What is the primary factor affecting noise travel?

The primary factor affecting noise travel is indeed the height of the noise source. The elevation of the source has a significant impact on how sound waves propagate. When a noise source is positioned higher off the ground, sound waves can travel further without encountering as many obstacles as they might if the source were lower. This increased elevation allows the sound waves to disperse over a larger area, reducing the effects of nearby structures that could absorb or reflect sound.

Height plays a vital role in urban environments where buildings and other structures can obstruct or diffuse sound. When noise sources are elevated, they may also encounter fewer barriers that would dampen the sound, thus allowing it to travel farther and maintain its intensity.

While material choices of surroundings, presence of sound barriers, and wind direction can influence sound propagation, they do not have the same foundational impact as the height of the noise source itself. Material choices can affect how sound is absorbed or reflected, sound barriers can obstruct or diminish sound, and wind direction can indeed carry sound waves, but the inherent attributes of the sound source's height create the primary conditions for noise travel.