Sound is an important element in a house, usually how to diminish the sound between walls and floors. Soundproofing a house is an art and a science. There are many things that at first go against logic, but once you understand the mechanics of sound they make perfect sense.
For example in one situation a very thin layer of one thing stops much more sound than a thick layer of another. But in another sutuation it might be the opposite, where a thick substance is more effective than a thing substance, whatever the substance is at the time (foam, metal, wood, caulk etc…).
These two sides offer concrete technical information that are invaluable if you want to build or renovate a house. The sites are not selling any product so the information isn’t very biased.