How does sticking weirdly shaped foam blocks on the walls of a room make noise hard to hear from inside and out?
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First off, it’s not soundproofing, it’s deadening. Rooms with hard surfaces have tiny echoes, the more you can break them up, the cleaner the sound will be. Those reflected sounds interact and cancel out frequencies, so a room can sound un-natural, and recording or mixing music in it can be problematic.
The room where I edit video and audio is kind-of-deadened. Rug on the floor, foam blocks in the corners, a large and deep frame on the back wall filled with very dense foam (Owens Corning 703 IIRC), and frames hanging a few inches off the ceiling, and stuck to the walls, with more of that foam inside them. If you’re talking as you enter the room, you can notice how much the sound changes – it’s more “dead” and voices sound fuller. A “civilian” (not into this stuff) may not notice, but point it out and they’ll say “wow, it did feel weird to walk in here”. Stick a drummer in there and things like cymbal harshness will be better controlled, but – everyone in the house is gonna KNOW there’s a drummer playing.
Some studios use diffusers, which are blocks of solid wood that look like a cityscape. Those are designed and tuned to break up reflections without deadening everything, and can make rooms “sound good” vs. removing all the sonic character from a room. High-end audio designers understand how to design and make them, I don’t use anything like that.
Sound *proofing*, on the other hand – it’s mass and isolation. Lay down a concrete pad, build a cinder block wall and fill the cells with concrete, pour a slab roof with steel reinforcing, use a steel door with a dense foam core, and seal any gaps – not much sound is getting out of there. You can go even further, float a floor above the concrete with rubber isolaters, and build a frame and drywall room on top of that, where nothing touches the walls, and low-end vibrations won’t make it out. Cheaper alternatives are to use double layers of drywall in a room with staggered seams, and use 2×6 header and base plates; then stagger the 2×4 drywall framing so the drywall only touches the common framing at the top and bottom. Fill that wall with dense foam for even more deadening. This is a good way to build apartments for more quiet between units, but it won’t be enough isolation to do something like record a rock drummer without the neighbors hearing/feeling it. Treble and midtones are easier to block than bass sounds, which are huge soundwaves.
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