1. The science of sound and the phenomena of hearing.
2. In physics, the science and study of sound, including its production, transmission, and effects.
3. In architecture:

• The sum of the qualities, as absence of echo or reverberation, that determine the value of a room, enclosure, or auditorium with respect to distinct hearing.
• The science of planning and building an enclosure so that sound will be perfectly transmitted within it.

4. In psychology: the part of psychology dealing with hearing.

Acoustics is usually construed as a singular noun, except in the sense with reference to the science of sound qualities for buildings as indicated above.

A special article about acoustics.

A science career in the production, transmission, and effects of sound.

1. The propagation of sound through the atmosphere, which affects sound in predictable ways according to atmospheric conditions; such as, temperature and precipitation.
2. The science of sound waves in the open air.

The field of acoustics that deals with the production, detection, and control of sound by electrical devices, including the study, design, and construction of such instruments as microphones, loudspeakers, sound recorders and reproducers, and public address systems.

A reference to the senses or faculties of both equilibration (equilibrium or being evenly balanced) and hearing.