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46 CHAPTER 3. MEASURING SOUNDFigure 3.12: pistonphone for the calibration of a microphone. Source:Bruël&Kjær.3.8 Quantitative parameters3.8.1 The equivalent sound pressure levelTo characterize sound that highly varies in time, one introduces the equivalentsound level. A constant sound at this level contains the same acousticenergy as the highly varied sound. The equivalent sound level is obtained byaveraging the average quadratic sound pressure over the desired time intervaland converting it again to dB. From the definition of the sound pressure levelone obtains:this gives :p 2 rmsp 2 0( ) p2L eq = 10log rmsp 2 0= 10 Lp/10 (3.2)( 1= 10logT∫ T0)10 Lp/10 dt(3.3)With L eq the equivalent sound level (dBA), p 2 rms the time average of theaverage quadratic sound pressure and T the time over which the averaging
3.8. QUANTITATIVE PARAMETERS 47operation takes place. The integration in Equation 3.3 is replaced by a sumover a set of N measurements in practice:(1L eq = 10logTN∑i=110 L i/10)(3.4)Theequivalent soundlevel isdirectlymeasured withtheaidofamicroprocessorcontrolled sound level meter. This can usually be programmed to executeand record a whole set of measuring cycles over a period of 24 hours.3.8.2 Sound Exposure LevelThe sound exposure level (SEL) is used to characterize a single event, bothin sound level and duration. The SEL is defined as:∫ TSEL = 10log( 10 L/10 dt) (3.5)0with T the time measured in seconds. The SEL can also be measured withan integrating sound level meter. The SEL can be used to characterize thenoise produced by say, a certain machine action.A dosimeter or noise exposure meter is an instrument that is designed tomeasure the accumulated noise exposure of workers in an industrial environment(like dosimeters exist for radiation). The dosimeter is a compact device(see Figure 3.13) with an integrating sound level meter that can be worn byworkers during their normal activities at work. Usually the dosimeter hasan internal memory to track the sound exposure of several workers. Apartfrom the sound exposure levels in dBA, the percentage of the allowed leveland the peak level is displayed. Also the data and duration of the measuringperiod are registered.3.8.3 Statistic sound levelsIn lots of real life situations the sound level will vary strongly in function oftime. When registering such a sound over an extended period, it is difficultto interpret. Apart from often continuously present sound, there is a wholeset of interferences. Because of this the sound can be registered in a statisticway. Per time period, all sound pressure levels are registered. This can bestatistically displayed in a statistic or cumulative distribution. These cumulativemeasured values are also called the fractional sound pressure levels.
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VRIJE UNIVERSITEITBRUSSELAcousticsB
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iiWhen sound becomes noise, it will
Page 7 and 8: ContentsI Introduction to acoustics
Page 9 and 10: CONTENTSvii4.3 Measuring the acoust
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Page 69 and 70: Chapter 4Sound AbsorptionAll(constr
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5.3. THE ACOUSTICAL BARRIER 97Figur
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Chapter 6Noise control6.1 Origin of
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6.1. ORIGIN OF NOISE 101Figure 6.2:
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6.2. REDUCING NOISE AT THE LEVEL OF
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6.3. TACKLING NOISE TRANSMISSION 11
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6.3. TACKLING NOISE TRANSMISSION 11
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6.4. RADIATION NOISE 115Figure 6.17
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6.4. RADIATION NOISE 117Figure 6.20
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Part IIINoise directives119
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124CHAPTER 7. DIRECTIVE 2000/14/EG:
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126CHAPTER 7. DIRECTIVE 2000/14/EG:
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128 CHAPTER 8. NOISE ON THE WORK FL
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140 CHAPTER 9. COMMUNITY NOISE2. No
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142 CHAPTER 9. COMMUNITY NOISE
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144 APPENDIX A. MATERIAL PROPERTIES
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152 BIBLIOGRAPHY[12] Bruel and Kjae
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