Acoustics－Description and measurement of physical properties of sonic booms
Some standard content:
National Standard of the People's Republic of China
Acoustics-Descriptiox and measurement of physical properties of sonic hoomsGB/T 15484—1995
This standard refers to the international standard ISU2249:1973\Acoustic boom-Description and measurement of physical characteristics". 1 Subject content and scope of application
1.1 This standard describes the physical characteristics and related terms of the boom generated by supersonic aircraft during overflight, and specifies the minimum requirements for the performance of equipment used in the boom measurement system and the measurement methods. 1.2 This standard is applicable to the measurement of boom sound pressure and to the estimation of the impact of attenuated sound on people, structures, animals and unstable terrain. Note: It is best to know the direction and time of the sound pressure disturbance before measuring, but it is not necessary to know the approximate intensity of the disturbance in advance. ② The physical characteristics described in this standard refer to the characteristics of the boom at a specific receiving location, and cannot be considered as the characteristics of a specific aircraft, because the measured quantity is also related to the flight conditions, atmospheric conditions and ground conditions at the time. 2 Original language
2.1 Boom sonic sonie: Bang The shock wave generated when an airplane flies at a speed greater than the local speed of sound. It includes the front shock wave, the tail shock wave and the sound pressure drop that occurs between the two shock waves. Although the front and rear shock waves can be heard separately, the entire signal is usually considered as a bang. Note: A typical sound pressure characteristic of a bang reflected by the ground is shown in the figure, which helps to understand the following terms. 2.2 Overpressureoyerpressure
The difference between the pressure at any time at a base point in space and the ambient atmospheric pressure. When the pressure is greater than the ambient atmospheric pressure, the overpressure is positive; otherwise, the overpressure is negative. The symbol is P and the unit is Pascal, Pa. Note: In the past, the symbol AP was often used to represent the overpressure of a bang, while the overpressure symbol P used in this standard is consistent with the symbol of (instantaneous> sound pressure in "Acoustic Quantities and Units".
2.3 Peak overpressurepeak overpressule The maximum positive value of overpressure, symbol is fumx! Unit is Pa, Pa. 2.4 Sound pressure signature pressurrsignature Curve of overpressure change with time.
The sound pressure characteristic of the free field, its waveform often has a similar shape to the letter N, so it is called N. 2.5 Sound pressure rise presure rise
The sound pressure rise between the start rise and the end rise of a given shock wave, symbol is △P; unit is Pa, Pa. Note: In fact, the start time of the shock wave is very easy to determine. But the end rise time often has uncertain interpretations, which can be defined according to its interpretation. 2.5.1 Incident sound pressure rise incident pressure rise The sound pressure rise between the start of a given shock wave and the time it directly reaches the measurement point. It is not affected by reflection from the ground or other objects. Symbol is: Unit is Pa, Pa.
2.5.2 Reflected sound pressure rise reflectedpressurcrisc The sound pressure rise between a given shock wave and the time it reaches the measurement point after being reflected by the ground or other surfaces. The symbol is △F, and the unit is Pa.
State Administration of Technology Supervision 1995-07-03 approved 1996-02-01 implementation
: com2.6 Free field canditinnsCB/T 15484—1995
The conditions that exist when the ground and other reflectors are far enough away that the impact on the shock wave can be ignored: The quantities measured under free field conditions are represented by symbols with subscript f.
2.7 Ground conditions Ground conditions Conditions that exist when other reflectors other than the ground are far enough away that the impact on the shock wave can be ignored. The quantities measured under ground conditions are represented by symbols with subscript names.
2. Ground reflection coefficient ground reflection coefficient The ratio of the sound pressure rise of the radiated sound to the sound pressure rise of the radiated sound. The symbol is. 2.9 Ground reflection factor Rround reflection factor is defined by the following formula:
where K is the ground reflection factor, and the ground reflection coefficient is the reflection coefficient. Note: For weak shock waves and smooth rigid ground, K is approximately equal to 2.2.10 Total duration (of asonic boorn signature) The time interval between the beginning and end of the sound pressure signature. The symbol is , and the unit is milliseconds, m9. For V-wave type shocks, the total duration is the time between the beginning of the first shock wave and the end of the tail shock wave. Note: Although it is usually difficult to determine the end time of the sound signature accurately, it is practical to use it to express the approximate total duration. 2.11 Rise time (of a shock) The time interval between the beginning of the shock wave and the given end of the rise. The symbol is ; the unit is seconds, ms2. Incident rise time The time interval between the beginning of the shock wave and the end of its rise before it is affected by reflection from the ground and other objects. The symbol is △t, and the unit is milliseconds, ms.
2.11.2 Reflected rise time The time interval from the moment the shock wave is reflected from the ground or other surface to the moment the given reflection stops rising. Symbol: Unit: millisecond, ms.
2.12 Peak time timelopeak The time interval from the beginning of the shock wave to the occurrence of the maximum peak overpressure. Symbol: At; Unit: millisecond, ms. 2.13 Itipulse
The continuous integral of the overpressure over time, which is a function of the integral time. Symbol: I; Unit: milliPascal second, mPa·s. 2.13.1 Maximum impulse The maximum value of the overpressure integral over time, which is the impulse of the positive pulse. Symbol: Imx; Unit: milliPascal second, mPa·s. 2.13.2 Minimum impulse The minimum value of the overpressure integral over time, which is the sum of the impulses of the positive and negative pulses. Symbol: I. Unit: mPa·s. 2.14 Phase impulse
The impulse at a certain stage. Symbols are 1.-1, 2, 3, *); unit is milliPascal second, mPaS. 2.15 Signature interval The time interval from the start of the first impulse wave to the start of the last impulse wave, which is the sum of the time intervals of all impulse waves. Symbol is A; unit is millisecond, ms.
2.16 Characteristic overpressure, characteristicoverpressure This quantity is defined by the following formula
AP. - 4(1. - In)/Ar
Where: 4P. is characteristic overpressure, Par
is characteristic interval, ms:
I. is maximum impulse, mPast
I:nim is minimum impulse + mPa·s,
GB/T15484—1995
Note: For ideal √ wave, characteristic overpressure is equal to maximum overpressure. 3 Measurement system
The characteristic sound pressure is detected by a sound pressure microphone, and the microphone signal is amplified and recorded by a suitable recorder. The equipment should meet the following requirements.
3.1 General Performance Requirements
The free-field frequency response of the measurement system shall be flat within ±2 dB from at least 0.1 Hz to 5000 Hz. The required frequency response of the measurement system shall, to some extent, depend on the purpose of the measurement and the duration of the free-field feature. The frequency range may extend to 0.02 Hz and/or 10 000 Hz, depending on the duration of the feature and the requirement for the required acoustic energy information within the total width. If such a width is only available from a response curve with greater deviations, the spectrum of the feature shall be corrected accordingly. NOTE: Depending on the purpose of the measurement, the measurement system may cover the entire frequency range, or it may be divided into two channels, one covering the entire frequency range and the other covering a limited frequency range, e.g. 100 to 5000 Hz. Using two channels may improve the signal-to-noise ratio within the acoustic compliance range. 3.2 Microphone Assistance
The sensitivity of the microphone system shall have a smooth roll-off outside the useful frequency range.To limit the overshoot distortion produced when recording sounds with very short rise times.
Note: The size of the microphone receiving surface is determined by the severity of the overpressure at a certain location. For most cases, it is recommended to use a microphone with a size not exceeding 20mm.
The total shear wave span of the microphone and its connected amplifier when measuring the maximum overpressure should not exceed 4. (When using fully sealed microphone heads, special care should be taken to avoid sound pressure imbalance during calibration or measurement. Changes in microphone sensitivity due to environmental conditions should be corrected so that the final recording sensitivity is within 2/3 of the calibration value. Microphones are calibrated with free-field sensitivity, but when the microphone is installed in ground conditions (see 6.1), sound pressure sensitivity is used for problems where the difference between free-field sensitivity and sound pressure sensitivity cannot be ignored. ③ For calibration at very low frequencies, that is, below about 25Hz, an acoustic calibrator can be used. Calibrate the microphone. For condenser microphones, the calibration environment should be consistent with the measurement environment. Pay special attention to the acoustic short circuit between the calibration source and the air volume behind the diaphragm. Calculate the sound pressure generated based on the known piston displacement and capacitance. Allow for the transition from adiabatic to isothermal conditions to make the correction. 3.3 Recording
The dynamic range of the recorder should be at least 45 dB under the condition that the total harmonic distortion measured at 1000 Hz is less than 1%. Note:) Due to the difficulty of correctly predicting the overpressure, the maximum system gain position cannot be predetermined. For this reason, it is recommended to record simultaneously with more than one channel at different gain positions with a difference of 5 dB or 1 dB. This method will ensure that the sound recording has a sufficient signal-to-noise ratio when at least one channel in the recording system is fully dynamic! A failure indicator is also required, which may be in the form of a peak reading meter or an automatic recording overload indication. The minimum dynamic range of the recorder specified in (②) may not be available to ensure that the noise is analyzed over the entire frequency range. For these measurements, it may be necessary to apply frequency response pre-correction in one of the channels of the recording system to improve the signal-to-noise ratio at high frequencies. When performing frequency analysis, frequency response restoration should be added to the playback system. When recording and replaying sound pressure characteristics. The frequency response of the measurement system in Section 3.1 must be met, and this method should not be used. 3.4 Equipment for unattended recording
For long-term recording of decaying sound, specially designed digital recorders should be used, because the application of general recording systems for this purpose is limited.
The recorder should have the ability to operate unattended and respond immediately to transient signals. In order to provide operation for immediate response to noise during predetermined times of the day, suitable control circuits should be used. The equipment should be equipped with an accompanying signal conditioning network. A suitable calibration signal should be provided and recorded for each channel after each recording. Note: The equipment should comply with the provisions of 3.1, 3.2 and 3.3 as far as possible, and its deviations should be explained in order. 4 Measurement analysis
For preliminary evaluation of the acoustic characteristics of the boom, the signal can be displayed on an oscilloscope. For detailed analysis, other display devices such as digital readouts or precision galvanometers must be used according to the required accuracy. The results of the signal frequency analysis are given in the form of spectral density functions or band spectra. 5 Environmental conditions
5.1 Reference conditions
It can be described by two main reference conditions, namely ground conditions and free field conditions. 5.1.1 Ground reference conditions
The conditions of an open space with basically no local undulations and a total image size of 0.004 steradian (sr) solid angle without obstacles. There should be a hard surface around the measurement point, and a solid flat baffle can be used to directly contact the ground. The diameter of the baffle should not be less than 1.5m. 5.1.2 Free-field reference conditions
The conditions when obstacles are within a solid angle of less than 0.004sr in the upper half space and when the microphone is installed at a sufficiently high height. Note: Under free-field conditions, to determine the entire sound pressure characteristics of the aircraft flight, the altitude must be greater than 100m. For this reason, ground conditions are preferred. At this time, if the rise time is to be analyzed, a height of 5m is sufficient. ② The overpressure measured under free-field conditions is approximately half of that measured under ground conditions. 5.2 Deviations from reference conditions
In order to obtain results similar to reference conditions, the requirements of Article 5.1 should be met as much as possible on board mountainous areas or built-up areas. Any deviations or special circumstances (such as sea surface conditions) should be explained. 5.3 Specific environmental conditions
For measurements aimed at the specific environment caused by the response of the human body structure or when the environment does not meet Articles 5.1 or 5.2, measurements should be made at the height of the human ear (1.2m), which represents the acoustic environment including reflecting and absorbing surfaces and obstacles. 6 Microphone installation
6.1 Measurements under ground conditions
The microphone should be installed so that its main axis is straight with the ground, the sound receiving surface is facing upwards, and it should be in the same plane as the hard surface of the ground plane (the penetration error is ±3 mm),
Note: If it is a concrete surface, it is impossible to install it on the same plane. In this case, the microphone is installed so that its main axis is perpendicular or parallel to the ground, and its sound receiving surface is as close to the ground as possible but avoids the downward situation. Microphone auxiliary equipment should be placed below the ground level or away from the site so that their presence does not affect the measurement. 6.2 Measurement under free field conditions
The microphone is installed so that its main axis is perpendicular to the ground, and its sound receiving surface should be upward. 6.3 Removing external signals
It should be able to remove external signals, such as reducing the impact of wind on sound transmission, preventing rain or dust from intruding, and a protective device must be used. The designed protective cover should not significantly affect the frequency response of the microphone. The microphone should have a suitable anti-grip device to reduce the vibration transmitted from the base. Additional instructions:
GB/T 15484—1995
Figure 1 Example of graphic display of ground reflected sound
This standard was proposed by the National Technical Committee for Acoustic Standardization. This standard was drafted by the Institute of Acoustics of the Chinese Academy of Sciences, with the Third Institute of the Ministry of Electronics Industry as the main participating unit. The main drafters of this standard were Zhang Ruwei and Yang Jingang.1 Reference conditions
Two main reference conditions can be described, namely ground conditions and free-field conditions. 5.1.1 Ground reference conditions
The condition of an open space with essentially no local undulations and a total area of 0.004 steradians (sr) of solid angle without obstacles. There should be a hard surface around the measurement point, and a solid flat baffle can be used in direct contact with the ground. The diameter of the baffle should not be less than 1.5 m. 5.1.2 Free-field reference conditions
The condition when obstacles are within a solid angle of less than 0.004 sr in the upper half space and when the microphone is installed at a sufficiently high height. Note that under free-field conditions, the altitude must be greater than 100 m to determine the overall sound pressure characteristics of the aircraft flight. For this reason, ground conditions are preferred. At this time, if the rise time is to be analyzed, a height of 5 m is sufficient. ② The overpressure measured under free-field conditions is approximately half of that measured under ground conditions. 5.2 Deviations from reference conditions
In order to obtain results similar to reference conditions, the requirements of Article 5.1 should be met as much as possible on board mountainous areas or built-up areas. Any deviations or special circumstances (such as sea surface conditions) should be explained. 5.3 Specific environmental conditions
For measurements aimed at the specific environment caused by the response of the human body structure or when the environment does not meet Articles 5.1 or 5.2, measurements should be made at the height of the human ear (1.2m), which represents the acoustic environment including reflecting and absorbing surfaces and obstacles. 6 Microphone installation
6.1 Measurements under ground conditions
The microphone should be installed so that its main axis is straight with the ground, the sound receiving surface is facing upwards, and it should be in the same plane as the hard surface of the ground plane (the penetration error is ±3 mm),
Note: If it is a concrete surface, it is impossible to install it on the same plane. In this case, the microphone is installed so that its main axis is perpendicular or parallel to the ground, and its sound receiving surface is as close to the ground as possible but avoids the downward situation. Microphone auxiliary equipment should be placed below the ground level or away from the site so that their presence does not affect the measurement. 6.2 Measurement under free field conditions
The microphone is installed so that its main axis is perpendicular to the ground, and its sound receiving surface should be upward. 6.3 Removing external signals
It should be able to remove external signals, such as reducing the impact of wind on sound transmission, preventing rain or dust from intruding, and a protective device must be used. The designed protective cover should not significantly affect the frequency response of the microphone. The microphone should have a suitable anti-grip device to reduce the vibration transmitted from the base. Additional instructions:
GB/T 15484—1995
Figure 1 Example of graphic display of ground reflected soundwwW.bzxz.Net
This standard was proposed by the National Technical Committee for Acoustic Standardization. This standard was drafted by the Institute of Acoustics of the Chinese Academy of Sciences, with the Third Institute of the Ministry of Electronics Industry as the main participating unit. The main drafters of this standard were Zhang Ruwei and Yang Jingang.1 Reference conditions
Two main reference conditions can be described, namely ground conditions and free-field conditions. 5.1.1 Ground reference conditions
The condition of an open space with essentially no local undulations and a total area of 0.004 steradians (sr) of solid angle without obstacles. There should be a hard surface around the measurement point, and a solid flat baffle can be used in direct contact with the ground. The diameter of the baffle should not be less than 1.5 m. 5.1.2 Free-field reference conditions
The condition when obstacles are within a solid angle of less than 0.004 sr in the upper half space and when the microphone is installed at a sufficiently high height. Note that under free-field conditions, the altitude must be greater than 100 m to determine the overall sound pressure characteristics of the aircraft flight. For this reason, ground conditions are preferred. At this time, if the rise time is to be analyzed, a height of 5 m is sufficient. ② The overpressure measured under free-field conditions is approximately half of that measured under ground conditions. 5.2 Deviations from reference conditions
In order to obtain results similar to reference conditions, the requirements of Article 5.1 should be met as much as possible on board mountainous areas or built-up areas. Any deviations or special circumstances (such as sea surface conditions) should be explained. 5.3 Specific environmental conditions
For measurements aimed at the specific environment caused by the response of the human body structure or when the environment does not meet Articles 5.1 or 5.2, measurements should be made at the height of the human ear (1.2m), which represents the acoustic environment including reflecting and absorbing surfaces and obstacles. 6 Microphone installation
6.1 Measurements under ground conditions
The microphone should be installed so that its main axis is straight with the ground, the sound receiving surface is facing upwards, and it should be in the same plane as the hard surface of the ground plane (the penetration error is ±3 mm),
Note: If it is a concrete surface, it is impossible to install it on the same plane. In this case, the microphone is installed so that its main axis is perpendicular or parallel to the ground, and its sound receiving surface is as close to the ground as possible but avoids the downward situation. Microphone auxiliary equipment should be placed below the ground level or away from the site so that their presence does not affect the measurement. 6.2 Measurement under free field conditions
The microphone is installed so that its main axis is perpendicular to the ground, and its sound receiving surface should be upward. 6.3 Removing external signals
It should be able to remove external signals, such as reducing the impact of wind on sound transmission, preventing rain or dust from intruding, and a protective device must be used. The designed protective cover should not significantly affect the frequency response of the microphone. The microphone should have a suitable anti-grip device to reduce the vibration transmitted from the base. Additional instructions:
GB/T 15484—1995
Figure 1 Example of graphic display of ground reflected sound
This standard was proposed by the National Technical Committee for Acoustic Standardization. This standard was drafted by the Institute of Acoustics of the Chinese Academy of Sciences, with the Third Institute of the Ministry of Electronics Industry as the main participating unit. The main drafters of this standard were Zhang Ruwei and Yang Jingang.
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