| 摘要 |
A noise attenuation arrangement, particularly suitable for attenuating noise radiated by a conduit (10) carrying pressurised air from a turbo-compressor in an internal combustion engine, is in the form of cavities (14) (Figure 2) arranged around the outside of the surface of the conduit (10), and connected to the interior of the conduit by slots (16). In this case, sound attenuation is produced in part by the Helmholtz resonator effect and in part by reflection of the acoustic waves caused by the change in section between the conduit (10) and the attenuator (12). The Helmholtz resonator effect of the different cavities produces attenuation at different frequencies according to the volume of each cavity and the sizes of the slots (16). The attenuator arrangement is advantageously produced by a plastics injection process in two parts, one comprising a portion of the conduit (10) and a body portion forming the cavities (14) with longitudinally positioned adjacent ends, which are closed off by the second part which is in the form of a cover plate. Other noise attenuation arrangements using the quarter-wave resonator effect are also disclosed, comprising cavities arranged round the outside of the conduit.
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