Acoustics is the study of sound and how it behaves in various environments. Sound effects such as absorption, reflection, refraction or interference are also studied by acoustics. The broad acceptance of the term ‘acoustics’ refers to all the aspects of sound. Until not long ago, the notions ‘acoustics’ and ‘sound’ referred to waves and elastic vibrations that humans could hear. However, in the twentieth century, the development of technology and science has led to the broadening of the field of acoustics, in that it now comprises aspects not directly related to the hearing process, such as intensities and frequencies which are above or below the audible limits of humans.