In general, the frequency of an acoustic wave does not change as it propagates through a medium, assuming there are no external factors affecting it. This principle is rooted in the physics of wave propagation.
When a sound wave travels through a homogeneous medium, such as air, its frequency remains constant because the wave's source continuously produces vibrations at a specific frequency. These vibrations create compressions and rarefactions in the medium, which propagate as the sound wave.
The frequency of a sound wave is determined by the source of the wave, such as a vibrating object or a sound-producing device. It represents the number of oscillations or cycles of the wave that occur per unit of time. As long as the source maintains a consistent frequency, the wave will propagate with the same frequency.
However, it's worth noting that the frequency of a sound wave can be affected by certain factors or phenomena. For instance, when sound waves encounter a medium with a different acoustic impedance, such as when transitioning between different substances or encountering a moving medium, some frequency changes can occur due to reflection, refraction, or the Doppler effect. Additionally, in more complex scenarios involving interference or modulation, frequency changes or shifts may occur. But in the absence of such influences, the frequency of an acoustic wave remains constant throughout its propagation.