A Vaccum

[The_Q_Man]

I've always wondered whether or not a vaccum would effectively reduce sound in a room. For example, if you stuck a speaker in a thermos, would you hear it? I assume it would, because the sound waves wouldn't be able to be transferred as well, but I'll leave it to the experts to answer, since you guys probably know

[johnbergstromslc]

If by "vacuum", you mean an absence of air molecules, well, since airborne sound is a vibration of air molecules, then no sound can traverse a vacuum.  

If you stuck a speaker in a thermos (a vacuum bottle) you would hear it because the vibrations would be transferred mechanically and vibrate the whole bottle (there is a connection between the inner and outer bottles at the top of the thermos.)  This is called 'structure-borne' sound.  

To try to reduce sound in a room with some kind of vacuum would be folly.  You'd have to turn the whole room into a vacuum chamber (so much for breathing...).   A container pulling a vacuum placed in the middle of the room would create a nice dead spot and would absorb some sound, but overall it wouldn't be practical.