Branch of physics that studies sounds, their properties and the mechanisms of their production, propagation, and reception. The earliest researches date from classical antiquity. Aristotle (384-322 B.C.E.) reports observations on the production and propagation of sound. Ptolemy (2nd half 2nd C.C.E.) apparently formulated the hypothesis that the loudness of a sound depends on the mechanical properties of its source. The systematic study of acoustic phenomena dates from Galileo Galilei (1564-1642).