Modal Damping Estimation for Structure-Borne Sound Predictions Using an Extended Modal Strain and Kinetic Energy Method

A practical method for predicting vibration and structure-borne sound in buildings is developed using an extended Modal Strain and Kinetic Energy (MSKE) method. The proposed method introduces a complex Young's Modulus for structural materials, a complex bulk modulus and an effective density for the acoustical fluid in order to express damping behaviour of the system. This method allows for the modal loss factor to be obtained without solving complex eigenvalue problems under the assumption that the complex eigenvector can be approximated by the real eigenvector. Under the given assumptions, the proposed method reduces complexity and computational requirements compared to the traditional MSKE method by solving for the scalar pressure rather than the vector quantity displacement. The proposed method was experimentally validated in a two-story structure made of reinforced concrete. The second floor slab was excited by an impact hammer while the driving point acceleration and sound pressure were measured in the room below. The building frame and cavity were modeled and discretized by a five centimeter rectangular mesh. Accelerance and the sound transfer function were calculated and compared to the measured results. In the low-frequency region (up to 150 Hz), both calculated results agreed well with the measured results.