​Normal sound intensity (I) normal sound intensity is the sound intensity component perpendicular to the measurement plane defined by the unit normal vector n. I,-I·n
The unit normal vector pointing outside the measurement plane. In the formula: n-
3.5 Normal sound intensity level (L,) normal sound intensity level The logarithm of the absolute value of the normal sound intensity [I,I] is expressed as follows: L, 1olg[lI,[/I]
· (4)
The unit is decibel, where I. is the reference sound intensity (-10-12W/m2). Unless used in the calculation of 3r, when I is negative, the sound intensity level is expressed as () × × dB (see 3.11). 3.6 Sound power sound power
3.6.1 Local sound power (W.) The partial sound power is the time-averaged sound energy flow rate of a surface element on the measurement surface, which is expressed as follows: W. =S.
Where: "Im") - the average normal sound intensity amplitude measured on the i-th element of the measurement surface S, - the area of ​​the element i.
Similarly, IW.I is the absolute value of W;.
3.6.2 Sound power (W) sound power The total sound power generated by a sound source measured by the method of this standard. Given by equations (6) and (7): w
(5)
Where: N - the total number of elements on the measurement surface.
GB/T16404.2—1999
3.6.3 Local sound power level (Lw.) partial sound powerlevel W.
The logarithm of the sound power of the i-th element of the measurement surface, which is given by equation (8): Lw.= iolgEIW.l/WJ
Where: W. Reference sound power (=10-12 W). The unit is expressed in decibels. When W is negative, the local sound power level is expressed as (-) × × dB. 3.6.4 Sound power level (Lw) sound power level The logarithm of the sound power of a sound source measured according to the method of this standard. It is given by formula (9): Lw - 10lg[IW|/W.]bzxz.net
The sound power level is expressed in decibels. When W is a negative value, the sound power level is expressed as (-) × X dB. It is only used for recording. 3.7 Measurement surface measurement surface (7)
The imaginary surface on which the sound intensity measurement is performed, which either completely surrounds the noise source being measured, or surrounds the noise source being measured together with an acoustically rigid continuous surface. In the case where the imaginary surface is penetrated by an object with a rigid surface, the measurement surface is bounded by the intersection of the object and the imaginary surface. 3.8 segment
A group of smaller surfaces divided by the measurement surface. 3.9 extraneous intensity The sound intensity component produced by a sound source outside the measurement surface. 3.10 probe
The component of the sound intensity measurement system with a sensor. 3.11 pressure-residual intensity index (opr,) The difference between the sound pressure level L, displayed when the sound intensity probe is placed in the sound field and pointed at a direction where the sound intensity is equal to zero, and the sound intensity level L, expressed in decibels.
The detailed method for determining Spr. is given in IEC 1043. opl. = (Lp- L)
3.12 dynamic capability index (La) It is given by equation (11):
La= opl.- K
Expressed in dB. The value of K is selected according to the accuracy requirements (see Table 1). Table 1 Bias factor K
Accuracy level
Engineering (level 2)
Jian Jia (level 3)
3.13 Stationary signal Bias factor, dB
A signal is stationary if the time-averaged characteristic of a single measurement on an element of the measurement surface is equal to the time-averaged characteristic of the same element when the measurement is made over all elements of the measurement surface. NOTE 2 According to this definition, a periodic signal is stationary if the measurement time is extended by at least 10 periods on each element. 3.14 Field indicators (FprF+/-) See Appendix A.
3.15 Scan scan
The continuous movement of the sound intensity probe along a specified distance on an element of the measurement surface. 249
S Scan-line density scan-line density
The reciprocal of the average spacing between adjacent scan lines.
4 General requirements
4.1 Size of noise source
GB/T 16404.2-1999
The size of noise source is not limited, and the range of the measured sound source depends on the selection of the measurement surface. 4.2 Noise characteristics of sound source radiation
The sound source signal should be steady in time. If a sound source operates according to a working cycle, during which there are obvious continuous stable operation time periods, the sound power level of each obvious time period should be measured and reported. Measurements should be avoided during the operation of possible non-steady external noise sources (see Appendix B Table B1). 4.3 Uncertainty of measurement
The sound power value of the noise source obtained by a single measurement using this standard is likely to be different from the true value, and its actual difference cannot be estimated. However, the values ​​obtained by multiple measurements using this method are usually distributed around the true value, so the confidence level that the measured value falls within a certain range of the true value can be expressed. From a statistical point of view, for a sound source in a given location, the values ​​obtained by repeated measurements under the same rated conditions using the same test method and test instrument constitute a set of statistical data describing the repeatability of the measurement. The values ​​obtained by testing a given sound source in different locations and using different instruments according to this standard are a set of data describing the reproducibility of the measurement. Reproducibility is affected by the environmental conditions of the test location and the test technology. The standard deviation does not take into account the changes in the sound power output caused by changes in the operating conditions of the sound source (i.e. speed, grid voltage). For the methods specified in this standard, the maximum standard deviation of reproducibility is listed in Table 2. Note 3: If the operator is fixed and similar facilities and instruments are used, the standard deviation of the sound power measurement results for a given location and a given sound source may be smaller than that indicated in Table 2. Note 4: For a series of sound sources of similar size and similar sound power spectra, when they are operated in similar environmental conditions and measured according to a specified test rule, the standard deviation of their reproducibility may be smaller than that indicated in Table 2. GB/T 14573.4 gives statistical methods for batch machine characteristics. NOTE 5: This standard method and the standard deviations stated in Table 2 can be used for the measurement of a given sound source. The sound power level characterization of a group of sound sources of the same series or model involves the use of random sampling techniques within a specified interval of measurement, the results of which are expressed as statistical upper limits. When these techniques are used, the total standard deviation is either known or estimated. The total standard deviation includes the manufacturing standard deviation, as defined in GB/T 14573.1, which is a measure of the variation in sound power output between individual machines in a batch of machines. Table 2 defines two accuracy levels, the uncertainties in which take into account not only the maximum measurement deviation but also the random errors associated with the measurement method. The maximum measurement deviation is limited by the choice of the deviation factor K corresponding to the required accuracy level (see Table 1). They do not take into account the tolerances of the performance of the standard instrument specified in IEC 1043. Also, they do not take into account the effects of variations in the installation, support and operating conditions of the sound source.
NOTE 6: There are not enough data below 50 Hz to serve as a basis for uncertainty. The A-weighted data of this standard usually covers the frequency band from 63 Hz to 4 kHz in the octave band and from 50 Hz to 6.3 kHz in the 1/3 octave band. If there are no obviously high sound levels in the 31.5-40 Hz and 8-10 kHz bands, then the A-weighted values ​​calculated based on the sound levels in the 63-4000 Hz octave band and the 50-6300 Hz 1/3 octave band are correct. The method to determine whether the sound levels in the 31.5-40 Hz and 8-10 kHz bands are too high is to A-weight these bands. If the sound levels are not less than 6 dB below the calculated total A-weighted sound level, they are obviously high sound levels. If the A-weighted measurements and the corresponding sound power level determinations are made within a narrower frequency range, then the range should be explained in accordance with 10.6b). The uncertainty of the sound power level of a noise source is related to the sound field characteristics of the sound source, the characteristics of the external sound field, the sound absorption of the measured sound source, the way of sampling the sound intensity, and the measurement method used. For this reason, this standard specifies the initial steps for estimating the indicated values ​​of the sound field characteristics within the selected measurement surface area (see Appendix A). Using this preliminary test result, select the appropriate measurement process according to Table B1. 250
1/1 octave band center frequency
63~125
250~500
1 000~4 000
A weighting1)
GB/T 16404.2—1999
Table 2 Uncertainties in sound power level determination
1/3 octave band center frequency
50~160
200~315
400~5000
Engineering (Level 2)
Standard deviation,
Simple (Level 3)
Note: If the total A-weighted sound power in the 1/3 octave band outside the range 400~5000 Hz exceeds the total A-weighted sound power within this range, the uncertainty of the A-weighted estimate mentioned here cannot be used, and the uncertainty of the individual band should be used instead. 1) 63~4 000 Hz or 50~~6 300 Hz. 2) The true value of the A-weighted sound power level has a 95% confidence level within ±3 dB of the measured value. If only A-weighted measurements are required, any single A-weighted band level that is 10 dB or more lower than the highest A-weighted band level can be ignored. If the sum of the A-weighted sound power levels of more than one band is 10 dB or more lower than the highest A-weighted band sound power level, they can all be ignored. If only an A-weighted total sound power level is required, the uncertainty in the measurement of any band sound power level that is 10 dB or more lower than the total weighted sound power level has no effect on the measurement result. 5 Acoustic environment
5.1 Test environment requirements
The test environment shall ensure that sound intensity measurements using measuring instruments that comply with IEC1043 are valid. In addition, it shall meet the requirements specified in 5.2 to 5.5.
5.2 External sound intensity
5.2.1 External sound intensity level
The external sound intensity level should be as small as possible to ensure that the accuracy of the measurement is not reduced to an unacceptable level (see formula B2 in Appendix B). Attempts should be made to reduce the indicated value Fpr (A2.1 of Appendix A) to less than 10 dB by selecting an appropriate measurement surface and controlling the external sound intensity. NOTE 7: If a considerable part of the sound source being measured is sound-absorbing material, high levels of external sound intensity will lead to an underestimation of the sound power. Appendix D gives a method for estimating the error caused by external sound intensity in the special case of switching off the sound source being measured. 5.2.2 Variability of external sound intensity
Appropriate measures should be taken before the test to minimize the variation of external sound intensity during the measurement (e.g., deactivate the automatic switching function of external noise sources that are not important for the operation of the sound source; and select an appropriate measurement time). 5.3 Wind and airflow
Appendix C describes the adverse effects of airflow and turbulence on sound intensity measurements. When there is airflow on the measurement surface, the probe should be shielded. When the wind and airflow near the sound intensity probe exceed the limits specified by the manufacturer to ensure that the measurement system can be tested well, the measurement should be stopped. Unless the maximum time-averaged wind speed or airflow speed at all positions on the measurement surface is less than 4 m/s, the following steps should be taken to check the test environment before the sound power measurement: Select a measurement surface element with the greatest wind or airflow instability. According to the selected scanning process (8.1), only two consecutive scans can be used to determine the surface element average normal sound intensity level L1 to verify whether criterion 3 of B1.3 is met. In those frequency bands where criterion 3 is not met, the sound power of the sound source cannot be determined according to this standard. It is not allowed to repeat the process of 8.1 continuously to achieve the satisfaction of criterion 3.
5.4 Temperature
If the temperature of the sound source is significantly different from that of the ambient air, the probe should be at least 20 mm away from the sound source. NOTE 8: The temperature gradient along the axis of the probe will produce a time-dependent differential change in the response of the two microphones, which will cause a deviation in the sound intensity estimation. 251
5.5 Site conditions
GB/T 16404. 2—1999
During the test, the test site conditions should remain as constant as possible; especially for sound sources with pure tone characteristics. If changes in the site conditions during the test are unavoidable, they should be recorded in the report. It should be ensured that during the measurement, at any position, the operator does not stand on or near the probe axis. If possible, external objects should be removed from the vicinity of the sound source being measured. 5.6 Atmospheric conditions
Atmospheric pressure and temperature affect air density and sound speed. The influence of these quantities on the calibration of the instrument should be determined and appropriate corrections should be made for the given sound intensity (see IEC1043).
6 Measuring instruments
6.1 Overview
Sound intensity measuring instruments and probes that meet the requirements of IEC1043 should be used. Engineering-level measurements should use Class I instruments, and simple-level measurements should use Class I or Class II instruments. When commissioning the instrument according to IEC1043, it is necessary to take into account the ambient atmospheric pressure and temperature and record the residual sound intensity index of the sound pressure for each measuring frequency band of the measuring instrument as defined in IEC1043. 6.2 Calibration and field verification
The instrument and probe shall comply with the provisions of IEC1043. For this purpose, a laboratory calibration shall be carried out at least once a year in accordance with the relevant standards. If a sound intensity calibrator is used before each sound power measurement, a laboratory calibration shall be carried out at least once every two years. The calibration results shall be reported in accordance with 10.5. Before each series of measurements, the instrument shall be checked for proper operation. The field inspection method specified by the manufacturer shall be used. If there is no provision for field inspection, the following steps can be used to check for abnormal phenomena in the measuring system that may have occurred during transportation or other reasons. 6.2.1 Sound pressure level
The sound pressure sensitivity of each microphone of the sound intensity probe shall be determined using a calibrator of class 0 or 1, or class 0L or 1L in accordance with GB/T15173.
6.2.2 Sound intensity level
Place the sound intensity probe at a place with high sound intensity on the measurement surface, with the axis of the probe pointing perpendicular to the measurement surface, and measure the normal sound intensity level of all specified frequency bands. Rotate the sound intensity probe 180° (i.e. turn the probe upside down) and keep its acoustic center at the same position as the first measurement, and then measure the sound intensity. It is best to fix the sound intensity probe on a bracket so that the position remains unchanged when the probe is rotated. The signs of the maximum sound intensity levels Lr of the 1/1 octave band or 1/3 octave band measured twice should be opposite and the difference should be less than 1.5 dB for all frequency bands. The measuring instrument is then considered acceptable.
7 Installation and operation of sound sources
7.1 Overview
The sound source should be installed in the manner of normal use or in the manner specified in the test specifications for special types of machinery and equipment. It should be ensured that the sound source under test/external sound source/sound source that may change in the test environment can be identified. 7.2 The working conditions of the sound source to be measured shall be the working conditions specified in the corresponding noise test specifications. If there is no such specification, the following corresponding conditions shall be selected: a) rated load conditions; b) full load conditions; c) no load conditions (no load); d) conditions corresponding to the loudest sound during normal use; e) conditions with carefully specified simulated loads; f) conditions with characteristic duty cycle operation. 8 Measurement of sound intensity level
Figure B1 describes the entire measurement process.
8.1 Scanning
GB/T16404.2—1999
Scanning is achieved manually or by a mechanical system. The external sound intensity level produced by the mechanical scanning system measured by the probe shall be at least 20 dB lower than the sound intensity level on the measurement surface.
On each element of the selected measurement surface, the sound intensity probe is continuously moved (scanned) along the specified route. Let the measuring instrument take the total duration T of scanning on a measuring surface element to make a time average of the sound intensity and sound pressure. When performing the scanning operation, the specified scanning route should be accurately followed, the probe axis should always be kept perpendicular to the measuring surface, and the probe movement speed should be uniform. For any shape of measuring surface, mechanical scanning can technically accurately meet these conditions.
For irregular or curved measuring surfaces, manual scanning is essentially impossible to accurately meet these conditions, so the passband selects a simple, regular shape (see Appendix E). The basic unit of scanning is a straight line. The scanning route should ensure that each surface element can be evenly covered at a uniform speed. Figure 1 gives an example. The average distance between two adjacent lines should be equal; on the initial measuring surface, it should not exceed the average distance between the surface element and the sound source surface. The scanning line density has been defined in 3.16. Figure 1 Scanning route example
The manual scanning speed should be between 0.1 and 0.The scanning speed should be within the range of 5m/s, and the mechanical scanning speed should be within the range of 0.1m/s. The duration of any scan on a single element should not be less than 20s. Time averaging should be performed from the beginning of the scan on any element until the scan is completed on that element (see Appendix E). Note 9: Time averaging can be suspended when the probe encounters an obstacle in the scanning path. During manual scanning, the operator should not face the element scanning, but should stand to the side so that his body does not block the sound radiation of the sound source. For mechanical scanning, in order to reduce the interference caused by the scanning mechanism, the scattering cross-section size of the scanning mechanism parts should be much smaller than the wavelength of the measured sound signal.
Note 10: For the case where Fp exceeds 10 dB, regardless of whether the sound field is stable, a scanning speed greater than 0.25m/s may cause the measurement result to fail to meet criterion 3 of B1.3.
8.2 Initial measurement surface
First, an initial measurement surface should be defined around the sound source to be measured. This surface may include a reflecting surface (reverberation field absorption coefficient less than 0.06), such as a concrete floor or a masonry wall. No sound intensity measurement is performed on this surface, and this area is not included when calculating the sound power according to formula (6).
The measurement surface should be divided into at least four surface elements. The geometry of each surface element should ensure that the probe scans along a predetermined route and always keeps the probe axis perpendicular to the measurement surface, while ensuring that the area of ​​the surface element can be accurately determined (see Appendix E). If manual scanning is performed, it is recommended that the surface element be a plane or a single curved surface. Figure E1 of Appendix E gives examples of suitable surface element shapes. The surface elements should be selected as far as possible in combination with the geometry, material type, connection points, holes, etc. of the various parts of the sound source. If most of the sound power is radiated by one or several special parts of the sound source, the surface elements should be delineated as far as possible according to the parts above and below the average sound power. The measurement surface should be defined as far as possible in such a way that the areas through which negative local sound power mainly passes are separated from the areas through which positive local sound power mainly passes, for example, the measurement surface is located between the sound source to be measured and a very strong external sound source. The maximum size of any surface element should be such that the probe can be scanned along the specified route at a constant speed and constant line density, while ensuring that the probe axis is always perpendicular to the measurement surface.
If the sound source to be measured is in the shape of an unfolded plate or shell-shaped vibration surface, the average distance between the measurement surface element and the sound source surface should not be less than 200 mm. If the sound source is very small and compact, the average distance may be reduced to 100 mm; in the latter case, measure "a" in Table B1 and Figure B1 are not used.
8.3 Preliminary tests
GB/T 16404. 2—1999
The average normal sound intensity level and sound pressure level in the frequency bands required for the sound power determination should be measured for each surface element. 8.3.1 Repeatability of local sound power
For engineering-grade determinations, according to the definition in 3.6.3, it is necessary to scan all measurement frequency bands twice on each measurement bin and record the local sound power levels Lw (1) and Lw (2) for each frequency band. The paths of the two separate scans should be orthogonal (the scanning pattern is rotated 90°, see Figure 1). Substitute the difference in local sound power levels into formula (B3) of B1.3. If criterion 3 is not met, try to find the cause of the difference and try to reduce it. If it cannot be reduced, take appropriate measures according to B2. If criterion 3 is still not met, it means that in such bins and frequency bands, the local power level determined according to this standard cannot reach engineering-grade accuracy. For this reason, its impact should be stated in the test report, that is, in these frequency bands, the uncertainty of the sound power level measurement exceeds the uncertainty of the required accuracy level in Table 2. If, in any frequency band, the sum of the local sound power levels through the bins that do not meet criterion 3 is more than 10 dB lower than the sum of the local sound power levels through the remaining bins that meet criterion 3, the sound power level can be measured in accordance with this standard.
8.3.2 Evaluation of instrument performance
Estimate the indicated value FpI for all measured frequency bands according to formula (A1) in A2.1, and substitute its value into formula (B1) given in the evaluation method. Efforts should be made to make the indicated value Fp of each frequency band less than 10 dB. 8.3.3 Estimation of negative local sound power
Estimate the indicated value F+/- for all measured frequency bands according to formula (A2) in A2.2, and substitute its value into formula (B2) given in evaluation method B1.2. For simple level determination, it is not necessary to estimate the indicated value F+/-. 8.4 Further measures
For engineering-level sound power measurements, if criteria 1, 2, and 3 are met for each frequency band, the initial sound power measurement is the final result. For simple-level measurements, only criteria 1 and 3 need to be met. Otherwise, appropriate measures need to be taken according to B2. At this time, the normal component sound intensity level and the corresponding sound pressure level should be measured according to the modified plan, the sound field indication value Fp and F+/- value should be recalculated, and evaluated according to B1, and then measures should be taken according to B2. Repeat this process until the accuracy level indicated in B1 is obtained. If repeated measures still cannot meet the specified criteria, the invalid test results should be recorded and the relevant reasons should be stated. 9 Calculation of sound power level
9.1 Calculation of local sound power of each face element of the measurement surface The local sound power of each frequency band of each measurement face element is calculated according to formula (12): W;2. The indicated value F+/- for all measurement frequency bands is estimated by formula (A2) and its value is substituted into formula (B2) given in evaluation method B1.2. For simple-level determinations, it is not necessary to estimate the indicated value F+/-. 8.4 Further measures
For engineering-level sound power determinations, if criteria 1, 2, and 3 are met for each frequency band, the initial sound power determination is the final result. For simple-level determinations, only criteria 1 and 3 need to be met. Otherwise, appropriate measures need to be taken according to B2. At this time, the normal component sound intensity level and the corresponding sound pressure level should be measured according to the modified scheme, the sound field indicated value Fp and F+/- value should be recalculated, and evaluated according to B1, and then measures should be taken according to B2. Repeat this process until the level of confidence indicated in B1 is obtained. If repeated measures still fail to meet the specified criteria, the invalid test results should be recorded and the relevant reasons should be stated. 9 Calculation of sound power level
9.1 Calculation of local sound power of each element of the measurement surface The local sound power of each frequency band of each measurement element is calculated according to formula (12): W;2. The indicated value F+/- for all measurement frequency bands is estimated by formula (A2) and its value is substituted into formula (B2) given in evaluation method B1.2. For simple-level determinations, it is not necessary to estimate the indicated value F+/-. 8.4 Further measures
For engineering-level sound power determinations, if criteria 1, 2, and 3 are met for each frequency band, the initial sound power determination is the final result. For simple-level determinations, only criteria 1 and 3 need to be met. Otherwise, appropriate measures need to be taken according to B2. At this time, the normal component sound intensity level and the corresponding sound pressure level should be measured according to the modified scheme, the sound field indicated value Fp and F+/- value should be recalculated, and evaluated according to B1, and then measures should be taken according to B2. Repeat this process until the level of confidence indicated in B1 is obtained. If repeated measures still fail to meet the specified criteria, the invalid test results should be recorded and the relevant reasons should be stated. 9 Calculation of sound power level
9.1 Calculation of local sound power of each element of the measurement surface The local sound power of each frequency band of each measurement element is calculated according to formula (12): W; S.
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