Major goals in geophysics involve improving our understanding of (a) the source physics of geophysical processes, such as earthquakes, and (b) the medium through which the signatures from these processes are observed (the ‘path’). This talk summarizes the use of seismic and infrasound waves for understanding source and path. Following a primer on the atmosphere for Geoscientists, this talk begins by focusing on source physics, examining a new model of earthquakes using loudspeaker theory and applying this model to data from the January 3rd, 2011 earthquake near Circleville, Utah. Next, the talk focuses on path by exploring the use of low-frequency sound to measure winds in the stratosphere, an altitude range that is difficult to measure but important for predicting weather and climate. Finally, the talk will conclude by examining some Grand Challenges in Geosciences that fuse source and path physics.