(Greek: akouein = to hear) Commonly, the study of SOUND and its behaviour in various media and environments, including the effects of ABSORPTION, DIFFRACTION, INTERFERENCE, REFLECTION, and REFRACTION. See: SOUND PROPAGATION.

In the broader sense, acoustics is the physics of sound, treated in all of its aspects. Up until the early 20th century, 'sound' and 'acoustics' referred to elastic vibrations and waves in the audible human range, but today, there are large fields of acoustics dealing with vibrations and waves not associated directly or indirectly with the hearing process, and often with frequencies and intensities above and below the human audible limits. The term SONICS has recently come into use for those aspects of acoustics not directly associated with the hearing process. See: ULTRASONIC, INFRASONIC.

Architectural acoustics refers to the study and design of sound transmission in enclosed spaces. The acoustics of a room are its qualities related to sound transmission and reception. Applied acoustics is generally termed acoustical engineering, and is practised by an ACOUSTICIAN or acoustical engineer.