Validating structure-borne sound predictions

The need of predicting underground traffic induced noise and vibration is apparent. There exist several methods for predicting structure-borne sound, however none of them is suitable for predictions covering the entire audible frequency range. Numerical methods, like the conventional Boundary Element Method (BEM) and the acoustical Finite Element Method (FEM) are mainly used in the lower frequency range, on the other hand, empirical formulas (such as [1]) give rather rough results with non-satisfactory certainties. There exist also new or modified, hybrid methods that try to combine efficiency and accuracy: Spectral Finite Element Method (S-FEM), Wave Based Method (WBM, [2]) and the Fast Multipole BEM (FM-BEM, [3]), or eg. a Rayleigh integral based method (ForREst, [7]). The paper introduces a database that can serve as basis for validating different structure-borne sound prediction techniques. Two of the newer methods are investigated: S-BEM and the Rayleigh-based calculations were performed to determine the levels of radiated sound from the wall vibration data. Other possible applications of the database as structural modal analysis of a glass pane and acoustical modal analysis of a room are also shown. The investigations have proven the consistency and reliability of the database. There was a good agreement in calculated and measured sound pressure levels. The results also have pointed out the limits of applicability at both examined methods.