Soundproofing, Insulation and Acoustics [Part 2]

Actual soundproofing is a whole different story from acoustics. Remember the egg-carton we talked about? The stuff that doesn't even work well for reducing sound reflection? Well some people even try to use that for soundproofing! Here in The Netherlands new buildings often have 25 cm thick concrete cavity walls and that doesn't even stop the sound of a neighbor's party. Compare that to the 5 mm carbon.

If you want a quite room (or a soundproofed room) there are two kinds of sounds you want to reduce. Sounds moving through the air and sounds moving through mass.
You see, if you build one solid wall to separate one room from another that wall will conduct the sound and transmit it right to the next room.

The reduce the conduction sound we build two walls next to eachother and instead of anchoring them to the floor/ ceiling you have to press them in felt.

To reduce low frequency sounds you have to add mass to the wall. Multiple layers of drywall will work. Drywall has a high resonance (own frequency) and if you make the drywall to thick the resonance will drop and might get just in the freq. of the sound you want to block. If this happens the wall will amplify that frequency. Applying viscous material between drywall will keep its on freq. high.