Acoustics

Acoustics is a branch of physics that studies sound, namely mechanical waves in gases, liquids, and solids. A scientist that works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers.

...[A]coustics is characterized by its reliance on combinations of physical principles drawn from other sources; and that the primary task of modern physical acoustics is to effect a fusion of the principles normally adhering to other sciences into a coherent basis for understanding, measuring, controlling, and using the whole gamut of vibrational phenomena in any material. Origins in Acoustics. F.V. Hunt. Yale University Press, 1978

Divisions of acoustics
The following are the main sub-disciplines of acoustics. 
 * Acoustical measurements and instrumentation.
 * Acoustic signal processing.
 * Aeroacoustics is the study of aerodynamic sound, generated when a fluid flow interacts with a solid surface or with another flow. It has particular application to aeronautics, examples being the study of sound made by jets and the physics of shock waves (sonic booms).
 * Architectural acoustics is the study of how sound and buildings interact including the behavior of sound in concert halls and auditoriums but also in office buildings, factories and homes.
 * Bioacoustics is the study of the use of sound by animals such as whales, dolphins and bats.
 * Biomedical acoustics is the study of the use of sound in medicine, for example the use of ultrasound for diagnostic and therapeutic purposes.
 * Environmental noise is the study of the sound propagation in the human environment, noise health effects and noise mitigation analysis.
 * Psychological acoustics is the study of how people react to sound, hearing, perception, and localization.
 * Physiological acoustics is the study of the mechanical, electrical and biochemical function of hearing in living organisms.
 * Physical acoustics is the study of the detailed interaction of sound with materials and fluids and includes, for example, sonoluminescence (the emission of light by bubbles in a liquid excited by sound) and thermoacoustics (the interaction of sound and heat).
 * Speech communication is the study of how speech is produced, the analysis of speech signals and the properties of speech transmission, storage, recognition and enhancement.
 * Structural acoustics and vibration is the study of how sound and mechanical structures interact; for example, the transmission of sound through walls and the radiation of sound from vehicle panels.
 * Transduction is the study of how sound is generated and measured by loudspeakers, microphones, sonar projectors, hydrophones, ultrasonic transducers and sensors.
 * Ultrasonics is the study of high frequency sound, beyond the range of human hearing.
 * Musical acoustics is the study of the physics of musical instruments.
 * Underwater acoustics is the study of the propagation of sound in the oceans. Closely associated with sonar research and development.