Eli5 Why is the soundproofing that is used foam-like materials instead of dense materials?

Question

Eli5 Why is the soundproofing that is used foam-like materials instead of dense materials?

In: Other

Answer 1

You use foam when you want to have a space that is quiet. This is because foam is good at absorbing sound energy and stopping it from bouncing around the room.
You use dense materials when you want to stop the sound from one area from going into another area (i.e. a “sound barrier”). They tend to be ‘reflected’ sound back so the ‘loud’ side of the barrier will get even louder.