Those intrinsic to the medium and those associated with boundaries of the medium.
Losses in the medium may be further subdivided into the basic types: viscous losses, heat
conduction losses, and losses associated with internal molecular processes. Viscous losses
occurs whenever there is relative motion between adjacent portions of the medium, such as
during compressions and expansions that accompany the transmission of a sound wave. Heat
conduction losses results from conduction of thermal energy from higher temperature
condensations to lower temperature rarefactions. The molecular processes leading to
absorption include the conversion of kinetic energy of molecules into1: