EN ISO 11688-2:2000

Acoustics - Recommended practice for the design of low-noise machinery and equipment - Part 2: Introduction to the physics of low-noise design (ISO/TR 11688-2:1998)

Migrated from Progress Sheet (TC Comment) (2000-07-10): BC/CEN/88/13.212 is covered by WI 36 and 37. ++ Selected as type'B' (comparison) in the one language experiment ++ The TC Secretary want to publish a European Standard based on a published Inter- ++ national Technical Report ISO/TR 11688-2:1998 (TA/981012)

Akustik - Richtlinien für die Gestaltung lärmarmer Maschinen und Geräte - Teil 2: Einführung in die Physik der Lärmminderung durch konstruktive Maßnahmen (ISO/TR 11688-2:1998)

Dieser Teil von ISO/TR 11688 stellt den physikalischen Hintergrund zu den in Teil 1 wiedergegebenen Konstruktionsregeln und Beispielen dar. Darüber hinaus wird die Anwendung umfangreicher Fachliteratur gefördert. Die beabsichtigten Anwender sind Maschinen- und Gerätekonstrukteure ebenso wie deren Nutzer und/oder Käufer von Maschinen sowie Behörden im Bereich der Gesetzgebung und Überwachung. Die in dieser Norm wiedergegebenen Gleichungen fördern das allgemeine Verständnis der Lärmminderung und erlauben in vielen Fällen den Vergleich unterschiedlicher Konstruktionsvarianten.

Acoustique - Pratique recommandée pour la conception de machines et équipements à bruit réduit - Partie 2: Introduction à la physique de la conception à bruit réduit (ISO/TR 11688- 2:1998)

L'ISO/TR 11688-2:2002 traite du contexte physique, des règles et des exemples de conception à bruit réduit donnés dans l'ISO/TR 11688-1 et vient à l'appui d'une importante documentation spécialisée.
Elle est destinée à être utilisée par les concepteurs de machines et d'équipements ainsi que par les utilisateurs et/ou acheteurs de machines et les autorités agissant dans le domaine de la législation, ou de l'inspection.
Les équations indiquées dans l'ISO/TR 11688-2:2002 sont destinées à faciliter la compréhension générale de la réduction du bruit. Dans de nombreux cas, elles permettent une comparaison entre différentes versions d'une conception, mais ne sont pas utilisables pour la prévision de valeurs absolues d'émission sonore.
Les informations sur les sources sonores internes, les chemins de transmission et les parties d'une machine rayonnant du bruit constituent les données de base pour la réduction du bruit des machines. C'est pourquoi, des méthodes de mesurage et des méthodes de calcul appropriées pour obtenir ces informations sont décrites aux articles 7 et 8 et à l'annexe A.

Akustika - Priporočila za konstruiranje tihih strojev in naprav - 2. del: Fizikalne osnove za načrtovanje (ISO/TR 11688-2:1998)

General Information

• Status: Published
• Publication Date: 12-Dec-2000
• ICS: 17.140.20 - Noise emitted by machines and equipment
• ICS: 21.020 - Characteristics and design of machines, apparatus, equipment
• Technical Committee: CEN/TC 211 - Acuostics
• Drafting Committee: CEN/TC 211 - Acuostics
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 30-Oct-2009
• Completion Date: 30-Oct-2009
• Directive: 98/37/EC - Machinery
• Mandate: M/BC/CEN/88/13 - Standardization request to CEN/CENELEC relating to machinery
• Ref Project: SIST EN ISO 11688-2:2001 - Acoustics - Recommended practice for the design of low-noise machinery and equipment - Part 2: Introduction to the physics of low-noise design (ISO/TR 11688-2:1998)

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2001
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RVQRYH]DQDþUWRYDQMH,6275
Acoustics - Recommended practice for the design of low-noise machinery and
equipment - Part 2: Introduction to the physics of low-noise design (ISO/TR 11688-
2:1998)
Akustik - Richtlinien für die Gestaltung lärmarmer Maschinen und Geräte - Teil 2:
Einführung in die Physik der Lärmminderung durch konstruktive Maßnahmen (ISO/TR
11688-2:1998)
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EUXLWUpGXLW3DUWLH,QWURGXFWLRQDODSK\VLTXHGHODFRQFHSWLRQDEUXLWUpGXLW,6275


Ta slovenski standard je istoveten z: EN ISO 11688-2:2000
ICS:
17.140.20 Emisija hrupa naprav in Noise emitted by machines
opreme and equipment
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL ISO/TR
REPORT 11688-2
First edition
1998-09-01
Acoustics — Recommended practice for
the design of low-noise machinery and
equipment —
Part 2:
Introduction to the physics of low-noise design
Acoustique — Pratique recommandée pour la conception de machines et
équipements à bruit réduit —
Partie 2: Introduction à la physique de la conception à bruit réduit
A
Reference number
ISO/TR 11688-2:1998(E)
ISO/TR 11688-2:1998(E)
Contents
1  Scope . 1
2  References. 1
3  Definitions . 1
4  Acoustical modelling. 1
5  Control of airborne and liquid-borne noise. 2
5.1 Generation of fluid-dynamic noise. 2
5.2 Noise control measures . 8
6  Control of structure-borne sound. 10
6.1 Model of sound generation. 10
6.2 Internal sources . 15
6.3 Transmission of structure-borne sound . 18
6.4 Control of structure-borne sound transmission
by damping . 28
6.5 Radiation. 30
7  Analysis by measurement methods . 35
7.1 Purpose of the analysis. 35
7.2 Internal sources . 36
7.3 Transmission paths. 36
7.4 Radiation. 36
7.5 Summary of procedures for the analysis of existing
machinery by measurement methods. 37
8  Analysis by computational methods . 39
8.1 Purpose of the analysis. 39
8.2 Deterministic methods . 39
8.3 Statistical methods. 39
8.4 Applicability of computational methods . 39
Annex A Example of the estimation of airborne sound emission
of a machine caused by structure-borne and airborne sound
emission from a component . 41
Annex B Glossary. 44
Bibliography. 46
©  ISO 1998
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 • CH-1211 Genève 20 • Switzerland
Internet [e-mail]
Printed in Switzerland
ii
©
ISO ISO/TR 11688-2:1998(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 organisations, 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 main task of technical committees is to prepare International
Standards, but in exceptional circumstances a technical committee may
propose the publication of a Technical Report of one of the following types:
— type 1, when the required support cannot be obtained for the
publication of an International Standard, despite repeated efforts;
— type 2, when the subject is still under technical development or where
for any other reason there is the future but not immediate possibility
of an agreement on an International Standard;
— type 3, when a technical committee has collected data of a different
kind from that which is normally published as an International
Standard ("state of the art", for example)
Technical Reports of types 1 and 2 are subject to review within three years
of publication, to decide whether they can be transformed into International
Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until the data they provide are considered to be no longer valid or
useful.
ISO/TR 11688-2, which is a Technical Report of type 3, was prepared by
Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
ISO 11688 consists of the following parts, under the general title Acoustics
— Recommended practice for the design of low-noise machinery and
equipment:
— Part 1: Planning
— Part 2: Introduction to the physics of low-noise design
iii
©
ISO/TR 11688-2:1998(E) ISO
Introduction
The objective of this part of ISO/TR 11688 is noise reduction in existing
machinery and noise control at the design stage of new machinery.
It is important that non-acoustic engineers are engaged in noise control
practice. It is of great importance for these engineers to have a basic
knowledge of noise generation and propagation characteristics and to
understand the principles of noise control measures.
iv
TECHNICAL REPORT  © ISO ISO/TR 11688-2:1998(E)
Acoustics — Recommended practice for the design of low-noise
machinery and equipment —
Part 2:
Introduction to the physics of low-noise design
1 Scope
This part of ISO/TR 11688 provides the physical background for the low-noise design rules and examples given in
1)
ISO/TR 11688-1 and supports the use of extensive special literature.
It is intended for use by designers of machinery and equipment as well as users and/or buyers of machines and
authorities in the field of legislation, supervision or inspection.
Equations given in this Technical Report will improve the general understanding of noise control. In many cases
they allow a comparison of different versions of design, but they are not useful for the prediction of absolute noise
emission values.
Information on internal sound sources, transmission paths and sound radiating parts of a machine is the basis for
noise control in machines. Therefore measurement methods and computational methods suitable to obtain this
information are described in clauses 7 and 8 and annex A.
2 References
See ISO/TR 11688-1 and the bibliography.
3 Definitions
See ISO/TR 11688-1 and annex A.
4 Acoustical modelling
In order to facilitate the understanding of complex sound generation and propagation mechanisms in machinery and
equipment or vehicles (the latter are also called "machines" in this part of ISO/TR 11688), it is necessary to create
simple acoustical models. The models provide a basis for noise control measures at the design stage.

1)
ISO/TR 11688-1:1995, Acoustics — Recommended practice for the design of low-noise machinery and equipment — Part 1:
Planning.
© ISO
ISO/TR 11688-2:1998(E)
A universal approach is to distinguish between
 internal sources;
 transmission paths inside the machine;
 radiation from its boundaries.
The internal sources and the transmission paths can each be assigned to three categories according to the media
used:
 airborne;
 liquid-borne;
 structure-borne.
Radiation is considered for air only.
Figures 1 and 2 serve to illustrate the principle of acoustical modelling. Figure 1 shows a simplified machine
consisting of an electric motor and a housing with an opening in it.
The motor is the only internal source. It generates airborne and structure-borne sound.
There are three internal transmission paths:
 through the air inside the housing to the opening;
 through the air inside the housing to the walls of the housing;
 through the fastenings to the walls of the housing.
Radiation occurs from the opening and from the walls of the housing.
Figure 2 illustrates this in a block diagram.
The total sound power emitted from the machine is the sum of the three contributions.
A systematic approach starts with an assessment of the relative importance of these contributions. The next step is
examining the blocks in Figure 2 looking for possibilities to reduce source strength, transmission and/or radiation
(see also following clauses). This should be done in relation to the various aspects of the design process (see
ISO/TR 11688-1:1995, Figure 1).
5 Control of airborne and liquid-borne noise
The basic principles of generation, transmission and radiation of sound in air (or other gases) and liquids are
basically identical and are therefore considered together in this clause. There is only one important exception:
cavitation. Occurring in liquids only, this phenomenon is considered separately in 5.1.3.
5.1 Generation of fluid-dynamic noise
Important noise-generating phenomena in gases and liquids are turbulence, pulsation and shock. Fluid-dynamic
processes generate noise if flow rate and pressure vary over time in a limited volume of a liquid or a gas, for
example in a turbulent flow. This leads to the transmission of sound from the disturbed volume of the fluid to the
surrounding medium. A classic example of this is the escape of compressed air from a nozzle.
© ISO
ISO/TR 11688-2:1998(E)
Figure 1 — Simplified machine for the illustration of acoustical modelling
Figure 2 — Block diagram for the illustration of generation, transmission and radiation of sound in the
"machine" of Figure 1
Mechanisms of fluid-dynamic sound generation can be related to properties of elementary sound sources with
known characteristics:
 monopoles;
 dipoles;
 quadrupoles.
5.1.1 Elementary model sources
A monopole
source is an in-phase volume change, such as a pulsating volume of any shape or a piston in a large
rigid surface. In the far field, monopoles have a spherical radiation pattern. The sound radiated from a monopole
source can be reduced by reducing the temporal variation in the volume flow rate.
EXAMPLE 1: Outlets of internal combustion engines, rotary piston fans, multi-cell compressors, piston pumps, piston
compressors, flares.
A dipole source arises as a result of external time-variable forces acting on a fluid without volume change, such as
in an oscillating rigid body of any shape. The dipole source can be replaced by two monopole sources of equal
strength and opposite phase situated very closely together. The far-field directivity pattern of a dipole is shown in
Table 1. Radiation from a dipole can be reduced by reducing the temporal variation of the forces acting on the fluid.
EXAMPLE 2: Vibrating rigid parts of machinery, parts of machinery running out of balance, ducts, propellers and fans.
A quadrupole source can be represented by a time-variable deformation of a body without change of its volume or
position. It can be replaced by two dipole sources of equal strength and opposite phase situated very closely
© ISO
ISO/TR 11688-2:1998(E)
together. The far-field directivity pattern is shown in Table 1. Radiation from a quadrupole is reduced when the time-
variable deformation is reduced.
EXAMPLE 3: Free turbulent flow as in safety valves, compressed-air nozzles, pipe fittings.
Most sound sources encountered in machinery contain aspects of more than one elementary source.
NOTE  Because of the stochastic nature of turbulence the sound spectrum is broad-band. An example is the turbulent flow in
the mixing zone of a free jet, particularly for Mach numbers Ma > 0,8. The definition of the Mach number is:
u
Ma = (1)
c
where
u is the flow velocity;
c is the speed of sound.
Table 1 summarizes and illustrates the information on the properties of the elementary sources.
Table 1 — Properties of elementary model sources
Type of source Schematic illustration Example(s) Far-field directivity
Monopole Siren, piston compressor
or pump, exhaust of
"Breathing"
internal combustion
sphere
engine, cavitation
phenomena,
compressed air engine,
gas burner
Dipole Slow machines (axial
and centrifugal fans),
Oscillating
obstacles in the flow
sphere
(flow separation),
ventilating or air-
conditioning systems,
...