ISO/TS 19425:2024

Technical
Specification
ISO/TS 19425
Second edition
Reciprocating internal combustion
2024-07
engines — Measurement method
for air cleaners — Sound power
level of combustion air inlet noise
and insertion loss using sound
pressure
Moteurs alternatifs à combustion interne — Méthode de mesure
du bruit des purificateurs d'air — Niveau de puissance sonore du
bruit d'entrée d'air de combustion et de perte d'insertion utilisant
une pression sonore
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test environment . 5
4.1 General .5
4.2 Criterion for background noise.5
4.3 Criterion for acoustic adequacy of test environment .6
5 Instrumentation . 6
5.1 General .6
5.2 Calibration .6
5.3 Application .7
6 Installation and operation conditions . 7
6.1 General .7
6.2 Installation condition .7
6.3 Operation condition .8
7 Measurement . 9
7.1 General .9
7.2 Measurement uncertainty .9
7.3 Characteristic source dimension .10
7.4 Measurement radius .10
7.5 Measurement surface and area .10
7.6 Microphone arrays .10
8 Calculation .12
8.1 General . 12
8.2 Calculation of sound power level. 12
8.2.1 Mean time-averaged sound pressure levels . 12
8.2.2 Corrections for background noise . 13
8.2.3 Corrections for environmental . 13
8.2.4 Surface time-averaged sound pressure levels .14
8.2.5 Sound power levels .14
8.3 Calculation of insertion loss .14
9 Information to be recorded .15
10 Test report .16
Annex A (normative) Qualification procedures for the acoustic environment . 17
Annex B (normative) Calculation of A-weighted sound power levels from frequency band levels .20
Annex C (normative) Sound power level under reference meteorological conditions .22
Bibliography .23

iii
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
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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 document 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).
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This document was prepared by Technical Committee ISO/TC 70, Air-borne noise.
This second edition cancels and replaces the first edition (ISO 19425:2015), which has been technically
revised.
The main changes are as follows:
— the terms and definitions have been revised and sources have been added (see Clause 3);
— the criterion for background noise has been changed (see 4.2);
— the application has been changed (see 5.3);
— the installation condition has been changed (see 6.2);
— the operation condition has been changed (see 6.3);
— the measurement radius has been changed (see 7.4).
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.

iv
Technical Specification ISO/TS 19425:2024(en)
Reciprocating internal combustion engines — Measurement
method for air cleaners — Sound power level of combustion
air inlet noise and insertion loss using sound pressure
1 Scope
This document specifies the measurement method and requirements for combustion air inlet noise of
air cleaners which are installed on reciprocating internal combustion engines, including laboratory
measurement (engineering method and survey method) and site measurement (survey method).
This document applies to all air cleaners installed on reciprocating internal combustion engines
(reciprocating internal combustion engine is referred to as engine hereafter, except for specific explanations)
falling within the field of application of ISO 3046-1 and/or other air induction installation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3046-1, Reciprocating internal combustion engines — Performance — Part 1: Declarations of power, fuel
and lubricating oil consumptions, and test methods — Additional requirements for engines for general use
ISO 3046-3, Reciprocating internal combustion engines — Performance — Part 3: Test measurements
ISO 6926, Acoustics — Requirements for the performance and calibration of reference sound sources used for
the determination of sound power levels
IEC 60942, Electroacoustics — Sound calibrators
IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1, Electroacoustics — Sound level meters—Part 1: Specifications
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in ISO 3046-1, ISO 3046-3, ISO 6926,
IEC 60942, IEC 61260 and IEC 61672-1 and the following apply.
ISO and IEC maintain terminology 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
sound pressure
p
difference between instantaneous pressure and static pressure
Note 1 to entry: It is expressed in pascals.
[SOURCE: ISO 80000-8:2007, 8-9.2]

3.2
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure (3.1), p, to the square of
a reference value, p
p
L =10lg
p
p
where the reference value, p , is 20 μPa
Note 1 to entry: If specific frequency and time weightings, as specified in IEC 61672-1, and/or specific frequency bands
are applied, this is indicated by appropriate subscripts, e.g. L denotes the A-weighted sound pressure level.
pA
Note 2 to entry: It is expressed in decibels.
[SOURCE: ISO 3744:2010, 3.2]
3.3
time-averaged sound pressure level
L
p,T
ten times the logarithm to the base 10 of the ratio of the time average of the square of the sound pressure (3.1),
p, during a stated time interval of duration, T (starting at t and ending at t ), to the square of a reference
1 2
value, p
t
 2 
pt dt
()
 ∫ 
t
T
L =10lg
 
pT,
 p 
 
 
where the reference value, p , is 20 μPa
Note 1 to entry: In general, the subscript “T” is omitted since time-averaged sound pressure levels are necessarily
determined over a certain measurement time interval (3.5).
Note 2 to entry: Time-averaged sound pressure levels are often A-weighted, in which case they are denoted by L ,
pA,T
which is usually abbreviated to L .
pA
Note 3 to entry: It is expressed in decibels.
[SOURCE: ISO 3744:2010, 3.3]
3.4
surface time-averaged sound pressure level
L
p
mean (energy average) of the time-averaged sound pressure levels (3.3) over all the microphone positions,
or traverses, on the measurement surface (3.11), with the background noise correction (3.13), K , and the
environmental correction (3.14), K , applied
Note 1 to entry: It is expressed in decibels.
[SOURCE: ISO 3744:2010, 3.18]
3.5
measurement time interval
T
portion or a multiple of an operational period or operational cycle of the noise source under test for which
the time-averaged sound pressure level (3.3) is determined
Note 1 to entry: It is expressed in seconds.
[SOURCE: ISO 3744:2010, 3.5]
3.6
acoustic free field
sound field in a homogeneous, isotropic medium free of boundaries
Note 1 to entry: In practice, an acoustic free field is a field in which the influence of reflections at the boundaries or
other disturbing objects are negligible over the frequency range of interest.
[SOURCE: ISO 3744:2010, 3.6]
3.7
reflecting plane
sound-reflecting planar surface on which the noise source under test is located
[SOURCE: ISO 3744:2010, 3.8]
3.8
acoustic free field over a reflecting plane
acoustic free field (3.6) in the half-space above an infinite reflecting plane (3.7) in the absence of any other
obstacles
[SOURCE: ISO 3744:2010, 3.7]
3.9
frequency range of interest
frequency range of octave bands with nominal mid-band frequencies from 63 Hz to 8 000 Hz (including one-
third octave bands with mid-band frequencies from 50 Hz to 10 000 Hz)
[SOURCE: ISO 3744:2010, 3.9]
3.10
measurement radius
r
radius of a spherical measurement surface (3.11)
Note 1 to entry: It is expressed in metres.
[SOURCE: ISO 3744:2010, 3.13]
3.11
measurement surface
hypothetical spherical surface of area, S, on which the microphone positions are located at which the sound
pressure levels (3.2) are measured, enveloping the noise source under test
[SOURCE: ISO 3744:2010, 3.14]
3.12
background noise
noise from all sources other than the noise source under test
Note 1 to entry: Background noise includes contributions from airborne sound, noise from structure-borne vibration,
and electrical noise in the instrumentation.
[SOURCE: ISO 3744:2010, 3.15]
3.13
background noise correction
K
correction applied to the mean (energy average) of the time-averaged sound pressure levels (3.3) over all the
microphone positions on the measurement surface (3.11), to account for the influence of background noise (3.12)
Note 1 to entry: The background noise correction is frequency dependent; the correction in the case of a frequency band
is denoted by K , where f denotes the relevant mid-band frequency and that in the case of A-weighting is denoted by K .
1f 1A
Note 2 to entry: It is expressed in decibels.
[SOURCE: ISO 3744:2010, 3.16]
3.14
environmental correction
K
correction applied to the mean (energy average) of the time-averaged sound pressure levels (3.3) over all the
microphone positions on the measurement surface (3.11), to account for the influence of reflected sound
Note 1 to entry: The environmental correction is frequency dependent; the correction in the case of a frequency band is
denoted by K , where f denotes the relevant mid-band frequency, and that in the case of A-weighting is denoted by K .
2f 2A
Note 2 to entry: It is expressed in decibels.
[SOURCE: ISO 3744:2010, 3.17]
3.15
sound power
W
through a surface, product of the sound pressure (3.1), p, and the component of the particle velocity, u , at a
n
point on the surface in the direction normal to the surface, integrated over that surface
Note 1 to entry: The quantity relates to the rate per time at which airborne sound energy is radiated by a source.
Note 2 to entry: It is expressed in watts.
[SOURCE: ISO 3744:2010, 3.20]
3.16
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power (3.15) of a source, W, to a reference
value, W , expressed in decibels
W
L =10lg
W
W
where the reference value, W , is 1 pW
Note 1 to entry: If a specific frequency weighting, as specified in IEC 61672-1, and/or specific frequency bands are
applied, this is indicated by appropriate subscripts, e.g. L denotes the A-weighted sound power level.
WA
Note 2 to entry: It is expressed in decibels.
[SOURCE: ISO 3744:2010, 3.21]
3.17
air cleaner
air filter
device which removes particles suspended in the fresh charge as it is drawn into the engine
Note 1 to entry: The air cleaner generally comprises the entire part from its air inlet but does not include the air
induction manifold and pipe.
3.18
substitution pipe
rigid, non-absorbing circular pipe having the same length and the same cross section area of outlet as the
tested air cleaner (3.17)
3.19
bent transition pipe
bent pipe used to change the airflow direction and to connect two pipes of the same cross section area

3.20
characteristic source dimension
d
characteristic dimension of source to determine the measurement radius (3.10)
3.21
insertion loss
D
I
difference between the sound power level (3.16) of combustion air inlet noise when the substitution pipe
(3.18) is installed on the engine and when the air cleaner (3.17) is installed on the engine
DL=−L
ISWW((P) AC)
where
L is the sound power level of combustion air inlet noise when the substitution pipe is installed on
W(SP)
the engine, in decibels;
L is the sound power level of combustion air inlet noise when the air cleaner is installed on the
W(AC)
engine, in decibels.
Note 1 to entry: It is expressed in decibels.
4 Test environment
4.1 General
For the engineering method, the test environments that are applicable for measurements in accordance with
this document are the following:
a) a room or a flat outdoor area which is adequately isolated from background noise and which provides
an acoustic free field over a reflecting plane;
b) a room or a flat outdoor area which is adequately isolated from background noise and in which an
environmental correction can be applied to allow for a limited contribution from the reverberant field
to the sound pressures on the measurement surface.
For the survey method, the test environment that is applicable for measurements in accordance with this
document is a room or a flat outdoor area which is adequately isolated from background noise and which
meets the qualification requirements given in 4.3.
Environmental conditions having an adverse effect on the microphones used for the measurements (e.g.
wind, impingement of air discharge, high or low temperatures) shall be avoided. The instructions of the
manufacturer of the measuring instrumentation regarding adverse environmental conditions shall be
followed. Particular care should be exercised to ensure that the plane does not radiate any appreciable
sound due to vibrations.
4.2 Criterion for background noise
For the engineering method, the time-averaged sound pressure level of the background noise measured
and averaged over the microphone positions shall be at least 6 dB, and preferably more than 15 dB, below
the corresponding uncorrected time-averaged sound pressure level of the noise source under test when
measured in the presence of this background noise.
For frequency band measurements, it is possible that the criteria for background noise is not achievable in
all frequency bands, even when the background noise levels in the test room are extremely low and well
controlled.
For measurements in frequency bands, the following steps shall be followed to determine whether meeting
the requirements of the background noise criteria.
a) The A-weighted sound power level is computed using the data from every frequency band within the
frequency range of interest.
b) The computation of A-weighted sound power level is repeated but excluding those bands within the
frequency range of interest for which ΔL < 6 dB (see 8.2.2).
p
c) If the difference between these two levels is less than 0,5 dB, the A-weighted sound power level
determined from the data for all bands may be considered as conforming to the background noise
criteria of this Technical Specification, or the measurement is not valid.
For survey method, the time-averaged sound pressure level of the background noise measured and
averaged over the microphone positions, shall be at least 3 dB, and preferably more than 10 dB, below
the corresponding uncorrected time-averaged sound pressure level of the noise source under test when
measured in the presence of this background noise.
4.3 Criterion for acoustic adequacy of test environment
Annex A specifies procedures for determining the magnitude of the environmental correction, K .
For the engineering method, as long as it is practicable, the test environment shall be free from reflecting
objects other than the reflecting plane(s). The reflecting plane(s) shall extend at least 0,5 m beyond the
projection of the measurement surface on the plane(s). The sound absorption coefficient of the reflecting
plane(s) shall be less than 0,1 over the frequency range of interest.
NOTE 1 Smooth concrete or smooth sealed asphalt surface(s) are generally satisfactory.
Measurements in accordance with the engineering method of this document are only valid where K ≤ 4 dB.
2A
NOTE 2 The environmental correction, K , is assumed to be zero for measurements made in hemi-anechoic rooms
which meet the requirements of ISO 3745.
The environmental correction, K , shall first be determined without reference to frequency band data,
2A
using one of the procedures of Annex A. Where it is decided to make measurements in frequency bands, the
relevant environmental correction K shall be determined in each band over the frequency range of interest
in accordance with A.4. L of a noise source shall be calculated in accordance with Annex B.
WA
Measurements in accordance with the survey method of this document are only valid where K ≤ 7 dB.
2A
5 Instrumentation
5.1 General
The instrumentation system, including the microphones, cables and windscreen, if used, shall meet the
requirements of IEC 61672-1, class 1 for results of accuracy grade 2 and class 2 for results of accuracy grade
3, and the filters shall meet the requirements of IEC 61260.
The sound level meter in acoustic measurement includes traditional handheld sound level meter and data
acquisition and analysis equipment.
5.2 Calibration
Before and after each series of measurements, a sound calibrator meeting the requirements of IEC 60942,
class 1 shall be applied to each microphone to verify the calibration of the entire measuring system at one
or more frequencies within the frequency range of interest. Without any adjustment, the difference between
the readings made before and after each series of measurements shall be less than or equal to 0,5 dB. If this
value is exceeded, the results of the series of measurements shall be discarded.

The calibration of the sound calibrator, the compliance of the instrumentation system with the requirements
of IEC 61672-1, the compliance of the filter set with the requirements of IEC 61260, and the compliance of
the reference sound source with the requirements of ISO 6926 shall be verified at intervals in a laboratory
making calibrations traceable to appropriate standards.
The sound calibrator should be calibrated at intervals not exceeding 1 y, the reference sound source
should be calibrated at intervals not exceeding 2 y, the compliance of the instrumentation system with the
requirements of IEC 61672-1 should be verified at intervals not exceeding 2 y, and the compliance of the
filter set with the requirements of IEC 61260 should be verified at intervals not exceeding 2 y. National
regulations stating other requirements can exist.
5.3 Application
To minimize the influence of observers on the noise measurements, the microphones shall preferably be
mounted on a rigid frame or stand which is not connected to the vibrating surface; the microphone shall
always be oriented in such a way that the angle of incidence of the sound waves is that for which the
microphone is calibrated and always be oriented to the centre of the air inlet.
The time-averaged sound pressure level shall be measured using an integrating sound level meter. If the
sound level meter is used to measure time-weighting sound pressure level, the time-weighting characteristic
“S” shall be used for the noise source under test operated in steady condition, and the time-weighting
characteristic “F” shall be used for the noise source under test operated in non-steady condition (e.g. engine
operated in the accelerated or decelerated condition). The measured average value can be expressed as the
time-averaged sound pressure level.
The period of measurement for the time-averaged sound pressure level shall be at least 4 s, 8 s or longer is better.
The period of observation for the A-weighted sound pressure level shall be at least 4 s. For the frequency
bands centred on or below 160 Hz, the period of observation shall be at least 16 s. For the frequency bands
centred on or above 200 Hz, the period of observation shall be at least 8 s.
6 Installation and operation conditions
6.1 General
The manner in which the air cleaner is installed and operated can have a significant influence on the sound
power emitted by a noise source under test; for example, the shape, inner diameter, and length of the air
inlet may have influence on the sound power. The flow noise generated by high-flow speed can be greater
due to the smaller inner diameter of the air inlet. The air cleaner to be tested shall be installed as if it were
in normal use when the measurement is made in the laboratory. This Clause specifies conditions that are
intended to minimize variations of the sound power level due to the installation and operating conditions of
the noise source under test.
6.2 Installation condition
For the engineering method, the air inlet shall be installed outdoors or in a test room which meets the
requirements given in 4.2 and 4.3 (engineering method). The distance between the cen
...