Acoustics - Measurement of sound pressure levels in the interior of aircraft during flight
Some standard content:
ICS 17.140
National Standard of the People's Republic of China
GB/T 20248-—2006/ISO 5129:2001 Acoustics
Measurement of sound pressure levels in the interior ofaircraft during flight
Acoustics-Measurement of sound pressure levels in the interior ofaircraft during flight flight
(JSO5129:2001, IDT)
2006-05-08 Issued
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Standardization Administration of China
2006-11-01 Implementation
2 Normative Reference Documents
3 Terms and Definitions
4.1 Overview
Microphone System
Acoustic Calibrator
Conformance Verification
Test Method
5.1 Measurement Method
5. 2 Test conditions
Aircraft flight conditions
6 Data processing
Averaging time
Frequency response correction
Background noise correction
Broadband sound pressure level and frequency-weighted sound pressure level
Transient sound
Measurement uncertainty
７ Report content
Test report
7.2 Sound pressure level result report
Appendix A (Informative Appendix)
Appendix B (Informative Appendix)
Measurement uncertainty
References,
GB/T 20248--2006/IS0 5129:20012
This standard is equivalent to ISO5129:2001 "Acoustic front
GB/T 20248-2006/ISO 5129:2001 Measurement of sound pressure level in aircraft cabin during flight". This standard has made some editorial changes to ISO5129:2001 according to the requirements of national standards. Appendix A and Appendix B of this standard are informative appendices. This standard was proposed by the Chinese Academy of Sciences.
This standard is under the jurisdiction of the National Technical Committee for Acoustic Standardization (SAC/TC17). The drafting units of this standard are: Institute of Acoustics, Chinese Academy of Sciences, Tongji University, and Shanghai Institute of Aeronautical Measurement and Control Technology. The main drafters of this standard are: Cheng Mingkun, Mao Dongxing, Tian Jing, Mu Jingkun, Lv Yadong, and Xu Xin. m
1 Scope
GB/T20248—2006/IS05129:2001 Acoustics Measurement of sound pressure level in aircraft cabin during flight 1.1 This standard specifies the requirements for instruments and equipment for measuring sound pressure level at crew and passenger positions in aircraft cabin during steady-state flight, as well as the requirements for measurement methods and measurement reports. Sound pressure level can be used to determine various parameters describing the acoustic environment in aircraft cabin. The measurement methods specified in this standard are intended to ensure the consistency of measurement results and provide a basis for determining measurement uncertainty. 1.2 This standard provides the technical specifications for the electroacoustic performance of a complete measurement system from microphone to readout device. As long as the total measurement system meets the technical specifications of this standard, various measurement system components can be selected. 1.3 The recommended measurement method can either record the sound pressure signal for 1/3 octave band sound pressure level analysis or directly perform 1/3 octave band sound pressure level measurement.
2 Normative references
The provisions in the following documents become the provisions of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties to an agreement based on this standard 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 standard. GB/T3102.7—1993 Acoustic quantities and units (eqvISO31-7:1992) GB/T3240—1982 Common frequencies in acoustic measurements (neqISO266:1975) GB/T3241—1998 Octave and fractional octave filters (eqvIEC61260:1995) GB/T3947—1996 Acoustic terminology
GB/T17312—1 998 Calibration of random incident and diffuse fields of sound level meters (eqvIEC61183:1994) GB/T15173-1994 Sound calibrator (eqvIEC60942:1988) IEC61672-1:2002 Electroacoustic sound level meters Part 1: Specifications 3 Terms and definitions
GB/T3102.7-1993, GB/T3947-1996 and the following terms and definitions apply to this standard. 3.1
Aircraft
Any machine that obtains lift in the atmosphere by reaction with the air other than the reaction of the air on the surface of the earth. 3.2
Beats
Periodic variation formed by the addition of simple harmonic quantities of different frequencies f1 and f2. The amplitude increases and decreases periodically according to the beat frequency (fi-f2). 3.3
crew station
A place occupied or used only by the crew of the aircraft during flight. 3.4
crew sleeping quartersA compartment used for rest or sleeping by the crew. 3.5
passenger compartment
Any place occupied by passengers during flight.
GB/T20248—2006/IS05129:20013.6
synchrophaserA device for controlling the speed and phase of propeller rotation in multi-engine aircraft. 3.7
steady flightsteady flight
Flight under conditions where the aircraft parameters that significantly affect the cabin sound pressure level are controlled to obtain reproducible results. 4 Instruments
4.1 Overview
A complete acoustic measurement system consists of a microphone system, data recording and analysis equipment, a sound pressure level display device, and an acoustic calibrator that provides full system acoustic sensitivity. The measurement system may include multi-channel instruments and must comply with at least the corresponding Class 2 performance specifications of IEC61672-1:2002. Use an integrating average sound level meter containing a microphone system in accordance with 4.2 or a traditional sound level meter measurement system with exponential time weighting, which must comply with at least the corresponding Class 2 performance specifications of IEC61672-1:2002. The time-averaged sound pressure level in the 1/3 octave band must be determined using a spectrum analyzer that complies with at least the corresponding Class 2 specifications of GB/T3241-1998. 4.2 Microphone system
The microphone system shall comply with the relevant technical indicators of IEC61672-1:2002 for random radiated sound. The random radiated response of the microphone system shall be verified according to the method of GB/T17312-1998. Note: A microphone system includes those parts of the measurement system that can generate electrical signals corresponding to sound pressure. These parts usually include one or more microphones with preamplifiers and extension cables and other necessary equipment such as wind shields. 4.3 Sound calibrator
The sound calibrator shall at least meet the requirements of Class 1C of GB/T15173-1994. The rated frequency of the sinusoidal sound signal generated by the sound calibrator shall be in the range of 200 Hz to 1250 Hz. 4.4 Conformity Verification
Within one year before testing according to this standard, the instrument performance of the measurement system shall be verified to meet the corresponding requirements of IEC61672-1:2002, GB/T15173-1994, and GB/T3241-1998. 5 Test Method
5.1 Measurement Method
5.1.1 Measurement Position
5.1.1.1 Cabin
The sound pressure signal at the typical head position of the passenger or crew seat shall be measured when there are no passengers or crew members. The microphone shall be placed vertically upward on the center line of the seat, 0.15m±0.025m from the headrest, and 0.65m±0.05m above the empty seat cushion. The number and distribution of cabin measurement points depend on the aircraft seating arrangement and the specific test purpose. The selection of cabin measurement points shall ensure that they represent the cabin acoustic environment. 5.1.1.2 Crew Positions
Sound pressure signal measurements should be placed at a typical crew head position. At the pilot position, the microphone should be placed at a representative sitting head height, within 0.1m of the typical ear position, which is usually the receiving position for speech communication, and the crew should be seated during the measurement. Measurements at the cabin crew standing position should be made when the crew is not present, and the microphone should be 1.65m ± 0.1m. The measurement of the seat position of cabin personnel not in the cabin shall be carried out in accordance with the provisions of 5.1.1.1, and the foldable seats shall be in use. 5.1.1.3 Crew lounge
The sound pressure signal measurement shall be carried out at the head position of the crew members in the resting state, and the crew members should not be present during the measurement. The microphone should be placed 0.15m ± 0.02m above the mattress, blanket or headrest. If the head position is against the wall, the microphone should be not less than 0.15m away from the wall. 5.1.1.4 Microphone installation
, in order to reduce the interference and shielding caused by the operator including the operator holding the microphone extension rod or supporting equipment, it is more appropriate to install the microphone in a fixed position with a bracket or extension rod. If there is airflow affecting the microphone during the test, the microphone should be equipped with a windshield. The windshield insertion loss as a function of frequency and sound incidence angle in the windless state can be obtained from the data provided by the manufacturer or other experimental data. 5.1.2 Acoustic sensitivity and background electrical noise
5.1.2.1 Acoustic sensitivity
Before and after the sound pressure level measurement inside the aircraft, the overall acoustic sensitivity of the measurement system should be calibrated on the ground. The calibration can be performed using a sound calibrator or a combination of a sound calibrator and a sinusoidal electrical signal provided by an electrical input device output by a substitute microphone. A supplementary check of the acoustic sensitivity can also be performed during the test. Taking into account the difference between the actual atmospheric pressure and air temperature and the reference atmospheric pressure and reference temperature specified in GB/T15173-1994, the actual indicated sensitivity level should be appropriately corrected. 5.1.2.2 Background electrical noise
The background electrical noise should be measured in order to determine the sound level range used for data collection. When measuring the background electrical noise of the system, the microphone should be placed in a low sound level sound field and measured in a 1/3 octave band. When recording, the recording duration shall be at least 30 s. 5.1.3 Acoustic Data Acquisition
5.1.3.1 Data Recording
The recording duration for each measurement shall be at least 30 s. To ensure that the signal is recorded within the range close to the optimum recording level, the sound level range control setting of the recording system shall be monitored to avoid input level overload. If beat phenomena exist, the recording time for one measurement point shall include at least 4 beat periods, with a minimum recording time of 30 s. 5.1.3.2 Direct Measurement
Direct measurement of 1/3 octave band sound pressure levels is best performed using an integrating averaging sound level meter or a spectrum analyser with a set of 1/3 octave band filters. The averaging time is as specified in 6.1.
Note: If the sound pressure level is measured using a conventional sound level meter, the time weighting should be in the slow gear. 5.1.3.3 Crew lounge
The sound pressure signal should be recorded for at least 30 seconds at the measurement points mentioned in 5.1.1.3, and the transient sound in the cabin and cockpit should be minimal (i.e., no conversation, radio transmission or transient operation of equipment should be heard). If transient sound is to be measured, the sound pressure signal should be recorded when the transient sound is generated, such as: toilet flushing, cabin or toilet door opening and closing, kitchen operation. The sound pressure signal should be recorded 5 times for each transient sound source.
5.2 Test conditions
5.2.1 Aircraft interior configuration
The aircraft interior should be fully equipped with carpets, seats, curtains, and their configuration should be recorded. The description of the aircraft configuration should include those factors that affect the internal sound pressure level, such as the location of the cabin partitions and the material of the seat covers. The seat backs should be restored to their normal upright position. The number of people in the test aircraft should be controlled to the minimum required for the test. If possible, it is best to have no personnel present to avoid significant impact on the sound field at the measurement point. Except at the pilot's station, no person should be sitting or standing within 1m of the microphone during testing. The position of all personnel should be noted during the test.
5.2.2 Aircraft System Configuration
The pressurization and air conditioning systems should be operating normally or in automatic mode. If the aircraft is not equipped with an automatic environmental control system, the system should be set to deliver 100% of the maximum design flow. For non-pressurized aircraft or environmental control systems that can only deliver 100% of the maximum design flow in an emergency, the air flow rate should be representative of the flow rate under normal operating conditions. All air outlets for passengers or crew members should be closed except those that need to be opened for normal operation. The public address system should be turned off. The noise and vibration system control should be in normal operating conditions.
5.2.3 Crew Rest Room
The layout of the crew rest room should represent the normal use state and no one should be in the room. The passage door should be closed, the room should be equipped with special mattresses and blankets, and the public address system should be turned off. The aircraft environmental control system shall operate normally to maintain a comfortable air temperature in the lounge. The diffusers of the environmental control system shall be set according to the design airflow requirements of the lounge. The berths are unoccupied. 3
GB/T 20248—2006/ISO 5129:20015.3 Aircraft flight conditions
5.3.1 Overview
The aircraft flight condition refers to the stable flight state in which the Mach number and indicated airspeed (or either of them), engine power and shaft speed (or either of them) are stable to the specified values of the specified permissible limits. 5.3.2 Flight Condition Data When measuring the sound pressure signal, the following data should be recorded at appropriate time intervals: a) flight altitude or the corresponding air pressure value; b) aircraft Mach number and indicated airspeed, or either; engine power setting (such as engine shaft speed or pressure ratio and synchronizer setting, or propeller speed and engine torque c) and synchronizer setting); main rotor and tail rotor rotation speed for hang-wing aircraft; d) rated position of the center of gravity of the aircraft; rated parameters of the fuel in the fuel tank, such as the total weight of fuel or the percentage of the maximum fuel load; f) g) external ambient static air temperature (if the aircraft instrument cannot directly give the static temperature, please record the corresponding data for later calculation of the static temperature); h) cabin pressure differential (the difference between the internal pressure of the aircraft and the external pressure of the aircraft) or cabin pressure and rated cabin air temperature; i) environmental control system settings.
6 Data Processing
6.1 Averaging Timewww.bzxz.net
The averaging time used to determine the 1/3 octave band sound pressure level shall be at least 16 seconds. If there is a beat, the averaging time shall include at least three beat periods with a minimum averaging time of 16 seconds, in addition to not being less than 16 seconds. 6.2 Sound Spectrum
The sound spectrum in the aircraft shall be determined using a 1/3 octave band filter. The octave band sound pressure level shall be determined by taking the ratio of the sum of the mean square sound pressure of three adjacent 1/3 octave bands to the square of the reference sound pressure and then taking 10 times the logarithm with a base of 10. The rated center frequency of the filter shall cover the corresponding aircraft frequency range and be consistent with the preferred frequency of GB/T3240-1982. The minimum frequency range shall be 50Hz to 10kHz. For helicopters, the low frequency range shall extend to at least the 1/3 octave band with a center frequency of 16Hz. NOTE: The method of IEC 61400-11\I may be considered for evaluating the audibility of discrete frequency components that may exist in the sound spectrum. 6.3 Frequency response correction
All 1/3 octave band sound pressure levels should be corrected due to the deviation of the random incident frequency response and the frequency-independent response of the entire measurement system. If wind shields are used when measuring the sound pressure levels, their insertion loss effects should also be corrected. 6.4 Background noise correction
If necessary, when the tested 1/3 octave band sound pressure level is greater than the corresponding background electrical noise level by more than 3 dB, the electrical noise component should be removed from the tested sound pressure level. When the tested 1/3 octave band sound pressure level is not greater than 3 dB of the background electrical noise, the test sound pressure level is not recorded and the test report should state the reason.
The test report can provide the sound pressure level affected by the background electrical noise of the measuring instrument. Any affected frequency band sound pressure level should be clearly marked and the corresponding spectrum affecting the background electrical noise should be reported. 6.5 Broadband sound pressure level and frequency-weighted sound pressure level The "broadband" or "full-band" sound pressure level is determined by 10 times the base 10 logarithm of the ratio of the sum of the mean square sound pressure in the 1/3 octave bands to the square of the reference sound pressure within the specified frequency range. The frequency-weighted sound pressure level (such as the A-weighted sound pressure level) can be obtained by adding the standard frequency weighting in IEC61672-1:2002 to the 1/3 octave band sound pressure level in the same way. 6.6 Transient sound Transient sound can be expressed by the maximum value of the time-weighted fast block and the A-weighted sound pressure level during the recording period. The definitions of time-weighted fast block and A frequency weighting4 are given in IEC61672-1:2002.
6.7 Measurement uncertainty
GB/T20248—2006/IS05129:The method given in Appendix A of 2001 can be used to estimate the expanded measurement uncertainty of the acoustic level characterizing the acoustic environment inside the aircraft. 7 Report Contents
7.1 Test Report
The measurement results of the sound pressure level inside the aircraft should be compiled into a test report. The report shall include the following specific information: a) Reference to this standard; b) Description of the aircraft being tested and its propulsion system, including propeller type, serial number and aircraft takeoff gross mass; instruments used for recording, spectrum analysis and calibration, including manufacturer, model and serial number, and c) Location of the recording equipment in the aircraft; Description of the flight conditions specified in 5.3 and the operating conditions of the engine, propeller or blades; d) e) Operating conditions of audible sound sources not included in d); Rated position of the center of gravity of the aircraft when measuring the sound pressure signal in the aircraft; f) Rated amount of fuel when measuring the sound pressure signal in the aircraft; g) If special noise and vibration control systems are installed, their description, including propeller phasors or engine h) Blade synchronization device; Plane and section views. Description of the layout of the aircraft cabin, crew lounge, crew posts and aisles; i)
Description of the positions of seated and standing personnel in various areas during measurement; j)
k) Description of the locations of the measuring points for sound pressure level measurement using plan and section diagrams corresponding to the locations of the measuring points; Description of the test method;
If discrete frequencies and discrete frequency sound sources, transient sounds and beat frequencies exist, they should be indicated; All measured 1/3 octave band sound pressure levels and calculated octave band sound pressure levels are tabulated in printed or electronic format, and n)
Figures of sound pressure level spectra at corresponding measuring points can be provided;
For transient sounds, the maximum fast-shift time-weighted and A-weighted sound levels are tabulated in printed or electronic format; 0)
Values calculated based on the measured band-time-average sound pressure levels (such as speech interference level, A-weighted sound pressure level and broadband sound pressure level). When the test report contains A-weighted or broadband time-averaged sound pressure levels, the frequency range of the corresponding 1/3 octave band should also be given. When calculating the speech interference level, the corresponding octave band sound pressure level center frequency should also be given in the report. It is recommended that the test report should also provide an estimate of the expanded measurement uncertainty of the quantities that characterize the aircraft internal acoustic environment. 7.2 Report of sound pressure level results
The reference sound pressure of all sound pressure levels and derived acoustic quantities in the report is 20μPa. If the sound pressure level is to be rounded to an integer, it should be rounded up.
GB/T20248—2006/IS05129:2001A.1 Overview
Appendix A
(Informative Appendix)
Measurement uncertainty
A.1.1 A measurement is always accompanied by an uncertainty. Reference [2] provides a general method for determining measurement uncertainty, and reference [3] provides definitions of metrological terms.
A.1.2 The combined standard deviation of the uncertainty in the sound pressure level measurement is determined by the square root of the sum of the variances of all the associated uncertainties. The combined uncertainty of the cumulative indication value of the acoustic environment is different from the combined uncertainty of the corresponding 1/3 octave band or octave band sound pressure level. The square root of the sum of all applicable variances is the combined standard deviation of the uncertainty. The positive square root of each variance is the standard deviation of the uncertainty associated with its contribution.
A.1.3 The measurement uncertainty shall have a 95% confidence level as specified in document E2I and as approved by the ISO/TC43 Technical Committee responsible for international standards for acoustics. The interval on either side of a measurement result with a 95% confidence level will include several replicates of the measurement. The coverage factor multiplied by this interval is the expanded uncertainty of the quantity. The calculated combined standard deviation is multiplied by the "coverage factor" to obtain the expanded uncertainty of the measurement for a given location.
A.1.4 If the contributions of each variance in the determination of the combined standard deviation are normally distributed, a coverage factor of 2 approximates a 95 % confidence level. For some measurements, a coverage factor other than 2 may be required to achieve a 95 % confidence level. A.2 Application
A.2.1 For a given aircraft type and interior configuration and propulsion system, there is only one opportunity to measure the interior sound pressure level in accordance with this standard.
A.2.2 There are at least four sources that contribute independently to the combined standard deviation of the uncertainty in aircraft interior sound measurements. The estimate of the standard deviation is usually denoted by s. The sources include:
standard deviation SI related to the acoustic measuring instrument, which represents the deviation from the design target; - standard deviation Sp related to the characteristics of the sound field at the measurement location and the reproducibility of the measurement at a specific location (see 5.1.1); if the sound field contains discrete frequency components, there may be standing waves, and their influence must be considered when calculating the standard deviation (see 5.1.3); - standard deviation SF related to the reproducibility of flight conditions and the influence of the end flow of the air mass through which the aircraft flies on the measured sound pressure level. Flight conditions include the settings of the environmental control system, airspeed, altitude and engine power settings (see 5.2, 5.3); standard deviation Sc related to deviations in aircraft manufacturing and the effects of configuration changes between aircraft of a given model. The various standard deviations may be related to each other. The corresponding values of the standard deviations may also be related to the selection of the values representing the internal sound environment of the aircraft and the sound spectrum of the measurement location.
A.2.3 Assuming that all four independent standard deviations are used for one measurement, the general expression for calculating the expanded uncertainty of measurement U is as shown in equation (A.1):
U=±kVs+s++s
The coverage factor that achieves a 95% confidence level is represented by the symbol in equation (A.1). The units of the individual standard deviations of the aircraft interior acoustic environment indicator and the expanded measurement uncertainty are both decibels. The square of the standard deviation is the variance associated with the contribution. A.2.4 Of the various contributions to the combined standard deviation of equation (A.1), the standard deviation associated with the measuring instrument appears to be the smallest. For measuring instruments, the standard deviation can be minimized by calibration and the use of the adjustment methods of this standard. The standard deviation of the measuring instrument may be less than the allowable limit for design and manufacturing in the IEC standard referenced in this standard. A.2.5 The method of reference [2] recognizes two methods for calculating uncertainty: Type A and Type B. Type A uncertainty is obtained by statistical analysis of a series of observations, while Type B uncertainty is calculated based on the best available information, relevant experience and engineering judgment. Reference 6
Reference [2] provides guidance on the calculation of Type A and Type B uncertainties. GB/T20248--2006/IS05129:2001A. 2.6
6The contribution to the combined measurement uncertainty in equation (A.1) should be calculated as a Type B uncertainty. It is not possible to recommend a universally applicable method for calculating Type B uncertainties. For a given measurement, the appropriate allocation of uncertainty depends on a detailed understanding of the acoustic field, flight conditions, and the effects of the aircraft configuration. | |tt | IUPAP, OIML, 19945(ISBN92-67-10188-9)[3J International vocabulary of basic and general terms in metrology. BIPM, IEC, IFCC, ISO,IUPAC, IUPAP,OIML, 19943(ISBN92-67-01075-1)[4J ISO 9921-1, Ergonomic assessment of speech.communication-Part 1: Speech interferencelevel and communication distances for persons with normal hearing capacity in direct communication (SIL method)1 Test Report
The results of the sound pressure level measurement inside the aircraft shall be compiled into a test report. The report shall include the following specific contents:a) References to this standard;
b) Description of the aircraft under test and its propulsion system, including propeller type, serial number and aircraft takeoff gross mass; Instruments used for recording, spectrum analysis and calibration, including manufacturer, model and serial number, and c) Location of the recording equipment in the aircraft;
Description of the flight conditions specified in 5.3 and the operating conditions of the engine, propeller or blade;d)
e) Operating conditions of audible sound sources not included in d); Rated position of the center of gravity of the aircraft when measuring the sound pressure signal inside the aircraft;f)
Rated amount of fuel when measuring the sound pressure signal inside the aircraft;g)
If special noise and vibration control systems are installed, their description, including propeller synchrophasers or engineh)
Blade synchronization device;
Use plane and section Description of the layout of the aircraft cabin, crew lounge, crew posts and aisles; i)
Description of the positions of seated and standing personnel in various areas during measurement; j)
k) Description of the locations of the measuring points for sound pressure level measurement using plan and section diagrams corresponding to the locations of the measuring points; Description of the test method;
If discrete frequencies and discrete frequency sound sources, transient sounds and beat frequencies exist, they should be indicated; All measured 1/3 octave band sound pressure levels and calculated octave band sound pressure levels are tabulated in printed or electronic format, and n)
Figures of sound pressure level spectra at corresponding measuring points can be provided;
For transient sounds, the maximum fast-shift time-weighted and A-weighted sound levels are tabulated in printed or electronic format; 0)
Values calculated based on the measured band-time-average sound pressure levels (such as speech interference level, A-weighted sound pressure level and broadband sound pressure level). When the test report contains A-weighted or broadband time-averaged sound pressure levels, the frequency range of the corresponding 1/3 octave band should also be given. When calculating the speech interference level, the corresponding octave band sound pressure level center frequency should also be given in the report. It is recommended that the test report should also provide an estimate of the expanded measurement uncertainty of the quantities that characterize the aircraft internal acoustic environment. 7.2 Report of sound pressure level results
The reference sound pressure of all sound pressure levels and derived acoustic quantities in the report is 20μPa. If the sound pressure level is to be rounded to an integer, it should be rounded up.
GB/T20248—2006/IS05129:2001A.1 Overview
Appendix A
(Informative Appendix)
Measurement uncertainty
A.1.1 A measurement is always accompanied by an uncertainty. Reference [2] provides a general method for determining measurement uncertainty, and reference [3] provides definitions of metrological terms.
A.1.2 The combined standard deviation of the uncertainty in the sound pressure level measurement is determined by the square root of the sum of the variances of all the associated uncertainties. The combined uncertainty of the cumulative indication value of the acoustic environment is different from the combined uncertainty of the corresponding 1/3 octave band or octave band sound pressure level. The square root of the sum of all applicable variances is the combined standard deviation of the uncertainty. The positive square root of each variance is the standard deviation of the uncertainty associated with its contribution.
A.1.3 The measurement uncertainty shall have a 95% confidence level as specified in document E2I and as approved by the ISO/TC43 Technical Committee responsible for international standards for acoustics. The interval on either side of a measurement result with a 95% confidence level will include several replicates of the measurement. The coverage factor multiplied by this interval is the expanded uncertainty of the quantity. The calculated combined standard deviation is multiplied by the "coverage factor" to obtain the expanded uncertainty of the measurement for a given location.
A.1.4 If the contributions of each variance in the determination of the combined standard deviation are normally distributed, a coverage factor of 2 approximates a 95 % confidence level. For some measurements, a coverage factor other than 2 may be required to achieve a 95 % confidence level. A.2 Application
A.2.1 For a given aircraft type and interior configuration and propulsion system, there is only one opportunity to measure the interior sound pressure level in accordance with this standard.
A.2.2 There are at least four sources that contribute independently to the combined standard deviation of the uncertainty in aircraft interior sound measurements. The estimate of the standard deviation is usually denoted by s. The sources include:
standard deviation SI related to the acoustic measuring instrument, which represents the deviation from the design target; - standard deviation Sp related to the characteristics of the sound field at the measurement location and the reproducibility of the measurement at a specific location (see 5.1.1); if the sound field contains discrete frequency components, there may be standing waves, and their influence must be considered when calculating the standard deviation (see 5.1.3); - standard deviation SF related to the reproducibility of flight conditions and the influence of the end flow of the air mass through which the aircraft flies on the measured sound pressure level. Flight conditions include the settings of the environmental control system, airspeed, altitude and engine power settings (see 5.2, 5.3); standard deviation Sc related to deviations in aircraft manufacturing and the effects of configuration changes between aircraft of a given model. The various standard deviations may be related to each other. The corresponding values of the standard deviations may also be related to the selection of the values representing the internal sound environment of the aircraft and the sound spectrum of the measurement location.
A.2.3 Assuming that all four independent standard deviations are used for one measurement, the general expression for calculating the expanded uncertainty of measurement U is as shown in equation (A.1):
U=±kVs+s++s
The coverage factor that achieves a 95% confidence level is represented by the symbol in equation (A.1). The units of the individual standard deviations of the aircraft interior acoustic environment indicator and the expanded measurement uncertainty are both decibels. The square of the standard deviation is the variance associated with the contribution. A.2.4 Of the various contributions to the combined standard deviation of equation (A.1), the standard deviation associated with the measuring instrument appears to be the smallest. For measuring instruments, the standard deviation can be minimized by calibration and the use of the adjustment methods of this standard. The standard deviation of the measuring instrument may be less than the allowable limit for design and manufacturing in the IEC standard referenced in this standard. A.2.5 The method of reference [2] recognizes two methods for calculating uncertainty: Type A and Type B. Type A uncertainty is obtained by statistical analysis of a series of observations, while Type B uncertainty is calculated based on the best available information, relevant experience and engineering judgment. Reference 6
Reference [2] provides guidance on the calculation of Type A and Type B uncertainties. GB/T20248--2006/IS05129:2001A. 2.6
6The contribution to the combined measurement uncertainty in equation (A.1) should be calculated as a Type B uncertainty. It is not possible to recommend a universally applicable method for calculating Type B uncertainties. For a given measurement, the appropriate allocation of uncertainty depends on a detailed understanding of the acoustic field, flight conditions, and the effects of the aircraft configuration. | |tt | IUPAP, OIML, 19945(ISBN92-67-10188-9)[3J International vocabulary of basic and general terms in metrology. BIPM, IEC, IFCC, ISO,IUPAC, IUPAP,OIML, 19943(ISBN92-67-01075-1)[4J ISO 9921-1, Ergonomic assessment of speech.communication-Part 1: Speech interferencelevel and communication distances for persons with normal hearing capacity in direct communication (SIL method)1 Test Report
The results of the sound pressure level measurement inside the aircraft shall be compiled into a test report. The report shall include the following specific contents:a) References to this standard;
b) Description of the aircraft under test and its propulsion system, including propeller type, serial number and aircraft takeoff gross mass; Instruments used for recording, spectrum analysis and calibration, including manufacturer, model and serial number, and c) Location of the recording equipment in the aircraft;
Description of the flight conditions specified in 5.3 and the operating conditions of the engine, propeller or blade;d)
e) Operating conditions of audible sound sources not included in d); Rated position of the center of gravity of the aircraft when measuring the sound pressure signal inside the aircraft;f)
Rated amount of fuel when measuring the sound pressure signal inside the aircraft;g)
If special noise and vibration control systems are installed, their description, including propeller synchrophasers or engineh)
Blade synchronization device;
Use plane and section Description of the layout of the aircraft cabin, crew lounge, crew posts and aisles; i)
Description of the positions of seated and standing personnel in various areas during measurement; j)
k) Description of the locations of the measuring points for sound pressure level measurement using plan and section diagrams corresponding to the locations of the measuring points; Description of the test method;
If discrete frequencies and discrete frequency sound sources, transient sounds and beat frequencies exist, they should be indicated; All measured 1/3 octave band sound pressure levels and calculated octave band sound pressure levels are tabulated in printed or electronic format, and n)
Figures of sound pressure level spectra at corresponding measuring points can be provided;
For transient sounds, the maximum fast-shift time-weighted and A-weighted sound levels are tabulated in printed or electronic format; 0)
Values calculated based on the measured band-time-average sound pressure levels (such as speech interference level, A-weighted sound pressure level and broadband sound pressure level). When the test report contains A-weighted or broadband time-averaged sound pressure levels, the frequency range of the corresponding 1/3 octave band should also be given. When calculating the speech interference level, the corresponding octave band sound pressure level center frequency should also be given in the report. It is recommended that the test report should also provide an estimate of the expanded measurement uncertainty of the quantities that characterize the aircraft internal acoustic environment. 7.2 Report of sound pressure level results
The reference sound pressure of all sound pressure levels and derived acoustic quantities in the report is 20μPa. If the sound pressure level is to be rounded to an integer, it should be rounded up.
GB/T20248—2006/IS05129:2001A.1 Overview
Appendix A
(Informative Appendix)
Measurement uncertainty
A.1.1 A measurement is always accompanied by an uncertainty. Reference [2] provides a general method for determining measurement uncertainty, and reference [3] provides definitions of metrological terms.
A.1.2 The combined standard deviation of the uncertainty in the sound pressure level measurement is determined by the square root of the sum of the variances of all the associated uncertainties. The combined uncertainty of the cumulative indication value of the acoustic environment is different from the combined uncertainty of the corresponding 1/3 octave band or octave band sound pressure level. The square root of the sum of all applicable variances is the combined standard deviation of the uncertainty. The positive square root of each variance is the standard deviation of the uncertainty associated with its contribution.
A.1.3 The measurement uncertainty shall have a 95% confidence level as specified in document E2I and as approved by the ISO/TC43 Technical Committee responsible for international standards for acoustics. The interval on either side of a measurement result with a 95% confidence level will include several replicates of the measurement. The coverage factor multiplied by this interval is the expanded uncertainty of the quantity. The calculated combined standard deviation is multiplied by the "coverage factor" to obtain the expanded uncertainty of the measurement for a given location.
A.1.4 If the contributions of each variance in the determination of the combined standard deviation are normally distributed, a coverage factor of 2 approximates a 95 % confidence level. For some measurements, a coverage factor other than 2 may be required to achieve a 95 % confidence level. A.2 Application
A.2.1 For a given aircraft type and interior configuration and propulsion system, there is only one opportunity to measure the interior sound pressure level in accordance with this standard.
A.2.2 There are at least four sources that contribute independently to the combined standard deviation of the uncertainty in aircraft interior sound measurements. The estimate of the standard deviation is usually denoted by s. The sources include:
standard deviation SI related to the acoustic measuring instrument, which represents the deviation from the design target; - standard deviation Sp related to the characteristics of the sound field at the measurement location and the reproducibility of the measurement at a specific location (see 5.1.1); if the sound field contains discrete frequency components, there may be standing waves, and their influence must be considered when calculating the standard deviation (see 5.1.3); - standard deviation SF related to the reproducibility of flight conditions and the influence of the end flow of the air mass through which the aircraft flies on the measured sound pressure level. Flight conditions include the settings of the environmental control system, airspeed, altitude and engine power settings (see 5.2, 5.3); standard deviation Sc related to deviations in aircraft manufacturing and the effects of configuration changes between aircraft of a given model. The various standard deviations may be related to each other. The corresponding values of the standard deviations may also be related to the selection of the values representing the internal sound environment of the aircraft and the sound spectrum of the measurement location.
A.2.3 Assuming that all four independent standard deviations are used for one measurement, the general expression for calculating the expanded uncertainty of measurement U is as shown in equation (A.1):
U=±kVs+s++s
The coverage factor that achieves a 95% confidence level is represented by the symbol in equation (A.1). The units of the individual standard deviations of the aircraft interior acoustic environment indicator and the expanded measurement uncertainty are both decibels. The square of the standard deviation is the variance associated with the contribution. A.2.4 Of the various contributions to the combined standard deviation of equation (A.1), the standard deviation associated with the measuring instrument appears to be the smallest. For measuring instruments, the standard deviation can be minimized by calibration and the use of the adjustment methods of this standard. The standard deviation of the measuring instrument may be less than the allowable limit for design and manufacturing in the IEC standard referenced in this standard. A.2.5 The method of reference [2] recognizes two methods for calculating uncertainty: Type A and Type B. Type A uncertainty is obtained by statistical analysis of a series of observations, while Type B uncertainty is calculated based on the best available information, relevant experience and engineering judgment. Reference 6
Reference [2] provides guidance on the calculation of Type A and Type B uncertainties. GB/T20248--2006/IS05129:2001A. 2.6
6The contribution to the combined measurement uncertainty in equation (A.1) should be calculated as a Type B uncertainty. It is not possible to recommend a universally applicable method for calculating Type B uncertainties. For a given measurement, the appropriate allocation of uncertainty depends on a detailed understanding of the acoustic field, flight conditions, and the effects of the aircraft configuration. | |tt | IUPAP, OIML, 19945(ISBN92-67-10188-9)[3J International vocabulary of basic and general terms in metrology. BIPM, IEC, IFCC, ISO,IUPAC, IUPAP,OIML, 19943(ISBN92-67-01075-1)[4J ISO 9921-1, Ergonomic assessment of speech.communication-Part 1: Speech interferencelevel and communication distances for persons with normal hearing capacity in direct communication (SIL method)Speech interferencelevel and communication distances for persons with normal hearing capacity in direct communication (SIL method)
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.