SIST EN ISO 11821:1999
(Main)Acoustics - Measurement of the in situ sound attenuation of a removable screen (ISO 11821:1997)
- Status
- Published
- Publication Date
- 31-Oct-1999
- Technical Committee
- AKU - Acoustics
- Current Stage
- 6060 - National Implementation/Publication (Adopted Project)
- Start Date
- 01-Nov-1999
- Due Date
- 01-Nov-1999
- Completion Date
- 01-Nov-1999
SIST EN ISO 11821:1999 is the Slovenian standard identical to EN ISO 11821:1997, published by SIST. It specifies an engineering-grade method for measuring the in situ sound attenuation of a removable screen, indoors or outdoors, by comparing screened and unscreened sound pressure levels. The standard is meant for people who need repeatable screen-performance data for complete screens used to shield a work station or an area from noise.
What does SIST EN ISO 11821:1999 specify?
SIST EN ISO 11821:1999 specifies how to evaluate the sound attenuation of a removable screen in its installed position. The method is based on insertion loss, using either the actual sound source(s) or an artificial sound source.
The document applies to complete screens, not to separate parts such as panels, doors or windows. It is also limited to screens used for industrial noise shielding; it is not for open plan office screens, outdoor barriers for community noise, or qualification purposes.
It is organized into these clauses and one informative annex:
- Clause 1 - Scope
- Clause 2 - Normative references
- Clause 3 - Definitions
- Clause 4 - Instrumentation
- Clause 5 - Determination of in situ sound attenuation
- Clause 6 - Uncertainty
- Clause 7 - Information to be recorded
- Clause 8 - Information to be reported
- Annex A - Bibliography
What are the key requirements of SIST EN ISO 11821:1999?
The standard is built around comparing measurements with the screen removed and with the screen in its intended position. In practice, that means the test must represent the real installation as closely as possible.
Measurement conditions and applicability
Clause 5 requires the same environmental conditions for the screened and unscreened measurements. Nearby reflective surfaces, room fittings, operating conditions and, for outdoor tests, wind and other environmental conditions must remain comparable. This matters because the result describes the whole installation, not just the screen material.
The screen shall be mounted in its specified normal position. The standard recommends measurements within 25 m of the screen outdoors, unless the interested parties agree otherwise. It also notes that indoor results depend on room geometry and reflections, so comparisons only make sense when the test conditions are the same.
Sound source and instrumentation
Clause 4 requires type 1 sound level meters or integrating-averaging sound level meters, class 1 octave or one-third-octave filters, and calibration with a class 1 sound calibrator before and after each measurement series. Outdoors, a microphone windscreen is required. This is what makes the measurements traceable and repeatable.
Clause 5 prefers the actual sound source(s) to be used, provided the sound is reproducible and the level behind the screen is at least 6 dB above background noise, preferably more than 10 dB. If that is not possible, an artificial sound source may be used in octave or one-third-octave bands. For that source, the standard sets directivity requirements and a 12-position measurement arrangement around the source.
Microphone positions and data handling
For a well-defined operator position, Clause 5 requires three microphone positions on a sphere of 0.3 m radius centered at the head position. For a shielded area, the microphones are placed along at least one line perpendicular to the screen, at typical operator height. This matters because screens for open work areas often protect more than one point.
Clause 5 defines in situ sound attenuation [Dp] as the difference between unscreened and screened sound pressure levels, and A-weighted in situ sound attenuation [DpA] only when the actual sound source(s) are used. Background noise correction is required when the source-to-background difference is between 6 dB and 10 dB; below 6 dB the conditions are not acceptable.
Clause 6 gives the uncertainty guidance: for A-weighted measurements under similar conditions with stable broad-band noise, the standard deviation of the mean is estimated at about 2 dB. The document also warns that impulsive sources, pure tones and changing environments reduce confidence in the result.
What terms does SIST EN ISO 11821:1999 define?
- Screen - An object designed to shield one or more specified positions from noise from specific sound source(s).
- Removable screen - A screen that can be dismantled without changing the other environmental conditions.
- Actual sound source(s) - The sound source(s) that are to be shielded in the test.
- Unscreened sound pressure level [Lp1] - The sound pressure level measured at a position with the screen removed.
- Screened sound pressure level [Lp2] - The sound pressure level measured at the same position with the screen in place.
- In situ sound attenuation [Dp] - The difference between Lp1 and Lp2 in decibels, measured in octave or one-third-octave bands.
- A-weighted in situ sound attenuation [DpA] - The A-weighted difference between unscreened and screened levels when the actual sound source(s) are used.
- Directivity index [Dli] - A measure of how directional an artificial sound source is across 12 positions around it.
Who uses SIST EN ISO 11821:1999?
SIST EN ISO 11821:1999 is used by acoustic test laboratories, screen manufacturers, workplace noise-control engineers, and purchasers or quality managers who need to compare screen performance. It is especially relevant when a removable screen is installed around a machine, maintenance area, or work station and the user needs measured attenuation in the real setting. It also helps when documenting test conditions so results can be compared only on a like-for-like basis.
Which standards are used with SIST EN ISO 11821:1999?
The normative references in Clause 2 are:
- IEC 651 - basis for type 1 sound level meters and A-weighting.
- IEC 804 - requirements for integrating-averaging sound level meters.
- IEC 942 - sound calibrators for calibration checks.
- IEC 1260 - octave and fractional-octave filters.
The document also names related standards and references in its introduction and bibliography, including ISO 10053, ISO 10847, ISO 11546-2, ISO 11690-2, ISO 11957, ISO 11200, ISO 140-3, ISO 3743-1 and ISO 3744.
What does the SIST EN ISO 11821:1999 document contain?
The document contains the measurement definitions, instrument requirements, sound source requirements, microphone layouts, background-noise correction, and the formulas used to calculate Dp and DpA. It also gives the information to record and report, including test object identification, test conditions, instrumentation, acoustic data and measurement uncertainty. Annex A provides a bibliography for further background on acoustics measurements, screens, enclosures, cabins and workplace noise control.
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- 28-Jan-2026
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Frequently Asked Questions
SIST EN ISO 11821:1999 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Acoustics - Measurement of the in situ sound attenuation of a removable screen (ISO 11821:1997)". This standard covers: La présente Norme internationale prescrit des méthodes d'évaluation des performances d'atténuation acoustique in situ d'un écran amovible, à l'intérieur ou à l'extérieur. Cette méthode d'expertise est basée sur le mesurage de la perte d'insertion qui peut être effectué avec la (les) source(s) sonore(s) réelle(s) dont on veut se protéger ou à l'aide d'une source sonore artificielle. Les performances d'atténuation acoustique d'un tel écran, évaluées de la manière indiquée dans la présente Norme internationale, dépendent -- de la diffraction par les bords de l'écran; -- de la transmission à travers les composants de l'écran; -- de l'absorption des panneaux constituant l'écran, ainsi qu'à son voisinage; -- du local dans lequel l'écran est placé dans le cas d'un essai à l'intérieur. Lorsqu'un poste de travail donné est à protéger, la valeur de l'atténuation acoustique in situ décrit l'effet de l'écran. Toutefois, lorsqu'une zone complète est à protéger, les performances de l'écran varient avec la position de mesure. Il est par conséquent recommandé de fournir les valeurs maximale et minimale de l'atténuation acoustique. Les performances d'atténuation acoustique sont déterminées en termes de perte acoustique par insertion. Lors de l'évaluation des performances d'un écran placé dans une salle, les performances sont influencées par la géométrie de la s 1511alle et les réflexions dues aux murs, au plafond et aux autres éléments de la salle. C'est pourquoi les performances d'écrans ne peuvent être comparées que si les conditions d'essai sont identiques. La présente Norme internationale est applicable aux écrans dont la hauteur ou la longueur est supérieure à 1,5 m. Néanmoins, elle peut être utilisée, par accord entre les parties intéressées, pour de plus petits écrans. Comme les conditions d'environnement peuvent affecter les mesurages en extérieur, il est recommandé de limiter ceux-ci à des distances à l'écran inférieures à 25 m. Néanmoins
La présente Norme internationale prescrit des méthodes d'évaluation des performances d'atténuation acoustique in situ d'un écran amovible, à l'intérieur ou à l'extérieur. Cette méthode d'expertise est basée sur le mesurage de la perte d'insertion qui peut être effectué avec la (les) source(s) sonore(s) réelle(s) dont on veut se protéger ou à l'aide d'une source sonore artificielle. Les performances d'atténuation acoustique d'un tel écran, évaluées de la manière indiquée dans la présente Norme internationale, dépendent -- de la diffraction par les bords de l'écran; -- de la transmission à travers les composants de l'écran; -- de l'absorption des panneaux constituant l'écran, ainsi qu'à son voisinage; -- du local dans lequel l'écran est placé dans le cas d'un essai à l'intérieur. Lorsqu'un poste de travail donné est à protéger, la valeur de l'atténuation acoustique in situ décrit l'effet de l'écran. Toutefois, lorsqu'une zone complète est à protéger, les performances de l'écran varient avec la position de mesure. Il est par conséquent recommandé de fournir les valeurs maximale et minimale de l'atténuation acoustique. Les performances d'atténuation acoustique sont déterminées en termes de perte acoustique par insertion. Lors de l'évaluation des performances d'un écran placé dans une salle, les performances sont influencées par la géométrie de la s 1511alle et les réflexions dues aux murs, au plafond et aux autres éléments de la salle. C'est pourquoi les performances d'écrans ne peuvent être comparées que si les conditions d'essai sont identiques. La présente Norme internationale est applicable aux écrans dont la hauteur ou la longueur est supérieure à 1,5 m. Néanmoins, elle peut être utilisée, par accord entre les parties intéressées, pour de plus petits écrans. Comme les conditions d'environnement peuvent affecter les mesurages en extérieur, il est recommandé de limiter ceux-ci à des distances à l'écran inférieures à 25 m. Néanmoins
SIST EN ISO 11821:1999 is classified under the following ICS (International Classification for Standards) categories: 17.140.01 - Acoustic measurements and noise abatement in general. The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN ISO 11821:1999 has the following relationships with other standards: It is inter standard links to SIST EN 13898:2004+A1:2009. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
SIST EN ISO 11821:1999 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
01-november-1999
$NXVWLND0HUMHQMH]YRþQHJDGXãHQMDRGVWUDQOMLYLK]DVORQRYQDPHVWXSRVWDYLWYH
,62
Acoustics - Measurement of the in situ sound attenuation of a removable screen (ISO
11821:1997)
Akustik - Messung der Schalldämpfung von versetzbaren Schallschirmen im Einsatzfall
(ISO 11821:1997)
Acoustique - Mesurage d l'atténuation acoustique in situ d'un écran amovible (ISO
11821:1997)
Ta slovenski standard je istoveten z: EN ISO 11821:1997
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.
INTERNATIONAL Is0
STANDARD
First edition
1997-04-O 1
Acoustics - Measurement of the in sifu
sound attenuation of a removable screen
Acoustique - Mesurage de I’atthuation acoustique in situ d’un &ran
amovible
Reference number
IS0 11821:1997(E)
IS0 11821: 1997(E)
Page
Contents
Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.
Normative references
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*.
Instrumentation . . . . . . . . . .*.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Determination of in situ sound attenuation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Uncertainty
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Information to be recorded
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Information to be reported
Annex
..,.....,......................................................................
A Bibliography
0 is0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii
IS0 11821:1997(E)
@ IS0
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 11821 was prepared by Technical Committee
lSO/TC 43, Acoustics, Subcommittee SC 1, Noise.
Annex A of this International Standard is for information only.
IS0 11821 :1997(E) @ IS0
Introduction
This International Standard specifies in situ methods for the determination
of the sound attenuation performance of removable sound-protecting
screens for industrial purposes A screen is any object (e.g. panels, flexible
curtains, etc.) breaking the line of sight between source and receiver; such
a screen may be flat or curved. A removable screen is a screen that can be
dismantled without the other environmental conditions being changed. The
purpose of such a screen is to shield a work station or a complete work
area from the noise emitted by sound source(s). Such an area can be a
zone where one operator is located or a zone occupied by several
operators at no fixed positions. For example, screens can be used by a
maintenance unit to reduce the effect of noise at a given location, from
repair work, and to reduce the noise at a work station located close to a
machine or process.
Related standards concern noise attenuation measurements of enclosures
under in situ conditions (IS0 1154602), and sound insulation measure-
ments of cabins under in situ conditions (IS0 II 957).
Other International Standards dealing with screens in other situations are
IS0 10053 (sound attenuation of screens for open plan offices) and
IS0 10847 (sound attenuation of outdoors screens).
Technical information about noise reduction in workrooms can be found in
IS0 11690-2.
IV
INTERNATIONAL STANDARD o Iso
IS0 11821 :1997(E)
Acoustics - Measurement of the in sifu sound attenuation
of a removable screen
1 Scope
This International Standard specifies methods for evaluating the in situ sound attenuation performance of a
removable screen, either indoors or outdoors. This engineering grade method is based on an insertion loss
measurement that can be carried out either with shielding of the actual sound source(s) or using an artificial sound
source.
The sound attenuation performance achieved by such a screen, as evaluated by the present International Standard,
depends on:
- diffraction around the edges of the screen;
- transmission through the components of the screen;
absorption of the panels of the screen, as well as in its surroundings;
-
- the room in which the screen stands if indoors.
When a specific work station is to be shielded, the in situ sound attenuation value describes the effect of the screen.
However, when a complete area is to be shielded, the performance of the screen will vary depending on the
positions used for measurement. Therefore, it is recommended that the maximum and minimum values of sound
attenuation are given. The sound attenuation performance is determined in terms of insertion loss.
When assessing the performance of a screen located indoors, the room geometry and reflections from walls,
ceilings and room fittings will influence the performance. As a consequence, the comparison of screen performance
can only be made if the test conditions are identical.
This International Standard is applicable to screens with height and length greater than 1,5 m. However, it may also
be used for smaller screens provided that the interested parties come to an agreement on this.
As environmental conditions can affect the measurements outdoors, it is recommended that measurements should
be restricted to within 25 m of the screen. However, measurements may also cover a greater distance provided that
the interested parties come to an agreement on this.
Differences can occur between in situ test results Therefore, comparison of the performance of different screens
can be made only on the basis of data based on the same measurement method performed at the same location.
This International Standard applies to a complete screen only and not to individual components from which it is
made. Sound insulation and sound absorption for screen components (such as panel elements, doors, windows)
should be measured according to other relevant standards.
This International Standard is not applicable to open plan offices screens nor to outdoor barriers dealing with
community noise. It is also not intended for qualification purposes
@ IS0
IS0 11821:1997(E)
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
IEC 651 :I 979, Sound /eve/ meters.
IEC 804:1985, Integrating-averaging sound level meters.
I EC 942: 1988, Sound calibrators.
I EC 1260: 1995, Hectroacoustics - Octave-band and fractional-octave-band filters.
3 Definitions
For the purposes of this International Standard, the following definitions apply.
3.1 screen: Any object that is specially designed to shield one or more specified positions in a given area from the
noise of specific sound s ource(s).
NOTE - Examples are panels and flexible curtains.
3.2 removable screen: A screen that can be dismantled without the other environmental conditions being
changed.
3.3 actual sound source(s): The sound source(s) to be shielded.
3.4 sound pressure level, Lp: Ten times the logarithm to the base 10 of the ratio of the mean-square sound
pressure of a sound to the square of the reference sound pressure 20 FPa. The sound pressure level is expressed
in decibels.
3.5 A-weighted sound pressure level, Lp~: Sound pressure level weighted in accordance with IEC 651. The A-
weighted sound pressure level is expressed in decibels.
3.6 unscreened sound pressure level, Lpj: Sound pressure level measured at one position not screened from
the sound source(s) without the screen in its intended position. The unscreened sound pressure level is expressed
in decibels.
3.7 screened sound pressure level, Lp2: Sound pressure level measured at the same position as in 3.6 but
screened from the sound source(s) by the screen in its intended position. the screened sound pressure level is
expressed in decibels.
3.8 in situ sound attenuation, Dp: Difference, in decibels, between Lpl and L+ at the particular position defined
in 3.6, LIP1 and LIP2 being determined in either one-third-octave or octave bands.
3.9 A-weighted in situ sound attenuation, Dp~: Difference, in decibels, between L+l and L@ at the position
defined in 3.6 when using the actual sound source(s).
3.10 directivity index, Dli: Difference, in decibels, between L360 (the logarithmic mean value of the sound
pressure level in 12 positions evenly distributed on a horizontal circle surrounding the sound source) and ~~~ i (the
I
sound pressure level in position i of the twelve positions).
The radius of the circle shall be approximately I,5 m.
DI
i = L360 - L30,i
NOTE - The definition of the directivity index stated in this International Standard is in principle equivalent to the definition
given in IS0 140-3. However, the procedure in this International Standard is somewhat simplified by allowing the directivity
@ IS0
IS0 11821 :1997(E)
index to be determined in 12 discrete positions in the horizontal plane instead of using “gliding averaging” in different planes as
described in IS0 140-3.
4 Instrumentation
The instrumentation system, including the microphones and cables, shall meet the requirements for a type 1
instrument as specified in IEC 651 or, in the case of integrating-averaging sound level meters, the requirements for
a type 1 instrument as specified in IEC 804.
For measurements in octave or one-third-octave bands, the instrumentation system shall meet the requirements for
a class 1 filter as specified in IEC 1260.
Before and after each series of measurements, the calibration of the entire measuring system shall be verified at
one or more frequencies over the frequency range of interest, using a sound calibrator with an accuracy of + 0,3 dB
(class 1 as specified in IEC 942).
methods are permissible, provided
NOTE - Other calibration that it is shown tha t the instrume ntation system is stable during
the measu rements and that measurements with and without the scree n are carried out using the same measurement system.
When measuring outdoors, a microphone windscreen with negligible influence on the frequency response of the
microphone shall be used during the measurements.
5 Determination of in situ sound attenuation
5.1 General
The unscreened acoustic field can be generated using the actual sound source(s) to be shielded, provided the
provisions outlined in 5.2 are met. If needed, an artificial sound source can be used instead. The use of the actual
sound source(s) is the preferred method.
nts, ensure that the same operating conditions are for the screened and
When perfo rming the measureme used
unscre lened situat ions.
5.2 Sound source requirements
5.2.1 Actual sound source(s): Preferred method
The generated sound shall be reproducible and the same sound shall be used for measurements with and without
the screen.
The output shall be sufficiently high to give a sound pressure level behind the screen exceeding the background
noise level by at least 6 dB and preferably more than 10 dB for all frequency bands of interest.
lnditions, all relevant sound sou rce s) at the test site should be listed, together with
NOTE - In order to check the operating co
their operating conditions (such as rotational speed, flow rate, power, etc.).
52.2 Artificial sound source
the measurements shall be carried out in
If the requirements in 52.1 are not met by the actual sound source(s)
octave or one-third-octave bands using an artificial sound source instead of the actual sound source(s).
NOTE 1 The artificial sound source may be a loudspeaker, a pistol shot, a bursting membrane, but it can also be machinery
brought in for the purpose of testing the screen.
The artificial sound source must have at least one axis of symmetry which shall be directed perpendicular to the
floor during operation. The directivity index should not exceed + 8 dB in any of
...