ISO 1996-2:2017

INTERNATIONAL ISO
STANDARD 1996-2
Third edition
2017-07
Acoustics — Description,
measurement and assessment of
environmental noise —
Part 2:
Determination of sound pressure levels
Acoustique — Description, évaluation et mesurage du bruit de
l’environnement —
Partie 2: Détermination des niveaux de pression acoustique
Reference number
ISO 1996-2:2017(E)
©
ISO 2017

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ISO 1996-2:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

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ISO 1996-2:2017(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement uncertainty . 3
5 Instrumentation for acoustical measurements . 5
5.1 General . 5
5.2 Calibration . 6
5.3 Verification . 6
5.4 Long-term monitoring . 6
6 Principles . 6
6.1 General . 6
6.2 Independent measurements . 7
7 Operation of the source . 8
7.1 General . 8
7.2 Road traffic . 8
7.2.1 L measurement . 8
eq
7.2.2 L measurement . 9
max
7.3 Rail traffic . 9
7.3.1 L measurement . 9
eq
7.3.2 L measurement . 9
max
7.4 Air traffic .10
7.4.1 L measurement .10
eq
7.4.2 L measurement .11
max
7.5 Industrial plants . .11
7.5.1 L measurement .11
eq
7.5.2 L measurement .11
max
8 Meteorological conditions .12
8.1 General .12
8.2 Favourable propagation .13
8.3 Effects of precipitation on measurements .13
9 Measurement procedures .13
9.1 Selection of measurement time interval .13
9.1.1 Long-term measurements .13
9.1.2 Short-term measurements .14
9.2 Microphone location .14
9.2.1 Outdoors .14
9.2.2 Indoors .15
9.3 Measurements .15
9.3.1 Long-term unattended measurements .15
9.3.2 Short-term attended measurements .16
9.3.3 Residual sound .17
9.3.4 Frequency range of measurements .17
9.3.5 Measurements of meteorological parameters .17
10 Evaluation of the measurement results .18
10.1 General .18
10.2 Determination of L , L and L .
E,T eq,T N,T 18
10.2.1 L and L .
E,T eq,T 18
10.2.2 L .
N,T 18
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ISO 1996-2:2017(E)

10.3 Treatment of incomplete or corrupted data .19
10.3.1 General.19
10.3.2 Wind sound .19
10.4 Level correction for residual sound .19
10.5 Determination of standard uncertainty .19
10.6 Determination of L .
den 20
10.6.1 Determination from long-term L measurements .20
eq
10.6.2 Determination from long-term L measurements of individual events.20
E
10.6.3 Determination from short-term measurements .21
10.7 Maximum level, L .
max 22
11 Extrapolation to other locations .22
11.1 General .22
11.2 Extrapolation by means of calculations.22
11.3 Extrapolation by means of measured attenuation functions .23
12 Calculation .23
12.1 General .23
12.2 Calculation methods .24
12.2.1 General.24
12.2.2 Specific procedures .24
13 Information to be recorded and reported .24
Annex A (informative) Determination of radius of curvature .26
Annex B (informative) Microphone locations relative to reflecting surfaces .29
Annex C (informative) Selection of measurement/monitoring site .34
Annex D (informative) Correction to reference condition .36
Annex E (informative) Elimination of unwanted sound .41
Annex F (informative) Measurement uncertainty .42
Annex G (informative) Examples of uncertainty calculations .44
Annex H (informative) Maximum sound pressure levels .49
Annex I (informative) Measurement of residual sound .52
Annex J (informative) Objective method for assessing the audibility of tones in noise —
Engineering method .54
Annex K (informative) Objective method for assessing the audibility of tones in noise —
Survey method .56
Annex L (informative) National and European source specific calculation models .57
Bibliography .60
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ISO 1996-2:2017(E)

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 . i so .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This third edition cancels and replaces the second edition (ISO 1996-2:2007), which has been technically
revised.
A list of all the parts in the ISO 1996 series can be found on the ISO website.
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ISO 1996-2:2017(E)

Introduction
Measurements of environmental noise are complicated because there is a great number of variables to
consider when planning and performing the measurements. As each measurement occasion is subject
to current source and meteorological conditions which cannot be controlled by the operator, it is often
not possible to control the resulting uncertainty of the measurements. Instead, the uncertainty is
determined after the measurements based on an analysis of the acoustic measurements and collected
data on source operating conditions and on meteorological parameters important for the sound
propagation.
Because this document has the ambition both to comply with new and stricter requirements on
measurement uncertainty calculations and to cover all kinds of sources and meteorological conditions,
it has become more complicated than what a standard covering a single, specific source and application
could have been. The best use of the standard is to use it as a basis for developing more dedicated
standards serving specific sources and aims.
vi © ISO 2017 – All rights reserved

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INTERNATIONAL STANDARD ISO 1996-2:2017(E)
Acoustics — Description, measurement and assessment of
environmental noise —
Part 2:
Determination of sound pressure levels
1 Scope
This document describes how sound pressure levels intended as a basis for assessing environmental
noise limits or comparison of scenarios in spatial studies can be determined. Determination can be
done by direct measurement and by extrapolation of measurement results by means of calculation.
This document is primarily intended to be used outdoors but some guidance is given for indoor
measurements as well. It is flexible and to a large extent, the user determines the measurement effort
and, accordingly, the measurement uncertainty, which is determined and reported in each case. Thus,
no limits for allowable maximum uncertainty are set up. Often, the measurement results are combined
with calculations to correct for reference operating or propagation conditions different from those
during the actual measurement. This document can be applied on all kinds of environmental noise
sources, such as road and rail traffic noise, aircraft noise and industrial noise.
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 1996-1:2016, Acoustics — Description, measurement and assessment of environmental noise — Part 1:
Basic quantities and assessment procedures
ISO 20906:2009/Amd 1:2013, Acoustics — Unattended monitoring of aircraft sound in the vicinity of
airports — Amendment 1
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
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 given in ISO 1996-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
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ISO 1996-2:2017(E)

3.1
measurement time interval
time interval during which measurements are conducted
Note 1 to entry: For measurements of sound exposure level or equivalent-continuous sound pressure level, the
measurement time interval is the time period of integration.
Note 2 to entry: For measurements of maximum sound pressure level or percent exceedance level, etc., the
measurement time interval is the observation time interval (3.2).
3.2
observation time interval
time interval during which a series of measurements is conducted
3.3
prediction time interval
time interval over which levels are predicted
Note 1 to entry: It is now perhaps more common to predict sound levels using computers than to measure
them for some sources such as transportation noise sources. The prediction time interval corresponds to the
measurement time interval (3.1) except, for the former, the levels are predicted, and for the latter, the levels are
measured.
3.4
long-term measurement
measurement sufficiently long to encompass all emission situations and meteorological conditions
which are needed to obtain a representative average
3.5
short-term measurement
measurement during measurement time intervals (3.1) with well-defined emission and meteorological
conditions
3.6
receiver location
location at which the noise is assessed
3.7
calculation method
set of algorithms to calculate the sound pressure level at a specified receiver location (3.6) from
measured or predicted sound power levels and sound attenuation data
3.8
prediction method
subset of a calculation method (3.7), intended for the calculation of future noise levels
3.9
meteorological window
set of weather conditions during which measurements can be performed with limited and known
variation in measurement results due to weather variation
3.10
emission window
set of emission conditions during which measurements can be performed with limited variation in
measurement results due to variations in operating conditions
3.11
sound path radius of curvature
R
cur
radius approximating the curvature of the sound paths due to atmospheric refraction
Note 1 to entry: R is given in metres.
cur
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ISO 1996-2:2017(E)

Note 2 to entry: Often, the parameter used is 1/R to avoid infinitely large values during straight ray
cur
propagation.
3.12
monitor
instrumentation used for a single automated continuous sound monitoring terminal which monitors
the A-weighted sound pressure levels, their spectra and all relevant meteorological quantities such as
wind speed, wind direction, rain, humidity, atmospheric stability, etc.
Note 1 to entry: Meteorological measurements need not be taken at each monitor provided such measurements
are taken within an appropriate distance from the monitors and such distance is given in the report.
3.13
automated sound monitoring system
entire automated continuous sound monitoring system including all monitors (3.12), the base or central
data collection position (host station) and all software and hardware involved in its operation
3.14
reference condition
condition to which the measurement results are to be referred (corrected)
Note 1 to entry: Examples of reference conditions are atmospheric sound absorption at yearly average
temperature and humidity and yearly average traffic flows for day, evening and night, respectively.
3.15
independent measurement
consecutive measurements carried out with a time space long enough to make both source operating
conditions and sound propagation conditions statistically independent of the same conditions of other
measurements in the series
Note 1 to entry: In order to achieve independent conditions for meteorological conditions, a time space of several
days is normally required.
3.16
low-frequency sound
sound containing frequency components of interest within the range covering the one-third octave
bands 16 Hz to 200 Hz
Note 1 to entry: This definition is specific for this document. Other definitions can apply in different national
regulations.
4 Measurement uncertainty
The uncertainty of sound pressure levels determined as described in this document depends on the
sound source and the measurement time interval, the meteorological conditions, the distance from
the source and the measurement method and instrumentation. The measurement uncertainty shall be
determined in compliance with ISO/IEC Guide 98-3 (GUM). Choose one of the following approaches that
are all GUM-compatible:
a) The modelling approach that consists in identifying and quantifying all major sources of uncertainty
(the so-called uncertainty budget). This is the preferred method.
b) The inter-laboratory approach that consists in carrying out a round-robin test in order to determine
the standard deviation of reproducibility of the measurement method.
NOTE 1 If more than one measurement method exists for a certain measurand, any systematic deviations
[1]
are taken into account, for example, by implementing ISO 21748 .
c) The hybrid approach that consists in using jointly the modelling approach and the inter-laboratory
approach. In this case, the inter-laboratory approach is used for components of the uncertainty
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ISO 1996-2:2017(E)

budget for which the contributions cannot be quantified using the mathematical model of the
modelling approach because of lack of technical knowledge.
NOTE 2 Note 1 equally applies.
According to the modelling approach, each significant source of uncertainty shall be identified.
Systematic effects shall be eliminated or reduced by the application of corrections wherever possible. If
the quantity to be measured is L, which is a function of the quantities x , the formula becomes:
j
Lf= xx,,xx,., (1)
()
12 3 j
If each quantity has the standard uncertainty u , the combined standard uncertainty is given by
j
Formula (2):
n
2
uL()= cu (2)
()
jj
∑
1
assuming that the input quantities x are independent. Under the same assumptions, the sensitivity
j
coefficient c is given by Formula (3):
j
∂f
c = (3)
j
∂x
j
The measurement uncertainty to be reported is the uncertainty associated with a chosen coverage
probability, the so-called expanded uncertainty. By convention, a coverage probability of 95 % is usually
chosen, with an associated coverage factor of 2. This means that the result becomes L ± 2 u.
NOTE 3 Cognizant authorities can set other coverage probabilities. A coverage factor of 1,3 will, for example,
provide a coverage probability of 80 %.
For environmental noise measurements f(x ), it is extremely complicated and it is hardly feasible to
j
[2]
put up exact formulae for the function f. Following the principles given in ISO 3745, some important
sources of uncertainty can be identified. For an in
...

SLOVENSKI STANDARD
oSIST ISO/DIS 1996-2:2016
01-junij-2016
$NXVWLND2SLVPHUMHQMHLQRFHQDKUXSDYRNROMXGHO'RORþDQMHUDYQL
]YRþQHJDWODND
Acoustics - Description, measurement and assessment of environmental noise -- Part 2:
Determination of sound pressure levels
Acoustique - Description, évaluation et mesurage du bruit de l'environnement -- Partie 2:
Détermination des niveaux de pression acoustique
Ta slovenski standard je istoveten z: ISO/DIS 1996-2
ICS:
13.140 Vpliv hrupa na ljudi Noise with respect to human
beings
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
oSIST ISO/DIS 1996-2:2016 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST ISO/DIS 1996-2:2016

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oSIST ISO/DIS 1996-2:2016
DRAFT INTERNATIONAL STANDARD
ISO/DIS 1996-2
ISO/TC 43/SC 1 Secretariat: DIN
Voting begins on: Voting terminates on:
2015-06-02 2015-09-02
Acoustics — Description, measurement and assessment of
environmental noise —
Part 2:
Determination of environmental noise levels
Acoustique — Description, évaluation et mesurage du bruit de l’environnement —
Partie 2: Détermination des niveaux de bruit de l’environnement
ICS: 17.140.01; 13.140
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 1996-2:2015(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2015

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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2:2015(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2015
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2015 – All rights reserved

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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2
Contents Page
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement uncertainty . 3
5 Instrumentation . 5
5.1 Instruments for acoustical measurements . 5
6 Principles . 6
6.1 General . 6
6.2 Independent measurements . 8
7 Operation of the source . 8
7.1 General . 8
7.2 Road traffic . 8
7.3 Rail traffic . 9
7.4 Air traffic . 9
7.5 Industrial plants . 11
7.6 Low-frequency sound sources . 11
8 Meteorological conditions . 12
8.1 General . 12
8.2 Favourable propagation . 12
8.3 Effects of precipitation on measurements . 13
9 Measurement procedures . 13
9.1 Selection of measurement time interval . 13
9.2 Microphone location . 14
9.3 Measurements . 15
10 Evaluation of the measurement results . 17
10.1 General . 17
10.2 Determination of L , L and L . 18
E,T eq,T N,T
10.3 Treatment of incomplete or corrupted data . 18
10.4 Level correction for residual sound . 19
10.5 Determination of standard uncertainty . 19
10.6 Determination of L . 20
den
10.7 Maximum level, L . 22
max
11 Extrapolation to other locations . 22
11.1 General . 22
11.2 Extrapolation by means of calculations . 22
11.3 Extrapolation by means of measured attenuation functions . 22
12 Calculation . 23
12.1 General . 23
12.2 Calculation methods . 24
13 Information to be recorded and reported . 24
Annex A (informative) Determination of radius of curvature . 25
Annex B (informative) Microphone locations relative to reflecting surfaces . 28
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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2
Annex C (informative) Selection of measurement/monitoring site .33
Annex D (informative) Correction to reference condition .35
Annex E (informative) Elimination of unwanted sound .40
Annex F (informative) Measurement uncertainty .41
Annex G (informative) Examples of uncertainty calculations .43
Annex H (informative) Maximum sound pressure levels .48
Annex I (informative) Measurement of residual sound .51
Annex J (informative) Objective method for assessing the audibility of tones in noise –
Engineering method .52
Annex K (informative) Objective method for assessing the audibility of tones in noise – Survey
method .53
Annex L (informative) National source specific calculation models .54
Bibliography .57

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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2
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 WTO principles in the Technical Barriers to Trade (TBT)
see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This third edition cancels and replaces the second edition (ISO 1996-2:2007), of which it constitutes a
technical revision.
ISO 1996 consists of the following parts, under the general title Acoustics — Description, measurement and
assessment of environmental noise:
⎯ Part 1: Basic quantities and assessment procedures
⎯ Part 2: Determination of environmental noise levels
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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2
Introduction
Measurements of environmental noise are complicated because there is a very great number of variables to
consider when planning and performing the measurements. As each measurement occasion is subject to
current source and meteorological conditions which cannot be controlled by the operator it is often not
possible to control the resulting uncertainty of the measurements. Instead the uncertainty has to be
determined after the measurements based on an analysis of the acoustic measurements and collected data
on source operating conditions and on meteorological parameters important for the sound propagation.
Because this standard has the ambition both to comply with new and stricter requirements on measurement
uncertainty calculations and to cover all kinds of sources and meteorological conditions it has become rather
complicated to use. The best use of the standard is to use it as a basis for developing more dedicated
standards serving specific sources and aims.
vi © ISO 2015 – All rights reserved

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oSIST ISO/DIS 1996-2:2016
DRAFT INTERNATIONAL STANDARD ISO/DIS 1996-2

Acoustics — Description, measurement and assessment of
environmental noise — Part 2: Determination of environmental
noise levels
1 Scope
This part of ISO 1996 describes how sound pressure levels intended as a basis for assessing environmental
noise can be determined by direct measurement and by extrapolation of measurement results by means of
calculation. This International Standard is primarily intended to be used outdoors but some guidance is given
for indoor measurements as well. It is flexible and to a large extent the user determines the measurement
effort and, accordingly, the measurement uncertainty, which has to be determined and reported in each case.
Thus no limits for allowable maximum uncertainty are set up. Often the measurement results have to be
combined with calculations to correct for reference operating or propagation conditions different from those
during the actual measurement. This International Standard can be applied on all kinds of environmental noise
sources, such as road and rail traffic noise, aircraft noise and industrial noise.
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 1996-1, Acoustics — Description, measurement and assessment of environmental noise — Part 1: Basic
quantities and assessment procedures
ISO 9613-1, Attenuation of sound during propagation outdoors — Part 1: Calculation of the absorption of
sound by the atmosphere
ISO 20906, Acoustics — Unattended monitoring of aircraft sound in the vicinity of airports
ISO 20906:2009/Amd 1, Acoustics — Unattended monitoring of aircraft sound in the vicinity of airports —
Amendment 1
1)
ISO/PAS 20065 , Acoustics — Objective method for assessing the audibility of tones in noise — Engineering
method
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
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1996-1 and the following apply.

1) To be published
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1

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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2
3.1
measurement time interval
time interval during which measurements are conducted
Note 1 to entry: For measurements of sound exposure level or equivalent-continuous sound pressure level, the
measurement time interval is the time-period of integration.
Note 2 to entry: For measurements of maximum sound pressure level or percent exceedance level, etc., the
measurement time interval is the time-period of observation.
3.2
observation time interval
time interval during which a series of measurements is conducted
3.3
prediction time interval
time interval over which levels are predicted
Note 1 to entry: It is now perhaps more common to predict sound levels using computers than to measure them for
some sources such as transportation noise sources. The prediction time interval corresponds to the measurement time
interval except, for the former, the levels are predicted, and for the latter, the levels are measured.
3.4
long-term measurements
measurements sufficiently long to encompass all emission situations and meteorological conditions which are
needed to obtain a representative average
3.5
short-term measurements
measurements during measurement time intervals with well-defined emission and meteorological conditions
3.6
receiver location
location at which the noise is assessed
3.7
calculation method
set of algorithms to calculate the sound pressure level at a specified receiver location from measured or
predicted sound power levels and sound attenuation data
3.8
prediction method
sub-set of a calculation method, intended for the calculation of future noise levels
3.9
meteorological window
set of weather conditions during which measurements can be performed with limited and known variation in
measurement results due to weather variation
3.10
emission window
set of emission conditions during which measurements can be performed with limited and known variation in
measurement results due to variations in operating conditions
3.11
sound path radius of curvature
R
cur
radius approximating the curvature of the sound paths, due to atmospheric refraction
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2

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oSIST ISO/DIS 1996-2:2016
ISO/DIS 1996-2
Note 1 to entry: R is given in m.
cur
Note 2 to entry: Often the parameter used is 1/R to avoid infinitely large values during straight ray propagation.
cur
3.12
monitor
instrumentation used for a single automated continuous sound monitoring terminal which monitors the A-
weighted levels, its spectra and all relevant meteorological quantities such as wind speed, wind direction, rain,
humidity, atmospheric stability etc.
Note 1 to entry: Meteorological measurements need not be taken at each monitor provided such measurements are
taken within an appropriate distance from the monitors and such distance is given in the report.
3.13
automated sound monitoring system
entire automated continuous sound monitoring system including all monitors, the base or central data
collection position (host station) and all software and hardware involved in its operation
3.14
reference condition
condition to which the measurement results are to be referred (corrected)
Note 1 to entry: Examples of reference conditions are atmospheric sound absorption at yearly average temperature and
humidity and yearly average traffic flows for day, evening and night respectively.
3.15
independent measurements
consecutive measurements carried out with a time space long enough to make both source operating
conditions and sound propagation conditions statistically independent of the same conditions of other
measurements in the series
Note 1 to entry: In order to achieve independent conditions for meteorological conditions a time space of several days
is normally required.
3.16
low frequency sound
sound containing frequency components of interest within the range covering the one-third octave bands
16 Hz to 200 Hz.
Note 1 to entry: This definition is specific for this standard. Other definitions may apply in different national regulations.
4 Measurement uncertainty
The uncertainty of sound pressure levels determined as described in this document depends on the sound
source and the measurement time interval, the weather conditions, the distance from the source and the
measurement method and instrumentation. The measurement uncertainty shall be determined in compliance
with the ISO/IEC Guide 98-3 (GUM). Choose one of the following approaches that all are GUM-compatible:
i) The modelling approach that consists in identifying and quantifying all major sources of uncertainty (the
so-called uncertainty budget). This is the preferred method.
ii) The inter-laboratory approach that consists in carrying out a round robin test in order to determine the
standard-deviation of reproducibility of the measurement method.
iii) The hybrid approach that consists in using jointly the modelling approach and the inter-laboratory
approach. In this case, the inter-laboratory approach is used for components of the uncertainty budget
which contribution cannot be quantified using the mathematical model of the modelling approach
because of lack of technical knowledge.
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According to the modelling approach each significant source of uncertainty has to be identified. Systematic
effects shall be eliminated or reduced by the application of corrections wherever possible. If the quantity to be
measured is L, which is a function of the quantities x the formula becomes
j
L = f (x ,x ,x ,.,x ) (1)
1 2 3 j
the combined standard uncertainty is given by
If each quantity has the standard uncertainty u
j
n
2
u(L ) = ()c u (2)
j j

1
assuming that the input quantities x are independent. Under the same assumptions the sensitivity coefficient
j
c is given by
j
∂f
c = (3)
j
∂x
j
The measurement uncertainty to be reported is the uncertainty associated with a chosen coverage probability.
By convention, a coverage probability of 95 % is usually chosen, with an associated coverage factor of 2. This
means that the result becomes L + 2 u.
NOTE Cognizant authorities may set other coverage probabilities. A coverage factor of 1,3 will, e.g., provide a
coverage probability of 80 %.
For environmental noise measurements f(x ) is extremely complicated and it is hardly feasible to put up exact
j
equations for the function f. Following the principles given in ISO 3745 [1], some important sources of
uncertainty can be identified; for an individual measurement, Formula (4) applies:
−0,1(L'−L )
res
L = L'+10lg(1−10 )dB +δ +δ +δ (4)
sou met loc
where
L is the estimated value during the specified conditions for which a measured value is wanted,
L' is the measured value including residual sound, L ,
res
δ is an input quantity to allow for any uncertainty due to deviations from the expected operating
sou
conditions of the source,
δ is an input quantity to allow for any uncertainty due to meteorological conditions deviating from the
met
assumed meteorological conditions,
δ is an input quantity to allow for any uncertainty due to the selection of receiver location.
loc
Often δ + δ is determined directly from measurements, see 10.5.
sou met
L' and L are both dependent on δ which is an input quantity to allow for any uncertainty of the
res slm
measurement chain (sound level meter in the simplest case). In addition L depends on δ wich is an input
res res
quantity to allow for any uncertainty due to residual sound. Table 1 explains further the relationship between
the quantities in Formula (4) and their estimate and uncertainty.
Formula (4) is very simplified and each source of uncertainty is a function of several other sources of
uncertainty. In principle Formula (4) could be applied on any measurement lasting from seconds to years. In
6.1 and 6.2 the measurements are divided into long- and short-term measurements respectively. A short-term
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measurement may typically range between 10 minutes and a few hours whereas a typical long-term
measurement may range between a month and a year.
In Table 1 guidance is given how to determine c and u for insertion into Formula (2).
j j
Table 1 — Example of an uncertainty budget for a measured value
Quantity Estimate Standard Magnitude of Clause for
uncertainty, u sensitivity guidance
j
dB coefficient, c
j
dB
L’ u(L’) Annex F
L’+δ 1
slm

1) −0,1(L'−L )
res
1−10
0,5
0 u 1 7.2 – 7.5
δ
sou sou
Annex D
0 u 1 8, Annex A
δ met
met
0,0 - 6,0 u 1 Annex B
δ loc
loc
−0,1(L'−L )
L u Annex F
L +δ res res res
res res
10

−0,1(L'−L )
res
1−10
1)
0,5 refers to a class 1 sound level meter. A class 2 sound level meter would have the standard uncertainty
1,5 dB.

The numbers given in Table 1 refer to A-weighted equivalent-continuous sound pressure levels only. Higher
uncertainties are to be expected on maximum levels, frequency band levels and levels of tonal components in
noise. In many cases the measured values have to be corrected to other source operating conditions not
representing the measured cases but the yearly average. Similarly other measurements may have to be
corrected to other meteorological conditions in order to make L -calculations possible. Uncertainty
den
calculations for such cases are given in Annex F.
NOTE Some examples, including a spread sheet, of complete uncertainty calculations are given in Annex G.
5 Instrumentation
5.1 Instruments for acoustical measurements
5.1.1 General
The instruments for measuring sound pressure levels, including microphone(s) as well as cable(s),
windscreen(s), recording devices and other accessories, if used, shall meet the requirements for a class 1
instrument according to IEC 61672-1 for free field or random incidence application, as appropriate. Filters
shall meet the requirements for a class 1 instrument according to IEC 61260. A windscreen shall always be
used during outdoor measurements.
NOTE Class 1 tolerance limits of IEC 61672-1 apply over a temperature range of -10°C to +50°C. If the instrument is
to be used in temperatures outside the range -10°C to +50°C, then there may be an increase in measurement uncertainty.
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5.1.2 Calibration
At the beginning and at the end of every measurement the entire sound pressure level measuring system
shall be checked at one or more frequencies by means of a sound calibrator meeting the requirements for a
class 1 instrument according to IEC 60942. Without any further adjustment, the difference between the
readings of two consecutive checks shall be less than or equal to 0,5 dB. If this value is exceeded, the results
of measurements obtained after the previous satisfactory check shall be discarded. For long-term monitoring
of several days or more, the requirements of ISO 20906:2009/Amd 1 apply.
5.1.3 Verification
Compliance of the sound pressure level measuring instrument, the filters and the sound calibrator shall be
verified by the existence of a valid certificate of compliance with the measurement parameters specified in the
relevant test methods in IEC 61672-3 [5], IEC 61260 and IEC 60942.
All compliance testing shall be conducted by a laboratory being accredited or otherwise nationally authorized
to perform the relevant tests and calibrations and ensuring metrological traceability to the appropriate
measurement standards. The recommended time interval for testing of system performance is once a year.
The maximum allowable interval is two years.
5.1.4 Long-term monitoring
The maximum permissible error for instruments used for meteorological measurements shall be
⎯ ± 0,5 K for temperature measuring devices,
...