Sound phenomena refer to various effects and behaviors of sound waves as they travel through different mediums. These phenomena include concepts like echo, where sound reflects off surfaces, and reverberation, which is the persistence of sound in an environment due to multiple reflections. Another interesting aspect is Doppler effect, which describes the change in frequency or wavelength of sound as the source moves relative to an observer. This effect is commonly experienced with passing vehicles or emergency sirens, where the pitch seems to change as they approach and then move away.