VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...
VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...
VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...
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Chapter 6Noise control6.1 Origin <strong>of</strong> noiseWhen considering different sources <strong>of</strong> noise, it is useful to make a distinctionbetween <strong>the</strong> following three different types :Aerodynamic noise : <strong>the</strong> sound is generated by oscillations or friction<strong>of</strong> air molecules in an air flow.Hydrodynamic noise : sound generated by oscillations or friction <strong>of</strong> aliquid flow.Structure-borne noise : sound generated by vibrations <strong>of</strong> a solid.Fur<strong>the</strong>rmore, a classification can also be made between :Active noise components : components <strong>of</strong> machines which producenoise. Usually <strong>the</strong>se are <strong>the</strong> power-converting components which delivermechanical work from energy sources (electrical, mechanical ormagnetic energy, hydraulic pressure, internal forces or friction). O<strong>the</strong>ractive noise components are regions with non-stationary flow and contactsurfaces between moving parts.Passive noise components : These components conduct <strong>the</strong> noise generatedby <strong>the</strong> active components. This class can contain dominant noiseradiators, but no noise sources. Typical passive noise components arestructural components like panels.A heating system is an example <strong>of</strong> a machine with both active and passivenoise components as indicated in Figure 6.1.99
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