Q: How can you hear someone through a closed door?

[Cookies?]

A question about the simplest of things: Based on the physics of sound, how can you hear someone through a closed door?

I'm quite confused because someone once told me its was because the sound passes through the door; since its causing the air molecules to vibrate, when this vibration hits the door, it similarly causes the door to vibrate and transfer the sound energy through to the other side.

I've also read about diffraction as the cause so, what, is it a combination of both? Or just one. If its just diffraction, then if I was in a completely airtight room, would I then, technically, be unable to hear anything from outside?

 

[Curl]

They were talking about diffraction when the door is cracked open slightly.

The first explanation is the correct one when the door is closed/sealed.

 

[Drakkith]

I believe both effects happen, as most doors are probably not airtight, especially the ones in houses.

 

[Sophos]

Scenario 1: In this case, sound acts much like light in regards to the double split experiment. Sound -> crack in door. A new origin of the sound is created, and the process is repeated until the waves of sound are eventually deflected by particles in the air and the sound dissipates.

Scenario 2: In this case, sound waves interact directly with the door, causing it to vibrate. The door's vibrations create new sound waves that are similar to the ones that it was hit by. Smooth, hard, and some-what rigid objects tend to translate sound more effectively - which is why a cotton coat doesn't translate sound very well. ;)

 

[pmacias]

I would like to provide a comprehensive explanation for how sound can be transmitted through a closed door. Firstly, sound is a form of energy that travels in the form of waves. When someone speaks or makes a sound, they are creating a disturbance in the air molecules around them, causing them to vibrate. These vibrations then travel through the air as sound waves.

When these sound waves reach a solid object, such as a closed door, they can cause the object to vibrate as well. This is because the sound waves transfer their energy to the object, causing it to vibrate at the same frequency as the sound waves. This is known as mechanical resonance.

So, in the case of a closed door, the sound waves from the person's voice cause the door to vibrate, which then creates sound waves on the other side of the door. This is why we are able to hear someone speaking through a closed door.

However, as you mentioned, there is also the phenomenon of diffraction at play here. Diffraction is the bending of waves around obstacles or through small openings. In the case of sound, when it encounters an obstacle such as a closed door, the sound waves can bend and spread out around the edges of the door, allowing some sound to pass through to the other side. This is why we can still hear muffled sounds even when a door is closed.

To answer your question about being in a completely airtight room, it is true that if there are no openings or cracks for sound waves to pass through, then you would not be able to hear anything from outside. However, most rooms are not completely airtight and have small openings or cracks that allow sound waves to pass through.

In conclusion, the ability to hear someone through a closed door is due to a combination of mechanical resonance and diffraction. The sound waves from the person's voice cause the door to vibrate and also bend around the edges, allowing some sound to pass through to the other side. This is a fundamental principle of the physics of sound and helps us to understand how sound travels and can be transmitted through solid objects.