VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...

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100 CHAPTER 6. NOISE CONTROLFigure 6.1: Heating system. The boiler is an active noise component and theradiators radiate the noise (they’re passive noise components).In order to consider noise control, determining the source of the noise, isthe first thing to do. Depending on the nature of this source, there are anumber of possible ways of transmission of noise and radiation of noise, asindicated in Figure 6.2.For each machine, following procedure has to be used :1. Divide the machine in active and passive noise components.2. For each component, determine whether structure-, hydrodynamic- oraerodynamic noise is generated.3. Locate the transmission paths and determine whether structural, hydrodynamicor aerodynamic noise is transmitted.4. Identify the radiating surfaces.5. Identify the primary contributions (sources, transmission paths andradiating surfaces).As an example, consider the hydraulic group in Figure 6.3. The activenoise components are : the electrical motor, the hydraulic pump and a valve.The hydraulic group has sources generating structure-borne, hydrodynamic
6.1. ORIGIN OF NOISE 101Figure 6.2: Basic model of the origin of noise in machines.and aerodynamic noise. The different types of sources and the transmissionpaths of noise are indicated in Figure 6.4.Sound power measurements are then performed on the group and theeffect of various changes is measured :1. Thepower ofsoundoftheentire aggregateismeasured (L W = 90dBA)2. The whole of motor and pump is mounted on a separate frame withvibration dampers on the reservoir. One can measure a reduced soundpower level due to the loss in transmission of structure-borne noisetransmission between the machine and the reservoir (L W = 89 dBA).3. The frame (with motor and pump) is completely decoupled from thereservoir. The connection between the pump and the valve is achievedusinga2meterlonghydraulicline. Anadditionalreductionofstructurebornenoise is realized (L W = 86 dBA).4. The reservoir is removed from the measuring chamber (L W = 86 dBA).From this, one can decide that the decoupling between pump/motorand the reservoir is sufficiently large.5. Switching to water cooling instead of air cooling with fan (L W = 85dBA).
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VRIJE UNIVERSITEITBRUSSELAcousticsB
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iiWhen sound becomes noise, it will
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ContentsI Introduction to acoustics
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CONTENTSvii4.3 Measuring the acoust
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Part IIntroduction to acoustics1
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4 CHAPTER 1. FUNDAMENTAL CONCEPTS O
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10 CHAPTER 1. FUNDAMENTAL CONCEPTS
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24 CHAPTER 2. THE HUMAN HEARING SYS
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36 CHAPTER 3. MEASURING SOUNDFigure
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44 CHAPTER 3. MEASURING SOUNDfactor
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150 APPENDIX A. MATERIAL PROPERTIES
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152 BIBLIOGRAPHY[12] Bruel and Kjae
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