SIST EN 21680-1:1997
(Main)Acoustics - Test code for the measurement of airborne noise emitted by rotating electrical machinery - Part 1: Engineering methods for free-field conditions over a reflecting plane (ISO 1680-1:1986)
Acoustics - Test code for the measurement of airborne noise emitted by rotating electrical machinery - Part 1: Engineering methods for free-field conditions over a reflecting plane (ISO 1680-1:1986)
Specification of an engineering method (grade 2) for measuring the sound pressure levels on a rectangular parallelepiped surface enveloping the machine and for calculating the sound power level produced by the machines. It outlines the procedures which may be used to evaluate the test environment and specifies the characteristics of suitable measuring instruments.
Akustik - Verfahren zur Messung der Geräuschemission von rotierenden elektrischen Maschinen - Teil 1: Verfahren der Genauigkeitsklasse 2 für Freifeldbedingungen über einer reflektierenden Ebene (ISO 1680-1:1986)
Acoustique - Code d'essai pour le mesurage du bruit aérien émis par les machines électriques tournantes - Partie 1: Méthode d'expertise pour les conditions de champ libre au-dessus d'un plan réfléchissant (ISO 1680-1:1986)
Akustika - Preskusni postopek za meritev hrupa v zraku, ki ga sevajo električni vrtilni stroji - 1. del: Inženirska metoda v prostem zvočnem polju nad odbojno ravnino (ISO 1680-1:1986)
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Verfahren zur Messung der Geräuschemission von rotierenden elektrischen Maschinen - Teil 1: Verfahren der Genauigkeitsklasse 2 für Freifeldbedingungen über einer reflektierenden Ebene (ISO 1680-1:1986)Acoustique - Code d'essai pour le mesurage du bruit aérien émis par les machines électriques tournantes - Partie 1: Méthode d'expertise pour les conditions de champ libre au-dessus d'un plan réfléchissant (ISO 1680-1:1986)Acoustics - Test code for the measurement of airborne noise emitted by rotating electrical machinery - Part 1: Engineering methods for free-field conditions over a reflecting plane (ISO 1680-1:1986)29.160.01Rotacijski stroji na splošnoRotating machinery in general17.140.20Emisija hrupa naprav in opremeNoise emitted by machines and equipmentICS:Ta slovenski standard je istoveten z:EN 21680-1:1991SIST EN 21680-1:1997en01-april-1997SIST EN 21680-1:1997SLOVENSKI
STANDARD
SIST EN 21680-1:1997
SIST EN 21680-1:1997
SIST EN 21680-1:1997
International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.MEX~YHAPO~HAR OPTAHM3ALWlR fl0 CTAH~APTM3A~MM.ORGANISATION INTERNATIONALE DE NORMALISATION Acoustics - Test code for the measurement of airborne noise emitted by rotating electrical machinery - Part 1: Engineering method for free-field conditions over a reflecting plane Acoustique - Code d’essai pour Ie mesurage du bruit akrien emis par les machines Hectriques tournantes - Partie 1: IWthode d’expertise pour les conditions de champ libre au-dessus d’un plan r6flkhissant First edition - 198646-15 UDC 534.6 : 621.313 Ref. No. ISO 1680/1-1986 (E) Descriptors : acoustics, rotating electric machines, tests, acoustic*tests, determination, airborne Sound, Sound pressure, Sound power. s: Price based on 15 pages SIST EN 21680-1:1997
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, govern- mental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 1680/1 was prepared by Technical Committee ISO/TC 43, Acoustics. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. lt cancels and replaces ISO Recommendation R 1680-1970 of which it constitutes a technical revision. 0 International Organkation for Standardkation, 1986 Printed in Switzerland SIST EN 21680-1:1997
INTERNATIONAL STANDARD ISO 1680/1-1986 (E) Acoustics - Test code for the measurement of airborne noise emitted by rotating electrical machinery - Part 1 : Engineering method for free-field conditions over a reflecting plane 0 lntroduction This part of ISO 1680 is based on ISO 3744 and has been drafted in accordance with ISO 3746. The main purpose of this part of ISO 1680 is to specify a clearly defined measurement method for rotating electrical machines operating under steady-state conditions, the results of which tan be expressed in Sound power levels so that all machines tested using this code tan be directly compared. Other methods, such as the precision methods sf ISO 3741,3742 and 3745, may also be used for determining Sound power levels if the installation and operating conditions of this part of ISO 1680 are used. 1 Scope and field sf application 1.1 General This part of ISO 1680 specifies, in accordance with ISO 2264, an engineering method (grade 2) for measuring the Sound pressure levels on a rectangular parallelepiped surface envelop- ing the machine and for calculating the Sound power level pro- duced by the machine. lt outlines the procedures which may be used to evaluate the test environment and specifies the charac- teristics of suitable measuring instruments. A method is given for determining the A-weighted Sound power level and, if re- quired, octave or one-third octave band Sound power levels of the machine from the mean of the Sound pressure levels. measured on the rectanguiar parallelepiped surface. This part of ISO 1680 applies to the measurement of airborne noise from rotating electrical machines, such as motors and generators (d.c. and a.c. machines) without any limitation on the output or voltage, when fitted with their normal auxiliaries. lt applies to rotating electrical machines with any linear dimen- sion (length, width or height) not exceeding 15 m. This part of ISO 1680 applies to measurements carried out in environmental conditions that meet the criteria given in clause 4 and annex A (environmental correction K < 2 dB, correction for background noise < 1 dß). If these criteria are not met, Standard deviations of the test results may be greater than those given in table 1, i.e. the engineering grade of accuracy may not be achieved. The method given in ISO 1680/2 shall. then be used, which will result in A-weighted Sound power levels of lower accuracy. In this case, no reference shall be made to this patt of ISO 1680. 1.2 Measurement uncertainty Measurements carried out in conformity with this part of ISO 1660 usually result in Standard deviations which are equal to or less than those given in table 1. The Standard deviations given in table 1 reflect the cumulative effects of all Causes of measurement uncertainty, excluding variations in the Sound power level of the machine from test to test. For a machine which emits noise with a relatively “flat” spectrum in the 100 to 10 000 Hz frequency range, the A-weighted Sound power level is determined with a Standard deviation of approximately 2 dB. For outdoor measurements, the Standard deviation in the oc- tave band centred on 63 Hz will be approximately 5 dB. NOTE - The Standard deviations in table 1 include the effects of allowable variations in the positioning of the measurement positions and in the selection of the stipulated measurement surface. Table 1 - Uneertainty in determining Sound power levels for engineering measurements indoors or outdoors Octave band centre frequencies Hz 125 250 to 500 1 000 to 4 000 8000 One-third octave band centre f requencies Hz Standard deviation of mean value dB 100 to 160 200 to 630 800 to 5 000 6300to 10000 3,O 2s) L5 2,5 2 References ISO 266, Acoustics - Preferred frequencies for measure- men ts. ISO 354, Acoustics - Measurement of Sound absorption in a reverberation room, ISO 1680/2, Acoustics - Test Code for the measurement of airborne noise emitted by rotating electrical machinery - Part 2: Survey method. 1 SIST EN 21680-1:1997
ISO 1680/1-1986 EI ISO 2204, Acoustics - Guide to International Standards on the measurement of airborne acoustical noise and evaluation of its effects on human beings. ISO 3746, Acoustics - Determination of Sound power levels of noise sources - Guidelines for the use of basic Standards and for the preparation of noise test Codes. ISO 3741, Acoustics - Determination of Sound power levels of noise sources - Precision methods for broad-band sources in reverbera tion rooms. ISO 3742, Acoustics - Determination of soundpower levels of noise sources - Precision methods for discrete- frequency and narrow-band sources in reverberation rooms. ISO 3744, Acoustics - Determination of Sound power levels of noise sources - Engineering methods for free- field conditions over a reflecting plane. ISO 3745, Acoustics - Determination of Sound power levels of noise sources - Precision methods for anechoic and semi- anechoic rooms. ISO 6926, Acoustics - Determination of Sound power levels of noise sources - Charac teriza tion and calibra tion o f re ference Sound sources. l) IEC Publication 34-1, Rotating electrical machines - Part 1: Rating and Performance. IEC Publication 225, Octave, half-octave and third-octave band filters intended for the analysis of Sounds and vibrations. IEC Publication 651, Sound level meters. 3 Definitions For the purposes of this patt of ISO 1680, the following defini- tions apply. 3.1 free field: A Sound field in a homogeneous, isotropic medium free of boundaries. In practice, it is a field in which the effects of the boundaries are negligible over the frequency range of interest. 3.2 free field over a reflecting plane: A Sound field in the presence of a reflecting plane on which the Source is located. 3.3 anechoic room : A test room the surfaces of which ab- sorb essentially all the incident Sound energy over the fre- quency range of interest, thereby affording free-field conditions over the measurement surface. 3.4 semi-anechoic room: A test room with a hard reflect- ing floor the other surfaces of which absorb essentially all the incident Sound energy over the frequency range of interest, thereby affording free-field conditions above a reflecting plane. 3.5 Sound pressure level, L,, in decibels : Twenty times the logarithm to the base 10 of the ratio of the Sound pressure 1) At present at the Stage of draft. 2 to the reference Sound pressure. The weighting network or the width sf the frequency band and its centre frequency used shall be indicated: for example, A-weighted Sound pressure Level, L pB, octave band Sound pressure level, one-third octave band Sound pressure level, etc. The reference Sound pressure is 20 ppa. 3.6 surface Sound pressure : The Sound pressure averaged in time on a mean-Square basis and also averaged over the measurement surface using the averaging procedures specified in 8.1 and corrected for the effects of background noise and the influence of reflected Sound at the measurement surface. 3.7 surface Sound pressure level, LTf, in decibels: Ten times the logarithm to the base 10 of the ratio of the Square of the surface Sound pressure to the Square of the reference Sound pressure. 3.8 Sound power level, Lw, in decibels : Ten times the logarithm to the base 10 of the ratio of a given Sound power to the reference Sound power. The weighting network or the width of the frequency band used shall be indicated: for example, A-weighted Sound power level, LWA, octave band Sound power level, one-third octave band Sound power level, etc. The reference Sound power is 1 pW ( = ‘10-12 W). NOTE - The surface Sound pressure level is numerically different from the Sound power level and its use in lieu of the Sound power level is not correct because the size of the measurement surface is not covered by this quantity. 3.9 frequency range of interest : For general purposes, the frequency range of interest includes the octave bands with centre frequencies between 125 and 8 000 Hz or the one-third octave bands with centre frequencies between 100 and 10 000 Hz. Any band may be excluded in which the level is more than 40 d5 below the highest band pressure level. For special purposes, the frequency range of interest may be ex- tended at either end, provided that the test environment and in- strument accuracy are satisfactory for use over the extended frequency range. For sources which radiate predominantly high (or low) frequency Sound, the frequency range of interest may be limited in Order to optimize the test facility and procedures. 3.10 measurement surface : A hypothetical surface of area S enveloping the Source on which the measurement posi- tions are located and which terminates on the reflecting plane. 3.11 reference box: A hypothetical surface which is the smallest rectangular parallelepiped that just encloses the Source and terminates on the reflecting plane. 3.12 measurement distance : The minimum the reference box to the measurement surface. distance from 3.13 background noise: The Sound pressure level at each microphone Position with the Source inoperative. SIST EN 21680-1:1997
4 Acoustic environment ISO mO/l-1986 0 Instrumentation 4.1 General 5.1 General The test environments that are suitable for measurements in ac- cordante with this part of ISO 1680 include the following: a) a plane room which provides a free field over a reflecting The instrumentation shall be designed to measure the mean- Square value of the A-weighted Sound pressure level and the octave or over the one-third octa measurement ve band surface. levels, averaged over time and Surface averaging is usually b) a flat outdoor area that meets the requirements of 4.2 and annex A; c) a room in which the contributions of the reverberant field to the Sound pressures on the measurement surface are small compared with those sf the direct field of the Source. carried out by measuring the time-averaged Sound pressure levels with a prescribed time constant for a fixed number of microphone positions (7.2) and computing the average value in accordance with 8.2. The instrumentation used tan perform the required time- averaging in one of two different ways : Conditions described under c) above are met in very large rooms as well as in smaller rooms with sufficient sound- absorptive materials on their Walls and ceilings. a) By continuous averaging of the squared Signal using RC-smoothing with a time constant TA. Such continuous averaging provides only an approximation of the true time- 4.2 Criteria for adequacy sf the test environment average, and it places restrictions on the “settling” and Observation times (see 7.3.3). Annex A describes a procedure for determining whether or not a test environment is adequate for measurements in accor- dance with this part of ISO 1680. Test environments which are suitable for engineering measurements permit the Sound power level to be determined with an uncertainty that does not exceed the values given in table 1. Ideally, the test environments are free from reflecting objects other than a reflecting plane so that the Source radiates into a free field over a reflecting plane. Annex A describes procedures for determining the magnitude of the environmental correction (if any) to account for departures of the test environment from NOTE - An example of an instrument using such averaging is a Sound level meter fulfilling at least the requirements for a type 1 in- strument in accordance with IEC Publication 651 with the time weighting “S”. b) By integrating the squared Signal over a fixed time- interval rD. This integration may be performed by either digital or analogue means. Examples of suitable instrumentation Systems are given in ISO 3744. the ideal condition. To comply with this part of ISO 1680, the environmental correc- tion K shall not exceed 2 dB. If it is necessary to make measurements in spaces which do not meet the criteria of annex A, Standard deviations of the test results may be greater than those given in table 1. In those cases, ISO 1680/2 shall be used. (See clause 0.) 5.2 The microphone and its associated cable A condenser microphone, or the equivalent in accuracy, sta- bility and frequency response, shall be used. The microphone shall have a flat frequency response, over the frequency range of interest, for the angle of incidence specified by the manu- facturer. 4.3 Criterion for background noise At each microphone Position, the Sound pressure level of the background noise shall be at least 6 dB, and preferably more than 10 dB, below the Sound pressure level to be measured in each frequency band within the frequency range of interest. NOTE - This requirement is met by a microphone of a standardized Sound level meter fulfilling at least the requirements for a type 1 instru- ment in accordance with IEC Publication 651 and calibrated for free- field measurements. Background noise less than 6 dB below the Sound pressure levels to be measured is too high for the purposes of this part of ISO 1680. Under such circumstances, the Survey method of ISO 1680/2 shall be used. (See clause 0.) The microphone and its associated cable shall be Chosen so cables or sliding contacts) that could interfere with the that their sensitivity does not Change over the temperature measurements. range encountered in the measurement. If the microphone is moved, care shall be exercised to avoid noise of acoustical origin (for example, noise from wind, gears, mechanical mov- ing Parts) or electrical noise (for example, noise from flexing 4.4 Wind The wind velocity existing at the test site or caused by the machine under test shall be less than 6 m/s. A Windscreen should be used for wind velocities above 1 m/s to ensure that the level of the background noise (caused by the cumulative ef- fett of the wind and other background noise sources) is at least 6 dB, and preferably more than 10 dB, below the level with the Source operating. The appropriate instructions provided by the microphone manufacturer shall be followed. 5.3 Frequency response of the instrumentation System The frequency response of the instrumentation System for the angle of incidence specified by the manufacturer shall be flat over the frequency range of interest within the tolerantes given for a type 1 instrument in IEC Publication 651. 3 SIST EN 21680-1:1997
ISO 1680/1-1986 (El 5.4 Weighting network and frequency analyser An A-weighting network complying with the tolerante require- ments of IEC Publication 651 and, if required, an octave band or one-third octave band filter set fulfilling the requirements of IEC Publication 225 shall be used. The centre frequencies of the frequency bands shall correspond to those of ISO 266. 5.5 Calibration Before and after each series of measurements, an acoustical calibrator with an accuracy + 0,5 dB shall be applied to the microphone to check the calibration of the entire measuring System at one or more frequencies over the frequency range of interest. The calibrator shall be checked annually to verify that its acoustical output has not changed. In addition, an acoustical and an electrical calibration of the instrumentation System over the entire frequency range of interest shall be carried out at intervals of not more than 2 years. 6 Installation and Operation of the machine 6.1 Machine mounting If practicable, the machine should be mounted in the same way as it would be for normal usage. Care should be taken to minimize the transmission and the radiation of structure-borne noise from all mounting elements including the foundation. Usually, this minimizing tan be achieved by resilient mounting for smaller machines. Larger machines tan usually only be tested under rigid mounting conditions. 6.1 .l Resilient mounting The natura1 frequency of the support System and the machine under test shall be lower than a quarter of the frequency cor- responding to the lowest rotational Speed of the machine. The effective mass of the resilient support shall not be greater than l/lO of that of the machine under test. 6.1.2 Rigid mounting The machines shall be rigidly mounted to a surface with dimen- sions adequate for the machine type (for example by foot or flange fixed in accordance with the manufacturer’s specifica- tions). The machine shall not be subject to additional mounting Stresses from incorrect shimming. The mass of the support shall be at least twice that of the machine under test. 6.2 Operation of machine during test The machine shall operate at no load, at rated voltage(s) and Speed(s), and with the corresponding excitation(s) (sec IEC Pu blication 34-1). For a.c. machines, the sinusoidality of the supply voltage and the degree of Unbalance of the supply voltage System shall comply with the same limits that are specified in IEC Publica- tion 34-1. Synchronous machines shall be run with the excitation current which permits the rated volltage at no load. For machines not suitable for no-load Operation, e.g. machines with the behaviour sf series-wound motors, the operating con- ditions shall be agreed upon and stated in the test report. A method for estimating the differente in the level of the noise from a machine between no-load operating conditions and rated load or any other specified load is given in annex C. 6.3 Auxiliary equipment and coupled machines All auxiliary equipment (Ioading machines, gears, transformers, external cooling Systems) and coupled machines which are necessary for the Operation of the machine under test, but which do not form an integral part of the machine, shall not significantly affect the noise measurement (see 8.1). If they do, they should be shielded acoustically or located outside the test environment. 7 Sound pressure levels on the measurement surface 7.1 Reference box and measurement surfaces In Order to facilitate the positioning of the microphone posi- tions, a hypothetical reference box is defined (see 3.11). When defining the dimensions of this reference box, elements pro- truding from the machine which are unlikely to be major radiators of Sound energy may be disregarded. The microphone positions lie on the measurement surface (sec 3.10). For rotating electrical machines, regardless of their size, the measurement surface shape is a rectangular parallelepiped (sec figures 2 to 4) the sides of which are parallel to the sides of the reference box and spaced out at a distance d (measurement distance) from the reference box. The measurement distance, d, shalll be at least 0,25 m. Distances larger than 1 m may be excluded by the environ- mental requirements given in this part of ISO 1680 (see 4.2,4.3 and annex A). The preferred measurement distance is 1 m. The area S of the measurement surface is given by the equation s = 4 (ab + bc + ca) where, in accordance with figures 2, 3 or 4, a = 0,5 1, + d; b = 0,5 Z2 + d; c = l3 + d; IJ, 12 and Zs are the dimensions of the reference box; d is the measurement distance, normally 1 m. 4 SIST EN 21680-1:1997
ISO 1680/1-1986 (El 7.2 Microphone array 7.2.1 Complete measurement Position array From figure 1, the principle of how to construct the measure- ment array for different sizes of reference box tan be derived. example, due to strong electric or magnetic fields, wind, im- pingement of air discharged from the machine under test, high or low temperatures) shall be minimized by proper selection or positioning of the microphone. The microphone shall always be directed in such a way that the angle of incidence of the Sound waves is that for which the microphone is calibrated. Esch side of the measurement surface shall be treated separ- ately. If the length or width of the side of the measurement sur- face under consideration exceeds 3d, this side is divided into a minimum number of partial areas so that their lengths and widths do not exceed 3d (see figure 1). The observer shall not stand between the microphone and the Source under test. The measurements shall be carried out once the machine under test is operating under steady-state conditions. To comply with the engineering method of this part of The Sound pressure level shall be observed over a typical period ISO 1680, measurement positions shall be placed at the middle of Operation of the Source. Readings of the Sound pressure and the corners of each partial area, except at those corners level (corresponding to the level of the mean-Square Sound which lie in the reflecting plane. The corner positions of a pressure) shall be taken at each measurement Point with partial area are identical with the corner positions of the A-weighting and, if required, for each frequency band within neighbouring partial areas. 1) the frequency range of interest. The resulting complete measurement array is shown in figures 2 to 4 for different sizes of the reference box. The following data shall be obtained: Neighbouring measurement positions may be connected to achieve continuous paths along which the microphone is car- ried continuously with constant velocity (see figures 2 to 4). a) the A-weighted Sound pressure levels and, if required, the band pressure levels during Operation of the machine under test ; NOTE - For the Survey method complying with ISO 1680/2, only the positions in the middle sf the partial areas (or the relevant paths through these positions) are used. b) the A-weighted Sound pressure levels and, if required, the band pressure levels produced by the background noise. 7.2.2 Simplified measurement Position array For the frequency bands centred on or below 160 Hz, the Observation period shall be at least 30 s. For A-weighted Sound pressure levels and for the frequency bands centred on or above 200 Hz, the Observation period shall be at least 10 s. The arrangement of the measurement positions given in figures 1 to 4 may, especially for Iarge machines, be simplified, if, for that type of machine, it tan be shown, with the help of preliminary investigations on some machines of that type, that the Sound field is adequately uniform and that measurements lead to values of Sound power level deviating by no more than 1 dB from those determined with a complete arrangement of measurement positions. 7.3.2 Measurements with a Sound level meter For sources that produce a symmetrical radiation Pattern, it may be sufficient to distribute the measurement positions over only a Portion of the measurement surface. This is acceptable if, for that type of machine, it tan be shown, with the help of preliminary investigations on some machines of that type, that the measurements lead to values of Sound power level deviating by no more than 1 dB from those determined with a complete arrangement of measurement positions. If the indicating meter of a Sound level meter is used, the time weig hting “S” shall be used. If the fluctuations of the in- dicating pointer on the Sound level meter are less than +3 dB using the time weighting “S”, the noise is considered to be steady for the purposes of this patt of ISO 1680 and the level is taken to be the average of the maximum and minimum levels during the period of Observation. If the meter fluctuations dur- ing the period of Observation are greater than +3 dB, the noise is considered to be non-steady and one of the instrumentation Systems described in ISO 3744 shall be used. 7.3.3 Measurements with RC-smoothing or integration Systems 7.3 Conditions of measurement 7.3.1 General If RC-smoothing is used, the time-constant ?A should be lang enough to obtain an estimate of the r.m.s. level during the period of Observation with an accuracy of +0,5 dB. Environmental conditions may have an adverse effect on the microphone used for the measurements. Such conditions (for 16 true integration is used, it is necessary for the integration time to be equal to the period of Observation. 1) The array is in complete accordance with ISO 3744 for small machines (sec figure 3) and, in principle, in accordance with ISO 3744 for large machines, taking into account the Sound field structure of rotating electrical machinery. 5 SIST EN 21680-1:1997
SIST EN 21680-1:1997
SIST EN 21680-1:1997
ISO 1680/1-1986 EI 8 Calculation of surface Sound pressure level and Sound power level 8.1 Corrections for background noise The measured Sound pressure levels shall be corrected for background noise in accordance with table 2. For the purposes of this part of ISO 1680, the maximum accep- table range of the environmental correction, K, is -2 dB to +2 dB. NOTE - The environmental correction, K, accounts for the influence of a non-ideal environment (for example, the presence of reflected Sound). lt ranges typically from -2 dB (for measurements outdoors with absorbing ground) to + 10 dB (for measurements indoors in highly reverberant rooms). The procedures given in annex A at-e used to calculate the value of the environmental correction. Table 2 - Corrections for backgroun pressure levels d Sound 84 . Calculation of Sound power lewel Differente A between Corrections to be Sound pressure level subtracted from Sound measured with machine pressure level measured operating and background with machine operating to Sound pressure obtain Sound pressure level alone level due to machine alone dB dB <6 Measurements invalid 6 1,o 7 Ir0 8 LO 9 0,5 10 0,5 > 10 0 The Sound power level characterizing the noise emitted Source shall be calculated from the following equation : by the (3) Lw is the A-weighted or band Sound power level of the Source, in decibels; reference : 1 pW; L,, is the surface Sound pressure level determined in accordance with 8.3, in decibels ; reference : 20 PPa ; S is the area of the measurement surface, in Square metres (see 7.1); 2 So = 1 m . 8.2 Calculation of Sound pressure level averaged over the measurement surface For the A-weighted Sound pressure level and the level in each frequency band of interest, an average Sound pressure level over the measurement surface, Lp, is calculated from the relevant measured Sound pressure levels L,i (after corrections for background noise are applied in accordance with 8.1) by using the following equation : If only band Sound power levels are determined, the A-weighted Sound power level may be determined in accor- dance with annex B. L, = 10 Ig m 1 N F = 1 l()OJ Lpi m i=l 9 Information to be recorded . . . (1) The following information shall be compiled and recorded for all measurements carried out in accordance with the re- quirements of this part of ISO 1680. where Lp is the Sound pressure level averaged over the measurement surface, in decibels; reference : 20 FPa ; 91 . Machine under test a) Description dimensions). of the machine under test (including its L . is ttii ifh the A-weighted or band pressure level resulting from measurement, in decibels ; reference : 20 PPa; IV is the total numb
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