Eli5 Why is the soundproofing that is used foam-like materials instead of dense materials?
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The two main components to soundproofing/sound isolation are density and separation.
In professional studios, the recording booth is generally acoustically isolated by separating the room from its surrounding structure by building a ‘room within a room’ using two sets of parallel walls with the inner walls standing on a floating floor platform which is then generally sitting on something like dense neoprene spacers. And then the walls are hung with heavy drywall, sometimes two layers.
All of this serves to minimize the transfer of mechanical energy between the inner room and the larger structure by minimizing contact and using materials that minimize energy transfer where there must be contact.
The foam products you’re thinking of are for sound deadening/acoustic tuning which isn’t about isolation but about changing the ‘sound’ of the room — that is, largely how much echoing and reverberation there is inside of the room. Since foam has many tiny surfaces which all point in more or less random directions, it helps the sound to disperse in random directions instead of harshly reflecting off of the flat, hard walls.
It’s basically the same difference you notice between an empty room with wood floors and a carpeted room with soft furniture in it. The room sounds better and more ‘dead’ with a couch in it. But it doesn’t change how well you can hear the truck that’s going by outside.
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