Sound travels much faster in solids than liquids and gases.
Then why do we hear a fainter sound from the other room if we close the door than open it?
As sound travels faster through solids…shouldn't we hear a much louder sound from the other room when the door is closed? (I know that loudness depends on amplitude but still…I don't get how a solid can make sound fainter)
Best Answer
On the boundary of two substances with different propagation velocities, a wave traveling from A to B experiences both reflection and transmission. See the last animation on this site.
It can be shown that the reflection index (R) is the following $$R=\frac {Z_A-Z_B} {Z_A+Z_B}$$ where $Z=\rho v$ is the impedance of the materials, specifically $Z_\text {air}=420 \frac {\text {Pa}\cdot s} m$, $Z_\text {wood}=2.3\times 10^6 \frac {\text {Pa}\cdot s} m$, thus $R=-0.99963$. Moreover the sound exiting the door experiences the same degree of reflection.