# Why doesn't sound wave cancel out waves of same frequency after reflecting from the ear

We just finished our sound waves class at my university. I was taught that reflection of sound waves from an elastic boundary is accompanied by a phase change of $\pi$ while that from a rigid boundary is not.

Let us assume that the ear membrane is an elastic boundary ( I really am unable to figure out what type of boundary it would be so please correct me if I am wrong). In that case the sound reflected would have a phase change of $\pi$.

Let us additionally assume that this wave had come from a continuous sound source $A$. This source would still be producing sound when our wave comes back after reflection.

Shouldn't our reflected wave interfere destructively with incoming sound waves from A and stop us from listening all further sounds ?

• I have come up with this : when the reflected wave comes out of the ear it encounters a rarer boundary (air) and thus the wave transmitted through this rarer boundary is such that it does not cause any destructive interference. Am I right ? – Raghav Jan 28 '17 at 6:37

A phase change of $\pi$ is not likely unless you assume the eardrum is completely rigid, which of course it is not.