SIST EN ISO 11690-2:2021
(Main)Acoustics - Recommended practice for the design of low-noise workplaces containing machinery - Part 2: Noise control measures (ISO 11690-2:2020)
Acoustics - Recommended practice for the design of low-noise workplaces containing machinery - Part 2: Noise control measures (ISO 11690-2:2020)
This document deals with the technical aspects of noise control in workplaces. The various technical measures are stated, the related acoustical quantities described, the magnitude of noise reduction discussed, and the verification methods outlined.
This document deals only with audible sound.
Akustik - Richtlinien für die Gestaltung lärmarmer maschinenbestückter Arbeitsstätten - Teil 2: Lärmminderungsmaßnahmen (ISO 11690-2:2020)
Dieses Dokument befasst sich mit technischen Gesichtspunkten des Schallschutzes in Arbeitsstätten. Es werden die verschiedenen technischen Maßnahmen angegeben, die entsprechenden akustischen Größen beschrieben, das Ausmaß der Lärmminderung diskutiert und die Nachprüfverfahren grob beschrieben.
Dieses Dokument befasst sich ausschließlich mit Hörschall.
Acoustique - Pratique recommandée pour la conception de lieux de travail à bruit réduit contenant des machines - Partie 2: Moyens de maîtrise du bruit (ISO 11690-2:2020)
Le présent document traite des aspects techniques de la maîtrise du bruit sur les lieux de travail. Les différents moyens techniques sont énumérés, les grandeurs acoustiques associées sont décrites, la valeur de la réduction du bruit est abordée et les méthodes de vérification sont présentées.
Le présent document ne traite que des sons audibles.
Akustika - Priporočena praksa za oblikovanje tihih delovnih mest - 2. del: Ukrepi za obvladovanje hrupa (ISO 11690-2:2020)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-marec-2021
Nadomešča:
SIST EN ISO 11690-2:1997
Akustika - Priporočena praksa za oblikovanje tihih delovnih mest - 2. del: Ukrepi
za obvladovanje hrupa (ISO 11690-2:2020)
Acoustics - Recommended practice for the design of low-noise workplaces containing
machinery - Part 2: Noise control measures (ISO 11690-2:2020)
Akustik - Richtlinien für die Gestaltung lärmarmer maschinenbestückter Arbeitsstätten -
Teil 2: Lärmminderungsmaßnahmen (ISO 11690-2:2020)
Acoustique - Pratique recommandée pour la conception de lieux de travail à bruit réduit
contenant des machines - Partie 2: Moyens de maîtrise du bruit (ISO 11690-2:2020)
Ta slovenski standard je istoveten z: EN ISO 11690-2:2020
ICS:
13.140 Vpliv hrupa na ljudi Noise with respect to human
beings
17.140.20 Emisija hrupa naprav in Noise emitted by machines
opreme and equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 11690-2
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2020
EUROPÄISCHE NORM
ICS 13.140 Supersedes EN ISO 11690-2:1996
English Version
Acoustics - Recommended practice for the design of low-
noise workplaces containing machinery - Part 2: Noise
control measures (ISO 11690-2:2020)
Acoustique - Pratique recommandée pour la Akustik - Richtlinien für die Gestaltung lärmarmer
conception de lieux de travail à bruit réduit contenant maschinenbestückter Arbeitsstätten - Teil 2:
des machines - Partie 2: Moyens de maîtrise du bruit Lärmminderungsmaßnahmen (ISO 11690-2:2020)
(ISO 11690-2:2020)
This European Standard was approved by CEN on 17 October 2020.
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 CEN-CENELEC 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 CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11690-2:2020 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 11690-2:2020) 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 DIN.
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 May 2021, and conflicting national standards shall be
withdrawn at the latest by May 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 11690-2:1996.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 11690-2:2020 has been approved by CEN as EN ISO 11690-2:2020 without any
modification.
INTERNATIONAL ISO
STANDARD 11690-2
Second edition
2020-10
Acoustics — Recommended practice
for the design of low-noise workplaces
containing machinery —
Part 2:
Noise control measures
Acoustique — Pratique recommandée pour la conception de lieux de
travail à bruit réduit contenant des machines —
Partie 2: Moyens de maîtrise du bruit
Reference number
ISO 11690-2:2020(E)
©
ISO 2020
ISO 11690-2:2020(E)
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Technical aspects of noise control. 1
5 Noise control at source. 3
5.1 General . 3
5.2 Noise control at source by design . 3
5.3 Information on noise emission . 4
5.4 Use of low-noise machines . 4
5.5 Modification or replacement of machine components . 7
5.6 Low noise working and production technologies . 8
5.7 Maintenance of machines and noise control devices. 8
6 Noise control on the transmission path . 8
6.1 Noise control by means of a proper spatial arrangement of the noise sources . 8
6.2 Use of noise control devices . 8
6.3 Noise control by use of sound-absorbing materials . 8
6.4 Sound propagation in structures and noise control measures .11
7 Noise control at the work station .11
8 Verification methods .12
8.1 General .12
8.2 Sound sources .12
8.3 Noise control devices.12
8.4 Workroom .12
8.5 Specified positions, work stations.12
9 New technologies .13
Annex A (informative) Modification or replacement of machine components .14
Annex B (informative) Arrangement of sound sources .16
Annex C (informative) Enclosures .17
Annex D (informative) Silencers .20
Annex E (informative) Noise barriers and screens in rooms .21
Annex F (informative) Acoustical treatment of surfaces .22
Annex G (informative) Structure-borne sound insulation .24
Annex H (informative) Airborne sound insulation of partitions .25
Annex I (informative) Noise control at the work station .26
Annex J (informative) Example of a new technology .27
Bibliography .29
ISO 11690-2:2020(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 of the voluntary nature of standards, 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 www .iso .org/
is o/ f or ewor d . ht m l .
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise,
in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/
TC 211, Acoustics, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 11690-2:1996), of which it constitutes a
minor revision. The changes compared to the previous edition are editorial.
A list of all parts in the ISO 11690 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
Introduction
Several standards specify methods for measurement and/or evaluation of noise. The final objective of
the ISO 11690 series is noise reduction.
A number of noise control measures are offered. However, in order to be effective, the most appropriate
noise control measure(s) should be chosen for a given situation.
It is important when non-acoustic engineers are involved in noise control practice for these engineers
to have a basic knowledge of noise emission and propagation characteristics and to understand the
basic principles of noise control.
To assist in the development of noise control in the workplace, it is essential that the information
contained in these recommended practices is disseminated through International Standards.
In order to reduce noise as a hazard in the workplace, individual countries have produced national
legislation. Generally, such national legislation requires noise control measures to be carried out in
order to achieve the lowest reasonable levels of noise emission, noise immission and noise exposure,
taking into account:
— known available measures;
— the state of the art regarding technical progress;
— the treatment of noise at source;
— appropriate planning, procurement and installation of machines and equipment.
This document, together with the two other parts in the series, outlines procedures to be considered
when dealing with noise control at workplaces, within workrooms and in the open. These recommended
practices give in relatively simple terms the basic information necessary for all parties involved in noise
control in workplaces and in the design of low-noise workplaces to promote the understanding of the
desired noise control requirements.
The purpose of the ISO 11690 series is to bridge the gap between existing literature on noise control and
the practical implementation of noise control measures. In principle, the series applies to all workplaces
and its main functions are:
— to provide simple, brief information on some aspects of noise control in workplaces;
— to act as a guide to help in the understanding of requirements in standards, directives, textbooks,
manuals, reports and other specialized technical documents;
— to provide assistance in decision making when assessing the various measures available.
The ISO 11690 series should be useful to persons such as plant personnel, health and safety officers,
engineers, managers, staff in planning and purchasing departments, architects and suppliers of plants,
machines and equipment. However, the above-mentioned parties should keep in mind that adherence
to the recommendations of the ISO 11690 series is not all that is necessary to create a safe workplace.
The effects of noise on health, well-being and human activity are many. By giving guidelines for noise
control strategies and measures, the ISO 11690 series aims at a reduction of the impact of noise on
human beings at workplaces. Assessment of the impact of noise on human beings is dealt with in other
documents.
INTERNATIONAL STANDARD ISO 11690-2:2020(E)
Acoustics — Recommended practice for the design of low-
noise workplaces containing machinery —
Part 2:
Noise control measures
1 Scope
This document deals with the technical aspects of noise control in workplaces. The various technical
measures are stated, the related acoustical quantities described, the magnitude of noise reduction
discussed, and the verification methods outlined.
This document deals only with audible sound.
2 Normative references
The following documents are referred to in the text in such 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 11690-1:2020, Acoustics — Recommended practice for the design of low-noise workplaces containing
machinery — Part 1: Noise control strategies
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11690-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Technical aspects of noise control
Noise reduction measures can be applied at source (emission), between the source and the receiver
(transmission path), and at the work station (receiver) (see Figure 1).
When dealing with the noise emission of a machine, an installation or a production process, etc., all
possible noise reduction measures should be considered (see Clause 5 and ISO 11690-1). To determine
whether noise emission is the lowest level feasible, it is necessary to consider noise emission quantities;
these are given in the noise emission declaration (see ISO 11690-1:2020, Clause 8) or determined by
measurements (carried out in compliance with the relevant standard).
An assessment of noise control devices such as enclosures, partial enclosures, barriers and screens,
silencers, etc. can be carried out by using, for example, the insertion loss data (see 6.2).
The acoustic quality of workrooms and buildings is assessed with reference to the sound insulation
regarding airborne and structure-borne sound (see 6.4), and that of workrooms with reference to
sound propagation parameters (see 6.3).
ISO 11690-2:2020(E)
The overall effectiveness of noise control measures is determined from the noise immission values at
the work stations.
Generally, people located at a work station or in the vicinity of a machine are affected by the direct noise
emitted by the machine. Therefore, to reduce noise in the workplace, the most effective solution is to
reduce noise at source (primary measures). Additional measures on the transmission paths (secondary
measures) may be impractical because they hinder the work task and the production process. When
assessing the state of noise reduction technology, low noise emission of sound sources is therefore
given high priority with regard to occupational safety.
The basic aspects of noise control (see also ISO 11690-1) are illustrated in Figure 1. These are reviewed
in Clauses 5 to 7.
Figure 1 — Basic aspects of noise control
In order to minimize noise at the workplace, all noise control measures should be considered (see
Figure 2).
Figure 2 — Steps for the implementation of noise control measures
Noise control is most effective if it is carried out when planning, modifying, changing existing
machinery or equipment, or when acquiring new machinery or equipment in plants, workrooms and
buildings. From the outset, all parties involved (see ISO 11690-1:2020, Clause 6) and, in particular,
the noise experts, should take part in the process. Noise control measures are most effective if they
are integrated at the design stage of machines, production processes, workrooms and tasks (see
ISO 11690-1:2020, Clause 7). Machine operation, material transport, safety technology, ergonomics and
environmental protection should also be considered at that stage.
2 © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
5 Noise control at source
5.1 General
The measures described in this clause deal with the reduction of noise generated by working processes
and machines. They should be implemented at the design stage because retrospective measures can
affect operational requirements and are generally more expensive. However, they are also recommended
for existing noise sources, when practicable.
Control of noise at its source in workplaces deals in particular with the noise reduction of existing
machines, the development and selection of low noise working processes and production technologies,
the replacement of machine parts and the assessment of the results obtained.
The effectiveness of noise control at its source is based on measurements and is assessed by
comparison with the noise emission data, for example, provided by the supplier/manufacturer (see
ISO 11690-1:2020, Clause 8).
5.2 Noise control at source by design
When machine noise (or noise from technical production equipment) is considered, two types of noise
generation should be distinguished: fluid dynamic noise generation (gas and/or liquid) and mechanical
generation.
Fluid dynamic noise arises from temporary fluctuations in pressure and velocity of fluids. Examples
are combustion processes, fans, blow-out openings and hydraulic systems.
Mechanically-generated noise is caused by vibrations of machine components that are excited by
dynamic forces which are generated, for example, by impacts or out-of-balance masses. The vibrations
are transmitted to noise-radiating surfaces, such as machine casing, workpieces, etc. Examples are
tooth-wheel gears, electric motors, hammers, shakers and mechanical presses (see Figure 3).
Key
1 excitation
2 machine
3 transmission
4 radiation
Figure 3 — Generation process of mechanical noise
In order to control noise at its source, the noise-generation mechanism should be taken into account.
ISO 11690-2:2020(E)
Examples of reduction of fluid dynamic noise are the following:
a) reduction of periodical pressure fluctuations at the excitation source (e.g. in-line hydraulic
dampers);
b) reduction of flow velocities (e.g. speed-controlled fans);
c) avoidance of sudden changes in pressure (e.g. graduated vs abrupt transitions in HVAC ducting);
d) effective design of through-flow components (e.g. design layouts that do not put obstacles
immediately in front of air movers).
Examples of reduction of mechanically-generated noise are the following:
e) reduction of exciting dynamic forces (e.g. by means of elastic layers to extend the impulse duration
of impacts);
f) reduction of the vibrational velocity of the machine structure at the excitation point for a given
dynamic force [e.g. by means of stiffeners or additional masses (inertia blocks)];
g) reduction of the vibration (structure-borne sound) transmission from the excitation point to the
sound-radiating surfaces [e.g. by using elastic elements and materials with high internal damping
(cast iron)];
h) reduction of the sound radiated by a vibrating structure, for example by use of
— thin walls with ribs instead of thick stiff walls,
— damping layers on thin metal sheets,
— perforated metal sheets (provided noise insulation is not required);
i) sound-insulating wrappings or thick-walled structures (thin damped metal sheets near the
radiating surface).
Further information on reducing noise at its source can be found in ISO/TR 11688-1 and ISO/TR 11688-2.
5.3 Information on noise emission
In addition to the information on noise emission given by suppliers/manufacturers in technical
documentation (see ISO 11690-1:2020, Clause 8), there may be measures specific to industrial sectors.
Information on such measures can be found in databases, professional magazines, trade association
journals, etc.
For some machine families, there are lists of noise emission data obtained under specified operating
conditions. These lists can help purchasers select low-noise machines/equipment (see ISO 11690-1:2020,
Annex A).
5.4 Use of low-noise machines
In some circumstances, rather than implementing costly retrospective noise control measures, it is
feasible to replace a noisy unit in a plant with a low-noise one (see Table 1).
4 © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
Table 1 — Examples of alternative processes with lower noise
High-noise processes Low-noise processes
Percussion riveting Compression and roll riveting
Drive by compressed air or internal combustion engine Electrical drive
Cutting or making holes in, for example, stone or con- Use of machines that can be fitted with drills or circular
crete by the use of pneumatic or internal combustion saw blades equipped with diamond teeth
percussive machines
Heading in the die Tapering/full-forward extrusion
Push cutting Pull cutting
Flow drying Radiation drying
Plasma oxygen cutting Plasma cutting under water
Cutting shock, punching Laser-beam cutting
Conventional TIG/TAG welding TIG/TAG shielded arc welding
Flame-hardening Laser-beam hardening
Fastening with rivets Pressure fixing
Stroke forming Hydraulic pressing
Spot welding Seam welding
NOTE 1 A change of the material and/or form of the component under manufacture may allow the use of low-noise
production processes.
NOTE 2 This list is by no means exhaustive.
There are also noisy operations which are not connected with fixed machines, for example from the use
of hand-held tools. These can often be the dominating noise sources in a workroom. If care is taken in
selecting the tools or the working arrangement (e.g. sound-deadened hammers, cushioned work tables,
low-noise grinding discs, magnetic damping mats, etc.), considerable noise reductions can be achieved
as shown in Figures 4 to 7.
ISO 11690-2:2020(E)
Key
X octave-band frequency, in Hz
Y A-weighted sound pressure level at the work station, in dB
a
Conventional steelhammer, L = 115 dB.
pA
b
Sound-deadened hammer (with little recoil), L = 107 dB.
pA
Figure 4 — Example of sound pressure level during hammering
Key
X octave-band frequency, in Hz
Y A-weighted sound pressure level at the work station, in dB
a
Hard grinding wheel, L = 100 dB.
pA
b
Bonded abrasive grinding wheel, L = 89 dB.
pA
Figure 5 — Example of sound pressure level when grinding during the cleaning of a cast iron
electromotor housing
6 © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
Key
Y A-weighted sound pressure level, in dB
a
Steel working plate, 25 mm thick.
b
Steel working plate, damped by viscous material, 40 mm thick.
c
Steel working plate, 200 mm thick.
Figure 6 — Example of sound pressure level when hammering
Key
X octave-band frequency, in Hz
Y A-weighted sound pressure level at the work station, in dB
a
Without magnetic mat, L = 111 dB.
pA
b
With magnetic mat, L = 102 dB.
pA
Figure 7 — Example of sound pressure level when grinding a steel plate
5.5 Modification or replacement of machine components
It is possible, by replacing or modifying machine components, to reduce noise transmission inside the
machine and noise radiation by the machine surface, without affecting performance. Annex A gives
examples of such noise reduction measures.
ISO 11690-2:2020(E)
5.6 Low noise working and production technologies
It is always beneficial, if feasible, to replace a particularly noisy machine or unit in a plant with a
quieter one, for example by using a machine that works to a different principle (e.g. replacing an impact
screwdriver by a continuous direct-driven screwdriver).
With regard to existing processes, particular attention should be paid to the possibility of substituting
the process with an equally effective but quieter method.
When substituting a production process, low-noise alternatives should be systematically searched for.
The successive replacement of machines, plant items and processes by less noisy ones will in the long
term lead to quieter working environments even though low-noise machines have to be positioned
alongside existing noisy ones.
5.7 Maintenance of machines and noise control devices
Noise emission levels from machines or processes can be unnecessarily high due to lack of maintenance,
poor lubrication, misalignment, unbalanced and loose parts, etc. Optimum operating conditions should
be maintained at all times. Any maintenance defect normally increases the noise levels.
Maintenance of noise control devices is also of prime importance. Therefore, the integrity of enclosures,
screens and silencers should be carefully monitored.
6 Noise control on the transmission path
6.1 Noise control by means of a proper spatial arrangement of the noise sources
An optimized spatial arrangement of machines can provide a substantial noise level reduction at work
stations. This is mainly applicable when planning new plants and installations but should also be
considered for existing plants.
Noise reduction can be obtained by increasing the distance between the noise sources and the work
stations (see Annex B).
6.2 Use of noise control devices
Enclosures (see Annex C), silencers (see Annex D) and screens (see Annex E) can be effective measures
for the reduction of the noise emitted from machines, installations, piping systems and openings.
An enclosure is a structure completely surrounding the machine or installation. It consists mainly of
a sound-insulating shell (metal, wood, concrete, etc.) with and without an internal sound-absorbing
lining. The achievable noise reduction depends on the insulation of airborne sound provided by the
shell and on the degree of absorption by the internal surface of the enclosure if absorption exists. In
practice, it is limited by openings, ineffective seals and by transmission of structure-borne sound. This
limitation can be minimized by using measures such as silenced openings.
The effectiveness of noise control by using enclosures, silencers or screens can be measured and assessed
by the insertion loss, the transmission loss and the reduction of sound level (see ISO 11690-1:2020,
Clause 3, for definitions).
6.3 Noise control by use of sound-absorbing materials
The relationship between noise emission and noise immission is determined by sound propagation
(see ISO/TR 11690-3). Sound propagation and therefore the acoustical quality of a room are influenced
by the treatment of surfaces (ceiling and walls) by using sound-absorbing materials, which should be
selected in relation to the frequency spectrum of the noise. For attenuation of noise at low frequencies,
the use of absorptive materials is less effective.
8 © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
Noise in rooms consists of direct noise from sources and reflected noise from room boundaries (floors,
walls, ceilings, other equipment, fittings, etc.). Absorptive surface treatment reduces exclusively the
reflected noise.
It is possible to assess the acoustical quality of a room and therefore the effectiveness of a surface
treatment by using the sound propagation quantities, e.g. the rate of spatial decay (DL ) and the excess
(DL ) of sound pressure levels. These quantities are derived from the spatial sound distribution curves
f
(see ISO 11690-1 for definitions and also ISO/TR 11690-3). Recommended values of DL are given
in ISO 11690-1:2020, Table 3 (see also Table 2 of this document). The assessment can be made from
quantities measured (see Clause 8) or calculated using noise-prediction methods (see ISO/TR 11690-3).
Table 2 — Typical values for the mean sound absorption coefficient α and sound propagation
descriptors DL and DL in the middle region
f 2
α DL DL
f 2
Description of rooms
dB dB
With small/intermediate volume (V < 10 000 m and
<0,2 8 to 13 1 to 3
h < 5 m) without absorbing ceiling, empty
With large volume (V ≥ 10 000 m and h ≥ 5 m) without
0,2 6 to 9 2,5 to 4
absorbing ceiling, with fittings
All rooms with absorbing ceiling, with fittings >0,3 5 to 8 3,5 to 5
NOTE DL is the excess of sound pressure level. DL is the rate of spatial decay of sound pressure levels per distance
f 2
doubling. See ISO 11690-1 for definitions.
The acoustical quality of a room is best if DL is low and DL is high. Typical values for average sound
f 2
absorption coefficient and for sound propagation parameters DL and DL are given in Table 2 for
2 f
different types of rooms and surface treatments.
Generally, industrial noise lies in the frequency range 500 Hz to 2 000 Hz. In such situations, the
following reductions in sound pressure level relative to rooms with hard walls and ceiling may be
achieved.
a) In the near region, the reduction of the A-weighted sound pressure level is in the range 1 dB to 3 dB
because surface treatment has very little effect (see ISO 11690-1 for definitions).
b) In the middle region, this reduction is usually between 3 dB and 8 dB.
c) In the far region, it usually lies between 5 dB and 12 dB, depending on the room dimensions and the
extent of wall treatment and fittings.
In order to assess the effectiveness of a surface treatment outside the direct field, distinction should
be made between rooms with and without diffuse field conditions (see ISO 11690-1 for definitions and
also Annex F and ISO/TR 11690-3).
Typical spatial sound distribution curves in rooms of different shapes and sizes before and after
installation of a variety of surface treatments are given in Figures 8 and 9.
ISO 11690-2:2020(E)
Key
X distance from source, in m
Y sound pressure level, L , in dB
p
1 reflecting floor, walls and ceiling
2 with absorption at ceiling
3 with absorption at ceiling and walls
4 without reflections (free field)
NOTE All three dimensions of the room are of the same order of magnitude.
Figure 8 — Typical spatial sound distribution curve for a room with diffuse field conditions,
without and with several surface treatments
10 © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
Key
X distance from source, in m
Y sound pressure level, L , in dB
p
1 Scattering objects and reflecting ceiling
2 Scattering objects and absorbent ceiling
3 without reflections (free field)
NOTE The height of the room is much smaller than the other two dimensions.
Figure 9 — Typical spatial sound distribution curve for a fitted room without diffuse field
conditions, with and without sound-absorbing ceiling
The combination of surface treatment and noise barriers is normally quite effective and leads to a
noise level reduction which is substantially higher than that obtained with only one of these measures
(see Annexes E and F). In addition to the noise reduction which can be measured objectively, there will
be an important subjective improvement.
More information on surface treatment is given in Annex F.
6.4 Sound propagation in structures and noise control measures
Transmission of airborne noise into adjacent rooms or into the open is reduced by increasing the sound
insulation of walls, ceilings, windows and doors (see Annex H).
Propagation of structure-borne sound should be prevented initially as it is very difficult to eliminate
once in the structure. Measures to reduce the transmission of airborne and structure-borne sound
(see Annexes G and H) should be considered at the planning stage, otherwise their implementation may
not be feasible.
7 Noise control at the work station
Noise control measures at the source and on the transmission paths can be supplemented by further
measures taken at the work station, for example with screens and cabins (see Annexes E and I).
ISO 11690-2:2020(E)
8 Verification methods
8.1 General
Sound sources, noise control devices, sound propagation, noise levels in workplaces and sound
insulation of buildings are described by acoustical quantities. These acoustical quantities and sound
level reductions by means of specific measures are frequently determined or agreed upon in plans,
programmes and contracts. The value of these acoustical quantities and the success of noise control
measures should be verifiable in situ. When comparing these values with the verified ones, the
uncertainty should be taken into account.
8.2 Sound sources
The declaration of noise emission can be verified by using the methods given in ISO 4871. Noise
emission data should be verified by using the machine-specific noise test code and the basic standards
for noise emission measurement (the ISO 3740 series, the ISO 9614 series and the ISO 11200 series).
When verifying the declared values, it is essential that the operating and mounting conditions are the
same as those specified in the noise emission declaration or machine documents. The noise control
measures are assessed by determining the difference in noise emission.
8.3 Noise control devices
The effectiveness of noise control devices can be measured and verified by using the insertion loss,
transmission loss or the reduction of sound pressure levels (see Annexes C, D, E and I). The buyer and
seller should agree on which descriptor to use.
8.4 Workroom
The acoustic quality of workrooms and offices can be assessed by using the following sound propagation
parameters: spatial decay (DL ) and excess (DL ) of sound pressure level and reverberation time. These
2 f
three quantities can be measured or calculated (see ISO/TR 11690-3). Values agreed upon between the
parties at the planning stage are usually calculated. Verified values are measured.
Verification method: an omnidirectional sound source of known sound power should be used. The
source should be located near the floor with the measurement points all set at the same height. The
influence of a directional characteristic of the source can be avoided if the source is rotating and the
sound pressure level is integrated at each measurement point.
Sound propagation should be determined for the overall sound pressure level with a given frequency
distribution or in octave bands. Normally, it is measured on a path that ensures a clear line of sight
between the source and measurement point. When comparing the given and the verified values, it is
essential that the path and the range of distances be the same.
When measuring the spatial sound distribution curve, the sound pressure level behind obstacles such
as machines (e.g. at work stations) can be up to 10 dB lower (on average 3 dB to 4 dB) than the sound
pressure level measured on a path with a clear line of sight. These differences must be taken into
account when the spatial sound distribution curve in rooms and the sound pressure level at the work
station are to be determined.
8.5 Specified positions, work stations
The effectiveness of noise control and the noise immission can be determined and verified by taking
into account the sound pressure level at specific positions, normally the work stations. The acoustical
conditions present following the deployment of noise control measures can be compared to those
proceding them only if the operating conditions and the measurement method used are identical.
12 © ISO 2020 – All rights reserved
ISO 11690-2:2020(E)
9 New technologies
In some cases, it may be necessary to consider noise control strategies offered by the application of new
technologies.
Annex J gives some information on one of these technologies: anti-noise active/adaptive techniques
where the undesired mechanical and/or acoustical waves interfere destructively with artificially
generated ones in the opposite phase. No such systems are commercially available for workplaces as yet.
ISO 11690-2:2020(E)
Annex A
(informative)
Modification or replacement of machine components
A.1 Restriction of noise generation and transmission
The following procedures are recommended.
a) Avoid impacts or rapid moveme
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