They do cancel enough noise to minimize exterior sounds, but not enough to block out all sound from your world. There is another more expensive pair of bose headphones in the same series of products that does exactly that. These headphones do limit your sound to just a low tone that can be heard from people around you. I use mine to practice electric guitar at a high volume while people are still sleeping in a room nearby. My dog has a problem with amplified sound and he leaves me alone when i use the headphones too, so it's pretty quiet.