ISO 362-3:2022

INTERNATIONAL ISO
STANDARD 362-3
Second edition
2022-09
Acoustics — Measurement of noise
emitted by accelerating road vehicles
— Engineering method —
Part 3:
Indoor testing M and N categories
Acoustique — Mesurage du bruit émis par les véhicules routiers en
accélération — Méthode d'expertise —
Partie 3: Essais en intérieur pour les catégories M et N
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms.2
5 Acceleration for vehicles of categories M1 and M2 having a maximum authorized
mass not exceeding 3 500 kg, and of category N1 . 5
5.1 Applicability and conditions . . . 5
5.2 Calculation of acceleration . 5
5.2.1 Calculation procedure for vehicles with manual transmission, automatic
transmission, adaptive transmission, and continuously variable
transmission (CVT) tested with locked gear ratios . 5
5.2.2 Calculation procedure for vehicles with automatic transmission, adaptive
transmission, and CVT tested with non-locked gear ratios. 5
5.3 Calculation of the target acceleration . 5
5.4 Calculation of the reference acceleration . 5
5.5 Partial power factor, k . 6
P
6 Instrumentation . 6
6.1 Instruments for acoustical measurement . 6
6.1.1 General . 6
6.1.2 Calibration . . . 6
6.2 Conformity with requirements. 7
6.3 Instrumentation for speed measurement . 7
6.4 Meteorological instrumentation . 7
7 Test room requirements . 7
7.1 General . 7
7.2 Test room dimensions . 8
7.2.1 Test room dimensions for measurements where the length of the test track
is greater than 20m . 10
7.3 Acoustical qualification of the room . 11
7.3.1 General . 11
7.3.2 Validation of free-field conditions of the microphone array . 11
7.3.3 Qualification procedure . 14
7.4 Condition of the floor .15
7.5 Cooling, ventilation, air temperature, exhaust gas management.15
7.6 Background noise. 15
8 Dynamometer requirements .16
8.1 Type of texture of the rollers . 16
8.2 Diameter of the rollers. 16
8.3 Reproducibility of the pass-by dynamics. 17
8.4 Single-axle or multi-axle operation . 17
8.5 Noise emission limit under operating conditions produced by the dynamometer
rollers . 17
9 Test procedures .18
9.1 General . 18
9.2 Microphone array — Hardware and software . 18
9.3 Vehicle fixing system . 18
9.4 Conditions of the vehicle . 18
9.4.1 General conditions . 18
9.4.2 Test mass of the vehicle . 19
iii
9.4.3 Tyre selection and tyre condition . 19
9.4.4 Calculation of total engine power . 20
9.4.5 Battery state of charge . . .20
9.4.6 Additional sound emitting devices . 20
9.4.7 Vehicle cooling fans or cooling systems . 20
9.5 Operating conditions . 20
9.5.1 Vehicles of categories M1, M2 having a maximum authorized mass not
exceeding 3 500 kg, and N1 . 20
9.5.2 Vehicles of categories M2 having a maximum authorized mass exceeding
3 500 kg, M3, N2 and N3 . 21
9.6 Measurement readings and reported values . 22
9.6.1 General .22
9.6.2 Data compilation .23
9.6.3 Vehicles of categories M1 and M2 having a maximum authorized mass not
exceeding 3 500 kg, and of category N1 . 23
9.6.4 Vehicles of categories M2 having a maximum authorized mass exceeding
3 500 kg, M3, N2, and N3 . 23
9.7 Measurement uncertainty . .23
10 Test methods and test report .24
10.1 General . 24
10.2 Variant A . 24
10.2.1 General . 24
10.2.2 Power train noise . 24
10.2.3 Tyre/road noise .25
10.2.4 Calculation of the total vehicle noise using variant A . 25
10.3 Test report . 25
Annex A (normative) Validation of method .27
Annex B (normative) Procedure for measurement, evaluation, and calculation of tyre/road
noise when using variant A .31
Annex C (informative) Procedure for description of tyre torque influence by an energetic
model .49
Annex D (informative) Procedure for measurement, evaluation, and calculation of tyre/
road noise when using variant B .54
Annex E (informative) Measurement uncertainty — Framework for analysis according to
ISO/IEC Guide 98-3 .56
Annex F (informative) Room length deviation from recommendation .64
Bibliography .66
iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This second edition cancels and replaces the first edition (ISO 362-3:2016), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Improvement of the wording for a better understanding
— Definition of a data exchange format for the tyre-/road noise coefficients
— Introduction of an energetic model of the tyre torque influence (Annex C)
— Revision of 9.7, Annex B and Annex E.
A list of all parts in the ISO 362 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
The external sound emission of a vehicle is one out of a multitude of requirements that needs to be
considered by manufacturers during design and development of vehicles. For health and environmental
protection reasons, the sound emission should be reduced under all relevant driving conditions.
However, there is a growing awareness that vehicles should not be too quiet either to ensure that they
are still acoustically perceivable by pedestrians and don’t endanger them as they might be missed.
To meet all these demands, an efficient test site is needed that can be operated the whole year round,
independent of weather conditions or other outside factors. In many countries, the meteorological
conditions are so adverse that outdoor testing on a classical proving ground is only possible in a very
limited timeframe. While this was acceptable in the past, the increasing workload in the future will
make it nearly impossible to do the complete development of a vehicle on a single test track at one
particular place. However, performing sound emission tests on various test tracks highly increases the
uncertainty and multiplies the workload for a manufacturer.
This document gives specifications for an indoor noise test bench and a test procedure that delivers
precise results for indoor testing, comparable to a certified type approval test track. The results are
intended to be within the run-to-run variation of the actual valid exterior noise test described in
ISO 362-1, which is the test standard used for type approval of vehicles.
An indoor test bench requires tight specifications for the equipment and set up, such as the acoustical
treatment, the microphone arrays, the roller bench, the adjustment for the dynamic behaviour of the
vehicle on the roller test bench, the preconditioning of the vehicle, as well as the thermal conditions for
testing. Special treatment needs to ensure that all rolling sound components of the tire are comparable
to the rolling sound on a road surface as specified in ISO 10844 and as applied in type approvals.
It is conceivable that in the future, certain sound emissions of vehicles (like e.g. minimum sound
emission of electric vehicles) can be verified on an indoor test bench, as the natural background noise
might prohibit testing on a classical outdoor test track. The specifications set forth in this document
could be transferred to a future minimum noise test procedure.
This document provides all necessary specifications and procedures to ensure comparability between
todays common and well accepted testing on outdoor test tracks with future indoor facilities. It
incorporates all relevant International Standards for equipment, measurement uncertainty, and test
procedures.
vi
INTERNATIONAL STANDARD ISO 362-3:2022(E)
Acoustics — Measurement of noise emitted by accelerating
road vehicles — Engineering method —
Part 3:
Indoor testing M and N categories
1 Scope
This document specifies an engineering method for measuring the noise emitted by road vehicles of
categories M and N by using a semi anechoic chamber with a dynamometer installed.
The specifications are intended to achieve an acoustical correlation between testing the exterior noise
of road vehicles in a semi anechoic chamber and outdoor testing as described in ISO 362-1.
This document provides all necessary specifications and procedures for indoor testing to obtain results
which are comparable to typical run-to-run variations of measurements in today’s type approval tests.
This document provides a method designed to meet the requirements of simplicity as far as they are
consistent with the reproducibility of results under the operating conditions of the vehicle.
NOTE 1 The results obtained by this method give an objective measure of the noise emitted under the specified
conditions of test. It is necessary to consider the fact that the subjective appraisal of the noise annoyance of
different classes of motor vehicles is not simply related to the indications of a sound measuring system. As
annoyance is strongly related to personal human perception, physiological human conditions, culture, and
environmental conditions, there is a large variation and annoyance is therefore not useful as a parameter to
describe a specific vehicle condition.
NOTE 2 If measurements are carried out in rooms which do not fulfil the requirements stated in this
document, the results obtained can deviate from the results using the specified conditions.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 362-1, Measurement of noise emitted by accelerating road vehicles — Engineering method — Part 1: M
and N categories
ISO 1176, Road vehicles — Masses — Vocabulary and codes
ISO 2416, Passenger cars — Mass distribution
ISO 3745, Acoustics — Determination of sound power levels and sound energy levels of noise sources using
sound pressure — Precision methods for anechoic rooms and hemi-anechoic rooms
ISO 10844, Acoustics — Specification of test tracks for measuring sound emitted by road vehicles and their
tyres
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 26101, Acoustics — Test methods for the qualification of free-field environments
IEC 60942, Electroacoustics — Sound calibrators
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
IEC 61672-3, Electroacoustics — Sound level meters — Part 3: Periodic tests
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 362-1, ISO 1176 and ISO 2416
and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
virtual vehicle speed
virtual speed of the test vehicle calculated from the circumference and the revolutions of the roller
Note 1 to entry: See Formula 1.
3.2
virtual line AA'
virtual position for the definition of the virtual vehicle speed (3.1), v
AA’
3.3
virtual line PP'
virtual position for the definition of the virtual vehicle speed (3.1), v
PP’
3.4
virtual line BB'
virtual position for the definition of the virtual vehicle speed (3.1), v
BB’
4 Symbols and abbreviated terms
Table 1 lists the symbols used in this document and the clause number where they are used for the first
time.
Table 1 — Symbols used and corresponding clauses
Symbol Unit Clause Designation
a, a m/s B.3.3 vehicle acceleration (at power train noise measurement)
PTN
AA' — 3.1 line perpendicular to vehicle travel which indicates beginning of zone in
which to record sound pressure level during test
BB' — 3.1 line perpendicular to vehicle travel which indicates end of zone in which
is 10,00 m behind line PP'
d m 7.2 thickness of absorbing elements
absorb
d m 5.1.1 diameter of dynamometer roller
roller
F N B.4.1 propulsion force of the vehicle
F dB D.4 correction for tyre/road noise in variant B
Cor
F N B.4.4 propulsion force of the vehicle to be tested indoor
PTN
F N B.4.3 propulsion force of the tyre test vehicle
TRN
K dB/°C B.2.4 temperature correction coefficient
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Unit Clause Designation
k — 5.5 partial power factor
P
virtual length of test section for calculation of acceleration from AA' to
l m 3.2
AB
BB'
l m 7.2 minimum length of the test room
min,room
virtual length of test section for calculation of acceleration from PP' to
l m 3.2
PB
BB'
l m 7.2 length of vehicle
veh
L dB E.2.1 reported vehicle sound pressure level at wide-open throttle
acc rep
L dB E.2.1 reported vehicle sound pressure level at constant speed
crs rep
L dB B.4.1 free rolling noise sound pressure level
FRN
L dB 10.2.4 power train noise sound pressure level
PTN
L dB D.3 power train noise sound pressure level indoor
PTNi
L dB C.2 torque influence sound pressure level
TI
L dB 10.2.4 tyre/road noise sound pressure level
TRN
L dB D.3 tyre/road noise sound pressure level indoor
TRNi
L dB B.6 calculated tyre/road noise sound pressure level indoor
TRN indoor
L dB D.4 tyre/road noise sound pressure level outdoor
TRNo
L dB 10.2.4 total vehicle noise sound pressure level
TVN
L dB B.6 total vehicle noise sound pressure level indoor
TVNi
L dB D.5 total vehicle noise sound pressure level outdoor
TVNo
L dB 9.7 reported vehicle sound pressure level representing urban operation
urban
m kg 9.4.2.2.3 maximum rear axle capacity
ac ra max
m kg 9.4.2.2.3 mass of driver
d
m kg 9.4.2.2.3 unladen front axle load
fa load unladen
m kg 9.4.2.2.3 kerb mass of the vehicle
kerb
m kg 9.4.2.2.3 unladen rear axle load
ra load unladen
m kg 9.4.2.2.3 kerb mass + 75 kg for the driver
ref
m kg 9.4.2.2.3 mass in running order
ro
m kg B.6 mass in running order of the vehicle to be tested indoor
ro indoor test
m kg B.4.3 test mass of the tyre test vehicle (including driver and test equipment)
tyre test
m kg 9.4.2.2.3 virtual or actual physical test mass of the vehicle, that is used as an input
t
for simulating the vehicle transient behaviour by the dynamometer
control system
m kg 9.4.2.2.3 target mass of the vehicle
target
m kg 9.4.2.2.3 unladen vehicle mass
unladen
m kg 9.4.2.2.3 extra loading
xload
n r/min 10.3 engine speed when the reference point passes BB’
BB'
n r/min 10.3 engine speed when the reference point passes PP’
PP'
n r/min 5.1.1 rotational speed of the dynamometer roller for the test run i
roller AA‘ test i
P hPa B.2.3 Tyre inflation pressure recommended by the vehicle manufacturer
ref
P hPa B.2.3 Tyre test inflation pressure
test
PP' — 3.2 line perpendicular to vehicle travel which indicates location of micro-
phones
Q kg B.2.3 weight of the vehicle to be tested indoor
ref
Q kg B.2.3 weight of the tyre test vehicle
test
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Unit Clause Designation
r m 7.3.2.4 reference path length of the centre measurement position
r m 7.3.2.4 path length to the microphone at distance x
x
is the standard deviation of the sound pressure level under urban condi-
u dB E.2.2
L,urban,i
tions for the quantity i
v km/h B.4.2 vehicle speed
v km/h 5.1.1 vehicle speed when reference point passes line AA’
AA'
v km/h 5.1.1 vehicle speed when reference point passes line AA' for the test run i (see
AA' test i
5.1 for definition of reference point)
v km/h 5.1.1 vehicle speed when reference point or rear of vehicle passes line BB' (see
BB'
5.1 for definition of reference point)
v km/h 5.1.1 vehicle speed when reference point passes line PP' (see 5.1 for definition
PP'
of reference point)
v km/h B.5 vehicle speed at the power train noise measurement indoor
PTN
v km/h 9.5.1.2 target vehicle test speed
test
v km/h B.4.3 vehicle speed at the tyre/road noise measurement outdoor
TRN
w m 7.2 width of the room
room
w m 7.2 width of the room for a single-sided facility
single,room
w m 7.2 width of the room for a dual-sided facility
dual,room
w m 7.2 width of the vehicle
veh
x m B.3.3 vehicle position on the (virtual) test track
x m 7.3.2.4 position of the microphone in the arrays in driving direction
micro
α dB B.4.2 coefficients of free rolling noise
β dB B.4.2 coefficients of free rolling noise
γ — B.4.3 coefficient of the exact torque influence
δ — B.4.3 coefficient of the exact torque influence
the maximum deviation of the quantity i of the sound pressure level from
ΔL dB E.2.1
acc, max dev,i
acceleration tests
the maximum deviation of the quantity i of the sound pressure level from
ΔL dB E.2.1
crs, max dev,i
cruise tests
ΔL dB B.3.3 torque influence of the sound pressure level
TI
ΔL the estimated maximum deviation (peak-to-peak) of the sound pressure
urban, max
dB E.2.1
level under urban conditions for the quantity i
dev, i
ΔL dB(A) 7.3.2.4 relative sound pressure level decay at position x
x
Δn r/min D.2 maximum parameter variability in the test situation for the engine speed
Δs m D.2 maximum parameter variability in the test situation for the acceleration
position
ζ — B.3.3 coefficient of standard torque influence
ϑ °C B.5 reference air temperature at the power train noise measurements indoor
REF
averaged air temperature from all runs of the free rolling noise measure-
ϑ °C B.5
FRN
ment
λ m 7.2 wavelength at the cut-off frequency
cut off
5 Acceleration for vehicles of categories M1 and M2 having a maximum
authorized mass not exceeding 3 500 kg, and of category N1
5.1 Applicability and conditions
All accelerations are calculated using different vehicle speeds during the test. All virtual vehicle speeds
are calculated from the number of revolutions of the roller as given in Formula (1) (as example for AA'):
36,
vd=⋅π⋅⋅n (1)
AA'test iirollerroller AA'test
where
v is the vehicle speed when the reference point passes virtual line AA' for the test run
AA' test i
i;
d is the diameter of the dynamometer roller;
roller
n are the revolutions per minute of the dynamometer roller for the test run i.
roller AA' test i
The virtual line AA' indicates the beginning of the test track, PP' indicates the virtual position of the
two pass-by microphones, and BB' indicates the end of the test track, as defined in ISO 362-1:2022, 7.1.
The simulated vehicle speed at AA', v , or PP', v , is defined by the roller speed when the reference
AA' PP'
point of the vehicle (as defined in ISO 362-1:2022, 3.5) passes the virtual line AA' or PP', respectively.
The simulated vehicle speed at BB', v , is defined when the rear of the vehicle passes the virtual line
BB'
BB'.
The method used for the determination of the acceleration shall be indicated in the test report.
Due to the large variety of technologies, it is necessary to consider different modes of calculation. New
technologies (such as continuously variable transmission) as well as dated technologies (e.g. automatic
transmissions without electronic control units) require a more specific treatment for a proper
determination of the acceleration. Any alternatives for calculation of the acceleration shall cover these
needs.
5.2 Calculation of acceleration
5.2.1 Calculation procedure for vehicles with manual transmission, automatic transmission,
adaptive transmission, and continuously variable transmission (CVT) tested with locked gear
ratios
As defined in ISO 362-1:2022, 5.2.1.
5.2.2 Calculation procedure for vehicles with automatic transmission, adaptive transmission,
and CVT tested with non-locked gear ratios
As defined in ISO 362-1:2022, 5.2.2.
5.3 Calculation of the target acceleration
As defined in ISO 362-1:2022, 5.3.
5.4 Calculation of the reference acceleration
As defined in ISO 362-1:2022, 5.4.
5.5 Partial power factor, k
P
As defined in ISO 362-1:2022, 5.5.
6 Instrumentation
6.1 Instruments for acoustical measurement
6.1.1 General
The apparatus used for measuring the sound pressure level shall be a sound level meter or equivalent
measurement system meeting the requirements of Class 1 instruments (including a recommended
windscreen, if used). These requirements are specified in IEC 61672-1.
The entire measurement system shall be checked by means of a sound calibrator that fulfils the
requirements of Class 1 sound calibrators in accordance with IEC 60942.
Measurements shall be carried out using time weighting “F” and frequency weighting “A” as specified in
IEC 61672-1. When using a system that includes periodic monitoring of the A-weighted sound pressure
level, a data extract should be made at a time interval not greater than 30 ms.
When no general statement or conclusion can be made about conformance of the sound level meter
model to the full specifications of IEC 61672-1, the apparatus used for measuring the sound pressure
level shall be a sound level meter or equivalent measurement system meeting the conformity
requirements of Class 1 instruments as described in IEC 61672-3.
NOTE The tests of IEC 61672-3 cover only a limited subset of the specifications in IEC 61672-1 for which the
scope is large (temperature range, frequency requirements up to 20 kHz, etc.). It is economically not feasible
to verify the whole IEC 61672-1 requirements on each item of a computerized data acquisition systems model.
Apparently, until today, no computerized data acquisition system available complies with the full specifications of
IEC 61672-1. It is beyond the possibilities of the users of these systems to prove conformity of the instrumentation
required by the test code.
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.
6.1.2 Calibration
At the beginning and at the end of every measurement session, the entire sound measurement system
shall be checked by means of a sound calibrator as described in 6.1.1. Without any further adjustment,
the difference between the readings shall not exceed 0,5 dB. If this value is exceeded, the results of the
measurements obtained after the previous satisfactory check shall be discarded.
As an alternative, at the beginning and at the end of every measurement session, the entire sound
measurement system shall be checked by means of a calibration system (i.e. electrical calibration),
provided by the hardware supplier and implemented in the measurement software used as a simulated
pass-by run as described in 6.1.1.
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.
6.2 Conformity with requirements
Conformity of the sound calibrator with the requirements of IEC 60942 shall be verified once a year.
Conformity of the instrumentation system with the requirements of IEC 61672-3 shall be verified at
least every 2 years or at each modification of the system (software, microphone, etc.). All conformity
testing shall be conducted by a laboratory which meets the requirements of ISO/IEC 17025.
6.3 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 road speed of the vehicle shall be measured using instruments with an uncertainty of not more
than ±0,5 km/h. The road speed of the vehicle is calculated by using the roller speed.
The minimum update rate for the continuous speed device shall be 20 Hz.
6.4 Meteorological instrumentation
The meteorological instrumentation used to monitor the environmental conditions during the test
shall have an uncertainty of not more than the following:
— ±1 °C for a temperature measuring device;
— ±5 hPa for a barometric pressure measuring device;
— ±5 % for a relative-humidity measuring device.
7 Test room requirements
7.1 General
One of the principal criteria of ISO 362-1 is testing in an acoustic free field.
To reproduce this acoustic criterion in a laboratory, the room design shall be able to provide the same
effective propagation characteristics as an open space over a reflecting surface (see specifications in
7.3).
One solution is a semi-anechoic chamber with absorptive materials. Several different techniques are
available for this purpose. An example of a test room is shown in Figure 1.
Key
L left-hand side microphone array 4 virtual line AA'
L microphone array centre point 5 rear ventilation
R right-hand side microphone array 6 front ventilation
R microphone array centre point 7 rollers
1 absorbing elements 8 centre of room
2 virtual line BB' 9 driving direction
3 virtual line PP' 10 additional microphones for test track extension
Figure 1 — Example of a test room; configuration for rear wheel drive vehicles
7.2 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, l (base size), is recommended as given in
min, room
Formula (2):
ll=+20m +⋅22d +⋅ ⋅λ (2)
min,room vehabsorbcutoff
where
20 m is the original length of test track;
l is the length of longest vehicle to be tested for vehicles of categories M1 and M2
veh
having a maximum authorized mass not exceeding 3 500 kg, and category N1;
is 5 m for vehicles of category M2 having a maximum authorized mass exceeding
3 500 kg, and categories M3, N and N3;
d is the thickness of absorbing elements;
absorb
1/4 λ is 1/4 of the wavelength at the cut-off frequency (2 times 1/4 wavelength from the
cut off
outer microphones to the absorbing walls).
If this is not possible, see Annex F for further information on minimum room length. The width, w ,
room
of the room is dependent on whether it is a single-sided facility or a dual-sided facility. In any case, the
distance from the centreline to the microphone line shall be 7,5 m. A shorter distance with a correction
of the sound pressure level is not permissible.
When measurements shall be performed for distances longer than the length of the test track plus the
length of the vehicle, additional microphones, additional signal processing algorithms, or a combination
of both are required. (see Figure 1).
The width, w , of single-sided facilities is as given in Formula (3):
single,room
1 1
wd=+75, m 22⋅+ ⋅⋅λ +⋅w (3)
single,room absorb cutoff veh
4 2
where
7,5 m is the original distance from the centreline to the microphone line;
d is the thickness of absorbing elements;
absorb
1/4 λ is 1/4 of the wavelength at the cut-off frequency (1 time 1/4 of the wavelength from
cut off
the microphones to the absorbing elements + one time 1/4 of the wavelength from the
vehicle to the absorbing elements);
w is the width of vehicle.
veh
The width, w , of dual-sided facilities is as given in Formula (4):
dual,room
wd=⋅27,52m+⋅ +⋅2 ⋅λ (4)
dual,room absorb cutoff
where
7,5 m is the original distance from the centreline to the microphone line;
d is the thickness of absorbing elements;
absorb
1/4 λ is 1/4 of the wavelength at the cut-off frequency (two times 1/4 of the wavelength
cut off
from the microphones to the absorbing elements).
It is recommended to ensure a distance of 1/4 of the wavelength from the microphones to the absorbing
elements for single-sided and dual-sided facilities. If this is not fulfilled, the free-field condition at the
microphone array shall be checked as described in 7.3.
The minimum height of the room is dependent on the vehicle height and the location of noise sources
(exhaust outlet). See 7.3. To minimize the influences, the distance from the relevant source to the
absorbing elements shall be at least 1/2 of the wavelength at the cut-off frequency.
7.2.1 Test room dimensions for measurements where the length of the test track is greater
than 20m
To account for test track dimensions longer than 20 m, additional microphones may be placed at the end
of the test chamber (see Figure 2; Key No. 6). When such microphones are used, corrections (e.g. inverse
square distance law) shall be determined to account for the physical location of the microphones in the
room as compared to the virtual location of the microphones (see Figure 2; Key No. 8) of an extended
microphone array. This setup ensures a correct con
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