EN ISO 14257:2001

SLOVENSKI STANDARD
01-december-2002
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Acoustics - Measurement and parametric description of spatial sound distribution curves
in workrooms for evaluation of their acoustical performance (ISO 14257:2001)
Akustik - Messung und Parametrisierung von Schallausbreitungskurven in Arbeiträumen
zum Zweck der Beurteilung der akustischen Qualität der Räume (ISO 14257:2001)
Acoustique - Mesurage et description paramétrique des courbes de décroissance sonore
spatiale dans les locaux de travail en vue de l'évaluation de leur performance acoustique
(ISO 14257:2001)
Ta slovenski standard je istoveten z: EN ISO 14257:2001
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 14257
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2001
ICS 13.140
English version
Acoustics - Measurement and parametric description of spatial
sound distribution curves in workrooms for evaluation of their
acoustical performance (ISO 14257:2001)
Acoustique - Mesurage et description paramétrique des Akustik - Messung und Parametrisierung von
courbes de décroissance sonore spatiale dans les locaux Schallausbreitungskurven in Arbeiträumen zum Zweck der
de travail en vue de l'évaluation de leur performance Beurteilung der akustischen Qualität der Räume (ISO
acoustique (ISO 14257:2001) 14257:2001)
This European Standard was approved by CEN on 5 October 2001.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
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Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14257:2001 E
worldwide for CEN national Members.

prEN ISO 14257:2001 (E)
CORRECTED  2001-12-12
Foreword
The text of the International Standard ISO 14257:2001 has been prepared by Technical
Committee ISO/TC 43 "Acoustics" in collaboration with Technical Committee CEN/TC 211
"Acoustics", the secretariat of which is held by DS.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by April 2002, and conflicting national
standards shall be withdrawn at the latest by April 2002.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of the International Standard ISO 14257:2001 was approved by CEN as a European
Standard without any modification.
NOTE: Normative references to International Standards are listed in annex ZA (normative).
prEN ISO 14257:2001 (E)
(normative)
Annex ZA
Normative references to international publications
with their relevant European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of
any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).
NOTE Where an International Publication has been modified by common modifications, indicated
by (mod.), the relevant EN/HD applies.
Publication Year Title EN Year
ISO 3741 1999 Acoustics - Determination of sound EN ISO 3741 1999
power levels of noise sources using
sound pressure - Precision
methods for reverberation rooms
ISO 3744 1994 Acoustics - Determination of sound EN ISO 3744 1995
power levels of noise sources using
sound pressure - Engineering
method in an essentially free field
over a reflecting plane
ISO 6926 2000 Acoustics - Requirements for the EN ISO 6926 2001
performance and calibration of
reference sound sources used for
the determination of sound power
levels
INTERNATIONAL ISO
STANDARD 14257
First edition
2001-10-15
Acoustics — Measurement and parametric
description of spatial sound distribution
curves in workrooms for evaluation of their
acoustical performance
Acoustique — Mesurage et description paramétrique des courbes de
décroissance sonore spatiale dans les locaux de travail en vue de
l'évaluation de leur performance acoustique
Reference number
ISO 14257:2001(E)
©
ISO 2001
ISO 14257:2001(E)
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ii © ISO 2001 – All rights reserved

ISO 14257:2001(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Sound distribution in a room.3
4.1 General.3
4.2 Spatial sound distribution curves.3
5 Measurement of the spatial sound distribution curve.5
5.1 Specifications regarding the sound source used for the test .5
5.2 Measurement instrumentation .6
5.3 Measurement path and points.7
5.4 Measurement procedure .8
5.5 Representation of the measured data .8
6 Parametric description of the measured spatial sound distribution curve in view of evaluation
of the acoustical performance of workrooms.9
6.1 General.9
6.2 Distance ranges .9
6.3 Determination of the rate of spatial decay of sound pressure levels per distance doubling,DL .9
6.4 Determination of the excess of sound pressure level with respect to a reference sound
distribution curve,DL .10
f
6.5 Evaluation of measured data.12
7 Information to be recorded and reported.12
Annex A (normative) Performance requirements for the sound source to be used for the test .14
Annex B (normative) Correction of measured sound distribution curves to account for differences in
ground reflections and source directivity.16
Annex C (informative) Example of use of this International Standard .17
Bibliography.25
ISO 14257:2001(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 14257 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee
SC 1, Noise.
Annexes A and B form a normative part of this International Standard. Annex C is for information only.
iv © ISO 2001 – All rights reserved

ISO 14257:2001(E)
Introduction
According to ISO 11690-1, the spatial sound distribution in a workroom is described by a curve characterizing the
sound pressure level from a point source with a known sound power level, and with steady emission and
omnidirectional sound radiation as a function of the distance from the source. This International Standard specifies
a method for the determination of that spatial sound distribution curve, and for the derivation of two characteristics
(rate of spatial decay of sound pressure levels per distance doubling and excess of sound pressure level) for the
room in question.
Data obtained using this International Standard are of use for the following:
� acoustical qualification of a room with respect to noise control;
� determination of appropriate positions of a machine and of work stations in a room;
� assessment of the necessity to increase the sound absorption in the room;
� qualitative estimation of the potential performance of screens installed in the room;
� calculation of the noise-immission levels to be expected when machines with known emission are operated at
specified positions in the room.
INTERNATIONAL STANDARD ISO 14257:2001(E)
Acoustics — Measurement and parametric description of spatial
sound distribution curves in workrooms for evaluation of their
acoustical performance
1 Scope
This International Standard specifies a method for measuring the spatial sound distribution curve(s) of a given
workroom. A method is given for determining, from the measured data, two descriptors of the acoustical
performance of a workroom regarding noise control: i.e. the excess of sound pressure level with respect to a free
field, and the sound pressure level decay per distance doubling.
This International Standard does not deal with assessment of the acoustical quality with respect to speech
communication or other psychological factors.
This International Standard is applicable to workrooms of any shape and any dimensions provided that the number
of microphone positions allows the regression calculation to be performed.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 3741, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Precision methods for reverberation rooms
ISO 3744:1994, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Engineering method in an essentially free field over a reflecting plane
ISO 3745, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Precision methods for anechoïc and semi-anechoic rooms
ISO 6926, Acoustics — Requirements for the performance and calibration of reference sound sources used for the
determination of sound power levels
IEC 60651, Sound level meters
IEC 60804, Integrating-averaging sound level meters
IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
ISO 14257:2001(E)
3.1
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure, p, radiated by a sound
source to the square of the reference sound pressure (p =20µPa)
NOTE 1 The sound pressure level is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used, and the time weighting (S, F or I, see IEC 60651),
should be indicated.
3.2
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power radiated by a sound source to the reference
–12
sound power (P =10 W)
NOTE 1 The sound power level is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used should be indicated. For example, the A-weighted
sound power level is L .
WA
3.3
spatial sound distribution curve
curve which shows how the sound pressure level from a reference sound source decreases when the distance to
the source increases
NOTE 1 Such curves are frequency dependent and characterize the acoustic properties of rooms. In some cases, several
spatial sound distribution curves are necessary to characterize a room.
From this curve and for a given range of distances from the source, two main quantities are determined:
� the rate of spatial decay of sound pressure levels per distance doubling (DL ), and
� the excess of sound pressure level (DL ).
f
Three distance ranges are normally of interest: near, middle and far regions. These two quantities (DL and DL ) are useful for
2 f
assessing the acoustic quality of a room.
NOTE 2 Adapted from ISO 11690-1:1996, definition 3.4.11.
3.4
sound distribution value
D (r)
j
difference, in decibels, between the sound pressure level, in a given octave band and at a microphone position
located at a given distance from the reference sound source, and the sound power level of the reference sound
source in the same octave band, as given by
Dr��L r L (1)
� � � �
jpj Wj
where
L is the sound power level of the reference sound source used for the test;
Wj
L is the sound pressure level at each measurement point located at a distance r from the sound source;
pj
j is the number of the octave band.
NOTE The sound distribution value for a given sound power spectrum can be calculated according to equation (3).
2 © ISO 2001 – All rights reserved

ISO 14257:2001(E)
3.5
rate of spatial decay of sound pressure levels per distance doubling
DL
slope, in decibels per distance doubling, of the spatial sound distribution curve for a given range of distances
3.6
excess of sound pressure level
DL
f
average difference, in decibels, over a given distance range, between the spatial sound distribution curve of the
room and the spatial sound distribution curve for a free field
NOTE The spatial sound distribution curve for a free field falls off with 6 dB per distance doubling.
4 Sound distribution in a room
4.1 General
For basic information on sound propagation in a room and on the spatial sound distribution curves, see
ISO 11690-1, ISO/TR 11690-3 and other references in the Bibliography.
4.2 Spatial sound distribution curves
4.2.1 Reference spatial sound distribution curve
The reference curve is the spatial sound distribution curve which would occur in a free field, without any reflecting
surfaces or scattering objects. At each microphone position, values D for this curve are given by the following
ref
equation:
��
rr
��
Dr��10 lg dB 20 lg�11 dB (2)
� �
��
ref ��
��
r
��4�r
where
r is the distance, in metres, between the sound source and the measurement point considered;
r is the reference distance (= 1 m).
Experience shows that ground reflections and the directivity of the source influence the measured sound
distribution curve if the influence of the room is low, such as in very large rooms and/or in rooms with highly
absorbent boundary surfaces. This may be taken into account by applying the correction method described in
annex B.
It is recommended to draw the reference curve in all diagrams showing spatial sound distribution curves (see
Figure 1).
4.2.2 Spatial sound distribution curves in frequency bands and for a given frequency spectrum
For the purposes of this International Standard, spatial sound distribution curves are measured in octave bands.
NOTE In narrower frequency bands (such as one-third-octave bands), interference effects can occur. These can affect
spatial sound distribution curves in a complex manner so that extensive experience is required for correct interpretation. Thus,
such measurements are not recommended.
The spatial sound distribution curve in a given octave band and on a given path is determined from equation (1).
ISO 14257:2001(E)
The sound distribution curve for a given octave band j is the diagram of the sound distribution values D (r) where a
j
logarithmic scale is used for r (see Figure 1).
For practical purposes, there is often particular interest in the spatial sound distribution curve for a given sound
power spectrum, e.g. the spectrum of a specific machine. This curve is determined from octave-band data
according to the following equation that gives the value, D ,of D at distance r:
S
Dr �L /10
��
��jWmachj
�
j
Dr � 10 lg dB (3)
� �
S
L /10
Wjmach
�
j
where
D (r)isthevalueof D in octave band j, at position r;
j
L is the value of the sound power level of the machine in octave band j.
W mach j
4.2.3 Frequency-normalized spatial sound distribution curve
If the frequency spectra of the sound power of the machines that operate or will operate in the workroom under test
are not known, it is often sufficient and useful to determine the spatial sound distribution curve(s) of the workroom
under test for a normalized frequency spectrum. The normalized frequency spectrum for the purpose of this
International Standard is A-weighted pink noise so that the frequency-normalized spatial sound distribution curve
relative to this particular spectrum is calculated from octave-band data, D , according to the equation:
j
��
DP� /10
��jj
D��10lg��10 dB 6,2 dB (4)
Norm �
��
��j
where
j is the number of the octave band;
D is the value of D for the frequency-normalized spatial sound distribution curve;
Norm
P is given in Table 1.
j
Table 1 — Values of P for the frequency-normalized spatial sound distribution curve
j
Octave band j,
125 250 500 1 000 2 000 4 000
centre frequency,Hz
Subscript j 123 45 6
P,dB – 16,1 – 8,6 – 3,2 0 1,2 1
j
NOTE A-weighted pink noise has been retained as a normalized frequency spectrum because the range of frequency
spectra met in practice is so large that the use of an average industrial frequency spectrum can imply that a frequency-
normalized spatial sound distribution curve is meaningful for all possible industrial situations, which is not true.
For special purposes, such as optimizing the sound absorption in a room, a specific spectrum may be used.
4 © ISO 2001 – All rights reserved

ISO 14257:2001(E)
Key
1 Free-field sound distribution curve
2 Spatial sound distribution curve
x Measurement points
r Distance from the source to the receiver (logarithmic scale)
Figure 1 — Representation of a spatial sound distribution curve
5 Measurement of the spatial sound distribution curve
5.1 Specifications regarding the sound source used for the test
5.1.1 Performance requirements to be met by the source
Part of the requirements for reference sound sources according to ISO 6926 are more stringent than necessary for
the purposes of this International Standard. Some characteristics of the reference sound source, however,
must meet more stringent requirements for measurements to be in accordance with this International Standard.
Annex A therefore specifies the requirements for a reference sound source for the purposes of this International
Standard.
5.1.2 Calibration and verification of the sound power of the source
The sound source shall be calibrated in octave and one-third-octave frequency bands in accordance with
ISO 6926. Table 2 indicates the acoustical environments to be used for sound power and directivity determinations,
depending on the position of the source in normal use, for calibration and verification purposes. The method for
determining the directional characteristics of the sound source is specified in annex A. Checks shall be done in
octave bands. Intervals between checks depend on experience gathered with the source system used.
ISO 14257:2001(E)
Table 2 — Appropriate environments for the determination of the sound power of the source
for calibration and verification purposes
Height above floor of Appropriate environments for Appropriate environments for
acoustical centre of sound determination of sound power determination of directional
source in normal use characteristics
0,5 m or less Reverberation room (see ISO 3741) Hemi-anechoic room (see ISO 3745)
or hemi-anechoic room
(see ISO 3745)
More than 0,5 m Reverberation room (see ISO 3741) Anechoic room (see ISO 3745)
or anechoic room (see ISO 3745)
If the source system is used rather frequently, it is recommended to determine its sound power level in octave
bands every 3 months or more frequently until there are at least six individual measurement results. Later on, time
intervals between checks may be longer.
NOTE The purpose of the determination of the spatial sound distribution curve may not require knowledge of the sound
power level of the source. This is the case, for example, when the acoustical performance of a workroom (see clause 6) is
evaluated using only the rate of spatial decay of sound pressure levels per distance doubling (see 3.5).
5.1.3 Location of the source
For measurement of the spatial sound distribution curve, the acoustical centre of the sound source shall be located
� either as close as possible to the floor, or
� at a height above the floor of more than 0,5 m.
A source is considered as being close to the floor if its acoustical centre is at a height less than or equal to 0,5 m.
The acoustical centre of the source shall be located at least 3 m away from any wall and any reflecting object other
than the floor. If this requirement cannot be fulfilled because of the room dimensions, the distance used for the test
shall be recorded and reported.
5.1.4 Sound power versus background noise
The sound power of the source shall be such that, for all distances and for all octave bands for which the spatial
sound distribution curve is to be measured, the sound pressure level due to the source is at least 10 dB higher than
the background noise from other sources. If, at a given measurement point and in a given octave band, the sound
pressure level, when the source used for the test is in operation, is less than 10 dB but more than 6 dB higher than
background noise, a background noise correction determined as specified in ISO 3744 shall be made.
5.2 Measurement instrumentation
Sound pressure levels in each octave band and at each microphone position shall be measured using a class 1
sound level meter in compliance with IEC 60651 or a class 1 integrating-averaging sound level meter in compliance
with IEC 60804. The microphone shall be omnidirectional (taking into account any supplementary equipment
connected to it). Octave-band filters shall comply with IEC 61260.
If the signal is recorded (using, for example, analog or digital recorders) for off-line processing, it shall be ensured
that the instrumentation as a whole complies with the above-mentioned requirements.
6 © ISO 2001 – All rights reserved

ISO 14257:2001(E)
5.3 Measurement path and points
5.3.1 Measurement path
The measurement path shall be parallel to the floor and begin on the source. The last measurement point on the
path shall be located at a minimum distance of 1,5 m from any wall or large reflecting object. A larger distance is
recommended.
Preferred path heights are 1,55 m (so simulating a person standing up) and 1,2 m (so simulating a person seated).
Any other path height is acceptable as long as the path remains parallel to the floor and its value is recorded and
reported.
The path shall be such that there is no obstacle on the floor below it. If this condition cannot be met, this shall be
recorded and reported together with the precise location of the obstacle(s) with respect to the measurement path.
The path shall be oriented along a free line of sight from the source, if possible, and it shall be clear of any large
reflecting structures to a distance of at least 1,5 m to either side. Otherwise, a different path or height of the path
above floor level shall be chosen. If possible, measurements shall be carried out along a second preferably
orthogonal path.
5.3.2 Measurement points
The measurement points shall be distributed on the measurement path. Possible distributions of microphone
positions along a path are many. It is recommended to choose one of the following distributions:
� 1m, 2m, 3m, . , 10m, 12m, 14m, . , 20m, 24m, 28m, . , 40m, 48m, 56m, . (constant increment
within each range and logarithmically growing increment from one range to the next);
� 2m,3m,4m,6m,8m,12m,16m,24m,32m,48m,64m,. .
The number of measurement positions in a given distribution is a minimum number. More measurement positions
may be added. Continuous recording of the sound pressure level versus distance, when practical, provides the best
possible description of the spatial sound distribution.
The distances indicated in the above distributions are from the acoustical centre of the source to the microphone.
For sources whose acoustical centre is on the floor, Table 3 relates the above distance to the horizontal distance
for the two microphone heights given in 5.3.1.
Table 3 — Correspondence between the distance r from a microphone to the acoustical centre of
the source and the horizontal distance, for a sound source whose acoustical centre is on the floor
Values in metres
Distance to acoustical centre of 2 345 678 9 10
source
Horizontal distance for a path height
1,60 2,75 3,82 4,85 5,88 6,90 7,91 8,92 9,93
of 1,2 m
Horizontal distance for a path height
1,26 2,57 3,69 4,75 5,80 6,83 7,85 8,87 9,88
of 1,55 m
NOTE The horizontal distance is rounded to the nearest centimetre. From a distance of 10 m, these two
distances may be taken as equal.
NOTE 1 The 1-m position of the first recommended distribution is not possible if the acoustical centre of the sound source is
on the floor.
ISO 14257:2001(E)
NOTE 2 When the room is large enough, there can be several possibilities regarding the choice of paths. Two of them are of
special relevance depending on the purpose of the measurements, as follows.
a) Determination of several spatial sound distribution curves along the longitudinal and lateral axis of the room in different
contiguous zones of it, e.g. when the purpose is
...