Checking Of Sound Emission Values - DataKustik GmbH

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Schriftenreihe der Bundesanstalt für Arbeitsschutz- Forschung Fb 851Wolfgang ProbstChecking of Sound Emission ValuesBy the author with the permission of theFederal Institute for Occupational Safety and Healthprovided copy of the out-of-print original reportDipl.-Phys. Dr. Wolfgang ProbstDataKustik GmbHDornierstr. 482205 ik.com

Verfasser:Dr. Wolfgang ProbstVerlag/Druck:Wirtschaftsverlag NWVerlag für neue Wissenschaft GmbHBürgermeister-Smidt-Str. 74 - 76, D-27568 BremerhavenPostfach 10 11 10, D-27511 BremerhavenTelefon: (0471) 945 44 - 0Telefax: (0471) 9 45 44 77Herausgeber:Bundesanstalt für Arbeitsschutz und ArbeitsmedizinHauptsitz Dortmund:Friedrich-Henkel-Weg 1 - 25, D-44149 DortmundPostfach 17 02 02, D-44061 DortmundTelefon: (0231) 90 71 - 0Fax: (0231) 90 71 - 454Sitz Berlin:Fachbereich ArbeitsmedizinNölnerstr. 40 - 42, D-10317 BerlinPostfach 5, D-10266 BerlinTelefon: (030) 51 54 8 - 0Fax: (030) 51 54 81 70Alle Rechte einschließlich der fotomechanischen Wiedergabeund des auszugsweisen Nachdrucks vorbehalten. Aus Gründendes Umweltschutzes wurde diese Schrift auf chlorfreigebleichtem Papier gedruckt.

IndexAbstract . 6Kurzreferat . 7Résumé. 81Introduction . 92Sound power level LWA and emission sound pressure level LpA . 112.1 What does the sound power level state - definition and application . 112.2 What does the emission sound pressure level state Defintion and application . 142.3 How does the noise immission at working places result fromthe noise emission values LWA and LpA . 153Standards for measurement of noise emission values . 173.1 Standards for the measurement of the sound power level . 173.2 Standards for the measurement of the emission sound pressure level . 203.3 Remarks for a proper choice of the measuring method . 224Approximate methods for the measurement of emission values . 234.1 Measurement on partial surfaces with different density of measuring points . 234.2 Use of symmetry relations . 244.2.1 Determination of the environmental correction K2 with the reference soundsource on a smaller measuring surface . 244.2.2 Measurement on partial measuring surfaces . 254.2.3 Measurement on short distance surfaces . 264.2.4 Measurement in openings . 265Systematical deviations dependent on the measurement method and theircorrection. 275.1 The true value of the sound power level . 275.2 The angle error when measuring the sound power level according to the soundpressure envelopping surface method . 295.2.1 The reason of an angle error . 29

5.2.2 The smallest possible angle error in a box shaped measuring surface . 305.2.3 The angle error with reference sound source or machine usinga box-shaped measuring surface . 335.3 The total correction of the angle error and the influence of the environment . 395.4 Summary - proposal for a standardized total correction . 416Examinations regarding the accuracy of the standard series ISO 11200for the determination of the emission sound pressure level . 436.1 Scope . 436.2 Description of the procedure . 446.3 The vehicle as model machine . 456.3.1 The measurement setup . 456.3.2 The emission measured with free field conditions as reference . 486.4 The measurements in halls . 506.4.1 The acoustical properties of the halls . 506.5 Measurements with the Model-machine and Determination ofthe Sound Power Level . 536.6 Examination of errors when using K3-corrections according toISO 11200 series . 546.6.1 Statistical Approach . 546.6.2 The correction according to the ISO 11200 series. . 556.7 Summary - results of the analysis . 586.8 Measurement of the sound intensity level in three axes (ISO 11205 - 1997) . 617Examination regarding the accuracy of the standard draftISO 3747 for the determination of the sound power level. . 697.1 Scope . 697.2 Description of the procedure . 707.3 The vehicle as model machine . 717.3.1 The measurement setup . 717.3.2 The emission measured with free field conditions as reference . 717.4 The measurements in halls . 737.4.1 The acoustical properties of the halls . 737.4.2 Measurements with the model machine and determination ofthe sound power level . 767.5 Evaluation and results . 79

7.5.1 The method of evaluation . 797.5.2 Results of the examination - evaluation for single points . 837.5.3 Results of the evaluation for domains . 907.5.4 Results of the evaluation with the statistical method . 927.5.5 Results of the examination - number of RSS positions . 937.5.6 Results of the examination - rotating microphone . 947.6 The use of indicators . 957.7 Summary - recommendations for the use of ISO 3747 . 967.8 Proposal for an improvement of ISO 3747 The selection of RSS and microphone positions . 987.8.1 Determination of the minimum distance with DLf 7 dB. 987.8.2 Determination of main radiating areas and their extension . 987.8.3 Determination of RSS positions . 997.8.4 Determination of microphone positions. 1008 Literature . 101

6Checking of Sound Emission ValuesAbstractWith the machine directive the supplier must give appropriate information about thenoise emission of his products. The main topics of the standards are explained.Often it is not possible to use these standards in a strong sense and approximativemethods have to be applied. Especially the measurement with very little microphonedistance or even the measurement directly in radiating openings have proved to beeffective, because environmental influences and noise impact from other machines isminimized in this case.A consequence of the measurement with the soundpressure envelopping surfacemethod is the angle error, that is determined with simulating calculations andpresented as a function of the geometric parameters.With an examination of the ISO 11200 series the accurracy of these standards wasdetermined by using a van with calibrated broad band source as model machine.From the sound pressure levels measured at 94 points on an envelopping surface infreefield and in several industrial halls the emission soundpressure level and theresulting deviations are determined when using one of these standards. Thosedeviations are lowest when using ISO 11204 and ISO 11205.A similar examination with ISO 3747 when measuring sound power levels shows,that the positioning the microphones in regions with DLf 7 dB is sufficient and thatthe use of further indicators don’t give better results. A procedure for the positioningof reference sound source and microphones is proposed.Key words:Sound power level, emission sound pressure level, angle error, ISO 11200 serie, ISO3747.

7Überprüfung von GeräuschemissionswertenKurzreferatDie Maschinenrichtlinie verlangt vom Hersteller, daß er die Geräuschkennwerte seiner Produkte als Information für den Anwender zur Verfügung stellt. Die dabeianzuwendenden Normen werden kurz erläutert.Oft ist es nicht möglich, die genormten Verfahren streng anzuwenden, und esmüssen Näherungsverfahren zugrundegelegt werden. Insbesondere die Messung insehr kleinen Abständen und in den tatsächlich abstrahlenden Öffnungsflächen hatsich als sehr effektiv erwiesen, weil auf diese Weise der Raumeinfluß und auch derFremdlärm von anderen, nicht abschaltbaren Maschinen minimiert wird.Aufgrund des Winkelfehlers beim Schalldruck-Hüllflächenverfahren ergeben sichsystematische Abweichungen, die mit Simulationsberechnungen in Abhängigkeit vonden geometrischen Parametern ermittelt und dargestellt werden.Mit einem Kraftfahrzeug als Modellmaschine wird die Genauigkeit der Normen derReihe ISO 11200 untersucht. Im Freifeld und in mehreren Industriehallen wurde derSchalldruckpegel auf 94 Punkten einer Quadermeßfläche ermittelt. Mit den Normender ISO 11200 Reihe wird für jeden dieser Punkte der Emissions-Schalldruckpegelund dessen Abweichung vom wahren Wert bestimmt. Dabei zeigt sich, daß mit ISO11205 bei Anwendung der 3-Achs-Intensitätsmessung und mit ISO 11204 diegenauesten Ergebnisse erzielbar sind.Eine ähnliche Untersuchung mit Anwendung der ISO 3747 zeigt, daß das Kriteriumeines Meßpunktabstands mit einer Pegelüberhöhung DLf von 7 dB ausreichend istund daß die Einbeziehung von anderen vorgeschlagenen Schallfeldindikatoren keineVerbesserung bringt. Ein Konzept zur Anordnung von Vergleichsschallquellen- undMikrophonpositionen wird vorgeschlagen.Schlagwörter:Schalleistungspegel, Emissions-Schalldruckpegel, Winkelfehler, ISO 11200 - Reihe,ISO 3747.

8Contrôle des valeurs d’émission sonoreRésuméLa directive sur les machines exige du fabricant qu'il informe l'utilisateur descaractéristiques sonores de ses produits. Les normes applicée pour ce cas sontexpliquées succinctement.Souvent, il n'est pas possible d'appliquer strictement les procédés décrits dans lanorme. Dans ces cas, il peut s'avérer opportun de se baser sur des procédésd'approximation. En particulier, le mesurage à de très petites distances et dans lessurfaces réellement réfléchissantes s'est révélé très efficace parce que de cettemanière l'influence environnementale ainsi que le bruit étranger d'autres machinesne pouvant pas être arrêtées ne jouent plus aucun rôle.Un problème dans la palette de différents procédés normalisés offerte pour lemesurage du niveau de puissance sonore consiste dans le fait que ceux-ci offrent enpartie des résultats systématiquement différents. En résultat de cette partie del'étude, un concept est présenté qui permet d'intégrer toutes les normes concernantla détermination de la puissance sonore dans un système global sans déviationssystématiques.La précision des normes de la série ISO 11200 est étudiée avec un véhicule servantde machine-modèle. Le véhicule est doté d'une source de bruit et en ouvrant oufermant une fenêtre, les deux conditions, rayonnement directionnel ouomnidirectionnel, peuvent être simulées. En plein air, le niveau de pression sonore aété déterminé une surface enveloppante à 1 m de distance dans différents bâtimentsindustriels. Lors de l'évaluation, chacun de ces 94 points est considéré comme unposte de travail et le niveau de pression sonore d'émission a été respectivementdéterminé en appliquant la méthode ISO 11200. L'étude montre que les résultats lesplus précis peuvent être obtenus avec l'ébauche de la norme ISO 11205 présentéeavec le mesurage triaxial d'intensité du son ainsi qu'avec la norme ISO 11204.Une étude similaire a été réalisée pour vérifier la norme ISO 3747 pour le mesuragedu niveau de puissance sonore selon le procédé par comparaison.L'étude montre qu'une distance des points de mesure garantissant une augmentationde niveau DLf de 7 dB suffit. L'application d'autres indicateurs ne s'est pas révéléeefficace. Sur la base de cette étude, un concept de disposition optimal de positionsde sources sonores comparatives et de microphones est proposé.Mots clés:Niveau de puissance sonore, niveau de pression sonore d'émission, défaut d'angle,ISO 11200 - série, ISO 3747

91IntroductionThe sound power level and the emission sound pressure level are the most importantvalues for the characterization of noise generated by machines. They are the basisfor the evaluation of the acoustic quality and their knowledge is the absoluteminimum condition for the assessment of the expected noise impact at workingplaces. The latter refers to facilities in free field as well as to installations in rooms.Since the coming into force of the machine-directive /1/ the determination anddeclaration of these parameters is an obligation for the machine producing industry.Corresponding contractual obligations provided, they are taken more and more as abasis in the economic field.The measurement of these values is regulated in a rather complex number ofstandards and guidelines. These documents describe as well the uncertainties anddeviations. In the sense of their implementation it is of great importance that thissystem of standards is practical and corresponds to the company’s requirements.With regard to the determination of noise emission values by the manufacturer andthe inspection by the user as well as to the application of the noise immissionprognosis, there is of course quite a number of unsolved problems left.The low acceptance in the machine producing industry but as well in companiesoperating these machines is consisting to a great extent in the fact that the physicalcontext is not easily understandable. In the following we will give some hints whichare as well useful for non experts.An other problem is the relatively complicated measuring procedure for thedetermination of the two values, especially if the measurement must be done in theinstallation place in the company’s environment. This is the case for all machines thatcannot be moved easily. In this context approximate procedures are necessary whichare keeping the expenditure of the measurement in acceptable limits and which canbe applicated in the framework of the quality management in the final control and bythe operating staff during the taking-over. However, this requires the taking intoconsideration of conditions on which the approximate procedures may be applicatedin the framework of the required exactness. In the following, a number of possibilitiesfor those simplifications which are always based on the involvement offoreknowledge is fundamentally presented. By means of a principal examinationdepending on the respective kind of machines these approaching procedures can bedetermined in a specific way and can be taken as alternative methods in thecorresponding C-standard.

10It is necessary to consider that the measurement of the sound power level withdifferent measurement procedures systematically can result in different values inspite of a correct application of all prescribed corrections in accordance with therelevant standard.This is especially referring to the typical difference between the measurement resultswhich can be realized with the sound power level - envelopping surface method onone side and with the reverberation chamber - or intensity measurement on the otherside. Since this difference caused by the angle error during the measurementaccording to the sound power level - envelopping surface method can be greaterthan the deviation allows according to the grade of accuracy depending on thestandard, an evident lack has to be noticed here. In the following we will discuss thisin a more detailed way and suggest an improvement for further standardization.In this report, as well the results of several examinations which have been realizedwith reference to the standards of the series ISO 11200 and to the standard ISO3747 are represented. On the basis of these results, improvements are suggestedwhich shall lead to more easily applicable, transparent and practice orientedstandards for the measurement of noise emission of machines.

112Sound power level LWA and emission soundpressure level LpA2.1What does the sound power level state - definition andapplicationSound is like heat or light a form of energy. The energy which is emitted per time unitby a source, for example by a machine, is the sound power. It is measured in wattresp. in joule/sec. (1 watt 1 Nm/s).The sound which is radiating from a machine is indicated as sound power resp. - withreference to the values referring to the immission - as sound power level Lw. In thiscontext the following definition is applicable:LW 10 logPdBP0(2/1)(with P sound power in watt, P0 reference power in 10 -12 watt)The higher the sound power level of a machine is, the more sound energy it willradiate per time unit into the environment. The sound power level quantifies thewhole sound that is radiated in all directions.For a better understanding may serve the following experiment of thoughts:Assuming that we put on the machine a funnel inside completely reflecting which isdirecting the whole raditated power into a channel with a cross-section of 1 m2, themeasurable sound pressure level in this channel would be equivalent in terms offigures to to the sound power level.

121m2LpA Lsound power LFig. 2.1WAWIn the channel with a cross-section of 1 m2 the sound pressure level is equivalent to thesound power level of the sourceThe sound power level of a

Reihe ISO 11200 untersucht. Im Freifeld und in mehreren Industriehallen wurde der Schalldruckpegel auf 94 Punkten einer Quadermeßfläche ermittelt. Mit den Normen der ISO 11200 Reihe wird für jeden dieser Punkte der Emissions-Schalldruckpegel und dessen Abweichung vom wahren Wert bestimmt. Dabei zeigt sich, daß mit ISO

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