system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does closing a door lessen the amount of sound that enters a room even though sound travels best through solids?

My understanding is that sound travels best through solids, then liquids, and worst through the air. If that’s the case, then why do walls and other barriers inhibit sound travel?
gpt
Because sound will be lost when it goes from one medium to another(for example: from air to water). 
  When you close a door, the sound has to make this ' medium shift ' twice: from the air to the door (solid), and from the door to the air.