The application of acoustics to research on the properties of condensed matter at low temperatures. Acoustic techniques are readily adaptable to the cryogenic environment and make possible many measurements of the structural and thermodynamic properties of materials at temperatures approaching absolute zero (0 K, which is −460°F or −273°C). The study of sound propagation has also yielded major insights into the low-temperature phenomena of superconductivity in metals and superfluidity in liquid helium.