LOW FREQUENCY AIRBORNE SOUND TRANSMISSION

摘要

Although sound sources with strong energy content at low frequencies are proliferating, current standards fail to describe sound transmission at these frequencies. Thus, prediction methods for airborne sound transmission, which are able to deal with the modal characteristics of sound fields generated at low frequencies, particularly in rooms with volumes lower than 50 m~3, need to be developed. In the present paper, a method based on modal analysis is implemented. The method is valid only for rectangular rooms and considers a simplified problem where the modal coupling between the emitting room and the separating wall is neglected. The model was validated by comparison with experimental results obtained by other authors. Application of the method in a preliminary parametric study indicated that vibration modes of the separating wall control sound insulation only at very low frequencies, below the first excited room modes. Above these frequencies, modal coupling between the wall and the receiving room becomes more important. The study also showed that low frequency sound insulation depends greatly on the room dimensions: it reduces significantly for identical emitting and receiving rooms; and increases for smaller receiving rooms. The method also was used to compare the performance of a given wall installed in a number of different rooms with that predicted by the method described in EN ISO 12354-1.