ISO 1996-2:2007

INTERNATIONAL ISO
STANDARD 1996-2
Second edition
2007-03-15
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

Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved

Contents Page
Foreword. v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Measurement uncertainty . 2
5 Instrumentation. 3
5.1 Instrumentation system . 3
5.2 Calibration . 3
6 Operation of the source . 4
6.1 General. 4
6.2 Road traffic . 4
6.3 Rail traffic . 5
6.4 Air traffic . 5
6.5 Industrial plants . 5
6.6 Low-frequency sound sources. 6
7 Weather conditions. 6
7.1 General. 6
7.2 Conditions favourable to sound propagation. 6
7.3 Average sound pressure levels under a range of weather conditions . 7
8 Measurement procedure . 7
8.1 Principle. 7
8.2 Selection of measurement time interval. 7
8.3 Microphone location. 7
8.4 Measurements. 9
9 Evaluation of the measurement result. 10
9.1 General. 10
9.2 Time-integrated levels, L and L . 11
E eqT
9.3 Maximum level, L . 11
max
9.4 Exceedance levels, L . 12
N,T
9.5 Indoor measurements . 12
9.6 Residual sound . 13
10 Extrapolation to other conditions . 13
10.1 Location . 13
10.2 Other time and operating conditions. 13
11 Calculation. 14
11.1 General. 14
11.2 Calculation methods. 14
12 Information to be recorded and reported.15
Annex A (informative) Meteorological window and measurement uncertainty due to weather . 16
Annex B (informative) Microphone positions relative to reflecting surfaces . 23
Annex C (informative) Objective method for assessing the audibility of tones in noise —
Reference method. 27
Annex D (informative) Objective method for assessing the audibility of tones in noise —
Simplified method . 36
Annex E (informative) National source-specific calculation methods. 37
Bibliography . 40

iv © ISO 2007 – All rights reserved

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 1996-2 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This second edition of ISO 1996-2, together with ISO 1996-1:2003, cancels and replaces the first edition
(ISO 1996-2:1987), ISO 1996-1:1982 and ISO 1996-3:1987. It also incorporates the Amendment
ISO 1996-2:1987/Amd.1:1998.
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

INTERNATIONAL STANDARD ISO 1996-2:2007(E)

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 can be determined by direct measurement, by
extrapolation of measurement results by means of calculation, or exclusively by calculation, intended as a
basis for assessing environmental noise. Recommendations are given regarding preferable conditions for
measurement or calculation to be applied in cases where other regulations do not apply. This part of ISO 1996
can be used to measure with any frequency weighting or in any frequency band. Guidance is given to
evaluate the uncertainty of the result of a noise assessment.
NOTE 1 As this part of ISO 1996 deals with measurements under actual operating conditions, there is no relationship
between this part of ISO 1996 and other ISO standards specifying emission measurements under specified operating
conditions.
NOTE 2 For the sake of generality, the frequency and time weighting subscripts have been omitted throughout this part
of ISO 1996.
2 Normative references
The following referenced documents are indispensable for the application 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 1996-1:2003, Acoustics — Description, measurement and assessment of environmental noise —
Part 1: Basic quantities and assessment procedures
ISO 7196, Acoustics — Frequency-weighting characteristic for infrasound measurements
IEC 60942:2003, Electroacoustics — Sound calibrators
IEC 61260:1995, Electroacoustics — Octave-band and fractional-octave band filters
IEC 61672-1:2002, Electroacoustics — Sound level meters — Part 1: Specifications
Guide to the expression of uncertainty in measurement (GUM), BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML,
1993 (corrected and reprinted, 1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1996-1 and the following apply.
3.1
receiver location
location at which the noise is assessed
3.2
calculation method
set of algorithms to calculate the sound pressure level at arbitrary locations from measured or predicted sound
emission and sound attenuation data
3.3
prediction method
subset of a calculation method, intended for the calculation of future noise levels
3.4
measurement time interval
time interval during which a single measurement is conducted
3.5
observation time interval
time interval during which a series of measurements is conducted
3.6
meteorological window
set of weather conditions during which measurements can be performed with limited and known variation in
measurement results due to weather variation
3.7
soundpath radius of curvature
R
radius approximating the curvature of the sound paths due to atmospheric refraction
NOTE R is expressed in kilometres.
3.8
low-frequency sound
sound containing frequencies of interest within the range covering the one-third octave bands from 16 Hz to
200 Hz
4 Measurement uncertainty
The uncertainty of sound pressure levels determined as described in this part of ISO 1996 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
accordance with the GUM. Some guidelines on how to estimate the measurement uncertainty are given in
Table 1, where the measurement uncertainty is expressed as an expanded uncertainty based on a combined
standard uncertainty multiplied by a coverage factor of 2, providing a coverage probability of approximately
95 %. Table 1 refers to A-weighted equivalent continuous sound pressure levels only. Higher uncertainties
can be expected on maximum levels, frequency band levels and levels of tonal components in noise.
NOTE 1 Table 1 is not complete. When preparing this part of ISO 1996, insufficient information was available. In many
cases, it is appropriate to add more uncertainty contributions, e.g. the one associated with the selection of microphone
location.
NOTE 2 Cognizant authorities can set other levels of confidence. A coverage factor of 1,3, for example, provides a
level of confidence of 80 % and a coverage factor of 1,65, a level of confidence of 90 %.
2 © ISO 2007 – All rights reserved

In test reports, the coverage probability shall always be stated together with the expanded uncertainty.
Table 1 — Overview of the measurement uncertainty for L
Aeq
Standard uncertainty Combined standard Expanded
uncertainty measurement
Due to Due to Due to weather Due to residual
uncertainty
a d
σ
instrumentation operating and ground sound
t
b c
± 2,0 σ
conditions conditions
22 2 2 t
1, 0++X YZ+
1,0 Z
dB dB
X Y
dB dB
dB dB
a
For IEC 61672-1:2002 class 1 instrumentation. If other instrumentation (IEC 61672-1:2002 class 2 or IEC 60651:2001/
IEC 60804:2000 type 1 sound level meters) or directional microphones are used, the value will be larger.

b
To be determined from at least three, and preferably five, measurements under repeatability conditions (the same measurement
procedure, the same instruments, the same operator, the same place) and at a position where variations in meteorological conditions
have little influence on the results. For long-term measurements, more measurements are required to determine the repeatability
standard deviation. For road-traffic noise, some guidance on the value of X is given in 6.2.

c
The value varies depending upon the measurement distance and the prevailing meteorological conditions. A method using a
simplified meteorological window is provided in Annex A (in this case Y = σ ). For long-term measurements, it is necessary to deal with
m
different weather categories separately and then combined together. For short-term measurement, variations in ground conditions are
small. However, for long-term measurements, these variations can add considerably to the measurement uncertainty.

d
The value varies depending on the difference between measured total values and the residual sound.
5 Instrumentation
5.1 Instrumentation system
The instrumentation system, including the microphone, wind shield, cable and recorders, if any, shall conform
to the requirements of one of the following:
⎯ a class 1 instrument as specified in IEC 61672-1:2002,
⎯ a class 2 instrument as specified in IEC 61672-1:2002.
A wind shield shall always be used during outdoor measurements.
Cognizant authorities may require instruments conforming with IEC 61672-1:2002 class 1.
NOTE 1 IEC 61672-1:2002 class 1 instruments are specified over the range of air temperatures from − 10 °C to
+ 50 °C and IEC 61672-1:2002 class 2 instruments from 0 °C to + 40 °C.
NOTE 2 Most sound level meters that meet the requirements in IEC 60651 and IEC 60804 also meet the acoustic
requirements of IEC 61672-1.
For measurements in octave or one-third-octave bands, the class 1 and class 2 instrumentation systems shall
meet the requirements of a class 1 or class 2 filter, respectively, specified in IEC 61260:1995.
5.2 Calibration
Immediately before and after each series of measurements, a class 1, or, in the case of class 2 instruments, a
class 1 or a class 2 sound calibrator in accordance with IEC 60942:2003 shall be applied to the microphone to
check the calibration of the entire measuring system at one or more frequencies.
If measurements take place over longer periods of time, e.g. over a day or more, then the measurement
system should be checked either acoustically or electrically at regular intervals, e.g. once or twice a day.
It is recommended to verify the compliance of the calibrator with the requirements of IEC 60942 at least once
a year and the compliance of the instrumentation system with the requirements of the relevant IEC standards
at least every two years in a laboratory with traceability to national standards.
Record the date of the last check and confirmation of the compliance with the relevant IEC standard.
6 Operation of the source
6.1 General
The source operating conditions shall be statistically representative of the noise environment under
consideration. To obtain a reliable estimate of the equivalent continuous sound pressure level as well as the
maximum sound pressure level, the measurement time interval shall encompass a minimum number of noise
events. For the most common types of noise sources, guidance is given in 6.2 to 6.5.
NOTE The operating conditions of this part of ISO 1996 are always the actual ones. Accordingly, they normally differ
from the operating conditions stated in International Standards for noise emission measurements.
The equivalent continuous sound pressure level, L of noise from rail and air traffic can often be determined
eqT,
most efficiently by measuring a number of single event sound exposure levels, L , and calculating the
E
equivalent continuous sound pressure level based on these. Direct measurement of the equivalent continuous
sound pressure level, L , is possible when the noise is stationary or time varying, such as is the case with
eqT
noise from road traffic and industrial plants. Single-event sound exposure levels, L , from road vehicles can
E
be measured only at roads with a small traffic volume.
6.2 Road traffic
6.2.1 L measurement
eq
When measuring L , the number of vehicle pass-bys shall be counted during the measurement time interval.
eq
If the measurement result is converted to other traffic conditions, distinction shall be made between at least
the two categories of vehicles “heavy” and “light”. To determine if the traffic conditions are representative, the
average traffic speed shall be measured and the type of road surface noted.
NOTE A common definition of a heavy vehicle is one exceeding the mass 3 500 kg. Often heavy vehicles are divided
into several sub-categories depending on the number of wheel axles.
The number of vehicle pass-bys needed to average the variation in individual vehicle noise emission depends
on the required accuracy of the measured L . If no better information is available, the standard uncertainty
eq
denoted by X in Table 1 can be calculated by means of Equation (1):
X ≅ dB (1)
n
where n is the total number of vehicle pass-bys.
NOTE Equation (1) refers to mixed road traffic. If only one category of vehicles is involved, the standard uncertainty will
be smaller.
When L from individual vehicle pass-bys are registered and used together with traffic statistics to calculate
E
L over the reference time interval, the minimum number of vehicles per category shall be 30.
eq
6.2.2 L measurement
max
The maximum sound pressure levels as defined in ISO 1996-1 differ among vehicle categories. Within each
vehicle category, a certain spread of maximum sound pressure levels is encountered due to individual
differences among vehicles and variation in speed or driving patterns. The maximum sound pressure level
should be determined based on the sound pressure level measured during at least 30 pass-bys of vehicles of
the category considered.
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6.3 Rail traffic
6.3.1 L measurement
eq
Measurements shall consist of the pass-by noise from at least 20 trains. Each category of train potentially
contributing significantly to the overall L shall be represented by at least five pass-bys. If necessary,
eq
measurements shall be continued on a subsequent day.
6.3.2 L measurement
max
To determine the maximum sound pressure level for a certain category of train, the maximum sound pressure
level during at least 20 pass-bys shall be recorded. If it is not possible to obtain this many recordings, it shall
be stated in the report how many train pass-bys were analysed and the influence on the uncertainty shall be
assessed.
6.4 Air traffic
6.4.1 L measurement
eq
Measurements shall consist of the pass-by noise from five or more of each type of aircraft contributing
significantly to the sound pressure level to be determined. Ensure that traffic pattern (runway use, take-off and
landing procedures, airfleet mix, time-of-day distribution of the traffic) is relevant for the issue under
consideration.
6.4.2 L measurement
max
If the purpose is to measure the maximum sound pressure level from air traffic in a specific residential area,
ensure that the measurement period contains the aircraft types with the highest noise emission using the flight
tracks of nearest proximity. Maximum sound pressure levels shall be determined from at least five and
preferably 20 or more occurrences of the most noisy relevant aircraft operation. To estimate percentiles of the
distribution of maximum sound pressure levels, record at least 20 relevant events. If it is not possible to obtain
this many recordings, it shall be stated in the report how many aircraft pass-bys are analysed and the
influence on the uncertainty shall be assessed.
NOTE Pass-by noise can be caused by aircraft in flight or on the ground, e.g. taxiing.
6.5 Industrial plants
6.5.1 L measurement
eq
The source operating conditions shall be divided into classes. For each class, the time variation of the sound
emission from the plant shall be reasonably stationary in a stochastical sense. The variation shall be less than
the variation in transmission-path attenuation due to varying weather conditions (see Clause 7). The time
variation of the sound emission from the plant shall be determined from 5 min to 10 min L values measured
eq
at a distance long enough to include noise contributions from all major sources and short enough to minimize
meteorological effects (see Clause 7) during a certain operating condition. If the source is cyclic, the
measurement time shall encompass a whole number of cycles. A new categorization of the operating
conditions shall be made if the criterion is exceeded. If the criterion is met, measure L during each class of

eq
operating condition and calculate the resulting L , taking into account the frequency and duration of each
eq
class of operating condition.
6.5.2 L measurement
max
If the purpose is to measure the maximum sound pressure level of noise from industrial plants, ensure that the
measurement period contains the plant operating condition with the highest noise emission occurring at the
nearest proximity to the receiver location. Maximum sound pressure levels shall be determined from at least
five events of the most noisy relevant operation condition.
NOTE The operating condition is defined by the activity as well as its location.
6.6 Low-frequency sound sources
Examples of low-frequency sound sources are helicopters, sound from bridge vibrations, subway trains,
stamping plants, pneumatic construction equipment, etc. ISO 1996-1:2003, Annex C, contains a further
discussion on low-frequency sound. Procedures to measure low-frequency noise are given in 8.3.2 and 8.4.9.
7 Weather conditions
7.1 General
The weather conditions shall be representative of the noise exposure situation under consideration.
The road or rail surface shall be dry and the ground surface shall not be covered with snow or ice and should
be neither frozen nor soaked by excessive amounts of water, unless such conditions are to be investigated.
Sound pressure levels vary with the weather conditions. For soft ground such variation is modest when
Equation (2) applies:
hh+
sr
W 0,1 (2)
r
where
h is the source height;
s
h is the receiver height;
r
r is the distance between the source and receiver.
If the ground is hard, larger distances are acceptable.
The meteorological conditions during measurement shall be described or, if necessary, monitored. When the
condition in Equation (2) is not fulfilled, the weather conditions can seriously affect the results of the
measurement. General guidance is given in 7.2 and 7.3, while more precise guidance is given in Annex A.
Upwind of the source, measurements have large uncertainties and such conditions are not usually suitable for
short-term environmental-noise measurements.
7.2 Conditions favourable to sound propagation
To facilitate the comparison of results, it is convenient to carry out measurements under selected
meteorological conditions, so that the results are reproducible. This is the case under rather stable sound
propagation conditions.
Such conditions exist when the sound paths are refracted downwards, for example during downwind, meaning
high sound pressure levels and moderate level variation. The sound path radius of curvature, R, is positive
and its value depends on the wind speed and temperature gradients near the ground, as expressed in
Equation (A.1).
With one dominant source, choose meteorological conditions with downward sound-ray curvature from the
source to the receiver and adopt measurement time intervals corresponding to the conditions given in
Annex A, for example R < 10 km.
As a guidance, the condition R < 10 km holds when
⎯ the wind is blowing from the dominant sound source to the receiver (daytime within an angle of ± 60°,
night-time within an angle of ± 90°),
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⎯ the wind speed, measured at a height of 3 m to 11 m above the ground, is between 2 m/s and 5 m/s
during the daytime or more than 0,5 m/s at night-time,
⎯ no strong, negative temperature gradient occurs near the ground, e.g. when there is no bright sunshine
during the daytime.
7.3 Average sound pressure levels under a range of weather conditions
Estimating average environmental noise levels as they occur over a range of weather conditions requires long
measurement time intervals, often several months. Alternatively, well monitored, short-term measurements
representing different weather conditions can be combined with calculations taking weather statistics into
account to determine long-term averages.
The combination of source operating conditions and weather-dependent sound propagation shall be taken into
account, so that every important component of sound exposure is represented in the measurement results.
To determine a long-term average noise level as it can occur during a year, it is necessary to take into
account the variations in source emission and sound propagation during a whole year.
8 Measurement procedure
8.1 Principle
For the selection of appropriate observation and measurement time intervals, it can be necessary to take
survey measurements over relatively long time periods.
8.2 Selection of measurement time interval
Select the measurement-time interval to cover all significant variations in noise emission and propagation. If
the noise displays periodicity, the measurement time interval should cover an integer number of at least three
periods. If continuous measurements over such a period cannot be made, measurement time intervals shall
be chosen so that each represents a part of the cycle and so that, together, they represent the complete cycle.
When measuring the noise from single events (e.g. aircraft fly-over, during which the noise varies during the
fly-over but is absent during a considerable portion of the reference time interval), measurement time intervals
shall be chosen so that the sound exposure level, L , of the single event can be determined (see 8.4.3).
E
8.3 Microphone location
8.3.1 Outdoors
To assess the situation at a specific location, use a microphone at that specific location.
For other purposes, use one of the following positions:
a) free-field position (reference condition);
This case is either an actual case or a theoretical case for which the hypothetical free field over ground sound
pressure level of the incident sound field outside a building is calculated from results of measurements made
close to the building [see 8.3.1 b) and 8.3.1 c)]. The incident field notation refers to the fact that all reflections,
if any, from any building behind the microphone are eliminated. A position behind a house that acts as a
barrier is also considered to be an incident field position but in this case positions 8.3.1 b) and 8.3.1 c) are not
relevant and reflections from the back side of the building are included.
b) position with the microphone flush-mounted on the reflecting surface;
In this case, the correction applied to get the incident sound field is − 6 dB. Guidance on the conditions to
meet is given in Annex B. For other conditions, it is necessary to use different corrections.
NOTE 1 + 6 dB is the difference between a façade-mounted microphone and a free-field microphone in an ideal case.
In practice, minor deviations from this value do occur.
c) position with the microphone 0,5 m to 2 m in front of the reflecting surface;
In this case, the correction applied to get the incident sound field is − 3 dB. Guidance on the conditions to
meet is given in Annex B. For other conditions, it is necessary to use different corrections.
NOTE 2 The difference between the sound pressure level at a microphone placed 2 m in front of the façade and at a
free-field microphone is close to 3 dB in an ideal case where no other vertical reflecting obstacle influences sound
propagation to the studied receiver. In complex situations, e.g. high building density on the site, canyon street, etc., this
difference can be much higher. Even in the ideal case, there can be some restrictions. For near-grazing incidence, this
position is not recommended as the deviations can be greater. For further guidance, see Annex B.
In principle, any of the positions described in this subclause can be used, provided that the position used is
reported together with a statement of whether or not any correction to the reference condition was made. In
some specific cases, the positions described in this subclause are subject to further restrictions. For further
guidance see Annex B.
For general mapping, use a microphone height of (4,0 + 0,5) m in multi-storey residential areas. In one-storey
residential areas and recreational areas, use a microphone height of (1,2 + 0,1) m or (1,5 + 0,1) m.
For permanent noise monitoring, other microphone heights may be used.
Noise levels in grid points for use in noise mapping are normally calculated. If, in special cases,
measurements are carried out, the density of grid points selected in an area depends on the spatial resolution
required for the study concerned and the spatial variation of sound pressure levels of the noise. This variation
is strongest in the vicinity of sources and large obstacles. The density of grid points should, therefore, be
higher in these places. In general, the difference in sound pressure levels between adjacent grid points should
not be greater than 5 dB. If significantly higher differences are encountered, intermediate grid points shall be
added.
8.3.2 Indoors
Use at least three discrete positions evenly distributed in areas of the room where affected persons preferably
spend time, or, as an alternative for continuous noise, use a rotating microphone system.
If dominant low-frequency noise is suspected (see 6.6), one of the three positions shall be in a corner and no
rotating microphone is allowed. The corner position shall be 0,5 m from all boundary surfaces in a corner with
the heaviest walls and without any wall openings nearer than 0,5 m.
The other microphones shall be positioned at least 0,5 m from walls, ceiling or floor, and at least 1 m from
significant sound-transmission elements such as windows or air-intake openings. The distance between
neighbouring microphone positions shall be at least 0,7 m. If a continuously moving microphone is used, its
sweep radius shall be at least 0,7 m. The plane of traverse shall be inclined in order to cover a large portion of
the permitted room space and shall not lie within 10° of the plane of any room surface. The above
requirements concerning the distance from discrete microphone positions to walls, ceiling, floor and
transmission elements also apply to moving microphone positions. The duration of a traverse period shall be
not less than 15 s.
NOTE 1 In cases where there are only A-weighted measurements and only small contributions to the A-weighted level
from low frequencies, it can, in some cases, be sufficient to use one microphone position.
The procedures in this subclause are primarily intended for rooms with volumes < 300 m . For larger rooms,
more microphone positions can be appropriate. In such cases, for low-frequency noise, one third of the extra
positions should be corner positions.
8 © ISO 2007 – All rights reserved

8.4 Measurements
8.4.1 General
NOTE Variables and rating levels such as the yearly average, L , L and L , are defined in ISO 1996-1.
day evening den
8.4.2 Equivalent continuous sound pressure level, L
eqT
Normal measurement of L : if the traffic density is low or the residual sound pressure level high, the L
eq eq
levels shall, if possible, be determined from L measurements of individual pass-bys. This is often the case for
E
rail- and air-traffic noise; see 6.3.1 and 6.4.1, respectively. For short-term averaging, unless the condition in
Equation (2) is fulfilled, measure for at least 10 minutes to average weather-induced variations in the
propagation path. If the condition in Equation (2) is fulfilled, 5 min is usually sufficient. It can be necessary to
increase these minimum times in order to get a representative sample of source operating conditions (see
Clause 6).
8.4.3 Sound exposure level, L
E
If it is not practicable to measure L for the required number of events, measure L for each individual event.
eq E
Measure a minimum number of events of the source operation as specified in Clause 6. Measure each event
during a time period that is long enough to include all important noise contributions. For a pass-by, measure
until the sound pressure level has dropped at least 10 dB below the maximum level.
8.4.4 N percent exceedance level, L
N,T
During the measurement time interval, record the short-term L (where T u 1 s) or record the sound
eqT
pressure level with a sampling time less than the time constant of the time weighting used. The class interval
into which recorded results are placed shall be 1,0 dB or less. The parameter basis and, where applicable,
time weighting, of the recording period and the class interval used to determine the L shall be reported, e.g.
N,T
“based on 10 ms sampling of L with a class interval of 0,2 dB” or “based on L , class width 1,0 dB”.
F eq1s
8.4.5 Maximum time- and frequency-weighted sound pressure level, L , L
Fmax Smax
Using time weighting F or S, as specified, measure L or L for a minimum number of events of the
Fmax Smax
source operating conditions as specified in Clause 6. Record each result.
NOTE Time weighting F correlates better with human perception than time weighting S. Using time weighting S, in
general, improves the reproducibility.
8.4.6 Peak sound pressure level, L
peak
See ISO 10843 for sonic booms, blasts, etc.
NOTE IEC 61672-1 specifies the accuracy only of a peak detector using C-weighting.
8.4.7 Tonal sound
If the noise characteristics at the receiver location include audible tone(s), an objective measurement of the
prominence of the tones should be carried out. The microphone positions with the most audible tone(s) should
be selected and the analysis should be carried out as described in Annex C for the reference method and as
described in Annex D for a simplified method.
NOTE In general, tonal analysis of indoor noise is not recommended due to the modal behaviour of tones in rooms.
For some frequency bands, it is also problematical at microphones in front of a façade.
8.4.8 Impulsive sound
There is no generally accepted method to detect impulsive sound using objective measurements. If impulsive
sound occurs, identify the source and compare it to the list of impulsive sound sources in ISO 1996-1. In
addition, make sure that the impulsive sound is representative and present in the measurement time interval.
8.4.9 Low-frequency sound
Indoors, measure at three microphone positions as specified in 8.3.2. Outdoors, measure in the free field or
directly on a façade; see Annex B.
The methods in this part of ISO 1996 are generally valid down to the 16 Hz octave band. However, for these
low-frequency measurements, the microphone shall be at least 16 m from the nearest significant reflecting
surface other than the ground in order to be a free-field (incident-sound field) measurement.
NOTE The microphone position in front of the reflecting surface mentioned in 8.3.1 c) has not been defined for
low-frequency sound measurements.
8.4.10 Residual sound
When measuring environmental noise, residual sound as defined in ISO 1996-1, as all noise other than the
specific sounds under investigation, is often a problem. One reason is that regulations often require that the
noise from different types of sources be dealt with separately. This separation, e.g. of traffic noise from
industrial noise, is often difficult to accomplish in practice. Another reason is that the measurements are
normally carried out outdoors. Wind-induced noise, directly on the microphone and indirectly on trees,
buildings, etc., may also affect the result. The character of these noise sources can make it difficult or even
impossible to carry out any corrections. However, see 9.6 to carry out corrections if it is necessary to measure
the residual sound.
8.4.11 Frequency range of measurements
If the frequency content of the noise is required, then, unless otherwise specified, measure the sound
pressure level using octave-band filters having the following mid-band frequencies:
63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 000 Hz, 2 000 Hz, 4 000 Hz, 8 000 Hz
Optionally, the measurements can be made in one-third-octave bands with mid-band frequencies from 50 Hz
to 10 000 Hz.
Frequency bands without significant influence (< 0,5 dB) on the A-weighted sound pressure level may be
excluded and this exclusion should be reported.
For low-frequency sound, the frequency range of interest appears to be from about 5 Hz to about 100 Hz. In
the range below about 20 Hz, the G-weighting in accordance with ISO 7196 is used in some countries to
assess sound. Above about 15 Hz, octave-band or one-third-octave band analysis in the range from about
16 Hz to 100 Hz is used in several countries. For low-frequency sound, this part of ISO 1996 includes the
extended frequency range from about 12 Hz to 200 Hz (the 16 Hz, 31 Hz, 63 Hz, 125 Hz and 160 Hz
one-third-octave bands) and evaluation shall be made in accordance with ISO 7196.
9 Evaluation of the measurement result
9.1 General
Correct all measured outdoor values to the reference condition, if applicable, that is to the free-field level
excluding all reflections but those from the ground.
10 © ISO 2007 – All rights reserved

9.2 Time-integrated levels, L and L
E eqT
For each microphone position and each category of source operating conditions determine the energy
average of the measured values of L or L .
E eqT
NOTE Guidance on how to obtain rating levels such as L and L is given in ISO 1996-1.
Rdn Rden
9.3 Maximum level, L
max
For each microphone position and each category of source operating conditions, determine the following
values, whenever relevant:
⎯ the maximum;
⎯ the arithmetic average;
⎯ the energy average;
⎯ the standard deviation;
⎯ the statistical distribution of the measured values of L .
max
For homogeneous groups of single events with a Gaussian distribution of maximum sound pressure levels,
use Equation (3) and Figure 1 to estimate percentiles of the distribution of maximum sound pressure levels.
_
L =+Lymax ⋅s (3)
max,p
where
L is the maximum level exceeded by p % of the events;
max,p
_
L is the arithmetic average of L from all events;
max
max
s is the standard deviation of the maximum levels from the events (an estimate of the standard
deviation of the Gaussian distribution);
y is the number of standard deviations given by Figure 1.
Figure 1 — Percentage, p, of single events with a maximum sound pressure level
exceeding, by a certain number, y, of standard deviations,
the (arithmetic) mean of a normal distribution of maximum sound pressure levels
EXAMPLE If the fifth highest maximum sound pressure level is required out of 500 vehicles passing, then the
wanted percentile is (5/500) × 100 = 1 % and from Figure 1 the factor, y, to insert in Equation (3) is given by y = 2,33 ≅ 2,3,
that is:
L =+Ls2,3
max()5th highest max()arithmatic average
where s is the standard deviation of the maximum levels.
9.4 Exceedance levels, L
N,T
Analy
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