| 摘要 |
PURPOSE:To make a more rational noise countermeasure in a duct system by a method wherein an air conditioning duct is provided with a normal mode resonance reducing means having a characteristic frequency of low mode along a sectional surface direction of the duct set as either a sound absorbing frequency or an attenuation frequency. CONSTITUTION:A sectional shape of a pipe wall 2 constituting an air conditioning duct 1 is formed of a substantial trapezoid and shapes of opposing pipe walls 2 in view of sectional shapes are made to be non-parallel. Accordingly, differing from the air conditioning duct having a square sectional shape, a resonant frequency may not be stabilized, but it is necessary to make a practical calculation of it with a method of definite element or the like. However, the opposing pipe walls 2 are made non-parallel to each other, thereby, the resonance frequency does not have an integer ratio such as that of rectangular shape, but dispersed and thus an occurrence of normal mode can be restricted while an energy of a stable wave energy being reduced. With such an arrangement, it is possible to increase a sound shielding performance of the duct pipe wall 2 or an apparent effect of the vibration-proof characteristic and then a noise countermeasure in the duct system can be made more rational. |
