One factor that increases the speed of a sound wave is the temperature of the medium through which the sound is traveling. In general, as the temperature of a medium increases, the speed of sound in that medium also increases. This relationship holds true for gases, liquids, and solids.
The reason behind this is that as temperature rises, the average kinetic energy of the particles in the medium increases. This increase in kinetic energy leads to faster molecular motion and collisions between particles, resulting in a higher propagation speed of sound waves.
It's important to note that the relationship between temperature and the speed of sound is not linear and can vary depending on the specific properties of the medium.