Book excerpt: The subject of vibro-acoustics is important for the design of machine elements and structures, to minimize sound generated by them. For better machine designing, it is necessary for machine designers (mechanical engineers) to have a thorough knowledge of vibro-acoustics. Furthermore, since the design cycles of machines have become shorter, designers will have to design quiet machines at the drawing-board stage rather than applying "band-aid" techniques after the machine has been built. Although there is common ground in the treatment of acoustics, the subject of vibration is not very fortunate. Those interested in low-frequency vibration are generally concerned with the modal approach of using natural frequencies and mode shapes, whereas those interested in vibro-acoustics in medium and high frequencies are generally concerned with the wave approach. Since both modal and wave approaches have their advantages, it is a good idea to study both together to get the best out of them. This is useful for a better understanding the physics of vibro-acoustics. Written for students and professionals interested in gaining knowledge, this book systematically integrates the relevant aspects of vibro-acoustics from various viewpoints.