Study on reduction of floor impact sound by heavy impact source using double-layered ceiling with damping by granular materials

Abstract

Acoustic control is an important factor in ensuring a comfortable living environment. There has been much discussion about floor impact sound by heavy impact source causing problems in buildings for years. Many studies have focused on the floor slab and double-layered flooring in the source room, but there has been little research into measures in the sound-receiving room. The present study was undertaken in order to reduce floor impact sound by heavy impact source in the sound-receiving room, using a double-layered ceiling with damping provided by granular materials. The study focused on the effect of damping using granular materials in a double-layered ceiling experimentally and by applying a practical prediction using the finite element method. First, the experimental results show that the resonant characteristic of a double-layered ceiling acts on floor impact sound by heavy impact source, with the damping effect of the granular materials on a double-layered ceiling effectively suppressing such impact noise. In this paper, a sack of granular charcoal intended for humidity control was used as the granular material. It is evident from the experimental results that the resonance of double-layered ceilings, especially steel furring, is a major determinant in floor impact sound by heavy impact source. As a result, it was confirmed that the floor impact sound pressure level increased after double-layered ceiling was installed. Floor impact sound pressure levels when granular materials are inserted into the double-layered ceiling are about 10 dB lower than without granular materials in the 63 Hz band. Furthermore, vibration acceleration levels when incorporating granular materials in the double-layered ceiling are about 10 to 20 dB lower than without such granular materials. The reduction in floor impact sound by heavy impact source by using granular materials with a double-layered ceiling is similar to the reduction in vibration acceleration level on the ceiling board. Next, a numerical prediction concerning the effect of damping by granular materials with a double-layered ceiling was examined. Some studies have proved that damping performance with granular materials can be numerically analyzed using the discrete element method (DEM). However, in the case of a general architectural space, since DEM takes into account the performance of each granular material, many restrictions on the modeling and calculating time are imposed. In this study a practical prediction method was examined using the finite element method (FEM). The experimental results show that the effect of damping by granular materials on a double-layered ceiling is in close agreement with increasing internal losses of both ceiling board and steel furring. Therefore, we suggest that the effect of damping with granular materials can be treated as an internal loss factor for double-layered ceiling materials in the FEM. The validity of the suggested method substituted as an internal loss factor for damping by granular materials is examined by comparison with the experimental results. A further study on how double-layered ceilings damped by granular materials are designed should be conducted. A further aim is to establish a method of construction for double-layered ceiling that incorporates damping by granular materials.