Soundproofing

[Sapphire Guard]

How does soundproofing work? If you need total silence in a room, is it necessarily airtight?

(Fictional scenario writing purposes)

[factotum]

No, they don't need to be airtight, any more than the door of a microwave oven needs to be opaque to block microwaves. There are a number of techniques to soundproof a room, but what it basically boils down to is using a material on the walls that absorbs the sound (and maybe heats up a smidgeon in the process), and to sculpt that material into baffles so you don't have a big flat surface for sound to bounce off.

[gomipile]

NCIX Tech Tips had a video recently where they talked a bit about the use of soundproofing foam tiles provided by a sponsor of theirs: https://www.youtube.com/watch?v=aFQoukSpE_Y

[Trekkin]

In short: maybe and no, depending on where the noise is.

In long: "soundproofing" isn't like waterproofing but for sound or anything like that; it's simply a collection of techniques for reducing how much sound is transmitted from point A to point B. Most people are familiar with anechoic chambers, with the recognizable wedge-shaped extrusions of soft material on the walls and ceiling to diffuse and absorb sound that would otherwise bounce off the walls and also exclude exterior sound. This setup is ideal for recording studios and sound booths, for example, and need not be airtight; the system can still work with patches of the walls left bare.

However, acoustic decoupling can involve a controlled air supply as part of its isolation; a chamber designed to dampen sound transmission from a source inside to outside listeners might well be airtight in order to avoid transmission of sound through the air vents. It is not strictly required to be, though.

So if a room is soundproof because listeners inside can't hear the outside world, it probably isn't airtight. If a room is soundproof so loud noises inside don't get out, it might be.