The spe ifications ar int en ed t o achieve an acous ical cor elation betwe n t es ing the ext erior noise of ro d vehicles in a semi ane hoic chambe an outdo r t es ing as desc ibed in
General
Applicability and conditions
All accelerations are determined based on varying vehicle speeds recorded during testing, with these speeds calculated from the roller revolutions For example, in the case of AA’, vehicle speed is derived directly from the number of roller revolutions, ensuring precise measurement of acceleration performance This method provides accurate insights into vehicle dynamics across different test conditions.
AA' test i roller roller AA' test v = 3 6 ⋅ ⋅d ⋅n
The vehicle speed at the moment the reference point passes line AA’ during test run i is denoted as vAA' test i The dynamometer roller's diameter, represented as droller, plays a crucial role in calculating performance metrics Additionally, nroller AA’ test i indicates the revolutions per minute of the dynamometer roller for each test run, providing essential data for accurate testing analysis.
The test track is defined by the virtual line AA’ at its starting point and BB’ at its endpoint, as specified in ISO 362-1:2015, 7.1 The two pass-by microphones are positioned at the virtual point PP’ along the track, ensuring accurate sound measurement during testing.
The simulated vehicle speeds at points AA’ and PP’ (v AA’ and v PP’) are determined by the roller speed when the vehicle's reference point, as defined in ISO 362-1:2015, section 3.5, passes the virtual lines AA’ and PP’, respectively The simulated speed at point BB’ (v BB’) is recorded when the rear of the vehicle crosses the virtual line BB’ Additionally, the method used to calculate the acceleration must be clearly specified in the test report.
Given the wide range of automotive technologies, it is essential to adopt diverse calculation methods for accurate acceleration determination Modern innovations like continuously variable transmissions (CVTs) demand specialized analysis, while older technologies such as automatic transmissions without electronic control units require tailored approaches To ensure precise assessment, any alternative acceleration calculation methods must address the specific requirements of both advanced and legacy systems.
Calculation of total engine power
Battery state of charge
Calculation of acceleration
Calculation procedure for vehicles with manual transmission, automatic transmission, adaptive transmission, and continuously variable
transmission, adaptive transmission, and continuously variable transmission (CVT) tested with locked gear ratios
Calculation of the target acceleration
Calculation of the reference acceleration
Partial power factor, k P
Instruments for acoustical measurement
General
The sound pressure level should be measured using a sound level meter or an equivalent measurement system that meets Class 1 instrument standards, ensuring high accuracy The device should include a recommended windscreen if necessary for precise readings These measurement requirements are defined by the IEC 61672-1 standard, ensuring compliance and consistency in sound level assessments.
The entire measurement system shall be checked by means of a sound calibrator that fulfills the requirements of Class 1 sound calibrators according to IEC 60942.
Sound measurements should be conducted using time weighting “F” and frequency weighting “A” in accordance with IEC 61672-1 standards For systems that periodically monitor the A-weighted sound pressure level, data should be extracted at intervals no longer than 30 milliseconds to ensure accurate and consistent results.
When a definitive assessment of a sound level meter model's adherence to IEC 61672-1 full specifications is not possible, the measurement must be conducted using a sound level meter or an equivalent system that complies with Class 1 standards outlined in IEC 61672-3, ensuring accurate and reliable sound pressure level measurements.
IEC 61672-3 tests only a limited subset of the comprehensive specifications outlined in IEC 61672-1, which covers extensive criteria such as temperature ranges and frequency requirements up to 20 kHz Due to practical and economic constraints, it is not feasible to verify all IEC 61672-1 standards for each model of computerized data acquisition systems Currently, no available system fully complies with the entire IEC 61672-1 standards, making it difficult for users to prove complete conformity of their instrumentation to the test requirements.
When no general statement or conclusion can be made about conformity of the sound level meter by conformity of each channel of the array (this applies, e.g., if the signal of each individual microphone is used to recompose one overall time progression of the signal for the complete pass-by test, to which subsequently the A-weighted assessment is applied), a simulated pass-by run shall be performed at a constant roller speed of 50 km/h without a vehicle on the dynamometer while a constant tone signal is supplied to all channels of the array, e.g by using a signal generator The simulated A-weighted sound level is processed and the deviation from a reference tone signal shall be determined in accordance with IEC 61672-3.
Simulation algorithms using noise source localization detection should deactivate that feature for these tests.
A qualified calibration method (i.e electrical calibration) is recommended to be provided by the hardware supplier and, in that case, shall be implemented in the measurement software used.
The instruments shall be maintained and calibrated in accordance with the instructions of the instrument manufacturer.
Calibration
Prior to and following each measurement session, the complete sound measurement system must be verified using a sound calibrator as specified in section 6.1.1 The maximum allowable deviation between readings without any adjustments is 0.5 dB If this limit is exceeded, the measurement results obtained after the last successful calibration shall be considered invalid and discarded.
To ensure accurate sound measurements, the entire measurement system must be checked at the start and end of each session using a calibration system provided by the hardware supplier This electrical calibration, implemented in the measurement software, simulates a pass-by run as detailed in section 6.1.1 Regular calibration guarantees reliable results and maintains measurement integrity throughout the testing process. -**Sponsor**Looking to enhance your content creation process and ensure your articles comply with SEO rules? With [Blogify](https://pollinations.ai/redirect-nexad/y8YNDVUv), you can transform existing content into SEO-optimized blog posts effortlessly Blogify's AI-driven platform excels at identifying and rewriting important sentences to create coherent paragraphs, ensuring your articles are both meaningful and optimized for search engines Repurpose your content from various formats and boost your online visibility with ease using Blogify's versatile and user-friendly interface, streamlining your blogging efforts and engaging your audience like never before.
For this alternative, at least every six months, the entire sound measurement system shall be checked by means of a sound calibrator as described in 6.1.1.
Conformity with requirements
The sound calibrator must be verified annually to ensure it meets IEC 60942 standards, guaranteeing accurate calibration Similarly, the instrumentation system’s conformity with IEC 61672-3 should be checked at least every two years or following any system modifications such as updates to software or microphone components All conformity assessments must be performed by a laboratory accredited under ISO/IEC 17025 to ensure reliable and compliant testing.
Instrumentation for speed measurement
The rotational speed of the engine shall be measured using an instrument with an uncertainty of not more than ±2 % at the engine speeds required for the measurements being performed.
The vehicle's road speed must be measured with instruments that have an uncertainty of no more than ±0.5 km/h to ensure accuracy Road speed calculation is performed using roller speed measurements, providing a reliable method for assessing vehicle performance Accurate speed measurement is essential for vehicle testing and compliance with safety standards.
Meteorological instrumentation
The meteorological instrumentation used to monitor the environmental conditions during the test shall have an uncertainty of not more than the following:
— ±5 hPa for a barometric pressure measuring device;
— ±5 % for a relative-humidity measuring device.
General
One of the principal criteria of ISO 362-1 is testing in an acoustic free field.
To accurately replicate the acoustic criterion in a laboratory setting, the room design must mimic the effective propagation characteristics of an open space over a reflecting surface, as detailed in section 7.3 One effective solution is a semi-anechoic chamber constructed with absorptive materials to simulate outdoor acoustic conditions Various techniques are available for designing such test chambers, ensuring precise measurement and analysis of sound propagation An example of a suitable test room configuration is illustrated in Figure 1.
L left-hand side microphone array 4 virtual line AA’
L0 microphone array centre point 5 rear ventilation
R right-hand side microphone array 6 front ventilation
R0 microphone array centre point 7 rollers
1 absorbing elements 8 centre of room
2 virtual line BB’ 9 driving direction
Figure 1 — Example of a test room; configuration for rear wheel drive vehicles
Test room dimensions
All room dimensions shall be adjusted to meet the specific application for the products being tested.
The length of the room depends on several factors including the following:
— the length of the longest vehicle to be tested;
— the location where the relevant sound pressure levels are expected;
— the lowest frequency of concern (see 7.3).
To cover all possible cases, the minimum room length, lmin, room (base size), is recommended as follows: l min,room m+l veh + ⋅2 d absorb + ⋅ ⋅2 1 cut off
The original length of the test track is 20 meters The length of the longest vehicle to be tested, denoted as lveh, varies depending on vehicle categories For vehicles classified as M1 and M2 with a maximum authorized mass not exceeding 3,500 kg, lveh is specified as 5 meters For category N1 vehicles, lveh is determined based on specific testing requirements, ensuring accurate and standardized testing conditions across different vehicle types.
3 500 kg, and categories M3, N2 and N3; dabsorb is the thickness of absorbing elements;
1/4 λcut off is 1/4 of the wavelength at the cut-off frequency (2 times 1/4 wavelength from the outer microphones to the absorbing walls).
For optimal setup, refer to Annex E for detailed guidelines on minimum room length if initial specifications are unfeasible The room width (wroom) varies depending on whether the facility is single-sided or dual-sided, ensuring proper acoustic configuration In all cases, the distance from the centreline to the microphone line must be exactly 7.5 meters; reducing this distance is not allowed, even with sound pressure level adjustments These standards are essential for maintaining consistent acoustic performance and meeting regulatory requirements.
The width, wsingle,room, of single-sided facilities is as follows: single,room absorb veh w =7 5, + ⋅2 d + ⋅ ⋅2 1 + ⋅w
7,5 m is the original distance from the centreline to the microphone line; dabsorb is the thickness of absorbing elements;
The cutoff wavelength, denoted as 1/4 λ, corresponds to one-quarter of the total wavelength at the cutoff frequency This includes one-quarter of the wavelength from the microphones to the absorbing elements and an additional quarter wavelength from the vehicle to the absorbing elements The variable wveh represents the width of the vehicle, which is a key factor in determining the placement and effectiveness of absorbing components in noise control applications.
The width, wdual,room, of dual-sided facilities is as follows: dual,room w = ⋅2 7 5 + ⋅2 d + ⋅ ⋅2 1
7,5 m is the original distance from the centreline to the microphone line; d absorb is the thickness of absorbing elements;
1/4 λcut off is 1/4 of the wavelength at the cut-off frequency (two times 1/4 of the wavelength from the microphones to the absorbing elements).
For optimal performance, it is recommended to maintain a distance of one-quarter of the wavelength between microphones and absorbing elements in both single-sided and dual-sided facilities Failing to meet this spacing may compromise measurement accuracy, so it is essential to verify the free-field conditions at the microphone array, following the procedures outlined in section 7.3.
The minimum room height is determined by the vehicle height and the position of noise sources, such as the exhaust outlet (see Section 7.3) To effectively reduce noise influence, the distance between the noise source and absorbing elements should be at least half of the wavelength at the cut-off frequency, ensuring optimal sound absorption and noise control.
Acoustical qualification of the room
General
The free field shall meet the requirements of ISO 3745 or, alternatively, ISO 26101 To consider special use of the room, the validation shall be done for indoor microphone arrays.
Validation of free-field conditions
Three options of evaluation are possible to validate the free field conditions; see 7.3.2.2 to 7.3.2.4.
7.3.2.2 Validation of the inverse square law on lines from the centre of the room to microphone position
The sound source is positioned on the floor along the virtual line PP’, centrally located between the microphone arrays (see Figure 2) Sound propagation lines are drawn from the source to each microphone in the indoor arrays to evaluate system performance To optimize analysis efficiency, these lines can be reduced by selecting representative microphone positions and leveraging the room’s symmetry.
For each line, at least 10 equidistant points shall be measured (see Figure 2) and processed according to ISO 3745 or, alternatively, ISO 26101.
X distance from the sound source, m
• measured points on the line
Figure 2 — Example of validation according to 7.3.2.2
7.3.2.3 Validation of the inverse square law with at least one line from the centre of the room to a microphone position and the points of concern of the microphone arrays
The source is placed on the floor on the virtual line PP’ in the centre between the microphone arrays (see Figure 3) A line to be evaluated is plotted from the source to each microphone at the corners At least
Ten equidistant measurement points will be established, including specific points of concern for indoor microphone arrays, as illustrated in Figure 3 All measurements taken at these points will be processed in accordance with ISO 3745 or, alternatively, ISO 26101 standards to ensure accurate and compliant acoustic data analysis This approach guarantees precise evaluation of indoor microphone array performance for optimal sound quality and noise control.
X distance from the sound source, m
• measured points on the line
∘ measured points on the microphone array
Figure 3 — Example of validation according to 7.3.2.3
7.3.2.4 Validation of the inverse square law along the complete microphone arrays
The source is positioned on the floor along the virtual line PP’ at the center between the microphone arrays, as shown in Figure 4 Free-field conditions are confirmed along both the left (L) and right (R) microphone array lines, each situated 7.5 meters from the room's center line in the direction of travel Tests are conducted along the full length of the microphone array lines, typically 20 meters, at measurement points located 1.2 meters above each microphone position Symmetrical testing can be performed on both sides of the lines L and R, using the intersection points R0 and L0 with the virtual line PP’ at microphone height as reference starting points.
To evaluate measured sound pressure levels in accordance with the inverse square law, calculate the theoretical level decay at each microphone test position using the individual path lengths, denoted as rn, from the source to each measurement point along lines L and R These calculations should also incorporate the reference path length, r0, which corresponds to the center measurement position, ensuring accurate comparison between measured and theoretical sound pressure levels.
With the source on the floor and the reference microphone at the centre measurement position, the reference path length, r 0 , is given by Formula (5): r 0 = ( ,7 5m) 2 + 1 2, m) 2 =7 595, m (5)
The path lengths, denoted as rₓ, from the microphone positioned at distance x to the reference microphone are described by Formula (6): rₓ = √(r₀² + x²) Here, x_micro represents the microphone’s position within the array along the driving direction, measured as the distance from the reference microphone position.
The relative sound pressure level decay, ΔL x , is then computed according to Formula (7):
• measured points on the line
Figure 4 — Example of validation according to 7.3.2.4
These predicted relative sound pressure level decays are used for the comparison with the measured sound pressure levels at the same measurement positions (see Figure 4) The centre positions R0 and
Microphone lines R and L at L0 serve as references for measuring the relative sound pressure level decay The differences between the measured and predicted decays are compared against permissible deviations specified in section 7.3.3 This comparison ensures accuracy in sound level measurements and adherence to standards Proper reference points and deviation checks are essential for reliable acoustic analysis.
Qualification procedure
The lowest frequency which meets the requirements given in Table 2 defines the cut-off frequency of the room The cut-off frequency of the room shall be less than the lowest frequency of concern Frequency of concern referred to a single frequency or band which influences the overall level by more than 0,4 dB.
NOTE For evaluation below 100 Hz, ISO 3745 indicates that difficulties can occur due to the growth of the nearfield of the source.
The deviations of measured sound pressure levels from those estimated using the inverse square law shall not exceed the values given in Table 2.
Table 2 — Maximum permissible deviation of measured sound pressure levels from theoretical levels using the inverse square law
One-third-octave-band mid frequency
NOTE An additional tolerance of 1 dB has been added on the ISO 3745 requirement considering that indoor pass-by is an engineering and not a laboratory method.
Condition of the floor
The absorption coefficient of the floor shall not exceed the coefficient defined in ISO 10844 for propagation area.
Cooling, ventilation, air temperature, exhaust gas management
The room temperature shall be within the limits as defined in ISO 362-1:2015, 7.3, i.e 5 °C to 40 °C.
During the measurements, the exhaust system of the vehicle shall be acoustically fully exposed to the acoustic space Exhaust gas extraction systems present inside the room are not recommended.
When utilizing dedicated exhaust gas extraction systems, it is essential to position the devices at least 0.5 meters away from the tailpipe outlet to ensure effective operation Additionally, these systems must be installed in a manner that does not obstruct the line of sight from the exhaust outlet to any microphones within the microphone arrays, optimizing acoustic measurement accuracy Proper placement of exhaust extraction devices helps maintain safety standards and enhances the performance of acoustic testing setups.
The volume flow of the room ventilation system is dependent on the room dimensions, the geometry, and orientation of the test object and the type of test run.
Installing an air conditioning system is recommended to effectively cover a wide range of room temperatures This ensures a comfortable indoor environment by mimicking outdoor track temperature conditions, making it ideal for various applications.
All safety regulations for indoor testing facilities concerning harmful substances shall be fulfilled.
Background noise
According to ISO 362-1:2015, section 7.3, indoor test facilities must be designed to maintain background noise levels at least 10 dB below the maximum A-weighted sound pressure level emitted by the vehicle during testing This includes noise from air handling systems and vehicle cooling If the background noise level is between 10 dB and 15 dB below the vehicle's noise level, measurements should be corrected based on the guidelines outlined in Table 3 Ensuring proper noise level separation is essential for accurate vehicle noise testing and compliance with international standards.
Table 3 — Correction for background noise
Level difference from background noise to maximum sound pressure level of the vehicle under test, dB 10 11 12 13 14 15
Type of texture of the rollers
The texture of the rollers shall be rough enough to transfer the torque of the tested vehicle under the required conditions.
NOTE A texture comparable to an abrasive paper P80 or P100 (as defined in ISO 6344–1) is a good compromise between grip and emitted noise.
Diameter of the rollers
The roller diameter of a four-wheel dynamometer is constrained by the shortest wheelbase of the vehicle being tested, ensuring proper fit and functionality To optimize performance, the roller diameter should be as large as possible, which helps minimize acoustical effects compared to a flat track Increasing roller size enhances measurement accuracy while reducing noise disturbances during testing.
NOTE For example, a diameter of 1,91 m (6 m circumference) is applicable for vehicles with a wheelbase down to 2,2 m (with consideration of some tolerance between the rollers).
1 wheel base d roller diameter t tolerance
Reproducibility of the pass-by dynamics
The dynamometer must accurately follow the rapid transient cycles of vehicle acceleration, ensuring its response time does not exceed that of the vehicle being tested This is essential for precise measurement and reliable performance testing under dynamic conditions.
To ensure accuracy, the vehicle on the roller bench must replicate outdoor dynamics, measured by average engine and vehicle speeds from at least four outdoor and indoor tests The results should match within a maximum deviation of ±2% between points PP’ and BB’ for vehicles in categories M1 and M2 weighing up to 3,500 kg and N1 vehicles Due to increased variation in measurements, a higher maximum deviation is permitted for M2 vehicles exceeding 3,500 kg.
Single-axle or multi-axle operation
When evaluating variant A (see 10.1), which assesses tyre/road noise independently on an outdoor test track and combines these results with powertrain noise from indoor testing, it is advisable to minimize the number of driven axles Using the fewest driven axles helps reduce tyre/road noise interference on the dynamometer, ensuring more accurate and reliable test results.
When using variant B (see 10.1), which measures the overall vehicle noise directly on the dynamometer, it is recommended to use the operation of all axles of the vehicle under test.
Noise emission limit under operating conditions produced by the dynamometer rollers 16
The noise emitted by the roller bench under operating conditions (without vehicle on the rollers) shall be low enough not to influence the expected sound levels of interest.
Normally, this is fulfilled if the difference between the measurements with and without vehicle is greater than 15 dB (measured with the microphones at the 7,5 m line).
Typical measurements taken 1.2 meters above the rotating dynamometer indicate that A-weighted sound pressure levels remain below 45 dB up to approximately 70 km/h, regardless of drum speed The primary contributor to the roller bench sound pressure level is the air-handling noise, which dominates the overall sound environment Achieving sound pressure levels below 45 dB for both air-handling and dynamometer noise is feasible, ensuring quieter operational conditions.
General
Tyre selection and tyre condition
When using variant A (see 10.1), which measures tyre/road noise independently on the test track, it is essential to ensure minimal tyre noise on the rollers Slick tyres with no tread are suitable for achieving this low noise level, while incorporating noise barriers can also be effective, provided that sound propagation from other sources is not obstructed.
If using variant B (see 10.1), the tyres shall be appropriate for the vehicle and shall be inflated to the pressure recommended by the vehicle manufacturer for the test mass of the vehicle.
Using snow tyres, traction tyres, and special-use tyres can lead to inconsistent results due to factors like temperature behavior and tread pattern influence Therefore, these types of tyres should not be used to ensure reliability and safety.
For certification and related purposes, tyres must meet specific regulatory requirements, including selection criteria set by the vehicle manufacturer The tyres used for testing should match one of the sizes and types specified by the manufacturer and be commercially available at the time of vehicle release Additionally, the tread depth must conform to ISO 362-1:2015, 8.2.3 standards to ensure safety and compliance.
NOTE The tread depth can have a significant influence on the acoustic test result.
The exact knowledge of the tyre noise is crucial to obtain reliable results For this reason, the condition of the tyres shall be observed very exactly.
Operating conditions
500 kg, and N1
Vehicles of categories M2 having a maximum authorized mass exceeding
9.5.2.2.2 Vehicles of category M2 having a maximum authorized mass exceeding 3 500 kg, and category N2
9.5.2.3.2 Manual transmission, automatic transmission, adaptive transmission, or transmission with continuously variable gear ratio (CVT) tested with locked gear ratio
9.5.2.3.3 Automatic transmission, adaptive transmission, and transmission with variable gear ratio tested with non-locked gear ratio
9.5.2.3.4 Power trains with no rotational engine speed available
Measurement readings and reported values
At least four measurements for all test conditions shall be made on each side of the vehicle and for each gear ratio.
During each vehicle run between the virtual lines AA’ and BB’, record the maximum A-weighted sound pressure level to the first significant digit after the decimal Any abnormal sound peaks that stand out significantly from the overall sound pressure level should be discarded to ensure accurate measurement.
The initial four valid consecutive measurement results under any test condition, allowing for the exclusion of non-valid results within 2.0 dB, are used to calculate the appropriate intermediate or final measurement outcome.
The speed measurements at lines AA’, BB’, and PP’ shall be noted and used in the calculations to one digit after the decimal place.
500 kg, and of category N1
Vehicles of categories M2 having a maximum authorized mass exceeding
Measurement uncertainty
The measurement procedure outlined in 9.6 is influenced by various parameters such as surface texture variations, environmental conditions, and system uncertainties, which can cause fluctuations in the observed sound levels for the same vehicle These perturbations are often unpredictable in origin and impact, making the results inherently uncertain To evaluate this uncertainty, the procedure recommended by ISO/IEC Guide 98-3 is applied, supplemented by interlaboratory comparisons based on ISO 5725, though comprehensive data are limited The uncertainties, as shown in Table 5, are derived from statistical data, tolerance analyses, and engineering judgment, and are categorized into three groups: (a) minor variations within the same indoor test facility and test series; (b) day-to-day variations within the same facility due to changing ambient conditions and equipment; and (c) differences between indoor test sites, considering factors like ambient conditions, equipment, staff, and outdoor road surface variations for tire/road noise measurements.
For accurate measurement reporting, include the expanded measurement uncertainty along with the corresponding coverage factor, ensuring a coverage probability of 80% in accordance with ISO/IEC Guide 98-3 Detailed guidance on determining the expanded uncertainty can be found in Annex D.
NOTE Annex D gives a framework for analysis in accordance with ISO/IEC Guide 98-3, which can be used to conduct future research on measurement uncertainty for this part of ISO 362.
Table 5 presents the uncertainty data for all vehicle categories according to ISO 362, with a coverage probability of 80% These values reflect the variability of test results for individual vehicles but do not account for broader product variations.
Table 5 — Variability of measurement results for a coverage probability of 80 %
Vehicle category Run-to-run dB
M1, M2, M3 and N1, N2, N3 0,3 0,5 to 0,9 1,4 a The actual measurement uncertainty for the day-to-day situation is dependent on which kind of test room, e.g open test room, or which kind of climatic control is used A lower temperature variation causes a smaller measurement uncertainty.
10 Test methods and test report
General
There are two methods for conducting an indoor pass-by test The first, Variant A, involves measuring powertrain noise on a dynamometer in accordance with ISO 362-1 standards, combined with the energetic addition of tyre/road noise, which is measured separately on an outdoor test track (see section 10.2).
Variant A
This method is a combination of indoor testing (power train noise) and outdoor testing (tyre/road noise).
Routine measurement of tyre/road noise is not required for every vehicle test; instead, data from multiple tyre samples can be stored in a database, enabling the use of pre-existing matching data sets to streamline testing processes and improve efficiency.
It shall be ensured that there is no remaining tyre/road noise affecting the measurements.
NOTE For example, this can be accomplished by using tyres with no tread (slicks).
Ensure that the remaining tyre/road noise is at least 10 dB below the maximum A-weighted sound pressure level produced by the vehicle during testing If this criterion cannot be met, a correction must be applied, as detailed in section B.6.
The vehicle shall be measured according to the operating condition specified in 9.5.
Tyre/road noise measurements should be conducted on a test track in accordance with ISO 10844 standards The assessment of tyre noise involves two key procedures: first, evaluating free rolling noise; and second, determining tyre/road noise that accounts for torque influence, which can be derived from the free rolling noise using a simplified method.
All conditions for evaluation of tyre/road noise, free rolling noise, and torque influence are described in Annex B.
10.2.4 Calculation of the total vehicle noise using variant A
The total vehicle noise LTVN is the energetical sum of tyre/road noise LTRN and power train noise LPTN This calculation shall be carried out for each single run.
The calculation of the tyre/road noise is described in B.5.
Test report
The test report must reference ISO 362-3 and include details of the test site, ambient conditions such as air temperature, barometric pressure, and humidity It should specify the measuring equipment used, the maximum background noise level, and vehicle identification information—including engine type, power, transmission system with ratios, tyre size, pressure, and type, test mass, power-to-mass ratio, vehicle dimensions, and reference point location Details of the transmission gears employed, initial vehicle and engine speeds, and the starting point of acceleration are essential The report must record vehicle and engine speeds at key test points (line PP’ and end of acceleration), outline the calculation method for acceleration, and specify whether variant A or B is used for tyre/road noise analysis Any auxiliary vehicle equipment and its operating conditions should be documented Finally, all valid A-weighted sound pressure levels measured during testing, categorized by vehicle side and movement direction, must be included.
Annex A (normative) Validation of method
This annex defines a procedure which shall be used to ensure that the used method delivers results within a defined accuracy.
To ensure the transparency and reliability of the measurement method, it is essential to compare indoor results with real outdoor measurements This comparison helps validate the accuracy of the method by demonstrating that the deviation between the two sets of data remains within an acceptable range Such validation confirms the method's effectiveness and supports its practical application in real-world conditions.
In order to check whether the method used is delivering stable results, this validation shall be repeated after any relevant software release.
The validation process is shown in Figure A.1.
Accelerated indoor measurement according to variant A
Accelerated outdoor measurement according to ISO 362-1
Figure A.1 — Chart for the process of validation
Additional validations with changed boundary conditions shall deliver results with a comparable precision.
NOTE Changed boundary conditions can include different vehicles, different environmental conditions, like temperature or different tyres.
A.2.2 Master measurement for validation (outdoor measurement according to ISO 362-1)
A complete accelerated test as described in ISO 362-1:2015, 8.3.1.4, shall be carried out.
The environmental conditions (especially the air temperature) shall be within a range which can be simulated in the test room.
The following should be reported:
— surface temperature of the catalyst or the diesel particulate filter;
— surface temperature of the rear muffler;
The measured temperatures of the exhaust system should be within a range of 30 °C during four valid measurements Intake air temperatures should be within a range of 10 °C during 4 valid measurements.
If using the indoor variant A (see 10.2), additional tyre rolling noise measurements as described in Annex B shall be carried out.
A.2.3 Validation measurement (indoor measurement according variant A or variant B)
A complete accelerated test as described in this part of ISO 362 (variant A or variant B) shall be carried out, using the same vehicle as used during the master measurement (see A.2.2).
The following parameters shall be controlled:
— intake air temperature compared to the intake air temperature of the master measurement (average of four valid measurements);
— surface temperature of the exhaust system compared to the master measurement (average of four valid measurements);
— engine speed curves shall be within a range of ±2 % compared to the master measurement for vehicles of category M1, M2 not exceeding 3 500 kg, and N1;
— engine speed curves shall be within a range of ± 4 % compared to the master measurement for vehicles of category M2 exceeding 3 500 kg, M3, N2, and N3;
— vehicle speed curves shall be within a range of ±1 km/h compared to the master measurement. A.2.4 Evaluation of the results
The deviation of Lwot between the both measurements (indoor and outdoor) shall not exceed 1 dB.
The deviation of L crs between the both measurements (indoor and outdoor) shall not exceed 1 dB.
Basis of an exact validation are comparable relevant parameters (within the above-mentioned tolerances) Examples for a validation (variant A) are shown in Figures A.2 and A.3.
Y2 catalyst temperature, °C 3 limits of 5 °C temperature range
Y3 rear muffler temperature, °C 4 limits of 15 °C temperature range
Y4 speed, km/h a Deviation of speed is ±1 km/h.
Y5 engine rotational speed, r/min b Deviation of engine rotational speed is ±2 %.
Figure A.2 — Examples for the most relevant parameters
X x-position, m 3 power train noise indoor
Y1 sound pressure level, dB(A) 4 tyre/road noise calculated
1 total vehicle noise outdoor 6 lower limit of permissible maximum deviation
2 total vehicle noise indoor 7 upper limit of permissible maximum deviation Figure A.3 — Example of an indoor/outdoor validation with indication of the permissible maximum deviation
Procedure for measurement, evaluation, and calculation of tyre/ road noise when using variant A
This annex outlines the method for measuring and evaluating tyre/road noise using variant A, as described in section 10.2 The approach involves decomposing tyre/road noise into its main components—free rolling noise and torque influence—and modeling these with specific regression techniques The analysis yields a dataset of regression coefficients for each test track position, which are specific to the track used during the measurement process.
The vehicle used shall be representative of vehicles to be tested indoors.
The test motor vehicle shall have the same number of axles as the vehicle tested indoors or two axles, with two test tyres on each axle by default.
The weight on each tyre of the vehicle shall be equal or higher to vehicles to be tested indoors.
The vehicle’s track width and wheelbase fitted with test tyres shall be equal to vehicles to be tested indoors ±25 %.
To ensure that tyre noise is not significantly affected by the test vehicle design, the following requirements shall be fulfilled:
— spray suppression flaps or other extra devices to suppress spray shall not be fitted;
— addition or retention of elements in the immediate vicinity of the rims and tyres which might screen the emitted sound is not permitted;
— wheel alignment (toe in, camber, and caster) shall be checked on the unloaded vehicle and found to be in full accordance with the vehicle manufacturer’s recommendations;
— additional sound absorbing material shall not be mounted in the wheel housings or under the underbody;
— the windows and sliding roof of the vehicle shall be closed during testing.
To ensure that there is no power train noise affecting the measurements, the use of a silent propulsion vehicle is recommended (tyre test vehicle) If such a vehicle is not available, using a normal vehicle to measure the free rolling noise is possible A “simplified procedure” may then be used for the torque influence evaluation.
When a normal vehicle is used (not a tyre test vehicle), the following conditions apply:
— the transmission is in neutral position;
— the engine is switched off or at idle In this case vehicle noise shall be evaluated at idle to ensure that it does not affect the free rolling noise.
When a tyre test vehicle is used, it shall be ensured that the remaining power train noise shall be at least
The vehicle's noise level must be at least 10 dB below the A-weighted sound pressure produced under all relevant driving conditions specified in the acceleration test section 9.5.1.4 This requirement is verified by conducting the test on a dynamometer equipped with fitted slick tires and additional noise barriers on the tires to suppress tyre/roller noise, ensuring accurate measurement of the vehicle's sound emission.
To meet these testing requirements, a tyre test vehicle can either be an internal combustion engine vehicle or an electric vehicle Essential components such as the powertrain, exhaust system, intake system, transmission, and other major accessories operating during the test may be encapsulated to ensure accurate and reliable results.
Figure B.1 shows an example for a checking procedure of a tyre test vehicle It is applicable to all vehicle categories of this part of ISO 362.
Vehicle with encapsulated engine or electric vehicle
Measure cruise noise (CRS) Measure free rolling noise (FRN)
Measure noise with wide open throttle (WOT)
35 km/h at BB', n BB' = n targetb yes no yes no
Engine is silent Engine is not silent
Tyre masking is ef?icient, evaluation of the silent vehicle is valid
Tyre not correctly masked, 10 dB will be dif?icult to reach
Improve masking of tyres and go to step “Masked tyres”
Key a For vehicles of category M1, M2 not exceeding 3 500 kg, and N1. b For vehicles of category M2 exceeding 3 500 kg, M3, N2, and N3.
Figure B.1 — Example for a checking procedure of a tyre test vehicleB.2.3 Tyre conditions
Test tyres must be mounted on rims approved by the tyre manufacturer to ensure safety and compatibility Tyre inflation pressure should not exceed the manufacturer's recommended levels for indoor testing If the test vehicle's weight exceeds that of the indoor-tested vehicle, it is acceptable to adjust the tyre inflation pressure (Ptest) during testing to maintain an equivalent tyre footprint, ensuring accurate and consistent results.
Pref is the inflation pressure recommended by the manufacturer;
Q test is the weight of the tyre test vehicle;
Qref is the weight of the vehicle to be tested indoors.
To adapt rolling noise testing conditions from track to indoor, a temperature correction of the tyre rolling noise level LTRN is needed using the following relationship:
LTRN(20 °C) = LTRN(ϑ) + C ⋅ (20 °C − ϑ) (B.2) where ϑ is the measured temperature of the test track surface in degree Celsius (° C);
For C1 tyres (passenger cars), the coefficient C is:
For C2 tyres (heavy commercial vehicles), the coefficient C is:
NOTE The tyre classes are defined in ISO 13325:2003, 3.1.
B.3 Procedure for tyre/road noise evaluation
B.3.1 Vehicle operating conditions for the free rolling noise component
Several pass-by measurements shall be carried out with different constant speeds.
Vehicles classified as M1 and M2 with a maximum authorized mass up to 3,500 kg should have a speed range from 40 km/h to 90 km/h, increasing in 10 km/h steps Similarly, category N1 vehicles fall within this speed range For larger vehicles, such as M2 exceeding 3,500 kg, M3, N2, and N3 categories, the speed range is set from 25 km/h to 65 km/h, also in 10 km/h increments If noise measurement reproducibility is maintained within a spread of less than ±0.3 dB, the number of testing runs and the designated speed range can be adjusted accordingly.
For each side of the test vehicle, at least four measurements should be taken at test speeds below each specified reference speed and at least four measurements at speeds above those reference speeds These measurements must be taken at speeds that are approximately equally spaced within the respective speed ranges.
When measuring free rolling noise with a standard vehicle, the vehicle should approach the measurement area at a speed just above the target speed near line PP’ As it enters the measurement zone, the engine should be switched off if possible or the gear lever placed in neutral to allow for smooth, controlled deceleration The vehicle must then decelerate at a rate not exceeding 0.3 m/s² before crossing line AA’, ensuring accurate noise measurement conditions.
Figure B.2 shows an example for vehicle speed profiles to determine the free rolling noise component.
Figure B.2 — Example for vehicle speed profiles to determine the free rolling noise component
B.3.2 Vehicle operating conditions for the torque influence component
This procedure is possible only with a tyre test vehicle In case of a normal vehicle, the torque influence is evaluated with the simplified procedure described in B.3.3.
Several accelerated pass-by measurements will be conducted using varying acceleration levels, ranging from zero up to the maximum available acceleration It is important to ensure that the acceleration does not exceed the specified maximum limit to maintain measurement accuracy and safety These measurements are essential for analyzing vehicle performance and noise emissions under different dynamic conditions Proper testing protocols should be followed to obtain reliable and consistent results for comprehensive assessment.
3 m/s 2 and the step size shall not exceed 1 m/s 2 The speed range shall correspond approximately to the typical testing situation (e.g for M1 from 40 km/h to 60 km/h at line PP’, and for N3 from 25 km/h to 45 km/h at line BB’).
For accurate and consistent tyre/road noise measurements, it is recommended to perform tests that account for torque influence and are conducted under free rolling conditions Conducting two consecutive test series under similar environmental conditions ensures reliable results, minimizing variability and improving the correlation of data across measurements.
Figure B.3 shows an example for vehicle speed profiles to determine the torque influence component.
Figure B.3 — Example for vehicle speed profiles to determine the torque influence component
B.3.3 Simplified procedure for the torque influence component
When a test vehicle is unavailable, the torque influence component can be estimated from free rolling noise measurements using a standard torque influence function This approach assumes the standard function remains consistent across different x-positions and is solely dependent on acceleration The torque influence component of the sound pressure level, ΔL TI, is calculated with the formula: ΔL TI (a, x) = 2 ⋅ ζ ⋅ a² (x) + ζ ⋅ a(x), where ζ represents the coefficient of the standard torque influence, a is the vehicle acceleration during the powertrain noise measurement, and x denotes the vehicle's x-position.
Experience shows that the coefficient ζ is between 0,075 for loud test tracks and 0,15 for quieter test tracks.
If this simplified method is used, the attributes of the test track used need to be known.
Free rolling noise measurement with a standard vehicle must be conducted with the engine off, preventing accurate measurement at a constant speed To ensure reliable results, it is crucial that the vehicle's deceleration does not exceed 0.3 m/s² during testing Maintaining controlled deceleration is essential for consistent and valid noise measurement outcomes.
Figure B.4 shows an example for the standard function torque influence.
Figure B.4 — Example for standard function torque influenceFigure B.5 gives, by way of an example, a procedure for checking which method to use.
B.4 Calculation of tyre/road noise coefficients