Speaker Damping and Filling

There are two types of speaker enclosure, sealed and ported. For sealed enclosure, we want the sound to disappear inside the enclosure. So dense filling material is better. For ported speaker enclosure, we want to get rid of the standing wave/reflection, etc, but keep the Q unchanged and let the bass out. For that, we need to damp the wall with heavy material but fill the space with light, thin damping material like polyester. (see this post).