ISO TR 11690-3-1997 Acoustics - Recommended practice for the design of low-noise workplaces containing machinery - Part 3 Sound propagation and noise prediction.pdf

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1、TECHNICAL REPORT lSO/TR 11690-3 First edition 1997-02- 15 Acoustics - Recommended practice for the design of low-noise workplaces containing machinery - Part 3: Sound propagation and noise prediction in workrooms Acoustique - Pratique recommand4e pour la conception de locaux de travail B bruit rkdui

2、t contenant des machines - Partie 3: Propagation du son et pr a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii 0 IS0 ISOmR 11690-3: 1997(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The w

3、ork 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- gover

4、nmental, 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. The main task of technical committees is to prepare International Standards, but in exceptional circumstance

5、s 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

6、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 exampl

7、e). Technical Reports of types 1 and 2 are subject to review within three years of publication, to decice 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 Technical Reports of type 3 do not necessarily have to be reviewed until the data they provide are considered to be no longer valid

8、or useful. lSO/TR 11690-3, which is a Technical Report of type 3, was prepared by Technical Committee lSO/TC 43, Acoustics, Subcommittee SC 1, Noise. IS0 11690 consists of the following parts, under the general title Acoustics - Recommended practice for the design of low-noise workplaces containing

9、machinery - Part 1: Noise control strategies - Part 2: Noise control measures - Part 3: Sound propagation and noise prediction in workrooms . . . III lSO/TR 11690-3: 1997(E) Introduction This Technical Report is intended for use by all parties involved in noise reduction in workplaces and design of

10、low-noise workplaces. The objective is: - to make them aware of what is the current technical consensus regarding sound propagation and noise prediction in workrooms, - to aid the interaction between them within a common technical framework, - to promote the understanding of the desired noise contro

11、l requirements. This Technical Report provides the connection between the emission of sound sources e.g. machines and the sound pressure level at workstations caused by their operation in a workroom. Therefore, it allows an interchange of information between machine suppliers, who are responsible fo

12、r noise emission values, and machine users, who require low noise immission values. A further target is the assessment of the acoustical performance of a workroom. These tasks are connected by the determination of the sound propagation descriptors of a workroom. A methodology for noise prediction in

13、 workrooms is presented and a structure is given for the classification of prediction methods according to the level of detail of input parameters. TECHNICAL REPORT o IS0 ISO/TR 11690-3:1997(E) Acoustics - Recommended practice for the design of low-noise workplaces containing machinery - Part 3 : So

14、und propagation and noise prediction in workrooms 1 Scope In this part of IS0 11690, sound propagation in a room is considered together with the prediction of sound pressure levels and of noise immission at the workplace. Details of the description of the physical phenomena involved in a noise predi

15、ction scheme are strongly dependent on the situation being considered and the way this situation is modelled (input parameters, calculation techniques). This dependency is surveyed and the methodology for noise prediction is described. Recommendations are provided concerning the use of noise predict

16、ion as an aid for noise control in workrooms. Examples of use of noise prediction methods are given in annexes A to E. 2 References References listed in IS0 11690-l should also be consulted when using this Technical Report. 3 Definitions Definitions given in IS0 11690-l apply to this Technical Repor

17、t. 4 Basic principles of sound propagation in rooms 4.1 Sound propagation descriptors A basic element for noise prediction in workrooms is the prediction of the distribution of sound pressure levels caused by an omnidirectional point source. This distribution is influenced by : - the shape and the v

18、olume of the room, - the absorption of the surfaces, - the fittings. 1 ISOmR 11690-3:1997(E) IS0 The resulting sound level distribution can be considered using a spatial sound distribution curve (see definition 3.4.11 of part 1 and figures 1 and 2 of this Technical Report). The information contained

19、 in this curve can be summarized, for a given distance range, by two quantities (see definitions 3.4.12 and 3.4.13 of part 1) : - the rate of spatial decay of sound pressure level per distance doubling (DW - the excess of sound pressure level with respect to a free field (DLf). The spatial sound dis

20、tribution curve and these two quantities are used to describe the acoustical characteristics of a room. The sound pressure level caused by a given source is indeed smaller if DLf is low and DL2 is high (see 6.3 of part 2). Annex D shows how the acoustical characteristics of a room can be described f

21、rom spatial sound distribution curves. The spatial sound distribution curve is determined on a free path with no obstacle between the source and the receiver. For its measurement, see 8.4 of part 2. NOTES 1 An International Standard specific to the measurement of spatial sound distribution curves in

22、 rooms is in preparation (IS0 14257 presently at the stage of draft). 2 When sound sources (machines) with dimensions too large to be neglected are considered, the sound distribution curve may differ from that of a point source for distances less than the typical dimension of the machine. 4.2 Rooms

23、with diffuse sound fields If diffuse sound field conditions are met (see definitions 3.4.8 and 3.4.9 of part l), at a certain distance from the source, sound pressure levels are nearly constant and independent of receiver position, as shown in figure 1. 85 80 I5 ?O 1 2 3 4 5 - hall 15 m x 15 m x 5 m

24、 L w hall 30 m x 30 m x 12 m _.-_- free field IO m ISOmR 11690-3:1997(E) - distance - Figure 1 : Examples of spatial sound distribution curves for an omnidirectional point source and two rooms with different sizes, equal absorption coefficients and diffuse field. The dotted curve is the spatial soun

25、d distribution curve under total free field conditions. Lp denotes the sound pressure level at a given point when the sound power level of the source is 100 dB. The sound pressure level of the diffuse field depends only on the total sound power level of all sources in the room and on the equivalent

26、absorption area A. In rooms with a diffuse sound field, there is a direct connection between the reverberation time and the expected spatial sound distribution curve. It is therefore also possible to qualify such rooms by their reverberation time. In this case, noise prediction is relatively simple.

27、 3 lSO/TR 11690-3: 1997(E) D IS0 4.3 Rooms with uniform sound propagation In many workrooms, diffuse sound field conditions cannot be assumed e.g. because the height of the room is less than one third of the length (flat rooms). In such rooms, even far from the source, the sound field depends on the

28、 position being considered and is characterized by a spatial sound distribution curve. In many workrooms, it can be assumed that the absorption and the fitting density are similar in different parts of the room (this includes a room with an absorbing ceiling and a reflecting floor). In this case, a

29、single spatial sound distribution curve along a free path (not close to walls or fittings) represents the sound propagation and the acoustical quality of the room. As an example, figure 2 shows two typical spatial sound distribution curves flat room containing fittings. 85 80 75 30 10 m - - - -r in

30、a - with fittings, with reflecting ceiling I w with fittings, with absorbing ceiling m-.-v. free field distance - Figure 2 : Examples of typical spatial sound distribution curves for the same flat and fitted room, with and without sound absorbing ceiling. The dotted curve is the spatial sound distri

31、bution curve under total free field conditions. Lp denotes the sound pressure level at a given point when the sound power level of the source is 100 dB. 4 0 IS0 ISO/TR 11690-3: 1997(E) It is often useful to split the spatial sound distribution curve into three sections depending on the distance from

32、 the source (see 3.4.11 of part 1). The first section corresponds to the region near the source. In this region, the sound field is dominated by the direct field. The rate of spatial decay per distance doubling, DL2, is in most cases approximately 5 dB to 6 dB. Increasing the number of fittings in t

33、he vicinity of the source tends to increase the sound pressure level close to the source and to reduce it far from the source. The second section of this curve corresponds to a middle region. In this region, DL2 lies in the range 2 dB to 5 dB and DLf in the range 2 dB to 10 dB. In the far region (th

34、ird part), scattering effects of fittings are important. The absorption of the walls, the density and the absorption of fittings have a dominant influence on the sound propagation far away from the source. Therefore, in this region, DL2 may be greater than 6 dB and DLf may be negative. 4.4 Rooms wit

35、h non uniform sound propagation In some situations, the room shape, absorption and fitting density differ from one part of the room to the other to such an extent that it is not possible to describe the sound propagation in the room with a single spatial sound distribution curve. In such situations,

36、 it may be necessary to describe the sound field in a way which takes into account the above factors. Fittings can also be considered individually. 5 Noise prediction in workrooms Noise prediction in workrooms (see 9 of part 1) is an aid in making decisions regarding noise control measures. It allow

37、s calculation of the sound pressure level at any point and determination of sound propagation descriptors. It is therefore possible to compare these values with specified values or limits and to compare various solutions of a noise control programme. Although several noise prediction methods are ava

38、ilable, all of them are based on a common procedure. This procedure is summarized in the flow chart shown in figure 3 and is outlined in the next clause. 6 Methodology for noise prediction in workrooms Noise prediction in workrooms should follow five steps described below. 6.1 Objectives - Values to

39、 be achieved At an early stage of a noise prediction scheme, acoustical descriptors must be chosen and target values defined by the parties involved, taking account of the various constraints associated with the project. Such descriptors can be sound pressure levels at workstations, immission and/or

40、 exposure data, spatial sound lSO/TR 11690-3:1997(E) 0 IS0 distribution curves, rates of spatial decay per distance doubling, excesses of sound pressure level, reverberation times etc. 6.2. Collection of input data The level of detail of input parameters should be in accordance with the desired or p

41、ossible value of the accuracy of the results. Different levels of detail in the description of the input parameters are shown in tables 1 to 3. The sound field that can be assumed in the room, the degree of knowledge of the input parameters and the acoustical description of the room are key factors

42、for the selection of the prediction method. 6.2.1 Empty room description The empty room is the space limited by the room surfaces such as the boundaries of the workroom (ceiling, floor, walls) and large internal surfaces which limit the space in it (screens, partitions, enclosures, cabins, etc.). Pr

43、ediction methods need the characteristics of the hall surfaces, such as their geometry (position, dimension, shape etc.), their absorption and reflection properties. Due to their complexity in real workrooms, room surfaces often need to be partitioned into sub-elements with different acoustical prop

44、erties. Absorption coefficients are also important parameters whose values affect the result of the prediction. Any prediction method should specify clearly the procedure to be used for estimating these parameters. Table 1 shows several possible degrees of complexity in the description of the workro

45、om. 1 Table 1 - Absorption and shape of the room Level of detail of the description Absorption and shape of the room The room is characterized by its volume and by the mean absorption coefficient of its surfaces. Box-like shape. Each surface is characterized by a single absorption coefficient. Box-like shape. Sub-division of the room surfaces into elements of different absorption coefficients. Actual room shape. Distribution of absorption and reflection oroDerties of the room surfaces.