The energy is contained in the wave motion of matter. To set up this problem you need some Region of matter ie fluid or solid then a boundary with vacuum. This boundary will have conditions imposed on the pressure, fluid velocity or lattice displacement wave equation of the sound. With a solid-vacuum boundary it will cause a full reflection of the wave at the boundary and the energy will remain constrained in the matter region and eventually be dissipated in the solid.
With a fluid vacuum boundary things are a bit more interesting because typically that boundary will not be sharp because of diffusion. For exampke,, in the upper atmosphere of earth you will get a gradient of air density with altitude. The sound's wavelength and speed will be a function of density and temperature and therefore altitude as will its impedance per unit length so if you launch a wave up from the surface it will both spread out transversely and some of the power will be reflecting back toward the surface as it moves per unit length.
MoodiusJ t1_j4uy70q wrote
Reply to What happens to the energy of sound in space? by full_hammer
The energy is contained in the wave motion of matter. To set up this problem you need some Region of matter ie fluid or solid then a boundary with vacuum. This boundary will have conditions imposed on the pressure, fluid velocity or lattice displacement wave equation of the sound. With a solid-vacuum boundary it will cause a full reflection of the wave at the boundary and the energy will remain constrained in the matter region and eventually be dissipated in the solid.
With a fluid vacuum boundary things are a bit more interesting because typically that boundary will not be sharp because of diffusion. For exampke,, in the upper atmosphere of earth you will get a gradient of air density with altitude. The sound's wavelength and speed will be a function of density and temperature and therefore altitude as will its impedance per unit length so if you launch a wave up from the surface it will both spread out transversely and some of the power will be reflecting back toward the surface as it moves per unit length.