What stops sounds from traveling?

Answer 1

Sound waves exhibit the same properties as most other waves, e.g. light or water.

Sound waves stop forward motion when they are experience either total reflection

or total absorption.

A dramatic change in the density of material will cause significant reflection of sound and, in principle, you can make a surface reflect sound in the way a mirror reflects light. It is not 100% perfect, but an echo is an example of reflected sound.

A perfectly absorbing material is another example that stops sound from propagating. Usually this is accomplished by selecting a material that absorbs the energy in sound.

There is a third option that disperses waves without destroying them and that is a highly scattering medium. For instance, light does not pass through milk because the light waves are scattered. Sound waves would be strongly scattered in passing through a heterogeneous compound made with materials of dramatically different acoustical properties on a length scale close to the wavelength of the sound.