1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 17497-2:2012Acoustics Sound-scatteringproperties of surfacesPart 2: Measurement of the directionaldiffusion coefficient in a free fieldBS ISO 17497-2:2012 BRITISH STANDARD
2、National forewordThis British Standard is the UK implementation of ISO 17497-2:2012.The UK participation in its preparation was entrusted to TechnicalCommittee EH/1/6, Building acoustics.A list of organizations represented on this committee can beobtained on request to its secretary.This publication
3、 does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 71826 7ICS 91.120.20Compliance with a British Standard cannot confer immunity fromleg
4、al obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 May 2012.Amendments issued since publicationDate Text affectedBS ISO 17497-2:2012 ISO 2012Acoustics Sound-scattering properties of surfaces Part 2: Measurement of the directiona
5、l diffusion coefficient in a free fieldAcoustique Proprits de dispersion du son par les surfaces Partie 2: Mesurage du coefficient de diffusion directionnel en champ libreINTERNATIONAL STANDARDISO17497-2First edition2012-05-15Reference numberISO 17497-2:2012(E)BS ISO 17497-2:2012ISO 17497-2:2012(E)i
6、i ISO 2012 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2012All 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 fro
7、m either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 17497-2:2012ISO 17497-2:2012(E) ISO 2012 All righ
8、ts reserved iiiContents PageForeword ivIntroduction v1 Scope 12 Normative references . 13 Terms and definitions . 14 Measurement principle 35 Frequency range 46 Test arrangement . 46.1 Measurement environment . 46.2 Measurement field . 56.3 Test specimen 67 Test procedure . 77.1 Test signals . 77.2
9、Source and receiving equipment 77.3 Measurements 77.4 Polar response processing . 88 Expression of results . 118.1 Directional diffusion coefficient 118.2 Normalized directional diffusion coefficient 128.3 Calculation of area factors 128.4 Random incidence diffusion coefficient .128.5 Presentation o
10、f results .139 Test report .13Annex A (normative) Qualification of a measurement space .14Bibliography .15BS ISO 17497-2:2012ISO 17497-2:2012(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of pre
11、paring 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
12、 liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task o
13、f technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attention is
14、 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.ISO 17497-2 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 2, Building acoustics.ISO 17
15、497 consists of the following parts, under the general title Acoustics Sound-scattering properties of surfaces: Part 1: Measurement of the random-incidence scattering coefficient in a reverberation room Part 2: Measurement of the directional diffusion coefficient in a free fieldiv ISO 2012 All right
16、s reservedBS ISO 17497-2:2012ISO 17497-2:2012(E)IntroductionThe degree of acoustic scattering from surfaces is very important in all aspects of room acoustics, e.g. in concert halls, sound studios, industrial halls and reverberation chambers. The degree of scattering and absorption in a room are imp
17、ortant factors related to the acoustic quality of the room. This part of ISO 17497 addresses the measurement and characterization of scattering surfaces.The scattering coefficient is introduced in ISO 17487-1. In this part of ISO 17487, a measurement method for the directional diffusion coefficient
18、is introduced. The diffusion coefficient is different from, but related to, the random incidence scattering coefficient. While the scattering coefficient is a rough measure that describes the degree of scattered sound, the diffusion coefficient describes the directional uniformity of the scattering,
19、 i.e. the quality of the diffusing surface. Consequently, there is a need for both concepts, and they have different applications.The work has been coordinated with the working group of the Audio Engineering Society, AES SC-04-02 for the Characterization of Acoustical Materials. ISO 2012 All rights
20、reserved vBS ISO 17497-2:2012BS ISO 17497-2:2012Acoustics Sound-scattering properties of surfaces Part 2: Measurement of the directional diffusion coefficient in a free field1 ScopeThis part of ISO 17497 specifies a method of measuring the directional diffusion coefficient of surfaces.The diffusion
21、coefficient characterizes the sound reflected from a surface in terms of the uniformity of the reflected polar distribution. The diffusion coefficient is a measure of quality designed to inform producers and users of surfaces that, either deliberately or accidentally, diffuse sound. It can also info
22、rm developers and users of geometric room acoustic models. The diffusion coefficient is not suitable for direct use as an input to current diffusion algorithms in geometric room acoustic models.This part of ISO 17497 details a free-field characterization method.2 Normative referencesThe following do
23、cuments, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 266, Acoustics Prefe
24、rred frequenciesIEC 61260, Electroacoustics Octave-band and fractional-octave-band filters3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1sound rayline following one possible direction of sound propagation from a source point3.2specular reflecti
25、onreflection that obeys Snells law, i.e. the angle of reflection is equal to the angle of incidenceNote 1 to entry Specular reflection can be obtained approximately from a plane, rigid surface with dimensions much larger than the wavelength of the incident sound.3.3specular zonearea contained by ima
26、ginary lines that are constructed from the image source, which is created about the plane of a specified reference flat surface via the edges of that surface to the receiver arc or hemisphereNote 1 to entry The reference flat surface is a plane and rigid surface, with the same projected shape or foo
27、tprint as the test surface.Note 2 to entry The position at which an imaginary line from the image source to a receiver crosses the diffuser is the specular reflection point (see Figure 1).INTERNATIONAL STANDARD ISO 17497-2:2012(E) ISO 2012 All rights reserved 1BS ISO 17497-2:2012ISO 17497-2:2012(E)K
28、ey1 source2 specular zone3 diffuser4 image source5 receiver arcFigure 1 Representation of specular zone3.4far fieldregion in which the reflected sound pressure level from the test surface decays by 6 dB per doubling of distanceNote 1 to entry In the near field, the shape of the angular field distrib
29、ution is dependent on the distance from the diffuser.3.5single plane diffusersurface that displays distinct anisotropic behaviour, as can be the case for a cylinder or a one-dimensional Schroeder diffuserNote 1 to entry For these surfaces, the diffusion is measured in the plane of maximum diffusion.
30、3.6multiple-plane diffusersurface that is expected to display more approximately isotropic behaviour, as can be the case for a hemisphere or a two-dimensional Schroeder diffuserNote 1 to entry For these surfaces, hemispherical evaluation is appropriate, yielding a single diffusion coefficient. Alter
31、natively, measurements can be done in two orthogonal planes.3.7semicircular polar responsesound pressure level created by energy scattered from the surface as a function of angle measured about the reference normal, generated under free-field or pseudo-free-field conditions, in a specified plane, on
32、 a semicircle centred at the reference point, at an appropriate radial distanceNote 1 to entry The reference normal is an outward-pointing vector perpendicular to the front face of a reference flat surface. The reference point is the geometric centre of gravity of the reference flat surface2 ISO 201
33、2 All rights reservedBS ISO 17497-2:2012ISO 17497-2:2012(E)3.8hemispherical polar responsesound pressure level scattered from the surface as a function of spherical coordinates measured about the reference normal, generated under free-field or pseudo-free-field conditions, on a hemisphere centred at
34、 the reference point3.9directional diffusion coefficientd,measure of the uniformity of diffusion produced by a surface for one source positionNote 1 to entry The value of d,is bounded between 0 and 1. When complete diffusion is achieved by the surface, the diffusion coefficient is 1. However, real d
35、iffusers rarely have diffusion coefficients higher than 0,7. If only one receiver receives non-zero scattered sound pressure, the diffusion coefficient is 0. The subscript is used to indicate the angle of incidence relative to the reference normal of the surface. The indicates the azimuth angle.3.10
36、random incidence diffusion coefficientdmeasure of the uniformity of diffusion for a representative sample of sources over a complete semicircle for a single plane diffuser, or a complete hemisphere for a hemispherical diffuserNote 1 to entry A mean or a weighting of the directional diffusion coeffic
37、ients for the difference source positions is used to calculate the diffusion coefficient, as specified in 8.4. A guideline to achieve a representative sample of sources is given in 6.2.2. The lack of a subscript for d indicates random incidence.3.11normalized directional diffusion coefficientd,ndire
38、ctional diffusion coefficient of the test specimen normalized to that of the reference flat surface3.12normalized diffusion coefficientdnrandom incidence diffusion coefficient determined from the normalized directional diffusion coefficient3.13physical scale ratio1:Nratio of any linear dimension in
39、a physical scale model to the same linear dimension in full scaleNote 1 to entry The wavelength of the sound used in a scale model for acoustic measurements obeys the same physical scale ratio. Therefore, if the speed of sound is the same in the model as in full scale, the frequencies used for the m
40、odel measurements are a factor of N times higher than in full scale.4 Measurement principleThe diffusion coefficient quantifies how the energy reflected from a surface is spatially distributed. This spatial distribution is described by polar responses of the reflected sound pressure level. A source
41、is used to irradiate the test surface, and microphones at radial positions in front of the surface are used to measure the sound. The reflected sound is extracted from the microphone signals using the process outlined in Clause 7. The diffusion coefficient is then calculated from the reflected sound
42、 pressure levels using the equations shown in Clause 8. To remove finite-panel effects, which cause the diffusion coefficient to decrease as the frequency increases, a normalized diffusion coefficient is calculated.The microphone positions should map out a semicircle or hemisphere, for a single plan
43、e or hemispherical measurement, respectively. Single-plane diffusers can be measured using a two-dimensional goniometer, either using a boundary plane measurement (see Figure 3) or in an anechoic chamber. A multi-plane diffuser can be characterized by making two single plane measurements in orthogon
44、al planes in a two-dimensional goniometer this is the quickest and easiest approach. Alternatively, a hemispherical measurement can be done using a three-dimensional goniometer (see Figure 2). ISO 2012 All rights reserved 3BS ISO 17497-2:2012ISO 17497-2:2012(E)5 Frequency rangeThe measurements shall
45、 be performed in one-third-octave bands with centre frequencies covering the frequency range from 100 Hz to 5 000 Hz, in accordance with IEC 61260 and ISO 266. This refers to full-scale measurements. If a physical scale factor of 1:N is used, the centre frequencies should cover the frequency range f
46、rom N 100 Hz to N 5 000 Hz.If the scale model is filled with a gas in which the speed of sound is different from that in atmospheric air, the measurement frequencies shall be chosen in such a way that the wavelength obeys the physical scale ratio 1:N.High frequencies may be omitted from the measurem
47、ents if the attenuation in the air is too high.6 Test arrangement6.1 Measurement environmentAnnex A describes the measurement environments that shall be used. A qualified anechoic chamber can be used. An implementation of such a set-up is illustrated in Figure 2. Alternatively, a large non-anechoic
48、space can be used to simulate a reflection-free environment if certain techniques described in Annex A are used.Figure 2 Three-dimensional measurement goniometerBoundary measurements may also be carried out to remove the necessity for a space to be anechoic in one plane provided conditions in Annex
49、A are satisfied. An implementation of such a set-up is illustrated in Figure 3.4 ISO 2012 All rights reservedBS ISO 17497-2:2012ISO 17497-2:2012(E)Figure 3 Two-dimensional boundary measurement techniqueScale models may be used to evaluate the diffusion from test surfaces. If the speed of sound is the same in the model as in full scale, then the frequencies used for the model measurements shall be a factor of N higher than in full scale. For scale models, the absorption properties shall be the same for both the ful
