SIST EN ISO 3743-1:1997
(Main)Acoustics - Determination of sound power levels of noise sources - Engineering methods for small, movable sources in reverberant fields - Part 1: Comparison method for hard-walled test rooms (ISO 3743-1:1994)
Acoustics - Determination of sound power levels of noise sources - Engineering methods for small, movable sources in reverberant fields - Part 1: Comparison method for hard-walled test rooms (ISO 3743-1:1994)
This part of ISO 3743 specifies a relatively simple engineering method for determining the sound power levels of small, movable noise sources. The measurements are carried out when the source is installed in a hard-walled test room . A comparison method is used to determine to the octave-band sound power levels of the source. The spatial average (octave-band) sound pressure levels produced by a reference sound source of known sound power output. The difference in sound pressure levels is equal to the difference in sound power levels if conditions are for both sets of measurements. The A-weighted sound power level is then calculated from the octave-band sound power levels. Note: Precision methods for the determination of sound power levels of small noise sources are specified in ISO 3741 and ISO 3745.
Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen - Verfahren der Genauigkeitsklasse 2 für kleine, transportable Quellen in Hallfeldern - Teil 1: Vergleichsverfahren in Prüfverfahren mit schallharten Wänden (ISO 3743-1:1994)
Dieser Teil von ISO 3743 beschreibt ein verhältnismäßig einfaches Verfahren der Genauigkeitsklasse 2 zur Bestimmung der Schalleistungspegel kleiner, transportabler Geräuschquellen. Für die Messungen wird die Quelle in einem Prüfraum mit schallharten Wänden aufgestellt. Zur Bestimmung der Schalleistungspegel in Oktavbändern wird ein Vergleichsverfahren verwendet. Dazu werden die räumlichen Mittelwerte der von der Quelle erzeugten (Oktavband-) Schalldruckpegel mit jenen einer Vergleichsschallquelle bekannter Schalleistung verglichen.
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit - Méthodes d'expertise en champ réverbéré applicables aux petites sources transportables - Partie 1: Méthode par comparaison en salle d'essai a parois dures (ISO 3743-1:1994)
Akustika - Ugotavljanje ravni zvočnih moči virov hrupa - Inženirske metode za majhne premične vire v odmevnih poljih - 1. del: Primerjalna metoda v prostoru za preskušanje z zvočno odbojnimi stenami (ISO 3743-1:1994)
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen - Verfahren der Genauigkeitsklasse 2 für kleine, transportable Quellen in Hallfeldern - Teil 1: Vergleichsverfahren in Prüfverfahren mit schallharten Wänden (ISO 3743-1:1994)Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit - Méthodes d'expertise en champ réverbéré applicables aux petites sources transportables - Partie 1: Méthode par comparaison en salle d'essai a parois dures (ISO 3743-1:1994)Acoustics - Determination of sound power levels of noise sources - Engineering methods for small, movable sources in reverberant fields - Part 1: Comparison method for hard-walled test rooms (ISO 3743-1:1994)17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:EN ISO 3743-1:1995SIST EN ISO 3743-1:1997en01-april-1997SIST EN ISO 3743-1:1997SLOVENSKI
STANDARD
SIST EN ISO 3743-1:1997
SIST EN ISO 3743-1:1997
SIST EN ISO 3743-1:1997
SIST EN ISO 3743-1:1997
SIST EN ISO 3743-1:1997
INTERNATIONAL STANDARD ISO 3743-1 First edition 1994-02-15 Acoustics - Determination of Sound power levels of noise sources - Engineering methods for small, movable sources in reverberant fields - Part 1: Comparison method for hard-walled test rooms Acoustique - Determination des niveaux de puissance acoustique 6mis par /es sources de bruit - Methodes d’expertise en champ r&erb&6 applicables aux petites sources transportables - Partie 1: M6thode par comparaison en salle d’essai ti parois dures Reference number ISO 3743-1: 1994(E) SIST EN ISO 3743-1:1997
ISO 3743=1:1994(E) Contents Page 1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 Def initions .,. 3 4 Requirements for hard-walled test room . 4 5 Instrumentation . 5 6 Installation and Operation of Source under test . 5 7 Measurements in test room . 6 8 Calculation of Sound power levels . 8 9 Information to be recorded . 8 10 Information to be reported . 9 Annex A Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 63 ISO 1994 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronie or mechanical, including photocopying and microfilm, without per- mission in writing from the publisher. International Organization for Standardization Case Postale 56 l CH-l 211 Geneve 20 l Switzerland Printed in Switzerland ii SIST EN ISO 3743-1:1997
ISO 374391:1994(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. Esch 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 patt in the work. ISO collaborates closely with the International Electrotechnical Commission (1 EC) 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 ISO 3743-1 was prepared by Technical Committee lSO/TC 43, Acoustics, Sub-Committee SC 1, Noise. ISO 3743 consists of the following Parts, under the general title Acoustics - Determination of Sound power levels of noise sources - Engineering methods for small, movable sources in reverberant fields: - Part 1: Comparison method for hard-waled test rooms - Part 2: Methods for special reverberation test rooms Part 2 is a revision of ISO 3743:1988. Annex A of this part of ISO 3743 is for information only. . . . Ill SIST EN ISO 3743-1:1997
ISO 3743=1:1994(E) Introduction 0.1 ISO 3743 is one of the ISO 3740 series, which specifies various methods for determining the Sound power levels of machines, equipment and their sub-assemblies. These basic Standards specify the acoustical requirements for measurements appropriate for different test environ- ments as shown in table 0.1. When selecting one of the methods of the ISO 3740 series, it is necessary to select the most appropriate for the conditions and purposes of the noise test. General guidelines to assist in the selection are provided in ISO 3740. The ISO 3740 series gives only general principles regarding the operating and mounting conditions of the machine or equipment under test. Reference should be made to the noise test code for a specific type of machine or equipment, if available, for specifications on mounting and operating conditions. 0.2 The method given in this part of ISO 3743 enables measurement of Sound pressure levels in octave bands at prescribed fixed microphone positions or along prescribed paths. A comparison method is used which allows determination of Sound power levels in octave bands; A-weighted Sound power Ievels may be calculated from the octave-band Sound power Ievels. Quantities which cannot be determined are the directivity charac- teristics of the Source and the temporal Pattern of noise radiated by sources emitting non-steady noise. 0.3 Parts 1 and 2 of ISO 3743 specify engineering methods for deter- mining the A-weighted and octave-band Sound power Ievels of small noise sources. The methods are applicable to small machines, devices, compo- nents and sub-assemblies which tan be installed in a hard-walled test room with prescribed acoustical characteristics or in a special reverber- ation test room. The methods are particularly suitable for small items of portable equipment; they are not intended for larger pieces of stationary equipment which, due to their manner of Operation or installation, cannot readily be moved into the test room and operated as in normal usage. The procedures are intended to be used when an engineering grade of accu- racy is desired without requiring the use of laboratory facilities. iv SIST EN ISO 3743-1:1997
International Classification of Test environment Volume of Source Sound power levels Optional information Standard Character of noise methodl) obtainable available 3741 Reverberation room Steady, broad-band Precision (grade 1) In one-thirdoctave or A-weighted Sound power meeting specified require- 3742 Steady, discrete fre- ments octave bands level Preferably less than 1 % quency or narrow-band 3743-1 Hard-walled test room of test room volume Steady, broad-band, ’ Engineering (grade 2) A-weighted and in octave Other weighted Sound Special reverberation test narrow-band, or discrete 3743-2 frequency bands power levels room 3744 Engineering (grade 2) Outdoors or in large room Greatest dimension less than 15 m Av Directivity information A-weighted and in one- and Sound pressure levels Preferably less than ’ third-octave or octave as a function of time; 3745 Precision (grade 1) Anechoic or semi- 0,5 % of test room vol- AnY bands other weighted Sound anechoic room ume power levels No restrictions; limited Sound pressure levels as 3746 Survey (grade 3) No special test environ- only by available test en- AnY A-weighted a function of time; other ment vironment weighted Sound power levels No special test environ- Steady, broad-band, 3747 Survey (grade 3) ment; Source under test No restrictions Sound power levels in narrow-band, or discrete A-weighted not movable frequency octave bands 1) See ISO 2264. SIST EN ISO 3743-1:1997
ISO 3743=1:1994(E) 0.4 In ISO 3743-2, the comparison method tan also be used, but an al- ternative method permits the determination of the A-weighted Sound power Ievel of the Source under test from a Single A-weighted Sound pressure level measurement at each microphone Position, rather than from a summation of octave-band levels. This direct method eliminates the need for a reference Sound Source, but requires the use of a special reverberation test room. The direct method is based on the premise that the Sound pressure Ievel, averaged in space and time in the test room, tan be used to determine the Sound power level emitted by the Source. The properties of the special reverberation test room are Chosen so that the room’s influence on the Sound power output of the equipment under test is small. The number of microphone positions and Source locations re- quired in the test room are specified. The requirements to be fulfilled by the special reverberation test room for measurements in accordance with the method given in ISO 3743-2 are significantly more restrictive than those placed on the hard-walled test room by the comparison method given in this part of ISO 3743. vi SIST EN ISO 3743-1:1997
INTERNATIONAL STANDARD ISO 3743=1:1994(E) Acoustics - Determination of Sound power levels of noise sources - Engineering methods for small, movable sources in reverberant fields - Part 1: Comparison method for hard-walled test rooms 1 Scope 1.1 General This patt of ISO 3743 specifies a relatively simple en- gineering method for determining the Sound power levels of small, movable noise sources. The measurements are carried out when the Source is in- stalled in a hard-walled test room. A comparison method is used to determine to the octave-band Sound power levels of the Source. The spatial average (octave-band) Sound pressure levels produced by the Source under test are compared to the spatial average (octave-band) Sound pressure levels produced by a reference Sound Source of known Sound power out- put. The differente in Sound pressure levels is equal to the differente in Sound power Ievels if conditions are the same for both sets of measurements. The A-weighted Sound power Ievel is then calculated from the octave-band Sound power Ievels. NOTE 1 Precision methods for the determination of Sound power levels of small noise sources are specified in ISO 3741 and ISO 3745. 1.2 Types of noise The method specified in this part of ISO 3743 is suit- able for measurements of all types of noise within a specified frequency range, except intermittent noise consisting of isolated bursts of Sound energy. NOTES 2 A classification of different types of noise is given in ISO 2204. 3 For sources of intermittent noise consisting of short- duration noise bursts, the free-field methods specified in ISO 3744 and ISO 3745 should be used. 1.3 Noise Source The noise Source may be a device, machine, compo- nent or sub-assembly. The maximum size of the Source under test depends upon the size of the room used for the acoustical measurements. (See also 4.1). 1.4 Measurement uncertainty Determinations made in accordance with this part of ISO 3743 result, with few exceptions, in Standard deviations of reproducibility of the A-weighted Sound power Ievel equal to or less than 1,5 dß (see table 1). A Single value of the Sound power Ievel of a noise Source determined according to the procedures of this part of ISO 3743 is likely to differ from the true value by an amount within the range of the measure- ment uncertainty. The uncertainty in determinations of the Sound power level arises from several factors which affect the results, some associated with en- vironmental conditions in the measurement laboratory and others with experimental techniques. If a particular noise Source were to be transported to each of a number of different laboratories, and if, at each laboratory, the Sound power level of that Source were to be determined in accordance with this part of ISO 3743, the results would show a scatter. The Standard deviation of the measured Ievels could be calculated (see examples in ISO 7574-4:1985, annex B) and would vary with frequency. With few ex- ceptions, these Standard deviations would not exceed those listed in table 1. The values given in table 1 are Standard deviations of reproducibility, Q, as defined in ISO 7574-1. The values of table 1 take into account the cumulative effects of measurement uncertainty in applying the procedures of this part of ISO 3743, but exclude variations in the Sound power output caused 1 SIST EN ISO 3743-1:1997
ISO 3743=1:1994(E) by cha nges i n operat Speed, line vo Ita ge) or ing mo conditions (e g . . unting cond itions. rotational The measurement uncertainty depends on the stan- dard deviation of reproducibility tabulated in table 1 and on the degree of confidence that is desired. As examples, for a normal distribution of Sound power levels, there is a 90 % confidence that the true value of the Sound power level of a Source lies within the range + 1,645 OR of the measured value and a 95 % confidkce that it lies within the range & 1,96 aR of the measured value. For further examples, reference should be made to the ISO 7574 and ISO 9296 series. Table 1 - Estimated values of the Standard deviation of reproducibility of Sound power levels determined in accordance with this part of ISO 3743 Octave-band centre Standard deviation of frequency reproducibility, flR Hz dB 125 3,O 250 zo 5ooto 4 000 115 8 000 23 A-weighted 1,5") *) Applicable to a Source which emits noise with a relatively “flat” spectrum in the frequency range 100 Hz to 10 000 Hz. NOTES 4 The Standard deviations listed in table 1 are associated with the test conditions and procedures defined in this part of ISO 3743, and not with the noise Source itself. They arise partly from variations between measurement laboratories in the geometry of the test room, the acoustical properties of the test room boundaries, background noise, the type and calibration of instrumentation, and the reference Sound Source. They are also due to variations in experimental measurement techniques, including microphone placement and spatial averaging, location of Source under test, inte- gration times, and measurement of reverberation time. 5 If several laboratories use similar facilities and instru- mentation, the results of Sound power determinations on a given Source in those laboratories may be in better agree- ment than would be implied by the Standard deviations given in table 1. 6 For a particular family of Sound sources, of similar size with similar Sound power spectra and similar operating conditions, the Standard deviations of reproducibility may be smaller than the values given in table 1. Hence, a noise test code for a particular type of machinery or equipment making reference to this part of ISO 3743 may state stan- dard deviations smaller than those listed in table 1 if sub- stantiation is available from the results of suitable interlaboratory tests. 7 The Standard deviation of reproducibility, as tabulated in table 1, includes the uncertainty associated with repeated measurements on the same noise Source under the same conditions (for Standard deviation of repeatability, see ISO 7574-1). This uncertainty is usually much smaller than the uncertainty associated with interlaboratory variability. However, if it is difficult to maintain stable operating or mounting conditions for a particular Source, the Standard deviation of repeatability may not be small compared with the values given in table 1. In such cases, the fact that it was difficult to obtain repeatable Sound power level data on the Source should be recorded and stated in the test report. 8 The procedures of this part of ISO 3743 and the stan- dard deviations given in table 1 are applicable to measure- ments on an individual machine. Characterization of the Sound power levels of batches of machines of the same family or type involves the use of random sampling tech- niques in which confidence intervals are specified, and the results are expressed in terms of statistical upper Iimits. In applying these techniques, the total Standard deviation must be known or estimated, including the Standard deviation of production, as defined in ISO 7574-1, which is a measure of the Variation in Sound power output between individual machines within the batch. Statistical methods for the characterization of batches of machines are described in ISO 7574-4. 2 Normative references The following Standards contain provisions which, through reference in this text, constitute provisions of this part of ISO 3743. At the time of publication, the editions indicated were valid. All Standards are subject to revision, and Parties to agreements based on this part of ISO 3743 are encouraged to investigate the possibility of applying the most recent editions of the Standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 2204:1979, Acoustics - Guide to International Standards on the measurement of airborne acoustical noise and evaluation of its effects on human beings. ISO 3744:1994, Acoustics - Determination of Sound power levels of noise sources using Sound pressure - Engineering method in an essentially free field over a reflecting plane. ISO 3745:1977, Acoustics - Determination of Sound power levels of noise sources - Precision methods for anechoic and semi-anechoic rooms. ISO 6926:1990, Acoustics - Determination of Sound power levels of noise sources - ßequirements for the Performance and calibration of reference Sound sources. ISO 7574-1:1985, Acoustics - Statistical methods for determining and verifying stated noise emission val- ues of machinery and equipment - Part 1: General considera tions and de finitions. 2 SIST EN ISO 3743-1:1997
ISO 3743=1:1994(E) ISO 7574-4:1985, Acoustics - Statistical methods for determining and verifying stated noise emission val- ues of machinery and equipment - Part 4: Methods for stated values for ba tches of machines. I EC 225: 1966, Octave, half-octave and third-octave band filters intended for the analysis of Sounds and vibra tions. I EC 651: 1979, Sound level meters. I EC 804: 1985, Integrating-averaging Sound level me- ters. I EC 942: 1988, Sound calibrators. 3 Definitions For the purposes of this part of ISO 3743, the follow- ing definitions apply. 3.1 Sound pressure, p: A fluctuating pressure superimposed on the static pressure by the presence of Sound. lt is expressed in Pascals. NOTE 9 The magnitude of the Sound pressure tan be expressed in several ways, such as instantaneous Sound pressure or maximum Sound pressure, but, in this part of ISO 3743 the term defines the Sound pressure averaged on a mean-Square basis (Square root of the time average of the squared value) in time, and in space (i.e. over all microphone positions). 3.2 Sound pressure level, Lp: Ten times the logar- ithm to the base 10 of the ratro of the Square of the Sound pressure to the Square of the reference Sound pressure. Sound pressure Ievels are expressed in decibels. The reference Sound pressure is 20 PPa (2 x p10w5 Pa). The frequency weighting or the width of the fre- quency band used and the time weighting (S, F or 1, see IEC 651) shall be indicated. NOTE IO For example, the A-weighted level with time weighting S is hAs. Sound pressure 3.3 time-averaged Sound pressure level, Lpeq + Sound pressure level of a continuous steady Sound that, within a measurement time interval, T, has the same mean Square Sound pressure as a Sound under consideration which varies with time. Lpeq,*= 10 Ig [+[lO”.lLtifJ dt] dB =lOlg [+[$- di] dß . . . (1) Time-averaged Sound pressure Ievels are expressed in decibels and shall be measured with an instrument which camplies with the requirements of IEC 804. NOTES 11 Time-averaged Sound pressure levels are usually A- weighted and denoted by GAeq,T which is usually abbrevi- ated to LPA. 12 In general, the subscripts “eq” and “T” are omitted since time-averaged Sound pressure levels are necessarily determined over a certain measurement time interval. 3.4 Sound power, W: The rate per unit time at which Sound energy is radiated by a Source. lt is ex- pressed in Watts. 3.5 Sound power level, L,: Ten times the logarithm to the base IO of the ratio of the Sound power radi- ated by the Source under test to the reference Sound power. lt is expressed in decibels. The reference Sound power is 1 pW (IO-‘* W). The f requency weighting or the width of the fre- quency band used shall be indicated. NOTE 13 For example, the A-weighted Sound power level is &*. 3.6 reverberant Sound field: That Portion of the Sound field in the test room over which the contri- bution of the Sound received directly from the Source is negligible compared to the Sound reflected from the boundaries of the room and from objects within the room. 3.7 hard-walled test room: Room in which the acoustical reflectivity of all room surfaces (including floor and ceiling) is high over the frequency range of interest. 3.8 frequency range of interest: For general pur- poses, the frequency range of interest includes the octave bands with midband frequencies from 125 Hz to 8 000 Hz, i.e. from the lower tut-off of the 125 Hz band (90 Hz) to the upper tut-off of the 8 000 Hz band (11 200 Hz). NOTE 14 For special purposes, the frequency range of interest may be extended or reduced, but this places ad- ditional requirements on the characteristics of the test room which are not described in this part of ISO 3743. 3.9 reference Sound Source (RSS): Stable Sound Source emitting steady, broad-band noise with ad- equate Sound power over a wide frequency range, calibrated in accordance with ISO 6926. The Sound power levels of the reference Sound Source are known over the frequency range of interest. 3.10 reference box: Hypothetical surface which is the smallest rectangular parallelepiped that just en- closes the Source under test and terminates on the floor of the test room. SIST EN ISO 3743-1:1997
ISO 3743-1: 1994(E) NOTE 15 Small individual components of the Source which do not contribute to its Sound radiation may lie out- side the reference box. 3.11 comparison method: That method in which the Sound power level of a Source under test is de- termined by comparing the averaged value (on a mean-Square basis) of the Sound pressure levels produced by the Source in the test room to the aver- aged value of the Sound pressure levels produced in the Same room by a reference Sound Source of known Sound power output. The differente in Sound press- ure levels is equal to the differente in Sound power levels when conditions are the same for both sets of measurements. 3.12 direct method: That method in which the Sound power level of a Source under test is deter- mined from the averaged value (on a mean-Square basis) of the Sound pressure levels produced by the Source in the test room, the reverberation time, and the volume of the test room. 3.13 other background noise: Noise from all sources than the Source unde r test. NOTE 16 Background noise may include contributions from airborne Sound, structure-borne Vibration, and elec- trical noise in instrumentation. 3.14 background noise level: Sound pressure level measured in the test room when the Source under test is not operating. lt is expressed in decibels. 3.15 Sound absorption coefficient: In a specified frequency band, a measure of the absorptive property of a material or surface. Ideally, the Sound absorption coefficient is the fraction of the randomly incident Sound power absorbed or otherwise not reflected. 3.16 highly directional Sound Source: Sound Source with a maximum directivity index measured in accordance with ISO 3745 which exceeds 15 dB. 4 Requirements for hard-walled test room 4.1 Volume of test room The volume of the test room shall be at least 40 m3, and at least 40 times the volume of the reference box. In rooms with volumes between 40 m3 and 100 m3, the largest dimension of the Source shall not exceed 1,O m. In rooms with volumes greater than 100 m3, the largest dimension of the Source shall not exceed 2,0 m. 4.2 Acoustical properties of test room A hard-walled room shall be used. This means that the Sound absorption coefficient of any Portion of any boundary surface shall not exceed 0,20 at all fre- quencies within the frequency range of interest. Most ordinary, unfurnished rooms without special acous- tical treatment (e.g. acoustical ceilings and/or absorp- tive wall coverings) will comply with this requirement. Table2 may be used for guidance. Table 2 - Acceptable and unacceptable rooms Acceptable rooms Unacceptable rooms Nearly empty rooms with smooth hard Walls and ceiling made of concrete, brick, plaster or tile Rooms with upholstered furniture, machinery or in- dustrial rooms with a small amount of Sound absorptive material on ceiling or Walls (for exam- ple, partially absorptive ceiling) Partly empty rooms, rooms Rooms with some Sound with smooth hard Walls absorptive materials on both ceiling and Walls Rooms without Rooms with large upholstered furniture, rec- amounts of Sound absorp- tangular machinery rooms tive materials on either or industrial rooms, no ceiling or Walls Sound absorptive materials on surfaces Irregularly shaped rooms without upholstered furni- ture, irregularly shaped ma- chinery rooms or industrial rooms, no Sound absorp- tive materials on surfaces 4.3 Test of room suitability The suitability of a test room may differ from one Source to another. The requirements for the room are most critical when a highly directional Source is to be evaluated. When testing the general suitability of a test room, the following procedure shall be followed. A highly directional, broad-band Sound Source is lo- cated in the test room as given in 7.2. Microphone positions are Chosen according to 7.4 and the average (energy basis) octave-band Sound pressure level, LP,, is determined (see LP ST) in clause 8). The Sound Source is then turned 4 5 O to 135” in compliance with the requirement of 7.5 and the corresponding octave-band Sound pressure level, LP2, is determined. This procedure is repeated twice more to determine LP3 and Lp4. The fourth Position shall be within 45” to 90” of the first Position. If the maximum differente between the octave-band Sound pressure levels of any two Source positions for the frequency bands with midband frequencies between 125 Hz and 8 000 Hz does not exceed the Standard deviations of 4 SIST EN ISO 3743-1:1997
ISO 3743=1:1994(E) table 1, the test room is considered to fulfil the re- quirements of this patt of ISO 3743. NOTE 17 As an alternative to the highly directional Sound Source, a Sound Source of the same type as the Source un- der test may be used. However, if the alternative procedure is used, the qualification is valid for this type of Source only. 4.4 Criterion for background noise At each microphone Position, the octave-band Sound pressure levels due to background noise shall be at least 6 dB and preferably more than 15 dß below the octave-band Sound pressure Ievels measured with both the reference Sound Source and the Source un- der test in Operation. 4.5 Temperature and humidity For measurements according to this part of ISO 3743, the temperature and the relative humidity of the test room shall be controlled during the acoustical measurements and maintained at as nearly constant values as practicable. These values shall be reported in the test report. 5 Instrumentation 51 . Instrumentation System The instrumentation System, including the micro- phone and cable, shall meet the requirements for a type 1 instrument specified in IEC 804. For measurements in octave bands, the instrumen- tatio n System shall me et the requirements of IEC 225. 5.2 Calibration During each series of measurements, a Sound calibrator with an accuracy of + 0,3 dB (class 1 as specified in IEC 942) shall be applied to the micro- phone to verify the calibration of the entire measuring System at one or more frequencies over the fre- quency range of interest. The compliance of the calibrator shall be verified with the requirements of IEC 942 once a year and the compliance of the instrumentation System with the requirements of IEC 804 shall be verified at least ev- ery 2 years in a laboratory making calibrations traceable to appropriate Standards. The date of the last verif icatio n of compl relevant I EC stan dards shall be reco rded. iance with 6 Installation and Operation of Source under test 6.1 General The manner in which the Source under test is installed and operated may have a significant influence on the Sound power emitted by the Source. This clause specifies conditions that minimize variations in the Sound power output due to the installation and oper- ating conditions of the Source under test. The in- structions of a noise test Code, if any exists, shall be followed in so far as installation and Operation of the Source under test are concerned. 6.2 Source location Install the Source in the test room in one or more lo- cations as if it were being installed for normal usage. If no such location(s) tan be defined, place the Source on the floor of the test room. Additional requirements for Source location are given in 7.2. The location(s) of the Source in the test room shall be described in the test report. 6.3 Source mounting In many cases, the Sound power emitted will depend upon the support or mounti
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