by echo Sound travels in waves, and it requires a medium through which to travel (unlike light, which needs no medium). Sound emanates outward from a source essentially in "domes, bubbles or spheres" of pressure. Insulating or absorbing substances around the source, like the ground, buildings, our bodies, or speaker boxes, will affect the way the sound propagates. People often talk about "sound waves", and this might lead us to think of the typical sine-wave displays on oscilloscopes, or to the shapes of 'waves' as we see them on bodies of water. But sound does not actually move through the air in some squiggly way that looks like the display. The display is in reality a graph that shows differences in intensity of air pressure, and how far apart the peaks and valleys of pressure are. Think of these bubble-like waves as pressure fronts of air moving very rapidly, and also changing in pressure values very rapidly. These differences make your ear drums vibrate the way the air is vibrating, and the rest is neurophysiology!