Control of Sound Propagation in Ducts
The final group of noise control problems which we will briefly discuss here concerns the control of sound propagation in ducts. Ducts can be viewed as enclosures where one dimension is very long, often terminating into open space. Common examples of a duct include the airways used in central heating and cooling systems, and any piping system (including vehicle exhaust systems). Another example of a duct which may not be so obvious is a long hallway connecting two adjacent rooms or halls. The essential acoustic ingredient for a duct is that sound waves be constrained in two dimensions while being allowed to travel more-or-less freely in the third. For this reason, ducts are often referred to in acoustics literature as waveguides, where the constraining walls guide the travel of sound waves in the third dimension.
KeywordsSound Propagation Sound Field Noise Control Expansion Chamber Helmholtz Resonator
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