How can sound waves be blocked?

You can use an approach called 'anti-noise', this is a system which uses a microphone outside and then speakers inside which replay the the outside noise but 180deg out of phase. read more

The human ear can only hear a small range of sound waves. Even if you blocked all of the sounds you could hear, an elephant may still hear extremely low frequency sounds that would be unheard by a person. Sound can be completely blocked by building a vacuum between you and the outside world. read more

Sound waves have a "spreading out in all directions" that makes them very hard to block except by using large fixed walls or large acoustically absorbing materials like especially heavy curtains. If you try to generate sound waves so as to somehow cancel other waves, the cancellation will turn out to be effective only along certain very narrow channels. read more