What are the main acoustic phenomena? figuraReflection is the bouncing of waves off a large obstacle; reflected waves produce echoes and reverberations.Resonance occurs when the vibrations emitted by a sound source reach another body, which begins to vibrate with the same frequency. Interference occurs when several sound waves with the same frequency become superimposed while travelling along the same medium. The Doppler effect is the perception by a fixed observer of a change in the pitch of a sound coming from a moving source.