Low Frequency Acoustic Performance in Ducts Using Honeycomb Layer Systems

The use of composite materials, like honeycomb structures, in the building industry is growing rapidly, due to their superior performance (very high Sound Transmission Loss) and significant weight reduction over conventional materials. An experimental investigation into low-frequency duct noise reduction using honeycomb sandwich panels is presented. Composite sandwich structures with an air gap between panels provide low-frequency sound absorption. The waves in the duct are coupled with those in the porous layer and the air cavities. The energy is dissipated as a result of the resonant mass-spring behavior of the system. A significant impact on the noise reduction is obtained by using a comparatively stiff honeycomb panel, in combination with a thin metallic duct wall with minimum weight. A noise reduction up to 12dB, below 300 Hz, is demonstrated.