• (n.) That branch of natural philosophy which treats of the properties of sound as affected by passing through different mediums; -- called also diaphonics. See the Note under Acoustics.
Di`a·cous'tics noun [ Confer French diacoustique .] That branch of natural philosophy which treats of the properties of sound as affected by passing through different mediums; -- called also diaphonics . See the Note under Acoustics . 
Diacoustics is a now obsolete term for the science of refracted sounds.
diacoustics, diacoustic A name for the science of refracted sounds.